The organization of chemically characterized afferents to the perivascular neuronal groups of the hypothalamic magnocellular neurosecretory system in the rat

The effect of amisulpride, olanzapine, quetiapine, and aripiprazole single administration on c-Fos expression in vasopressinergic and oxytocinergic neurons of the rat hypothalamic paraventricular nucleus

Antipsychotics, including amisulpride (AMI), quetiapine (QUE), aripiprazole (ARI), and olanzapine (OLA), are used to treat mental illnesses associated with psychotic symptoms. The effect of these drugs on c-Fos expression in vasopressinergic (AVP) and oxytocinergic (OXY) neurons was studied in the hypothalamic paraventricular nucleus (PVN) of rats. The presence of c-Fos in AVP and OXY perikarya was investigated in seven PVN cells segregations: the anterior (Ant), dorsal cup (Dc), wing-shaped (Wi), periventricular zone (Pe), circle-shaped core (Co) and shell of core (Sh), and the posterior (pPVN) after an acute treatment with AMI-20 mg/kg, QUE-15 mg/kg, ARI-10 mg/kg, and OLA-5 mg/kg/bw in rats. Ninety min after treatments, the animals were sacrificed by transcardial perfusion with fixative and the PVN area sliced into 35 μm thick coronal sections for immunohistochemistry. The c-Fos was processed by avidin-biotin-peroxidase complex intensified with nickel-enhanced 3,3'-diaminobenzidine tetrahydrochloride. Visualization of AVP- and OXY-synthesizing neurons was achieved by a fluorescent marker Alexa Flour 568. The c-Fos-AVP and c-Fos-OXY colocalizations were evaluated from c-Fos stained sections merged with AVP or OXY ones. AMI, QUE, ARI, and OLA, single administration distinctly increased the c-Fos expression in each of the PVN cells segregations. QUE induced the highest magnitude of activation of AVP and OXY neurons, while OLA and AMI had only moderate effects. Incontestable variabilities detected in c-Fos expression in PVN AVP and OXY neurons extend the knowledge of selected antipsychotics extra-striatal actions and may also be helpful in a presumption of their possible functional impact.

The role of serotonin, vasopressin, and serotonin/vasopressin interactions in aggressive behavior

Aggression control has been investigated across species and is centrally mediated within various brain regions by several neural systems that interact at different levels. The debate over the degree to which any one system or region affects aggressive responding, or any behavior for that matter, in some senses is arbitrary considering the plastic and adaptive properties of the central nervous system. Nevertheless, from the reductionist point of view, the compartmentalization of evolutionarily maladaptive behaviors to specific regions and systems of the brain is necessary for the advancement of clinical treatments (e.g., pharmaceutical) and novel therapeutic methods (e.g., deep brain stimulation). The general purpose of this chapter is to examine the confluence of two such systems, and how their functional interaction affects aggressive behavior. Specifically, the influence of the serotonin (5HT) and arginine vasopressin (AVP) neural systems on the control of aggressive behavior will be examined individually and together to provide a context by which the understanding of aggression modulation can be expanded from seemingly parallel neuromodulatory mechanisms, to a single and highly interactive system of aggression control.

Different antipsychotics elicit different effects on magnocellular oxytocinergic and vasopressinergic neurons as revealed by Fos immunohistochemistry

Acute administration of antipsychotics elicits regionally distinct patterns of Fos expression in the rat brain. Stimulation of oxytocin (OXY) and vasopressin (AVP) release in the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei indicates that antipsychotics may play a role in autonomic, neuroendocrine, and behavioral processes. This study was focused to reveal the responsiveness of hypothalamic OXY- and AVP- producing magnocellular neurons, in terms of quantitative and topographical distinctions, to antipsychotics displaying different pharmacological profiles. Naive male Wistar rats were injected intraperitoneally with haloperidol (1 mg/kg), clozapine (30 mg/kg), olanzapine (30 mg/kg), risperidone (2mg/kg), and vehicle (5% chremophor) and were sacrificed 60 min later by a fixative. Fos, Fos/OXY, and Fos/AVP labelings were visualized by immunohistochemistry in the SON, 5 accessory (ACS) cell groups, and 4 distinct PVN subdivisions using a computerized light microscope. Most apparent activation of single Fos, Fos/OXY, and Fos/AVP cells was induced by clozapine and olanzapine; effects of risperidone and haloperidol were substantially lower; no colocalizations were revealed in naive or vehicle treated control rats. The data indicate the existence of a substantial diversity in the stimulatory effect of the selected antipsychotics on quantity of Fos, Fos/OXY, and Fos/AVP immunostainings with the preferential action of the atypicals clozapine over olanzapine and little effects of risperidone and haloperidol. Variabilities in Fos distribution in the PVN, SON, and ACS induced by antipsychotics may be helpful to understand more precisely the extent of their extra-forebrain actions with possible presumption of their functional impact and side effect consequences.

Angiotensin II type 2 receptors have a major somatodendritic distribution in vasopressin-containing neurons in the mouse hypothalamic paraventricular nucleus

The hypothalamic paraventricular nucleus (PVN) and angiotensin II (AngII) play critical roles in cardiovascular and neurohumoral regulation ascribed in part to vasopressin (VP) release. The AngII actions in the PVN are mediated largely through angiotensin II type 1 (AT1) receptors. However, there is indirect evidence that the functionally elusive central angiotensin II type 2 (AT2) receptors are also mediators of AngII signaling in the PVN. We used electron microscopic dual immunolabeling of antisera recognizing the AT2 receptor and VP to test the hypothesis that mouse PVN neurons expressing VP are among the cellular sites where this receptor has a subcellular distribution conducive to local activation. Immunoreactivity for the AT2 receptor was detected in somatodendritic profiles, of which approximately 60% of the somata and approximately 28% of the dendrites also contained VP. In comparison with somata and dendrites, axons, axon terminals, and glia less frequently contained the AT2 receptor. Somatic labeling for the AT2 receptor was often seen in the cytoplasm near the Golgi lamellae and other endomembrane structures implicated in receptor trafficking. AT2 receptor immunoreactivity in dendrites was commonly localized to cytoplasmic endomembranes, but was occasionally observed on extra- or peri-synaptic portions of the plasma membrane apposed by astrocytic processes or by unlabeled axon terminals. The labeled dendritic plasmalemmal segments containing AT2 receptors received asymmetric excitatory-type or more rarely symmetric inhibitory-type contacts from unlabeled axon terminals containing dense core vesicles, many of which are known to store neuropeptides. These results provide the first ultrastructural evidence that AT2 receptors in PVN neurons expressing VP and other neuromodulators are strategically positioned for surface activation by AngII and/or intracellular trafficking.

Zolpidem, a selective GABAA receptor α1 subunit agonist, induces comparable Fos expression in oxytocinergic neurons of the hypothalamic paraventricular and accessory but not supraoptic nuclei in the rat

Functional activation of oxytocinergic (OXY) cells in the hypothalamic paraventricular (PVN), supraoptic (SON), and accessory (ACC) nuclei was investigated in response to acute treatment with Zolpidem (a GABA(A) receptor agonist with selectivity for alpha(1) subunits) utilizing dual Fos/OXY immunohistochemistry. Zolpidem was administered intraperitoneally in dose 10 mg/kg of BW and 60 min later the animals were sacrificed by transcardial perfusion with fixative. The Fos/OXY co-labelings were analyzed on 40 microm thick serial coronal sections using computerized light microscopy. Zolpidem elicited a concordant Fos/OXY staining in all four PVN sub-areas investigated, including the anterior (15.71+/-2.35%), middle (14.52+/-2.53%), dorsal (13.34+/-2.61%), and periventricular (18.21+/-4.75%) ones, however, had no significant stimulatory effect on OXY cells in the SON. In response to Zolpidem, statistically significant activations were also seen in certain groups of accessory structures including the circular nucleus (13.99+/-3.43%), small clusters of accessory neurons (10.55+/-1.94%), and the lateral hypothalamic perivascular nucleus (9.42+/-2.74%). Between the naive and vehicle controls, the dual Fos/OXY labelings did not elicit any significant differences. Our data provide insight into the topographic patterns of brain activity within the clusters of magnocellular OXY cells in the hypothalamus associated with stimulation of GABA(A) benzodiazepine receptors and for the first time illustrate the triggering contemporaneousness within the cells of the principal and accessory magnocellular nuclei in response to Zolpidem treatment. The present study provides a comparative background that may help in the further understanding of a possible extend of Zolpidem effect on the brain.

Projections from bed nuclei of the stria terminalis, dorsomedial nucleus: implications for cerebral hemisphere integration of neuroendocrine, autonomic, and drinking responses

The overall projection pattern of a tiny bed nuclei of the stria terminalis anteromedial group differentiation, the dorsomedial nucleus (BSTdm), was analyzed with the Phaseolus vulgaris-leucoagglutinin anterograde pathway tracing method in rats. Many brain regions receive a relatively moderate to strong input from the BSTdm. They fall into eight general categories: humeral sensory-related (subfornical organ and median preoptic nucleus, involved in initiating drinking behavior and salt appetite), neuroendocrine system (magnocellular: oxytocin, vasopressin; parvicellular: gonadotropin-releasing hormone, somatostatin, thyrotropin-releasing hormone, corticotropin-releasing hormone), central autonomic control network (central amygdalar nucleus, BST anterolateral group, descending paraventricular hypothalamic nucleus, retrochiasmatic area, ventrolateral periaqueductal gray, Barrington's nucleus), hypothalamic visceromotor pattern-generator network (five of six known components), behavior control column (ingestive: descending paraventricular nucleus; reproductive: lateral medial preoptic nucleus; defensive: anterior hypothalamic nucleus; foraging: ventral tegmental area, along with interconnected nucleus accumbens and substantia innominata), orofacial motor control (retrorubral area), thalamocortical feedback loops (paraventricular, central medial, intermediodorsal, and medial mediodorsal nuclei; nucleus reuniens), and behavioral state control (subparaventricular zone, ventrolateral preoptic nucleus, tuberomammillary nucleus, supramammillary nucleus, lateral habenula, and raphé nuclei). This pattern of axonal projections, and what little is known of its inputs suggest that the BSTdm is part of a striatopallidal differentiation involved in coordinating the homeostatic and behavioral responses associated thirst and salt appetite, although clearly it may relate them to other functions as well. The BSTdm generates the densest known inputs directly to the neuroendocrine system from any part of the cerebral hemispheres.

Intracerebroventricular injection of senktide-induced Fos expression in vasopressin-containing hypothalamic neurons in the rat

Intracerebroventricular injection of senktide, a selective agonist for neurokinin B receptor (NK3), induced Fos expression in many neurons of the rat hypothalamus. Fos-positive neurons were predominantly present in the supraoptic and paraventricular hypothalamic nuclei, and some of them were seen in the lateral preoptic area, lateral hypothalamic area, arcuate nucleus, perifornical region, posterior hypothalamic area, circular nucleus, and along relatively large blood vessels (lateral hypothalamic perivascular nucleus) in the anterior hypothalamus. A double labeling study was performed to examine if vasopressin-containing neurons in the hypothalamus could be activated by the treatment. Neurons with both Fos-like immunoreactivity (-LI) and vasopressin-LI were found in the paraventricular nucleus, supraoptic nucleus, circular nucleus and lateral hypothalamic perivascular nucleus. In the supraoptic nucleus, about 87% of vasopressin-containing neurons exhibited Fos-LI, which corresponded to about 64% of Fos-positive neurons in the nucleus. In the paraventricular nucleus, about 80% of vasopressin-like immunoreactive neurons exhibited Fos-LI, which constituted about 51% of the total population of Fos-positive neurons in the region. The results suggest that NK3 receptor may be involved in the modulation of release of vasopressin from the hypothalamus in the rat.

Hypervascularization in the magnocellular nuclei of the rat hypothalamus: relationship with the distribution of aquaporin-4 and markers of energy metabolism

In the magnocellular nuclei of the hypothalamus, there is a rich vascular network for which the function remains to be established. In the supraoptic nucleus, the high vascular density may be one element, which together with the water channel aquaporin-4 expressed in the astrocytes, is related to a role in osmoreception. We tested the osmoreception hypothesis by studying the correlation between vascular and cellular densities in the paraventricular nucleus and the supraoptic nucleus. Whether aquaporin-4 is likely to contribute to osmoreception was tested by studying the distribution in the magnocellular nuclei of the hypothalamus. The high vascular density may also reflect a high metabolic activity due to the synthesis of vasopressin and oxytocin. This metabolic hypothesis was tested by studying the regional cytochrome oxidase histochemistry, the local cerebral blood flow, and the density of glucose transporter type-1 in the supraoptic and paraventricular nuclei. All the magnocellular nuclei were characterized by an extended and intense aquaporin-4 labelling and a weak cytochrome oxidase histochemistry. The highest vascular density was found in the supraoptic nucleus and the magnocellular regions of the paraventricular nucleus. The local cerebral blood flow rates were surprisingly low in the paraventricular nucleus and the supraoptic nucleus in comparison to the cerebral cortex. Furthermore in these nuclei, the antibody for glucose transporter type-1 revealed two populations of vessels differing by their labelling intensity. The similarities observed between the different nuclei suggest that, in the hypothalamus, all magnocellular regions sense the plasma osmolarity. The low local cerebral blood flow, and the patterns of glucose transporter type-1 labelling and cytochrome oxidase histochemistry suggest that the high vascularization of these hypothalamic nuclei is not related to a high metabolic capacity in basal conditions.

Evolutionarily distinct classes of S27 ribosomal proteins with differential mRNA expression in rat hypothalamus

Using an in situ hybridization screen for cDNA clones of brain region-specific mRNAs, we isolated a rat transcript that encodes a ribosomal protein S27. Searching GenBank DNA databases, we found two S27 protein isoforms. One isoform, encoded by multiple genes, is extant in archaea and eukarya, but not bacteria. The second isoform appears to be recently evolved because it has been identified only in mammals. Multiple transcripts encode each isoform and exhibit different tissue expression patterns throughout rat brain and periphery, with abundant expression in the hypothalamus. In situ hybridization studies revealed predominant expression of S27(1) in distinct hypothalamic nuclei, such as the paraventricular, supraoptic, suprachiasmatic, arcuate, and circularis nuclei, whereas expression of S27(2) mRNA was discretely expressed in select neurons of the periventricular and supraoptic nuclei. Combined with the genetic evidence that S27 has extraribosomal functions in plants, the complexity of S27 biology observed here may suggest auxiliary functions for S27 proteins in the mammalian nervous system.