Individual Hypothalamic Nuclei Research Articles

Quantitative histochemical studies of the hypothalamus enzymes of acetylcholine metabolism.

The quantitative histochemical distribution of acetylcholinesterase and choline acetyltransferase activity has been measured in individual hypothalamic nuclei and median eminence, as well as in entire hypothalamic sections by a mapping technique. There was an 18-fold range of nuclear choline acetyltransferase activity with highest activities in the lateral preoptic nucleus and median eminence. There was a nine-fold range of nuclear acetylcholinesterase activity with highest activities in the lateral preoptic and magnocellular nuclei and lowest activity in the median eminence. The substantial gradients of choline acetyltransferase activity found in the hypothalamus indicate the importance of using a technique that provides an objective, permanent record of contiguous sample locations thereby allowing detailed analysis of tissue areas using, but not dependent on, anatomical boundaries.

Experimental aspects of the CNS-insular system

1. Application of the karyometric method to rats with experimentally induced alloxan diabetes allows for the identification and localization in the hypothalamus of nerve structures responding to insulin deficiency. 2. Nerve cells of individual hypothalamic nuclei, particularly the ventromedial and arcuate nuclei of the medial hypothalamus and the supraoptic nucleus of the anterior hypothalamus, react selectively to insulin deficiency.

Serotonergic innervation of the forebrain: Effect of lesions on serotonin and tryptophan hydroxylase levels

Concentrations of serotonin and tryptophan hydroxylase activity in individual hypothalamic and limbic nuclei, as well as cortical regions, were measured by radioenzymatic microassays after dorsal raphe nucleus lesions and various surgical transections of the brain stem. Fourteen days after lesioning of the dorsal raphe nucleus there were 43-65% decreases in 5-HT concentrations of certain hypothalamic and limbic nuclei. More pronounced decreases were found in the parietal cortex and in the locus coeruleus and substantia nigra. Degenerations of nerve terminals in various regions of the hypothalamus and the limbic system were detected by electron microscopic studies 1-8 days after dorsal raphe nucleus lesions. There was no change in the 5-HT concentration of the spinal cord following dorsal raphe nucleus lesions. Surgical transections at the level of mesencephalic-pontine junction caused no significant changes in 5-HT concentrations or tryptophan hydroxylase levels in the hypothalamus, limbic system, cerebral cortex or spinal cord. Serotonergic fibers ascending from the mesencephalic raphe nuclei constitute a well circumscribed bundle dorsal to the interpeduncular nucleus. The axons enter the hypothalamus between the mammillary body and crus cerebri just ventral to the medial forebrain bundle. The ascending pathway contains all the ascending 5-HT fibers innervating the hypothalamus and the rostral limbic and cortical areas.

Catecholamines in Individual Hypothalamic Nuclei of Acutely and Repeatedly Stressed Rats

Norepinephrine (NE) and dopamine (DA) concentrations in 17 individual hypothalamic nuclei and 3 other brain regions were measured in rats, acutely or repeatedly stressed by immobilization, using a microdissection technique and a radioisotopic-enzymatic assay. Following the first 20 min immobilization (IMO) a significant NE decrease in the ventromedial (NVM) and supraoptic (NSO) nuclei and a DA decrease in the arcuate nucleus (NA) as well as NE and DA increase in the dorsomedial nucleus (NDM) were seen. Repeated IMO (40 times) produced a NE increase in the NVM, NDM, NSO paraventricular nucleus (NPV) and median eminence (ME), and a DA increase in the NDM and NPV. Changes of NE and DA concentration found in some individual hypothalamic nuclei under the influence of stress indicate that catecholamines (CAs), particularly in the medial basal hypothalamus, could be involved in the regulation of some neuroendocrine processes which are being activated during stress, especially ACTH release.

Quantitative Histochemical Studies of the Hypothalamus: Dehydrogenase Enzymes following Androgen Sterilization

Four enzymes, selected as representative of major metabolic pathways (malic dehydrogenase, of the citric acid cycle, lactic dehydrogenase, of glycolysis, glucose-6-phosphate dehydrogenase, of the pentose pathway and glutamic dehydrogenase, of glutamate metabolism), were measured by quantitative histochemical methods in individual hypothalamic nuclei of adult neonatally androgenized female rats. Malic dehydrogenase (MDH) was significantly reduced in nuclei of the anterior hypothalamus: the suprachiasmatic, supraoptic and anterior. Lactic dehydrogenase (LDH) increased significantly in the lateral preoptic area. Glucose-6-phosphate dehydrogenase G-6-PDH was also significantly elevated in anterior hypothalamic nuclei: medial preoptic, lateral preoptic, supraoptic and paraventricular. Glutamic dehydrogenase (GDH) was generally elevated throughout the hypothalamus with significant increases of activity occurring in the paraventricular, lateral ventromedial, arcuate, medial mamillary and posterior nuclei.

Quantitative histochemical studies of the hypothalamus. Control point enzymes during the estrous cycle.

Three control point enzymes of the Embden-Meyerhof pathway, hexokinase (HK), phosphofructokinase (PFK) and pyruvate kinase (PK), have been measured in individual hypothalamic nuclei during the 5-day estrous cycle of adult rats by quantitative histochemical methods. PK levels, low during proestrus, rise to maximum activity during estrus; this rise is significantly greater than on all other days of the cycle in the lateral preoptic area (LP), ventromedial pars medialis (VMM) and pars lateralis (VML) and posterior hypothalamic (Post) nuclei. HK activity also rises from low proestrous levels during the cycle but, in contrast to PK, reaches maximum activity during diestrus-1 (D-1) or diestrus-2 (D-2). PFK showed variable changes during the estrous cycle with peaks occurring during estrus in some nuclei and during diestrus in others, but these changes were not significantly different. These metabolic changes occur in specific hypothalamic nuclei which have been shown by electrical stimulation, lesion production, stereotaxic hormone implantation and localization of luteinizing hormone-releasing factor experiments to have an important role in reproductive physiology and sexual behavior.

Quantitative histochemical studies of the hypothalamus. Control point enzymes following androgen sterilization.

Three control point enzymes of the Embden-Meyerhof pathway, hexokinase (HK), phosphofructokinase (PFK) and pyruvate kinase (PK) were measured by quantitative histochemical methods in individual hypothalamic nuclei of adult neonatally androgenized female rats. HK activity was significantly increased in anterior hypothalamic nuclei: medial preoptic, lateral preoptic, and suprachiasmatic. PK was significantly elevated in the lateral preoptic and suprachiasmatic nuclei of the anterior hypothalamus and also in the medial mamillary nucleus and median eminence. No significant changes occurred in PFK activity.

Effects of gonadectomy and thyroidectomy on the tyrosine hydroxylase activity in individual hypothalamic nuclei and lower brain stem catecholaminergic cell groups of the rat

Effects of gonadectomy and thyroidectomy on the tyrosine hydroxylase activity in individual hypothalamic nuclei and lower brain stem catecholaminergic cell groups of the rat

The effect of bilateral lesions of the ventral noradrenergic bundle on endocrine-induced changes of tyrosine hydroxylase in the rat median eminence.

With the microdissection method of Palkovits, individual hypothalamic nuclei were removed from the brains of adult male rats, and the tyrosine hydroxylase (TH) activity of each nucleus was determined 7 days after gonadectomy or thyroidectomy. Following gonadectomy, TH activity increased significantly in the median eminence with no change in the periventricular (NPV), arcuate (NARC), and dorsomedial nuclei (NDM), or medial forebrain bundle (MF). Following thyroidectomy, TH activity increased significantly in all 5 hypothalamic nuclei examined. Placement of bilateral lesions in the ventral norepinephrine bundles resulted in a greater than an 85% fall in the dopamine-beta-hydroxylase activity of the median eminence, arcuate nucleus, and ventromedial nucleus, but had no effect on tyrosine hydroxylase activity measured in those same areas. Furthermore, placement of such lesions had no effect on the endocrine-induced increases of TH activity found in the median eminence following gonadectomy and thyroidectomy, but did prevent the increase of TH activity found in the NPV, NDM, and MFB following thyroidectomy. Three conclusions appear to be justified: (a) noradrenergic axons which innervate the median eminence, arcuate, and ventromedial nuclei course in the ventral norepinephrine bundles; (b) the TH content of noradrenergic neurons in the median eminence, arcuate nucleus, and ventromedial nuclei is quite small; and (c) the majority, if not all, of the endocrine-responsive catecholaminergic neurons in the median eminence are dopaminergic.

Quantitative histochemical studies of the hypothalamus. Dehydrogenase enzymes during the estrous cycle.

Three enzymes selected as representative of major metabolic pathways (malic dehydrogenase, of the citric acid cycle, lactic dehydrogenase, of glycolysis and glucose-6-phosphate dehydrogenase, of the pentose pathway) were measured by quantitative histochemical methods in individual hypothalamic nuclei during the 5-day estrous cycle of adult rats. Malic dehydrogenase increases significantly from low proestrous levels to a peak at estrus and then declines during diestrus in the following nuclei and areas of the anterior hypothalamus: medial and lateral preoptic, suprachiasmatic, supraoptic, and anterior. Significant peaks of lactic dehydrogenase occur more often during diestrus-3 in hypothalamic nuclei of the middle and posterior hypothalamus, Glucose-6-phosphate dehydrogenase has a biphasic pattern with peaks usually occurring during the diestrous period.

Effect of Stress on Serotonin Concentration and Tryptophan Hydroxylase Activity of Brain Nuclei

The effects of a single stressful stimulus on serotonin (5-HT) concentration and of repeated stressful stimuli on tryptophan hydroxylase (THy) activity were measured in individual hypothalamic nuclei and other rat brain regions using specific sensitive radioisotopic enzymatic microassays. Two h after formalin injection, 5-HT levels were increased in the dorsal raphe (RDN). Acute immobilization stress, however, reduced the concentrations of 5-HT in several of the hypothalamic nuclei: the medium eminence (ME), lateral amygdaloid nucleus, hippocampus, cingulate cortex (CCX) and RDN. Five consecutive daily immobilization periods failed to alter THy activity in any region examined. These results suggest a rapid release of 5-HT both from the cells and the axon terminals in the central nervous system, and failure, even with repeated stresses, to elicit induction of increased levels of the biosynthetic enzyme regulating the synthesis of the neurotransmitter.

Effect of injury to hypothalamic nuclei on morphological and functional state of the hypothalamic-pituitary system and the development of experimental atherosclerosis

Injury to individual nuclei of the anterior and middle parts of the hypothalamus in rabbits by electrocoagulation (anode, 5 mA, 20–25 sec) through previously implanted electrodes was followed by changes in the morphological and functional state of the hypothalamic-pituitary neurosecretory system (HPNS). The closer the focus of injury to the region of the supraoptic nuclei, the higher the functional activity of HPNS. If injury to individual hypothalamic nuclei was combined with administration of an atherogenic diet, marked morphological and functional changes were detected both in HPNS and in the adrenals, but in animals with experimental atherosclerosis, this disease assumed a more severe form under these conditions than in animals simply receiving the atherogenic diet. The results of these experiments point to a close connection between the genesis of atherosclerosis and neurogenic factors.

A SENSITIVE MICROASSAY FOR TRYPTOPHAN HYDROXYLASE IN BRAIN

Abstract—A specific and sensitive, radioisotopic microassay for tryptophan hydroxylase (EC 1.14.36) is described, which is capable of determining enzymatic activity in as little as 5 μg of crude brainstem homogenate. 5‐Hydroxytryptophan, the immediate product of hydroxylation of tryptophan is enzymatically converted to N‐acetylserotonin. A radioisotopic label is then introduced by the enzymatic methylation of N‐acetylserotonin in the presence of [3H]methyl‐S‐adenosyl‐methionine. The [3H]‐melatonin thus formed is isolated by extraction and counted.With this assay, the activity in individual hypothalamic nuclei (arcuate nucleus, median eminence, suprachiasmatic nucleus, and medial forebrain bundle) has been measured.

Effects of Stress on Catecholamines and Tyrosine Hydroxylase Activity of Individual Hypothalamic Nuclei

The effects of acute stress on norepinephrine (NE) and dopamine (DA) concentrations and of repeated stress on tyrosine hydroxylase (TH) activity were measured in individual hypothalamic nuclei and other rat brain regions. A microdissection technique and radioisotopic enzymatic assays enables these studies to be performed. NE and DA concentrations were reduced and TH activity increased selectively in the arcuate nucleus. These results suggest that the arcuate nucleus may be selectively involved in the stress response and support the hypothesis that catecholamines in the medial basal hypothalamus mediate certain of the neuroendocrine changes observed in stress.

The effect of endocrinological manipulations on tyrosine hydroxylase and dopamine-beta-hydroxylase activities in individual hypothalamic nuclei of the adult male rat.

Using a recently developed microdissection method, individual hypothalamic nuclei were removed from the brains of adult male rats, and the tyrosine hydroxylase (TH) and dopamine-β- hydroxylase (DBH) activities in each nucleus were determined 9 days after adrenalectomy, thyroidectomy or gonadectomy. Following gonadectomy there was a significant rise in the TH activity in only the median eminence (ME). This increased TH activity was partially reversed by treatment of gonadectomized animals with testosterone. Thyroidectomy induced a significant increase in the TH activity in the ME, the dorsomedial (NDM), the periventricular (NPE) and the arcuate (NARC) nuclei. Twelve hr after administration of thyroxine, the TH activity in the ME of thyroidectomized rats was significantly reduced to levels below those of controls, whereas the TH activities of the other nuclei were returned to control values. Adrenalectomy produced a significant fall in TH activity in the ME, whereas dexamethasone significantly increased the...

Norepinephrine and dopamine content of hypothalamic nuclei of the rat

The concentrations of norepinephrine and dopamine of 27 isolated rat hypothalamic nuclei or nuclear subdivisions have been determined using an enzymatic-isotopic assay. The hypothalamic nuclei contain 3–20 times more NE and DA than is measured in the cortex. They are distributed unevenly throughout the hypothalamus and individual hypothalamic nuclei are heterogenous as regards their content of the amines. The dopamine content of the median eminence is among the highest measured in the brain (65 ng/mg protein). The norepinephrine content is about half that of dopamine. All of the hypothalamic nuclei contain dopamine. It is highly concentrated in the rostral subdivisions of the arcuate nucleus, the paraventricular and dorsomedial nuclei, the retrochiasmatic area, the medial posterior subdivision of the ventromedial nucleus and in the medial forebrain bundle at the posterior hypothalamic level. The highest concentrations of norepinephrine were found in the paraventricular and dorsomedial nuclei and in the retrochiasmatic area. The rostal subdivision of the arcuate nucleus and the periventricular and preoptic suprachiasmatic nuclei are also rich in norepinephrine. The posterior hypothalamus (premammillary nuclei, caudal subdivision of the arcurate nucleus, posterior hypothalamic nucleus) contains norepinephrine and dopamine in relatively low concentrations.

Histamine content of hypothalamic nuclei of the rat

Histamine was measured in individual hypothalamic nuclei and in the median eminence of the rat. The highest concentration of this biogenic amine was found in the median eminence. The basal and caudal hypothalamic nuclei were more richly endowed with histamine than the dorsal and rostral ones. The possibility that histamine may have a role in neuroendocrine regulation is discussed.

Hypothalamic influences on unit activity in the cat sensomotor cortex

Experiments on unanesthetized, immobilized cats showed different effects of individual hypothalamic nuclei on spontaneous unit activity in the sensomotor cortex. Compared with the posterior hypothalamic nucleus (PHN) and its anteromedial region (AMH), in response to stimulation of the lateral hypothalamic nucleus (LHN) changes in spontaneous activity were more frequently found. The ratio between activation and inhibitory responses was 36 and 36% for AMH, 51 and 30% for LHN, and 47 and 28% for PHN. An approximately equal number of sensomotor neurons (27–34%) gave tonic responses. Phasic changes in spontaneous activity were observed more often in response to stimulation of LHN, less frequently to stimulation of AMH and PHN. Responses of "nonpyramidal" neurons to stimulation of AMH and LHN were identical. "Pyramidal" units were more sensitive to LHN stimulation. Variations in hypothalamic effects depending on the type of response of sensomotor neurons to sensory stimuli were detected. Cells with tonic responses were more susceptible to influences of LHN and AMH than cells which responded by phasic changes in spontaneous activity to sensory stimuli. Fewer still positive responses were recorded in areactive neurons.