A combined light and electron microscopic immunocytochemical method for the simultaneous localization of multiple tissue antigens. Tyrosine hydroxylase immunoreactive innervation of corticotropin releasing factor synthesizing neurons in the paraventricular nucleus of the rat

Oestrogen receptor beta-immunoreactivity in gonadotropin releasing hormone-expressing neurones: regulation by oestrogen

Double-label immunohistochemistry was employed to establish whether immunoreactivity for the beta subtype of the oestrogen receptor (ER beta-IR) is present in gonadotropin releasing hormone (GnRH)-containing cells. In the immortalized GnRH cell line, GT1-7, almost all nuclei were immunoreactive for ER beta. In the preoptic area of ovariectomized rats, more than one-half of the GnRH neurones (52.0-63.5%) contained ER beta-IR within the nucleus; a smaller proportion of these neurones (5-10%) displayed a particularly intense nuclear signal for ER beta. The presence of ER beta-IR in the nuclei of GT1-7 cells and GnRH neurones is consistent with recent reports of ER beta mRNA in these cells. Oestrogen treatment reduced the percentage of GnRH neurones with detectable ER beta-IR. The range of signal intensity for ER beta and the incidence of the ER beta signal in GnRH neurones were comparable following double-label immunohistochemistry involving either bright field or fluorescent techniques. These findings raise the possibility that ER beta receptors mediate direct effects of oestrogen on GnRH neurones.

Reciprocal synaptic relationships between angiotensin II-containing neurons and enkephalinergic neurons in the rat area postrema

A preembedding double immunostaining technique was used to study synaptic relationships between angiotensin-II-like immunoreactive and enkephalin-like immunoreactive neurons in the rat area postrema. The angiotensin-II-like immunoreactive neurons were detected by silver-gold intensification of the DAB reaction results while the enkephalin-like immunoreactive neurons were detected by simple ABC-DAB reaction. The synaptic relationships were reciprocal between the two neurons. Most of the synapses found between these two neurons were the presynaptic enkephalin-like immunoreactive axon terminals that made synapses on the angiotensin-II-like immunoreactive perikarya and dendrites. Both the axo-somatic and axo-dendritic synapses were symmetrical. However, although angiotensin-II-like immunoreactive axon terminals also made synapses on enkephalin-like perikarya and dendrites, the axo-somatic synapses were symmetrical, while the axo-dendritic synapses were asymmetrical. The present results confirm the presence of angiotensin-II-like immunoreactive neurons in the area postrema and suggest that these angiotensinergic neurons in the area postrema may play a role in the regulation of blood pressure via coordinated synaptic interactions with enkephalinergic neurons.

Axon terminals containing CGRP-immunoreactivity form synapses with CRF- and Met-enkephalin-immunopositive neurons in the laterodorsal division of the bed nucleus of the stria terminalis in the rat

The lateral division of the bed nucleus of the stria terminalis (BSTL) is an important forebrain structure that relays information between limbic structures and the hypothalamus. The BSTL displays a very dense calcitonin gene-related peptide-immunoreactive (-ir) fiber terminal network, and contains a substantial number of the corticotropin releasing factor (CRF)-ir neurons. Several Met-enkephalin-ir perikarya have also been observed in the BSTL. The distributions of CRF- and Met-enkephalin-ir neurons and that of the calcitonin gene-related peptide (CGRP)-ir axon terminals overlap within the BSTL, suggesting synaptic connections between CRF- and Met-enkephalin-ir neurons and axon terminals immunoreactive for CGRP. Double staining immunohistochemistry revealed that CGRP-ir axon terminals were within close proximity to dendrites or perikarya of corticotropin releasing factor and Met-enkephalin-ir neurons. When viewed at the electron microscopic level, axodendritic or axosomatic synapses between CGRP-ir fiber terminals and neurons immunoreactive for CRF and Met-enkephalin were detected. Most of the CRF-ir neurons project to brainstem centers, which modulate the physiological changes accompanying stress, whereas the Met-enkephalin-ir perikarya are most likely interneurons that often colocalize with GABA. The parabrachial nucleus, a vital autonomic center, is the primary source of CGRP-ir fiber terminals to the BSTL. The synaptic contacts between the CGRP axon terminals and CRF- and Met-enkephalin-ir neurons underlie the importance of connections between autonomic brainstem centers and BSTL, which can be fundamental in the modulatory control of endocrine, physiological and behavioral responses during stress.

Hypothalamic dorsomedial nucleus neurons innervate thyrotropin-releasing hormone-synthesizing neurons in the paraventricular nucleus

To determine whether the hypothalamic dorsomedial nucleus (DMN) may serve as a relay center for the central actions of leptin on thyrotropin-releasing hormone (TRH)-synthesizing neurons in the paraventricular nucleus (PVN), axonal projections from the DMN to TRH-containing neurons in the PVN were studied using the anterogradely transported marker substance, Phaseolus vulgaris-leucoagglutinin (PHA-L). Stereotaxic injections of PHA-L were targeted to the mid-dorsal and mid-ventral portions of the DMN. After 10-14-day survival, the brains were prepared for immunohistochemistry and immunostained with an antibody directed against PHA-L. Focal injections confined to the DMN were identified in 14 animals and gave rise to a fiber bundle that entered the PVN at the caudal pole of the nucleus, densely innervating all parvocellular subdivisions of the PVN. In double-labeled preparations using antisera to PHA-L and preproTRH 178-199, the latter as a marker for TRH-containing neurons in the PVN, proTRH-IR neurons were observed to be enmeshed in a network of PHA-L-containing fibers. When the injection site covered the entire DMN or the mid-dorsal part of the DMN, PHA-L-containing axon varicosities were juxtaposed to approximately 97 and 90% of proTRH neurons, respectively, in all parvocellular subdivisions of the PVN, and by ultrastructural analysis were shown to be synaptic. In contrast, when the injection site was centered primarily in the mid-ventral part of the DMN, only approximately 52% of proTRH-synthesizing neurons appeared to be innervated by PHA-L-containing axons. These data demonstrate that a major projection pathway exists from the DMN, specifically to TRH-producing neurons in the PVN, and suggest that the DMN is anatomically situated to exert a regulatory effect on TRH-synthesizing neurons in the PVN.

Brainstem catecholaminergic neurons activated by hypoxemia express GR and are coordinately activated with fetal sheep hypothalamic paraventricular CRH neurons

In late gestation, challenges to fetal homeostasis are accompanied by increases in adrenocorticotropin (ACTH) concentrations in fetal peripheral plasma and Fos (c-fos protein) activation in corticotropin-releasing hormone (CRH) neurons of the fetal hypothalamic paraventricular nucleus (PVN). In adults, ventrolateral brainstem catecholaminergic (CA) neurons (A1/C1, A2/C2) project to the parvocellular neurons of the PVN, possess glucocorticoid receptors (GR) and are Fos activated in parallel with CRH neurons of the PVN during hypoxia. Such observations suggest a role for the aforementioned medullary neurons in the function of the hypothalamo-pituitary-adrenal axis. The present study utilized late gestation fetal sheep, stereotaxic methodology and retrograde axon tracing and immunocytochemical techniques to investigate the relationship between activation of fetal brainstem CA neurons and activation of fetal PVN CRH immunopositive neurons in response to hypoxemia. Results indicated that: (1) the largest brainstem CA projection to PVN CRH neurons is from A1/C1 neurons, (2) brainstem neurons exhibit GR immunostaining and (3) brainstem CA neurons show a strong correlation (A1/C1 - r(2)=0.894, P<0.005; A2/C2 - r(2)=0. 848; P<0.002) of Fos activation with Fos activation in PVN CRH cells. We conclude that in late gestation the brainstem A1/C1 and A2/C2 areas are in position to influence the function of the hypothalamo-pituitary-adrenal axis during hypoxemic challenges to homeostasis in a fashion similar to that which has been demonstrated in the adult rat.

Noradrenergic regulation of parvocellular neurons in the rat hypothalamic paraventricular nucleus

Noradrenergic projections to the hypothalamic paraventricular nucleus have been implicated in the secretory regulation of several anterior pituitary hormones, including adrenocorticotropin, thyroid-stimulating hormone, growth hormone and prolactin. In an attempt to elucidate the effects of norepinephrine on the central control of pituitary hormone secretion, we looked at the actions of norepinephrine on the electrical properties of putative parvocellular neurons of the paraventricular nucleus using whole-cell current-clamp recordings in hypothalamic slices. About half (51%) of the putative parvocellular neurons recorded responded to norepinephrine with either a synaptic excitation or a direct inhibition. Norepinephrine (30-300microM) caused a marked increase in the frequency of excitatory postsynaptic potentials in about 36% of the parvocellular neurons recorded. The increase in excitatory postsynaptic potentials was blocked by prazosin (10microM), but not by propranolol (10microM) or timolol (20microM), indicating that it was mediated by alpha(1)-adrenoreceptor activation. It was also blocked by ionotropic glutamate receptor antagonists, suggesting that the excitatory postsynaptic potentials were caused by glutamate release. The increase in excitatory postsynaptic potentials was completely abolished by tetrodotoxin, indicating the spike dependence of the norepinephrine-induced glutamate release. In a separate group comprising 14% of the parvocellular neurons recorded, norepinephrine elicited a hyperpolarization (6.2+/-0.69mV) that was blocked by the beta-adrenoreceptor antagonists, propranolol (10microM) and timolol (20microM), but not by the alpha(1)-receptor antagonist, prazosin (10microM). This response was not blocked by tetrodotoxin (1.5-3microM), suggesting that it was caused by a direct postsynaptic action of norepinephrine. The topographic distribution within the paraventricular nucleus of the norepinephrine-responsive and non-responsive parvocellular neurons was mapped based on intracellular biocytin labeling and neurophysin immunohistochemistry. These data indicate that one parvocellular subpopulation, consisting of about 36% of the paraventricular parvocellular neurons, receives an excitatory input from norepinephrine-sensitive local glutamatergic interneurons, while a second, separate subpopulation, representing about 14% of the parvocellular neurons in the paraventricular nucleus, responds directly to norepinephrine with a beta-adrenoreceptor-mediated inhibition. This suggests that excitatory inputs to parvocellular neurons of the paraventricular nucleus are mediated mainly by an intrahypothalamic glutamatergic relay, and that only a relatively small subset of paraventricular parvocellular neurons receives direct noradrenergic inputs, which are primarily inhibitory.

DARPP-32 and CREB are present in type 2 iodothyronine deiodinase-producing tanycytes: implications for the regulation of type 2 deiodinase activity

Type 2 iodothyronine deiodinase, an enzyme involved in the conversion of thyroxin to the biologically active 3,5, 3'-triiodothyronine, is highly concentrated in a group of specialized ependymal cells, tanycytes, lining the wall and floor of the third ventricle. As this distribution is highly reminiscent of the distribution of cells containing the phosphatase inhibitor, DARPP-32, we raised the possibility that these two proteins may coexist in tanycytes and that DARPP-32 may modulate type 2 deiodinase activity by regulating the phosphorylation state of the cAMP regulatory factor, CREB. To address this question, double-labeling histochemical studies were performed for type 2 deiodinase mRNA and DARPP-32 immunoreactivity (IR), or DARPP-32- and CREB-IR in the same tissue sections. Type 2 deiodinase mRNA was found in the cell bodies of all DARPP-32-immunolabeled tanycytes. Both type 2 deiodinase mRNA and DARPP-32-IR also extended into tanycyte processes that ramified in the arcuate nucleus and median eminence, in close association with blood vessels and portal capillaries. In contrast, type 2 deiodinase mRNA was not present in the same cells that contained DARPP-32-IR in the pituitary gland. All tanycytes containing DARPP-32-IR also contained CREB-IR in their nucleus. Since type 2 deiodinase activity can be induced by substances that increase cAMP, we hypothesize that DARPP-32 may regulate the activity of type 2 deiodinase by prolonging the activation of CREB. Selectivity for the colocalization of these factors to tanycytes but not the pituitary gland, may explain the heterogeneous response of type 2 deiodinase activity in these two loci in response to specific stimuli such as fasting.

alpha-Melanocyte-stimulating hormone is contained in nerve terminals innervating thyrotropin-releasing hormone-synthesizing neurons in the hypothalamic paraventricular nucleus and prevents fasting-induced suppression of prothyrotropin-releasing hormone gene expression

The hypothalamic arcuate nucleus has an essential role in mediating the homeostatic responses of the thyroid axis to fasting by altering the sensitivity of prothyrotropin-releasing hormone (pro-TRH) gene expression in the paraventricular nucleus (PVN) to feedback regulation by thyroid hormone. Because agouti-related protein (AGRP), a leptin-regulated, arcuate nucleus-derived peptide with alpha-MSH antagonist activity, is contained in axon terminals that terminate on TRH neurons in the PVN, we raised the possibility that alpha-MSH may also participate in the mechanism by which leptin influences pro-TRH gene expression. By double-labeling immunocytochemistry, alpha-MSH-IR axon varicosities were juxtaposed to approximately 70% of pro-TRH neurons in the anterior and periventricular parvocellular subdivisions of the PVN and to 34% of pro-TRH neurons in the medial parvocellular subdivision, establishing synaptic contacts both on the cell soma and dendrites. All pro-TRH neurons receiving contacts by alpha-MSH-containing fibers also were innervated by axons containing AGRP. The intracerebroventricular infusion of 300 ng of alpha-MSH every 6 hr for 3 d prevented fasting-induced suppression of pro-TRH in the PVN but had no effect on AGRP mRNA in the arcuate nucleus. alpha-MSH also increased circulating levels of free thyroxine (T4) 2.5-fold over the levels in fasted controls, but free T4 did not reach the levels in fed controls. These data suggest that alpha-MSH has an important role in the activation of pro-TRH gene expression in hypophysiotropic neurons via either a mono- and/or multisynaptic pathway to the PVN, but factors in addition to alpha-MSH also contribute to the mechanism by which leptin administration restores thyroid hormone levels to normal in fasted animals.

Estrogen receptor immunoreactivity is present in the majority of central histaminergic neurons: evidence for a new neuroendocrine pathway associated with luteinizing hormone-releasing hormone-synthesizing neurons in rats and humans

The central regulation of the preovulatory LH surge requires a complex sequence of interactions between neuronal systems that impinge on LH-releasing hormone (LHRH)-synthesizing neurons. The reported absence of estrogen receptors (ERs) in LHRH neurons indicates that estrogen-receptive neurons that are afferent to LHRH neurons are involved in mediating the effects of this steroid. We now present evidence indicating that central histaminergic neurons, exclusively located in the tuberomammillary complex of the caudal diencephalon, serve as an important relay in this system. Evaluation of this system revealed that 76% of histamine-synthesising neurons display ERalpha-immunoreactivity in their nucleus; furthermore histaminergic axons exhibit axo-dendritic and axo-somatic appositions onto LHRH neurons in both the rodent and the human brain. Our in vivo studies show that the intracerebroventricular administration of the histamine-1 (H1) receptor antagonist, mepyramine, but not the H2 receptor antagonist, ranitidine, can block the LH surge in ovariectomized estrogen-treated rats. These data are consistent with the hypothesis that the positive feedback effect of estrogen in the induction of the LH surge involves estrogen-receptive histamine-containing neurons in the tuberomammillary nucleus that relay the steroid signal to LHRH neurons via H1 receptors.

Expression of alpha1D adrenergic receptor messenger RNA in oxytocin- and corticotropin-releasing hormone-synthesizing neurons in the rat paraventricular nucleus

The paraventricular nucleus of the hypothalamus contains a number of intermingled populations of neuroendocrine cell groups involved in the hormonal stress response, including cells synthesizing corticotropin-releasing hormone and oxytocin. Ascending noradrenergic afferents to the paraventricular nucleus, acting through alpha1 adrenergic receptors, are thought to play a role in stress-induced activation of the hypothalamic-pituitary-adrenal axis. We have previously demonstrated that, of the three known alpha1 adrenergic receptor subtypes, messenger RNA for the alpha1D subtype is the most prominently expressed in the paraventricular nucleus. Thus, regulation of the expression of this receptor may be important in modulation of the stress response. It is currently unknown, however, which populations of stress-related neuroendocrine cells in the paraventricular nucleus express alpha1 receptors, or whether the excitatory influence of norepinephrine in stress is exerted directly on neurons expressing oxytocin or corticotropin-releasing hormone. Thus, in the present study, we used dual in situ hybridization, combining a digoxigenin-labeled riboprobe encoding the rat alpha1D adrenergic receptor with radiolabeled riboprobes for oxytocin or corticotropin-releasing hormone, to determine the degree to which these neurons in the paraventricular nucleus express alpha1D adrenergic receptors. In sections through the rostral and mid-level paraventricular nucleus, nearly all (>95%) oxytocin neurons also expressed alpha1D messenger RNA. In contrast, the populations of corticotropin-releasing hormone- and alpha1D-expressing cells overlapped only partially, with most alpha1D expression situated more laterally. A subset (37%) of the neurons expressing corticotropin-releasing hormone also expressed alpha1D messenger RNA, and these were found almost entirely within the region of overlap in the lateral aspect of the medial parvocellular region. These observations support a direct role for alpha1 receptors in regulation of oxytocin secretion. Expression of alpha1D messenger RNA in distinct subsets of cells synthesizing corticotropin-releasing hormone may also help to clarify contradictory and inconsistent observations in the literature regarding the role of norepinephrine in the stress response, and may account for a presumed stressor-specific role for norepinephrine in activation of the hypothalamic-pituitary-adrenal axis.

Immunohistochemical demonstration of serotonin-containing axons in the hypothalamus of the white-footed mouse, Peromyscus leucopus

The wild white-footed mouse, Peromyscus leucopus, is commonly used for photoperiod studies utilizing physiological, behavioral, and other biological measures indicative of hypothalamic functions. Indoleamines, like melatonin and serotonin, are implicated in regulating these hypothalamic functions. Although neurochemical analyses of hypothalamic serotonin and its receptors have been reported for this species, the relevant neuroanatomy of the serotonin system within mouse hypothalamus has not been studied. A sensitive immunohistochemical method was used to detect serotonin within axons of coronal sections of formaldehyde fixed forebrain from P. leucopus. Large, medium and small diameter serotonin axons were evaluated in most regions, or nuclei, of the hypothalamus rostral to the mammillary region. A fourth type of serotonin axon was observed to have morphology characteristic of terminal arbors. The density of serotonin axons ranged from no staining to very high density similar to other species for which reports exist, i.e., rat, cat, and monkey. The ventromedial hypothalamic nucleus had distinctively lesser density of serotonin axons in this mouse than other species. Evidence of terminal arborization in hypothalamic nuclei and regions was evident. Neuroendocrine, autonomic, and behavioral functions of the hypothalamus are suggested to be regulated by input from serotonin terminals in this wild species of mouse, in correlation with receptor localization as reported by others.

Neuron-glia interaction in the suprachiasmatic nucleus: a double labeling light and electron microscopic immunocytochemical study in the rat

The morphological interactions between astroglial and neuronal elements were elucidated in the rat suprachiasmatic nucleus (SCN) by light and electron microscopic immunocytochemistry using antibodies against glial fibrillary acidic protein (GFAP), vasoactive intestinal peptide (VIP) and arginine-vasopressin (AVP). Throughout the SCN, particularly in its ventral portion, GFAP-like-immunoreactive (GFAP-LI) astroglial elements were found. These astrocytes displaying GFAP-like immunoreactivity occasionally contained fairly well-developed organelles. Some of these astrocytes were found as satellite cells in close contact with non-immunoreactive neuronal perikarya and processes. Around the neurons, GFAP-LI astroglial processes were also observed to cover some portions of presynaptic and postsynaptic elements. In addition, these astroglial elements were seen between two neuronal somata and pericytes of blood capillaries as glial endfeet. By double labeling immunoelectron microscopy using antibodies against GFAP/VIP and GFAP/AVP, some portions of VIP-like-immunoreactive or AVP-like-immunoreactive neuronal somata and processes were found to be engulfed by GFAP-LI astroglial processes. The possible functional roles of the morphological interactions between astroglial and neuronal elements are discussed.

Synaptic connections between substance P-containing axons and estrogen receptor-synthesizing neurons in the medial preoptic area of the rat brain

Dual-label immunocytochemical procedures were employed to provide ultrastructural evidence for the presence of substance P (SP) in afferents to estrogen-receptive neurons in the medial preoptic area (MPO) of the female rat. SP-immunoreactive axon terminals were observed to innervate the periventricular (PvPO) and medial (MPN) preoptic nuclei of the MPO densely, and to form synaptic connections at these sites with neurons which contain estrogen receptors in their nucleus. These results indicate that estrogen-receptive preoptic neurons may be regulated by SP-containing neuronal pathways via synaptic mechanisms.

Axon terminals containing PACAP- and VIP-immunoreactivity form synapses with CRF-immunoreactive neurons in the dorsolateral division of the bed nucleus of the stria terminalis in the rat

The bed nucleus of the stria terminalis (BST) is a highly heterogeneous forebrain structure, within which the median and lateral BST play distinct functional roles. The medial BST (BSTM) is thought to be related to sexual behavior, while the lateral BST (BSTL) may have a stress-related function. In the human brain, the BST shows marked sexual dimorphism in the distribution of vasoactive intestinal polypeptide (VIP) immunoreactive fibers and also contains a very high concentration of pituitary adenylate cyclase activating polypeptide (PACAP) immunoreactivity (ir). Using immunohistochemistry (IHC) to examine the rat brain, the present study found that both VIP and PACAP containing afferent fibers are abundant in the BSTLd (dorsolateral division of BST), but not in the BSTM. IHC did not reveal any apparent difference between the sexes in the size of distribution of either immunoreactivity. Double staining IHC showed that axonal terminals of both VIP and PACAP neurons were in close proximity to dendrites or perikarya of corticotropin releasing factor (CRF) neurons. At the electron microscopic level IHC revealed the presence of axodendritic or axosomatic synapses between VIP-ir and PACAP-ir axon terminals and CRF-ir neurons. Although the origin of PACAP-ir fibers in the BSTLd remains to be determined, these morphological findings suggest that PACAP and VIP regulate the activity of CRF neurons in the BSTLd as neurotransmitters or neuromodulators.

I. Serotonin (5-HT) within dopamine reward circuits signals open-field behavior. II. Basis for 5-HT--DA interaction in cocaine dysfunctional behavior

Light microscopic immunocytochemical studies, using a sensitive silver intensification procedure, show that dopamine (DA) and serotonin (5-HT) axons terminate on neurons in the nucleus accumbens (NAcc) (A10) terminals and also in dorsal striatum (DSTr) (A9) terminals. The data demonstrate a prominent endogenous anatomic interaction at these distal presynaptic sites between the neurotransmitters 5-HT and DA; the pattern of the 5-HT-DA interaction differs between A10 and A9 terminals. Moreover, in distinction to the variance shown anatomically between 5-HT--DA interactions at distal A9 and A10 sites, the 5-HT--DA interactions at the level of DA somatodendrites, the proximal site, are similar, i.e. 5-HT terminals in the midbrain tegmentum are profuse and have a massive overlap with DA neurons in both ventral tegmental area (VTA) and substantia nigra pars compacta (SNpc). We suggest with reference to the DA neurons of A10 and A9 pathways, inclusive of somatodendrites (sites of proximal presynaptic interactions in the midbrain) and axons (sites of distal presynaptic interactions), that 5-HT--DA interactions in A10 terminals are more likely to exceed those in the DStr arrangement. Furthermore, our neuroanatomic data show that axonally released DA at A10 terminals may originate from proximal 5-HT somatodendrites, i.e. dorsal raphe (DR) or the proximal DA somatodendrites, VTA. In vivo microvoltammetric studies were done with highly sensitive temporal and spatial resolution; the studies demonstrate basal (endogenous) real time 5-HT release at distal A10 and distal A9 terminal fields and real time 5-HT release at proximal A10 VTA somatodendrites. In vivo microvoltammetric studies were performed concurrently and on line with studies of DA release, also at distal A10 and distal A9 terminal fields and at proximal A10 somatodendrites. Serotonin release was detected in a separate voltammetric peak from the DA voltammetric peak. The electrochemical signal for 5-HT release was detected within 10-12 s and that for DA release within 12-15 s, after each biogenic amine diffused through the synaptic environment onto the microelectrode surface. The electrochemical signal for 5-HT and a separate electrochemical signal for DA are detected on the same voltammogram within 22-27 s; each electrochemical signal represents current changes in picoamperes, within seconds of detection time. The amplitude of each electrochemical signal reflects the changes in diffusion of each biogenic amine to the microelectrode surface. Each neurotransmitter has a distinct potential at which oxidation occurs; this results in a recording which has a distinct peak for a specific neurotransmitter. The concentration of each neurotransmitter within the synaptic environment is directly related to the electrochemical signal detected via the Cottrell equation. Voltammograms were recorded every 5 min. At the time that basal 5-HT release and basal DA release were recorded within same animal control, open-field behavioral studies were performed, also concurrently, by infrared photocell beams. The frequency of each behavioral parameter was monitored every 100 ms; the number of behavioral events, were summated every 5 min during the time course of study. Thus, the detection of neurotransmitters occurs in real time, while simultaneously monitoring the animal's behavior by infrared photocell beams. The results from the in vivo microvoltammetric and behavioral data from this study show that basal 5-HT release at distal A10 and A9 terminals dramatically increased with DA release. Moreover, each increase in basal 5-HT release, at both A10 and at A9 terminal fields occurred consistently and at the same time as each increase in open-field locomotion and stereotypy occurred naturally during the animal's exploration in a novel chamber. Thus, the terminology 'synchronous and simultaneous' describes aptly the correlation between 5-HT release at distal A10 and A9 terminal fields and open-field locomo

Synaptic innervation of enkephalinergic neurons by axon terminals immunoreactive to dopamine-beta-hydroxylase in the rat area postrema

A preembedding double immunostaining technique was used to study synaptic relations between enkephalin-like immunoreactive and dopamine-beta-hydroxylase-like immunoreactive neurons in the rat area postrema. Enkephalin-like immunoreactive neuronal perikarya and dendrites were found to receive synapses from dopamine-beta-hydroxylase-like immunoreactive axon terminals. Synapses were also found between the same dopamine-beta-hydroxylase-like immunoreactive neurons. Compared with our previous study, the present results provide morphological evidence that dopaminergic and noradrenergic neurons have different synaptic relations with enkephalinergic neurons, suggesting that physiological functions, especially those related to enkephalinergic neurons, may be different from each other in the area postrema.

The use of peroxidase substrate Vector VIP in electron microscopic single and double antigen localization

Very few chromogens used in immunoperoxidase reactions can be combined to simultaneously localize two neural antigens with different labels at both light (LM) and electron (EM) microscopic levels. The objective of this study was to investigate the EM properties of a novel purple chromogen introduced by LM immunostaining by Vector Laboratories under the commercial name Vector VIP. The Vector VIP (VIP) was employed to demonstrate anterogradely transported Phaseolus vulgaris-leucoagglutinin (PHA-L), retrogradely transported cholera toxin subunit B (CTB) and acetylcholine synthesizing enzyme choline acetyltransferase (ChAT) in single and double antigen immunostaining in combination with the chromogen 3,3'diaminobenzidine (DAB). The VIP reaction product proved resistant to loss during post-fixation in OSO4 and dehydration in acetone. In EM preparation, the VIP reaction product was granular in appearance and easily distinguishable from the diffuse reaction product of DAB. Compared to the chromogen benzidine dihydrochloride (BDHC), the VIP reaction procedure is much simpler, more sensitive and consistently generates the same texture of the electron-dense precipitate. This study demonstrates the usefulness of VIP as a chromogen for correlative LM and EM immunoperoxidase staining. The VIP can be used either in single or double immunostaining in combination with DAB. In addition, we have examined the EM properties of another commercial chromogen, peroxidase substrate Vector SG (SG). The blue-gray reaction product of this chromogen is strongly osmiophilic and the electron-dense precipitate appears amorphous.

Immunoelectron microscopy of beta-endorphinergic synaptic innervation of nitric oxide synthase immunoreactive neurons in the dorsal raphe nucleus

On the basis of the comparing of the distribution of beta-endorphin-like immunoreactive neuronal fibres and nitric oxide synthase-like immunoreactive neurons in the dorsal raphe nucleus, the synapses between the two immunocytochemically identified neurons were studied with a modified DAB-silver-gold intensification double immunostaining technique at the electron microscopic level. Although both of them can be found in the mediodorsal and medioventral parts of the dorsal raphe nucleus, the synapses between them could only be found in the mediodorsal part. The majority of the beta-endorphin-like immunoreactive neuronal fibers contained many dense-cored vesicles. The synapses made by beta-endorphin-like immunoreactive neuronal axon terminals on nitric oxide synthase-like immunoreactive neurons were both symmetrical and asymmetrical with the former predominant, especially in the axo-dendritic ones. beta-Endorphin-like immunoreactive perikarya could only be found in the ventrobasal hypothalamus. These findings suggest the possibility that the beta-endorphin- producing neurons in the ventrobasal hypothalamus could influence nitric oxide synthase-containing neurons in the dorsal raphe nucleus by synaptic relations.

Effect of hypothyroidism on vasoactive intestinal polypeptide-immunoreactive neurons in forebrain-neurohypophysial nuclei of the rat brain

We have recently reported that hypothyroidism increases immunoreactive (IR)-vasoactive intestinal polypeptide (VIP) and VIP mRNA content in both parvocellular and magnocellular neurons of the rat, hypothalamic paraventricular nucleus (PVN). As VIP can stimulate vasopressin (AVP) secretion, we conducted an anatomical investigation to determine whether VIP-containing neurons in other regions of the brain that are involved with homeostatic mechanisms of water and salt conservation are also affected by hypothyroidism. The distribution and intensity of VIP immunostaining in neurons and fibers of the magnocellular-neurohypophysial system, including the hypothalamic PVN, supraoptic nucleus (SON) and accessory magnocellular cell groups, circumventricular subfornical organ (SFO), preoptic and anterior hypothalamus, midline thalamus, subthalamic zona incerta and posterior septal nuclei were studied using a highly sensitive immunocytochemical technique and unbiased neuronal counting methods, based on the optical dissector principle. Hypothyroidism increased the intensity of VIP immunostaining and/or the number/section, percentage and numerical density of IR-VIP neurons in the PVN, SON, nucleus circularis, periventricular preoptic nucleus of the hypothalamus and SFO. In addition, IR-VIP perikarya and/or fibers in the hypothalamic medial preoptic area and anterior periventricular nucleus, nucleus reuniens of the thalamus and dorsal fornix-triangular septal nucleus complex were also apparent in the hypothyroid animals while no immunostaining was seen in these areas in control animals. No quantitative and/or qualitative modifications in IR-VIP neurons and fibers were noted in the anterior hypothalamic area, suprachiasmatic nucleus, thalamic paraventricular nucles an subthalamic zona incerta between hypothyroid and control animals. These findings suggest an inverse relationship between thyroid hormone and VIP content and/or distribution of IR-VIP neurons in specific forebrain regions involved in the control of AVP release, extracellular fluid volume, thirst, blood pressure and anterior pituitary secretion. This raises the possibility that changes in fluid homeostasis and cardiovascular function occurring in hypothyroidism may be mediated, at least in part, by VIP-producing neurons in diverse regions of the brain.

Reciprocal synaptic relations between enkephalinergic and GABAergic neurons in the area postrema of the rat

A preembedding, double immunostaining technique was used to study synaptic relations between enkephalinergic and GABAergic neurons in the area postrema of the rat. As a main result, the enkephalinergic dendrites received many synapses from GABAergic axon terminals, and most of the synapses were symmetrical. Enkephalinergic neuronal perikarya received a few synapses from GABAergic axon terminals, and a few enkephalinergic axon terminals were found presynaptic to GABAergic neurons. Synapses between enkephalinergic profiles were frequent, but no axo-axonic synapses were seen. These findings suggest that GABAergic innervation of enkephalinergic neurons is the main relation between the two kinds of neurons in the area postrema. The synapses between the enkephalinergic axon terminals and GABAergic neurons might be explained as being part of the local servo system of the area postrema.

The reciprocal synaptic relations between enkephalinergic neurons and catecholaminergic neurons in the area postrema

A preembedding double immunostaining technique using antibodies against methionine-enkephalin and tyrosine hydroxylase was used to study synaptic relations between enkephalinergic and catecholaminergic neurons in the area postrema of the rat at the electron microscopic level. The large nuclei-containing cell bodies of the catecholaminergic neurons displayed well-developed Golgi apparatus. The catecholaminergic somata and dendrites received synapses from enkephalinergic axon terminals, and most of the synapses were symmetrical. Occasionally, the catecholaminergic axon terminals were also found to be presynaptic to the enkephalinergic dendrites. Because the enkephalinergic neurons have been reported to be involved in cardiovascular function and the catecholaminergic neurons involved in the vomiting behavior, the synapses observed in this study may provide morphological evidence of the relationship between the vomiting and cardiovascular functions that are triggered in the area postrema.

Light microscopic immunocytochemical evidence of converging serotonin and dopamine terminals in ventrolateral nucleus accumbens

The mesencephalic tegmentum contains monoaminergic neurons that project to the nucleus accumbens (NAcc). These monoaminergic neurons consist of the serotonergic (5-HT) neurons of the dorsal and median raphe and the dopaminergic (DA) neurons of the ventral tegmental area (VTA). Recent neurochemical reports describe cocaine-induced alterations in dopamine and serotonin release in NAcc that has coincidental occurrence both spatially and temporally, as shown by in vivo voltammetry. There is a functional role for 5-HT-DA interactions within the NAcc in the underlying mechanism of action of cocaine as well as for 5-HT in A10 DA neurons in the basal or endogenous state whether or not cocaine-relevant reward circuits are involved. Our objective was to study the neuroanatomic localization of tyrosine hydroxylase-containing (TH) and 5-HT-containing axons in the ventrolateral region of the rat NAcc, where codetection of monoamines had been assessed. The significance of this vINAcc is its reciprocal connectivity with VTA, which contains the somatodendritic portions of the mesoacumbens DA neurons. The results showed that, in the vINAcc, the core contained a dense terminal field of TH axons that had an extensive overlap with 5-HT axons in the periphery within the core. Because the in vivo electrochemical codetection of DA and 5-HT assessed in the ventral-most aspect of this overlap zone can be correlated with terminal release, a functional interaction of 5-HT and DA at postsynaptic sites in vINAcc is possible.

Basal and stress-induced release of noradrenaline in hypothalamus of spontaneously hypertensive rats at different ages

Basal and stress-induced noradrenaline (NA) release was studied by intracerebral microdialysis in the hypothalamic paraventricular nucleus of spontaneously hypertensive rats (SHR) at different ages (9 weeks, 6, 18 and 24 months). NA was measured in 20-min dialysate samples by high performance liquid chromatography with electrochemical detection. Microdialysis sampling was done at baseline, during a 20-min immobilization stress and for the next 100 min. Basal NA levels decreased with age, showing a highly significant correlation. Immobilization stress raised NA similarly in the four age groups (respectively 281%, 235%, 243%, 251% of baseline at 9 weeks, 6, 18, 24 months), indicating that the response to stress is maintained at all these ages and is not affected by the development of hypertension or by aging.

Adrenergic innervation of dopamine neurons in the hypothalamic arcuate nucleus of the rat

Tuberoinfundibular dopaminergic (TIDA) neurons, which represent the final common pathway in the inhibitory neuronal control of prolactin (PRL) secretion, are regulated by synaptic input from various transmitter systems. Because adrenergic receptors at hypothalamic sites were implicated in the central regulation of lactotrophs, we hypothesized that a synaptic communication might exist between adrenergic pathways ascending from the brain stem and the TIDA system. Polyclonal antisera directed towards phenylethanolamine N-methyltransferase (PNMT) and tyrosine hydroxylase (TH), biosynthetic enzymes of catecholamines, were used for the simultaneous immunocytochemical detection of adrenergic fibers and TIDA neurons, respectively, in Vibratome sections of the rat hypothalamus. By the light microscopic evaluation of double-immunostained sections, PNMT-immunoreactive (IR) axon varicosities were localized in juxtaposition to TH-IR cell bodies and dendrites in the arcuate nucleus (AN) which contains perikarya and dendrites of TIDA neurons. The ultrastructural analysis of contacts provided firm evidence for the occurrence of synaptic interactions between the adrenergic and TIDA neuronal systems. These morphological findings show that adrenergic neurons are involved in the afferent regulation of the TIDA system and indicate a putative pathway of central adrenergic effects upon PRL secretion.

Immunoelectron microscopy of enkephalinergic innervation of GABAergic neurons in the periaqueductal gray

The pre-embedding double immunoreaction method was used to study synaptic relations of enkephalinergic and GABAergic neuronal elements in the ventrolateral part of the periaqueductal gray of the Wistar albino rat. The enkephalin-like neuronal elements were immunoreacted by the silver-gold intensified peroxidase-antiperoxidase method and the GABA-like immunoreactive neurons were immunoreacted by the unintensified peroxidase-antiperoxidase method. GABA-like immunoreactive neuronal somata were post-synaptic to both the enkephalin-like immunoreactive and the non-immunoreactive axon terminals. Enkephalin-like immunoreactive axon terminals were found to make synapses with GABA-like immunoreactive and non-immunoreactive dendrites. The synapses between the two kinds of chemically characterized neurons appeared to be both asymmetrical and symmetrical. Possible functional activity related to pain modulation, and synaptic relations between the enkephalinergic and GABAergic neurons in the periaqueductal gray and the dorsal raphe nucleus, are discussed.

Galanin-containing axons synapse on tyrosine hydroxylase-immunoreactive neurons in the hypothalamic arcuate nucleus of the rat

Prolactin (PRL) secretion by the anterior pituitary gland is dependent upon the tonic inhibitory influence of the tuberoinfundibular dopaminergic (TIDA) neuronal system. TIDA neurons, in turn, are regulated by various afferent neuronal systems. To support the concept that the recently-discovered neuropeptide, galanin (GAL), is one of the neurotransmitter/neuromodulator substances which might synaptically regulate the function of the TIDA system, immunocytochemical double-labeling studies were carried out in the hypothalamic arcuate nucleus (AN) of the male rat. The analysis of light microscopic preparations revealed the overlapping of GALergic and dopaminergic (detected by tyrosine hydroxylase immunoreactivity) neuronal elements in both the dorsomedial and ventrolateral parts of the AN. TH-containing perikarya and dendrites were contacted by varicose GAL-IR axons in these regions. The electron microscopic studies of ultrathin sections demonstrated axosomatic and axodendritic synapses between GALergic axons and TH-IR neurons. These findings support the view that GAL may modulate PRL release, acting as a neurotransmitter/neuromodulator in synaptic afferents to the TIDA system.

The habituation of brainstem catecholaminergic groups to chronic daily restraint stress is stress specific like that of the hypothalamo-pituitary-adrenal axis

It has previously been shown that immobilization and ether stress induce activation of the hypothalamo-pituitary-adrenal (HPA) axis and that this activation occurs subsequent to activation of brain stem catecholaminergic neurones. In the present study we have investigated whether the brain stem catecholaminergic (CA) neurons show habituation to chronic daily intermittent exposure to the same restraint stress comparable to that of the HPA axis. The level of activity of the brainstem CA groups was estimated by measurement in tissue punches of content of 3,4-dihydroxyphenylacetic acid (DOPAC), a side metabolite of noradrenaline and adrenaline biosynthesis which has been shown to be a reliable index of the stress-induced activation of the CA groups. The level of activity of the HPA axis was determined by measurement of plasma corticosterone and adrenocorticotropic hormone (ACTH) levels. The animals were submitted to a 15 min restraint stress daily. They were sacrificed at the end of the stress session on day 3, 5 and 10. The ACTH response to the acute restraint stress whilst unchanged on day 3 was significantly decreased on day 5 (-54%) and day 10 (-70%) compared to the response in naive rats. The approximately twofold increase in DOPAC level induced by acute restraint stress in the so-called CA medullary group A1/C1 of naive rats was reduced in daily restraint rats on day 5 (-22%) and day 10 (-30%) but was unchanged on day 3. A small (-20%) decrease of the stress-induced DOPAC response in the A2/C2 CA group and locus coeruleus was also observed on day 10.(ABSTRACT TRUNCATED AT 250 WORDS)

Catecholamine-CRF synaptic interaction in a septal bed nucleus: afferents of neurons in the bed nucleus of the stria terminalis

Projections of catecholamine neurons to the bed nucleus of the stria terminalis (BST), especially its corticotropin releasing factor (CRF)-producing neurons, are implicated as being major contributors to the neurochemically mediated central regulation of the stress response. The purpose of the present study was to examine in the BST of the rat brain the morphological characteristics of interactions between two neuron populations of the brain, catecholaminergic and CRF neurons. A double-label immunocytochemical, light and electron microscopic technique allowed the demonstration of the synaptic interaction between dopamine (DA, i.e., tyrosine hydroxylase-containing) and norepinephrine (NE, i.e., dopamine-beta-hydroxylase-containing) axons and CRF neurons in the BST. DA terminals formed synapses with dendrites and soma of CRF neurons in the dorsolateral BST. NE terminals formed synapses with dendrites of CRF neurons in the ventrolateral BST. In conclusion, catecholamine afferents can directly affect the contribution of CRF neurons of the BST to an animals response to stress.

Ultrastructural changes in gonadotropin-releasing hormone neurons as a function of age and ovariectomy in rats

In this study we examined the effects of aging on various aspects of the ultrastructure of gonadotropin-releasing hormone neurons in female rats, including the density of synaptic input and the volume fraction of various subcellular organelles. In addition, we explored the possibility that removal of estrogen might provide a protective effect on the aging of the gonadotropin-releasing hormone neuron as exposure to gonadal steroids alters the time course of reproductive aging. Our experimental groups included four- and 18-20-month-old virgin female rats divided as follows: young intact, young short-term ovariectomized, old intact, old short-term ovariectomized and old long-term ovariectomized. Brain tissue was processed for immunocytochemical detection of gonadotropin-releasing hormone neurons and selected cells from the preoptic area were chosen for electron microscopic examination. The percentage of plasma membrane containing synaptic modification was quantified using a morphometrics program, and the volume fraction of lysosomes/lipofuscin, rough endoplasmic reticulum and Golgi apparatus were estimated using point count stereology. Whereas we had previously found a significant increase in the density of synaptic input to gonadotropin-releasing hormone neurons in aged virgin male rats, the density of synaptic input to gonadotropin-releasing hormone cells in the virgin female was not affected by age. The volume fraction of lysosomes/lipofuscin was increased in all age groups. Aging produced a dramatic decrease in the volume fraction of rough endoplasmic reticulum as well as a decrease in Golgi, suggesting a general decrease in biosynthetic activity of the cells.(ABSTRACT TRUNCATED AT 250 WORDS)

The dorsal raphe: an important nucleus in pain modulation

The dorsal raphe nucleus (DRN) is an important nucleus in pain modulation. It has abundant 5-HT neurons and many other neurotransmitter and/or neuromodulator containing neurons. Its vast fiber connections to other parts of the central nervous system provide a morphological basis for its pain modulating function. Its descending projections, via the nucleus raphe magnus or directly, modulate the responses caused by noxious stimulation of the spinal dorsal horn neurons. In ascending projections, it directly modulates the responses of pain sensitive neurons in the thalamus. It can also be involved in analgesia effects induced by the arcuate nucleus of the hypothalamus. Neurophysiologic and neuropharmacologic results suggest that 5-HT neurons and ENKergic neurons in the DRN are pain inhibitory, and GABA neurons are the opposite. The studies of the intrinsic synapses between ENKergic neurons, GABAergic neurons, and 5-HT neurons within the DRN throw light on their relations in pain modulation functions, and further explain their functions in pain mediation.

Catecholaminergic input to spinally projecting serotonin neurons in the rostral ventromedial medulla oblongata of the rat

The midline of the rostral ventral medulla (RVM) is the portion in which many serotonin (5-HT) neurons of the nucleus raphe magnus and the rostral nucleus raphe pallidus are located and where dense catecholaminergic (CA) fibers are distributed. In this study, we investigated the connection between spinally projecting 5-HT neurons and CA fibers in the rat RVM by light and electron microscopic immunocytochemistry. First, light microscopic immunocytochemistry using a triple labeling method revealed that the 5-HT-immunoreactive (IR) neuron containing retrograde tracer from the cervical cord was intimately surrounded by tyrosine hydroxylase (TH)-IR fibers. Second, silver-gold intensified TH-IR axon terminals were found to make synaptic contacts with 5-HT-IR neuronal perikarya and dendrites by double labeling immunoelectron microscopy. These morphological findings suggest that spinally projecting 5-HT neurons, presumed to be involved in pain modulation or sympathetic autonomic control, are directly regulated by CA neurons at the level of the RVM.

Light and electron microscopic immunocytochemical localization of PKC delta immunoreactivity in the rat central nervous system

Protein kinase C (PKC) is one of the major cellular signal transduction systems. Since at least nine different PKC isoenzymes have been described, the purpose of the present studies was to identify the regional, cellular, and subcellular distributions of PKC delta in the rat central nervous system (CNS) by light and electron microscopic immunocytochemistry. We have found that PKC delta immunoreactivity is present in all major subdivisions of the rat CNS. Within each of the subdivisions, PKC delta immunoreactivity is localized to perikarya that monitor sensory and motor functions. More specifically, PKC delta is found in the olfactory bulb, cerebral cortex, lateral septum, thalamus, vestibular and cochlear nuclei, inferior olive, nucleus of the solitary tract, cerebellum, and superficial layers of the dorsal horn in the spinal cord. In most cases, the distribution of this isoenzyme is distinct from that of the conventional isoforms. Within the CNS, PKC delta is localized primarily in neurons; however, neurons of the same type are not uniformly labeled. This is most evident in the cerebellum, where alternating columns of Purkinje cells are immunostained. While PKC delta is prominent in perikarya, occasional immunostaining is seen in dendrites, fibers or axons, and nerve terminal. Electron microscopic analysis of the posterolateral nucleus of the thalamus reveals that the cell nucleus, the rough endoplasmic reticulum, and the plasma membrane are all immunopositive. Since each of the PKC subspecies may have different substrate, lipid, and other co-factor requirements, the regional, cellular, and subcellular distribution of each of these isoforms should help to define their functional environments.

Aging prolongs the stress-induced release of noradrenaline in rat hypothalamus

A stress-induced increase in noradrenaline (NA) release was measured by intracerebral microdialysis in the hypothalamic paraventricular nucleus of freely moving Wistar-Kyoto rats at three different ages (6, 18 and 24 months). NA levels in 20-min dialysate samples were measured by high-performance liquid chromatography with electrochemical detection. Microdialysis sampling was done at the baseline during a 20-min immobilization stress and for the next 100 min. Basal NA release was not significantly different in the three age groups. The immobilization stress increased NA levels (247, 197 and 234% of the baseline for the 6-, 18- and 24-month animals, respectively) which was not significantly different in the three groups. In the two younger groups NA returned to the baseline in the first sample after the end of the stress (t = 40 min) whereas in the 24-month group it remained significantly higher for longer (until t = 60 min). Stress-induced release of hypothalamic NA thus appears to be prolonged in old rats.

High-affinity uptake of noradrenaline in postsynaptic neurones

1. Neurotransmitters released from nerve endings are inactivated by re-uptake into the presynaptic nerve terminals and possibly into neighbouring glial cells. While analysing the functional properties of alpha 1-adrenoceptors in the hypothalamus, we observed a high-affinity uptake process for noradrenaline in postsynaptic peptidergic neurones. 2. In primary hypothalamic cell cultures and in a hypothalamic neuronal cell line, [3H]-prazosin bound with high affinity and was displaced by unlabelled prazosin in concentrations of 10(-10) to 10(-7) M. However, at concentrations of unlabelled prazosin above 10(-7) M, there was a paradoxical increase in apparent [3H]-prazosin binding. 3. Methoxamine, an alpha 1-adrenoceptor ligand that is not subject to significant neuronal uptake, displaced [3H]-prazosin but did not cause the paradoxical increase in the apparent binding of [3H]-prazosin. Cooling the cells to 4 degrees C reduced the total amount of prazosin associated with the cells; under these conditions, methoxamine almost completely inhibited [3H]-prazosin binding to the cells. 4. In the presence of desipramine (DMI), unlabelled prazosin displaced [3H]-prazosin as before, but no paradoxical increase in apparent binding was seen above 10(-7) M. 5. The paradoxical increase of [3H]-prazosin binding was not observed in membrane preparations of hypothalamic neurones. These findings indicated that the paradoxical increase in apparent [3H]-prazosin binding was due to a cellular uptake process that becomes evident at high concentrations of the ligand. 6. DMI (10(-5) M) had no effect on the specific binding of [3H]-prazosin. The presence of alpha1-adrenoceptors was confirmed by binding of [125]-HEAT, but [3H]-idazoxan (an alpha2- ligand) did not bind to the cells.7. The uptake of prazosin obeyed the Michaelis-Menten model, with similar Km and Vmax values in both types of cultures.8. Noradrenaline was taken up with high affinity by both types of cultures. (+/-)-[3H]-noradrenaline uptake was reduced by DMI and by excluding sodium from the medium, indicating that this process has some of the properties of uptake 1. (+/-)-[3H]-noradrenaline uptake in the cell line was unaffected by testosterone.9. The measured uptake of (-)-noradrenaline in the cell line was considerably increased by blockade of catechol-omicron-methyl-transferase and monoamine oxidase, suggesting that (-)-noradrenaline is metabolized to lipophilic products that escape across the plasma membrane.10. Studies in rats, in which the noradrenaline isomer 6-hydroxydopamine was used, suggested that the post synaptic uptake process is operative in hypothalamic CRH and vasopressin neurones in vivo.11. The Km for (-)-noradrenaline was within the range for the high affinity uptake, process in noradrenergic neurones. Uptake takes place in concentrations at which noradrenaline activates alpha1-adrenoceptors.Removal of noradrenaline from the vicinity of the receptors may prevent desensitization,thus maintaining the responsiveness of postsynaptic neurones to the actions of the neurotransmitter.

Comparative single and double immunolabelling with antisera against catecholamine biosynthetic enzymes: criteria for the identification of dopaminergic, noradrenergic and adrenergic structures in selected rat brain areas

Immunodetection of catecholamine biosynthetic enzymes is frequently used for the visualization of central nervous catecholaminergic systems. Because of the method's limited specificity for the different catecholamines, interpretation of the results often presents difficulties. To determine criteria for the identification of dopaminergic, noradrenergic, and adrenergic afferents to the rat amygdaloid complex, comparative immunolabelling for tyrosine hydroxylase (TH), dopamine-beta-hydroxylase (DBH), and phenylethanolamine-N-methyl-transferase (PNMT) was carried out using single- and double-labelling for fluorescence, light- and electron microscopy. The observations were complemented by findings in brainstem and hypothalamic areas. The results indicated that TH-labelling detected preferentially dopaminergic afferents in the lateral central and intercalated amygdaloid nuclei. DBH-labelling detected noradrenergic axons in nuclei lacking PNMT-immunoreactive fibres, and PNMT was a marker for adrenergic axons in the entire complex. For nuclei with combined dense dopaminergic, noradrenergic and/or adrenergic innervation, morphological and immunolabelling characteristics were described which, to a certain extent, enabled identification of the different afferents in anti-TH or anti-DBH-preparations. Using a monoclonal TH-antiserum, noradrenergic and adrenergic axons displayed weaker immunoreactivity than dopaminergic ones, and possessed characteristic morphological features. TH-immunoreactivity in noradrenergic axons differed depending on their origin, and showed intra-axonal compartmentalization. The present study provides a basis for the use of the detection of biosynthetic enzymes in future investigations into the ultrastructure and connectivity of the catecholaminergic amygdala innervation.

Association of glucocorticoid receptor immunoreactivity with cell membrane and transport vesicles in hippocampal and hypothalamic neurons of the rat

The aim of the present study was to reveal at the ultrastructural level cytoplasmic loci that display glucocorticoid receptor (GR) immunoreactivity in pyramidal neurons of the CA1 sector of the hippocampus and in cells of the medial parvicellular subnucleus of the hypothalamic paraventricular nucleus (PVN). Adrenalectomized male rats were injected intraperitoneally with corticosterone (CS) (1 mg/100 g bw) and sacrificed within 4 hr. Vibratome sections of the perfusion-fixed forebrains were processed for immunocytochemical detection of type 2 GR by means of the BuGr, anti-rat liver GR monoclonal antibody and silver-gold-intensified diaminobenzidine chromogen. The corticosterone administration gradually shifted the GR immunoreactivity (IR) from the cytoplasm to the nucleus. Samples taken 20-40 min after the steroid treatment demonstrated pyramidal cells expressing GR IR in both the cytoplasmic and nuclear pools. Although the chromatin-associated appearance of GR in the nucleus was identifiable at the light microscopic level, the nature of immunoreactive intracytoplasmic loci was not. Ultrastructural analysis of the cytoplasm indicated that fine silver-gold grains marking GR-immunoreactive sites associated with the plasma membrane and coated and regular vesicles. Noted occasionally beneath the plasma membrane of the cell bodies and dendrites, the vesicles also appeared at deeper locations in dendritic processes and around the cell nuclei. These results suggest that glucocorticoid receptors participate in signal transduction at the level of the cell membrane, as well as at the level of the genome in the cell nucleus.

Stress update Adaptation of the hypothalamic-pituitary-adrenal axis to chronic stress

The hypothalamic-pituitary-adrenal (HPA) axis exhibits a circadian rhythm, activation by stress, and inhibition by corticosteroids. Activity in the HPA axis is very sensitive to inhibition by corticosteroids when they are administered exogenously. When stress-induced corticosteroid secretion occurs, however, normal activity in the HPA is not inhibited and may even be augmented. Experiments in rats have shown that stress also induces facilitation of subsequent activity in the HPA axis that appears to balance the inhibitory effects of corticosterone and thus maintains responsiveness to new, acute stresses in chronically stressed rats. Stress-induced facilitation of HPA axis activity may be mediated by a parallel stress-induced (CRH-dependent) increase in the capacity of brain noradrenergic cell groups to respond to acute stress. A continually responsive HPA axis, even under conditions of chronic stress, appears to be important for survival. Stress-induced increases in glucocorticoid secretion to levels sufficient to occupy glucocorticoid receptors enable appropriate thermoregulatory and cardiovascular responses to acute stress. There is, however, an overall metabolic cost to the animal of maintaining continued activity in the HPA axis during chronic stress.

The direct retinal projection to VIP neuronal elements in the rat SCN

The connection between optic nerve terminals and vasoactive intestinal peptide (VIP)-containing neurons in the rat suprachiasmatic nucleus (SCN) was investigated using double labeling immunocytochemistry. Cholera toxin B subunit (CT) was injected into the right eyeball, and coronal sections of the SCN were then processed for CT immunocytochemistry with silver-gold intensification and VIP immunocytochemistry consecutively with DAB staining alone. In the ventrolateral portion of the SCN, CT immunoreactive (CT-IR) optic nerve terminals were found to make synaptic contacts not only with VIP-like immunoreactive (VIP-LI) dendrites, but also with VIP-LI perikarya. CT-IR nerve endings were also found to make synaptic contacts with non-VIP immunoreactive neuronal dendrites.

Enkephalinergic innervation of GABAergic neurons in the dorsal raphe nucleus of the rat

The preembedding double immunoreaction method was used to study interrelations of enkephalinergic and GABAergic neuronal elements in the dorsal raphe nucleus of the Wistar albino rat. The enkephalin-like neuronal elements were immunoreacted by the peroxidase-antiperoxidase method and silver-gold intensified, which showed strongly and was specific. The GABA-like immunoreactive neurons were immunoreacted by the peroxidase-antiperoxidase method only. GABA-like neural somata were postsynaptic to both the enkephalin-like immunoreactive and the non-immunoreactive axon terminals. The enkephalin-like immunoreactive axon terminals were also found to synapse GABA-like immunoreactive dendrites. The GABA-like immunoreactive neuronal elements were also found to receive synapses from other non-immunoreactive as well as GABA-like immunoreactive axon terminals. Almost all of the synapses appeared to be asymmetrical. Possible functional activity of interactions among the enkephalinergic, GABAergic, and serotonergic neuronal elements in the dorsal raphe nucleus are discussed.

SSB, an antigen that selectively labels morphologically distinct synaptic boutons at the Drosophila larval neuromuscular junction

In this report we describe the expression of Small Synaptic Bouton (SSB), an antigen that is selectively expressed in a specific subset of neuromuscular junction terminals in the body wall of Drosophila larva. The expression of SSB was studied with a polyclonal antibody raised against the cAMP phosphodiesterase of the Drosophila learning mutant dunce (Nighorn et al., 1991, Neuron 6:455-467); however, immunoreactivity was not abolished by the dunce (dnc) alleles dncM14 and dncM11 or deficiencies of the dnc gene, indicating that the antigen labelled could not be the dnc gene product, but another antigen that we termed SSB. Immunoreactivity was localized in the body wall muscles to a specific subset of neuromuscular junction terminals that have been implicated in activity-dependent plasticity. This demonstrates that these morphologically distinct terminals can be immunocytochemically distinguished and that they probably represent innervation by a distinct neuronal population. Confocal and electron microscopic examination demonstrated that staining was restricted to the synaptic boutons themselves, not to neurites or motor axons. Ultrastructural analysis showed label close to synaptic vesicles in the presynaptic terminal and in the surrounding subsynaptic reticulum. Central nervous system (CNS) staining was restricted to a segmentally repeated pattern of cell bodies in the ventral ganglion and to a few small groups of cells in the brain lobes.

Beta-adrenergic receptor binding in human and rat hypothalamus

Quantitative autoradiographic analysis of beta-adrenergic binding sites was conducted in human postmortem hypothalamus using the radioligand 125I-pindolol. The focus was on the hypothalamic nuclei most clearly involved in corticotropin-releasing hormone (CRH) release, the PVN and SON. For comparison, the distribution of hypothalamic beta-adrenergic receptors was evaluated in the rat. A high level of beta-adrenergic receptor binding was found in the human paraventricular nucleus (PVN) and supraoptic nucleus (SON), but not in the rat. The majority of the beta-adrenergic receptors found in the human hypothalamus were of the beta 2-subtype. In contrast, in the rat hypothalamus, the majority of receptors were of the beta 1-subtype. These results show that the anatomical loci exist for direct beta-adrenergic influence on hypothalamic neuroendocrine function in the human and that the topography of beta-adrenergic receptors is markedly different in the rat and human hypothalamus.

Immunocytochemical characterization of afferents to estrogen receptor-containing neurons in the medial preoptic area of the rat

Double-label immunocytochemistry has been employed to elucidate the chemical nature of the afferent neuronal projections to the estrogen receptor-containing neurons located in the medial preoptic area of the rat brain. To ensure a clear separation of the immunolabelled afferent profiles from the estrogen receptors, the former were visualized first and the diaminobenzidine reaction product was silver-gold intensified. Using a monoclonal antibody raised against purified human estrogen receptors, we observed an intense nuclear immunoreactivity in Vibratome, semithin and ultrathin sections. Neuropeptide-Y, serotonin-, phenylethanolamine N-methyltransferase- and adrenocorticotrophin-immunoreactive axons and varicosities were observed in close apposition to the estrogen receptor-positive cells. At the ultrastructural level, neuropeptide-Y-immunoreactive boutons were seen in synaptic contact with cells showing estrogen receptor immunoreactivity in their nucleus. These results indicate that neurons located in the medial preoptic area, one of the principal sites for the control of female reproductive function, may be influenced by both estrogen and neurotransmitters/neuropeptides via, respectively, nuclear receptors and synaptic contacts.

Hemorrhage-Induced Activations of Adrenocorticotropin Release and Catecholamine Metabolism in the Ventrolateral Medulla are Differently Affected by Glucocorticoid Feedback

We have compared the effects of increasing doses of dexamethasone on the hemorrhage-induced stimulation of the corticotropic axis and the metabolism of the catecholamines of the A1 group in the ventrolateral medulla. Adrenocorticotropin was measured in sequential samples of plasma while the metabolism of the catecholamines was recorded by in vivo electrochemistry in urethane-anesthetized rats. Combined intracerebroventricular injection of specific adrenergic blockers (α(1) -antagonist, prazosin and ß-antagonist, propranolol) prevented the stimulation of the adrenocorticotropin release by hemorrhage. Pretreatment with dexamethasone (1 mg/kg sc) fully blocked the hemorrhage-induced adrenocorticotropin release but did not affect the concomitant stimulation of the catecholamine metabolism in A1 cells. The latter was partially decreased only with the highest dose (10 mg/kg sc). While a central catecholaminergic input appears to be necessary for the hemorrhage-induced stimulation of the corticotropic axis, it does not seem to play a significant role in the feedback regulation by glucocorticoids.

Serotonin-CRF interaction in the bed nucleus of the stria terminalis: a light microscopic double-label immunocytochemical analysis

The purpose of the present study was to examine in the bed nucleus of the stria terminalis (BST) of the rat brain the morphological characteristics of interactions between corticotropin-releasing factor (CRF)-producing neuron populations and serotonin (5-HT) axons. A double-label immunocytochemical, light microscopic technique was used to demonstrate axosomatic and axodendritic interactions between 5-HT axons and CRF neurons in the BST. Both the dorsolateral and ventrolateral subpopulations of CRF neurons were targets for the 5-HT afferents. Projections of monoamine neurons to the BST and the CRF neurons that are in the BST are implicated as being major contributors to the neurochemically mediated central regulation of the stress response.

Monoamine innervation of bed nucleus of stria terminalis: an electron microscopic investigation

Immunocytochemical studies showed distinctive monoamine input to the bed nucleus of the stria terminalis (BST). A comparison of axons immunoreactive (IR) for a catecholamine synthetic enzyme [tyrosine hydroxylase (TH) or dopamine beta-hydroxylase (DBH) or phenylethanolamine-N-methyl transferase (PNMT)] or serotonin (5-HT) was performed. TH-IR axons had a greater density in the lateral BST, but DBH-IR and 5-HT-IR axons had a greater density in the medial BST. PNMT-IR axons were dense in the intermediate BST. TH-IR axons had a greater density than DBH- and PNMT-IR axons in the dorsolateral BST, but DBH-IR axons had the greatest density in the ventrolateral BST. Ultrastructural studies revealed that TH-IR terminals formed synapses with soma, dendrites, spines, and axons in the dorsolateral BST. DBH-IR terminals formed synapses with dendritic shafts and spines, and 5-HT-IR terminals formed synapses with dendrites in the ventrolateral BST. Only some 5-HT-IR axons were myelinated. The medial vs. lateral organization of the noradrenergic and dopaminergic afferents in the BST of the rat brain is now evident and is similar to the human brain. The medial-lateral functional subdivision of the BST is supported by the pattern of dopaminergic, noradrenergic, and serotonergic afferents. This demonstration of epinephrine-producing afferents in the BST is the first detailed description of adrenergic input to the BST and aided the determination that catecholaminergic innervation of the ventrolateral BST is predominantly noradrenergic as has been proposed for many years. However, the additional demonstration of rich dopaminergic innervation of the dorsolateral subnucleus suggests further division of the BST into dorsal and ventral functional subgroups.

Central noradrenergic lesion impairs the adrenocorticotrophin response to release of endogenous catecholamines

Activation of hypothalamic α(1) -adrenoceptors stimulates the secretion of corticotrophin-releasing factors which in turn stimulate pituitary adrenocorticotrophin (ACTH). This mechanism is important in the physiological control of ACTH secretion. This study assesses the feasibility of using the ACTH response to release of endogenous catecholamines as a means of detecting a hypothalamic noradrenergic lesion in vivo. Intracerebroventricular infusion of the catecholamine neurotoxin, 6-hydroxydopamine, was used to destroy noradrenergic nerve endings in rats, with the purpose of producing a model that could be used to study alterations in ACTH responses that may result from a lesion involving central noradrenergic neurons. 6-Hydroxydopamine (250 μg icv) significantly reduced hypothalamic noradrenaline content, indicating damage to noradrenergic nerve endings, without affecting postsynaptic receptor function, as judged by preservation of the effect of a selective α(1) -adrenergic agonist. Pharmacological release of endogenous catecholamines, effected by combined administration of a catecholamine precursor and an α(2) -adrenergic antagonist, stimulated the secretion of ACTH in control, but not in 6-hydroxydopamine-treated rats. Degeneration of hypothalamic noradrenergic nerve endings is not followed by denervation hypersensitivity, and is therefore accompanied by impairment of the ACTH response to release of endogenous catecholamines.