(Received February 6, 1934.)

Transcription

1 218 6I2.327:6I2.826 THE EFFECTS OF HYPOTHALAMIC STIMULATION ON GASTRIC MOTILITY. BY J. BEATTIE AND D. SHE E HAN (Rockefeller Research Fellow). (From the Department of Anatomy, McGill University, Montreal.) (Received February 6, 1934.) INTRODUCTION. MCCREA, MCSWINEY and STOPFORD [1925,1927] described the effects of vagal and splanchnic stimulation on the active ("fed") and inactive ("unfed") stomach, and were able to show that the results depended to some extent on the pressure within the stomach before stimulation was commenced. Vagal stimulation was followed in the fed and unfed stomach by an initiation of gastric contractions, preceded by a latent period varying according to the initial state of the organ. Beattie [1932a], during an investigation of a possible parasympathetic centre within the hypothalamus, observed that faradic stimulation of the tuber region in cats caused increased gastric peristalsis, together with a flow of watery secretion from the gastric mucosa. In further development of this work, it was decided to make use of the method of recording intragastric pressure adopted by McCrea, McSwiney and Stopford, and to compare the effects on gastric motility of stimulation of different regions of the hypothalamus. By such a procedure it was hoped to obtain graphic evidence which would prove of value in the further elucidation of the hypothalamic mechanisms. METHOD. Cats were used throughout this series of experiments. We found at an early stage in our investigations that an "open" abdomen was not only inconvenient but unnecessary. It is true that our records show respiratory excursions, but these did not obscure the salient points which we were investigating.

2 HYPOTHALAMUS AND GASTRIC MOVEMENTS. 219 As McCrea, McSwiney and Stopford had used chloralose as their anesthetic, we decided to adopt this method of ansesthesia. We can agree that this drug does not affect the sensitivity of the stomach to vagal stimulation. Dale and Feldberg [1933] also used chloralose in their investigations of the effects of vagal stimulation on stomach activity and on the production in the stomach wall of an acetylcholine like substance. We have observed, however, quantitative discrepancies between hypothalamic stimulatiqn and vagal stimulation. These we consider are due to a depression of the vagal centre within the medulla. A like conclusion was reached by Raymond-Hamet [1928], who studied the effects of adrenaline on unanaesthetized dogs and dogs anaesthetized by chloralose. In earlier experiments we had used dial, but found that it depressed the hypothalamic centres more than chloralose; for these reasons we abandoned dial in favour of chloralose aneesthesia. It was found that an interval of several hours between the administration of the anaesthetic and the commencement of hypothalamic stimulation gave the most striking results. This may be explained by the gradual diminution of the depressor action of the chloralose on the medullary and other centres. Faradic stimulation was used in all the experiments. Bipolar electrodes were used at first, but it was found that unipolar electrodes gave a more accurately localized stimulation, with the minimum amount of damage to surrounding tissue. Three volts were used on the primary circuit, the secondary coil being placed at 10; the number of stimuli per second was approximately 30. When a unipolar electrode was used, the diffuse electrode was placed under the skin over the sacral region of the animal. Spread of the current was avoided and checked by observations of the pupil; stimulation of the anterior hypothalamus being accompanied by a contracted pupil, posterior hypothalamic stimulation by a dilated pupil. Both fed (active) and starved (24 hours) animals were used; but it was found that in practice the resting stomach gave more uniform and more easily interpreted records. The effects of stimulation of the hypothalamus in animals with food present in the stomach were exceedingly difficult to interpret. Blockage of the cesophageal catheter probably occurred quite frequently and in addition it was found difficult to establish a control tracing before stimulation was commenced. For these reasons we decided to carry out all our experiments on the starved animal. Following intravenous chloralose ansesthesia, a mid-line incision was made in the neck. A tracheal catheter was tied in position and the left common carotid artery isolated. An cesophageal catheter, holding a glass

3 220 J. BEATTIE AND D. SHEEHAN. nozzle at the end, was passed into the stomach, so that the nozzle projected through the cardiac orifice. The abdomen was opened, the pylorus tied, and the abdomen closed immediately, so that the minimum exposure of the gut to the air resulted. McCrea, McSwiney and Stopford state that tying of the pylorus was not a necessary step in their technique, but we found that much more accurate and comparable results could be obtained if the amount of fluid in the stomach remained constant through- Fig. 1. Changes in the intragastric pressure following stimulation of the peripheral end of the right vagus. Left vagus sectioned. For interpretation of the figure, see text. out the experiment. The animal was then placed lying on its abdomen, and the head of the animal slightly raised and fixed firmly in position c.c. warm saline were introduced into the stomach through the esophageal catheter, which was then attached to a water manometer. The tracheal catheter was connected with a Marey's tambour, and bloodpressure was recorded from the left common carotid. The hypothalamus was exposed by a dorsal approach, splitting the corpus callosum in the mid-line, and the floor of the third ventricle exposed by gentle separation of the lateral walls. By such an approach a clean exposure of the anterior and posterior hypothalamus can be obtained without haemorrhage.

4 HYPOTHALAMUS AND GASTRIC MOVEMENTS. 221 DIscussIoN OF RESULTS. Stimulation of the tuber region gave constantly a rise of intragastric pressure varying from 10 to 50 mm. (Figs. 3, 4). In no case was it as striking as that produced by stimulation of the peripheral end of the cut vagus. It was observed that there was a latent period of approximately Fig. 2. Changes in the intragastric pressure following stimulation of the peripheral end of the right vagus. Left vagus intact. 30 sec. between the commencement of stimulation and the first rise in intragastric pressure. With direct vagal stimulation the latent period was only a few seconds (never more than 10 sec.). The rise of intragastric pressure on tuber stimulation was accompanied by a fall in blood-pressure and by a subsequent increase in peristaltic movements of the stomach (Fig. 4). Peristaltic waves were not neces-

5 222 J. BEATTIE AND D. SHEEHAN. Fig. 3. The effect of stimulation of the tuber cinereum on the intragastric pressure. Fig. 4. The effect of stimulation of the tuber cinereum region on the intragastric pressure and the blood-pressure.

6 HYPOTHALAMUS AND GASTRIC MOVEMENTS. 223 sarily coincident with an upward stroke of the intragastric pressure recording system as we have been able to confirm by direct observation of the opened abdomen. The recording system indicated only changes in the total volume and pressure of the stomach. A well-established peristaltic wave frequently caused no alteration in the level of the recording lever, as it was accompanied by a relaxation of the stomach wall proximal and distal to the site of contraction. At times a well-marked contraction IEig. 5. Changes in the intragastric pressure and blood-pressure folowing mechanical stimulation (insertion ofa monopolar electrode without subsequent electrical stimulation) of two regions of the anterior hypothalamus. wave was recorded by a fall in the level of the recording lever. When the contraction waves followed one another rapidly there was invariably a rise in intragastric pressure with excursions of the recording lever which were not synchronous with the respiratory rhythm. In a completely inactive stomach only respiratory excursions were seen on the intragastric pressure tracing. When irregularities of this^tracing were observed, there was no doubt that such irregularities were due to peristaltic activity as the general presure level did not vary to any appreciable degree. This effect can be seen in Fig. 6 in the periods before and after stimulation, and in Fig. 7.

7 224 J. BEATTIE AND D. SHEEHAN. Stimulation of the tuber cinereum after unilateral vagal section showed a comparable effect to that described above, but decidedly less striking; after bilateral vagal section, the effect of tuber stimulation on both intragastric and blood-pressures was completely abolished (Fig. 7) although the stomach was still in an active state, as shown by the slight variations in the intragastric pressure tracing and by subsequent stimulation of the peripheral end of the right vagus (Fig. 8). There is therefore Fig. 6. Tracing of the intragastric and blood.pressure changes followingstimulation of the posterior hypothalamus. experimental evidence that the efferent pathway from the anterior hypothalamus includes vagal fibres to the stomach, an efferent mechanism for which we have evidence (unpublished observations by the senior author). Mechanical stimulation of the anterior hypothalamic region, as produced by the simple insertion of a monopolar electrode, produced a similar effect to that of electrical stimulation (Fig. 5). At the point indicated by the first arrow, the electrode was inserted anteriorly, in the neighbourhood of the supra-optic nuclear group. This resulted in a slight rise in

8 HYPOTHALAMUS AND GASTRIC MOVEMENTS. 225 intragastric pressure. When the electrode was placed in the tuber region (second arrow) a much more striking result was obtained. In the control experiments of stimulation of the vagus nerve we found, in contradistinction to McCrea, McSwiney and Stopford, that the right vagus gave a better response than the left. Further, iji the resting Fig. 7. The effect on the blood-pressure and intragastric pressure following stimulation of the tuber cinereum. Both vagi cut. stomach a marked rise in intragastric pressure seemed the more significant and constant effect. Peristaltic movements were not always initiated (cf. Figs. 1, 2). On cessation of vagal stimulation the intragastric pressure fell dramatically, often below the previous level, and peristaltic activity, if obtained during stimulation, ceased or became much diminished. If vagal stimulation was continued over a long period (5 min.), the intragastric

9 226 J. BEATTIE AND D. SHEEHAN. pressure usually fell 2 or 3 min. after commencement of stimulation; a subsequent rise in intragastric pressure during the latter part of the stimulatory period frequently occurred. In the resting stomach the latent period of vagal stimulation seemed very short, often only 1 or 2 sec. This was ob,erved by McCrea, McSwiney and Stopford, but they concluded that initiation of gastric contractions was a more constant feature of vagal stimulation than rise in intragastric pressure. In the Fig. 8. The first stimulation was applied to the posterior hypothalamus, causing a fall in intragastric pressure. Both vagi were sectioned. Subsequent stimulation of the peripheral end of the right vagus produced a rise in intragastric pressure and increased peristalsis. Fig. 8 is a continuation of the same experiment illustrated in Fig. 7. later paper McCrea and McSwiney [1927-8] found that with a low intragastric pressure (in active stomach) splanchnic stimulation resulted usually in a rise of intragastric pressure, and movements may or may not follow. With high intragastric pressures, splanchnic stimulation gave a fall in intragastric pressure with cessation of movements. Stimulation of the posterior hypothalamus showed, in contrast to the above, a slight fall in intragastric pressure, accompanied by a rise in blood-pressure, and, what appeared still more significant, a complete

10 HYPOTHALAMUS AND GASTRIC MOVEMENTS. 227 obliteration of all gastric motility. This is clearly demonstrated in Fig. 6, where only respiratory waves are seen in the intragastric record during posterior hypothalamic stimulation. More striking results were obtained when the initial intragastric pressure was high. The gastric phenomena produced by posterior hypothalamic stimulation were not affected by section of the vagi. It would appear from our results that a well-defined similarity exists between the effects of tuber stimulation and vagal stimulation on gastric motility, and similarly between posterior hypothalamic stimulation and splanchnic stimulation, though we never obtained a rise in intragastric pressure on pure posterior hypothalamic stimulation. This similarity is more qualitative than quantitative. The difference is probably due at least in part to the depressant action of chloralose on the hypothalamic and vagal centres. Beattie has shown [1932b] that there exists probably in the hypothalamus two distinct mechanisms-an anterior or "parasympathetic" and a posterior or " sympathetic "-and the results recorded above appear to give a direct experimental proof of such an arrangement, in so far as gastric motility is concerned. SUMMARY. 1. Faradic stimulation of the tuber region in the fasting cat, under chloralose ansesthesia, resulted in a rise of intragastric pressure, with a subsequent increase in peristaltic movements of the stomach. 2. Section of both vagi abolished this effect. 3. Faradic stimulation of the posterior hypothalamus in the fasting cat, under chloralose anesthesia, resulted in a slight fall in intragastric pressure and a complete obliteration of all gastric motility. We wish to acknowledge with thanks grants in aid of the expenses of the above research from the Banting Research Foundation, Toronto, and the Cooper Fund of McGill University. REFERENCES. Beattie, J. (1932 a). J. Canad. med. A , 278. Beattie, J. (1932 b). Ibid. 26, 400. Dale, H. H. and Feldberg, W. (1933). J. Phy8iol. 80, 16 P. McCrea, E. D., McSwiney, B. A. and Stopford, J. S. B. (1925). Quart. J. exp. Physiol. 15, 201. McCrea, E. D., McSwiney, B. A. and Stopford, J. S. B. (1927-8). Ibid. 18,301. Raymond-Hamet, M. (1928). C. R. Acad. Sci. Paris 188, 101. PH. LxxxI. 15