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

Regulation of corticotropin-releasing hormone neuronal network activity by noradrenergic stress signals

Noradrenaline is a neurotransmitter released in response to homeostatic challenge and activates the hypothalamic-pituitary-adrenal axis via stimulation of corticotropin-releasing hormone (CRH) neurons. Here we investigated the mechanism through which noradrenaline regulates activity within the CRH neuronal network. Using a combination of in vitro GCaMP6f Ca²⁺ imaging and electrophysiology, we show that noradrenaline induces a robust increase in excitability in a proportion of CRH neurons with many neurons displaying a bursting mode of activity. Noradrenaline-induced activation required α₁ -adrenoceptors and L-type voltage-gated Ca²⁺ channels, but not GABA/glutamate synaptic transmission or sodium action potentials. Exposure of mice to elevated corticosterone levels was able to suppress noradrenaline-induced activation. These results provide further insight into the mechanisms by which noradrenaline regulates CRH neural network activity and hence stress responses. KEY POINTS: GCaMP6f Ca²⁺ imaging and on-cell patch-clamp recordings reveal that corticotropin-releasing hormone neurons are activated by noradrenaline with many neurons displaying a bursting mode of activity. Noradrenaline-induced activation requires α₁ -adrenoceptors. Noradrenaline-induced Ca²⁺ elevations persist after blocking GABA_A , AMPA, NMDA receptors and voltage-gated Na⁺ channels. Noradrenaline-induced Ca²⁺ elevations require L-type voltage-gated Ca²⁺ channels. Corticosterone suppresses noradrenaline-induced excitation.

Involvement of the Dorsal Vagal Complex in Alcohol-Related Behaviors

The neurobiological mechanisms that regulate the development and maintenance of alcohol use disorder (AUD) are complex and involve a wide variety of within and between systems neuroadaptations. While classic reward, preoccupation, and withdrawal neurocircuits have been heavily studied in terms of AUD, viable treatment targets from this established literature have not proven clinically effective as of yet. Therefore, examination of additional neurocircuitries not classically studied in the context of AUD may provide novel therapeutic targets. Recent studies demonstrate that various neuropeptides systems are important modulators of alcohol reward, seeking, and intake behaviors. This includes neurocircuitry within the dorsal vagal complex (DVC), which is involved in the control of the autonomic nervous system, control of intake of natural rewards like food, and acts as a relay of interoceptive sensory information via interactions of numerous gut-brain peptides and neurotransmitter systems with DVC projections to central and peripheral targets. DVC neuron subtypes produce a variety of neuropeptides and transmitters and project to target brain regions critical for reward such as the mesolimbic dopamine system as well as other limbic areas important for the negative reinforcing and aversive properties of alcohol withdrawal such as the extended amygdala. This suggests the DVC may play a role in the modulation of various aspects of AUD. This review summarizes the current literature on neurotransmitters and neuropeptides systems in the DVC (e.g., norepinephrine, glucagon-like peptide 1, neurotensin, cholecystokinin, thyrotropin-releasing hormone), and their potential relevance to alcohol-related behaviors in humans and rodent models for AUD research. A better understanding of the role of the DVC in modulating alcohol related behaviors may lead to the elucidation of novel therapeutic targets for drug development in AUD.

Hormonal and neural responses to restraint stress in an animal model of perimenopause in female rats

The present study investigated the hormonal and neural responses to stress in a perimenopause animal model induced by 4-vinylcyclohexene diepoxide (VCD), which induces progressive follicular depletion in rodents, allowing studies on the transition to ovarian failure. Female rats, aged 28 days old, were s.c. injected for 15 consecutive days with corn oil or VCD. At 85 ± 5 days after the onset of treatment, the jugular vein was cannulated in the afternoon of metoestrus and in next morning (dioestrus) at 10.00 am, rats were subjected to 30 minutes of restraint stress. Blood samples were withdrawn before (-5 minutes), during (2, 5, 15 and 30 minutes) and after (45, 60 and 90 minutes) stress and plasma prolactin, progesterone and corticosterone levels were measured. Animals were perfused, brains processed for c-Fos/tyrosine hydroxylase (TH) in the locus coeruleus (LC) and c-Fos/corticotrophin-releasing factor (CRF) in the paraventricular nucleus (PVN). In unstressed rats the density of β-endorphin fibres was assessed in LC and PVN. In VCD-treated rats, stress-induced prolactin peak was higher, basal and peak progesterone levels were lower, and both levels of corticosterone were similar to controls. However, the recovery period was longer for both adrenal hormones. In VCD-treated rats the number of c-Fos/TH and c-Fos/CRF-immunoreactive neurones was higher whereas the density of β-endorphin fibres was lower in LC and PVN. We surmise that the hyperactivity of the LC and PVN neurones in VCD-treated rats may be a result of the lower progesterone levels that resulted in the decrease of β-endorphin content in both nuclei, thus impairing the negative-feedback mechanism in the recovery period.

Brainstem prolactin-releasing peptide contributes to cancer anorexia-cachexia syndrome in rats

Up to 80% of cancer patients are affected by the cancer anorexia-cachexia syndrome (CACS), which leads to excessive body weight loss, reduced treatment success and increased lethality. The area postrema/nucleus of the solitary tract (AP/NTS) region emerged as a central nervous key structure in this multi-factorial process. Neurons in this area are targeted by cytokines and signal to downstream sites involved in energy homeostasis. NTS neurons expressing prolactin-releasing peptide (PrRP) are implicated in the control of energy intake and hypothalamus-pituitary-adrenal (HPA) axis activation, which contributes to muscle wasting. To explore if brainstem PrRP neurons contribute to CACS, we selectively knocked down PrRP expression in the NTS of hepatoma tumor-bearing rats by an AAV/shRNA gene silencing approach. PrRP knockdown reduced body weight loss and anorexia compared to tumor-bearing controls treated with a non-silencing AAV. Gastrocnemius and total hind limb muscle weight was higher in PrPR knockdown rats. Corticosterone levels were increased in the early phase after tumor induction at day 6 in both groups but returned to baseline levels at day 21 in the PrRP knockdown group. While we did not detect significant changes in gene expression of markers for muscle protein metabolism (MuRF-1, myostatin, mTOR and REDD1), mTOR and REDD1 tended to be lower after disruption PrRP signalling. In conclusion, we identified brainstem PrRP as a possible neuropeptide mediator of CACS in hepatoma tumor-bearing rats. The central and peripheral downstream mechanisms require further investigation and might involve HPA axis activation.

Colocalized neurotransmitters in the hindbrain cooperate in adaptation to chronic hypernatremia

Chronic hypernatremia activates the central osmoregulatory mechanisms and inhibits the function of the hypothalamic-pituitary-adrenal (HPA) axis. Noradrenaline (NE) release into the periventricular anteroventral third ventricle region (AV3V), the supraoptic (SON) and hypothalamic paraventricular nuclei (PVN) from efferents of the caudal ventrolateral (cVLM) and dorsomedial (cDMM) medulla has been shown to be essential for the hypernatremia-evoked responses and for the HPA response to acute restraint. Notably, the medullary NE cell groups highly coexpress prolactin-releasing peptide (PrRP) and nesfatin-1/NUCB2 (nesfatin), therefore, we assumed they contributed to the reactions to chronic hypernatremia. To investigate this, we compared two models: homozygous Brattleboro rats with hereditary diabetes insipidus (DI) and Wistar rats subjected to chronic high salt solution (HS) intake. HS rats had higher plasma osmolality than DI rats. PrRP and nesfatin mRNA levels were higher in both models, in both medullary regions compared to controls. Elevated basal tyrosine hydroxylase (TH) expression and impaired restraint-induced TH, PrRP and nesfatin expression elevations in the cVLM were, however, detected only in HS, but not in DI rats. Simultaneously, only HS rats exhibited classical signs of chronic stress and severely blunted hormonal reactions to acute restraint. Data suggest that HPA axis responsiveness to restraint depends on the type of hypernatremia, and on NE capacity in the cVLM. Additionally, NE and PrRP signalization primarily of medullary origin is increased in the SON, PVN and AV3V in HS rats. This suggests a cooperative action in the adaptation responses and designates the AV3V as a new site for PrRP's action in hypernatremia.

Glycinergic Input to the Mouse Basal Forebrain Cholinergic Neurons

The basal forebrain (BF) receives afferents from brainstem ascending pathways, which has been implicated first by Moruzzi and Magoun (1949) to induce forebrain activation and cortical arousal/waking behavior; however, it is very little known about how brainstem inhibitory inputs affect cholinergic functions. In the current study, glycine, a major inhibitory neurotransmitter of brainstem neurons, and gliotransmitter of local glial cells, was tested for potential interaction with BF cholinergic (BFC) neurons in male mice. In the BF, glycine receptor α subunit-immunoreactive (IR) sites were localized in choline acetyltransferase (ChAT)-IR neurons. The effect of glycine on BFC neurons was demonstrated by bicuculline-resistant, strychnine-sensitive spontaneous IPSCs (sIPSCs; 0.81 ± 0.25 × 10-1 Hz) recorded in whole-cell conditions. Potential neuronal as well as glial sources of glycine were indicated in the extracellular space of cholinergic neurons by glycine transporter type 1 (GLYT1)- and GLYT2-IR processes found in apposition to ChAT-IR cells. Ultrastructural analyses identified synapses of GLYT2-positive axon terminals on ChAT-IR neurons, as well as GLYT1-positive astroglial processes, which were localized in the vicinity of synapses of ChAT-IR neurons. The brainstem raphe magnus was determined to be a major source of glycinergic axons traced retrogradely from the BF. Our results indicate a direct effect of glycine on BFC neurons. Furthermore, the presence of high levels of plasma membrane glycine transporters in the vicinity of cholinergic neurons suggests a tight control of extracellular glycine in the BF.SIGNIFICANCE STATEMENT Basal forebrain cholinergic (BFC) neurons receive various activating inputs from specific brainstem areas and channel this information to the cortex via multiple projections. So far, very little is known about inhibitory brainstem afferents to the BF. The current study established glycine as a major regulator of BFC neurons by (1) identifying glycinergic neurons in the brainstem projecting to the BF, (2) showing glycine receptor α subunit-immunoreactive (IR) sites in choline acetyltransferase (ChAT)-IR neurons, (3) demonstrating glycine transporter type 2 (GLYT2)-positive axon terminals synapsing on ChAT-IR neurons, and (4) localizing GLYT1-positive astroglial processes in the vicinity of synapses of ChAT-IR neurons. The effect of glycine on BFC neurons was demonstrated by bicuculline-resistant, strychnine-sensitive spontaneous IPSCs recorded in whole-cell conditions.

Regulation of Hypothalamo-Pituitary-Adrenocortical Responses to Stressors by the Nucleus of the Solitary Tract/Dorsal Vagal Complex

Hindbrain neurons in the nucleus of the solitary tract (NTS) are critical for regulation of hypothalamo-pituitary-adrenocortical (HPA) responses to stress. It is well known that noradrenergic (as well as adrenergic) neurons in the NTS send direct projections to hypophysiotropic corticotropin-releasing hormone (CRH) neurons and control activation of HPA axis responses to acute systemic (but not psychogenic) stressors. Norepinephrine (NE) signaling via alpha1 receptors is primarily excitatory, working either directly on CRH neurons or through presynaptic activation of glutamate release. However, there is also evidence for NE inhibition of CRH neurons (possibly via beta receptors), an effect that may occur at higher levels of stimulation, suggesting that NE effects on the HPA axis may be context-dependent. Lesions of ascending NE inputs to the paraventricular nucleus attenuate stress-induced ACTH but not corticosterone release after chronic stress, indicating reduction in central HPA drive and increased adrenal sensitivity. Non-catecholaminergic NTS glucagon-like peptide 1/glutamate neurons play a broader role in stress regulation, being important in HPA activation to both systemic and psychogenic stressors as well as HPA axis sensitization under conditions of chronic stress. Overall, the data highlight the importance of the NTS as a key regulatory node for coordination of acute and chronic stress.

Interoceptive modulation of neuroendocrine, emotional, and hypophagic responses to stress

Periods of caloric deficit substantially attenuate many centrally mediated responses to acute stress, including neural drive to the hypothalamic-pituitary-adrenal (HPA) axis, anxiety-like behavior, and stress-induced suppression of food intake (i.e., stress hypophagia). It is posited that this stress response plasticity supports food foraging and promotes intake during periods of negative energy balance, even in the face of other internal or external threats, thereby increasing the likelihood that energy stores are repleted. The mechanisms by which caloric deficit alters central stress responses, however, remain unclear. The caudal brainstem contains two distinct populations of stress-recruited neurons [i.e., noradrenergic neurons of the A2 cell group that co-express prolactin-releasing peptide (PrRP+ A2 neurons), and glucagon-like peptide 1 (GLP-1) neurons] that also are responsive to interoceptive feedback about feeding and metabolic status. A2/PrRP and GLP-1 neurons have been implicated anatomically and functionally in the central control of the HPA axis, anxiety-like behavior, and stress hypophagia. The current review summarizes a growing body of evidence that caloric deficits attenuate physiological and behavioral responses to acute stress as a consequence of reduced recruitment of PrRP+ A2 and hindbrain GLP-1 neurons, accompanied by reduced signaling to their brainstem, hypothalamic, and limbic forebrain targets.

Role of paraventricular nucleus-projecting norepinephrine/epinephrine neurons in acute and chronic stress

Chronic variable stress (CVS) exposure modifies the paraventricular nucleus of the hypothalamus (PVN) in a manner consistent with enhanced central drive of the hypothalamo-pituitary-adrenocortical (HPA) axis. As previous reports suggest that post-stress enhancement of norepinephrine (NE) action contributes to chronic stress regulation at the level of the PVN, we hypothesised that PVN-projecting NE neurons were necessary for the stress facilitatory effects of CVS. Following intra-PVN injection of saporin toxin conjugated to a dopamine beta-hydroxylase (DBH) antibody (DSAP), in rats PVN DBH immunoreactivity was almost completely eliminated, but immunoreactive afferents to other key regions involved in stress integration were spared (e.g. DBH fiber densities were unaffected in the central nucleus of the amygdala). Reductions in DBH-positive fiber density were associated with reduced numbers of DBH-immunoreactive neurons in the nucleus of the solitary tract and locus coeruleus. Following 2 weeks of CVS, DSAP injection did not alter stress-induced adrenal hypertrophy or attenuation of body weight gain, indicating that PVN-projecting NE [and epinephrine (E)] neurons are not essential for these physiological effects of chronic stress. In response to acute restraint stress, PVN-targeted DSAP injection attenuated peak adrenocorticotrophic hormone (ACTH) and corticosterone in controls, but only attenuated peak ACTH in CVS animals, suggesting that enhanced adrenal sensitivity compensated for reduced excitatory drive of the PVN. Our data suggest that PVN-projecting NE/E neurons contribute to the generation of acute stress responses, and are required for HPA axis drive (ACTH release) during chronic stress. However, loss of NE/E drive at the PVN appears to be buffered by compensation at the level of the adrenal.

Gonadal steroid hormones and the hypothalamo-pituitary-adrenal axis

The hypothalamo-pituitary-adrenal (HPA) axis represents a complex neuroendocrine feedback loop controlling the secretion of adrenal glucocorticoid hormones. Central to its function is the paraventricular nucleus of the hypothalamus (PVN) where neurons expressing corticotropin releasing factor reside. These HPA motor neurons are a primary site of integration leading to graded endocrine responses to physical and psychological stressors. An important regulatory factor that must be considered, prior to generating an appropriate response is the animal's reproductive status. Thus, PVN neurons express androgen and estrogen receptors and receive input from sites that also express these receptors. Consequently, changes in reproduction and gonadal steroid levels modulate the stress response and this underlies sex differences in HPA axis function. This review examines the make up of the HPA axis and hypothalamo-pituitary-gonadal (HPG) axis and the interactions between the two that should be considered when exploring normal and pathological responses to environmental stressors.

Inactivation of glucocorticoid receptor in noradrenergic system influences anxiety- and depressive-like behavior in mice

The aim of this study was to investigate whether conditional inactivation of the glucocorticoid receptors (GRs) in noradrenergic neurons affects animal behavior in mice. Selective ablation of GRs in the noradrenergic system was achieved using the Cre/loxP approach. We crossed transgenic mice expressing the Cre recombinase under the dopamine beta-hydroxylase (DBH) promoter with animals harboring the floxed GR gene. The resulting GR(DBHCre) mutant mice exhibited no alterations in terms of normal cage behavior, weight gain, spatial memory or spontaneous locomotor activity, regardless of gender. To assess depressive- and anxiety-like behaviors we performed the Tail Suspension Test and the Light-Dark Box Test. While male mutant animals did not show any alternations in both tests, female GR(DBHCre) mutants displayed depressive- and anxiety-like behavior. Additionally, male GR(DBHCre) mice were exposed to chronic restraint stress but still exhibited immobility times and anxiety statuses similar to those of non-stressed animals while stressed control mice clearly revealed depressive- and anxiety-like phenotype. Thus, in males the effects of the mutation were precipitated only after chronic restraint stress procedure. Our data reveal a possible gender-dependent role of GRs in the noradrenergic system in anxiety- and depressive-like behavior in mice.

Overnight food deprivation markedly attenuates hindbrain noradrenergic, glucagon-like peptide-1, and hypothalamic neural responses to exogenous cholecystokinin in male rats

Systemic administration of sulfated cholecystokinin-8 (CCK) activates neurons within the hindbrain nucleus of the solitary tract (NTS) that project directly to the paraventricular nucleus of the hypothalamus (PVN), and these projections underlie the ability of exogenous CCK to activate the hypothalamic-pituitary-adrenal (HPA) stress axis. CCK inhibits food intake, increases NTS neuronal cFos expression, and activates the HPA axis in a dose-dependent manner. While the hypophagic effects of exogenous CCK are attenuated in food-deprived rats, CCK dose-response relationships for NTS and hypothalamic activation in fed and fasted rats are unknown. Within the NTS, noradrenergic A2 and glucagon-like peptide-1 (GLP-1) neurons express cFos after high doses of CCK, and both neuronal populations project directly to the medial parvocellular (mp)PVN. We hypothesized that increasing and correlated proportions of A2, GLP-1, and mpPVN neurons would express cFos in rats after increasing doses of CCK, and that food deprivation would attenuate both hindbrain and hypothalamic neural activation. To test these hypotheses, ad libitum-fed (ad lib) and overnight food-deprived (DEP) rats were anesthetized and perfused with fixative 90min after i.p. injection of 1.0ml saline vehicle containing CCK at doses of 0, 3, or 10μg/kg BW. Additional ad lib and DEP rats served as non-handled (NH) controls. Brain tissue sections were processed for dual immunocytochemical localization of cFos and dopamine-β-hydroxylase to identify A2 neurons, or cFos and GLP-1. Compared to negligible A2 cFos activation in NH control rats, i.p. vehicle and CCK dose-dependently increased A2 activation, and this was significantly attenuated by DEP. DEP also attenuated mpPVN cFos expression across all treatment groups, and A2 activation was strongly correlated with mpPVN activation in both ad lib and DEP rats. In ad lib rats, large and similar numbers of GLP-1 neurons expressed cFos across all i.p. treatment groups, regardless of CCK dose. Surprisingly, DEP nearly abolished baseline GLP-1 cFos expression in NH controls, and also in rats after i.p. injection of vehicle or CCK. We conclude that CCK-induced hypothalamic cFos activation is strongly associated with A2 activation, whereas the relationship between mpPVN and GLP-1 activation is less clear. Furthermore, activation of A2, GLP-1, and mpPVN neurons is significantly modulated by feeding status, suggesting a mechanism through which food intake and metabolic state might impact hypothalamic neuroendocrine responses to homeostatic challenge.

Serotonergic innervation and serotonin receptor expression of NPY-producing neurons in the rat lateral and basolateral amygdaloid nuclei

Pharmacobehavioral studies in experimental animals, and imaging studies in humans, indicate that serotonergic transmission in the amygdala plays a key role in emotional processing, especially for anxiety-related stimuli. The lateral and basolateral amygdaloid nuclei receive a dense serotonergic innervation in all species studied to date. We investigated interrelations between serotonergic afferents and neuropeptide Y (NPY)-producing neurons, which are a subpopulation of inhibitory interneurons in the rat lateral and basolateral nuclei with particularly strong anxiolytic properties. Dual light microscopic immunolabeling showed numerous appositions of serotonergic afferents on NPY-immunoreactive somata. Using electron microscopy, direct membrane appositions and synaptic contacts between serotonin-containing axon terminals and NPY-immunoreactive cellular profiles were unequivocally established. Double in situ hybridization documented that more than 50 %, and about 30–40 % of NPY mRNA-producing neurons, co-expressed inhibitory 5-HT1A and excitatory 5-HT2C mRNA receptor subtype mRNA, respectively, in both nuclei with no gender differences. Triple in situ hybridization showed that individual NPY mRNA-producing interneurons co-express both 5-HT1A and 5-HT2C mRNAs. Co-expression of NPY and 5-HT3 mRNA was not observed. The results demonstrate that serotonergic afferents provide substantial innervation of NPY-producing neurons in the rat lateral and basolateral amygdaloid nuclei. Studies of serotonin receptor subtype co-expression indicate a differential impact of the serotonergic innervation on this small, but important, population of anxiolytic interneurons, and provide the basis for future studies of the circuitry underlying serotonergic modulation of emotional stimulus processing in the amygdala.

Involvement of noradrenergic transmission in the PVN on CREB activation, TORC1 levels, and pituitary-adrenal axis activity during morphine withdrawal

Experimental and clinical findings have shown that administration of adrenoceptor antagonists alleviated different aspects of drug withdrawal and dependence. The present study tested the hypothesis that changes in CREB activation and phosphorylated TORC1 levels in the hypothalamic paraventricular nucleus (PVN) after naloxone-precipitated morphine withdrawal as well as the HPA axis activity arises from α₁- and/or β-adrenoceptor activation. The effects of morphine dependence and withdrawal on CREB phosphorylation (pCREB), phosphorylated TORC1 (pTORC1), and HPA axis response were measured by Western-blot, immunohistochemistry and radioimmunoassay in rats pretreated with prazosin (α₁-adrenoceptor antagonist) or propranolol (β-adrenoceptor antagonist). In addition, the effects of morphine withdrawal on MHPG (the main NA metabolite at the central nervous system) and NA content and turnover were evaluated by HPLC. We found an increase in MHPG and NA turnover in morphine-withdrawn rats, which were accompanied by increased pCREB immunoreactivity and plasma corticosterone concentrations. Levels of the inactive form of TORC1 (pTORC1) were decreased during withdrawal. Prazosin but not propranolol blocked the rise in pCREB level and the decrease in pTORC1 immunoreactivity. In addition, the HPA axis response to morphine withdrawal was attenuated in prazosin-pretreated rats. Present results suggest that, during acute morphine withdrawal, NA may control the HPA axis activity through CREB activation at the PVN level. We concluded that the combined increase in CREB phosphorylation and decrease in pTORC1 levels might represent, in part, two of the mechanisms of CREB activation at the PVN during morphine withdrawal.

Correlative microscopy: a powerful tool for exploring neurological cells and tissues

Imaging tools for exploring the neurological samples have seen a rapid transformation over the last decade. Approaches that allow clear and specific delineation of targeted tissues, individual neurons, and their cell-cell connections as well as subcellular constituents have been especially valuable. Considering the significant complexity and extent to which the nervous system interacts with every organ system in the body, one non-trivial challenge has been how to identify and target specific structures and pathologies by microscopy. To this end, correlative methods enable one to view the same exact structure of interest utilizing the capabilities of typically separate, but powerful, microscopy platforms. As such, correlative microscopy is well-positioned to address the three critical problems of identification, scale, and resolution inherent to neurological systems. Furthermore, the application of multiple imaging platforms to the study of singular biological events enables more detailed investigations of structure-function relationships to be conducted, greatly facilitating our understanding of relevant phenomenon. This comprehensive review provides an overview of methods for correlative microscopy, including histochemistry, transgenic markers, immunocytochemistry, photo-oxidation as well as various probes and tracers. An emphasis is placed on correlative light and electron microscopic strategies used to facilitate relocation of neurological structures. Correlative microscopy is an invaluable tool for neurological research, and we fully anticipate developments in automation of the process, and the increasing availability of genomic and transgenic tools will facilitate the adoption of correlative microscopy as the method of choice for many imaging experiments.

Role of glucocorticoids in tuning hindbrain stress integration

The nucleus of the solitary tract (NTS) is a critical integrative site for coordination of autonomic and endocrine stress responses. Stress-excitatory signals from the NTS are communicated by both catecholaminergic [norepinephrine (NE), epinephrine (E)] and noncatecholaminergic [e.g., glucagon-like peptide-1 (GLP-1)] neurons. Recent studies suggest that outputs of the NE/E and GLP-1 neurons of the NTS are selectively engaged during acute stress. This study was designed to test mechanisms of chronic stress integration in the paraventricular nucleus, focusing on the role of glucocorticoids. Our data indicate that chronic variable stress (CVS) causes downregulation of preproglucagon (GLP-1 precursor) mRNA in the NTS and reduction of GLP-1 innervation to the paraventricular nucleus of the hypothalamus. Glucocorticoids were necessary for preproglucagon (PPG) reduction in CVS animals and were sufficient to lower PPG mRNA in otherwise unstressed animals. The data are consistent with a glucocorticoid-mediated withdrawal of GLP-1 in key stress circuits. In contrast, expression of tyrosine hydroxylase mRNA, the rate-limiting enzyme in catecholamine synthesis, was increased by stress in a glucocorticoid-independent manner. These suggest differential roles of ascending catecholamine and GLP-1 systems in chronic stress, with withdrawal of GLP-1 involved in stress adaptation and enhanced NE/E capacity responsible for facilitation of responses to novel stress experiences.

Distribution and morphology of the juxtapositions between growth hormone-releasing hormone-(ghrh)-immunoreactive neuronal elements

Previous studies revealed that growth hormone-releasing hormone (GHRH)-immunoreactive (IR) neurons form a circumscribed cell group in the basal infundibulum/median eminence of the human hypothalamus. GHRH from these neurons is released into the hypothalamo-hypophyseal portal circulatory system in a pulsatile manner. It is a common consensus that the pulsatile release of GHRH is the main driving force behind the pulsatile release of growth hormone (GH) and may contribute to the regulation of other hypothalamic functions. The pulsatile release of GHRH requires synchronized activity of GHRH-IR neurons. However, the morphological basis of this synchronization between the GHRH-IR neural elements has not been elucidated yet. Since the utilization of electron microscopy combined with immunohistochemistry is virtually impossible in the human brain due to the long post mortem period, immunohistochemistry, evaluated with oil immersion light microscopy, was used in order to reveal the associations between the GHRH elements. Numerous GHRH-GHRH juxtapositions have been detected in the infundibular area/median eminence, where GHRH-IR axonal varicosities often formed multiple contacts with GHRH-IR perikarya. Examination of these associations with high magnification oil immersion light microscopy revealed (1) axonal swellings at the site of the contacts and (2) no gaps between the contacting elements suggesting that these juxtapositions may be functional synapses. The large number of GHRH-GHRH juxtapositions in the infundibular area/median eminence suggests that these synapse-like structures may represent the morphological substrate of the synchronized activity of GHRH neurons that in turn may result in the pulsatile release of GHRH in human.

Current perspectives of the roles of the central norepinephrine system in anxiety and depression

Norepinephrine (NE) is a major monoamine neurotransmitter that has widespread effects across multiple brain areas to regulate arousal and stress responses. The underlying function of the NE cortical system is to balance vigilance/scanning behavior with focused attention on novel environmental stimuli and the state of arousal. The central NE system is involved intrinsically with the stress response system, and dysregulation within the NE system has been implicated in the pathogenesis of anxiety and depressive disorders. Central NE activity paradoxically has either anxiogenic or anxiolytic effects, depending on whether the time course of the stress is acute or chronic, whether the stress is predictable or unpredictable, and which underlying brain regions are affected. Under conditions of chronic stress, NE system activity dysregulation of the hypothalamic-pituitary-adrenal system may turn a homeostatic stress response into a pathological stress response. Data suggest that the NE interplay with the serotonin system may exert neurobiological normalization of the pathophysiological state of anxious depression. Accordingly, pharmacological interventions targeting the NE system can result in anxiolytic, rather than anxiogenic, outcomes when used to treat patients with anxiety and depression.

Gene expression profiling identifies key estradiol targets in the frontal cortex of the rat

Estradiol modulates a wide range of neural functions in the frontal cerebral cortex where subsets of neurons express estrogen receptor-alpha and -beta. Through these receptors, estradiol contributes to the maintenance of normal operation of the frontal cortex. During the decline of gonadal hormones, the frequency of neurological and psychiatric disorders increases. To shed light on the etiology of disorders related to declining levels of estrogens, we studied the genomic responses to estradiol. Ovariectomized rats were treated with a sc injection of estradiol. Twenty-four hours later, samples from the frontal cortices were dissected, and their mRNA content was analyzed. One hundred thirty-six estradiol-regulated transcripts were identified on Rat 230 2.0 Expression Array. Of the 136 estrogen-regulated genes, 26 and 36 genes encoded proteins involved in the regulation of transcription and signal transduction, respectively. Thirteen genes were related to the calcium signaling pathway. They comprised five genes coding for neurotransmitter receptors. Transcription of three neuropeptides, including cocaine- and amphetamine-regulated transcript, were up-regulated. Fifty-two genes were selected for validation, and 12 transcriptional changes were confirmed. These results provided evidence that estradiol evokes broad transcriptional response in the cortex. Modulation of key components of the calcium signaling pathway, dopaminergic, serotonergic, and glutamatergic neurotransmission, may explain the influence of estrogens on cognitive function and behavior. Up-regulation of cocaine- and amphetamine-regulated transcript contributes to the neuroprotective effects of estradiol. Identification of estradiol-regulated genes in the frontal cortex helps to understand the pathomechanism of neurological and psychiatric disorders associated with altered levels of estrogens.

Chronic stress-induced neurotransmitter plasticity in the PVN

Chronic stress precipitates pronounced enhancement of central stress excitability, marked by sensitization of hypothalamic-pituitary-adrenocortical (HPA) axis responses and increased adrenocorticotropic hormone (ACTH) secretagogue biosynthesis in the paraventricular nucleus of the hypothalamus (PVN). Chronic stress-induced enhancement of HPA axis excitability predicts increased excitatory and/or decreased inhibitory innervation of the parvocellular PVN. We tested this hypothesis by evaluating chronic variable stress (CVS)-induced changes in total (synaptophysin), glutamatergic (VGluT2), GABAergic (GAD65), and noradrenergic (DBH) terminal immunoreactivity on PVN parvocellular neurons using immunofluorescence confocal microscopy. CVS increased the total PVN bouton immunoreactivity as well as the number of glutamatergic and noradrenergic immunoreactive boutons in apposition to both the corticotropin-releasing hormone (CRH)-immunoreactive cell bodies and dendrites within the parvocellular PVN. However, the number of GABAergic-immunoreactive boutons in the PVN was unchanged. CVS did not alter CRH median eminence immunoreactivity, indicating that CVS does not enhance CRH storage within the median eminence. Taken together, the data are consistent with a role for both glutamate and norepinephrine in chronic stress enhancement of HPA axis excitability. These changes could lead to an enhanced capacity for excitation in these neurons, contributing to chronic stress-induced hyperreactivity of stress effector systems in the brain.

Glucocorticoid regulation of preproglucagon transcription and RNA stability during stress

Stress elicits a synchronized response of the endocrine, sympathetic, and central nervous systems to preserve homeostasis and well-being. Glucagon-like peptide-1 (GLP-1), a primary posttranslational product of the preproglucagon (PPG) gene, activates both physical and psychological stress responses. The current study examined mechanisms regulating expression of PPG gene products in the hindbrain. Our results indicate that PPG mRNA decreases rapidly after exposure to acute stressors of multiple modalities. Reduced mRNA levels are accompanied by reduced GLP-1 immunoreactivity in the paraventricular nucleus of hypothalamus, suggesting release at PPG terminals. Stress-induced decrements in PPG mRNA were attenuated in adrenalectomized-corticosterone-replaced rats, suggesting that mRNA down-regulation is due at least in part to glucocorticoid secretion. In contrast, acute stress increased levels of PPG heteronuclear RNA (hnRNA) in a glucocorticoid-dependent manner, suggesting that decreases in PPG mRNA are due to increased degradation rather than reduced transcription. Glucocorticoid administration to unstressed rats is sufficient to cause decrements in PPG mRNA and increments in PPG hnRNA. These findings suggest that glucocorticoids deplete the pool of transcribed PPG mRNA and concurrently stimulate PPG gene transcription, with the latter allowing a mechanism for replenishment of PPG mRNA after stress cessation. The combination of rapid PPG mRNA depletion and initiation of PPG transcription within 30 min is consistent with a rapid action of glucocorticoids on GLP-1 bioavailability, resulting in a transient reduction in the capacity for neuropeptidergic excitation of stress responses.

Critical period plasticity of axonal arbors of layer 2/3 pyramidal neurons in rat somatosensory cortex: layer-specific reduction of projections into deprived cortical columns

We examined the effect of whisker trimming during early postnatal development on the morphology of axonal arbors in rat somatosensory cortex. Axonal arbors from populations of layer 2/3 pyramidal neurons in the D2 column were labeled by lentivirus-mediated expression of green fluorescent protein. Axonal projection patterns were compared between untrimmed control animals and animals with all whiskers in A-, B-, and C-rows trimmed (D- and E-rows left intact) from postnatal days 7 to 15 (termed from here on DE-pairing). Control animals had approximately symmetrical horizontal projections toward C- and E-row columns in both supra- and infragranular layers. Following DE-pairing, the density of axons in supragranular layers projecting from the labeled neurons in the D2 column was higher in E- than in C-row columns. This asymmetry resulted primarily from a reduction in projection density toward the deprived C-row columns. In contrast, no change was observed in infragranular layers. The results indicate that DE-pairing during early postnatal development results in reduced axonal projection from nondeprived into deprived columns and that cortical neurons are capable of structural rearrangements at subsets of their axonal arbors.

Chronic intermittent hypoxia sensitizes acute hypothalamic-pituitary-adrenal stress reactivity and Fos induction in the rat locus coeruleus in response to subsequent immobilization stress

Obstructive sleep apnea (OSA) is associated with several pathophysiological conditions, including hypertension, obesity, insulin resistance, hypothalamic-pituitary-adrenal (HPA) dysregulation, and other endocrine and metabolic disturbances comprising the "metabolic syndrome." Repeated episodes of hypoxia in OSA may represent a chronic intermittent stress, leading to HPA dysregulation. Alterations in HPA reactivity could then contribute to or exacerbate other pathophysiological processes. We showed previously that another metabolic stressor, chronic intermittent cold stress, enhanced noradrenergic facilitation of acute HPA stress reactivity. In this study, we investigated whether chronic intermittent hypoxia (CIH), a rat model for the arterial hypoxemia that accompanies OSA, similarly sensitizes the HPA response to novel acute stress. Rats were exposed to CIH (alternating cycles of normoxia [3 min at 21% O(2)] and hypoxia [3 min at 10% O(2)], repeated continuously for 8 h/day during the light portion of the cycle for 7 days). On the day after the final CIH exposure, there were no differences in baseline plasma adrenocorticotropic hormone (ACTH), but the peak ACTH response to 30 min acute immobilization stress was greater in CIH-stressed rats than in controls. Induction of Fos expression by acute immobilization stress was comparable following CIH in several HPA-modulatory brain regions, including the paraventricular nucleus, bed nucleus of the stria terminalis, and amygdala. Fos induction was attenuated in lateral hypothalamus, an HPA-inhibitory region. By contrast, acute Fos induction was enhanced in noradrenergic neurons in the locus coeruleus following CIH exposure. Thus, similar to chronic cold stress, CIH sensitized acute HPA and noradrenergic stress reactivity. Plasticity in the acute stress response is important for long-term adaptation, but may also contribute to pathophysiological conditions associated with states of chronic or repeated stress, such as OSA. Determining the neural mechanisms underlying these adaptations may help us better understand the etiology of such disorders, and inform the development of more effective treatments.

Regulation of serine (Ser)-31 and Ser40 tyrosine hydroxylase phosphorylation during morphine withdrawal in the hypothalamic paraventricular nucleus and nucleus tractus solitarius-A2 cell group: role of ERK1/2

Our previous studies have shown that naloxone-induced morphine withdrawal increases the hypothalamic-pituitary-adrenocortical (HPA) axis activity, which is dependent on a hyperactivity of noradrenergic pathways [nucleus tractus solitarius (NTS) A(2)] innervating the hypothalamic paraventricular nucleus (PVN). Short-term regulation of catecholamine biosynthesis occurs through phosphorylation of tyrosine hydroxylase (TH), which enhances enzymatic activity. In the present study, the effect of morphine withdrawal on site-specific TH phosphorylation in the PVN and NTS-A(2) was determined by quantitative blot immunolabeling and immunohistochemistry using phosphorylation state-specific antibodies. We show that naloxone-induced morphine withdrawal phosphorylates TH at Serine (Ser)-31 but not Ser40 in PVN and NTS-A(2), which is associated with both an increase in total TH immunoreactivity in NTS-A(2) and an enhanced TH activity in the PVN. In addition, we demonstrated that TH neurons phosphorylated at Ser31 coexpress c-Fos in NTS-A(2). We then tested whether pharmacological inhibition of ERK activation by ERK kinase contributes to morphine withdrawal-induced phosphorylation of TH at Ser31. We show that the ability of morphine withdrawal to stimulate phosphorylation at this seryl residue is reduced by SL327, an inhibitor of ERK(1/2) activation. These results suggest that morphine withdrawal increases noradrenaline turnover in the PVN, at least in part, via ERK(1/2)-dependent phosphorylation of TH at Ser31.

Morphological interrelationship between astrocytes and nerve endings in the rat spinal trigeminal nucleus caudalis

It has been reported that the spinal trigeminal nucleus caudalis (Sp5C), which receives nociceptive information from the oro-facial regions, has four laminae. To clarify the role of glial cells in the transmission of the nociceptive information, the present study was conducted to examine the detailed distribution of astrocytes in each lamina and also to investigate a morphological interrelationship between the astrocytes and nerve endings in the rat Sp5C. After the preparation of the serial cryostat sections, immunohistochemistry for glial fibrillary acidic protein (GFAP) was employed to identify the astrocytes, and immunohistochemistry for substance P (SP), calcitonin gene-related peptide (CGRP), was used for the nerve endings. We also employed double-labeling immunofluorescence and electron microscopic immunohistochemistry for the GFAP/SP or GFAP/CGRP. GFAP-positive reactions were observed in all laminae of the Sp5C, and SP- or CGRP-positive nerve endings were observed in the lamina I and II. Additionally, we clarified the presence of GFAP/SP- or GFAP/CGRP-positive reactions by the double-labeling immunofluorescence and demonstrated the morphological interrelationship between the astrocytes and nerve endings by the double-labeling electron microscopic immunohistochemistry. These findings suggest that astrocytes might play some roles in the transmission of nociceptive information from the oro-facial region.

Ciliary neurotrophic factor-immunoreactivity in olfactory sensory neurons

Ciliary neurotrophic factor (CNTF) has been implicated in processes of neuroprotection, axonal regeneration and synaptogenesis in the lesioned CNS. In the olfactory system, which is characterized by particularly robust neuroplasticity throughout life, the concentration of CNTF is high even under physiological conditions. In the present study, the cellular localization of CNTF-immunoreactivity was studied in the rat and mouse olfactory epithelium. In both species, individual olfactory sensory neurons (ONs) displayed intense CNTF-immunoreactivity. The number of CNTF-ir ONs varied interindividually in rats and was lower in mice than in rats. In olfactory epithelia of mice expressing beta-galactosidase under control of the CNTF promoter, cells of the ON layer were immunoreactive for the reporter protein. CNTF-ir ONs were olfactory marker protein-positive and growth associated protein 43-negative. CNTF-ir ONs lacked apoptotic markers, and the number of specifically labeled ONs was apparently unchanged after light chemical lesioning of the epithelium, indicating that CNTF-immunoreactivity was not associated with ON death. Electron microscopy of CNTF-ir ON axons in innervated olfactory bulb glomeruli documented that they formed typical ON axonal synapses with target neurons. Three dimensional reconstructions of bulb pairs showed a striking similarity of the positions of glomeruli innervated by CNTF-ir ON axons in left and right bulbs of individual animals and interindividually. The number of innervated glomeruli differed interindividually in rats and was lower in mice than in rats. The results show that in rodents CNTF-immunoreactivity occurs in a subset of mature, functionally competent ONs. The localization of target glomeruli suggests that CNTF-immunoreactivity may be associated with the expression and/or activation of specific olfactory receptor proteins.

Chronic intermittent cold stress sensitises the hypothalamic-pituitary-adrenal response to a novel acute stress by enhancing noradrenergic influence in the rat paraventricular nucleus

Chronic intermittent cold stress sensitises activation of the hypothalamic-pituitary-adrenal (HPA) axis by novel acute stress. We have shown that enhanced noradrenergic function in limbic forebrain contributes to HPA sensitisation. In the present study, we investigated whether chronic intermittent cold also induced changes in noradrenergic function in the paraventricular nucleus (PVN), the primary mediator of the HPA stress response. Rats were exposed to chronic intermittent cold (7 days, 6 h per day, 4 degrees C). On the day after final cold exposure, there were no differences in baseline plasma ACTH, but the peak ACTH response to 30 min of acute immobilisation stress was greater in cold-stressed rats compared to controls. Bilateral microinjection of the alpha(1)-adrenergic receptor antagonist benoxathian into the PVN reduced acute stress-induced adrenocorticotrophic hormone (ACTH) levels by approximately 25% in controls. Furthermore, in cold-stressed rats, all of the sensitisation of the ACTH response was blocked by benoxathian, to a level comparable to benoxathian-treated controls. In a second study using microdialysis to measure norepinephrine release in the PVN, there were no differences in either baseline or acute stress-induced increases in norepinephrine release in the PVN of cold-stressed rats compared to controls. Thus, in a third study, we tested potential alterations in postsynaptic alpha(1)-receptor sensitivity after chronic cold stress. Dose-dependent activation of ACTH secretion by microinjection of the alpha(1)-adrenergic receptor agonist, phenylephrine, into the PVN was significantly enhanced in cold-stressed rats compared to controls. Thus, the sensitised HPA response to acute stress after chronic intermittent cold exposure is at least partly attributable to an enhanced response to alpha1-adrenergic receptor activation in the PVN. Chronic stress-induced plasticity in the acute stress response may be important for stress adaptation, but may also contribute to pathophysiological conditions associated with stress. Thus, understanding the neural mechanisms underlying such adaptations may help us understand the aetiology of such disorders, and contribute to the future development of more effective treatment or prevention strategies.

Monosynaptic pathway from rat vibrissa motor cortex to facial motor neurons revealed by lentivirus-based axonal tracing

The mammalian motor cortex typically innervates motor neurons indirectly via oligosynaptic pathways. However, evolution of skilled digit movements in humans, apes, and some monkey species is associated with the emergence of abundant monosynaptic cortical projections onto spinal motor neurons innervating distal limb muscles. Rats perform skilled movements with their whiskers, and we examined the possibility that the rat vibrissa motor cortex (VMC) projects monosynaptically onto facial motor neurons controlling the whisker movements. First, single injections of lentiviruses to VMC sites identified by intracortical microstimulations were used to label a distinct subpopulation of VMC axons or presynaptic terminals by expression of enhanced green fluorescent protein (GFP) or GFP-tagged synaptophysin, respectively. Four weeks after the injections, GFP and synaptophysin-GFP labeling of axons and putative presynaptic terminals was detected in the lateral portion of the facial nucleus (FN), in close proximity to motor neurons identified morphologically and by axonal back-labeling from the whisker follicles. The VMC projections were detected bilaterally, with threefold larger density of labeling in the contralateral FN. Next, multiple VMC injections were used to label a large portion of VMC axons, resulting in overall denser but still laterally restricted FN labeling. Ultrastructural analysis of the GFP-labeled VMC axons confirmed the existence of synaptic contacts onto dendrites and somata of FN motor neurons. These findings provide anatomical demonstration of monosynaptic VMC-to-FN pathway in the rat and show that lentivirus-based expression of GFP and GFP-tagged presynaptic proteins can be used as a high-resolution neuroanatomical tracing method.

Glutamatergic innervation of corticotropin-releasing hormone- and thyrotropin-releasing hormone-synthesizing neurons in the hypothalamic paraventricular nucleus of the rat

Glutamate plays a role in the central regulation of the hypothalamic-pituitary-adrenal (HPA) and thyroid (HPT) axes. Until the recent discovery of vesicular glutamate transporters (VGLUT1-3), there was no specific tool for the examination of the putative morphological relationship between the glutamatergic and the hypophysiotropic systems. Using antisera against VGLUT2, corticotropin-releasing hormone (CRH), and prothyrotropin-releasing hormone (proTRH) (178-199), we performed double-labeling immunocytochemistry at light and electron microscopic levels in order to study the glutamatergic innervation of the CRH- and TRH-synthesizing neurons in the hypothalamic paraventricular nucleus (PVN). Fine VGLUT2-immunoreactive (IR) axons very densely innervated the parvocellular subdivisions of the PVN. VGLUT2-IR axons established juxtapositions with all parvocellular CRH- and TRH-synthesizing neurons. The innervation was similarly intense in all parvocellular subdivisions of the PVN. At ultrastructural level, VGLUT2-IR terminals frequently established synapses with perikarya and dendrites of the CRH- and proTRH-IR neurons. These findings demonstrate that glutamatergic neurons directly innervate hypophysiotropic CRH and TRH neurons in the PVN and, therefore, support the hypothesis that the glutamate-induced activation of the HPA and HPT axes may be accomplished by a direct action of glutamate on hypophysiotropic CRH and TRH systems.

Histamine H3 receptors inhibit serotonin release in substantia nigra pars reticulata

The substantia nigra pars reticulata (SNr) plays a key role in basal ganglia function. Projections from multiple basal ganglia nuclei converge at the SNr to regulate nigrothalamic output. The SNr is also characterized by abundant aminergic input, including dopaminergic dendrites and axons containing 5-hydroxytryptamine (5-HT) or histamine (HA). The functions of HA in the SNr include motor control via HA H3 receptors (H3Rs), although the mechanism remains far from elucidated. In Parkinson's disease, there is an increase in H3Rs and the density of HA-immunoreactive axons in the SN. We explored the role of H3Rs in the regulation of 5-HT release in SNr using fast-scan cyclic voltammetry at carbon-fiber microelectrodes in rat midbrain slices. Immunohistochemistry identified a similar distribution for histaminergic and serotonergic processes in the SNr: immunoreactive varicosities were observed in the vicinity of dopaminergic dendrites. Electrically evoked 5-HT release was dependent on extracellular Ca2+ and prevented by NaV+-channel blockade. Extracellular 5-HT concentration was enhanced by inhibition of uptake transporters for 5-HT but not dopamine. Selective H3R agonists (R)-(-)-alpha-methyl-histamine or immepip inhibited evoked 5-HT release by up to 60%. This inhibition was prevented by the H3R antagonist thioperamide but not by the 5-HT1B receptor antagonist isamoltane. H3R inhibition of 5-HT release prevailed in the presence of GABA or glutamate receptor antagonists (ionotropic and metabotropic), suggesting minimal involvement of GABA or glutamate synapses. The potent regulation of 5-HT by H3Rs reported here not only elucidates HA function in the SNr but also raises the possibility of novel targets for basal ganglia therapies.

Galanin- but not galanin-like peptide-containing axon terminals innervate hypophysiotropic TRH-synthesizing neurons in the hypothalamic paraventricular nucleus

Galanin and galanin-like peptide (GALP) are both orexigenic peptides involved in the regulation of food intake and energy metabolism. To determine whether these peptides may directly influence the hypophysiotropic thyrotropin-releasing hormone (TRH)-synthesizing neurons, double-labeling immunocytochemistry was performed at light and electron microscopic levels using antisera against proTRH, galanin and GALP. Galanin-IR axons densely innervated all of the major parvocellular subdivisions of the PVN where proTRH neurons were identified. The periventricular and anterior parvocellular subdivisions exhibited a prominent network of galaninergic nerve fibers, while the density of fibers was less intense in the medial parvocellular subdivision. Galanin-immunoreactive (IR) axon varicosities were juxtaposed to the majority of TRH-synthesizing neurons in the anterior, medial and periventricular subdivisions of the PVN. Ultrastucturally, galanin-IR nerve terminals established symmetric type synapses with the perikarya of proTRH-IR neurons, suggesting an inhibitory nature of these contacts. In contrast, GALP immunoreactive fibers and nerve terminals concentrated primarily in the anterior parvocellular subdivision of the PVN and were found in association with only few proTRH-IR neurons in the periventricular and medial parvocellular subdivisions. In conclusion, the dense innervation of TRH neurons in all subdivisions of the PVN by galanin-IR axons indicates that galanin may be involved in the central regulation of the hypothalamic-pituitary-thyroid axis. In contrast, the relative paucity of GALP-containing axons in juxtapsoition to TRH neurons in the medial and periventricular parvocellular subdivisions of the PVN, the origin of hypophysiotropic TRH neurons, makes it unlikely that GALP similarly exerts direct regulatory effects on hypophysiotropic TRH neurons.

Oestrogen receptor-beta and neurohypophysial hormones: functional interaction and neuroanatomical localisation

Oestrogens affect fluid balance, influencing both ingestive behaviour and renal excretion. The renal effects are partly due to altered release of vasopressin and oxytocin. This study was designed to explore the role of oestrogen receptor-beta (ERbeta) in neurohypophysial hormonal function. Following dietary administration, soya isoflavones reach the brain in sufficient concentration to activate ERbeta, but not oestrogen receptor-alpha (ERalpha). ERbeta function was therefore manipulated by feeding rat diets differing in soya isoflavone content. Fluid balance and neurohypophysial hormone release were measured in male rats maintained for 14 days on a soya isoflavone-free diet or one containing 150 microg/g genistein+daidzein. Food and water intake, body weight, urine flow, osmolality and sodium concentrations were determined daily. After 14 days, plasma and urine osmolality and sodium, vasopressin and oxytocin concentrations were determined. There was no significant difference in weight gain between the two groups or in their excretion of sodium and water or plasma sodium and plasma oxytocin. However, plasma vasopressin was significantly lower in the iso-free group. Double-label immunocytochemistry was used to assess colocalisation of ERbeta with the neurohypophysial hormones in male rats. Cell nuclei showing ERbeta immunoreactivity were abundant in the posterior magnocellular paraventricular nucleus (PVNpm) and in the supraoptic nucleus (SON). Vasopressin-immunoreactive neurones were similarly distributed, forming the core of the PVNpm and the ventral portion of the SON; majority were positive for ERbeta. Cells with oxytocin immunoreactivity were located mainly at the periphery of the PVNpm and in the dorsal SON; only approximately a quarter of these cells showed ERbeta immunoreactivity. Thus, the difference in the effects of the soya diet on vasopressin and oxytocin release may be related to the ERbeta-activating properties of this diet and to the preponderance of this receptor in vasopressin as opposed to oxytocin cells.

Ciliary neurotrophic factor in the olfactory bulb of rats and mice

Ciliary neurotrophic factor (CNTF) is primarily regarded as an astrocytic lesion factor, promoting neuronal survival and influencing plasticity processes in deafferented areas of the CNS. Postnatal loss of neurons in CNTF-deficient mice indicates a function of the factor also under physiological conditions. In the olfactory bulb, where neurogenesis, axo- and synaptogenesis continue throughout life, CNTF content is constitutively high. The cellular localization of CNTF in the rat olfactory bulb is not fully resolved, and species differences between mouse and rat are not yet characterized. In the present study, four different CNTF antibodies and double immunolabeling with specific markers for glial and neuronal cells were used to study the cellular localization of CNTF in rat and mouse olfactory bulb. Specificity of the detection was checked with tissue from CNTF-deficient mice, and investigations were complemented by immunolocalization of reporter protein in mice synthesizing beta-galactosidase under control of the CNTF promoter (CNTF lacZ-knock-in mice). In both species, CNTF localized to ensheathing cell nuclei, cell bodies and axon-enveloping processes. Additionally, individual axons of olfactory neurons were CNTF immunoreactive. Both CNTF protein content and immunoreaction intensity were lower in mice than in rats. Scattered lightly CNTF-reactive cells were found in the granular and external plexiform layers in rats. Some CNTF-positive cells were associated with immunoreactivity for the polysialylated form of the neural cell adhesion molecule, which is expressed by maturing interneurons derived from the rostral migratory stream. In CNTF lacZ-knock-in mice, beta-galactosidase reactivity was found in ensheathing cells of the olfactory nerve layer, and in cells of the glomerular, external plexiform and granular layers. The study proves that CNTF is localized in glial and neuronal structures in the rodent olfactory bulb. Results in mice provide a basis for investigations concerning the effects of a lack of the factor in CNTF-deficient mice.

Glucagon like peptide-1 (7-36) amide (GLP-1) nerve terminals densely innervate corticotropin-releasing hormone neurons in the hypothalamic paraventricular nucleus

Glucagon like peptide-1 (7-36) amide (GLP-1), a potent regulator of glucose homeostasis, is also produced in the central nervous system and has been implicated in the control of hypothalamic-pituitary function and food intake. GLP-1 immunoreactive (IR) fibers and terminals are widely distributed in the septum, hypothalamus, thalamus and brainstem, likely originating from GLP-1-IR neuronal cell bodies from the nucleus of the solitary tract of the medulla oblongata. Central administration of GLP-1 increases plasma corticosterone levels and elicits c-fos expression in corticotropin releasing hormone (CRH) neurons of the hypothalamic paraventricular nucleus (PVN). To identify the endogenous neurocircuitry that may underlie this response, the present study determined whether there is an innervation of PVN CRH neurons by GLP-1-containing nerve terminals. GLP-1-IR fibers and nerve terminals were found in the parvocellular parts of the PVN, with highest concentrations in the anterior and medial parvocellular subdivisions. The magnocellular divisions of the PVN also showed moderate numbers of GLP-1-IR nerve fibers. Double immunolabelling revealed numerous GLP-1-IR nerve fibers in close apposition to approximately 65% of detectable CRH neurons in the medial parvocellular subdivision of the rat PVN. At the ultrastructural level, GLP-1-IR terminals were observed to establish synapses on both perikarya and dendrites of CRH neurons. These findings support the hypothesis that the GLP-1-induced activation of CRH neurons and the associated pituitary-adrenocortical activation may be accomplished by GLP-1's direct action on hypophysiotropic CRH neurons. Since central CRH is also thought to be an anorexigenic factor and GLP-1 neurons contain leptin receptors, activation of CRH neurons in the PVN by GLP-1 may contribute to the complex neuroendocrine and metabolic actions by the adipostatic hormone, leptin.

Histamine-immunoreactive neurons of the tuberomammillary nucleus are innervated by alpha-melanocyte stimulating hormone-containing axons. Generation of a new histamine antiserum for ultrastructural studies

Leptin regulates the release of histamine in the hypothalamus, however, the histaminergic neurons contain few leptin receptors. To reveal that alpha-melanocyte stimulating hormone (alpha-MSH)-containing neurons of the arcuate nucleus may mediate the effects of leptin to the histaminergic neurons, we studied the putative innervation of histamine-immunoreactive (IR) neurons by alpha-MSH-containing axons using double-labeling immunocytochemistry. In order to analyze the relationship of alpha-MSH- and histamine-IR elements, we also generated an antiserum against histamine that is compatible with acrolein-based fixatives commonly used for immuno-electron microscopic studies. The apposition of alpha-MSH-IR axons to histaminergic neurons was observed in all five subnuclei of the tuberomammillary nucleus. Both axo-somatic and axo-dendritic contacts were found. At the ultrastructural level, silver-intensified colloidal gold particles identified the histaminergic neurons, whose ultrastructure was well preserved after fixation with acrolein demonstrating that the new antiserum is a useful tool for the ultrastructural examination of the histaminergic system. The histamine-IR cells received synaptic inputs from alpha-MSH-IR axon terminals visualized by diaminobenzidine. These data indicate that alpha-MSH-synthesizing neurons innervate histaminergic neurons in the tuberomammillary nucleus and may relay the hormonal influence of leptin to the histaminergic system.

Regulation of tyrosine hydroxylase levels and activity and Fos expression during opioid withdrawal in the hypothalamic PVN and medulla oblongata catecholaminergic cell groups innervating the PVN

Morphine withdrawal increases the hypothalamic-pituitary-adrenocortical (HPA) axis activity, which is dependent on an hyperactivity of noradrenergic pathways innervating the hypothalamic paraventricular nucleus (PVN). However, the possible adaptive changes that can occur in these pathways during morphine dependence are not known. We studied the alterations in tyrosine hydroxylase (TH; the rate-limiting enzyme in catecholamines biosynthesis) immunoreactivity levels and TH enzyme activity in the rat NTS-A2/VLM-A1 noradrenergic cell groups and in the PVN during morphine withdrawal. In the same paradigm, we measured Fos expression as a marker of neuronal activation. TH and Fos immunoreactivity was determined by quantitative Western blot analysis, combined with immunostaining for TH and Fos for immunohistochemical identification of active neurons during morphine withdrawal. Dependence on morphine was induced by a 7-day s.c. implantation of morphine pellets. Morphine withdrawal was precipitated on day 8 by an injection of naloxone (5 mg/kg s.c.). Morphine withdrawal induced the expression of Fos in the PVN and NTS/VLM, which indicates an activation of neurons in these nuclei. TH immunoreactivity in the NTS/VLM was increased 90 min after morphine withdrawal, whereas there was a decrease in TH levels in the PVN at the same time point. Following withdrawal, Fos immunoreactivity was present in most of the TH-positive neurons of the A2 and A1 neurons. TH activity was measured in the PVN, a projection area of noradrenergic neurons arising from NTS-A2/VLM-A1. Morphine withdrawal was associated with an increase in the enzyme activity at different time points after naloxone-precipitated morphine withdrawal. The present results suggest that an increase in TH protein levels and TH enzyme activity might contribute to the enhanced noradrenergic activity in the PVN in response to morphine withdrawal.

Impaired central stress-induced release of noradrenaline in rats with heart failure: a microdialysis study

Sympathetic hyperactivity in rats with heart failure is associated with increased extracellular noradrenaline in the hypothalamic paraventricular nucleus at rest. However, it is unknown how this nucleus responds to stressful stimuli. In the present study we therefore examined the basal and stress-induced release of noradrenaline in the paraventricular nucleus of conscious Sprague-Dawley rats with heart failure measured by in vivo microdialysis. Basal noradrenaline concentration in the paraventricular nucleus of rats with heart failure was more than double that in sham-operated controls. Immobilization stress decreases noradrenaline levels in the paraventricular nucleus of rats with heart failure to 57% of baseline, while it increased in sham-operated controls to 228%. However, serum corticosterone was similarly elevated at 30 and 90 min post-stress in both experimental groups. We have shown that heart failure causes an impairment of the central noradrenergic system's response to acute sympatho-excitation but does not affect the hypothalamo-pituitary-adrenocortical response.

GABA-ergic innervation of thyrotropin-releasing hormone-synthesizing neurons in the hypothalamic paraventricular nucleus of the rat

To determine whether GABA-ergic axons are anatomically situated to directly influence TRH neurons in the PVN, double-labeling light- and electronmicroscopic immunocytochemistry was performed using antisera against glutamic acid decarboxylase (GAD) and prothyrotropin-releasing hormone (proTRH). In the anterior, periventricular and medial parvocellular subdivisions of the PVN, GAD-immunoreactive (IR) axon varicosities were closely apposed to all proTRH containing cell bodies and proximal dendrites. Ultrastucturally, GAD-IR nerve terminals established symmetric type synapses with both perikarya and dendrites of proTRH-IR neurons, indicating the inhibitory nature of the contacts. Since a subpopulation of neuropeptide Y (NPY) neurons in the hypothalamic arcuate nucleus co-synthesize GABA, and NPY-containing neurons of arcuate nucleus origin densely innervate TRH neurons in the PVN, we performed triple labeling immunocytochemistry to elucidate the origin of the GAD-IR innervation of hypophysiotropic TRH neurons. While axons co-containing GAD and NPY were observed throughout the PVN, only approximately 10% of GAD-IR terminals in contact with TRH neurons were found to contain NPY-immunoreactivity. We conclude that GABA-ergic neurons are in position to act directly on hypophysiotropic TRH neurons and while this innervation arises partly from neurons in the arcuate nucleus that co-synthesize NPY, the majority of the GABA-ergic input arises from other neuronal groups.

Morphine withdrawal-induced c-fos expression in the hypothalamic paraventricular nucleus is dependent on the activation of catecholaminergic neurones

We previously demonstrated that morphine withdrawal induced hyperactivity of noradrenergic pathways innervating the hypothalamic paraventricular nucleus (PVN) in rats, in parallel with an increase in the neurosecretory activity of the hypothalamus-pituitary-adrenocortical (HPA) axis, as evaluated by corticosterone release. These neuroendocrine effects were dependent on stimulation of alpha-adrenoceptors. In the present study, Fos immunostaining was used as a reflection of neuronal activity and combined with immunostaining for tyrosine hydroxylase (TH) for immunohistochemical identification of active neurones during morphine withdrawal. Dependence on morphine was induced by 7-day chronic subcutaneous implantation of six morphine pellets (75 mg). Morphine withdrawal was precipitated by administration of naloxone (5 mg/kg subcutaneously) on day 8. Fos immunoreactivity in the PVN and also in the nucleus tractus solitarius (NTS)-A2 and ventrolateral medulla (VLM)-A1 cell groups, which project to the PVN, increased during morphine withdrawal. Following withdrawal, Fos immunoreactivity was present in most of the TH-positive neurones of the A2 and A1 neurones. In a second study, the effects of administration of adrenoceptor antagonists on withdrawal-induced Fos expression in the PVN were studied. Pre-treatment with alpha1- or alpha2-adrenoceptor antagonists, prazosin (1 mg/kg intraperitoneally) and yohimbine (1 mg/kg intraperitoneally), respectively, 20 min before naloxone administration to morphine-dependent rats markedly reduced Fos expression in the PVN. Similarly, pre-treatment with the beta antagonist, propranolol (3 mg/kg intraperitoneally), significantly prevented withdrawal-induced Fos expression. Collectively, these results suggest the hypothesis that noradrenergic neurones in the brainstem innervating the PVN are active during morphine withdrawal, and that activation of transcriptional responses mediated by Fos in the HPA axis following withdrawal are dependent upon hypothalamic alpha- and beta-adrenoceptors.

Met-enkephalin immunoreactive neurons recruited by acute stress are innervated by axon terminals immunopositive for tyrosine hydroxylase and dopamine-alpha-hydroxylase in the anterolateral division of bed nuclei of the stria terminalis in the rat

The bed nuclei of the stria terminalis (BST) are highly heterogeneous forebrain structures, which play a central role in the regulation/modulation of stress responses. Studies using the inducible immediate early gene c-fos as a marker of activated neurons have demonstrated significant stress-induced neuronal activation in this limbic region. The BST also exhibit a dense network of dopamine and noradrenaline immunoreactive (ir) axon terminals. These catecholaminergic projections from various brainstem sources to the BST play an important role in a neurochemically mediated coordination of stress responses. In the anterolateral division of bed nuclei of the stria terminalis, the distribution of several Met-enkephalin immunopositive perikarya overlaps with that of catecholaminergic axon terminals. Both monoaminergic and enkephalinergic structures have been postulated to play a role in the regulation/modulation of the central regulatory pathways of endocrine, behavioural and physiological responses during stress. Therefore the aims of this study were: (i). to study the possible involvement of dopaminergic fibre terminals in stress-induced activation of BST perikarya; (ii). to investigate whether Met-enkephalin-immunoreactive neurons are recruited by acute volumen/osmotic challenge; and (iii). to demonstrate synaptic interactions between Met-enkephalin-ir neurons and fibre terminals immunopositive for dopamine or noradrenaline in the anterolateral division of the BST. From the results of this study we can conclude that depletion of dopamine in fibre terminals completely abolished stress-induced activation of perikarya in the anterolateral division of BST. Furthermore, the innervation of stress-induced Met-enkephalin-ir perikarya by dopaminergic fibre terminals in the oval nucleus of BST was demonstrated, whereas noradrenergic axons contacted enkephalinergic structures in the fusiform and subcomissural nuclei of BST. These interactions can be central in the modulatory control of the major stress regulatory pathway, the limbic hypothalamo-pituitary-adrenal axis.

Differential Expression of the GABAA Receptor Complex in the Dorsal Thalamus and Reticular Nucleus: An Immunohistochemical Study in the Adult and Developing Rat

The distribution of the GABAA receptor/benzodiazepine receptor/chloride channel complex was investigated in the thalamus of the rat by means of immunohistochemistry in adulthood, as well as during embryonic and postnatal development, using a monoclonal antibody. In adults, the immunoreactivity for the GABAA receptor complex was intensely expressed by neuronal processes throughout the dorsal thalamus. Neuronal perikaryal membranes were frequently outlined by punctate immunostaining; cell bodies, intrathalamic fibre bundles and the internal capsule did not display immunoreactivity for the GABAA receptor. Regional differences in the expression of the receptor were consistently observed: the immunostaining was much lighter in the thalamic reticular nucleus than in the dorsal thalamic nuclei and, among the latter, the anteroventral nucleus and the ventral nuclear complex displayed the most intense immunopositivity. Immunostaining for the GABAA receptor was already expressed in embryos at E14, and was homogeneously distributed throughout the neuropil of the dorsal and ventral thalamic primordia. During the first two postnatal weeks, a regional differentiation of the immunopositivity was appreciable in the thalamus, with a progressive reduction in the reticular nucleus and a parallel increase in the dorsal thalamic structures. Immunoreactive neuronal perikarya were not observed in the thalamus at any developmental stage. The expression of the GABAA receptor complex appeared to have reached a mature configuration by the end of the third postnatal week. These findings indicate that in adults the GABAA receptor is differentially expressed by thalamic nuclear structures, including the reticular nucleus. Furthermore, the maturation of the receptor in the thalamus undergoes a rearrangement during the first postnatal weeks that results in a considerable regression within the reticular nucleus.

Corticotropin-releasing hormone-synthesizing neurons of the human hypothalamus receive neuropeptide Y-immunoreactive innervation from neurons residing primarily outside the infundibular nucleus

Immunohistochemical single- and double-labeling studies were performed on the hypothalami of postmortem human brains to elucidate the distribution of corticotropin-releasing hormone (CRH)-immunoreactive (IR) neuronal elements and their interaction with the neuropeptide Y (NPY)-ergic neuronal system. The great majority of CRH-IR perikarya were found in the paraventricular nucleus (PVN), whereas a considerable number of CRH-IR neurons were also observed in the periventricular and infundibular nuclei. The dorsomedial nucleus and the perifornical region contained only scattered CRH-IR neurons. Dense CRH-IR fiber networks were found throughout the hypothalamus. However, the medial preoptic, the dorsolateral part of the supraoptic, the suprachiasmatic, the ventromedial, and the different mammillary nuclei showed a relative paucity of fibers. The terminal fields of NPY-IR axons overlapped the distribution of CRH-IR neurons in the hypothalamus. NPY-IR axon varicosities were juxtaposed to both dendrites and perikarya of the majority of CRH-IR neurons residing in the paraventricular, periventricular, and infundibular nuclei. These neurons were frequently contacted by multiple NPY axons that either formed baskets around their perikarya or completely ensheathed the emanating CRH dendrites. Because NPY and agouti-related protein (AGRP) are co-contained in neurons of the human infundibular nucleus, we used AGRP as a marker of NPY fibers originating exclusively from the infundibular nucleus. Only a small proportion of CRH neurons in the PVN was contacted by AGRP-IR axon varicosities, suggesting that NPY-IR innervation of CRH neurons in the PVN derive mainly from regions outside the infundibular nucleus. The present morphological findings support the view that NPY regulates the CRH system of the human hypothalamus and therefore at least some of the effects of NPY on metabolic, autonomic, and endocrine functions may be mediated through CRH.

Prenatal opiate exposure: long-term CNS consequences in the stress system of the offspring

Our data show that prenatal morphine exposure induces long-term alterations in adult brain and behavior in both male and female rats, and these alterations are sex-specific. It is also evident that the alterations are not restricted to a single brain site or to a single neurotransmitter or neuromodulator. Moreover, there are long-term alterations in both the norepinephrine (NE) and opioid systems in several brain regions involved in stress responses and in the maintenance of homeostatic balance between the external environment, the brain and the rest of the body. Thus, this short paper reviews the prenatal morphine exposure data and highlights gaps in stress response to drug vulnerability/predisposition as an adult.

Efferent projections of ProTRH neurons in the ventrolateral periaqueductal gray

Our previous study has shown that prothyrotropin-releasing hormone (proTRH) gene expression is increased in the ventrolateral periaqueductal gray (PAG) neurons following precipitated morphine withdrawal and continues to be activated even 24 h after withdrawal. We have hypothesized that peptide products of proTRH may participate in the recovery from morphine withdrawal. To identify neuroanatomical substrates of the proposed action of proTRH-derived peptides originating from the ventrolateral PAG proTRH neurons, projections of these neurons were investigated by a series of anterograde and retrograde tract-tracing experiments. First, Phaseolus vulgaris-leucoagglutinin (PHA-L) was injected in the ventrolateral PAG in Sprague-Dawley rats. Following transport of the tracer, simultaneous immunolabeling for PHA-L and proTRH peptides was performed and mapped in discrete brain regions. PHA-L-immunoreactive (IR) fibers showing preterminal and terminal-like arborization that contained proTRH were identified in the dorsolateral and lateral PAG, deep layer of superior colliculus (CS), parafascicular nucleus (PF), ventromedial zona incerta (ZI) and at the border of the locus coeruleus (LC) and Barrington's nucleus. Scattered double-labeled fibers were present in the lateral septal nucleus, ventromedial preoptic nucleus, lateral hypothalamus, perifornical area and in the periventricular region at the diencephalon/midbrain junction. The retrogradely transported marker, cholera toxin beta-subunit (CTb) was then injected in the dorsolateral PAG, CS, PF, ZI and medial to the LC. Double-labeled perikarya for both CTb and proTRH in the ventrolateral PAG were found for each region injected with CTb, corroborating the findings by the anterograde tracing experiment. These studies demonstrate that proTRH neurons in the ventrolateral PAG project to several regions of the brain that are involved in autonomic and behavioral regulation and thereby, may function as an integrating center to coordinate responses to opiate withdrawal.

Light and electron microscopic study of cholinergic and noradrenergic elements in the basolateral nucleus of the rat amygdala: evidence for interactions between the two systems

Pharmacological studies have suggested that the cholinergic (ACh) and noradrenergic (NA) systems in the amygdala (AM) play an important role in learning and memory storage and that the two systems interact to modulate memory storage. To obtain anatomical evidence for the interaction, the organization of the ACh and NA fibers in rat AM was investigated by immunocytochemistry for choline acetyltransferase (ChAT) and dopamine-beta-hydroxylase (DBH) in conjunction with light, confocal laser scanning, and electron microscopy (LM, CLSM, and TEM, respectively). LM showed that the ChAT immunoreactivity was densest in the basolateral nucleus (BL), whereas the DBH immunoreactivity was densest in the posterior BL. CLSM demonstrated that the ChAT-immunoreactive profiles in the BL were frequently located in juxtaposition to the DBH-immunoreactive axons. The TEM observations were as follows: The majority of the synapses formed by ChAT-immunoreactive terminals were symmetric, but DBH-immunoreactive axons formed both asymmetric and symmetric synapses. The ChAT-immunoreactive terminals usually established the symmetric synaptic contacts with the DBH-immunoreactive terminals and varicosities. The DBH-immunoreactive terminals formed the asymmetric synapses with the ChAT-immunoreactive dendrites of the intrinsic neurons within the AM. The results provide anatomical substrates for mnemonic functions of the ACh and NA systems and for the interactions between the two systems in the AM.

Axon terminals containing tyrosine hydroxylase- and dopamine-beta-hydroxylase immunoreactivity form synapses with galanin immunoreactive neurons in the lateral division of the bed nucleus of the stria terminalis in the rat

Catecholaminergic projections from brainstem sources to the bed nucleus of the stria terminalis play a central role in the neurochemically mediated modulation/regulation of stress response. The lateral division of the bed nucleus of the stria terminalis (BSTL) exhibits several galanin immunoreactive (ir) neurons that are also central in the modulatory control of acute stress responses. The distribution of galaninergic nervous structures overlaps with that of the dopaminergic and noradrenergic axon terminals in the BSTL. Since both monoamines and galanin regulate/modulate the central regulatory pathways of endocrine, behavioral and physiological responses during stress, the aim of this study was to demonstrate synaptic interaction between galanin-ir nervous structures and fiber terminals immunopositive for dopamine or noradrenaline in the BSTL, thereby providing morphological data to understand better the significance of catecholamine-galanin interactions in brain areas responding to stressful stimuli. Double-labeling immunohistochemistry applied both at light and electron microscopic levels made it possible to demonstrate synaptic interactions between galanin-ir nervous structures and axon terminals immunopositive for either dopamine or noradrenaline. The dopaminergic fiber terminals innervated galanin-ir cells and dendrites in the laterodorsal division of the bed nucleus of the stria terminalis (BST), whereas the noradrenergic axons contacted galaninergic neurons and dendrites in the lateroventral BST. In this study, interactions between monoamines and galanin-ir structures were demonstrated in the BSTL which can be central in the modulatory control of the major stress regulatory pathway of the limbic-hypothalamo-pituitary-adrenal axis.