Hypothalamic Distribution Research Articles

Brain sites involved in the regulation of growth hormone secretion in the young male domestic fowl.

To study brain sites involved in the regulation of GH secretion in the domestic fowl, lesions were placed in and around the hypothalamus of 1-week-old cockerels. Circulating concentrations of GH were then measured at weekly intervals for 4 weeks after the placement of lesions. At the termination of the experiment, histological procedures were used to determine the exact site of the lesion in each bird. Although a fair degree of overlap existed between the lesion sites leading to stimulation and those causing an inhibition of GH secretion, a clear distinction could be made in the overall distribution of stimulatory and inhibitory sites of GH control. A high concentration of lesion sites resulting in GH decline (presumed GH-releasing factor-rich areas) appeared to reside in the general area of the ventromedial and the arcuate nucleus of the hypothalamus. Lesion sites causing a GH rise (presumed somatostatin-rich areas), on the other hand, seemed to have a more caudal distribution. In addition, some evidence of an anterior hypothalamic distribution of these presumed 'somatostatin' neurones was observed. These agree with the existing immunohistochemical data on the distribution of somatostatin and constitute experimental evidence for localization of presumed GH-releasing factor sites within the avian brain.

In situ estradiol and progestin (R5020) localization in the vascularly separated and isolated hypothalamus of the rhesus monkey.

A neurosurgical procedure has been developed for vascular isolation of the hypothalamus-thalamus region of the rhesus monkey brain. Utilizing this preparation, the left and right halves of the hypothalamus were perfused simultaneously, but separately, with a dextran-blood solution. Radiolabeled steroids were directly perfused in the dextran-blood into either the left or right half of the hypothalamus. Studies with radiolabeled gonadal steroids indicate that the majority of the carotid circulation is confined to the hypothalamus-thalamus area in this brain preparation and the cross-circulation of labelled steroids between the left and right sides of the hypothalamus is less than 10%. The usefulness of the preparation is illustrated by an autoradiographic study of the in situ hypothalamic distribution of (3H)estradiol in ovariectomized rhesus monkeys and of the synthetic progestin(3H)R5020 in estrogen-primed, ovariectomized rhesus monkeys. The direct perfusion of the (3H) steroids into the hypothalamus greatly increases the sensitivity of such compared to systemic administration of the (3H) steroids. The perfusion of one-half of the hypothalamus with )3H) steroid and the other half with (3H) steroids. The perfusion of one-half of the hypothalamus with (3H) steroid and the other half with (3H) steroids. The perfusion of one-half of the hypothalamus with (3H) steroid and the other half with (3H)steroid plus radioinert steroids permits in 1 animal, acting as its own control, the examination of a saturable distribution of a gonadal steroid in the rhesus monkey hypothalamus.

Suppression of sexual receptivity in the female hamster: Neuroanatomical projections from preoptic and anterior hypothalamic electrode sites

Electrical simulation (ES) through fine-wire electrodes chronically implanted in the preoptic area and anterior hypothalamus suppressed the lordosis response in freely moving hormone-primed female hamsters. ES at these sites never induced or facilitated lordosis. When behavioral testing was completed small lesions were made at the tips of the electrodes, and the Fink-Heimer method was used to trace degenerating axons away from the sites of ES. This was done in an effort to determine the neural pathways important for the modulation of this behavior. The hypothalamic distribution of the stria terminalis was also charted for the hamster and was found to be similar to that in the rat, including projections to both the shell and core of the ventromedial nucleus (VMN). No single pattern of degeneration was common to all females showing ES-produced lordosis suppression. These data demonstrate that stimulation of several different pathways can produce behavioral states that are incompatible with the lordosis response. We suggest that ES in the medial preoptic-medial anterior hypothalamic continuum suppresses sexual receptivity by influencing neurons in the VMN region, while ES through more laterally placed electrodes suppresses receptivity by producing an incompatible state of behavioral activation, without directly influencing VMN region neural activity.

Effects of Lesions in the Organum Vasculosum Lamina Terminalis on the Hypothalamic Distribution of Luteinizing Hormone-Releasing Hormone and Gonadotropin Secretion in the Ovariectomized Rat*

Radiofrequency lesions were generated in the organum vasculosum lamina terminalis (OVLT) of ovariectomized rats in order to examine the relationship of LHRH in the OVLT to that in the median eminence (ME) and the possible role of the OVLT in the control of gonadotropin secretion. In the first experiment, OVLT destruction significantly decreased LHRH content, as measured by RIA, in blocks of tissue containing the OVLT and the ME at 1, 3, and 7 days after production of lesions but did not alter serum LH and FSH levels or pituitary gonadotropin content. In the second experiment, OVLT lesions similarly did not alter serum gonadotropins or the negative feedback effect of estrogen in the ovariectomized rats; however, the progesterone-induced gonadotropin surge was nearly abolished as a result of OVLT destruction. LHRH content was reduced in the region of the OVLT, in the ME, and in a zone between these two structures. Bilateral medial preoptic area lesions also did not alter the negative feedback effect of estr...

The use of neurotoxins to characterize the rates and subcellular distributions of axonally transported dopamine-ß-hydroxylase, tyrosine hydroxylase and norepinephrine in the rat brain

The effect of 6-hydroxydopamine (6-OHDA), colchicine and cytochalasin B on the transport and subcellular distribution of proteins, tyrosine hydroxylase (TH), dopamine-ß-hydroxylase (DBH) and norepinephrine (NE) were studied in the noradrenergic neurons of the rat locus coeruleus (LC). Four waves of transported 3H-labeled proteins and glycoproteins, defined by previous studies, as well as hypothalamic levels of TH, DBH and NE, were examined after injection of each neurotoxin into the ascending dorsal noradrenergic bundle. Blockade of subcellular components of TH, DBH and NE was compared to their endogenous hypothalamic distributions. 6-Hydroxydopamine variably blocked transport of all 4 waves of 3H protein and bilateral injections decreased hypothalamic levels of TH, DBH and NE by 58.2, 56.9 and 52.2% of controls, respectively. Cytochalasin B blocked transport of protein waves I (72–192 mm/day) and III (13–20 mm/day) and decreased hypothalamic levels of TH to 60.1% of control after bilateral injections. Colchicine blocked transport of waves I, II (24–48 mm/day) and V (1.4–2.9 mm/day) and blocked [ 3H]NE transport, while decreasing hypothalamic levels of DBH and NE to 56.6 and 69.3% of control after bilateral injections. Colchicine and 6-OHDA, but not cytochalasin B, caused a backup of DBH immunofluorescence proximal to the injection site. DBH and NE appeared to be transported primarily in particulate form, while TH transport was predominantly soluble in distribution. None of the toxins differentially affected the transport of one particular subcellular component of TH, DBH or NE. Based on the differential blocking effects of these toxins, DBH and NE appeared to be associated with wave II, and TH with wave III, travelling at 24–48 mm/day and 13–20 mm/day respectively.

Hypothalamic and extrahypothalamic distribution of somatostatin-immunoreactive elements in the rat brain.

Using a highly sensitive antibody to somatostatin, its hypothalamic and extrahypothalamic distribution in the rat was re-examined by light microscopic immunohistochemistry (PAP-method). The scattered somatostatin-producing perikarya occur in multiple layers within the subependymal neuropil surrounding the third ventricle. They supply with short-distance projections the following hypothalamic nuclei: 1) preoptic nuclei (especially their suprachiasmatic and medial components), 2) the peripheral zones of the suprachiasmatic nuclei, 3) the ventromedial and 4) arcuate nuclei, and 5) the ventral premammillary nuclei. Furthermore, the following long-distance projections have been observed: In a rostral direction (A1) rostral of the anterior commissure to the lamina terminalis, (A2) to the OVLT, (A3) to the olfactory tubercle, and (A4) rostrally and caudally by-passing the anterior commissure to the dorsal part of the stria terminalis.

RNA metabolism in the rat brain during learning following intravenous and intraventricular injections of 3H-cytidine

Bowman and Strobel [5] reported increased incorporation of tritiated cytidine into hippocampal RNA of rats learning 60 min of repeated spatial reversals for water reinforcement in an automated Y-maze. The present studies replicated this effect 3 times using intravenous (IV) injections of tritiated cytidine, but failed to observe such an effect in 3 other replications using intracranial (IC) injections of tritiated cytidine. Various control conditions appear to rule out injection trauma as a reason for the lauter failure. The observation of equal precursor distribution across brain regions following IV injections and of unequal distribution following IC injections, coupled with the autoradiographic observations of Altman and Chorover [1] of steep hypothalamic distribution gradients of IC injected nucleoside in the cat, indicate that regional metabolic measurements following IC injections of precursors do not equally assess the contributions of all brain cells and can lead to serious quantitative errors. This point needs reemphasis in view of the widespread use of IC injections in psychoneurochemical research. Concerning the possibility of stress or corticosterone effect on the observed hippocampal RNA effect, there were no differences found in plasma corticosterone concentrations between the learning and control rats at sacrifice.

The hypothalamic distribution of the stria terminalis in the rat

The hypothalamic distribution of the stria terminalis was studied by the Fink-Heimer methods and electron microscopy in rats sacrificed 3–6 days after unilateral amygdalectomy or stria terminalis section. Each of the major hypothalamic stria components was found to be distributed to fairly sharply defined regions, as follows: (1) The postcommissural component terminals massively in the rostral half of the anterior hypothalamic nucleus; an apparently small number of its fibers join the medial forebrain bundle. (2) The supracommissural component terminates predominantly in a dense synaptic zone surrounding the ventromedial nucleus and containing a massive plexus dendrites protruding from this nucleus, in smaller quantity also in lateral and ventral parts of the ventromedial nucleus proper and in the ventral premammillary nucleus. The prevalence in the hypothalamus of neurons with long dendrites suggests that the stria terminalis may have synaptic contracts not only with perikarya and dendrites of neurons lying within its synaptic fields, but also with dendrites of neurons whose cell bodies lie well outside these fields.

Contrasting effects of two identified amygdaloid efferent pathways on single hypothalamic neurons.

Contrasting effects of two identified amygdaloid efferent pathways on single hypothalamic neurons.