Activation of adenosine A2A receptors alters postsynaptic currents and depolarizes neurons of the supraoptic nucleus

Supraoptic nucleus (SON) neurons secrete oxytocin or vasopressin in response to various physiological stimuli (e.g., lactation/suckling, dehydration). Released near fenestrated capillaries of the neurohypophysis, these peptides enter the blood and travel to peripheral target organs. The pervasive neuromodulator adenosine, acting at A1 receptors, is an important inhibitory regulator of magnocellular neuroendocrine cell activity. Another high-affinity adenosine receptor exists in this system, however. We examined the physiological effects of adenosine A2A receptor activation and determined its localization among various cell types within the SON. In whole cell patch-clamp recordings from rat brain slices, application of the selective adenosine A2A receptor agonist CGS-21680 caused membrane depolarizations in SON neurons, often leading to increased firing activity. Membrane potential changes were persistent (>10 min) and could be blocked by the selective A2A receptor antagonist ZM-241385, or GDP-beta-S, the latter suggesting postsynaptic sites of action. However, +/--alpha-methyl-(4-carboxyphenyl)glycine or TTX also blocked CGS-21680 effects, indicating secondary actions on postsynaptic neurons. In voltage-clamp mode, application of CGS-21680 caused a slight increase (approximately 8%) in high-frequency clusters of excitatory postsynaptic currents. With the use of specific antibodies, adenosine A2A receptors were immunocytochemically localized to both the magnocellular neurons and astrocytes of the SON. Ecto-5'nucleotidase, an enzyme involved in the metabolism of ATP to adenosine, was also localized to astrocytes of the SON. These results demonstrate that adenosine acting at A2A receptors can enhance the excitability of SON neurons and modulate transmitter release from glutamatergic afferents projecting to the nucleus. We suggest that adenosine A2A receptors may function in neuroendocrine regulation through both direct neuronal mechanisms and via actions involving glia.     

Estradiol potentiates hypothalamic vasopressin and oxytocin neuron activation and hormonal secretion induced by hypovolemic shock

Estrogen receptors are located in important brain areas that integrate cardiovascular and hydroelectrolytic responses, including the subfornical organ (SFO) and supraoptic (SON) and paraventricular (PVN) nuclei. The aim of this study was to evaluate the influence of estradiol on cardiovascular and neuroendocrine changes induced by hemorrhagic shock in ovariectomized rats. Female Wistar rats (220-280 g) were ovariectomized and treated for 7 days with vehicle or estradiol cypionate (EC, 10 or 40 μg/kg, sc). On the 8th day, animals were subjected to hemorrhage (1.5 ml/100 g for 1 min). Hemorrhage induced acute hypotension and bradycardia in the ovariectomized-oil group, but EC treatment inhibited these responses. We observed increases in plasma angiotensin II concentrations and decreases in plasma atrial natriuretic peptide levels after hemorrhage; EC treatment produced no effects on these responses. There were also increases in plasma vasopressin (AVP), oxytocin (OT), and prolactin levels after the induction of hemorrhage in all groups, and these responses were potentiated by EC administration. SFO neurons and parvocellular and magnocellular AVP and OT neurons in the PVN and SON were activated by hemorrhagic shock. EC treatment enhanced the activation of SFO neurons and AVP and OT magnocellular neurons in the PVN and SON and AVP neurons in the medial parvocellular region of the PVN. These results suggest that estradiol modulates the cardiovascular responses induced by hemorrhage, and this effect is likely mediated by an enhancement of AVP and OT neuron activity in the SON and PVN.     

Galanin immunoreactivity increased in chicken supraoptic neurons after activation of the vasotocin system at oviposition

The avian arginine vasotocin (AVT) synthesized in the hypothalamic magnocellular neurons and released from the posterior pituitary is known to be involved in the regulation of uterine contractions for oviposition in chickens. However, regulation of AVT synthesis and release within the magnocellular hypothalamus has not been elucidated. Galanin, the oviposition inducing factor in the oviduct of the hen, has been demonstrated to have sexually dimorphic stimulatory action in oxytocin- and vasopressin neurons in the mammalian hypothalamus. In this study, galanin and AVT immunoreactivity was investigated around the time of oviposition in the supraoptic nucleus (SON) to determine if galanin modulates AVT synthesis and/or release. Within SON neurons increased AVT immunoreactivity before oviposition and the decreased AVT immunoreactivity after oviposition implied function-related peptide release. The significantly increased number of galanin neurons co-localizing with AVT immediately after oviposition suggests that galanin is involved in the negative feedback to limit AVT release in the SON. Thus, these data support the idea that AVT in the SON is involved in central regulation of oviposition and that AVT release could be modulated by the neuropeptide galanin.     

Galanin immunoreactivity increased in chicken supraoptic neurons after activation of the vasotocin system at oviposition.

The avian arginine vasotocin (AVT) synthesized in the hypothalamic magnocellular neurons and released from the posterior pituitary is known to be involved in the regulation of uterine contractions for oviposition in chickens. However, regulation of AVT synthesis and release within the magnocellular hypothalamus has not been elucidated. Galanin, the oviposition inducing factor in the oviduct of the hen, has been demonstrated to have sexually dimorphic stimulatory action in oxytocin- and vasopressin neurons in the mammalian hypothalamus. In this study, galanin and AVT immunoreactivity was investigated around the time of oviposition in the supraoptic nucleus (SON) to determine if galanin modulates AVT synthesis and/or release. Within SON neurons increased AVT immunoreactivity before oviposition and the decreased AVT immunoreactivity after oviposition implied function-related peptide release. The significantly increased number of galanin neurons co-localizing with AVT immediately after oviposition suggests that galanin is involved in the negative feedback to limit AVT release in the SON. Thus, these data support the idea that AVT in the SON is involved in central regulation of oviposition and that AVT release could be modulated by the neuropeptide galanin.     

Astroglial Regulation of Magnocellular Neuroendocrine Cell Activities in the Supraoptic Nucleus

Studies on the interactions between astrocytes and neurons in the hypothalamo-neurohypophysial system have significantly facilitated our understanding of the regulation of neural activities. This has been exemplified in the interactions between astrocytes and magnocellular neuroendocrine cells (MNCs) in the supraoptic nucleus (SON), specifically during osmotic stimulation and lactation. In response to changes in neurochemical environment in the SON, astrocytic morphology and functions change significantly, which further modulates MNC activity and the secretion of vasopressin and oxytocin. In osmotic regulation, short-term dehydration or water overload causes transient retraction or expansion of astrocytic processes, which increases or decreases the activity of SON neurons, respectively. Prolonged osmotic stimulation causes adaptive change in astrocytic plasticity in the SON, which allows osmosensory neurons to reserve osmosensitivity at new levels. During lactation, changes in neurochemical environment cause retraction of astrocytic processes around oxytocin neurons, which increases MNC’s ability to secrete oxytocin. During suckling by a baby/pup, astrocytic processes in the mother/dams exhibit alternative retraction and expansion around oxytocin neurons, which mirrors intermittently synchronized activation of oxytocin neurons and the post-excitation inhibition, respectively. The morphological and functional plasticities of astrocytes depend on a series of cellular events involving glial fibrillary acidic protein, aquaporin 4, volume regulated anion channels, transporters and other astrocytic functional molecules. This review further explores mechanisms underlying astroglial regulation of the neuroendocrine neuronal activities in acute processes based on the knowledge from studies on the SON.

     

Vasopressinergic and oxytocinergic pathways in the central nervous system

Recent data obtained by immunohistochemical and other anatomical tracing methods indicate that oxytocin and vasopressin pathways are much more complex and extensive than previously recognized. In addition to the classic magnocellular neurons that project from the supraoptic and paraventricular (PVN) nuclei to the posterior pituitary gland, generally smaller neurons in various parts of the PVN send vasopressin fibers to the portal capillary bed in the median eminence, or send oxytocin or vasopressin projections to other brain and spinal cord sites. In addition, vasopressin neurons are also found in the suprachiasmatic nucleus and may contribute to extrahypothalamic projection areas. Many of these axonal projections appear to form synapses with other neurons in forebrain, hindbrain, and spinal cord regions, which suggests roles for these peptides in neuronal communication. In brain stem and spinal cord, terminal fields include both parasympathetic and sympathetic regulatory centers. Oxytocin terminals are also found on large intracerebral arteries where the peptide may regulate cerebral blood flow.     

Two possible actions for circulating angiotensin II in the control of vasopressin release

The supraoptic-hypophyseal tract is a primary system for the synthesis and release of vasopressin. Angiotensin II (AII) has been shown to release vasopressin when injected into the cerebral ventricles (IVT). However, intravenous (IV) AII injections have not produced consistent results. The present studies were conducted to examine the effects of AII delivered by either route on the unit activity of supraoptic nucleus (SON) magnocellular neurons. Rats were prepared with intracranial cannulas to insure delivery of drugs to the left lateral ventricle and with polyethylene catheters in the left jugular vein, femoral vein, and femoral artery for systemic injections and arterial pressure recordings. A ventral approach permitted recording from the SON without violating the ventricular-SON partition. Magnocellular neurons were electrophysiologically identified. In the majority of identified cells, IVT AII increased activity. In others pressor doses of AII IV inhibited firing while blood pressure was elevated. After sino-aortic denervation, AII IV excited SON neurons. Based on latency, and the fact that lesioning the anteroventral third ventricle blocked the action of AII IVT, the results indicate that AII IVT acts on a periventricular site to influence SON magnocellular neurons. Furthermore, systemic AII may have two effects on SON neurons: a central excitatory action, and an inhibition due to a baroreceptor reflex.     

Genomic Effects of Cold and Isolation Stress on Magnocellular Vasopressin mRNA-Containing Cells in the Hypothalamus of the Rat

We assessed the effects of cold and isolation stress on arginine vasopressin (AVP) mRNA in the paraventricular (PVN) and supraoptic (SON) nuclei of the hypothalamus. Vasopressin mRNA levels were determined by in situ hybridization histochemistry at the cellular level. In posterior magnocellular neurons of the PVN isolation stress for 7 or 14 days increased vasopressin mRNA levels 28 and 29%, respectively, compared to group-housed controls. No significant alterations in vasopressin gene expression were observed in the SON after 7 or 14 days of isolation stress. Scattered magnocellular AVP mRNA-expressing cells of the medial parvocellular PVN showed increases of 19 and 34% after 7 and 14 days of isolation, respectively. We also studied the effect of cold or combined cold and isolation stress on vasopressin gene expression in the PVN and SON. Cold stress for 3 h daily for 4 consecutive days increased AVP mRNA levels in the posterior magnocellular PVN by 15%. Cold-isolated animals showed an increase of 21%. No significant effect on AVP mRNA levels in the SON was observed. In contrast to the posterior magnocellular PVN, cold or cold-isolation stress increased AVP mRNA in magnocellular neurons of the medial parvocellular region of the PVN by 25 and 43%, respectively, relative to control rats. These results suggest that psychological and metabolic stress may be added to the list of stressors that activate the hypothalamo-neurohypophysial system.     

Intranuclear coupling of hypothalamic magnocellular nuclei by glutamate synaptic circuits

Magnocellular neurons of the supraoptic nucleus (SON) and paraventricular nucleus (PVN) display bursting activity that is synchronized under certain conditions. They receive excitatory synaptic inputs from intrahypothalamic glutamate circuits, some of which are activated by norepinephrine. Ascending noradrenergic afferents and intrahypothalamic glutamate circuits may be responsible for the generation of synchronous bursting among oxytocin neurons and/or asynchronous bursting among vasopressin neurons located in the bilateral supraoptic and paraventricular nuclei. Here, we tested whether magnocellular neurons of the PVN receive excitatory synaptic input from the contralateral PVN and the region of the retrochiasmatic SON (SONrx) via norepinephrine-sensitive internuclear glutamate circuits. Whole cell patch-clamp recordings were performed in PVN magnocellular neurons in coronal hypothalamic slices from male rats, and the ipsilateral SONrx region and contralateral PVN were stimulated using electrical and chemical stimulation. Electrical and glutamate microdrop stimulation of the ipsilateral SONrx region or contralateral PVN elicited excitatory postsynaptic potentials/currents (EPSP/Cs) in PVN magnocellular neurons mediated by glutamate release, revealing internuclear glutamatergic circuits. Microdrop application of norepinephrine also elicited EPSP/Cs, suggesting that these circuits could be activated by activation of noradrenergic receptors. Repetitive electrical stimulation and drop application of norepinephrine, in some cases, elicited bursts of action potentials. Our data reveal glutamatergic synaptic circuits that interconnect the magnocellular nuclei and that can be activated by norepinephrine. These internuclear glutamatergic circuits may provide the functional architecture to support burst generation and/or burst synchronization in hypothalamic magnocellular neurons under conditions of activation.     

Activity of vasopressin neurons in the human supraoptic nucleus: estrogen inhibitory effect

Activity of magnocellular vasopressin (VP) neurons in the human hypothalamus is sex- and age-dependent as judged from the size of the Golgi apparatus, neuronal size and VP mRNA levels. These parameters are significantly higher in young (< or = 50 years old) men than in young women and are markedly increased in postmenopausal women compared to premenopausal women. This data suggest an inhibitory effect of estrogens on metabolic activity of VP neurons in the human supraoptic nucleus (2SON), which is likely to be mediated via estrogen receptor (ER) beta. Estrogens were shown to mediate their inhibitory effect via ER beta. It is expressed to a much higher degree in the SON of young women than in other groups, whereas estrogen receptor alpha, that mediates stimulatory effects of estrogens, is present in a small proportion of SON neurons. In addition, estrogens inhibit p75 neurotrophin receptor expression in VP cells. In conclusion, we discuss the inhibitory role of estrogens in functional activity of human VP neurons, which is most probably mediated directly via ER beta and indirectly by p75 neurotrophin receptor.     

Distribution pattern in the human pituitary and hypothalamus of a new neuropeptide: The C-terminal glycoprotein-fragment of human pro-pressophysin (CPP)

Summary The distribution pattern of CPP-containing neurons and fibers in the human pituitary and hypothalamus was studied with a specific antiserum to human CPP and the unlabeled antibody technique. Immunoreactive CPP was found in the magnocellular neurons of the supraoptic nucleus (SON), the paraventricular nucleus (PVN) and in neurons scattered in the supraoptic hypophyseal tract. CPP-containing parvocellular neurons were found in the suprachiasmatic nucleus (SCN). The CPP-containing fibers from the magnocellular neurons formed a tract coursing through the median eminence and the pituitary stalk to the posterior lobe of the hypophysis. In contrast, no such fibers from the SCN projected to SON, PVN and the median eminence. This pattern is identical to that of vasopressin and its associated neurophysin-containing neurons and fibers and strongly supports the concept that CPP is a part of the common precursor for vasopressin and neurophysin II. The biological importance of human CPP other than being a precursor fragment remains to be elucidated.To whom requests for reprints should be addressed     

Activity-dependent feedback modulation of spike patterning of supraoptic nucleus neurons by endogenous adenosine

Neuropeptide secretion from the dendrites of hypothalamic magnocellular supraoptic nucleus (SON) neurons contributes to the regulation of neuronal activity patterning, which ultimately determines their peptide output from axon terminals in the posterior pituitary gland. SON dendrites also secrete a number of other neuromodulators, including ATP. ATP degrades to adenosine in the extracellular space to complement transported adenosine acting on pre- and postsynaptic SON A1 receptors to reduce neuronal excitability, measured in vitro. To assess adenosine control of electrical activity in vivo, we made extracellular single-unit recordings of the electrical activity of SON neurons in anesthetized male rats. Microdialysis application (retrodialysis) of the A1 receptor antagonist, 8-cyclopentyl-1,3-dimethylxanthine (CPT) increased phasic vasopressin cell intraburst firing rates progressively over the first 5 s by 4.5 +/- 1.6 Hz (P < 0.05), and increased burst duration by 293 +/- 64% (P < 0.05). Hazard function plots were generated from interval interspike histograms and revealed that these effects were associated with increased postspike excitability. In contrast, CPT had no effect on the firing rates and hazard function plot profiles of continuously active vasopressin and oxytocin cells. However, CPT significantly increased clustering of spikes, as quantified by the index of dispersion, in oxytocin cells and continuously active vasopressin cells (by 267 +/- 113% and 462 +/- 67%, respectively, P < 0.05). Indeed, in 4 of 5 continuously active vasopressin cells, CPT induced a pseudophasic activity pattern. Together, these results indicate that endogenous adenosine is involved in the local control of SON cell activity in vivo.     

Intracellular electrophysiology of mammalian peptidergic neurons in rat hypothalamic slices

The magnocellular neuropeptidergic cells (MNCs) of the paraventricular and supraoptic nuclei have been a model for biochemical and physiological studies of peptidergic neurons in the mammalian brain, but nearly all the electrophysiological studies of these vasopressinergic and oxytocinergic neuroendocrine cells are based on extracellular recordings. This paper reviews recent literature on electrophysiological properties of neurons in the magnocellular nuclei in which the rat in vitro slice preparation and intracellular recording were used. Spontaneously occurring action potentials and synaptic potentials (excitatory and inhibitory) have been observed in hypothalamic slices. The spike patterns have included slow and irregular firing, short rapid bursts of inactivating spikes, and slow phasic discharge with prolonged active and silent periods. Some studies have shown that increased osmolality causes neuronal firing, but this area is controversial. Intracellular injections of lucifer yellow have shown that some MNCs are dye-coupled and electron microscopic observations with the freeze-fracture technique have revealed occasional gap junctions, thus suggesting that some MNCs are electrotonically coupled. Both excitatory and inhibitory postsynaptic potentials have been evoked with extracellular stimulation. Therefore, action potentials, synaptic potentials, burst discharges, and probably electrotonic coupling have been found with intracellular recording in mammalian neuroendocrine cells. Future studies with intracellular recording and staining followed by immunohistochemical identification of cells should provide significant new information on the membrane physiology and synaptic pharmacology of vasopressinergic and oxytocinergic cells.     

Potentiation of glutamatergic synaptic input to supraoptic neurons by presynaptic nicotinic receptors

The release of vasopressin and oxytocin from the supraoptic nucleus (SON) neurons is tonically regulated by excitatory glutamatergic and inhibitory GABAergic synaptic inputs. Acetylcholine is known to excite SON neurons and to elicit vasopressin release. Cholinergic receptors are located pre- and postsynaptically in the SON, but their functional significance in the regulation of SON neurons is not fully understood. In this study, we determined the role of presynaptic cholinergic receptors in regulation of the excitatory glutamatergic inputs to the SON neurons. The magnocellular neurons in the rat hypothalamic slices were identified microscopically, and the spontaneous miniature excitatory postsynaptic currents (mEPSCs) were recorded using the whole cell voltage-clamp technique. The mEPSCs were abolished by the non-NMDA receptor antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (20 microM). Acetylcholine (100 microM) significantly increased the frequency of mEPSCs of 38 SON neurons from 1.87 +/- 0.36 to 3.42 +/- 0.54 Hz but did not alter the amplitude (from 19.61 +/- 0.90 to 19.34 +/- 0.84 pA) and the decay time constant of mEPSCs. Furthermore, the nicotinic receptor antagonist mecamylamine (10 microM, n = 16), but not the muscarinic receptor antagonist atropine (100 microM, n = 12), abolished the excitatory effect of acetylcholine on the frequency of mEPSCs. These data provide new information that the excitatory effect of acetylcholine on the SON neurons is mediated, at least in part, by its effect on presynaptic glutamate release. Activation of presynaptic nicotinic, but not muscarinic, receptors located in the glutamatergic terminals increases the excitatory synaptic input to the SON neurons of the hypothalamus.     

Neural Connections Between Prosencephalic Structures Involved in Vasopressin Release

1. The diagonal band (DB) and the lateral septal area (LSA) are two prosencephalic structures, which were implicated in vasopressin release.2. The present experiment was designed to investigate neural connections between the DB and the LSA and from these nuclei to the paraventricular (PVN) and supraoptic (SON) nuclei, which could be related to vasopressin release.3. For the above purpose the bidirectional neuronal tracer biotinylated dextran amine (BDA) was injected into the DB or the LSA of male Wistar rats. Five days later the animals were sacrificed and brain slices were processed and analyzed to determine neuronal projections efferent from as well as afferent to these structures.4. Neuronal staining was more prominent in regions ipsilateral to the BDA injection site.5. After BDA injections into the DB, efferent projections from the DB were observed at the LSA, the PVN, the prefrontal cortex, the mediodorsal thalamic nucleus, and throughout the anterior hypothalamus, but not at the SON. At the PVN, labeled varicose fibers were observed at the magnocellular portion. The DB was found to receive a massive input from the LSA. More discrete projections to the DB were originated at the prefrontal cortex and from hypothalamic neurons outside the PVN and the SON.6. After BDA injections into the ventral portion of the LSA, efferent projections from the LSA were intense at the DB and throughout the hypothalamus. Labeled fibers were observed at the structures surrounding the SON or the PVN but not within those nuclei.7. The results indicate a massive neural output from the LSA to the DB and the existence of a direct neural connection from the DB to the PVN. No direct connections were observed between the LSA and the magnocellular nuclei (PVN and SON) or between the DB and the SON.     

Rapid Communication: Neuropeptide Expression and Processing as Revealed by Direct Matrix-Assisted Laser Desorption Ionization Mass Spectrometry of Single Neurons

Abstract: Neuropeptides were directly detected in single identified neurons and the neurohemal area of peptidergic (neuroendocrine) systems in the Lymnaea brain by using matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS). The samples were placed in matrix solution and ruptured to allow mixing of cell contents with the matrix solution. After formation of matrix crystals, the analytes were analyzed by MALDI-MS. It was surprising that clean mass spectra were produced, displaying extreme sensitivity of detection. In one of the neuroendocrine systems studied, we could demonstrate for the first time, by comparing the peptide patterns of soma and of neurohemal axon terminals, that processing of the complex prohormone expressed in this system occurs entirely in the soma. In the other system studied, novel peptides could be detected in addition to peptides previously identified by conventional molecular biological and peptide chemical methods. Thus, complex peptide processing and expression patterns could be predicted that were not detected in earlier studies using conventional methods. As the first MALDI- MS study of direct peptide fingerprinting in the single neuron these experients demonstrate that MALDI-MS forms a new and valuable approach to the study of the synthesis and expression of bioactive peptides, with potential application to single-cell studies in vertebrates, including humans.     

NO inhibits supraoptic oxytocin and vasopressin neurons via activation of GABAergic synaptic inputs

To study modulatory actions of nitric oxide (NO) on GABAergic synaptic activity in hypothalamic magnocellular neurons in the supraoptic nucleus (SON), in vitro and in vivo electrophysiological recordings were obtained from identified oxytocin and vasopressin neurons. Whole cell patch-clamp recordings were obtained in vitro from immunochemically identified oxytocin and vasopressin neurons. GABAergic synaptic activity was assessed in vitro by measuring GABA(A) miniature inhibitory postsynaptic currents (mIPSCs). The NO donor and precursor sodium nitroprusside (SNP) and L-arginine, respectively, increased the frequency and amplitude of GABA(A) mIPSCs in both cell types (P < or = 0.001). Retrodialysis of SNP (50 mM) onto the SON in vivo inhibited the activity of both neuronal types (P < or = 0.002), an effect that was reduced by retrodialysis of the GABA(A)-receptor antagonist bicuculline (2 mM, P < or = 0.001). Neurons activated by intravenous infusion of 2 M NaCl were still strongly inhibited by SNP. These results suggest that NO inhibition of neuronal excitability in oxytocin and vasopressin neurons involves pre- and postsynaptic potentiation of GABAergic synaptic activity in the SON.     

Neuropeptide FF (NPFF) control of magnocellular neurosecretory cells of the rat hypothalamic paraventricular nucleus (PVN)

Neuropeptide FF (NPFF) is an octapeptide belonging to an extended family of RF amide peptides that have been implicated in a wide variety of physiological functions in the brain. NPFF and its receptors are abundantly expressed in the rat brain and spinal cord including the hypothalamic paraventricular nucleus (PVN), an autonomic nucleus critical for the secretion of neurohormones and the regulation of sympathetic outflow. In this study, we sought to examine the effects of NPFF on GABAergic inhibitory synaptic input to magnocellular neurosecretory cells (MNCs) of the PVN, which secrete the neurohormones, vasopressin and oxytocin from their terminals in the neurohypophysis. Whole cell patch clamp recordings under voltage clamp conditions were performed from PVN MNCs in the brain slice. Bicuculline-sensitive inhibitory postsynaptic currents (IPSCs) were isolated in the presence of glutamate receptor blockers. In tetrodotoxin, NPFF (5 microM) caused an increase in frequency, but not amplitude of miniature inhibitory postsynaptic currents (mIPSCs) in MNCs indicating a presynaptic locus of action for this peptide. Intracerebroventricular application of NPFF resulted in an activation of GABAergic neurons located adjacent to the PVN as revealed by immunohistochemistry for Fos protein and in situ hybridization for glutamic acid decarboxylase (GAD67) mRNA. Based on these observations we conclude that NPFF facilitates inhibitory input to MNCs of the PVN via GABAergic interneurons located in immediate vicinity of the nucleus. These findings provide a cellular and anatomic basis for the NPFF-induced inhibition of vasopressin release has been reported consequent to hypovolemia and hyperosmolar stimulation.     

Effects of neonatal handling on social memory, social interaction, and number of oxytocin and vasopressin neurons in rats

Early-life environmental events can induce profound long-lasting changes in several behavioral and neuroendocrine systems. The neonatal handling procedure, which involves repeated brief maternal separations followed by experimental manipulations, reduces stress responses and sexual behavior in adult rats. The purpose of this study was to analyze the effects of neonatal handling on social behaviors of male and female rats in adulthood, as manifest by the results of social memory and social interaction tests. The number of oxytocin (OT) and vasopressin (VP) neurons in the paraventricular (PVN) and supraoptic (SON) nuclei of hypothalamus were also analyzed. The results did not demonstrate impairment of social memory. Notwithstanding, handling did reduce social investigative interaction and increase aggressive behavior in males, but did not do so in females. Furthermore, in both males and females, handling was linked with reduced number of OT-neurons in the parvocellular region of the PVN, while no differences were detected in the magnocellular PVN or the SON. On the other hand, handled males exhibited increased number of VP-neurons in the magnocellular zone of the PVN. We may conclude that the repeated brief maternal separations can reduce affiliative social behavior in adult male rats. Moreover, the disruption of the mother-infant relationship caused by the handling procedure induced long-lasting morphological changes in critical neuroendocrine areas that are involved in social bonding in mammals.     

Effects of chronic alcoholic disease on magnocellular and parvocellular hypothalamic neurons in men.

Although numerous data showing severe morphological impairment of magnocellular and parvocellular hypothalamic neurons due to chronic alcoholic consumption have been gathered from animal experiments, only one study (Harding et al., 1996) was performed on POST MORTEM human brain. This study showed a reduction in the number of vasopressin (VP)-immunoreactive neurons in the supraoptic (SON) and paraventricular (PVN) nuclei, but did not provide any data regarding the effect of chronic alcohol intake on human parvocellular neurons. In order to assess whether the changes observed in the animal model also occur in humans and provide a structural basis for the results of clinical tests, we performed immunohistochemical and morphometric analysis of magnocellular (VP and oxytocin, OT) and parvocellular (corticotropin-releasing hormone, CRH) neurons in post-mortem brains of patients afflicted with chronic alcoholic disease. We analyzed 26-male alcoholics and 22 age-matched controls divided into two age groups--"young" (< 40 yr) and "old" (> 40 yr). Hypothalamic sections were stained for OT, VP, and CRH. The analysis revealed: 1) decrease in VP-immunoreactivity in the SON and PVN as well as OT-immunoreactivity in the SON in alcoholic patients; 2) increase in OT-immunoreactivity in the PVN; 3) increase in CRH-immunoreactivity in parvocellular neurons in the PVN. Furthermore, the proportion of cells containing CRH and VP was increased in alcoholics. These findings indicate that chronic alcohol consumption does indeed impair the morphology of magnocellular neurons. The enhancement of CRH-immunoreactivity and increased co-production of CRH and VP in parvocellular neurons may be due to a decline in glucocorticoid production, implied by the hypoplasic impairment of adrenal cortex we observed in alcoholics during the course of this study.