HYPOTHALAMIC ELECTRICAL ACTIVITIES PRODUCED BY FACTORS CAUSING DISCHARGE OF PITUITARY HORMONES TERUO NAKAYAMA* Institute of Physiology, School of Medicine, University of Nagoya It is known that electrical stimulation of the hypothalamus (1, 2, 3) evokes a marked eosinopenic response, which is regarded satisfactorily as an index showing the rate of secretion of adrenal cortical hormone (4). On the other hand, certain centres in the hypothalamus are responsible for antidiuretic agents. It was found that intracarotid injections of hypertonic sodium chloride resulted in an inhibition of a water diuresis, the response being diminished by some 90 per cent after removal of the posterior pituitary (5, 6). The receptors sensitive to the osmotic change in the blood appear to lie in the stream bed of the internal carotid artery, probably in the supraotic nuclei, although proof is as yet lacking. It is believed that the antidiuretic activity seen in these experiments is due to the release of antidiuretic hormone from the posterior pituitary. With stimulation of the anterior hypothalamus in the vicinity of the supraoptic region, Harris (7) noted a release of the posterior pituitary hormone. From these findings, it may be supposed that the electrical activities of the hypothalamus are produced by antidiuretic stimuli. Investigations into these electrical activities have so far been rather limited. Grinker and Serota (8) were the first to observe the effects of epinephrine and other autonomic drugs on hypothalamic activity. On application of certain acute stress stimuli, it has recently been reported that the increased electrical activity was recorded in the posterior hypothalamus (9). The problem as to whether local electrical response could be elicited in the hypothalamus by means of osmotic stimuli is deserving of consideration. The present study examines whether or not certain stimuli which are interpreted as factors effecting the discharge of the pituitary can alter hypothalamic electrical activity. METHOD The experiments were made on 18 male rabbits of about 2 kg. body weight. Rabbits were slightly anesthetised with ether during the operation and mounting of electrodes. The electrodes were inserted into the anterior and posterior hypothalamus through the scalp, the base of electrodes fixed to the scalp with dental cement. In some cases, the carotid sinus was denervated. After the Received for publication August 2, 1955.
312 T. NAKAYAMA operation, the animals were liberated for about 1 hour. Test solutions or drugs were injected while recording the electrical activity of the brain by way of silver silver-chloride electrodes in unipolar or bipolar fashion. Encephalography was made with 4 or 6-channel balanced amplifier driving inkwriters. When injected into the carotid artery, solutions were kept warm at blood temperature. After the experiments, the hypothalamus and the pituitary region were hardened, by 10 per cent neutral formaline and examined histologically. RESULTS Epinephrine and Histamine. At first an injection of 20ƒÊg. of epinephrine was made into the auricular vein as slowly as possible. With this dose of epinephrine, animals did not show any kind of apparent disturbances. In fig. 1 C are shown the electrical activities of anterior and posterior hypothalamus 3 minutes after the injection. Increase of amplitude and sometimes of frequency of the wave was seen in the posterior hypothalamus. This augmented activity began 30 sec. after the injection and reached the maximum in 2 to 5 minutes. Its subsequent diminutions were variable, the resting state being restored usually within 15 minutes. These augmented activities could not be obtained in all parts of the posterior hypothalamus, for they disappeared when the electrodes A B C D FIG. 1. Records of electrical activities of anterior and posterior hypothalamus in bipolar fashion. A. Resting state. B. 7 minutes after the injection of epinephrine (100 ƒêg.). C. 3 minutes after the injection of epinephrine (20 ƒêg.). D. 3 minutes after the injection of epinephrine (20 ƒêg.) and 25 minutes after the administration of pituitrin.
HYPOTHALAMIC ELECTRICAL ACTIVITIES 313 were moved a short distance. The region responsible for epinephrine, though not detected exactly, was restricted to the vicinity of the mammillary body. In the anterior hypothalamus, alteration of the spontaneous rhythm did not occur. A few changes of the electrical activity of the frontal cortex were observed. This change appeared at the same time as the hypothalamic discharge, but disappeared and returned to the resting state usually within 1 minute. In a large dose of epinephrine, such as 100 Đg., augmented activities appeared also in the anterior hypothalamus (fig. 1B). In this case, marked changes occurred in the posterior hypothalamus and cortex, and continued for 30 to 40 minutes. 1.0 mg. of histamine phosphate was administered by intraperitoneal injection. About 5 to 10 minutes later, augmented activity appeared in the posterior hypothalamus as illustrated in fig. 2 B, and lasted for about 20 minutes. The changes of the pattern of the wave were gradual in nature and of lesser extent than those in epinephrine. A B FIG. 2. Records of electrical activities of anterior and posterior hypothalamus in unipolar fashion. A. Resting state. B. 8 minutes after the injection of histamine phosphate. Pituitrin. Posterior pituitary hormone (Pituitrin) was injected subcutaneously in a dose of 100 mu per 1 kg. body weight. Observations of the electrical activity of hypothalamus were made for about 1 hour. However, no change could be detected. In the course of this experiment, epinephrine was injected intravenously 10, 20 and 30 minutes respectively after the administration of pituitrin. The increased electrical activity was seen restricted to the posterior hypothalamus (fig. 1D), as was the case when the epinephrine alone was injected. The effect of pituitrin on the epinephrine induced electrical activity could not be found. Hypertonic NaCl solution. 5 cc. of 2.5 per cent NaC1 solution was at first
314 T. NAKAYAMA injected into the saphenous vein. In this treatment, no alteration of cortical or hypothalamic activities was observed. Intracarotid injection of the same solution, however, as shown in fig. 3 A, resulted in a transient increase of the electrical activity when the electrodes were in the supraoptic region. This activity began a few seconds after the injection and lasted for about 30 to 45 sec., the recovery to the resting state taking more than 1 minute. In the posterior hypothalamus and cortex of frontal lobe no change of activity appeared. 20 per cent glucose solution injected into artery had a similar effect. A B C FIG. 3. Records of electrical activities of anterior and posterior hypothalamus in bipolar fashion. A. 30 sec. after the injection of 2.5 per cent NaCI solution. B. 30 sec. after the injection of water. C. 30 sec. after the injection of 2 per cent urea solution. Distillated water. 5 cc. of water was injected into the carotid artery in 8 to 10 sec. Some diminution in the electrical activity occurred in the supraoptic region of the anterior hypothalamus (fig. 3 B). This depressive effect was not so manifest, the resting state being restored within 1 minute. These changes induced by hypertonic solution or water were not constantly recorded. The appearance seems to be dependent on the position of electrode, osmotic value Of the test solution, and the rate of infusion. 2 per cent Urea and Normal saline solution. An intravenous injection of these solutions had no influence, and even when injected into the carotid artery the hypothalamic and cortical activities did not show any alteration. DISCUSSION On application of epinephrine, Simms et al. (10) have shown an increased electrical activity in the cerebral cortex alone, and Porter (9) has reported that
HYPOTHALAMIC ELECTRICAL ACTIVITIES 315 the increased activities are noted in the cortex and posterior hypothalamus. In the present experiment, a similar effect of epinephrine on the hypothalamus was obtained on rabbits. Porter has already discussed this subject and I have nothing further to add. From electroencephalographic study alone, however, it cannot be concluded whether or not these augmented activities are essential for the production of stress-induced eosinopenia. With a large amount of epinephrine, increased electrical activity was also seen in the anterior hypothalamus, synchronously with augmented cortical activity. In general, epinephrine is known to inhibit the antidiuretic effect (11, 12). Regarding the augmented activity in the hypothalamus as an effecting factor for the release of antidiuretic hormone, these results may be preposterous. However, the administration of such a large dose of epinephrine seems to be far beyond the physiological limit and acts nonselectively directly or indirectly on the central nervous system. The injection of histamine was accompanied by a discharge of ACTH, and resulted in eosinopenia, but not when the lesion was made in the posterior hypothalamus (1). In this experiment, histamine evoked a change in the posterior part of the hypothalamus. This region, therefore, seems to be involved in the pituitary-adrenal response induced by histamine. It has been reported by Euler (13) that slow potential changes in the order of 1 mv occur in the supraoptic region of the hypothalamus by means of an injection of a 2 per cent NaC1 or 10 per cent glucose solution into the common carotid artery, and tap water similarly injected generally evokes a potential change of opposite polarity to that obtained by the hypertonic solution. These findings and the results here described probably may be another representation of the same physiological events in the hypothalamus, judging from the time course and the magnitude of the changes. It would seem likely that the osmoreceptors postulated by Verney (5, 6) lie within, or in the vicinity of, the supraoptic nuclei, and the pituitary begins to discharge antidiuretic hormone during the time of this evoked change in the supraoptic region. The injection of hypertonic urea solution did not change the hypothalamic activity. Urea is a substance which diffuses uniformly between the extra- and intracellular fluids. Osmotic effect can not be predicted on this substance even when administered in hypertonic solution. In Verney's experiments (6), this substance had no antidiuretic effect. In the light of these observations, it appears certain that osmotic stimuli which can induce an antidiuretic activity are also capable of altering the electrical activity of the hypothalamus. From the above experiments alone, however, it can not be decided whether this neural activity is actually concerned with the stimuli to the pituitary, or is merely a related event. It is another problem whether other stimuli which can induce antidiuretic effects can alter the electrical activity of the hypothalamus. Acetylcholine, in small or large doses, interrupts the course of a water diuresis, and the supraoptic nuclei are involved in this mechanism (11, 14, 15, 16, 17). By my unpublished observations, the so called "acetylcholine spike" was evoked with a small dose, and a large dose of this drug has a depressive effect on the cortical and hypothalamic electrical activity. However, it seems likely that the augmented activity in the
316 T. NAKAYAMA hypothalamus is not the result of the increased secretory activity of the posterior pituitary, because the administration of pituitrin failed to evoke such a change. Recently it has been reported that the vasopressor fraction of posterior pituitary hormone inhibits the release of ACTH provoked by epinephrine (18). Whether this inhibitory effect occurs in the hypothalamus, in the pituitary, or in other parts was in question. Pituitrin administered did not interfere with the increased activity induced by epinephrine. This result, therefore, suggests that the inhibitory effect of pituitary hormone does not occur in the hypothalamic level. SUMMARY Hypothalamic electrical activities were observed as follows; 1) The injection of epinephrine and histamine evoked increased electrical activity in the posterior hypothalamus. 2) Electrical activity in the supraoptic region showed a transient increase and decrease with intracarotid injections of hypertonic NaCl solution and water respectively. Normal saline or 2 per cent urea solution had no effect. 3) Pituitrin had nothing to do with hypothalamic electrical activity. The results were discussed in connection with the secretion of pituitary hormone. REFERENCES 1. PORTER, R. W. Am. J. Physiol. 172: 515, 1953. 2. DEGROOT, J. AND HARRIS, G. W. J. Physiol. 111: 335, 1950. 3. ANAND, B. K. AND DUA, S. J. Physiol. 127: 153, 1955. 4. MCDERMONT, W. V., FRY, E. G., BROBECK, J. R. AND LONG, C. N. H. Yale J. Biol. Med. 23: 52, 1950. 5. VERNEY, E. B. Lancet 2: 739, 781, 1946. 6. VERNEY, E. B. Proc. Roy. Soc. London B. 135: 25, 1947. 7. HARRIS, G. W. Philos. Trans. B. 232: 385, 1947. 8. GRINKER, R. R. AND SEROTA, H. J. Neurophysiol. 1: 573, 1938. 9. PORTER, R. W. Am. J. Physiol. 169: 629, 1952. 10. SIMMS, E., PFEIFFENBERGER, M. AND HEINBECKER, P. Endocrinol. 49: 45, 1951. 11. DUKE, H. N. AND PICKFORD, M. J. Physiol. 114: 325, 1951. 12. O'CONNOR, W. J. AND VERNEY, E. B. Quart. J. exp. Physiol. 33: 77, 1945. 13. EULER, C. v. Acta Physiol. Scand. 29: 133, 1953. 14. PICKFORD, M. J. Physiol. 95: 226, 1939. 15. PICKFORD, M. J. Physiol. 166: 264, 1947. 16. DUKE, H. N., PICKFORD, M. AND WATT, J. H. J. Physiol. 111: 81, 1950. 17. PICKFORD, M. AND WATT, J. A. J. Physiol. 114: 333, 1951. 18. ARIMURA, A. Jap. J. Physiol. 5: 37, 1955.