Heterogeneity in the neuropeptide Y-containing neurons of the rat arcuate nucleus: GABAergic and non-GABAergic subpopulations

Neuropeptide Y, produced in the arcuate nucleus of the hypothalamus, plays a key role in the central regulation of anterior pituitary and appetitive functions. The pleiotropic nature of neuropeptide Y in these mechanisms indicates the existence of heterogeneity in the hypothalamic neuronal population producing neuropeptide Y. In this study, we report the coexistence of neuropeptide Y and the amino acid transmitter, gamma-aminobutyric acid (GABA), in neuronal perikarya of the arcuate nucleus. Fluorescent double immunolabeling for neuropeptide Y and glutamic acid decarboxylase was carried out on vibratome sections collected through the hypothalamic arcuate nuclei of animals that were pretreated with colchicine. It was found that about one third of the neuropeptide Y-producing arcuate nucleus perikarya co-expressed glutamic acid decarboxylase. This population of neuropeptide Y-containing GABAergic neurons were distributed longitudinally within the arcuate nucleus located predominantly in its dorsomedial aspects. These results show that there are at least two distinct populations of neuropeptide Y-producing neurons in the arcuate nucleus: a subset of neuropeptide Y and GABA-co-producing neurons located in the dorsomedial arcuate nucleus and a subset of non-GABAergic neuropeptide Y cells located in the ventral arcuate nucleus. This heterogeneity in the neuropeptide Y-producing perikarya of the hypothalamus may help explain adverse neuroendocrine and behavioral effects of arcuate nucleus neuropeptide Y.

Evidence showing that beta-endorphin regulates cyclic guanosine 3',5'-monophosphate (cGMP) efflux: anatomical and functional support for an interaction between opiates and nitric oxide

Nitric oxide (NO) is now recognized as a diffusible messenger molecule that normally augments intercellular communication in the central nervous system, but is neurotoxic if released in excessive amounts. NO is synthesized from L-arginine by the Ca2+/calmodulin-dependent neuronal isoform NO synthase (NOS) localized in sub-populations of neurons throughout the brain, including the hypothalamus. In the hypothalamus, NO stimulates the release of GnRH, the primary neurohormone governing reproduction in mammals. Although the excitatory amino acid, glutamate, acting through the N-methyl-D-aspartate (NMDA) receptor is believed to be responsible for stimulation of NO release, the neuronal system(s) that inhibits NO efflux is unknown. As the endogenous opioids, primarily beta-endorphin (betaEND), exert a tonic restraint on GnRH secretion, we sought evidence for a possible functional link between betaEND and NOS pathways in the hypothalamus. We observed that restraining the opioid influence with the opiate receptor antagonist, naloxone, in intact, but not in castrated, rats rapidly augmented extracellular cGMP/NO efflux in the medial preoptic area, where GnRH, NOS, and betaEND immunoreactive pathways are coextensive. Pituitary LH secretion increased in conjunction with this augmented cGMP/NO response and pretreatment with the mu opiate receptor agonist, morphine, suppressed these naloxone-induced responses. Further, visualization of hypothalamic sections immunostained for both betaEND and NOS revealed betaEND-immunoreactive axon terminals in close proximity to NOS-positive cell bodies and dendrites in a number of hypothalamic subdivisions, including the medial preoptic area. These close appositions represented conventional synapses between betaEND nerve terminals and NOS-positive perikarya and dendrites under the electron microscope. Clearly, the experimental data, corroborated by morphological evidence, point to a direct inhibitory control of betaEND on NOS-immunoreactive neurons in monitoring cGMP/NO release. These findings together with the previous observations that the glutamate neurotransmitter acting through NMDA receptors located on NOS-immunopositive cells stimulates cGMP/NO efflux and plasma LH selectively in intact rats document the existence of a dual control comprised of the excitatory NMDA and the inhibitory mu opiate receptors in modulating cGMP/NO release, a response also directed by gonadal steroids. This new knowledge of an inhibitory opioid influence on cGMP/NO release is probably extremely important both in the generation of periodicities in GnRH secretion that underlie hypothalamic control of reproduction and in protecting against neurotoxic overstimulation of NO release by excitatory amino acids.

Control of gonadotropin feedback: the possible role of estrogen-induced hypothalamic synaptic plasticity

The preovulatory gonadotropin surge is a critical event in reproduction. Although many explanations have been given for the inhibition--disinhibition cycle referred to as positive feedback, none are completely satisfactory. Recent evidence indicates that the preovulatory surge of gonadotropin is induced, in part, by the disengagement of inhibitory synaptic connections in the hypothalamic arcuate nucleus. This disinhibition of gonadotropin-releasing hormone secretion results in a massive release by the estrogen-sensitized pituitary gonadotrophs. Investigations are presently under way to determine whether other areas of the hypothalamus are involved in this estrogen-induced synaptic plasticity.

Aromatase in axonal processes of early postnatal hypothalamic and limbic areas including the cingulate cortex

It has been shown that sexual dimorphic morphology of certain hypothalamic and limbic areas underlie gender-specific sexual behavior and neuroendocrine mechanisms. The key role played by locally formed estrogen in these developmental events has been revealed during a critical perinatal period. In this study, we aimed to document the presence of estrogen-synthetase (aromatase)-immunoreactive elements in the involved limbic system and hypothalamus of the developing rat brain. On postnatal day 5, animals of both sexes were perfusion-fixed, and sections from the forebrain and hypothalamus were immunolabelled for aromatase using an antiserum that was generated against a 20 amino acid sequence of placental aromatase. Aromatase-immunoreactivity was present in neuronal perikarya and axonal processes in the following limbic structures: the central and medial nuclei of the amygdala, stria terminalis, bed nucleus of the stria terminalis (BNST), lateral septum, medial septum, diagonal band of Broca, lateral habenula and all areas of the limbic (cingulate) cortex. In the hypothalamus, the most robust labelling was observed in the medial preoptic area, periventricular regions, ventromedial and arcuate nuclei. The most striking feature of the immunostaining with this antiserum was its intracellular distribution. In contrast to the heavy perikaryal labelling that can be observed with most of the currently available aromatase antisera, in the present experiments, immunoperoxidase was predominantly localized to axons and axon terminals. All the regions with fiber staining corresponded to the projection fields of neuron populations that have previously been found to express perikaryal aromatase. Our results confirm the presence of aromatase-immunoreactivity in developing limbic and hypothalamic areas. The massive expression of aromatase in axonal processes raises the possibility that estrogen formed locally by aromatase may not only regulate the growth, pathfinding and target recognition of its host neuronal processes, but may also exert paracrine actions on structures in close proximity, including the target cells.

Gonadal steroids target AMPA glutamate receptor-containing neurons in the rat hypothalamus, septum and amygdala: a morphological and biochemical study

Interactions between glutamate and gonadal steroids are involved in the regulation of limbic and hypothalamic functions. We hypothesized that hormonal signals affect excitatory neurotransmission by regulating the expression of glutamate receptors (GluR) in limbic and hypothalamic regions. To test this hypothesis, first, the coexpression of dl-alpha-amino-3-hydroxy-5-methyl-4-isoxazone-propionate (AMPA) GluR1, GluR2/3, and androgen receptors or estrogen receptors was revealed in the same cells of septal, amygdaloid, and hypothalamic areas by double immunocytochemistry. The highest incidence of co-localization was detected in hypothalamic regions. To demonstrate a regulatory role of testosterone or estradiol on AMPA receptor expression, the hormonal milieu of male and female rats was manipulated by gonadectomy and hormonal treatment. GluR1 and GluR2/3 expression was assessed by Western blots. Statistical analysis demonstrated that testosterone and estradiol have a stimulatory influence on the expression of AMPA receptors in the hypothalamus. The regulatory effect of estradiol on AMPA receptors was found to be site and gender specific: after estradiol treatment, samples taken from the hypothalamus contained increased levels of GluR1 and GluR2/3, whereas in the septum, bed nucleus and amygdala, no changes could be detected. Furthermore, the increase in hypothalamic GluR 2/3 levels was two times higher in females, compared with males, whereas the changes in hypothalamic GluR 1 levels showed no sex differences. Our results support the hypothesis that the interaction between gonadal steroids and glutamate involves hormone regulation of GluR. This mechanism seems to be gender and site specific, suggesting that excitatory neurotransmission and related physiological mechanisms also may be distinctly different in males and females.

Lack of gonadotropin-positive feedback in the male rat is associated with lack of estrogen-induced synaptic plasticity in the arcuate nucleus

We have demonstrated that estrogen induces synaptic reorganization in the hypothalamic arcuate nucleus of female rats during the ovarian cycle and proposed that estrogen-induced synaptic retraction plays a role in the disinhibition of gonadotropin secretion that occurs during the afternoon of proestrus. This so-called positive feedback of gonadotropins is developmentally determined. It is present in female rats and absent in males. To confirm the role of the estrogen-induced synaptic retraction in positive feedback, we tested whether administration of estrogen to male rats also fails to induce synaptic remodeling of the arcuate nucleus. Male and female rats were gonadectomized and studied as follows. One month following gonadectomy, animals received either a single injection of estradiol (100 micrograms/animal in sesame oil; 12 males and 12 females) or vehicle (6 males and 6 females). Twenty-four hours following injections, all animals in the vehicle-injected group and 6 animals of each sex in the treatment groups were sacrificed, while the rest of the animals were killed 48 h following the hormone injections (6 per group). As expected, quantitative electron microscopic analysis of the female arcuate nuclei revealed that compared to oil-injected controls, estradiol induced drastic decreases in the overall synapse counts by 24 h (121 +/- 10 vs. 74 +/- 5 synapses/1,000 microns membrane; p < 0.05). Synaptic counts had recovered to control levels by 48 h. On the contrary, in males, estradiol treatment did not cause changes in the total synapse counts at either time. As a further control, the lack of an estrogen-induced gonadotropin surge in long-term castrate males was also confirmed. Our study confirmed that in males estradiol does not alter the net synaptology of the arcuate nucleus or cause gonadotropin positive feedback. This is in clear contradistinction to females which show both synaptic plasticity and gonadotropin-positive feedback upon receiving exogenous or endogenous estrogen. The lack of estrogen-induced synaptic plasticity may be an underlying mechanism in the abolishment of positive gonadotropin, feedback in developing males and the development of constant estrus in aging female rats.

Synaptic remodeling in the arcuate nucleus during the estrous cycle is induced by estrogen and precedes the preovulatory gonadotropin surge

We have shown that the ovarian cycle is accompanied by a fall in the axosomatic synapses on randomly selected neurons of the arcuate nucleus by the morning of estrus, with a return to the preovulatory levels by the morning of metestrus, indicating a possible role in positive feedback. However, it remains to be proven that the circulating estradiol is the actual regulator of this physiological synaptic plasticity, or that estrogen-induced synaptic retraction precedes in the surge of gonadotropins at midcycle. To resolve these questions, we used an estradiol-immunoneutralization protocol and studied arcuate nucleus axosomatic synapses during the critical points of the estrous cycle. In addition to blocking positive feedback, estrogen immunoneutralization abolished synaptic retraction in the arcuate nucleus. As a positive control, the nonbinding estrogen diethylstilbestrol maintained the gonadotropin surge and synaptic retraction in the antiestradiol-treated animals. Furthermore, in the diluent-treated cycling control females, the synaptic retraction was found to precede the preovulatory LH surge. We demonstrated that the midcycle synaptic retraction of arcuate nucleus synapses is induced by the preovulatory estradiol surge, and that these morphological events precede the preovulatory gonadotropin surge. Taken together, these observations strongly suggest that the hypothalamic mechanism underlying the physiological disinhibition of gonadotropins at midcycle (positive feedback) requires estrogen-induced synaptic retraction in the arcuate nucleus.

Interaction of insulin-like growth factor-I and estradiol signaling pathways on hypothalamic neuronal differentiation

Neurotrophic effects of estradiol and insulin-like growth factor-I were assessed in primary cultures from fetal rat hypothalamus. Cultured neurons were immunostained with an antibody for the microtubule-associated protein-2. While both estradiol and insulin-like growth factor-I increased the number of microtubule-associated protein-2-immunoreactive neurons and the extension of immunoreactive processes, the effect of these two factors was not additive. The estradiol-induced increases in neuronal numbers and extension of neuronal processes were blocked by either the estrogen receptor antagonist ICI 182,780 or by an anti-sense oligonucleotide to the estrogen receptor. Furthermore, incubation of the cultures with an anti-sense oligonucleotide directed against the insulin-like growth factor-I messenger RNA also blocked the effect of estradiol. In turn, the effects of insulin-like growth factor-I were blocked by the estrogen receptor antagonist ICI 182,780 and by the anti-sense oligonucleotide to the estrogen receptor. These findings suggest that estradiol-induced activation of the estrogen receptor in developing hypothalamic cells requires the presence of insulin-like growth factor-I, and that both estradiol and insulin-like growth factor-I use the estrogen receptor as a mediator of their trophic effects on hypothalamic neurons.

Morphological and pharmacological evidence for neuropeptide Y-galanin interaction in the rat hypothalamus

Galanin (GAL) and neuropeptide Y (NPY) have been shown to play important roles in the regulation of pituitary hormone secretion, as well as ingestive and sexual behaviors, by acting within the hypothalamus. While the mechanism of action of these regulatory peptides is under intensive investigation, less attention has been paid to the possible interaction between them in influencing these central regulatory processes. Because NPY and GAL augment pituitary gonadotropin release, the present study was undertaken to evaluate the nature of morphological and functional relationships between these excitatory hypothalamic peptidergic systems. Double immunolabeling for NPY and GAL was carried out on vibratome sections taken from the hypothalamus of colchicine-pretreated female rats. Avidinbiotin peroxidase technique and a dark blue diaminobenzidine reaction was used to visualize NPY profiles, while the GAL neurons were labeled with a light brown diaminobenzidine reaction using either the avidin-biotin peroxidase or the peroxidase antiperoxidase technique. Light microscopic examination of the immunostained material showed that in the arcuate nucleus, paraventricular nucleus, supraoptic nucleus, anterior hypothalamus, and medial preoptic area, an abundant network of NPY-immunoreactive axons surrounded GAL-immunostained cells. Numerous dark blue NPY-containing putative boutons were observed in close proximity to GAL-immunolabeled cell bodies and dendrites. Correlated light and electron microscopic examination revealed that most of the immunoreactive NPY axon terminals established synaptic connections with GAL-expressing cells. Synaptic connections were most frequently found in the medial preoptic area and in the magnocellular region of the paraventricular nucleus and arcuate nucleus. Fewer connections were observed in the supraoptic nucleus. These morphological observations demonstrate the existence of a strong NPY input to hypothalamic GAL neurons, thereby suggesting a modulatory role for NPY in monitoring GAL release. To evaluate the functional relevance of this anatomical relationship, the effects of intraventricular injection of a GAL receptor antagonist, galantide, were examined on NPY-induced LH release in ovarian steroid-primed ovariectomized rats. As expected, intraventricular injection of NPY readily stimulated LH release. Although, while on its own, galantide was ineffective in altering basal LH release, it markedly attenuated the NPY-induced LH response, thereby suggesting that GAL released in response to NPY administration may, in part, mediate the excitatory effects of NPY. These experimental results, taken together with the morphological observations, document the involvement of an NPY --> GAL signaling modality in the release of gonadotropins and, likewise, raise the possibility of a similar signaling process in the release of other pituitary hormones and elicitation of behavioral effects attributed to NPY and GAL.

Action of steroid hormones on growth and differentiation of CNS and spinal cord organotypic cultures

During the prenatal period, gonadal steroid environment induces dramatic sexually dimorphic changes in the nervous system. We have used in vitro methods to study the mechanism and timing of hormonal influences on neuronal sprouting and myelination during the prenatal period. Organotypic cultures of hypothalamus and lumbar spinal cord (SC) slices from rat fetuses were grown on plasma clot or in hyaluronic acid and exposed to estrogen (17 beta estradiol) and testosterone (T) during cultivation. Both steroid hormones were active: 17 beta estradiol enhanced sprouting of hypothalamic neuronal fibers and increased the amount of synapses. In SC cultures T induced regeneration of thick nerve processes and an early onset of myelination, mainly of peripheral myelin.

Neuroplastic changes in the hypothalamic arcuate nucleus: the estradiol effect is accompanied by increased exoendocytotic activity of neuronal membranes

1. In the rat hypothalamic arcuate nucleus, estradiol induces coordinated changes in the number of axosomatic synapses, the amount of glial ensheathing, and the ultrastructure of the membrane of neuronal somas. In the present study we used conventional electron microscopy and freeze-fracture to examine cellular mechanisms responsible for the estradiol-induced changes at the membrane level. 2. In freeze-fracture replicas taken 10-60 min and 24 hr after injection of 17 beta-estradiol to adult ovariectomized females, it was found that there was a rapid increase in the number of exoendocytotic images that reached a plateau by 30 min. 3. In thin sections from animals injected 24 hr earlier we demonstrated a significant increase in coated vesicles in the periphery of the neurons and coated pits in the perikaryal membranes and decreased axosomatic synapses. 4. We conclude that these morphological alterations are signaling estrogen-induced transport and/or turnover of perikaryal membrane constituents and extracellular components which may affect interneuronal and neuroglial interactions.

Potential neuronal mechanisms of estrogen actions in synaptogenesis and synaptic plasticity

1. Studies conducted on the rat arcuate nucleus, an area involved in the development and control of LH and FSH secretion, have shown the existence of hormonally regulated developmental sex differences in synaptic patterns and estrogen-induced synaptic plasticity during adult life. Several questions raised by these findings are examined in this review: 2. The mechanisms of estrogen-regulated developmental synaptogenesis. These include the role of glycocalyx glycoproteins in neuronal membranes, neural cell adhesion molecules, and insulin-like growth factor I. 3. The relationship among circulating estrogen, gonadotropin levels, and hypothalamic synaptic plasticity. Recent evidence for the role of GABAergic and dopaminergic synaptic inputs and POMC projections from the arcuate nucleus to the GnRH cells is discussed. 4. The synaptologic basis of age-related failure of positive feedback. The role of the cumulative effect of repeated preovulatory synaptic retraction and reapplication cycles on sensescent constant estrus is analyzed.

Endocrine glia: roles of glial cells in the brain actions of steroid and thyroid hormones and in the regulation of hormone secretion

The development and functioning of the nervous system are known to be influenced in various ways by endocrine signals. In turn, neural tissue modulates internal homeostasis, not only by electrical signaling, but also by regulating the release of endocrine messengers. However, the mechanisms underlying these processes are not fully understood. Recent evidence indicates that glia may play a significant role in the link between the endocrine and nervous systems. Glial cells express nuclear receptors for both thyroid and steroid hormones and participate in the metabolism of these hormones, resulting in the production of neuroactive metabolites. Furthermore, glial cells synthesize endogenous neuroactive steroids, including pregnenolone and progesterone, from cholesterol. Thyroid hormones, glucocorticoids, gonadal steroids, and neurosteroids affect myelinization by acting on oligodendroglia and modulate astroglia morphology, differentiation, and gene expression in different brain areas. Under physiological conditions, hormonal effects on glia may have important consequences for neuronal development, metabolism, and activity and for the formation and plasticity of synaptic connections. In addition, glucocorticoids, gonadal steroids, and neurosteroids may affect regenerative processes in neurons by modulating glial responses after injury. These effects include the activation of microglia, which is regulated by glucocorticoids, and the proliferation of reactive astroglia, which is regulated by gonadal hormones and neurosteroids. Glial cells are also involved in the modulation of hormone release. Pituicytes and microglia in the neurohypophysis may influence hormonal secretion by regulating neurovascular contacts, while astroglia in the hypothalamus regulate the number of synaptic inputs to specific neuronal populations involved in pituitary hormone release, such as LHRH and oxytocinergic neurons. Furthermore, tanycytes and astrocytes in the arcuate nucleus and median eminence release trophic factors that regulate hormone secretion by hypothalamic neurons.

Gonadal steroids and astroglial plasticity

1. Recent evidence indicates that astroglia participate in the metabolism of gonadal hormones, in the synthesis of neurosteroids, and in the plastic responses of neurons to gonadal steroids. The role of astroglia on plastic responses of neural tissue to gonadal hormones and neurosteroids is examined in this review. 2. Gonadal steroids and neurosteroids promote astroglia plasticity in several areas of the central nervous system, including the hypothalamus, the striatum, and the hippocampus. 3. Gonadal steroids and neurosteroids modulate astroglia proliferation and the formation of reactive astroglia after brain injury. 4. Astroglia is a source of trophic factors that may mediate effects of gonadal steroids on neural tissue. 5. Astroglia is involved in the promotion of synaptic plastic changes by gonadal hormones. 6. The effect of gonadal hormones on astroglial plasticity is dependent on specific membrane interactions with neurons and on the expression of the embryonic highly polysialylated isoform of the neural cell adhesion molecule on neuronal membranes. 7. In conclusion, coordinated responses of neurons and astroglia appear to be involved in the modulation of neural function and response to injury by gonadal hormones and neurosteroids.

A new organotypic culture method to study the actions of steroid hormones on the nervous system

A new organotypic culture method for growing slices of nervous system tissue, based on the use of hyaluronic acid as a growth supporting milieu, is described. This method allows cultures derived from either fetuses or newborns to grow and develop with markedly reduced amounts of added serum. Organotypic cultures from fetal rat hypothalamus were exposed to 17 beta estradiol and compared to control cultures exposed to the ethanol vehicle. When exposed to estradiol, cultures showed an outgrowth of thick nerve fibers that was accompanied by an elevation in the number of microtubules present in the neuronal processes, an increment in the number of synapses, and an increased morphological differentiation of synaptic terminals. Freeze-fracture analysis of neuronal membranes from estradiol-treated cultures revealed a significant increase in the number of exoendocytotic images and a decrease in the number of intramembranous particles. Estradiol's effects parallel those found in in vivo studies, indicating that hyaluronic acid-based organotypic cultures represent an appropriate model to study hormonal influences on the developing nervous system.

Aromatase immunoreactivity in axon terminals of the vertebrate brain. An immunocytochemical study on quail, rat, monkey and human tissues

Intraneuronal production of estradiol from testosterone has been shown to play a pivotal role in gender-specific brain development of most vertebrates, and to participate in numerous functions of the adult central nervous system. Previous biochemical and morphological approaches demonstrated that estrogen synthetase (aromatase) is present in specific limbic and hypothalamic structures. On the other hand, less attention has been paid to revealing its subcellular distribution. The possibility of aromatase presence in axonal processes has been indicated by recent biochemical and morphological observations suggesting new insights for the role of aromatase in neural functions. The objective of the present study was to provide morphological evidence for the subcellular location of aromatase in neurons of different vertebrate species including Japanese quail, rat, monkey, and human. Immunocytochemistry using a purified polyclonal antiserum against human placental aromatase localized immunoreactivity to hypothalamic and limbic cell groups in all of these species. Light and electron microscopic examination of vibratome sections revealed the presence of aromatase immunoreactivity throughout the neuronal perikarya, including dendrites and axonal processes. In each species there were numerous boutons which contained labeled small clear synaptic vesicles. Many of these axon terminals formed synapses with immuno-negative and immuno-positive dendrites and perikarya. This study furnishes the first immunolocalization of aromatase in the brains of two primate species, humans and monkeys. The provision of further evidence for estrogen synthesis in axons and axon terminals may help resolve apparent differences between the measurement of aromatase activity and the lack of aromatase-immunopositive cell bodies in previous studies. The present findings may be coupled with recent evidence regarding the molecular biology and the diversity of functional properties of P450 aromatase to indicate previously unexpected effects of brain aromatase at the synaptic level.

Interaction of the signalling pathways of insulin-like growth factor-I and sex steroids in the neuroendocrine hypothalamus

Among the numerous endocrine signals that affect the central nervous system, sex steroids play an important role. It has been recently postulated that part of the effects of these hormones on the brain may be mediated by trophic factors, such as insulin-like growth factor I (IGF-I). Both estradiol and IGF-I increase the survival and differentiation of developing fetal rat hypothalamic neurons in culture. The effect of estradiol is blocked by the pure estrogen receptor antagonist ICI 182,780, by an antisense oligonucleotide to the estrogen receptor, and by an antisense oligonucleotide to IGF-I. In turn, the effect of IGF-I is blocked by ICI 182,780 and by the antisense oligonucleotide to the estrogen receptor. These findings indicate that estrogen-induced activation of the estrogen receptor in developing hypothalamic neurons requires the presence of IGF-I and that both estradiol and IGF-I use the estrogen receptor to mediate their trophic effects on hypothalamic cells. In vivo, sex steroids affect IGF-I levels in the endocrine hypothalamus. IGF-I levels in tanycytes, a specific subtype of glial cells present in the arcuate nucleus and median eminence, are sexually dimorphic in the rat, increase with the onset of puberty, and are regulated by perinatal and adult levels of sex steroids. These changes may be due to hormonal modifications of IGF-I uptake by tanycytes from blood or cerebrospinal fluid. Therefore, this type of glial cell appears to play a central role in the interaction of sex steroids and IGF-I in the hypothalamus.

Verapamil treatment attenuates immunoreactive GFAP at cerebral cortical lesion site

Cerebral cortical lesions were produced using a stereotactic injection system in Sprague-Dawley rats randomly assigned to three groups: (1) needle lesioned and uninjected (Lesioned), (2) needle lesion and simultaneous local injection of 50 or 100 microliters 0.9% saline (L/Saline), and (3) needle lesion and simultaneous local injection of 50 or 100 microliters Verapamil-HCl (VHCL) (2.5 mg/ml (5 mM) Abbott Labs, Chicago, IL), a passive, L-type calcium channel blocker (L/VHCL). The lesioning induced expression of glial fibrillary acidic protein (GFAP), a type of intermediate filament protein expressed in reactive astrocytes, at the lesion site. There was a reduction in GFAP-like immunoreactivity (GFAP-IR) in the L/VHCL group versus the Lesioned and the L/Saline groups. There was a five-fold increase of GFAP-IR at 24 h post lesion in the L/Saline group, but no statistically significant increase seen in the Lesioned or L/VHCL groups at either volume. Pretreatment of the anti-GFAP with VHCL did not impair the antigen labeling. To determine whether differences in pHs, or volume could account for these findings, a second experiment was performed using pH-matched saline or VHCL in 10 microliters volume injected into contralateral hemispheres at the time of lesioning. There was an 80% reduction in GFAP-IR in the L/VHCL group at 72 h compared with the L/Saline group. These data suggest that VHCL may suppress the early increase of GFAP-IR in response to cortical lesion and that reducing transmembrane calcium flux through L-type calcium channels may be the mechanism involved.

Psychiatric status after human fetal mesencephalic tissue transplantation in Parkinson's disease

This report describes the prospective and systematic psychiatric assessment of nine patients who received transplantation of human fetal mesencephalic tissue into the caudate nucleus for treatment of Parkinson's disease. Unlike adrenal medullary transplantation, which often causes psychosis or delirium, this procedure appeared to have few perioperative sequelae. On longer-term follow-up, there was some statistical evidence of deterioration in psychiatric status, as manifested primarily in depressive and nonspecific emotional and behavioral symptoms. This group effect was partly attributable to the occurrence of discrete episodes of illness (major depression and panic disorder with agoraphobia) in some patients, but it was unclear whether such episodes occurred more often than would ordinarily be expected in Parkinson's disease. Differences in the neurobiological effects of fetal mesencephalic and adrenal medullary grafts may account for differences in the psychiatric sequelae of patients receiving these procedures.

Morphological evidence for a galanin-opiate interaction in the rat mediobasal hypothalamus

It is well established that hypothalamic galanin- and beta-endorphin-containing circuits play important roles in the neuroendocrine regulation of pituitary hormone secretion and sexual behaviors, as well as in feeding. Recent experimental evidence suggests that an opiate-galanin interaction may be involved in these neuroendocrine responses. In particular, galanin and beta-endorphin have been shown to stimulate prolactin release from the pituitary, and concurrently, evoke feeding in the rat. The present study was designed to elucidate the morphological component underlying these responses in the hypothalamus. Sections of the mediobasal hypothalamus of colchicine-pretreated female rats were double immunostained for galanin and beta-endorphin. A dark blue nickel ammonium sulfate-intensified diaminobenzidine reaction was used to visualize galanin profiles, while beta-endorphin neurons were labeled with a light brown diaminobenzidine reaction. Light microscopy revealed putative connections between galanin boutons and beta-endorphin cells. Electron microscopic examination showed that galanin boutons form axo-somatic and axo-dendritic synaptic connections with beta-endorphin neurons. The vast majority (89.6%) of the beta-endorphin-immunoreactive neurons were found to be contacted by galanin-immunopositive fibers in the hypothalamus. To determine the origin of the galanin fibers innervating this region, the arcuate nuclei of additional rats were isolated unilaterally using a Halász-knife. After a ten day survival period, immunostaining was carried out for galanin. The relative surface occupied by galanin immunoreactive profiles on the ipsi- and contralateral sides were compared using an image analyzer. This analysis revealed that deafferentation of the arcuate nucleus did not decrease the density of galanin immunoreactive profiles on the isolated side of the arcuate nucleus compared to the control side, thus, indicating that the galanin boutons contacting beta-endorphin cells are most probably of local origin. These studies support the proposal that galanin-evoked prolactin secretion and feeding behavior may, in part, be mediated by enhanced beta-endorphin release and raises the possibility that a hypothalamic galanin-beta-endorphin axis may operate in the control of other pituitary hormones.

General cognitive ability following unilateral and bilateral fetal ventral mesencephalic tissue transplantation for treatment of Parkinson's disease

OBJECTIVE

To contrast the neuropsychological profiles of Parkinsonian patients, before and after fetal ventral mesencephalic tissue transplantation.

DESIGN

Case series of personally examined patients.

SETTING

Patients were evaluated by neurologists, neurosurgeons, and neuropsychologists as outpatients at a university hospital.

PATIENTS

Fetal mesencephalic tissue was implanted in the right caudate nucleus of three patients and both nuclei of one patient. These patients were evaluated prior to surgery and at 12, 24, and 26 months postoperatively.

RESULTS

Factor analysis of the test battery identified four statistically orthogonal test clusters. No statistically significant changes were identified postoperatively for clusters assessing verbal cognitive ability, nonverbal cognitive ability, and information-processing speed. An improvement of verbal memory cluster index was observed 12 months after surgery, and the improvement reached the level of statistical significance at 24 months after surgery. However, the verbal memory of all patients declined between 24 and 36 months after surgery.

CONCLUSIONS

Fetal tissue transplantation to one or both caudate nuclei did not permanently arrest cognitive dysfunction. Although there is some evidence of improved cognitive ability after transplantation, it is improbable that normal cognitive function can be restored by this procedure because the impairments of cognitive ability associated with Parkinson's disease do not appear to originate solely from dopamine deficiency.

Gonadal hormone regulation of neuronal-glial interactions in the developing neuroendocrine hypothalamus

Recent evidence indicates that, in addition to their well known effects on neurons, gonadal steroids may exert part of their neural effects through astroglia. In adult female rats astroglia participate in the phasic remodelling of synapses that takes place during the estrous cycle in the arcuate nucleus of the hypothalamus under the influence of estradiol. Astroglia also appear to be involved in the genesis of sex differences in synaptic connectivity. Gonadal steroids influence hypothalamic astroglia differentiation in vitro and in vivo. In monolayer mixed neuronal-glial cultures from fetal rat hypothalami, estradiol induces a progressive differentiation of astrocytes from a flattened epithelioid morphology to bipolar, radial and stellate shapes. This effect of estradiol on astroglia is dependent on the expression of specific molecules on the neuronal surface, such as the polysialic acid-rich form of the neural cell adhesion molecule. In the rat arcuate nucleus in situ, perinatal androgen influences astroglia gene expression and differentiation, resulting in a sex difference in astroglia organization by postnatal day 20. By this day, the amount of neuronal surface covered by astroglial processes is higher in males than in females. This difference in the coverage of neuronal surface by astroglia may be directly related to the reduced number of synaptic contacts that is established on the soma of male neurons compared to females.