Medial Hypothalamic Region Research Articles

Autoradiographic studies of a glucocorticoid agonist and antagonist: Localization of 3H-corticosterone and 3H-cortexolone in mouse brain

The localization in the mouse brain of corticosterone, the natural glucocorticoid in the mouse, and cortexolone, reported to be a glucocorticoid antagonist, was studied by autoradiography 30 min after in vivo administration of the tritiated compounds. After 3H-corticosterone (3HB) injection, radioactivity was preferentially concentrated in cell nuclei of several structures within the limbic system, and in nuclei of certain neurones of the cerebral cortex and medullar oblongata. This nuclear concentration was abolished after injection of 3H-corticosterone with an excess of unlabelled corticosterone. After 3H-cortexolone (3HS) injection, a diffuse radioactivity was observed throughout the brain. However, a higher concentration of grains was present in the ventral nucleus arcuatus and in the infundibulum. When excess unlabelled cortexolone was administered with 3H-cortexolone this preferential accumulation of grains was abolished. The accumulation of 3H-cortexolone in the medial basal hypothalamic region suggests that cortexolone concentrates preferentially in dexamethasone (DM) target regions, and in addition the autoradiographic results show that the cortexolone-receptor complex does not accumulate in the cell nucleus.

Effects of medial hypothalamic lesions on the lordosis response and other behaviors in female golden hamsters

The lordosis response in ovariectomized, hormone-primed females was measured in repeated weekly tests before and after bilateral lesions of various medial hypothalamic regions. Changes in body weight, frequency of vaginal marking, and agonistic behavior were also recorded. Forty-two females were divided into five groups based on lesion location: (1) medial preoptic (MPO), (2) medial anterior hypothalamus (MAH), (3) dorsomedial nucleus-dorsal premammillary nucleus (DM-DPM), (4) dorsal ventromedial nucleus (Dorsal VMN), (5) medial basal hypothalamus (MBH). Unoperated control females were tested in an identical manner. Only lesions in the region of the ventromedial nucleus eliminated lordosis. Lesions which disrupted lordosis also increased agonistic behavior in male-female pairs. The frequency of vaginal marking was reduced by lesions in the MPO, MAH, and Dorsal VMN groups. Rapid weight increases and obesity were also seen following certain medial hypothalamic lesions, however no significant correlations were found between degree of weight change and degree of lordosis deficit. A quantitative analysis of VMN damage revealed a relatively low, but statistically significant positive correlation between degree of VMN damage and lordosis deficits. There were no significant correlations between degree of VMN damage and weight change.

Estrogen Target Sites in the Brain of the Chick Embryo

Autoradiograms prepared from brains of chick embryos after injection of [3H]estradiol demonstrate the existence of target cells for estrogen in the medial preoptic and ventral hypothalamic regions as early as day 10 of incubation. Target cells also appear in telencephalic locations during later stages of embryonic development. These hormone-concentrating cells probably are the anatomical substrate for the formative action of sex steroids during embryonic life on certain brain functions such as control of sexual and aggressive behaviour and gonadotropin secretion.

Hypothalamic mechanisms involved in the control of gonadotropic hormone secretion in the guinea pig: evidence of elevated brain thresholds to electrical stimulation in the medial preoptic-anterior hypothalamic region during "early" diestrus.

The technique of electrical stimulation of the brain has revealed an increased neural threshold in the medial preoptic area anteriorhypothalamus (MPOA-AH) “early”(12 days since last ovulation) in the estrous cycleof the guinea pig when compared to that in thesame region “late” (14 days since last ovulation)in the cycle. With apeak-to-peak current of1 mA, none of the 12 animals stimulated in the MPOA-AH “earlyN in the cycle showed gonadotropichormone release. On the contrary, with stimulation parameters and brain localization of electrodes comparable to the above, stimulation “late” in the estrous cycle induced premature gonadotropic hormone release in 11 of 13animals. Stimulation of the medial basal hypothalamus (MBH) with 1 mA peak-to-peak inducedgonadotropic hormone release either “early” or “late” in the cycle. Furthermore,increasing the current to 2 mA peak-to-peak overcame the apparent refractoriness of theMPOA-AH “early” in the estrous cycle of the guinea pig; all 5 animalsshowed signs ofgonadotropi...

Effects of brain-stem stimulation upon hippocampal electrical activity, somatomotor reflexes and autonomic functions

In order to understand better the functional significance of hippocampal electrical activity, an attempt has been made to relate its changes with those of somatomotor, sudomotor and vasomotor activities. Experiments were conducted with locally anesthetized cats under Flaxedil. The animals were bilaterally vagotomized in the study of blood pressure. Four types of hippocampal electrical responses to the stimulation of various subcortical brain structures were observed. 1. 1. “Synchronization” (produced by the stimulation of the medial preoptic area, the medial hypothalamic region and the dorsolateral part of the midbrain tegmentum) was associated with facilitation of the monosynaptic gastrocnemius and mono- as well as polysynaptic peroneal reflexes, elevation of blood pressure and facilitation of skin potentials. 2. 2. “Desynchronization A” (elicited by the stimulation of the amygdala and the lateral preoptic area) was associated with inhibition of the gastrocnemius and peroneal reflexes, and depression of blood pressure. The skin potentials could be facilitated with strong stimulation. 3. 3. “Desynchronization B” (elicited by the stimulation of the bulbar ventromedial reticular formation) was associated with inhibition of the gastrocnemius and peroneal reflexes, skin potentials and elevation of blood pressure. However, depression of the latter was obtained after Nembutal administration. 4. 4. “Intermediate response” (elicited by the stimulation of the posterolateral hypothalamic region and the preoptic area) was associated with facilitation of the peroneal reflexes and of the skin potential, and with inhibition of the gastrocnemius reflex. Blood pressure, elevated in the absence of anesthesia, was depressed after Nembutal administration. In view of these experimental results, it is suggested that the slow wave components of hippocampal electrical activity might have a close relationship with somatomotor and vasomotor activities.

Two types of pattern of hippocampal electrical activity induced by stimulation of hypothalamus and surrounding parts of rabbit's brain.

1. The two types of electrical activities of the hippocampus evoked by direct stimulation of the brain have been studied in unanesthetized rabbits, immobilized by tubocurarine.2. The slow wave pattern of the hippocampal electrical activity, characterized by the regular slow waves at 5 to 7 cycles per second, was induced by direct stimulation of the medial preoptic area, medial hypothalamic region, central gray matter and dorso-lateral part of the tegmentum of the midbrain.3. The fast wave pattern of the hippocampal electrical activity, characterized by low voltage fast waves at 15 to 30 cycles per second, was elicited by direct stimulation of the medial septum, lateral hypothalamus and medio-ventral part of the tegmentum of the midbrain.4. The slow and fast wave pattern of the hippocampal electrical activity may represent activity of the separate system within the brain, sympathetic and parasympathetic activities.