AFFERENT IMPULSES FROM SINGLE MYELINATED FIBERS IN SPLANCHNIC NERVES, ELICITED BY MECHANICAL STIMULATION OF TOAD'S VISCERA

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1 AFFERENT IMPULSES FROM SINGLE MYELINATED FIBERS IN SPLANCHNIC NERVES, ELICITED BY MECHANICAL STIMULATION OF TOAD'S VISCERA AKIRA NIIJIMA Department Physiology, Niigata University School Medicine, Niigata Morphologically it is well known that abdominal viscera such as stomach, intestine, rectum, gall-bladder, pancreas, spleen, liver, urinary bladder mesentery are mainly innervated by, vagal or pelvic s. It is supposed that afferent impulses from abdominal viscera are conducted in se s. Recently, afferent impulses from vagal fibers stomach intestine have been studied by Paintal (9, 10, 11) Iggo (5). On or h, impulses in hypogastric pelvic s from urinary bladder have been recorded by Evans (2), Talaat (12) Iggo ( 5). Tower (14) recorded discharge impulses in sympatic rami frog showed clearly that y contain afferent fibers from intestine. Furr, Gammon Bronk (3) have recorded afferent impulses from mesenteric in cat discussed physiological meaning Pacinian corpuscles without obtaining any decisive results. Several years later Gernt Zotterman (4) observed afferent impulses from fine strs mesenteric s elicited by stimulation viscera in cat. The impulses recorded by Tower Gernt et al., fall into two main groups, characterized by different modes exitation rates conduction. In one group impulses were elicited by light mechanical stimuli conducted rapidly, spike heights being relatively large. On or h, nociceptive stimuli such as pinching, scraping, burning or application acid, evoked slowly conducted impulses. The size action potentials this group was small. In se studies, however, impulses from single afferent fibers were not recorded little is known about se single afferent fibers receptors belonging to se fibers. Very recently, author (8) reported on sensory innervation kidney testis toad by recording afferent impulses in single fibres from se organs. In this study it was found that kidney testis were segmentally innervated by afferent s receptive fields belonging to single afferent fibers were relatively small. The present paper will mainly deal with afferent impulses from single fibers sensory mechanism mechano receptors toad's viscera except kidney testis on which author has already reported ( 8 ). Received for publication July 23, 1959.

2 AFFERENT IMPULSES IN SPLANCHNIC NERVES 43 METHOD All excised experiments trunks from in 1. fig. cut as each side below viscera- as FIG. 1. viscera sympatic trunks rectum performed used. The from was diagram toad in supply freed toad routinely two viscra tube was cut beds with ir surrounding above viscera with liver, G: doudenal spleen, R: tic gall-bladder, loop, P: I: intestine, S: rectum, pancreas, St: M: stomach, mesentery,, Sp: SC: sympa- chain. FIG. 2. Dissected technique to. was sheath pulled selected out fibers (middle). One for use a The mounted is The single isolate on Photograph single afferent on are fiber: trunk glass plate or separated intact all side from fibers remaining shows fiber (above). The cut one across. anor desired ones in size are is cut (below). Horizontal bar FIG. 100ƒÊ FIG. 2 1 shown stomach s,. L: as an tissues made. toad's was abdominal from digestive freed preparation on Usually, chains were possible. Schematic been centrally away These D: have preparation thus

3 44 A. NIIJIMA The single fibers were dissected from trunks with aid a binocular microscope ( ~ 60) by technique described by Kato (6) Tasaki (13). In s ir connective-tissues were far thicker more sticky than that motor s it was more difficult to remove m (fig. 2). For mechanical stimulation, touch or pressure by a glass rod or von Frey's hair occasionally a specially made apparatus which was described in previous paper (8) were used. RESULTS Afferent impulses were recorded from single fibers when mechanical stimuli with sufficient intensity to elicit action potentials were given to mechano-receptors in abdominal viscera. Receptive fields: Receptive fields belonging to single afferent fibers were estimated by monitoring by a loud-speaker afferent impulses evoked by pressure von Frey's hair. Before use, single fiber preparation was reaffirmed by a high power microscope. In almost all cases it was observed that afferent impulses could be recorded from single fiber by mechanical stimulation several different abdominal viscera as shown in table 1 fig. 3. Namely, receptive fields belonging to single afferent fibers were suprisingly larger than expected ten had area from about 200 to 1000 mm2. TABLE 1 Usually, it seems true that mechano-receptors on mesentery belonging to large fibers are densely distributed along course blood vessels radiating from root mesentery, or receptors belonging to small fibers are distributed not only along courses blood vessels but also between m. Thus, afferent impulses could be elicited from almost whole abdominal viscera except liver. No impulse was recorded from s to liver. From se facts it may be assumed that generally in toad single afferent

4 AFFERENT IMPULSES IN SPLANCHNIC NERVES 45 fibers innervate not only large receptive fields but also many different abdominal viscera in common (fig. 3). FIG. 3. Impulses in a single afferent fiber during sustained pressure on stomach, pancreas, mesentery, intestine rectum. Shaded areas show sensitive parts to pressure stimulus. Vertical bar shows 100 ƒêv, horizontal 1 sec. in all succeeding figures if not orwise mentioned. Fiber diameter shape impulses: The diameter range single myelinated fibers from which afferent impulses could be recorded was about 3 to 14ƒÊ including myelinsheath. The dissection technique single small fibers was more difficult than that large ones. The spike heights action potentials recorded from large fibers were usually higher durations were shorter than that small fibers (fig. 4, 5). Adaptation: A study in detail many abdominal mechano-receptors showed that during maintained pressure stimulus re were two modes discharges. In some cases, when light mechanical stimuli were applied continuously to abdominal viscera, several afferent impulses were elicited from fibers at onset pressure stimulus. If stimulus-strength was increased, more frequent afferent impulses were elicited not only at moment onset but also several seconds after that (fig. 6, 8). In or cases, irrespective stimulus-strength, afferent impulses were observed instantaneously at begining end stimulation. During maintained stimulation no impulse

5 46 A. NIIJIMA FIG. 4. Afferent impulses from dual myelinated fibers with diameter 8.8 ƒê (A) 3.3ƒÊ (B) several unmyelinated fibers (C). Shaded areas show sensitive parts to pressure stimulus. Small spontaneous discharges are due to unmyelinated fibers. FIG. 5. Impulses in a small afferent fiber during sustained pressure on mesentery. Shaded areas shows sensitive parts to stimulation.

6 AFFERENT IMPULSES IN SPLANCHNIC NERVES 47 could be observed (fig. 7, 9). Namely, former was slowly adapting latter was rapidly adapting mechano-receptor. FIG. 6. Impulses in a afferent fiber: Discharge impulses during pressure stimulation pancreas in A upper part rectum in B. Intensity pressure 10 mm Hg/2 ~2 mm2. (above). 30 mmhg/2 ~2 mm2. ( below). 1 2 FIG. 7. Impulses in a afferent fiber: Discharges afferent impulses in a fiber during pressure stimulation to duodenal loop in A, pancreas in B mesentery in C. Intensity pressure 20 mm Hg/2 ~2 mm2. in part mmhg/2 ~2 mm2. in part 2.

7 48A. NIIJIMA FIG. 8. Adaptation curves receptors: Diagrams (A, B) show relationship between impulses per second time lapse after application continued pressure stimulus. A, pancreas, B, rectum. These viscera belong to same single afferent fiber. Abscissae: time in second. Ordinates: impulses per sec. FIG. 9. Adaptation curves receptors: Diagrams (A, B, C) show relationship between impulses per second time lapse after application continued pressure stimulus. A, dnodenal loop, B, pancreas, C, mesentery. These viscera belong to same single afferent fiber. Abscissae: time in second. Ordinates: impulses per sec. DISCUSSION Tower (14) reported that several afferent fibers are distinguished from ir spike heights shapes action potentials in a intercommunicating ramus sympatic chains she showed by her method that distribution individual fibers was always less wide than that ramus, yet area supplied each was suprisingly large.

8 AFFERENT IMPULSES IN SPLANCHNIC NERVES 49 However, by this method it will be difficult to distinguish afferent fibers with almost same diameters. In this paper it was confirmed from afferent impulses single fibers that se fibers supplied large receptive fields ranged from about 200 to 1000 mm2. Maruhashi, Tasaki et al. (7) reported that receptive fields single tactile fibers toads were about 20 mm2. that cats were spot-like but exceptionally wide-receptive fields cats were suprisingly large ranging from 1500 to 4000 mm2. Tower (15) was able to show by recording afferent impulses that terminal ramification a single afferent fiber from rabbit's cornea comprise a unit area from 50 to 200 mm2. that area has sharply circumscribed limits. She suggests term "sensory unit" for such terminations, in parallel with "motor unit". Namely, it can be said that sensory unit fiber toad is larger than that touch or pressure fiber skin toad cat except that wide-receptive fiber cat. But re remained a question, wher fiber itself peripheral part or than a receptor a single dissected afferent fiber could respond to mechanical stimuli or not. If it responds to stimuli, can se responses be attributed to afferent impulses from mechano-receptor itself? The answer was as follows: The afferent fibers could respond to tight pressure stimuli on ir course, but threshold was far higher than that mechano-receptors when such strong stimuli were applied, fibers were probably injured could not respond repeatedly. On or h, mechanoreceptors were brought to activity repeatedly by light stimuli such as touch by von Frey's hair. Furhter, Gernt Zotterman (4) reported that Pacinian corpuscles exposed mesentery were found to be extremely sensitive to most gentle pressure stimulation se corpuscles elicited large fast Ĉ-potentials. Furrmore y observed that injurious stimuli such as pinching applied to intestinal wall as well as to mesentery produced ĉ- C-potentials. From above mentioned it is probably true that single small afferent fibers toad with diameter about 3 to 5 Đ corresponds to ĉ-fibers large afferent fibers with diameter 6 to 14 Đ corresponds to Ĉ-fibers in Gernt Zotterman's classification in cat (fig. 4). But Pacinian corpuscles any or type specific receptors could not be found in toad's mesentery or abdominal organs in present work. Furr, re are two main groups abdominal mechano-receptors, which one is rapidly adapting, or slowly adapting receptors as in case skin. The former corresponds to rapidly adapting touch receptors type (a) latter to slowly adapting touch or stretch receptor type (b) by Catton's classification in skin (1). During strong pressure stimulation in present work, small, slowly adapting a-impulses were observed y may be evoked from nociceptors in viscera as in skin. Thus it may be concluded that afferent fibers in s are not essentially different from that somatic s.

9 50 A. NIIJIMA On multiple innervation abdominal viscera by afferent fibers which was suggested from facts above-described, furr studies must be done. SUMMARY The afferent impulses from single fibers during mechanical stimulation toad's viscera have been studied by means oscilloscopic recording. The results are summarized as follows: 1) In general it was recognized that a single myelinated afferent fiber innervated in common two or more different organs. 2) The range diameter myelinated afferent fibers was 3 to 14ƒÊ including myelinsheath. 3) In viscera toad two types adaptation were found in mechanoreceptors. The one was rapid-adapting or slow-adapting. 4) The receptive fields which were supplied by a single fiber were relatively large as compared to that skin fiber REFERENCES 1. CATTON, W. T. Some properties frog skin mechano-receptors. J. Physiol. 141: , EVANS, J. P. Observations on s supply to bladder urethra cat, with a study ir action potentials. J. Physiol. 86: , GAMMON, G. D. AND BRONK, K. W. The discharge impulses from Pacinian corpuscles in mesentery its relation to vascular changes. Amer. J. Physiol. 114: 77-84, GERNANDT, B. AND ZOTTERMAN, Y. Intestinal pain: an electrophysiological investigation on mesenteric s. Acta Physiol. Sc. 12: 56-72, IGGO, A. Tension receptors in stomach uninary bladder. J. Physiol. 128: , KATO, G. The microphysiology. Tokyo: Maruzen, MARUHASHI, J., MIZUGUCHI, K. AND TASAKI, I. Action currents in single afferent fibers elicited by stimulation skin toad cat. J. Physiol. 117: , NIIJIMA, A. The afferent innervation kidney testis toad. Jap. J. Physiol. 9: , PAINTAL, A. S. A method locating receptors visceral afferent fibers. J. Physiol. 124: , 1954 a. 10. PAINTAL, A. S. The response gastric stretch receptors certain or abdominal thoracic vagal receptors to some drugs. J. Physiol. 126: , 1954 b. 11. PAINTAL, A. S. Responses from mucosal mechanoreceptors in small intestine cat. J. Physiol. 139: , TALAAT, M. Afferent impulses in s supplying urinary bladder. J. Physiol. 89: 1-13, TASAKI, I. Nervous transmission. Springfield: C. C. Tomas, TOWER, S. Action potentials in sympatic s, elicited by stimulation frog's viscera. J. Physiol. 78: , Tower, S. Unit for sensory reception in cornea with notes on impulses from sclera, iris lens. J. Neurophysiol. 3: , 1940.