Ovarian steroids differentially modulate the gene expression of gonadotropin-releasing hormone neuronal subtypes in the ovariectomized cynomolgus monkey

In the present study, we compared the morphology and distribution of neurons expressing GnRH gene transcripts in the hypothalamus and forebrain of the cynomolgus monkey to that of the human. As in the human, three subtypes of GnRH neurons were identified. Type I GnRH neurons were small, oval cells with high levels of gene expression and were located within the basal hypothalamus. Type II GnRH neurons were small and sparsely labeled and were widely scattered in the hypothalamus, midline nuclei of the thalamus, and extended amygdala. Type III neurons displayed magnocellular morphology and intermediate labeling intensity and were located in the nucleus basalis of Meynert, caudate, and amygdala. In a second experiment, we determined the effect of estrogen or estrogen plus progesterone on the gene expression of GnRH neurons in the brains of young, ovariectomized cynomolgus monkeys. We report that hormone treatment resulted in a significant decrease in GnRH mRNA in type I neurons within the basal hypothalamus of ovariectomized monkeys. In contrast, there was no effect of hormone treatment on the gene expression of type III GnRH neurons in the nucleus basalis of Meynert. The present findings provide evidence that the increase in gene expression of type I GnRH neurons in postmenopausal women is secondary to the ovarian failure of menopause. The differential responses of type I and III GnRH neurons to hormone treatment provide additional evidence that distinct subpopulations of neurons expressing GnRH mRNA exist in the primate hypothalamus.

Testosterone modulates the dendritic architecture of arcuate neuroendocrine neurons in adult male rats

Recent studies have demonstrated that gonadectomy of adult male rats induces dendritic growth of neuroendocrine neurons in the arcuate nucleus. We have hypothesized that these changes are secondary to the loss of testosterone negative feedback. In the present study, we examined the effects of testosterone replacement on the dendritic morphology of arcuate neuroendocrine neurons in castrated rats. Rats were orchidectomized and implanted with silastic capsules designed to produce physiological levels of plasma testosterone (n=9) or empty silastic capsules (n=9) for 2 months. Retrograde labeling with systemically injected Fluoro-Gold, followed by intracellular injection of labeled neurons in a fixed slice preparation, were used to visualize arcuate neuroendocrine neurons. Quantitative analysis of dendritic morphology was performed using three-dimensional computer reconstruction. Serum levels of LH (luteinizing hormone) and testosterone were measured by radioimmunoassay. Treatment of castrated rats with physiological levels of testosterone significantly reduced dendritic length, volume and terminal branch number relative to the castrated rats receiving empty silastic capsules. Dendritic spine density was also greater in the testosterone-treated animals, although the total numbers of spines per dendrite was not significantly different between the two groups. In addition, testosterone replacement was effective in reducing serum LH to levels found in intact rats. These studies demonstrate that testosterone replacement suppresses the dendritic outgrowth of arcuate neuroendocrine neurons that occurs in response to castration. The parallel changes in dendritic arbor and serum LH after castration and hormone replacement suggests that the suppressive effects of testosterone are related to steroid negative feedback.

Stereologic study of the hypothalamic infundibular nucleus in young and older women

Aging in women is associated with dramatic changes in neuronal morphology and neuropeptide gene expression in the medial basal hypothalamus. There is hypertrophy of neurons expressing substance P and neurokinin B gene transcripts in the infundibular (arcuate) nucleus, accompanied by increased tachykinin gene expression. In addition, gonadotropin-releasing hormone (GnRH) gene expression is increased in a separate subpopulation of neurons within the medial basal hypothalamus. In contrast, the number of neurons expressing proopiomelanocortin (POMC) mRNA in the infundibular nucleus of older women is decreased. To determine whether neuronal degeneration contributes to these phenomena, unbiased stereologic methods were used to compare the total number of infundibular neurons between groups of young (premenopausal) and older (postmenopausal) women. There was no significant difference in the total number of infundibular neurons between young (520,000 +/- 42,000 neurons, mean +/- SEM) and older women (505,000 +/- 51,000 neurons, mean +/- SEM). The mean volume of neuronal somata, however, was increased by 40% in the older women (young, 1,860 +/- 180 microm(3) vs. older, 2,610 +/- 230 microm(3), mean +/- SEM, P < 0.05). These data demonstrate that neuronal hypertrophy in older women is not accompanied by degeneration of the infundibular nucleus. We conclude that the loss of menstrual cyclicity in middle-aged women cannot be explained by loss of neurons within the hypothalamic control center for reproduction.

Proopiomelanocortin gene expression is decreased in the infundibular nucleus of postmenopausal women

Previous studies have shown that estrogen withdrawal decreases the secretion of beta-endorphin from the monkey hypothalamus. In addition, there are consistent age-associated changes in beta-endorphin neurons in the rodent. Based on these findings, we hypothesized that the activity of hypothalamic beta-endorphin neurons would be decreased in the hypothalamus of postmenopausal women. In the present study, we examined the expression of proopiomelanocortin (POMC) mRNA, the precursor mRNA for beta-endorphin, in the medial basal hypothalamus of premenopausal and postmenopausal women. Every 20th sagittal section through the hypothalamus was hybridized with a synthetic [35S]labeled, 48-base oligonucleotide probe complementary to POMC mRNA. Labeled neurons were counted and their somatic profile areas were measured with an image-combining computer microscope system. The number of POMC mRNA-containing neurons/section in the infundibular nucleus was reduced by 65% in postmenopausal women. In contrast, there was no significant difference in the number of neurons expressing POMC gene transcripts in the retrochiasmatic region. The POMC neurons in the retrochiasmatic area were also distinct morphologically from those in the infundibular nucleus. The differences between the infundibular and retrochiasmatic regions suggest that functional subgroups of POMC neurons exist in the human hypothalamus. Our findings provide evidence that the activity of hypothalamic POMC neurons is decreased in the infundibular nucleus of postmenopausal women. Both aging and gonadal steroid withdrawal may contribute to the decline in POMC gene expression in postmenopausal women.

The effects of hormone replacement therapy on hypothalamic neuropeptide gene expression in a primate model of menopause

Menopause is associated with increased neurokinin B (NKB) gene expression and decreased proopiomelanocortin (POMC) gene expression in the human hypothalamus. In the present study, young, ovariectomized cynomolgus monkeys were used in a model of menopause to examine the effects of hormone replacement therapy (HRT) on hypothalamic neuropeptide gene expression. A secondary goal was to determine whether HRT produces signs of estrogen toxicity in the primate hypothalamus by examining POMC neurons and microglial cells. In situ hybridization was performed using synthetic, radiolabeled, 48-base oligonucleotide probes. Alpha-napthyl butyrate esterase histochemistry was used to visualize microglial cells. Both estrogen and estrogen plus progesterone treatments produced a marked suppression of the number of infundibular neurons expressing NKB gene transcripts. In contrast, HRT had no effect on the POMC system of neurons or the number of microglial cells in the infundibular nucleus. These results provide strong support for the hypothesis that the increased NKB gene expression in the hypothalamus of postmenopausal women is secondary to estrogen withdrawal. Conversely, these data suggest that the dramatic decline in the numbers of neurons expressing POMC gene transcripts in older women is caused by factors other than ovarian failure. Finally, we found no evidence that HRT, in doses designed to mimic currently prescribed regimens, produces signs of estrogen toxicity in the primate infundibular nucleus.

Sex steroid modulation of neurokinin B gene expression in the arcuate nucleus of adult male rats

Human menopause is associated with hypertrophy and increased gene expression of neurokinin (NKB) neurons in the infundibular (arcuate) nucleus of the hypothalamus. We have hypothesized that these changes are secondary to gonadal failure. In the present study, we determined that orchidectomy resulted in an increase in the mean profile area and the number of neurons expressing NKB mRNA in the rat arcuate nucleus. No changes were seen when orchidectomy was combined with testosterone or estradiol replacement. These findings support our hypothesis and demonstrate that gonadal steroids modulate NKB neurons in the arcuate nucleus of adult male rats.

Dendritic growth of arcuate neuroendocrine neurons following orchidectomy in adult rats

Recent studies have shown that changes in dendritic architecture are an important component of functional plasticity in the adult central nervous system. In the present study, we determined whether gonadectomy induces changes in dendritic architecture in the arcuate nucleus, a target tissue for gonadal hormones. A combination of retrograde labeling with systemically injected Fluoro-Gold and intracellular injection of neurons in a fixed-slice preparation was used to examine the morphology of neuroendocrine neurons in the rat arcuate nucleus. Intracellullary filled arcuate neuroendocrine neurons (8-21 neurons per brain) from intact (n = 5) and orchidectomized (n = 5) animals were reconstructed with the aid of a computer microscope. A quantitative analysis revealed that orchidectomy had no effect on the number and distribution of Fluoro-Gold-labeled neuroendocrine neurons in the rat arcuate nucleus. The morphology of arcuate neuroendocrine neurons in intact animals was relatively simple, with the majority of neurons (79%) having only two primary dendrites and few dendritic spines. Compared with intact controls, arcuate neuroendocrine neurons in the orchidectomized group had significantly larger somatic profile areas and exhibited significant increases in dendrite length, dendrite volume, terminal branch number, and spines per unit length of dendrite. The increase in terminal branch number in orchidectomized animals was due primarily to the appearance of short branches that gave a striking, claw-like appearance to many of the distal dendrites. These results provide evidence for hormonal regulation of dendritic morphology of arcuate neuroendocrine neurons in adult mammals.

Localization of neurons expressing substance P and neurokinin B gene transcripts in the human hypothalamus and basal forebrain

In situ hybridization histochemistry was used to map the distribution of neurons expressing the substance P (SP) or neurokinin B (NKB) genes in the human hypothalamus and basal forebrain. Hypothalami from five adult males were frozen in isopentane at -30 degrees C and serially sectioned at 20 jm thickness. Every 20th section was hybridized with [35S]-labeled, 48-base synthetic cDNA probes that were complementary to either SP or NKB mRNAs. Slides were dipped into nuclear emulsion for visualization of mRNAs at the single-cell level. The location of labeled neurons (greater than x 5 background) was mapped by using an image-combining computer microscope system. A distinct and complementary distribution pattern of SP and NKB neurons was observed in the human hypothalamus and basal forebrain. NKB was the predominant tachykinin in the rostral hypothalamus, whereas SP mRNA predominated in the posterior hypothalamus. Numerous NKB neurons were identified in the magnocellular basal forebrain, the bed nucleus of stria terminalis, and the anterior hypothalamic area. Scattered NKB neurons were present in the infundibular and paraventricular nuclei, paraolfactory gyrus, posterior hypothalamic area, lateral division of the medial mammillary nucleus, and amygdala. Numerous neurons expressing SP mRNAs were identified in the premammillary, supramammillary, and medial mammillary nuclei; the posterior hypothalamic area; and the corpus striatum. Scattered SP neurons were also observed in the preoptic area; the infundibular, intermediate, dorsomedial, and ventromedial nuclei; the infundibular stalk; the amygdala; the bed nucleus of stria terminalis; and the paraolfactory gyrus. These studies provide the first description of the location of neurons that express tachykinin gene transcripts in the human hypothalamus.

Gonadotropin-releasing hormone gene expression is increased in the medial basal hypothalamus of postmenopausal women

Quantitative In situ hybridization and computer-assisted microscopy were used to compare GnRH gene expression in the hypothalamus of premenopausal and postmenopausal women. Hypothalamic sections were incubated with 35S-labeled 48-base complementary DNA probes and dipped into nuclear emulsion for visualization of messenger ribonucleic acids at the single cell level. Two subtypes of GnRH neurons were examined: heavily labeled GnRH neurons located primarily in the medial basal hypothalamus (type I) and lightly labeled neurons in the dorsal preoptic-septal region (type II). We report a 50% increase in mean number of silver grains per type I neuron in the medial basal hypothalamus of postmenopausal women. In contrast to type I neurons, there was no difference in the number of grains per type II neuron in the dorsal preoptic-septal regions. The mean profile area and the number of type I GnRH neurons per section were not different between the two groups, and there was no change in the size of type II neurons. There was also a significant postmortem degradation of messenger ribonucleic acid in type I, but not type II, neurons. We hypothesize that the increase in GnRH gene expression in the medial basal hypothalamus of postmenopausal women is secondary to the ovarian failure of menopause and is not a nonspecific effect of age. The differential response of the two types of hypothalamic neurons provides additional evidence that distinct functional subgroups of GnRH neurons exist in the human brain.

Effects of excitatory amino acid lesions upon neurokinin B and acetylcholine neurons in the nucleus basalis of the rat

The nucleus basalis magnocellularis (NBM) contains cholinergic neurons that project to the neocortex and is densely innervated by excitatory amino acid-containing terminals. A dysfunction in the balance of excitatory inputs or an alteration in the sensitivity of NBM cells to glutamate may underlie the selective vulnerability to aging. Some large NBM neurons contain neurokinin B (NKB) mRNA. The present study investigated whether alpha-2-amino-3-hydroxy-5-methyl-isoxazole-4-propionic acid (AMPA) or N-methyl-D-aspartate (NMDA) differentially destroy NKB-containing, NKB-receptive, or cholinergic NBM cells, and whether this vulnerability is altered by aging. Injections of AMPA or NMDA significantly decreased neocortical ChAT activity, as compared to control levels, across all three age groups, with no interaction between lesion and age group. The results of in situ hybridization histochemistry and NKB receptor studies suggest that NKB-containing neurons in the NBM, and the neurons they innervate, are not vulnerable to NMDA or AMPA in either young or old rats. While NKB mRNA-positive cells were diffusely distributed throughout the basal forebrain, only a small proportion of the large NBM cells contained NKB mRNA. The results suggest that NKB does not extensively colocalize with acetylcholine within the basal forebrain of rats and that NBM NKB neurons do not directly innervate cholinergic cells.

Opioid precursor gene expression in the human hypothalamus

Using in situ hybridization histochemistry, we studied the distribution of neurons that express preproopiomelanocortin (pre-POMC), preprodynorphin (pre-PDYN), and preproenkephalin (pre-PENK) gene transcripts within the human hypothalamus and surrounding structures. Of the three opioid systems, pre-POMC neurons have the most restricted distribution. Pre-POMC cells are most numerous in the infundibular nucleus and retrochiasmatic area of the mediobasal hypothalamus; a few labeled cells are present within the boundaries of the ventromedial nucleus and infundibular stalk. Pre-POMC message was not found in the limited samples of structures adjacent to the hypothalamus. In contrast to neurons that express pre-POMC, neurons expressing pre-PDYN and pre-PENK are more widely represented throughout the hypothalamus and extrahypothalamic structures. However, pre-PDYN and pre-PENK cells differ from one another in distribution. Pre-PDYN message is especially abundant in neurons of the tuberal and mammillary regions, with a distinct population of labeled cells in the premammillary nucleus and dorsal posterior hypothalamus. Pre-PDYN gene expression also is found in neurons of the dorsomedial nucleus, ventromedial nucleus, caudal magnocellular portion of the paraventricular nucleus, dorsolateral supraoptic nucleus, tuberomammillary nucleus, caudal lateral hypothalamus, and retrochiasmatic area. In structures immediately adjacent to the hypothalamus, pre-PDYN neurons were observed in the caudate nucleus, putamen, cortical nucleus of the amygdala, and bed nucleus of the stria terminalis. Pre-PENK neurons occur in varying numbers in all hypothalamic nuclei except the mammillary bodies. The chiasmatic region is particularly rich in pre-PENK neurons, with the highest packing density in the intermediate nucleus [the intermediate nucleus (Braak and Braak [1987] Anat. Embryol. 176:315-330) has also been termed the sexually dimorphic nucleus of the preoptic area (SDA-POA; Swaab and Fliers [1985] Science 228:1112-1115) or the interstitial nucleus of the anterior hypothalamus 1 (Allen et al. [1989] J. Neurosci. 9:497-506)], dorsal suprachiasmatic nucleus, medial preoptic area, and rostral lateral hypothalamic area. Pre-PENK neurons are numerous in the infundibular nucleus, ventromedial nucleus, dorsomedial nucleus, caudal parvicellular portion of the paraventricular nucleus, tuberomammillary nucleus, lateral hypothalamus, and retrochiasmatic area. Only a few lightly labeled cells were found in the periphery of the supraoptic nucleus and lateral tuberal nucleus. In areas adjacent to the hypothalamus, cells that contain pre-PENK message occur in the nucleus basalis of Meynert, central nucleus of amygdala, bed nucleus of the stria terminalis, caudate nucleus, and putamen.(ABSTRACT TRUNCATED AT 400 WORDS)

Neurokinin B gene expression is increased in the arcuate nucleus of ovariectomized rats

Hypertrophy and increased gene expression of tachykinin neurons occur in the infundibular (arcuate) nucleus of postmenopausal women. We have hypothesized that the alterations in tachykinin gene expression in the hypothalami of postmenopausal women are secondary to ovarian failure and not due to age per se. In this study, in situ hybridization and computer-assisted microscopy were used to determine whether ovariectomy modulates neurokinin B (NKB), substance P (SP) or proopiomelanocortin (POMC) gene expression in the rat arcuate nucleus. Four groups were examined: proestrus; diestrous day 1; ovariectomized, and constant estrus induced by a single injection of 20 mg/kg estradiol valerate. Rats were sacrificed 2 months after treatment. Computer-assisted microscopy was used to determine the number of tachykinin neurons, cell areas, and the autoradiographic grain density of labeled neurons. We report marked changes in NKB gene expression in ovariectomized rats. The number of neurons containing NKB gene transcripts was significantly greater in ovariectomized rats (16.9 +/- 1.0 neurons/arcuate section) than all other groups. There was also a significant difference in the number of NKB neurons/arcuate section between proestrous (8.9 +/- 1.8 neurons) and diestrous (4.8 +/- 1.0 neurons) rats. The lowest number of neurons was detected in the estradiol valerate-injected rats (2.9 +/- 0.6 NKB neurons/arcuate section). Furthermore, the autoradiographic grain density of NKB neurons was doubled in the ovariectomized group compared to all other groups. In contrast, few SP neurons were identified in the rat arcuate nucleus and no changes were detected during the estrous cycle or in response to ovariectomy.(ABSTRACT TRUNCATED AT 250 WORDS)

Topography of neurons expressing luteinizing hormone-releasing hormone gene transcripts in the human hypothalamus and basal forebrain

The distribution of neurons expressing luteinizing hormone-releasing hormone (LHRH) gene transcripts was mapped in the human hypothalamus and basal forebrain by in situ hybridization and computer-assisted microscopy. Hypothalamic blocks were dissected from five adult males and one adult female and snap frozen in isopentane. The blocks were serially sectioned either in the coronal or in the sagittal plane at a thickness of 20 microns. Approximately every twentieth section was incubated with a 35S-labeled cDNA probe complementary to LHRH mRNA. Specificity was confirmed by hybridization of adjacent sections with a probe targeted to the gonadotropin-associated protein (GAP) region of LHRH messenger ribonucleic acids (mRNA). Maps of neurons containing LHRH mRNA were manually digitized with the aid of an image-combining computer microscope system. We report a much wider distribution and greater numbers of LHRH neurons than have been previously described in the human brain. Three morphological subtypes were observed based on cell size and labeling density: 1) small, heavily labeled, oval or fusiform neurons, located primarily in the medial basal hypothalamus, ventral preoptic area, and periventricular zone; 2) small, oval, sparsely labeled neurons located in the septum and dorsal preoptic region and scattered from the bed nucleus of the stria terminalis to the amygdala ("extended amygdala"); and 3) large round neurons (> 500 microns 2 sectional profile area), intermediate in labeling density, scattered within the magnocellular basal forebrain complex, extended amygdala, ventral pallidum, and putamen. The pronounced differences in morphology, labeling density, and location of the three subtypes suggest that distinct functional subgroups of LHRH neurons exist in the human brain.

Vasopressin and oxytocin gene expression in the human hypothalamus

We studied the distribution of messenger ribonucleic acids coding for vasopressin and oxytocin in the human hypothalamus by means of hybridization histochemistry. Numerous large and medium-sized neurons contain vasopressin messenger ribonucleic acid in the paraventricular nucleus, supraoptic nucleus, and accessory magnocellular nucleus. Small, lightly labeled vasopressin neurons also were detected in the suprachiasmatic nucleus. In addition, a relatively sparse band of mostly ovoid, medium-sized vasopressin neurons mingle with unlabeled neurons of the lateral hypothalamic area; these cells extend dorsoventrally from the region ventral to the stria terminalis to the ventrolateral hypothalamus, sometimes transgressing the boundaries of nearby nuclei. We did not detect vasopressin gene expression in neurons of the bed nucleus of the stria terminalis proper, although some of the dorsal-most labeled neurons of the lateral hypothalamus extend into the region of the caudal bed nucleus. Some lateral hypothalamic neurons also encroach upon other extrahypothalamic structures, such as the zona incerta. The nucleus basalis of Meynert complex was, with only rare exceptions, devoid of cells containing vasopressin messenger ribonucleic acid. Oxytocin messenger ribonucleic acid is found in the supraoptic nucleus, paraventricular nucleus, accessory magnocellular nucleus and, less frequently, in neurons of the lateral hypothalamus. In the hypothalamic magnocellular nuclei, oxytocin neurons are somewhat smaller than vasopressin neurons. Vasopressin cells outnumber oxytocin cells in the supraoptic nucleus, but their numbers are comparable in the paraventricular nucleus. As with vasopressin neurons, lateral hypothalamic oxytocin cells loosely span several diencephalic nuclei and encroach occasionally upon adjacent regions. These results confirm that the organization of vasopressin and oxytocin neurons in the human hypothalamus is largely comparable to that in nonhuman species and demonstrate the utility of hybridization histochemistry for elucidating the chemoarchitecture of the human brain.

Clinical utilization and complications of sural nerve biopsy

Surgeons frequently perform sural nerve biopsy as part of the work-up of patients with peripheral neuropathy. The indications for the procedure, therapeutic value, and complications associated with the procedure have received little attention in the surgical literature. A retrospective chart review of 60 patients with the suspected diagnosis of peripheral neuropathy undergoing sural nerve biopsy was performed. Vasculitis was suspected in 29 (48%) patients undergoing biopsy. This diagnosis was confirmed in 6 of the 29 patients and resulted in the alteration of therapy in 31% of patients with this suspected diagnosis. In 27 (45%) patients, the etiology of their peripheral neuropathy was unknown. Twelve (44%) patients in this group had sural nerve pathology; however, no change in therapy was required. Ten patients in our series had associated malignant tumors; some of these patients were diagnosed after referral for sural nerve biopsy. Twenty-five (42%) patients remained undiagnosed after biopsy. Nerve conduction studies were performed in 14 (22%) patients. Thirteen patients with abnormal lower extremity nerve conduction studies had 6 normal and 7 abnormal biopsy results. The one patient with a normal study had a normal nerve biopsy result. There were six (10%) patients with wound infections, seven (12%) patients with delayed wound healing, and three (5%) patients with new onset of chronic pain in the distribution of the sural nerve, for an overall complication rate of 27%. There was no correlation between the preoperative use of antibiotics, type of local anesthetic used, or length of nerve excised and complication rate. We conclude that the complication rate after sural nerve biopsy is significant. Strict criteria should be employed in selecting patients for sural nerve biopsy including a careful neurologic history and physical examination, nerve conduction studies, appropriate work-up for vasculitis if suspected, and implementation of a search for malignancy if this is not apparent. If the diagnosis is still in question, then sural nerve biopsy would seem appropriate, especially in patients with suspected vasculitis.

Neuronal hypertrophy in the hypothalamus of older men

A striking neuronal hypertrophy occurs in the infundibular nucleus of postmenopausal women. To determine the gender specificity of this response, we measured the areas of neuronal profiles in the infundibular nucleus of young (21, 32, and 41 years) and older (60, 61, and 68 years) men and compared them to data reported previously from the hypothalami of pre-(28, 32, and 40 years) and postmenopausal women (58, 62, and 74 years). Sagittal blocks of formalin-fixed hypothalami were paraffin embedded, serially sectioned and stained with cresyl-violet. The profile areas of 2,429 infundibular neurons were manually digitized using an image-combining computer microscope. The contralateral hypothalamus of each subject was cryoprotected, frozen-sectioned in the coronal plane and also stained with cresyl violet. The infundibular nuclear volume and the total number of neurons were estimated from the coronal sections using stereological methods. The mean profile area of infundibular neurons from older men (176.6 +/- 1.7 microns 2) was significantly larger than that of young men (147.0 +/- 1.3 microns 2). There was also a significant increase in the density of hypertrophied neurons (> 226 microns 2 profile area) in the infundibular nucleus of older men. There was no difference in infundibular nucleus associated with an average neurons was significantly increased in the older men. A comparison with previous data obtained from pre- and postmenopausal women revealed that the profile area of infundibular neurons was equal in young men and young women. However, the profile area of neurons in the postmenopausal women (190.4 +/- 2.1 microns 2) was significantly greater than that of older men.(ABSTRACT TRUNCATED AT 250 WORDS)

Basal forebrain neurons and memory: a biochemical, histological, and behavioral study of differential vulnerability to ibotenate and quisqualate

The differential vulnerability of basal forebrain cells to ibotenate (IBO) or quisqualate (QUIS) was investigated in rats. IBO was also coinjected with cystine (CYS) or zinc (Zn). Cortical choline acetyltransferase (ChAT) and glutamate decarboxylase (GAD) activity, neurotensin receptors, and high-affinity choline uptake sites were quantified in conjunction with radioimmunoassays for neurotensin, substance P, and somatostatin; immunocytochemistry for neurotensin-, somatostatin-, Leu-enkephalin-, and ChAT-positive cells; and in situ hybridization histochemistry of somatostatin, substance P, and enkephalin mRNAs. Compared with the performance of controls, continuous alternation performance in a T maze of IBO+Zn or IBO+CYS rats was better than that of IBO rats, whereas the performance of QUIS rats was unimpaired. Of those neurotransmitter systems examined, only ChAT-immunoreactive cells were vulnerable to IBO or QUIS. However, cholinergic cell loss did not correlate with impaired performance.

Tyrosine-hydroxylase-containing neurons in the primate basal forebrain magnocellular complex

Immunocytochemistry and in situ hybridization for tyrosine hydroxylase (TH) were used to study the distribution of putative catecholaminergic neurons in the basal forebrain magnocellular complex (BFMC) of monkeys and humans. Magnocellular TH-expressing neurons in the primate BFMC are distributed along a rostrocaudal gradient, with the largest proportion of these cells located in the medial septal nucleus and nucleus of the diagonal band of Broca; smaller TH-containing neurons generally follow the same distribution. These findings suggest that, within rostromedial segments of the BFMC, there is a distinct subpopulation of neurons that express catecholamine-synthesizing enzymes. Further research is necessary to establish whether these neurons utilize one or more catecholamines as neurotransmitters.

Cystic brain stem necrosis in a premature infant after prolonged bradycardia

A case is described of symmetrical cavitating brain stem necrosis produced by cardiac arrest in a premature infant. Two months after birth this 25-week gestational age infant suffered a prolonged episode of bradycardia. She was resuscitated and then died 3 weeks later. The autopsy revealed striking bilateral cavitation of the brain stem tegmentum extending in a columnar fashion from the upper portion of the spinal cord to the hypothalamus. The findings in this case are identical to the brain stem injury experimentally produced by complete cardiac arrest in the rhesus monkey.

Hormonal influences on morphology and neuropeptide gene expression in the infundibular nucleus of postmenopausal women

Neuronal hypertrophy occurs in a subpopulation of neurons in the infundibular nucleus of post-menopausal women. The hypertrophied neurons contain NKB, SP and estrogen receptor gene transcripts. Although associated with reproductive aging, post-menopausal neuronal hypertrophy is not a sign of central nervous system degeneration. Quite the opposite, because the hypertrophy is accompanied by marked increases in tachykinin gene expression, reflecting increased neuronal activity. We have proposed that infundibular neurons containing NKB, SP and estrogen receptor mRNAs participate in the hypothalamic circuitry regulating estrogen negative feedback on gonadotropin release in the human. In addition, there is evidence to suggest that the hypertrophied tachykinin neurons may be involved in the initiation of menopausal flushes. Because menopause affects a well characterized system, and has consistent and substantial changes in hormone levels, we have had the rare opportunity to correlate changes in hormone secretion with structural and neurochemical changes in the human hypothalamus. We suspect that future studies of the hypothalami of post-menopausal women will continue to be a fruitful avenue for investigating neuroendocrine regulation in the human.

Basal forebrain neurons and memory: A biochemical, histological, and behavioral study of differential vulnerability to ibotenate and quisqualate

The differential vulnerability of basal forebrain cells to ibotenate (IBO) or quisqualate (QUIS) was investigated in rats. IBO was also coinjected with cystine (CYS) or zinc (Zn). Cortical choline acetyltransferase (ChAT) and glutamate decarboxylase (GAD) activity, neurotensin receptors, and high-affinity choline uptake sites were quantified in conjunction with radioimmunoassays for neurotensin, substance P, and somatostatin; immunocytochemistry for neurotensin-, somatostatin-, Leu-enkephalin-, and ChAT-positive cells; and in situ hybridization histochemistry of somatostatin, substance P, and enkephalin mRNAs. Compared with the performance of controls, continuous alternation performance in a T maze of IBO+Zn or IBO+CYS rats was better than that of IBO rats, whereas the performance of QUIS rats was unimpaired. Of those neurotransmitter systems examined, only ChAT-immunoreactive cells were vulnerable to IBO or QUIS. However, cholinergic cell loss did not correlate with impaired performance.

Hypertrophy and increased gene expression of neurons containing neurokinin-B and substance-P messenger ribonucleic acids in the hypothalami of postmenopausal women

We have previously described hypertrophy of neurons containing estrogen receptor mRNA in the infundibular nucleus of postmenopausal women. In the present investigation we identified peptide mRNAs in the hypertrophied neurons and determined whether postmenopausal neuronal hypertrophy was accompanied by changes in gene expression. In the first study in situ hybridization was performed on sections from hypothalami of postmenopausal women (n = 3) using synthetic 35S-labeled cDNA probes complementary to mRNAs encoding estrogen receptor, substance-P (SP), neurokinin-B (NKB), POMC, cholecystokinin, dynorphin, CRF, enkephalin, galanin, neuropeptide-Y, GH-releasing hormone, and tyrosine hydroxylase. Neuronal cross-sectional areas and cell densities were measured with the aid of a computer microscope system. Neurons labeled with the NKB and SP probes were comparable in size, morphology, and distribution to the hypertrophied neurons containing estrogen receptor mRNA. In contrast, neurons labeled with other cDNA probes were sparsely distributed (CRF and dynorphin), smaller in size (neuropeptide-Y, galanin, GH-releasing hormone, enkephalin, cholecystokinin, and POMC), or located anterior to the hypertrophied population (tyrosine hydroxylase). In the second study sections from hypothalami of premenopausal (n = 3) and postmenopausal (n = 3) women were incubated with cDNA probes complementary to SP or NKB mRNAs. The mean cross-sectional areas of postmenopausal infundibular neurons containing NKB and SP mRNAs increased to 194% and 176% of premenopausal values, respectively. The autoradiographic grain densities of infundibular neurons labeled with either probe were also significantly increased in the postmenopausal group. Finally, the numbers of labeled neurons/tissue increased 6-fold (SP) and 15-fold (NKB) in the postmenopausal infundibular nucleus. These data demonstrate that human menopause is associated with marked increases in hypothalamic NKB and SP gene expression. We propose that neurons containing estrogen receptor, SP, and NKB mRNAs participate in the hypothalamic circuitry regulating estrogen negative feedback in the human.

Galanin mRNA in the nucleus basalis of Meynert complex of baboons and humans

Galanin, a 29-amino acid peptide, has been shown by immunocytochemistry to occur in most large acetylcholinergic neurons of the complex that includes the nucleus basalis of Meynert and the nucleus of the diagonal band of Broca in nonhuman primates. In contrast, several studies have reported that most large neurons of the human nucleus basalis of Meynert complex appear to lack galanin immunoreactivity. We investigated this apparent species-difference by hybridization histochemistry for galanin messenger ribonucleic acid (mRNA) in humans and baboons. The results confirm previous immunocytochemical data; very few large neurons of the nucleus basalis of Meynert complex in humans contained detectable galanin messenger RNA, whereas most such cells in baboons were labeled by the oligodeoxynucleotide probe. The few labeled neurons in humans were primarily medial or ventral to the main body of the nucleus basalis of Meynert and corresponded in location to a minor population of relatively intensely labeled cells in baboons. These findings indicate that the indetectability of immunoreactive galanin in most cells of the nucleus basalis of Meynert complex in humans is due to a paucity or an absence of galanin messenger RNA and not to differences in posttranslational processing or transport of the peptide. Inasmuch as the probe labeled neurons in several other nuclei of both species, it is unlikely that differences in galanin messenger RNA sequences underlie the species-related disparity in hybridization in the nucleus basalis of Meynert complex. The indetectability of galanin messenger RNA in most cells of the human nucleus basalis of Meynert complex indicates that the expression of the galanin gene is regulated by as yet unidentified influences that differ in human and nonhuman primates. The varying phenotypes of galanin in primates suggest potentially important species-differences in the function of galanin in neurons of the nucleus basalis of Meynert complex.

Postmenopausal hypertrophy of neurons expressing the estrogen receptor gene in the human hypothalamus

Computer microscopy and in situ hybridization were used to investigate neuronal hypertrophy in the infundibular nucleus of postmenopausal women. In the first experiment, hypothalami from premenopausal (n = 3) and postmenopausal (n = 3) women were formalin fixed, paraffin embedded, serially sectioned, and stained with cresyl violet. Soma areas of more than 3500 neurons were digitized using an image-combining computer microscope. The mean cross-sectional area of infundibular neurons in the postmenopausal women was 30% greater than that in premenopausal women, with no change in cell density. The mean cross-sectional area of mammillary neurons was unchanged, indicating that the infundibular neuronal hypertrophy was not an artifact of tissue processing. In the second experiment, hypothalami from premenopausal (n = 3) and postmenopausal (n = 2) women were frozen, serially sectioned, and incubated with a 48-base synthetic cDNA probe complementary to estrogen receptor (ER) mRNA. Adjacent sections were incubated with a cDNA probe complementary to GnRH mRNA. Morphometric analysis revealed that the mean cross-sectional area of infundibular neurons expressing the ER gene in the postmenopausal women was twice as large as the mean area in premenopausal hypothalami. The hypertrophied neurons did not contain GnRH mRNA. Finally, analysis of the infundibular nucleus from an oophorectomized 38-yr-old woman also revealed hypertrophied neurons containing ER mRNA. These data support the hypothesis that hypertrophy of infundibular neurons in postmenopausal women is secondary to loss of the inhibitory feedback of ovarian steroids.