Contribution of dopamine neurons in the medial zona incerta to the innervation of the central nucleus of the amygdala, horizontal diagonal band of Broca and hypothalamic paraventricular nucleus

Windows into stress: a glimpse at emerging roles for CRHPVN neurons

The corticotropin-releasing hormone cells in the paraventricular nucleus of the hypothalamus (CRH^PVN) control the slow endocrine response to stress. The synapses on these cells are exquisitely sensitive to acute stress, leveraging local signals to leave a lasting imprint on this system. Additionally, recent work indicates that these cells also play key roles in the control of distinct stress and survival behaviors. Here we review these observations and provide a perspective on the role of CRH^PVN neurons as integrative and malleable hubs for behavioral, physiological, and endocrine responses to stress.

The hypothalamic paraventricular nucleus as a central hub for the estrogenic modulation of neuroendocrine function and behavior

Estradiol and hypothalamic paraventricular nucleus (PVN) help coordinate reproduction with body physiology, growth and metabolism. PVN integrates hormonal and neural signals originating in the periphery, generating an output mediated both by its long-distance neuronal projections, and by a variety of neurohormones produced by its magnocellular and parvocellular neurosecretory cells. Here we review the cyto-and chemo-architecture, the connectivity and function of PVN and the sex-specific regulation exerted by estradiol on PVN neurons and on the expression of neurotransmitters, neuromodulators, neuropeptides and neurohormones in PVN. Classical and non-classical estrogen receptors (ERs) are expressed in neuronal afferents to PVN and in specific PVN interneurons, projecting neurons, neurosecretory neurons and glial cells that are involved in the input-output integration and coordination of neurohormonal signals. Indeed, PVN ERs are known to modulate body homeostatic processes such as autonomic functions, stress response, reproduction, and metabolic control. Finally, the functional implications of the estrogenic modulation of the PVN for body homeostasis are discussed.

Heterosynaptic modulation in the paraventricular nucleus of the hypothalamus

The stress response-originally described by Hans Selye as "the nonspecific response of the body to any demand made upon it"-is chiefly mediated by the hypothalamic-pituitary-adrenal (HPA) axis and is activated by diverse sensory stimuli that inform threats to homeostasis. The diversity of signals regulating the HPA axis is partly achieved by the complexity of afferent inputs that converge at the apex of the HPA axis: this apex is formed by a group of neurosecretory neurons that synthesize corticotropin-releasing hormone (CRH) in the paraventricular nucleus of the hypothalamus (PVN). The afferent synaptic inputs onto these PVN-CRH neurons originate from a number of brain areas, and PVN-CRH neurons respond to a long list of neurotransmitters/neuropeptides. Considering this complexity, an important question is how these diverse afferent signals independently and/or in concert influence the excitability of PVN-CRH neurons. While many of these inputs directly act on the postsynaptic PVN-CRH neurons for the summation of signals, accumulating data indicates that they also modulate each other's transmission in the PVN. This mode of transmission, termed heterosynaptic modulation, points to mechanisms through which the activity of a specific modulatory input (conveying a specific sensory signal) can up- or down-regulate the efficacy of other afferent synapses (mediating other stress modalities) depending on receptor expression for and spatial proximity to the heterosynaptic signals. Here, we review examples of heterosynaptic modulation in the PVN and discuss its potential role in the regulation of PVN-CRH neurons' excitability and resulting HPA axis activity. This article is part of the Special Issue entitled 'Hypothalamic Control of Homeostasis'.

Magnocellular Neurons and Posterior Pituitary Function

The posterior pituitary gland secretes oxytocin and vasopressin (the antidiuretic hormone) into the blood system. Oxytocin is required for normal delivery of the young and for delivery of milk to the young during lactation. Vasopressin increases water reabsorption in the kidney to maintain body fluid balance and causes vasoconstriction to increase blood pressure. Oxytocin and vasopressin secretion occurs from the axon terminals of magnocellular neurons whose cell bodies are principally found in the hypothalamic supraoptic nucleus and paraventricular nucleus. The physiological functions of oxytocin and vasopressin depend on their secretion, which is principally determined by the pattern of action potentials initiated at the cell bodies. Appropriate secretion of oxytocin and vasopressin to meet the challenges of changing physiological conditions relies mainly on integration of afferent information on reproductive, osmotic, and cardiovascular status with local regulation of magnocellular neurons by glia as well as intrinsic regulation by the magnocellular neurons themselves. This review focuses on the control of magnocellular neuron activity with a particular emphasis on their regulation by reproductive function, body fluid balance, and cardiovascular status. © 2016 American Physiological Society. Compr Physiol 6:1701-1741, 2016.

The Modulating Role of Stress in the Onset and Course of Tourette’s Syndrome

Accumulating data indicate a common occurrence of tic exacerbations and periods of psychosocial stress. Patients with Tourette’s syndrome (TS) also exhibit aberrant markers of hypothalamic-pituitary-adrenal (HPA) axis activation. Based on these findings, a functional relationship between stress and tic disorders has been suggested, but the underlying mechanism of how stress may affect tic pathology remains to be elucidated. We suggest that dopaminergic and noradrenergic neurotransmission as well as immunology play a crucial role in mediating this relationship. Two possibilities of causal direction might be assumed: (a) psychosocial stress might lead to an exacerbation of tics via activation of HPA axis and subsequent changes in neurotransmission or immunology and (b) TS-related abnormalities in neurotransmission or immunology result in a higher vulnerability of affected patients to respond to psychosocial stress with a strong activation of the HPA axis. It may also be the case that both assumptions hold true and interact with each other.

Physiological regulation of magnocellular neurosecretory cell activity: integration of intrinsic, local and afferent mechanisms

The hypothalamic supraoptic and paraventricular nuclei contain magnocellular neurosecretory cells (MNCs) that project to the posterior pituitary gland where they secrete either oxytocin or vasopressin (the antidiuretic hormone) into the circulation. Oxytocin is important for delivery at birth and is essential for milk ejection during suckling. Vasopressin primarily promotes water reabsorption in the kidney to maintain body fluid balance, but also increases vasoconstriction. The profile of oxytocin and vasopressin secretion is principally determined by the pattern of action potentials initiated at the cell bodies. Although it has long been known that the activity of MNCs depends upon afferent inputs that relay information on reproductive, osmotic and cardiovascular status, it has recently become clear that activity depends critically on local regulation by glial cells, as well as intrinsic regulation by the MNCs themselves. Here, we provide an overview of recent advances in our understanding of how intrinsic and local extrinsic mechanisms integrate with afferent inputs to generate appropriate physiological regulation of oxytocin and vasopressin MNC activity.

Brainstem origins of glutamatergic innervation of the rat hypothalamic paraventricular nucleus

Multiple lines of evidence document a role for glutamatergic input to the hypothalamic paraventricular nucleus (PVH) in stress-induced activation of the hypothalamic-pituitary-adrenocortical (HPA) axis. However, the neuroanatomical origins of the glutamatergic input have yet to be definitively determined. We have previously shown that vesicular glutamate transporter 2 (VGLUT2) is the predominant VGLUT isoform expressed in the basal forebrain and brainstem, including PVH-projecting regions, and that the PVH is preferentially innervated by VGLUT2-immunoreactive terminals/boutons. The present study employed a dual-labeling approach, combining immunolabeling for a retrograde tract tracer, Fluoro-Gold (FG), with in situ hybridization for VGLUT2 mRNA, to map the brainstem and caudal forebrain distribution of glutamatergic PVH-projecting neurons. The present report presents evidence for substantial dual labeling in the periaqueductal gray, caudal portions of the zona incerta and subparafascicular nucleus, and the lateral parabrachial nucleus. The current data also suggest that relatively few PVH-projecting neurons in ascending raphe nuclei, nucleus of the solitary tract, or ventrolateral medulla are VGLUT2 positive. The data reveal multiple brainstem origins of glutamatergic input to PVH that are positioned to play a role in transducing a diverse range of stressful stimuli.

L-amino acid decarboxylase- and tyrosine hydroxylase-immunoreactive cells in the extended olfactory amygdala and elsewhere in the adult prairie vole brain

Neurons synthesizing dopamine (DA) are widely distributed in the brain and implicated in a tremendous number of physiological and behavioral functions, including socioreproductive behaviors in rodents. We have recently been investigating the possible involvement of sex- and species-specific TH-immunoreactive (TH-ir) cells in the male prairie vole (Microtus ochrogaster) principal bed nucleus of the stria terminalis (pBST) and posterodorsal medial amygdala (MeApd) in the chemosensory control of their monogamous pairbonding and parenting behaviors. These TH-ir cells are not immunoreactive for dopamine-beta-hydroxylase (DBH), suggesting they are not noradrenergic but possibly DAergic. A DAergic phenotype would require them to contain aromatic L-amino acid decarboxylase (AADC) and here we examined the existence of cells immunoreactive for both TH and AADC in the pBST and MeApd of adult virgin male and female prairie voles. We also investigated the presence of TH/AADC cells in the anteroventral periventricular nucleus (AVPV), medial preoptic area (MPO), arcuate nucleus (ARH), zona incerta (ZI), substantia nigra (SN) and ventral tegmental area (VTA). Among our findings were: (1) the pBST and MeApd each contained completely non-overlapping distributions of TH-ir and AADC-ir cells, (2) the AVPV contained surprisingly few AADC-ir cells and almost no TH-ir cells contained AADC-ir, (3) approximately 60% of the TH-ir cells in the MPO, ARH, and ZI also contained AADC-ir, (4) unexpectedly, only about half of TH-ir cells in the SN and VTA contained AADC-ir, and (5) notable populations of AADC-ir cells were found outside traditional monoamine-synthesizing regions, including some sites that do not contain AADC-ir cells in adult laboratory rats or cats (medial septum and cerebral cortex). In the absence of the chemical requirements to produce DA, monoenzymatic TH-ir cells in the virgin adult prairie vole pBST, MeApd, and elsewhere in their brain may instead produce L-DOPA as an end product and use it as a neurotransmitter or neuromodulator, similar to what has been observed for monoenzymatic TH-synthesizing cells in the laboratory rat brain.

Intra-ventral tegmental area or intracerebroventricular orexin-A increases the intra-cranial self-stimulation threshold via activation of the corticotropin-releasing factor system in rats

Although orexin-A peptide was recently found to inhibit the brain reward system, the exact neural substrates for this phenomenon remain unclear. The aim of the present study was to investigate the role of orexin neurons in intra-cranial self-stimulation behavior and to clarify the pathways through which orexin-A inhibits the brain reward system. Immunohistochemical examination using Fos, a neuronal activation marker, revealed that the percentage of activated orexin cells was very low in the lateral hypothalamus even in the hemisphere ipsilateral to self-stimulation, suggesting that orexin neurons play only a small part, if any, in performing intra-cranial self-stimulation behavior. Intra-ventral tegmental area administration of orexin-A (1.0 nmol) significantly increased the intra-cranial self-stimulation threshold. Furthermore, the threshold-increasing effects of intra-ventral tegmental area or intracerebroventricular orexin-A were inhibited by administration of the nonspecific corticotropin-releasing factor receptor antagonist, d-Phe-CRF(12-41) (20 μg). Following intra-ventral tegmental area infusion of orexin-A, the percentage of cells double-labeled with corticotropin-releasing factor and Fos antibodies increased in the central nucleus of the amygdala but not in the bed nucleus of the stria terminalis, and brain microdialysis analyses indicated that dopamine efflux in both the central nucleus of the amygdala and bed nucleus of the stria terminalis were enhanced. Taken together, the present findings suggest that intra-ventral tegmental area or intracerebroventricular administration of orexin-A exerts its threshold-increasing effect via subsequent activation of the corticotropin-releasing factor system.

Circadian nursing induces PER1 protein in neuroendocrine tyrosine hydroxylase neurones in the rabbit doe

Rabbit does nurse their pups once a day with circadian periodicity and pups ingest up to 35% of their body weight in milk in < 5 min. In the doe, there is a massive release of prolactin. We hypothesised that periodic suckling synchronises dopaminergic populations that control prolactin secretion. We explored this by immunohistochemical colocalisation of PER1 protein, the product of the clock gene Per1 on tyrosine hydroxylase (TH) cells in three dopaminergic populations: tuberoinfundibular dopaminergic (TIDA), periventricular hypophyseal dopaminergic (PHDA) and incertohypothalamic dopaminergic (IHDA) cells. PER1/TH colocalisation was explored every 4 h through a complete 24-h cycle at postpartum day 7 in does that nursed their pups either at 10.00 h (ZT03) or at 02.00 h (ZT19; ZT0 = 07.00 h, time of lights on). Nonpregnant, nonlactating females were used as controls. In control females, there was a rhythm of PER1 that peaks at ZT15. By contrast, in nursed does, the PER1 peak shifted in parallel to scheduled nursing in TIDA and PHDA cells but not in IHDA cells, which are not related to the control of prolactin. Next, we determined that the absence of suckling for 48 h significantly decreases the number of PER1/TH colocalised cells in PHDA but not TIDA cells. Locomotor behaviour in control subjects was maximal at around the time of lights on but, in nursed females, shifted at around the time of scheduled nursing. Finally, in the suprachiasmatic nucleus, there is a maximal expression of PER1 at ZT11 in the three groups. However, this maximal expression was significantly lower in the nursed groups in relation to the control group and in the groups deprived of nursing for 48 h. We conclude that suckling synchronises dopaminergic cells related to the control of prolactin and appears to be a nonphotic stimulus for the suprachiasmatic nucleus.

Genetics of aggression in voles

Prairie voles (Microtus ochrogaster) are socially monogamous rodents that form pair bonds-a behavior composed of several social interactions including attachment with a familiar mate and aggression toward conspecific strangers. Therefore, this species has provided an excellent opportunity for the study of pair bonding behavior and its underlying neural mechanisms. In this chapter, we discuss the utility of this unique animal model in the study of aggression and review recent findings illustrating the neurochemical mechanisms underlying pair bonding-induced aggression. Implications of this research for our understanding of the neurobiology of human violence are also discussed.

Tuberoinfundibular peptide of 39 residues- immunoreactive fibers in the zona incerta and the supraoptic decussations terminate in the neuroendocrine hypothalamus

Tuberoinfundibular peptide of 39 residues (TIP39) is expressed by neurons in the subparafascicular area, the posterior intralaminar complex of the thalamus and the pontine medial paralemniscal nucleus. TIP39-positive fibers from these areas do not form individual bundles or fascicles, they join other pathways to reach their innervated brain areas. Fibers arise from TIP39 perikarya located in the subparafascicular area and the posterior intralaminar complex of the thalamus could be followed to the hypothalamus. After uni- and bilateral posterolateral surgical deafferentations of the hypothalamus, accumulation of TIP39 immunoreactivity was observed in the fibers caudal to the knife cut, while it disappeared completely rostral to the transection. In serial sections of the forebrain, we could follow TIP39-ir fibers coursing within the zona incerta and the supraoptic decussations. TIP39-positive fibers that join the incerto-hypothalamic pathway reach the medio-dorsal part of the hypothalamus and form moderate to high density networks in the dorsomedial and paraventricular nuclei. The other set of TIP39-positive axons from the subthalamic area join the fibers of the supraoptic decussations and run in an antero-medial direction through the most ventral portion of the hypothalamus up to the retrochiasmatic area, where they crossover. A certain portion of these TIP39-positive fibers terminates in the territories of the arcuate and the medial preoptic nuclei, as well as in the retrochiasmatic area.

Dopaminergic neurons expressing Fos during waking and paradoxical sleep in the rat

Formerly believed to contribute to behavioural waking (W) alone, dopaminergic (DA) neurons are now also known to participate in the regulation of paradoxical sleep (PS or REM) in mammals. Indeed, stimulation of postsynaptic DA1 receptors with agonists induces a reduction in the daily amount of PS. DA neurons in the ventral tegmental area were recently shown to fire in bursts during PS, but nothing is known about the activity of the other DA cell groups in relation to waking or PS. To fulfil this gap, we used a protocol in which rats were maintained in continuous W for 3h in a novel environment, or specifically deprived of PS for 3 days with some of them allowed to recover from this deprivation. A double immunohistochemical labeling with Fos and tyrosine hydroxylase was then performed. DA neurons in the substantia nigra (A9) and ventral tegmental area (A10), and its dorsocaudal extension in the periaqueductal gray (A10dc), almost never showed a Fos-immunoreactive nucleus, regardless of the experimental condition. The caudal hypothalamic (A11) group showed a moderate activation after PS deprivation and novel environment. During PS-recovery, the zona incerta (A13) group contained a significant number and percentage of double-labeled neurons. These results suggest that some DA neurons (A11) could participate in waking and/or the inhibition of PS during PS deprivation whereas others (A13) would be involved in the control of PS.

Dopamine D1 and D2 dopamine receptors regulate immobilization stress-induced activation of the hypothalamus-pituitary-adrenal axis

RATIONALE

Whereas the role of most biogenic amines in the control of the hypothalamus-pituitary-adrenal (HPA) response to stress has been extensively studied, the role of dopamine has not.

OBJECTIVES

We studied the effect of different dopamine receptor antagonists on HPA response to a severe stressor (immobilization, IMO) in adult male Sprague-Dawley rats.

RESULTS

Haloperidol administration reduced adrenocorticotropin hormone and corticosterone responses to acute IMO, particularly during the post-IMO period. This effect cannot be explained by a role of dopamine to maintain a sustained activation of the HPA axis as haloperidol did not modify the response to prolonged (up to 6 h) IMO. Administration of more selective D1 and D2 receptor antagonists (SCH23390 and eticlopride, respectively) also resulted in lower and/or shorter lasting HPA response to IMO.

CONCLUSIONS

Dopamine, acting through both D1 and D2 receptors, exerts a stimulatory role on the activation of the HPA axis in response to a severe stressor. The finding that dopamine is involved in the maintenance of post-stress activation of the HPA axis is potentially important because the actual pathological impact of HPA activation is likely to be related to the area under the curve of plasma glucocorticoid levels, which is critically dependent on how long after stress high levels of glucocorticoid are maintained.

Association of body mass and brain activation during gastric distention: implications for obesity

Background

Gastric distention (GD), as it occurs during meal ingestion, signals a full stomach and it is one of the key mechanisms controlling food intake. Previous studies on GD showed lower activation of the amygdala for subjects with higher body mass index (BMI). Since obese subjects have dopaminergic deficits that correlate negatively with BMI and the amygdala is innervated by dopamine neurons, we hypothesized that BMI would correlate negatively with activation not just in the amygdala but also in other dopaminergic brain regions (midbrain and hypothalamus).

Methodology/Principal Findings

We used functional magnetic resonance imaging (fMRI) to evaluate brain activation during GD in 24 healthy subjects with BMI range of 20–39 kg/m². Using multiple regression and cross-correlation analyses based on a family-wise error corrected threshold P = 0.05, we show that during slow GD to maximum volumes of 500 ml and 700 ml subjects with increased BMI had increased activation in cerebellum and left posterior insula, and decreased activation of dopaminergic (amygdala, midbrain, hypothalamus, thalamus) and serotonergic (pons) brain regions and anterior insula, regions that were functionally interconnected with one another.

Conclusions

The negative correlation between BMI and BOLD responses to gastric distention in dopaminergic (midbrain, hypothalamus, amygdala, thalamus) and serotonergic (pons) brain regions is consistent with disruption of dopaminergic and serotonergic signaling in obesity. In contrast the positive correlation between BMI and BOLD responses in posterior insula and cerebellum suggests an opposing mechanism that promotes food intake in obese subjects that may underlie their ability to consume at once large food volumes despite increasing gastric distention.

Catecholaminergic systems in stress: structural and molecular genetic approaches

Stressful stimuli evoke complex endocrine, autonomic, and behavioral responses that are extremely variable and specific depending on the type and nature of the stressors. We first provide a short overview of physiology, biochemistry, and molecular genetics of sympatho-adrenomedullary, sympatho-neural, and brain catecholaminergic systems. Important processes of catecholamine biosynthesis, storage, release, secretion, uptake, reuptake, degradation, and transporters in acutely or chronically stressed organisms are described. We emphasize the structural variability of catecholamine systems and the molecular genetics of enzymes involved in biosynthesis and degradation of catecholamines and transporters. Characterization of enzyme gene promoters, transcriptional and posttranscriptional mechanisms, transcription factors, gene expression and protein translation, as well as different phases of stress-activated transcription and quantitative determination of mRNA levels in stressed organisms are discussed. Data from catecholamine enzyme gene knockout mice are shown. Interaction of catecholaminergic systems with other neurotransmitter and hormonal systems are discussed. We describe the effects of homotypic and heterotypic stressors, adaptation and maladaptation of the organism, and the specificity of stressors (physical, emotional, metabolic, etc.) on activation of catecholaminergic systems at all levels from plasma catecholamines to gene expression of catecholamine enzymes. We also discuss cross-adaptation and the effect of novel heterotypic stressors on organisms adapted to long-term monotypic stressors. The extra-adrenal nonneuronal adrenergic system is described. Stress-related central neuronal regulatory circuits and central organization of responses to various stressors are presented with selected examples of regulatory molecular mechanisms. Data summarized here indicate that catecholaminergic systems are activated in different ways following exposure to distinct stressful stimuli.

Role of neuronal nitric oxide in the regulation of vasopressin expression and release in response to inhibition of catecholamine synthesis and dehydration

We used neuronal nitric oxide synthase (nNOS) gene knockout mice to study the effects of catecholamines and neuronal nitric oxide on vasopressin expression in the hypothalamic neurosecretory centers. nNOS gene deletion did not change the level of vasopressin mRNA in the supraoptic or paraventricular nuclei. In contrast, vasopressin immunoreactivity was lower in nNOS deficient mice than in wild-type animals. Dehydration increased vasopressin mRNA levels and decreased vasopressin immunoreactivity in both wild-type and nNOS knockout mice, but these responses were more marked in the nNOS knockout mice. Treatment with alpha-mpt, a pharmacologic inhibitor of catecholamine synthesis, resulted in increased vasopressin mRNA levels in wild-type mice and in reduced vasopressin immunoreactivity in both wild-type and nNOS knockout mice. From these results, we conclude: (1) neuronal nitric oxide suppresses vasopressin expression under basal conditions and during activation of the vasopressinergic system by dehydration; (2) catecholamines limit vasopressin expression; (3) nNOS is required for the effects of catecholamines on vasopressin expression.

Connectivity pattern suggests that incerto-hypothalamic area belongs to the medial hypothalamic system

The incerto-hypothalamic area (IHy) is a poorly defined diencephalic region located at the junction of the medial hypothalamus and zona incerta (ZI). This region is characterized by the presence of the A13 dopaminergic group and also cells expressing melanin-concentrating hormone (MCH) and cocaine- and amphetamine-regulated transcript (CART). The dopaminergic neurons appear to influence luteinizing hormone secretion, but the role of the MCH/CART-expressing cells is unclear. Even though IHy presents a singular neurochemistry, it has long been assumed that it is also part of the zona incerta. By injecting biotinylated dextran amine into the IHy and ZI of adult male Wistar rats, we analyzed the efferent projections from the IHy in comparison to the ZI. We have found that ZI projects mainly to laterally located brain stem structures, whereas the main efferents from the IHy are the reuniens thalamic nucleus, precommissural nucleus, posterior hypothalamic area and dorsolateral periaqueductal gray matter. The IHy projection pattern is quite similar to that of the anterior hypothalamic area and our hodological results suggest that IHy belongs to the medial hypothalamic system and might be part of the defensive behavior system. The IHy could be an integrative area associated with the regulation of neuroendocrine functions related to motivated behaviors, which are mediated by the medial hypothalamus.

The involvement of dopamine in the modulation of sleep and waking

Dopamine (DA)-containing neurons involved in the regulation of sleep and waking (W) arise in the ventral tegmental area (VTA) and the substantia nigra pars compacta (SNc). The VTA and SNc cells have efferent and afferent connections with the dorsal raphe nucleus (DRN), the pedunculopontine and laterodorsal tegmental nuclei (PPT/LDT), the locus coeruleus (LC), the lateral and posterior hypothalamus (LH), the basal forebrain (BFB), and the thalamus. Molecular cloning techniques have enabled the characterization of two distinct groups of DA receptors, D(1)-like and D(2)-like receptors. The D(1) subfamily includes the D(1) and D(5) receptors, whereas the D(2) subfamily comprises the D(2), D(3), and D(4) receptors. Systemic administration of a selective D(1) receptor agonist induces behavioral arousal, together with an increase of W and a reduction of slow wave sleep (SWS) and REM sleep (REMS). Systemic injection of a DA D(2) receptor agonist induces biphasic effects, such that low doses reduce W and increase SWS and REMS (predominant activation of the D(2) autoreceptor), whereas large doses induce the opposite effect (predominant facilitation of the D(2) postsynaptic receptor). Compounds with DA D(1) or D(2) receptor blocking properties augment non-REMS and reduce W. Preliminary findings tend to indicate that the administration of a DA D(3)-preferring agonist induces somnolence and sleep in laboratory animals and man. DA neurons in the VTA and the SNc do not change their mean firing rate across the sleep-wake cycle. It has been proposed that DA cells in the midbrain show a change in temporal pattern rather than firing rate during the sleep-wake cycle. The available evidence tends to indicate that during W there occurs an increase of burst firing activity of DA neurons, and an enhanced release of DA in the VTA, the nucleus accumbens (NAc), and a number of forebrain structures. A series of structures relevant for the regulation of the behavioral state, including the DRN, LDT/PPT, LC, and LH, could be partly responsible for the changes in the temporal pattern of activity of DA neurons.

Dopamine and monogamy

Social attachments play a central role in human society. In fact, such attachments are so important that deficits in the ability to form meaningful social bonds are associated with a variety of psychological disorders. Although mother-infant bonding has been studied for many years, we only recently have begun to examine the processes that underlie social bonds between adults. Over the past decade, central dopamine has become a focus of such research, especially its role in pair bonding between mates in species that display monogamous life strategies. Neuroanatomical and pharmacological studies in rodents have firmly established central dopamine systems, especially the mesocorticolimbic dopamine circuitry, in the formation, expression, and maintenance of monogamous pair bonds. As this research has progressed, it has become apparent that there is considerable overlap between the processes that underlie pair bonding and those that mediate responses to abused substances. This suggests that social bonding and substance abuse each may affect the other. Herein we review the current state of knowledge of central dopamine involvement in pair bond formation, expression, and maintenance. We first describe the neuroanatomical substrate within which dopamine exerts its effects on social bonding. We then describe dopamine receptor subtype-specific influences on pair bonding and how dopamine receptor activation may interact with activation of other neurochemical systems. Finally, we describe possible interactions between social bonding and substance abuse.

Acute and repeated cocaine induces alterations in FosB/DeltaFosB expression in the paraventricular nucleus of the hypothalamus

Apart from activation of the brain reward system, cocaine administration influences the activity of the hypothalamo-pituitary-adrenal (HPA) axis by affecting CRH neurons in the paraventricular nucleus of the hypothalamus (PVN). In order to find a molecular mechanism of cocaine-evoked effects in the PVN, in the present study, we investigated the impact of cocaine on the expression of FosB/DeltaFosB transcription factors in the PVN. Using an immunohistochemical method, we found that acute cocaine treatment (25 mg/kg) induced a relatively long-lasting (at least 72 h) expression of FosB/DeltaFosB in the PVN, whereas repeated cocaine administration (25 mg/kg, once daily for 5 consecutive days) caused accumulation of FosB/DeltaFosB in the PVN. The latter observation was further confirmed by the Western blot technique which revealed that repeated exposure to cocaine specifically increased the expression of a stable isoform of DeltaFosB (35 kDa). Using a double-labeling immunofluorescent method, it was established that FosB/DeltaFosB proteins induced by repeated cocaine treatment were present in a small population of CRF-immunoreactive neurons of the PVN. Furthermore, it was found that pretreatment with the specific antagonist of dopamine D1-like receptors SCH 23390 (1 mg/kg) attenuated the expression and accumulation of FosB/DeltaFosB in the PVN, evoked by repeated cocaine administration. Although functional consequences of the above effects for the process of addiction remain to be established, the obtained results indicate that cocaine administration can produce relatively long-lasting changes in the expression of FosB/DeltaFosB transcription factors in PVN neurons (in some populations of CRF-immunoreactive neurons, among others) and that dopamine D1-like receptors are involved in the above effects. Finally, it is proposed that the long-lasting expression as well as the accumulation of DeltaFosB in the PVN may constitute a molecular basis underlying adaptive changes occurring in the HPA axis after relatively high doses of cocaine.

Tyrosine hydroxylase-synthesizing cells in the hypothalamus of prairie voles (Microtus ochrogaster): sex differences in the anteroventral periventricular preoptic area and effects of adult gonadectomy or neonatal gonadal hormones

The vertebrate hypothalamus and surrounding region contain a large population of cells expressing tyrosine hydroxylase (TH), the rate limiting enzyme for synthesis of dopamine and other catecholamines. Some of these populations are sexually dimorphic in rats. We here examined sex differences in TH-immunoreactive populations in the forebrain of gonadally intact and gonadectomized prairie voles (Microtus ochrogaster), a species that sometimes shows unusual sexual differentiation of brain and behavior. A sex difference was found in the anteroventral periventricular preoptic area (AVPV; likely analogous to the rat rostral A14) only in gonadectomized subjects, which was due to a 50% reduction in the number of TH-immunoreactive cells after castration in males. There was no significant sex difference or effects of gonadectomy on the number of TH-immunoreactive cells in the anteroventral preoptic area (AVP), periventricular anterior hypothalamus (caudal A14), arcuate nucleus (A12), zona incerta (A13), or posterodorsal hypothalamus (A11). In a second experiment, testosterone propionate (TP; 500 microg), diethylstilbestrol (DES; 1 microg), or estradiol benzoate (EB; 30 microg) injected daily during the first week after birth each significantly reduced later TH expression in the AVPV of females by approximately 40-65% compared to oil-treated controls. Unlike rats, therefore, a sex difference in TH expression in the prairie vole AVPV is found only after removal of circulating gonadal hormones in males. Furthermore, unlike our previous findings on the generation of sex differences in extra-hypothalamic arginine-vasopressin expression in prairie voles, TH expression in the AVPV of female prairie voles can be highly masculinized by neonatal exposure to either aromatizable androgens or estrogens.

Distribution of corticotropin-releasing factor binding protein-immunoreactivity in the rat hypothalamus: association with corticotropin-releasing factor-, urocortin 1- and vimentin-immunoreactive fibres

Corticotropin-releasing factor binding protein (CRF-BP) is a 37-kDa protein with high affinity binding sites for both corticotropin-releasing factor (CRF) and urocortin 1. Previous studies have examined the distribution of CRF-BP mRNA and peptide within the central nervous system. Due to the predominant cortical localisation, very little is known about CRF-BP in subcortical structures including the hypothalamus. The present study employed immunohistochemistry to characterise the distribution of CRF-BP-like-immunoreactive (-ir) cells and fibres in the rat hypothalamus. Bipolar and multipolar CRF-BP-ir neurones were scattered throughout the rostro-caudal extent of the hypothalamus. Distinct clusters of CRF-BP-ir neurones were identified in the anterior and posterior parvocellular and dorsal cap subdivisions of the paraventricular nucleus (PVN), as well as in the dorsal hypothalamic area, dorsomedial hypothalamic nucleus (DMN), ventral premammillary nucleus and zona incerta. CRF-BP-ir fibres extending from the third ventricle were found in the mediobasal hypothalamus and within the arcuate nucleus-median eminence region. Double immunostaining together with confocal microscopy demonstrated that the CRF-BP-immunostained fibres within the mediobasal hypothalamus coincided with vimentin immunostaining indicating that CRF-BP-ir is present within tanycytes. To define the relationship between CRF-BP-ir cells and endogenous ligands for CRF-BP, double immunohistochemistry was performed to examine possible sites within the hypothalamus where CRF- or urocortin 1-ir fibres innervate regions that contain CRF-BP-ir cell bodies. CRF-BP-ir cell bodies typically coincided with dense CRF-ir, but not urocortin 1-ir fibre innervation. CRF-ir fibre innervation was moderate to high within the anterior and posterior parvocellular subdivisions of the PVN, the dorsal cap of the PVN, DMN and the zona incerta; all regions that contained CRF-BP-ir cell populations. These studies demonstrate that, within the hypothalamus, CRF-BP-ir cells and fibres are concentrated within a circuitry known to be involved in mediating neuroendocrine and autonomic responses to stress.

Dopamine modulates use-dependent plasticity of inhibitory synapses

The release of the hormones oxytocin (OT) and vasopressin (VP) into the circulation is dictated by the electrical activity of hypothalamic magnocellular neurosecretory cells (MNCs). In the paraventricular nucleus of the hypothalamus (PVN), MNC neuronal activity is exquisitely sensitive to changes in input from inhibitory GABAergic synapses. To explore the hypothesis that efficacy at these synapses is dictated by the rate at which a given synapse is activated, we obtained whole-cell recordings from MNCs in postnatal day 21-27 male Sprague Dawley rat brain slices. IPSCs were elicited by electrically stimulating GABAergic projections from either the suprachiasmatic nucleus or putative interneuron populations immediately ventral to the fornix at 5, 10, 20, and 50 Hz. Short-term plasticity was observed at 88% of the synapses tested. Of this group, synaptic depression was observed in 58%, and synaptic facilitation was observed in 41%. Identification of cells using a combined electrophysiological and immunohistochemical approach revealed a strong correlation between cell phenotype and the nature of the plasticity. Short-term facilitation was observed preferentially in OT cells (86%), whereas short-term depression was predominant in VP neurons (69%). We next examined the effects of dopamine, which increases MNC excitability, on short-term plasticity. Activation of presynaptic D(4) receptors decreased the frequency of miniature IPSCs and prevented the development of synaptic depression at higher rates of activity. Synaptic facilitation, however, was unaffected by dopamine. These findings demonstrate that, by lowering GABA release probability, dopamine confers high-pass filtering properties to the majority of inhibitory synapses onto MNCs in PVN.

Estrogen-receptor-? distribution in the human hypothalamus: Similarities and differences with ER? distribution

This study reports the first systematic rostrocaudal distribution of estrogen receptor beta immunoreactivity (ER beta-ir) in the human hypothalamus and adjacent areas in five males and five females between 20-39 years of age and compares its distribution to previously reported ER alpha in the same patients. ER beta-ir was generally observed more frequently in the cytoplasm than in the nucleus and appeared to be stronger in women. Basket-like fiber stainings, suggestive for ER beta-ir in synaptic terminals, were additionally observed in various areas. Men showed more robust nuclear ER beta-ir than women in the medial part of the bed nucleus of the stria terminalis, paraventricular and paratenial nucleus of the thalamus, while less intense, but more nuclear, ER beta-ir appeared to be present in, e.g., the BSTc, sexually dimorphic nucleus of the medial preoptic area, diagonal band of Broca and ventromedial nucleus. Women revealed more nuclear ER beta-ir than men of a low to intermediate level, e.g., in the suprachiasmatic, supraoptic, paraventricular, infundibular, and medial mamillary nucleus. These data indicate potential sex differences in ER beta expression. ER beta-ir expression patterns in subjects with abnormal hormone levels suggests that there may be sex differences in ER beta-ir that are "activational" rather than "organizational" in nature. Similarities, differences, potential functional, and clinical implications of the observed ER alpha and ER beta distributions are discussed in relation to reproduction, autonomic-function, mood, cognition, and neuroprotection in health and disease.

Systemic apomorphine alters HPA axis responses to interleukin-1 beta administration but not sound stress

Apomorphine is a dopamine receptor agonist that was recently licensed for the treatment of erectile dysfunction. However, although sexual activity can be stressful, there has been little investigation into whether treatments for erectile dysfunction affect stress responses. We have examined whether a single dose of apomorphine, sufficient to produce penile erections (50 microg/kg, i.a.), can alter basal or stress-induced plasma ACTH levels, or activity of central pathways thought to control the hypothalamic-pituitary-adrenal axis in rats. An immune challenge (interleukin-1 beta, 1 microg/kg, i.a.) was used as a physical stressor while sound stress (100 dB white noise, 30 min) was used as a psychological stressor. Intravascular administration of apomorphine had no effect on basal ACTH levels but did substantially increase the number of Fos-positive amygdala and nucleus tractus solitarius catecholamine cells. Administration of apomorphine prior to immune challenge augmented the normal ACTH response to this stressor at 90 min and there was a corresponding increase in the number of Fos-positive paraventricular nucleus corticotropin-releasing factor cells, paraventricular nucleus oxytocin cells and nucleus tractus solitarius catecholamine cells. However, apomorphine treatment did not alter ACTH or Fos responses to sound stress. These data suggest that erection-inducing levels of apomorphine interfere with hypothalamic-pituitary-adrenal axis inhibitory feedback mechanisms in response to a physical stressor, but have no effect on the response to a psychological stressor. Consequently, it is likely that apomorphine acts on a hypothalamic-pituitary-adrenal axis control pathway that is unique to physical stressors. A candidate for this site of action is the nucleus tractus solitarius catecholamine cell population and, in particular, A2 noradrenergic neurons.

Central mechanisms of stress integration: hierarchical circuitry controlling hypothalamo-pituitary-adrenocortical responsiveness

Appropriate regulatory control of the hypothalamo-pituitary-adrenocortical stress axis is essential to health and survival. The following review documents the principle extrinsic and intrinsic mechanisms responsible for regulating stress-responsive CRH neurons of the hypothalamic paraventricular nucleus, which summate excitatory and inhibitory inputs into a net secretory signal at the pituitary gland. Regions that directly innervate these neurons are primed to relay sensory information, including visceral afferents, nociceptors and circumventricular organs, thereby promoting 'reactive' corticosteroid responses to emergent homeostatic challenges. Indirect inputs from the limbic-associated structures are capable of activating these same cells in the absence of frank physiological challenges; such 'anticipatory' signals regulate glucocorticoid release under conditions in which physical challenges may be predicted, either by innate programs or conditioned stimuli. Importantly, 'anticipatory' circuits are integrated with neural pathways subserving 'reactive' responses at multiple levels. The resultant hierarchical organization of stress-responsive neurocircuitries is capable of comparing information from multiple limbic sources with internally generated and peripherally sensed information, thereby tuning the relative activity of the adrenal cortex. Imbalances among these limbic pathways and homeostatic sensors are likely to underlie hypothalamo-pituitary-adrenocortical dysfunction associated with numerous disease processes.

Afferent projections to the hamster intergeniculate leaflet demonstrated by retrograde and anterograde tracing

The intergeniculate leaflet (IGL) is considered involved in nonphotic shifting of the circadian clock through a direct connection, the geniculo-hypothalamic tract. The brain areas mediating nonphotic arousal to the hamster IGL have not been thoroughly investigated by both retrograde and anterograde tracing. We, therefore, reinvestigated the IGL afferent connections with the retrograde tracer Cholera toxin B and subsequently verified the results with the anterograde tracer Phaseolus vulgaris-leucoagglutinin. We also defined a subset of neurons projecting to the IGL that were activated by arousal using c-Fos immunocytochemistry. Apart from a dense afferent projection from the retina- and the contralateral leaflet, there were ipsilateral projections from other structures: layer V and VI of the prefrontal cortex, the zona incerta, the magnocellular part of the subparafascicular nucleus, the dorsal raphe nucleus, the locus coeruleus, and the cuneiform nucleus. Dense bilateral projections to the leaflet from the pretectal nuclei were found. Hypothalamic afferents were observed dorsal to the suprachiasmatic nuclei, in the retrochiasmatic area (RCh) and in the ventromedial hypothalamic nuclei. All of these projections were confirmed by anterograde tracing. Furthermore, arousal (wheel-running) induced c-Fos in neurons projecting to the IGL (prefrontal cortex, RCh, pretectum). Taken together, the data strengthen the view that the IGL integrates photic and nonphotic information.

Origin of the dopaminergic innervation of the central extended amygdala and accumbens shell: a combined retrograde tracing and immunohistochemical study in the rat

The origin of the dopaminergic innervation of the central extended amygdala (EAc; i.e., the lateral bed nucleus of the stria terminalis [BSTl]-central amygdaloid nucleus [Ce] continuum) and accumbens shell (AcSh) was studied in the rat by combining retrograde transport of Fluoro-Gold (FG) with tyrosine hydroxylase (TH) immunofluorescence. Perikaryal profiles (PP) immunoreactive to FG and to both FG and TH were counted in A8-A14 dopaminergic districts. Our results suggest that dopaminergic inputs to the EAc and AcSh arise from the ventral tegmental area-A10, substantia nigra, pars compacta-A9, and retrorubral nucleus-A8 groups as well as from the dorsal raphe nucleus and periaqueductal gray substance, housing the dorsocaudal part of A10 group (A10dc). Quantitative estimates reveal that the A10dc group contains approximately half of the total number of FG/TH double-labeled PP projecting to Ce and BSTl. By using an anti-dopamine serum, DR/PAG projections to Ce were confirmed to be in part dopaminergic. In contrast, modest numbers of FG/TH double-labeled PP were seen in the A10dc group after injections in the sublenticular extended amygdala, interstitial nucleus of the posterior limb of the anterior commissure or AcSh. Ventral mesencephalic projections to the EAc display a crude mediolateral topographic organization, whereas those to the AcSh are topographically organized along a mediolateral and an inverted dorsoventral dimension. The diencephalic dopaminergic groups do not innervate the EAc or AcSh, except for the periventricular gray-A11 which sends light dopaminergic projections to Ce and BSTl. Overall, the present results provide additional details on the organization of the mesolimbic dopaminergic system that critically controls behavioral responsiveness to salient environmental stimuli.

Systemic administration of interleukin-1beta activates select populations of central amygdala afferents

The central nucleus of the amygdala (CeA) is activated robustly by an immune challenge such as the systemic administration of the proinflammatory cytokine interleukin-1beta (IL-1beta). Because IL-1beta is not believed to cross the blood-brain barrier in any significant amount, it is likely that IL-1beta elicits CeA cell recruitment by means of activation of afferents to the CeA. However, although many studies have investigated the origins of afferent inputs to the CeA, we do not know which of these also respond to IL-1beta. Therefore, to identify candidate neurons responsible for the recruitment of CeA cells by an immune challenge, we iontophoretically deposited a retrograde tracer, cholera toxin b-subunit (CTb), into the CeA of rats 7 days before systemic delivery of IL-1beta (1 microg/kg, i.a.). By using combined immunohistochemistry, we then quantified the number of Fos-positive CTb cells in six major regions known to innervate the CeA. These included the medial prefrontal cortex, paraventricular thalamus (PVT), ventral tegmental area, parabrachial nucleus (PB), nucleus tractus solitarius, and ventrolateral medulla. Our results show that after deposit of CTb into the CeA, the majority of double-labeled cells were located in the PB and the PVT, suggesting that CeA cell activation by systemic IL-1beta is likely to arise predominantly from cell bodies located in these regions. These findings may have significant implications in determining the central pathways involved in generating acute central responses to a systemic immune challenge.

Distribution of dopamine D1 receptors in the nucleus paraventricularis of the hypothalamus in rats: an immunohistochemical study

The present study investigated the distribution of dopamine D1 receptor protein in the nucleus paraventricularis of the hypothalamus. It was found that the nucleus paraventricularis of the hypothalamus contains a relatively large number of cells which are positive for presence of dopamine D1 receptor protein. The vast majority of dopamine D1 receptor-positive neurons was found in the magnocellular part, but they were also present in considerable quantity in the parvocellular part of this subregion of the hypothalamus. When measured by the Western blot technique, the quantity of D1 receptor protein found in the paraventricular nucleus of the hypothalamus was at the level found in the prefrontal cortex. It was also found that dopamine D1 receptor protein was present in neurons constitutively displaying phosphorylated CREB protein, i.e. neurons which are, as might be speculated, under the tonic influence of neurotransmitters whose receptors operate via cAMP and pCREB as second or third messengers. The presence of dopamine D1 receptors in the nucleus paraventricularis of the hypothalamus may suggest, at an anatomical level, that these receptors are involved in controlling the release of hormones, as well as their synthesis at the level of transcription, which is regulated by phosphorylation of CREB protein. Finally, the present immunocytochemical findings offer an anatomical substrate for the role of dopamine and its receptors of D1 subtype in the regulation of the activity of paraventricular neurons seen in the functional studies.