PROPRIOCEPTIVE MOTOR CONTROL IN FISH RESPIRATION

Transcription

1 J. exp. Biol. (1975), 62, gg fcjw 9 figures inted in Gret Britin PROPRIOCEPTIVE MOTOR CONTROL IN FISH RESPIRATION BY C. M. BALLINTIJN AND O. S. BAMFORD* Zoologicl Lbortory of the University of Groningen, Kerkln 30, Hren, The Netherlnds (Received 5 July 1974) SUMMARY The response of single respirtory neurones in the medull oblongt of crp to short twitches of individul respirtory muscles were nlysed. The muscle contrctions were obtined through utomtic electricl stimultion nd could be consistently elicited in predetermined phse reltion to the ventiltory cycle. The results show tht, prt from nerve cells which tke prt in long-term processing of proprioceptive informtion from severl sources, neurones lso exist which possess the properties of elements of peripherl proprioceptive control loop such s tension receptor neurones, length or stretch receptor neurones nd motor neurones. INTRODUCTION In the pst, experiments hve been crried out on both teleosts nd elsmobrnchs to elucidte the function of mechnoreceptors in the respirtory system. Stchell & Wy (1962) studied receptors on the brnchil processes of the dogfish nd the role they ply in the regultion of respirtion, nd Sutterlin & Sunders (1969) studied the mechnoreceptors on the gills of the se rven. In generl, the interest of investigtors hs been focused on long-term processes such s the contribution of mechnoreception nd proprioception to the development of the respirtory rhythm, nd the influence of proprioceptive signls of one breth upon the execution of the following (Bllintijn, 1969 b; von Bumgrten & Slmoirghi, 1962; Stchell, 1959, 1961; Serbenyuk, 1964, 1965; Serbenyuk, Shishov & Kiprin, 1959; Shelton, 1970). A further spect of proprioceptive control in teleosts is whether there is direct proprioceptive reflex control of the ctivity of the respirtory pump muscles. In mmmls it hs been shown tht the respirtory centre, contrry to erlier theory, does not directly ctivte the motor neurones of the intercostl muscles, which only receive subliminl respirtory drive potentils, modifying their sensitivity. The y motor neurones of the muscle spindles, however, respond to the centrl drive potentils nd vi the y reflex loop ctivte the motor neurones. Thus control of the respirtory movements is exerted vi the proprioceptive y reflex loop in which externl disturbnces of the movements s result of posturl nd respirtory demnds re Present ddress: Zoology Deprtment, University of British Columbi, Cnd. 7-2

2 IOO C. M. BALLINTIJN AND 0. S. BAMFORD compensted. (For n extensive ccount nd survey of the literture see Grnit, 1970I nd Newsom Dvis, 1970.) Histologicl observtions on some teleost muscles (Bone, 1964) show tht such complicted orgns s the muscle spindles of higher vertebrtes re not present. Muscles mking complicted movements, however, re equipped with free nerve endings with sensory function, both in the muscle nd in the tendon. Thus the elements for simple proprioceptive control loop seem to be present in fish. To our knowledge no histologicl dt re vilble for the respirtory muscles. Electrophysiologicl reserch on proprioceptive motor control in fish respirtion is complicted by the fct tht, unlike the sitution in mmmls, the motor neurones of the respirtory pump muscles re locted in the medull oblongt ner the centrl respirtory neurones. Nevertheless it hs been possible to demonstrte tht proprioceptive regultion of the respirtory movements occurs in fish on the following evidence. Experimentl disturbnces of the respirtory movements re immeditely followed by compenstory chnges in the electromyogrm of the respirtory muscles influenced by the disturbnce (Bllintijin, 1969). The muscle ntgonized by the disturbnce show n increse in ctivity, those ssisted show diminution. The fct tht the compenstion is without dely nd is dpted to the sitution for ech muscle individully indictes tht it is cused by proprioceptive control rther thn by oxygen lck through impired ventiltion. In the ltter cse the rection would develop only fter dely, nd n incresed respirtory effort due to suffoction would result in n overll ugmenttion of respirtory muscle ctivity. Recording experiments lso showed tht neurones in the medull oblongt process proprioceptive informtion nd often stop firing when they re deprived of proprioceptive input (Bllintijn, 19696, 1972). The im of the present pper is to identify further the cells tht process proprioceptive informtion nd to demonstrte tht number of them hve properties identicl with those expected from the motor neurones, tension receptor neurones nd length receptor neurones of peripherl proprioceptive reflex loop. MATERIAL AND METHODS The experiments were performed in the following wy. The electricl ctivity of single respirtory neurones in the medull oblongt ws recorded. After determintion of the spontneous ctivity of the cell under observtion, respirtory pump muscles were stimulted one t time with short bursts of electricl pulses during predetermined prts of the respirtory cycle. The time reltion between the stimulus bursts nd the respirtory cycle could be vried. The effect of the resulting short muscle twitches upon the ctivity of the respirtory neurone ws nlysed. In ech sitution record ws mde with: 1 min. stimulus off, 1 min. stimulus on, 1 min. stimulus off. For ll experiments crp {Cyprinus crpio L.) were used nd these were kept in the bsement of the building in concrete tnks with running tp wter nd in lrge stock ponds outside. The fish mesured cm. During the experiments the fish were nesthetized through ddition of MS 222

3 Proprioceptive motor control in fish respirtion 101 Respirtory movement Neurone ctivity Triggered time bse Delyed gte. (Extended rnge modifiction)^''. Durtion stimulus \=±-,- Tek. 161 LL Frequency stimulus Stimulus pulses Integrtor M MM,;r Vi R.F. probe to muscle Fig. i. Schemtic digrm of the pprtus used for generting the muscle stimulus nd timing it with respect to the recorded neurone ctivity. For further explntion see text. to the wter in the experimentl tnk (30-50 mg/1) nd were fixed in clmp. A hole ws mde in the top of the skull exposing the cerebellum, fcil nd vgl lobes. The level of the wter in the tnk ws kept just below the border of the skull, but high enough to cover the operculr slits completely. Electricl ctivity of individul neurones in the medull oblongt ws recorded with bipolr glss-coted silver electrodes. The respirtory muscles were stimulted through monopolr stinless steel electrodes of /im plced fr prt in ech muscle. The stimulus, short burst of impulses, ws obtined from Tektronix 160 series genertor. To reduce the stimulus rtifcts picked up by the brin recording electrodes, the impulses were integrted with simple R.C. filter nd coupled to the muscle through rdio frequency isoltion unit. In combintion with the bipolr recording technique, stimulus rtifcts could thus usully be kept very smll. The phse reltion between the stimulus nd the respirtory ctivity of the fish could be controlled s follows (Fig. 1). Every first spike of the burst of ctivity recorded from respirtory cell triggered the time bse of Tektronix 532 oscilloscope.

4 102 C. M. BALLINTIJN AND 0. S. BAMFORD The sweep ws djusted to slightly shorter durtion thn one respirtory cycle. Tml onset of the 'delyed gte' of this oscilloscope served s trigger for the stimulus genertor. Thus the phse reltion between stimulus nd respirtory ctivity ws utomticlly kept constnt while the onset of the stimulus could be djusted throughout the respirtory cycle using the ' gte dely' control of the oscilloscope. In this wy it ws possible to stimulte in phse or in ntiphse with the norml ctivity of ny respirtory neurone or muscle. Aprt from synchronizing the signls, the oscilloscope lso served s monitor in displying the neurone ctivity nd the stimulus signl. As mesure of respirtion in generl, the movements of the hyomndibul or the extreme nterior border of the operculum which closely follows the hyomndibul movements, were recorded with very light mechno-electricl trnsducer. This prticulr recording site ws chosen becuse it gives the best overll impression of respirtion, s the hyomndibul plys role in the movements of the buccl nd of the operculr pumps. All the relevnt dt (nerve cell ctivity, the stimulus pulses nd the movement signl) were recorded on CEC instrumenttion tpe recorder. The tpes were nlysed on PDP 9 computer of the University Computing Centre. RESULTS Of the 53 cells studied in 33 fish, bout one-third chnged their firing chrcteristics s rection to electricl stimultion of the respirtory muscles. These units re exmined in this section, divided into groups ccording to the phse of respirtion in which the neurone under observtion ws ctive. This is convenient becuse, s will be shown in the discussion, the timing of the ctivity of neurone with respect to the ventiltory cycle gives first indiction of its possible functions. (1) Neurone ctivity during dduction Fig. 2 shows neurone firing during the complete dduction phse. On records 1 nd 3, tken respectively before nd fter record 2, it is spontneously ctive. Record 2 ws mde while the dductor mndibule ws stimulted electriclly with short bursts of pulses during the initil prt of the dduction. The result ws decrese in firing frequency. In records 4, 5 nd 6, where the pulse intervls of the neurone's spikes re plotted, this cn be seen more esily. There every spike is represented by dot, the height of which is mesure of the time elpsed since the previous spike. The higher the dot the shorter the intervl (or the higher the frequency), nd the lower the dot the longer the intervl (or the lower the frequency). During the norml ctivity of the neurone (trces 4 nd 6) its firing frequency grdully decresed in the course of every burst. When the dductor mndibule ws stimulted, however, discontinuity occurred fter the first few spikes nd the frequency suddenly dropped to lower level (trce 5). Another neurone (Fig. 3, records 1 nd 4) normlly ws ctive during the lst prt of the dduction. This cell, like tht described bove, is sensitive to dductor mndibule stimultion, nd lthough few other units were lso firing occsionlly, its spikes cn esily be recognized (records 2 nd 3). The bursts of norml ctivity in the

5 Proprioceptive motor control in fish respirtion 103 St.dd.md. Abd 1 St.d.md. Abd 1 Sec Fig. 2. Activity of neurone firing during dduction. In every record: first trce = neurone ctivity, second trce = respirtory movements, third trce = muscle stimulus signl. In records i, 2 nd 3 the neurone ctivity is shown s norml spike record, in 4, 5 nd 6 s pulse intervl or spike frequency plot. (A higher dot stnds for shorter intervl or higher frequency). Records 1, 3, 4 nd 6, norml ctivity. Records 2 nd 5, ctivity during dductor mndibule stimultion. Reduction of the firing frequency of the neurone, beginning during the stimulus period nd persisting throughout the burst (especilly cler in record 5). records re mrked with, those following stimultion with '. It is obvious tht the neurones responded with burst of ction potentils (coinciding with n inflexion in the movement trce) to stimultion of the dductor mndibule during ny prt of the respirtory cycle. Fig. 4 gin shows the behviour of neurone tht ws spontneously ctive during the lst prt of the dduction phse (records 1, 3, 4 nd 6). This cell, however, in

6 104 C. M. BALLINTIJN AND 0. S. BAMFORD 1 '71 - ^ ~ \ \ «. ' ' ' ' 2 " + ^ ^ - ^ 'ii v St.dd.md. ': ' ' A ' ' 3 " \ * -^ -- ^^^^^ " N \. ^ ^ St.dd.md. 4 ^ ^ ^ ^ s Abd.l Fig. 3. Activity of neurone firing during the lst prt of dduction. In every record: first trce = neurone ctivity, second trce = respirtory movement, third trce = muscle stimulus signl. Records 1 nd 4, norml neurone ctivity (burst mrked with ). Records 2 nd 3, neurone ctivity during dductor mndibule stimultion. (The norml bursts re mrked with nd those in response to stimultion with '.) Note tht in these records severl other units with no cler reltion to the stimulus re lso ctivted. contrst to the two described bove, responded to stimultion of the dductor mndibule (record 2) nd lso to stimultion of the levtor hyomndibule (record 5). In both cses the number of spikes per burst ws reduced from 3 to 2. However, to obtin this effect, stimultion of the levtor hyomndibule hd to occur during the lst prt of dduction, in phse with the neurone's ctivity, wheres stimultion of the dductor mndibule hd to be in ntiphse with the neurone, during the end of the bduction. (2) Neurone ctivity during the trnsition between dduction nd bduction The neurone of Fig. 5, like tht shown in Fig. 4, ws sensitive to seprte stimultion of more thn one muscle, e.g. the dductor mndibule nd the diltor operculi. It is uncertin whether it should be clssified s n 'dduction cell' or s 'trnsition cell'. In the discussion it will be shown, however, tht the distinction for the present purpose is not very importnt for this prticulr cell, which ws spontneously ctive during the lter prt of the dduction but becme trnsitionl during dductor mndibule stimultion (Fig. 5, records 2 nd 3). A stimulus of moderte intensity delivered to this muscle considerbly lengthened the burst of ctivity of the neurone, which then covered the complete bduction phse s well, nd ended long fter the

7 Proprioceptive motor control in fish respirtion I0 5 St.dd.md. St.lev.hyom. Abd I Fig. 4. Activity of neurone firing during the lst prt of dduction. In every record: first trce = neurone ctivity, second trce = respirtory movements, third trce = muscle stimulus signl. Records 1, 3, 4 nd 6, norml ctivity. Record 2, ctivity during stimultion of the dductor mndibule in ntiphse with the neurone. The number of spikes per burst is reduced. Record 5, ctivity during stimultion of the levtor hyomndibule in phse with the neurone. The number of spikes per burst is reduced. (In records 2 nd 5 stimulus rtifct could not be voided.) termintion of the stimulus (record 2). When stimulus of low intensity ws given, only one dditionl spike ws fired fter long dely (record 3). Its timing ws roughly comprble to tht of the lst spike of the burst resulting from strong stimultion. Intermedite intensity stimultion of the diltor operculi, triggered by the first spike of the neurone's ctivity, inhibited ll further ction potentils (records 5 nd 5, two consecutive rows). Furthermore the effect in this cse ws cumultive,

8 io6 C. M. BALLINTIJN AND O. S. BAMFORD St.dd.md St.dd.md.- St.dil.op. 5 St.dil.op. Abd4 Ill LLL III I Fig. 5. Activity of neurone firing during the lst prt of dduction. In every record: first trce = neurone ctivity, second trce = respirtory movements, third trce (dots) = muscle stimulus signl. Records 1, 4 nd 7, norml ctivity. Record 2, ctivity during stimultion of the dductor mndibule. The number of spikes per burst nd the burst length re incresed, nd the neurone is now firing during the bduction s well. Record 3, ctivity during weker stimultion of the dductor mndibule. One dditionl spike per burst is fired fter long ltency. Record 5 (continuous with 5 ). Activity during stimultion of the diltor operculi. The neurone is inhibited by the stimulus. The inhibition cn lst for severl cycles in which no stimulus is present. Record 6, ctivity during wek stimultion of the diltor operculi. Inhibition of the neurone which generlly only cts during one respirtory cycle. (In records 5 nd 6 stimulus rtifct could not be voided.) Sec

9 Proprioceptive motor control in fish respirtion 107 I'IIIIJI ' i n /\_> nun ' nnnru. 1 " HI i '~ n ' ' niii' ^ " \ ^. finrr -^X -^~X St.Iev.hyom. 1 fjjjh i ti'rjni ' r " nil rllli- IfjJIn ' l ^ \. S "\^ imuhi St.dil.op. Mil TIT Abd I Sec Fig. 6. Activity of neurone firing during the trnsition from dduction to bduction. In every record: first trce = neurone ctivity, second trce = respirtory movement, third trce = muscle stimulus signl. Records 1, 3 nd 5, norml ctivity. Record 2, ctivity during stimultion of the levtor hyomndibule. The number of spikes per burst is reduced except during the third respirtion where no stimulus ws given. Record 4, ctivity during stimultion of the diltor operculi. Neurone ctivity unchnged. (A stimulus rtifct could not be voided.) becuse fter while severl respirtory cycles without ny ctivity of the cell (nd consequently without stimulus) pssed before the cell fired once more. During weker stimultion this cumultive effect ws less pronounced (record 6). Record 7 gin shows the spontneous ctivity t the end of the experiment. The neurone of Fig. 6 ws clerly trnsitionl in chrcter. Its ctivity strted during the dduction nd ended during the bduction phse (records 1 nd 3). Stimultion of the levtor hyomndibule (record 2) resulted in shortening of the burst of ctivity nd reduction of the number of spikes. This effect ws not the result of generl expnsion movement becuse stimultion of the diltor operculi (record 4) ws without ny effect.

10 io8 C. M. BALLINTIJN AND O. S. BAMFORD b b b b 1 *^~ 1! V^ ~ "^ ~ - \ I >. 2 ^ ^ ^ b St.dil.op. Abd I Fig. 7. Activity of neurone firing during bduction (burst mrked with 6). In every record: first trce = neurone ctivity, second trce = respirtory movement, third trce = muscle stimulus signl. Records 1 nd 2, norml ctivity. In 1 the cell is spontneously ctive, in 2 it is not. Record 3, ctivity during diltor operculi stimultion. Except during the cough, when the cell is never ctive (see lso trce 1), stimultion of the diltor operculi elicits burst of ctivity. (3) Neurone ctivity during bduction Fig. 7 shows the ctivity of two cells recorded together. The ction potentils of one cell (mrked in the record) coincided with the dduction phse of respirtion nd do not concern us here. The burst of the other cell, if present, occurred during the bduction (b in the record). The neurone sometimes ws nd sometimes ws not spontneously ctive (Fig. 7, respectively trce 1 nd trce 2). Stimultion of the diltor operculi round the point of mximl dduction of the respirtory system ctivted the neurone (record 3) except in the middle of cough s cn be seen in the 4th respirtion of record 3. DISCUSSION Reserch on the muscle coordintion of fish respirtion (Bllintijn & Hughes, 1965; Bllintijn, 1969c; Hughes & Bllintijn, 1965; Osse, 1969) showed tht the elements of the respirtory system re coupled mechniclly so tht movements of given prt spred over the system. In fct this is one of the bsic properties giving rise to the high mechnicl efficiency of the respirtory pump in fish (Bllintijn, 1972). For the present investigtion in which the proprioceptive reflex effects of contrction of individul muscles re studied, this high degree of mechnicl coupling is very inconvenient. It ppered possible, however, to minimize spreding of the influence sufficiently by keeping the stimulus, nd thus the twitch of the muscle, smll nd short. The movement record tken from the hyomndibul, the best plce to obtin n overll impression of the pumping ctivity becuse it reflects expnsion nd contrction of the buccl s well s the operculr cvities, serves only s generl indiction

11 Proprioceptive motor control in fish respirtion 109 Muscles S. I I mill 11 I Length receptor Motor neurone Tension receptor' Bone movement Tension receptor b Motor neurone Muscle A. 1 Length receptor Fig. 8. Schemtic representtion of the norml firing pttern of the elements of proprioceptive control loop nd their rection to short muscle contrction. Muscle S is the muscle tht cn be stimulted, muscle A is the ntgonist of the stimulted muscle. Middle trce (4): movement record. The movement during stimultion is shown by broken line. Upper three trces: ctivity of motor neurone (2), tension receptor neurone (3) nd length receptor neurone (1) of muscle S, t during norml ctivity, t b during stimultion of muscle S. Lower three trces: ctivity of motor neurone (6), tension receptor neurone (5), nd length receptor neurone (7) of muscle A, t during norml ctivity, t 6 during stimultion of muscle S. of ventiltion. It certinly cn not be regrded s representtion of the chnges in movement of seprte muscles under the influence of stimultion. The choice of the muscles The most importnt respirtory muscles in the crp re: (1) The levtor hyomndibule nd its ntgonist the dductor rcus pltini, respectively expnding nd contrcting the buccl s well s the operculr cvities. (2) The diltor operculi nd its ntgonist the dductor operculi, respectively expnding nd contrcting the posterior prt of the operculr cvity nd bducting nd dducting the operculum. (3) The dductor mndibule (prt A 3 ) nd its ntgonist the levtor operculi, respectively dducting nd bducting the lower jw. It is to these three min groups of respirtory muscles tht the present investigtion ws limited, nd the experimentl conditions were such tht only these muscles took prt in respirtion. As will be explined below it is only necessry to stimulte one of n ntgonistic pir of muscles to obtin dt on the elements of the proprioceptive control system of both, when two experiments re crried out in succession. In one the muscle is stimulted in phse with its norml ctivity, nd in the other in ntiphse (i.e. in phse with its ntgonist). In the present cse, the levtor hyomndibule, the diltor operculi nd the dductor mndibule were selected becuse they re lrge, super-

12 110 C. M. BALLINTIJN AND O. S. BAMFORD ficil nd esy to rech nd it is not prticulrly difficult to stimulte them withjb problems of electricl leks to other muscles. In every experimentl series used for this pper, ll these muscles hve been stimulted both in phse nd in ntiphse with their spontneous ctivity. The properties of proprioceptive elements The rection to muscle twitch tht is cused by electricl stimultion cn be predicted for motor neurones, tension receptor neurones (tendon orgn neurones) nd length receptor neurones (muscle receptor neurones) of both the stimulted muscle nd its ntgonist. It should be stressed tht for the muscle receptors of teleosts, owing to their simple ntomicl structure, centrl driving cnnot be expected so tht they re tken to be of the pssive type. The result is summrized in Fig. 8. The middle trce (4) simultes the movement record of skeletl element to which n ntgonistic pir of muscles is ttched. For the muscle to be stimulted (S), the upwrd excursion of the trce stnds for contrction nd the downwrd excursion for extension. The movement s it is during stimultion is drwn in broken line. For the ntgonist (A) of the stimulted muscle the mening of the trce of course is the reverse: extension is 'up' nd contrction 'down'. The upper three pirs of trces (1, 2 nd 3) show the ctivity of motor neurone, tension receptor neurone nd length receptor neurone of the muscle tht cn be stimulted (S). Of every pir, the upper one () represents the norml ctivity nd the lower one (b) the ctivity during muscle stimultion, s given by the broken line in the movement trce (4). The lower three pirs of trces (5, 6 nd 7) re from motor neurone, tension receptor neurone nd length receptor neurone of the ntgonist (A) of the stimulted muscle. Here gin the upper trce of pir is norml nd the lower one during stimultion. During the upwrd excursion of the movement trce three types of cell re ctive: (1) The motor neurones of muscle S, which cuses the movement of the skeletl element to which it is connected. They fire during the rising phse of the movement trce nd not during the flling phse, the relxtion (trce z). (2) The tension receptor neurones of muscle S. They lsofire during the rising phse becuse then the tendon is under tension (trce 3 ). (3) The length receptor neurones of muscle A. They fire during both the rising nd the flling phse of the movement trce becuse during ll tht time the muscle is stretched (trce 7 ). Stimultion of muscle S, s illustrted by the broken line in trce 4, speeds up the contrction of this muscle. Becuse this results in greter tension in its tendon, the tension receptor neurones increse their firing rte (trce 3 b). This in turn results in utogenic inhibition of the motor neurones of muscle S (trce 2b), which s consequence decrese their firing rte or stop firing. Finlly stimultion of muscle S ccelertes the extension of muscle A. The firing frequency of its length receptor neurones will therefore rise (trce 76). During the downwrd excursion of the movement trce gin three types of cell re ctive: (1) The motor neurones of muscle A, which now cuses the movement. They fire during the flling phse of the movement trce nd not during the rising phse, the relxtion (trce 6 ).

13 Proprioceptive motor control in fish respirtion in Muscle 3 o - < Tendon orgn Muscle receptor * I I I III I I _LUU I I I I II I I Adduction j.abduction I Muscle Tendon orgn I I I III I Muscle receptor ll I I I I I III I I I Fig. 9. Hyomndibulr movements nd the period of ctivity of dductor nd bductor muscles together with the firing pttern of their tension receptor neurones nd length receptor neurones, during norml respirtion of crp. (2) The tension receptor neurones of muscle A. They lso fire during the flling phse becuse then the tendon is under tension (trce 5 ). (3) The length receptor neurones of muscle S. They fire during both the rising nd the flling phse of the movement trce becuse during ll tht time the muscle is stretched (trce 1 ). Stimultion of muscle S s indicted by the broken line of trce 4, countercts the ction of muscle A. This in the first plce results in n incresed tension in the tendon of muscle A nd thus in n increse in the firing frequency of its tension receptor neurones (trce 56). This incresed ctivity of the tension receptor neurone lso, s secondry rection, brings bout decrese in ctivity of the motor neurones of muscle A through utogenic inhibition (trce 6b). Becuse the stimulus durtion is kept short, mtters will not be complicted by the drop of tension this behviour initites. As the forces of muscle A nd muscle S which now both contrct, re cting in opposition, tension will lso develop in the tendon orgns of muscle S, nd ctivte their neurones (trce 3&). Further, stimultion of muscle S will decrese the extension forced upon it by the ction of muscle A. Consequently the length receptor neurones of muscle S will diminish their ctivity or stop firing (trce 1 b). Finlly Fig. 9 shows the time reltions of the ctivity of ll the elements described bove during the norml respirtory movements of crp. It should be noted, however, tht some dductor muscles normlly do not fire during the whole dduction phse but only during the lst prt of it. This is not shown in the generlized digrm of Fig. 9. The experimentl dt All the neurones which lter their firing pttern in response to the twitches cused by muscle stimultion re, in one wy or nother, under the influence of proprioceptive informtion. Anlysis of the experimentl dt presented in the Results section rill led to better understnding of the different wys in which these influences ct

14 ii2 CM. BALLINTIJN AND 0. S. BAMFORD nd of the nervous elements tht re involved. It is of specil interest to investigh whether neurones exist with the properties of the elements of peripherl proprioceptive control loop s indicted bove. () Neurones processing proprioceptive informtion t higher level of integrtion In the first plce, the records show group of nerve cells which rect to seprte stimultion of two or more muscles which re not members of n ntgonistic pir. This sitution is shown in Figs. 4 nd 5 where two different neurones rect to stimultion of the dductor mndibule nd of the levtor hyomndibule nd to stimultion of the dductor mndibule nd of the diltor operculi respectively. As these muscles re not ntgonists nd movements cused by dductor mndibule contrction re in no wy coupled to movements resulting from levtor hyomndibule or diltor operculi ctivity (s explined in Bllintijn, 1969, c), both neurones under observtion obtin their proprioceptive informtion from t lest two different sources. It my be concluded therefore tht they re not prt of peripherl proprioceptive control loop but process proprioceptive informtion t higher level of integrtion. This view is corroborted by other evidence. Delyed rections of the neurone to the stimulus nd n fter-effect of stimultion lsting for severl respirtory cycles cn occur. Neither would be expected in direct proprioceptive control loop. The first cse is illustrted in Fig. 4, trce 2, where short contrction of the dductor mndibule during the end of the bduction phse resulted in reduction of the number of spikes in the ctivity burst of neurone which fired during the lte dduction. A comprble effect cn be seen in Fig. 5 during dductor mndibule stimultion. A strong stimulus (trce 2) in this cse resulted in prolongtion of the burst of ctivity of the neurone under observtion up to long time fter the contrction hd finished. Lower intensity stimultion (trce 3) gve rise to one extr spike which, however, occurred well fter the end of the stimulus. In-phse stimultion of the diltor operculi (Fig. 5, trce 5) produced strong ftereffect on the ctivity of this sme neurone. Diltor operculi contrctions inhibited the neurone nd in the course of few respirtory cycles n fter-effect built up which stopped it completely for number of cycles. Together, the dt presented bove llow the conclusion tht these neurones re not prt of direct proprioceptive control loop but process proprioceptive informtion t higher level of integrtion. The fct tht long-term effects occur suggests tht these cells ply role in determining future respirtion on the bsis of proprioceptive signls integrted over period of time. The limited dt vilble t present, do not justify further specultions on the chrcteristics nd function of this group. (b) Neurones recting s elements of peripherl proprioceptive control loop In the remining experiments the neurones under observtion did not rect to twitches of muscles of more thn one ntgonistic pir. (As mentioned before, for every neurone investigted, muscles of ll three importnt ntgonistic pirs hve been stimulted, both in phse nd in ntiphse.) Thus they stisfy the first criterion for elements of the peripherl proprioceptive control loop. On the grounds of their firing chrcteristics nd responses to muscle stimultion, it cn be shown tht mosfc

15 Proprioceptive motor control in fish respirtion 113 these neurones exhibit the typicl properties expected of length receptor neurones, tension receptor neurones or motor neurones. Fig. 6 shows records of neurone tht behved s length receptor of the levtor hyodibulmne. Its spontneous ctivity (records 1, 3 nd 5) occurred during the trnsition of dduction to bduction, nd, s explined before (Figs. 8 nd 9), length receptors fire either during the trnsition from dduction to bduction or during the trnsition from bduction to dduction when their muscles re extended. Moreover, stimultion of the levtor hyomndibule during its extension resulted in decresed ctivity of the neurone (Fig. 6, record 2). As explined bove (Fig. 8), this is typicl rection for length receptor neurone. Tht this rection is not the result of generl expnsion movement cn be concluded from the fct tht stimultion of the diltor operculi, which lso cuses considerble expnsion of the respirtory cvity, did not influence the firing pttern of the neurone t ll (Fig. 6, record 4). The lrge difference in shpe of the movement trce of records 2 nd 4 is explined by the fct tht the trnsducer ws recording hyomndibulr movements. These of course re very sensitive to levtor hyomndibule contrctions, while diltor operculi contrctions, lthough giving rise to mrked expnsion movements, influence the position of the hyomndibul to much lesser extent. It is therefore justifible to conclude tht the neurone of Fig. 6 behved s length receptor neurone of the levtor hyomndibule. The neurones of Fig. 3 nd 7 behved s tension receptor neurones of the dductor mndibule nd the diltor operculi respectively. The spontneous ctivity of the first one (Fig. 3, records 1 nd 4) occurred during the lst prt of the dduction phse, when the ctivity of the dductor mndibule, which often strts t low level, generlly shows mrked increse. Thus the timing of the norml burst of the neurone ws in greement with wht is expected for either tension receptor neurone or motor neurone. However, electricl stimultion of the dductor mndibule during ll phses of the respirtory cycle elicited series of ction potentils from the neurone (Fig. 3, records 2 nd 3; = norml burst, ' is burst in response to stimultion). This rection rules out the possibility of motor neurone, since this would be inhibited by stimultion of its own muscle. The rection is, however, identicl to tht of tension receptor neurone, which would fire whenever the tension in the tendon is high, due to either norml muscle contrctions or to twitch following electricl stimultion. (Burst ', resulting from muscle stimultion in the mjority of cses, is shorter thn the durtion of the stimulus, but so is the disturbnce of the movement trce. Apprently movements compensting the tension-effect of the stimulus occur.) The neurone of Fig. 7 ppered to hve higher threshold thn tht of Fig. 3. If it ws spontneously ctive it fired during bduction (Fig. 7, record 1, burst b), but generlly it ws silent during norml respirtion (record 2). In those cses where it ws ctive, the movement trce ws slightly steeper, indicting tht the ppliction of more muscle power ws producing fster movement. The firing pttern thus resembled tht of motor neurone or tension receptor neurone. Stimultion of the diltor operculi, except during the cough when the neurone never fired, elicited burst of ction potentils (Fig. 7, record 3), so tht here lso the possibility of motor neurone is ruled out nd the neurone ppers to hve been tension receptor neurone of the diltor operculi. Finlly in Fig. 2 n exmple of motor neurone is given. The norml ctivity of the 8 EXB 62

16 ii4 C. M. BALLINTIJN AND O. S. BAMFORD cell occurred during the dduction phse when both motor neurones nd tensiob receptor neurones were firing (records i, 3, 4 nd 6). In this experiment, electricl stimultion of the dductor mndibule resulted in decrese in firing frequency of the neurone, which shows very clerly in the pulse intervl plots of Fig. 2 (record 5). Thus this cell behved s motor neurone nd not s tension receptor neurone. After termintion of the stimulus the firing frequency of the neurone did not return to its originl level. It continued from the new level becuse prt of the movement, being dduction of the lower jw, hd lredy been performed due to stimultion. Conclusions Proprioceptive signls re processed in the respirtory centre in the medull oblongt of the crp. This processing is of two kinds. At comprtively high level of integrtion, signls of severl sources converge nd fter-effects of medium or long durtion mke possible 'dvnce progrmming' of respirtion. At lower level, proprioceptive informtion is processed in proprioceptive control loops contining nerve cells with the properties of length receptor neurones, tension receptor neurones nd motor neurones. With the id of these networks, breth-by-beth disturbnces of the respirtory movements cn be quickly compensted. REFERENCES BALLINTIJN, C. M. (1969). Movement pttern nd efficiency of the respirtory pump of the crp. jf. exp. Biol. 50, BALLINTIJN, C. M. (19696). The influence of proprioception upon respirtory neurons in the medull oblongt of fishes. Ad Physiol. Phrmcol. Neerl. 15, BALLINTIJN, C. M. (1969c). Functionl ntomy nd movement co-ordintion of the respirtory pump of the crp. J. exp. Biol. so, BALLINTIJN, C. M. (1972). Efficiency, mechnics nd motor control of fish respirtion. Respir. Physiol. 14, BALLINTIJN, C. M. & HUGHES, G. M. (1965). The musculr bsis of the respirtory pumps in the trout. J. exp. Biol. 43, BAUMGARTEN, R. VON & SALMOIRAGHI, G. C. (1962). Respirtory neurons in the goldfish. Arch. Itl. de Biol. 100, BONE, Q. (1964). Ptterns of musculr innervtion in the lower chordtes. Intern. Rev. Neurobiol. 6, GRANIT, R. (1970). The Bsis of Motor Control, ch. vm, pp Intercostl muscles nd diphrgm. London-New York: Acdemic Press. HUGHES, G. M. & BALLINTIJN, C. M. (1965). The musculr bsis of the respirtory pumps in the dogfish. J. exp. Biol. 43, NEWSOM DAVIS, J. (1970). Spinl control. In The Respirtory Muscles, Mechnics nd Neurl Control, pp Ed. E. J. M. Cmpbell, E. Agostini nd J. Newsom Dvis. London: Lloyd-Luke. OSSE, J. W. M. (1969). Functionl morphology of the hed of the perch. Neth. y. Zool. 19, SATCHELL, G. H. (1959). Respirtory reflexes in the dogfish, y. exp. Biol. 36, SATCHELL, G. H. (1961). The response of the dogfish to noxi, y. exp. Biol. 38, SATCHELL, G. H. & WAY, H. K. (1962). Phryngel proprioceptors in the dogfish Squlus cnthis L. y. exp. Biol. 39, SERBENYUK, TS. V. (1964). Peculirities of the structure nd functioning of the respirtory centre in fishes. Adv. Mod. Biol. 58, SERBENYUK, TS. V. (1965). The importnce of fferenttion in the development of rhythmic ctivity of the respirtory centre in fish. In Essys on Physiologicl Evolution, pp Ed. J. W. S. Pringle. Oxford: Pergmon Press. SERBENYUK, TS. V., SHISHOV, B. A. & KIPRIAN, T. K. (1959). Reltionship between utonomic nd reflex processes in the rhythmicl ctivity of the respirtory centre in fish. Biofissik 4, SHELTON, G. (1970). The regultion of brething. In Fish Physiology, vol. IV, pp , Ed. W. S. Hor, D. J. Rndll. New York nd London: Acdemic Press. SUTTERLIN, A. M. & SAUNDERS, R. L. (1969). Proprioceptors in the gills of teleosts. Cn. y. Zool. 47,