Anteromedial Hypothalamus Research Articles

The content of gonadotropin-releasing hormone (GnRH), kisspeptin, and estrogen receptors (ERα/ERβ) in the anteromedial hypothalamus displays daily variations throughout the rat estrous cycle.

The content of gonadotropin-releasing hormone (GnRH), its mRNA, and estrogen receptor alpha (ERα) and beta (ERβ) in the hypothalamus varies throughout the estrous cycle. Furthermore, the abundance of these molecules displays asymmetry between the right and left side. In the present study, we investigated the changes in the content of ERα, ERβ, kisspeptin, and GnRH by western blot in the left and right anteromedial hypothalamus, at four different times during each stage of the rat estrous cycle. The serum levels of the follicle-stimulating hormone (FSH) and luteinizing hormone (LH) were also measured. ERα and ERβ levels changed depending on the stage of the estrous cycle, meanwhile that of kisspeptin was modified according to both the hour of the day and the stage of the cycle. Except in estrus day, ERβ was higher in the right hypothalamus, while ERα was similar in both sides. During both proestrus and estrus, the content of kisspeptin and GnRH was higher in the right hypothalamus. The highest levels of FSH and LH occurred at 17:00h of proestrus. But at estrus, the highest FSH levels were observed at 08:00h and the lowest at 17:00h. Thus, the current results show that the content of ERα, ERβ, kisspeptin, and GnRH in the anteromedial hypothalamus are regulated as a function of the stage of the estrous cycle and the hour of the day. Furthermore, the content of these proteins is regularly higher in the right anteromedial hypothalamus, regardless of the stage of the cycle or time of the day.

Changes in the Leukocyte Distribution and Surface Expression of Adhesion Molecules Induced by Hypothalamic Stimulation in the Cat

Emotions and the neuroendocrine system are known to affect leukocyte distribution. However, there have so far been few reports on the relationship between hypothalamically induced emotional behavior and the endocrine–immune response. We previously reported changes in the leukocyte distribution and adhesion molecules induced by anteromedial hypothalamus stimulation (AH stimulation), which elicits restlessness behaviors in the cat. In this study, we examined ventromedial hypothalamus stimulation (VMH stimulation), which elicits threat behaviors. In addition, the endocrine responses after VMH stimulation were evaluated. VMH stimulation as well as AH stimulation induced elevations of plasma cortisol and epinephrine levels and granulocytosis and lymphopenia. In contrast, VMH stimulation induced only an elevation of plasma norepinephrine and elicited an opposite pattern of CD62L expression on the leukocyte subpopulations. The different endocrine–immunological reactions between VMH stimulation and AH stimulation were thus associated with different types of behavioral responses.

Influence of hypothalamically induced restlessness under fasted and fed conditions on plasma levels of glucose, free fatty acids and total cholesterol

AbstractInfluence of hypothalamically induced emotional behavior on plasma levels of epinephrine (E), norepinephrine (NE), glucose, cortisol, free fatty acids (FFA) and total cholesterol (T‐C) were examined in cats under both fasted and fed conditions. Restlessness was evoked intermittently for 6 h by electrical stimulation of the anteromedial hypothalamus (AMH). Blood was sampled immediately before, 1 h after and 6 h after the start of stimulation. Both E and glucose levels in the restlessness group increased markedly after 1 h and then tended to decrease after 6 h in fasted and fed states. In the restlessness group the NE level increased after 1 h and further increased after 6 h and cortisol level increased markedly, whether cats were fasted or fed. The FFA level in the fasted restlessness group showed no change while it increased in the fasted control group after 6 h. By contrast, the FFA level in the fed restlessness group significantly increased after 6 h while no change was observed in the fed control group. The T‐C level decreased only under the fasted condition in both restlessness and control groups. These results indicated that AMH‐induced restlessness elicited marked sympatho‐adrenal activation and hyperglycemia whether cats were fasted or fed while the behavior showed a different pattern in the response of plasma FFA between fasted and fed conditions. Copyright © 2001 John Wiley & Sons, Ltd.

Effects of both the emotional behavior and feeding conditions on the circulating plasma volume and plasma glucose levels in cats

Influence of hypothalamically induced emotional behavior on the circulating plasma volume, plasma levels of glucose, epinephrine (E), norepinephrine (NE), dopamine (DA) and cortisol were examined in awake cats under both fasted and fed conditions. Restlessness was evoked intermittently for 6 h by electrical stimulation of the anteromedial hypothalamus (AMH). Blood was sampled immediately before, 1 h after and 6 h after the start of stimulation. Changes in the plasma volume was calculated by changes of hemoglobin (Hb) and hematocrit (Ht). As the control group, another 7 cats with electrodes implanted but unstimulated were identically treated under both fasted and fed conditions. Both E and glucose levels in restlessness group once markedly increased after 1 h and then tended to decrease after 6 h, whereas NE levels in restlessness group increased after 1 h and further increased after 6 h, whether cats were fasted or fed. DA levels increased under the fasted condition of restlessness. The cortisol level markedly increased in both fasted and fed restlessness groups. The plasma volume in control group increased under the fed condition, while in restlessness group it decreased remarkably and tended to decrease more in a fasted state than in a fed state. These results indicated that AMH induced restlessness elicited marked sympatho-adrenal activation, hyperglycemia and hemoconcentration, whether cats were fasted or fed. Relationship among such responses, and the difference in responses between fasted and fed conditions were also discussed in the paper.

Changes in the Leukocyte Distribution and Surface Expression of Adhesion Molecules Accompanied with Hypothalamically Induced Restlessness in the Cat

One type of emotional behavior called restlessness occurs when the anteromedial hypothalamus is stimulated in cats. We examined the changes in the distribution and surface expression of adhesion molecules in leukocytes accompanied with restlessness. Mature female cats were used for this study. The cats were stimulated with 60 Hz sine wave train pulses (20–90 μA, 10 s in duration, at 5-min intervals) for 60 min. Samples of blood were collected from 30 min before stimulation up to several hours after the final stimulation. The number of granulocytes increased just after stimulation, while at the same time the expression of L-selectin decreased. On the other hand, the number of CD4+ and CD8+ T lymphocytes decreased at 1–2 h after the end of the stimulation, while the expression of L-selectin increased. In addition, the expression of LFA-1 and VLA-4 did not change. These data suggest that hypothalamically elicited restlessness is thus accompanied by a leukocyte distribution change, which might be mediated by changes in the expression of L-selectin on leukocytes. Plasma cortisol increased during stimulation in restlessness. However, during in vitro culture experiments, cortisol did not alter the expression of leukocyte L-selectin which thus indicated that cortisol does not directly affect the surface expression of L-selectin. These results thus suggest that hypothalamically induced restlessness is a useful stress model for psychoneuroimmunological studies.

Kainic acid versus response in the cat

The emotional-defensive response (EDR) and accompanied neurotoxic and electroencephalographic (EEG) effects induced by injection of kainic acid (KA, 0.1; 0.2 pg[ into the midbrain periaqueductal grey region (PAG) and antero-medial hypothalamus (AMH) in the cat were examined and compared with EDR and accompanied neurotoxic and EEG effects induced by injection of cholinergic agent, carbachol (CCH[, into the same sites. The injections of KA (0.2 hg) into the PAG induced EDR which closely resembled the defense behavior typically observed after administration of CCH. However, in contrast to CCH-induced EDR, the defensive response induced by KA was found to be accompanied by EEG symptoms of epileptiform activity in the limbic cortex and a massive cell loss in the site of injection. It is proposed that KA-induced EDR and seizure activity may have resulted from the activation of different cell populations localized either in the vicinity of the injection (i.e. PAG region) and in the area remote from the injection loci, the limbic cortex. KA induced activation of PAG neuronal network would trigger the ‘local response’ (emotional-defensive response) and produce a remote effect — epileptiform activity.

Changes in urinary cortisol associated with hypthalamically elicited restlessness

AbstractUsing unanaesthetized and free‐moving mature female cats, we examined changes of cortisol levels in 24‐hr urine accompanying emotional behaviour such as restlessness elicited by electrical stimulation of the anteromedial hypothalamus(AMH). Urine was collected every 24 hr for 9 consecutive days and stimulation was applied for only the middle 3 days with chronically implanted electrodes placed in the AMH. Cat urine was hydrolysed with β‐glucuronidase and sulphatase; the levels of free cortisol, glucuronide and sulphate were determined by fluorescence polarization immunoassay. The mean (fSD) of the total cortisol level calculated in terms of the creatinine level in the 3 days before stimulation was 13.04 ± 4.89 ng/mg creatinine; the mean for the 3 days during stimulation was 19.06 ± 7.56 ng/mg creatinine; and the mean for the 3 days after stimulation was 13.97 ± 4.10 ng/mg creatinine. The cortisol level during stimulation showed a significant increase compared with that before stimulation (p < 0.05) and almost recovered to the prestimulation level 3 days after stimulation. These results indicate that the emotional behaviour such as restlessness induced by AMH stimulation in cats may have some relation to emotional stress.

Effects of Ibotenic Acid‐Induced Neuronal Degeneration in the Hypothalamus upon Proceptivity and Sexual Receptivity in the Female Marmoset (Callithrix jacchus)

The sexual behaviour of 16, oestradiol-treated, ovariectomized common marmosets was recorded before and after bilateral microinfusions of ibotenic acid (n = 8) or isotonic saline (n = 8) into the hypothalamus. Ibotenic acid-induced neuronal degeneration occurred in 5 females, mainly affecting the anterior and dorsomedial hypothalamus. Marked decreases in proceptivity (tongue-flicking, staring and immobile displays) occurred after ibotenic acid lesions, whereas sexual receptivity (refusals and terminations of male partners' mounts) was unchanged. In 3 females where microinfusions of ibotenic acid were attempted but failed to produce lesions, sexual behaviour was unaffected and resembled that measured in saline-treated controls. These results provide the first evidence that selective lesions of neuronal cell bodies in the anteromedial hypothalamus disrupt proceptivity whilst sparing sexual receptivity in a primate species.

Distribution and hypothalamic projection of tyrosine‐hydroxylase containing neurons of the nucleus of the solitary tract in the pigeon

The avian nucleus of the solitary tract has an extensive subnuclear organization. Several subnuclear cell groups can be distinguished on the basis of cytoarchitectonic criteria. In general, the subnuclei of the medial division of the nucleus of the solitary tract receive gastrointestinal afferents, whereas the subnuclei of the lateral division of the nucleus of the solitary tract receive cardiopulmonary afferents. Forebrain afferents to the nucleus of the solitary tract are segregated to medial and lateral subnuclei, which are located at the periphery of the nucleus. These peripheral subnuclei of the nucleus of the solitary tract are also the source of ascending axonal projections to the forebrain. In this study, the tyrosine hydroxylase (initial enzyme for catecholamine synthesis) content of the anteromedial hypothalamic projecting neurons of the nucleus of the solitary tract is determined by use of a combined retrograde fluorescent dye-immunofluorescence method. Fast Blue implanted into the anteromedial hypothalamus (in the region of the nucleus periventricularis magnocellularis) resulted in the retrograde labeling of neurons in the caudal two-thirds of the nucleus of the solitary tract. At levels rostral to the obex, dye-labeled cells were mostly observed in the dorsally located subnuclei medialis superficialis pars posterior and lateralis dorsalis pars posterior and in the ventrally located subnucleus medialis ventralis pars posterior. More centrally located subnuclei contained few labeled cells, if any. For example, subnucleus medialis intermedius pars posterior only had a few retrogradely labeled cells, whereas the centrally located subnucleus medialis dorsalis pars posterior was almost devoid of labeled cells. At levels caudal to the obex, many retrogradely labeled neurons of the nucleus of the solitary tract were observed. Neurons immunoreactively labeled for tyrosine hydroxylase were mostly found within subnuclei, which contain anteromedial hypothalamic projection neurons. In subnuclei medialis superficialis pars posterior and lateralis dorsalis pars posterior, 87% of the retrogradely dye-labeled cells were also immunoreactively labeled, whereas in the caudal nucleus of the solitary tract (at levels caudal to the obex), 68% of the retrogradely labeled cells were immunoreactively labeled. Not all tyrosine hydroxylase containing cells had projections to the implantation site in the anteromedial hypothalamus since only 40% of the immunoreactive cells in the caudal nucleus of the solitary tract and 59% of the immunoreactive cells in the subnucleus medialis superficialis pars posterior were retrogradely labeled with Fast Blue.(ABSTRACT TRUNCATED AT 400 WORDS)

Cardiac arrhythmias induced in cats by stimulation of the anteromedial hypothalamus

Negative emotional behavior induced during stimulation of the anteromedial hypothalamus is frequently accompanied by cardiac arrhythmias just after cessation of the stimulation (the poststimulus arrhythmias: the PSAs). A mechanism related to the PSAs may be neurogenic in origin. Whether or not the PSAs are influenced by hypothalamically induced adrenal catecholamines has not been settled. We assessed the correlation between these influences on the PSAs induced by anteromedial hypothalamic stimulation in anesthetized cats. Thirty-five adult cats were given stimulation through an electrode inserted stereotaxically into the hypothalamus and arterial blood pressure, electrocardiogram and heart rate were recorded on a polygraph. PSAs were never observed after vagotomy and intravenous injections of methyl-atropine and phentolamine. Carteolol was without effect. When an intentional gradual reduction of stimulus intensity was applied instead of sudden cessation of hypothalamic stimulation, there was a gradual decline in the blood pressure and no PSAs. Adrenalectomy did not alter the threshold for the PSAs but did reduce the frequency of the PSAs. Intravenous injections of catecholamines produced cardiac arrhythmias similar to those seen in PSAs. After vagotomy, stimulation of the distal nerve of the right vagus during or just after hypothalamic stimulation produced the same arrhytmias as seen in PSAs, but vagus stimulation alone did not. These results suggest that the PSAs are due to ‘sudden’ change from sympathetic to parasympathetic influences on the heart and that adrenal catecholamines are involved in the prolongation of the train of the PSAs. These findings support the proposal that the PSAs are a stress-related symptom induced by stimulation of the anteromedial hypothalamus.

The pathways mediating affective defense and quiet biting attack behavior from the midbrain central gray of the cat: an autoradiographic study

The purpose of this study was to describe the pathways which mediate feline affective defense and quiet biting attack behavior elicited from the midbrain central gray. In these experiments, methods of [ 3H]leucine and 2-deoxy-[ 14C]glucose (2-DG) radioautography were utilized in concert with the technique of electrical and chemical brain stimulation. Affective defense behavior elicited from the midbrain central gray is characterized by marked vocalization such as hissing and growling, pupillary dilatation, urination and piloerection. In contrast, quiet biting attack elicited from the midbrain central gray lacks overt autonomic signs observed with affective defense response as well as the stalking component which is typically associated with stimulation of the lateral hypothalamus. Nevertheless, central gray-elicited attack resulted in a directed bite of the neck of an anesthetized rat in a manner similar to that observed from the hypothalamus. Affective defense was elicited from the dorsal half of the midbrain central gray, while quiet biting attack was obtained following stimulation of the ventral half of the midbrain central gray, thus indicating a functional differentiation of the central gray with respect to these two forms of aggression. In a separate series of experiments, affective defense or quiet biting attack response was identified by electrical stimulation through a cannula electrode situated in the midbrain central gray. The affective defense responses were subsequently elicited following microinjections of d,l-homocysteic acid through the same cannula electrode in order to demonstrate that these responses were the result of direct stimulation of cell bodies within the central gray. Then, one of the following autoradiographic tracing procedures was utilized: (1) [ 3H]leucine was injected through a cannula electrode and the animal was sacrificed after a 4- to 14-day survival period; or (2) a 2-DG solution was systemically injected and electrical stimulation was applied through the cannula electrode in order to metabolically activate the pathways associated with each of these responses. In general, the pattern of labelled target regions as indicated by 3H-amino acid radioautography was similar to that obtained from the 2-DG autoradiographic analysis. The principal ascending pathway associated with affective defense was traced to the anteromedial hypothalamus and medial thalamus. Concerning descending projections, label was traced into the central tegmental fields of the midbrain and pons, locus coeruleus and motor and main sensory nuclei of the trigeminal complex. With regard to quiet biting attack, a different projection pattern appears to be present. Label was followed rostrally to the level of the posterior half of the perifornical hypothalamus. Caudally directed fibers associated with quiet attack appeared to be more restricted than those linked to the affective defense response. These axons were traced primarily to the superior colliculus, central tegmental fields and raphe complex of the midbrain and pons. The results suggest that: (1) the midbrain central gray serves as a critical structure for the expression of, at least, the vocalization component of affective defense behavior since axons associated with this response supply nuclei of the trigeminal complex; and (2) the expression of quiet biting attack from the midbrain central gray may involve the activation of both descending fiber bundles from the central gray to the tegmentum as well as those which innervate the perifornical hypothalamus.

Kainic acid lesions of the cat's antero-medial hypothalamus and emotional-defensive response evoked by carbachol injection to the same loci.

Injections of carbachol (CCh) through a chronic cannula into the antero-medial hypothalamus (AMH) of the cat induced the emotional-defensive response (EDR) which was evaluated by time duration and number of growls in a 30-min experimental session. That response was examined before and after injection of kainic acid (KA) to the same loci of hypothalamus. None of KA doses employed (3 micrograms/2 microliter and 6 micrograms/2 microliter of vehicle) brought about statistically significant changes in parameters of the vocal response. The results suggest that either the AMH neuronal perikarya responsible for CCh-induced EDR, are resistant to KA, or muscarinic receptors initiating the EDR are not localized on perikarya.

The role of the anteromedial hypothalamus in Dahl hypertension

Radiofrequency lesions were placed in the anteromedial hypothalamus in Dahl rats to investigate the role of this area in salt-induced hypertension. Lesions of the paraventricular and suprachiasmatic nuclei and intervening tissue (PVN-SCN lesions) prevented the rise in blood pressure (mmHg) in salt-sensitive (DS) rats fed a high-salt (8% NaCl) diet for 15 weeks (controls: 195 ± 9, lesioned: 128 ± 11, p < 0.01). Similar lesions in salt-resistant (DR) rats did not alter long-term blood pressure (controls: 121 ± 6 mmHg, lesioned: 131 ± 5). Lesions sparing the PVN had no effect on blood pressure in DS rats, while lesions primarily confined to the PVN delayed the rise of blood pressure in DS fed a high salt diet. Round-the-clock determinations demonstrated that the blood pressure of DS rats with PVN-SCN lesions was reduced relative to controls at all times of the day throughout the study. No differences were observed between the angiotensininduced drinking and plasma sodium concentrations of rats with PVN-SCN lesions and those of controls. Twenty-four hour mean heart rate was decreased by 10% in DS rats with PVN-SCN lesions. The anteromedial hypothalamus may participate in the initiation of Dahl hypertension.

The organization of the hypothalamic pathways mediating affective defense behavior in the cat

The purpose of this study was to describe the hypothalamic pathways which mediate affective defense in the cat utilizing the methods of [ 14C]2-deoxyglucose (2-DG) and [ 3H]leucine radioautography in concert with the technique of electrical brain stimulation. The feline affective defense response, characterized by pupillary dilatation, piloerection, ear retraction, hissing, growling and striking with the forepaws, was elicited consistently by stimulation of sites within the ventromedial hypothalamus and anterior aspect of the medial hypothalamus. In one series of experiments, 2-DG autoradiography was employed to describe the brain regions activated following stimulation of site in the region of the ventromedial hypothalamus from which affective defense had been elicited. Ventromedial hypothalamic stimulation produced activation primarily in forebrain regions situated rostral to the level of the stimulating electrode. These structures included principally the anteromedial hypothalamus and medial preoptic area, as well as the bed nuclei of the stria terminalis and anterior commissure, diagonal band and lateral septal area. The caudal extent of activation included only the dorsal and perifornical hypothalamus at the level of the stimulation site. In a second series of experiments, affective defense sites in the anteromedial hypothalamus were stimulated and the regional distribution of 2-DG label was identified. In contrast to the results obtained from ventromedial hypothalamic stimulation, these experiments revealed a marked descending distribution of label within the posterior hypothalamus, midbrain central gray and ventral tegmental area. Results obtained from studies in which tritiated amino acids were injected into affective defense sites in both the ventromedial nucleus and anteromedial hypothalamus confirmed the general findings observed with 2-DG autoradiography. From these observations, we have concluded that the organization of the pathway mediating affective defense behavior from the ventromedial hypothalamus to the midbrain involves an initial synapse within the region of the anteromedial hypothalamus and a second synapse in the midbrain central gray substance. The significance of the anteromedial hypothalamus for the expression of affective defense behavior was considered in the Discussion.

Effect of stimulation of visual cortex on limbic and diencephalic neurons

For most brain regions the responses of neurons to stimulation of the primary visual cortex (CTX) are unknown. The objective of this study was to determine how neurons (single-unit activity) in major limbic, thalamic, hypothalamic, and visual regions respond to electrical stimulation of the CTX. Cats underwent low cerveau isolé surgery (isolate forebrain) and electrode implantation. Unit activity was analyzed as action potentials recorded extracellularly under control (spontaneous firing rate) and experimental (poststimulus rate) conditions. A total sample of 2055 units were localized anatomically. The effect of CTX stimulation was primarily inhibitory in the initial 500-ms poststimulus responses. Only 20 cells (<1%) showed initial excitatory responses. Highly responsive regions included areas 17, 18, 19 and the hippocampal formation. Subcortical regions which showed marked ( P < 0.01) inhibitory responses form part of the ascending reticular system (anterior, intralaminar, and reticular thalamic nuclei, and tegmental nucleus). Similar effects were also observed in the anteromedial hypothalamus. Only two regions showed significant ( P < 0.05) prolonged responses (1 to 5 s) to CTX stimuli. One of them, the prostriatal cortex, exhibited increases in firing rates. The other, the cingulate cortex, showed inhibitory initial and prolonged responses. Therefore, information provided by CTX stimulation is distributed to different limbic and subcortical targets. We suggest that the mechanisms responsible for the effects of visual stimuli on arousal and emotion may be mediated by inhibition of ascending reticular pathways.

Effect of caffeine on neocortical unit responses to meso-diencephalic stimulation

Activity of sensomotor cortical neurons during high-frequency and single stimulation of the meso-diencephalon was recorded in acute experiments on anesthetized cats. Caffeine (20–40 mg/kg) increased the firing rate of the cells to some extent. Meanwhile the intensity of the activation shift gave stimulation of the reticular formation and the antero-medial and lateral hypothalamus was increased. The number of activation responses increased and areactive neurons were less frequent. At the same time no considerable changes were found in the inhibitory responses. Modulation of the cortical responses by caffeine is considered to be due chiefly to a change in the excitability of the cortical cells.

The effect of hypothalamic lesions and hypophysectomy on adrenal weight in Sceloporus cyanogenys

Adrenal hypertrophy was induced in male Sceloporus cyanogenys with Metyrapone. Radiofrequency lesions of the anteromedial hypothalamus and of the median eminence were followed by a decrease in the weights of the adrenal glands compared to those of the control animals, and hypertrophy of the glands did not occur following metyrapone. Both sham-operation and lesions of other areas of the brain (cerebral hemisphere, posterior and lateral hypothalamus) increased adrenal weight; however, the weight increase induced by sham-operation was less than that induced by lesions of these areas of the brain. While Metyrapone increased adrenal weight in all groups other than those with lesions of the anteromedial hypothalamus and median eminence, the increase over and above that caused by the lesions of other areas of the brain was not statistically significant. Lesions of the hypothalamus, wherever placed, increased thyroid weight whereas lesions of the cerebral hemispheres did not. Hypophysectomy prevented the adrenal weight response to Metyrapone, and the injection of ACTH increased adrenal weight in both intact and hypophysectomized animals.

Gastric secretory response of the unrestrained cat following electrical stimulation of the hypothalamus, amygdala, and basal ganglia

The effect of intracerebral stimulation on the basal gastric secretory response was examined in unanesthetized, unrestrained cats equipped with a permanent gastric fistula and indwelling electrodes. A consistent gastric acid response was obtained without concomitant behavioral or motor changes when specific regions located in the supraoptic area, the lateral amygdala and the anterior amygdala—globus pallidus area were stimulated for 15 min. The responses first appeared after a latent period of 15 to 30 min and persisted thereafter for periods ranging up to 75 min. Three of these responses were accompanied by an increase in pepsin output, while one showed a significant increase in chloride output and one displayed a significant decrease in secretory volume. All five of these sites failed to evoke a significant increase in total acidity or pepsin output when the intensity of the stimulus was raised to levels which produced gross autonomic, behavioral or motor changes. Stimulation of one of the two sites located in the caudate nucleus elicited a consistent and significant decrease in chloride output without concomitant behavioral and motor changes. The other site in the caudate nucleus and those in the lateral hypothalamus, and the pyriform cortex and putamen areas of the lateral amygdala were consistently negative at sign-free intensities. The results that were obtained with the five placements located in the supraoptic area, the lateral amygdala and the anterior amygdala—globus pallidus area support the view that the amygdala mediates its gastric secretory activity through the anteromedial hypothalamus.

The production of tremor by cholinergic drugs: Central sites of action

The tremorogenic effect of systemically administered oxotremorine has been examined in rats following brain transections and after placement of electrolytic lesions. Transections passing through the caudal midbrain or anterior pons prevent oxotremorine-induced tremor. Lesions placed in an area extending between the rostal midbrain and caudal pons, in all cases involving portions of the dorsal tegmentum, abolish or reduce this tremor. Lesions of diencephalic structures are without effect. Microinjections of oxotremorine or carbachol into four areas of the cat brain produce tremor: the basal forebrain, near the diagonal band of Broca; the medial preoptic area; the anteromedial hypothalamus; and the mesencephalo-pontine junction. Atropine sulfate administered into the same sites or systematically reverses this effect.

Cerebral involvement in the inhibition of ACTH secretion by hydrocortisone.

Cerebral and pituitary involvement in the feedback regulation of ACTH secretion was investigated by stereotaxic placement of single (roughly 0.2 mg) or double implants of crystalline hydrocortisone acetate in the brain or pituitary of male rats. Compensatory adrenal hypertrophy (CAH) was measured 9–10 days following unilateral adrenalectomy. Single hydrocortisone implants in the median eminence and the anteromedial hypothalamus resulted in abolition of CAH and in atrophy of the remaining adrenal. Ventral prostate weights in these rats were decreased somewhat, but testicular, thyroid and pituitary weights were unchanged, and prostatic, testicular and thyroid histology was normal. Hydrocortisone implants in the lateral basal hypothalamus produced only partial inhibition of CAH, and cholesterol implants in the median eminence had no effect. Single hydrocortisone implants in the pituitary gland were likewise ineffective, as were 3 of 4 double implants in the pituitary. Normal CAH followed single anterior fore...