Immunoelectronmicroscopic localization of vasopressin in the rat suprachiasmatic nucleus

Arginine vasopressin-Venus reporter mice as a tool for studying magnocellular arginine vasopressin neurons

Arginine vasopressin (AVP) synthesized in the magnocellular neurons of the hypothalamus is transported through their axons and released from the posterior pituitary into the systemic circulation to act as an antidiuretic hormone. AVP synthesis and release are precisely regulated by changes in plasma osmolality. Magnocellular AVP neurons receive innervation from osmosensory and sodium-sensing neurons, but previous studies showed that AVP neurons per se are osmosensitive as well. In the current study, we made AVP-Venus reporter mice and showed that Venus was expressed exclusively in AVP neurons and was upregulated under water deprivation. In hypothalamic organotypic cultures from the AVP-Venus mice, Venus-labeled AVP neurons in the supraoptic and paraventricular nuclei survived for 1 month, and Venus expression was upregulated by forskolin. Furthermore, in dissociated Venus-labeled magnocellular neurons, treatment with NaCl, but not with mannitol, decreased Venus fluorescence in the soma of the AVP neurons. Thus, Venus expression in AVP-Venus transgenic mice, as well as in primary cultures, faithfully showed the properties of intrinsic AVP expression. These findings indicate that AVP-Venus mice as well as the primary hypothalamic cultures could be useful for studying magnocellular AVP neurons.

Central and peripheral roles of vasopressin in the circadian defense of body hydration

Vasopressin is a neuropeptide synthesized by specific subsets of neurons within the eye and brain. Studies in rats and mice have shown that vasopressin produced by magnocellular neurosecretory cells (MNCs) that project to the neurohypophysis is released into the blood circulation where it serves as an antidiuretic hormone to promote water reabsorption from the kidney. Moreover vasopressin is a neurotransmitter and neuromodulator that contributes to time-keeping within the master circadian clock (i.e. the suprachiasmatic nucleus, SCN) and is also used as an output signal by SCN neurons to direct centrally mediated circadian rhythms. In this chapter, we review recent cellular and network level studies in rodents that have provided insight into how circadian rhythms in vasopressin mediate changes in water intake behavior and renal water conservation that protect the body against dehydration during sleep.

Oxytocin, Vasopressin, and the Motivational Forces that Drive Social Behaviors

The motivation to engage in social behaviors is influenced by past experience and internal state, but also depends on the behavior of other animals. Across species, the oxytocin (Oxt) and vasopressin (Avp) systems have consistently been linked to the modulation of motivated social behaviors. However, how they interact with other systems, such as the mesolimbic dopamine system, remains understudied. Further, while the neurobiological mechanisms that regulate prosocial/cooperative behaviors have been extensively examined, far less is understood about competitive behaviors, particularly in females. In this chapter, we highlight the specific contributions of Oxt and Avp to several cooperative and competitive behaviors and discuss their relevance to the concept of social motivation across species, including humans. Further, we discuss the implications for neuropsychiatric diseases and suggest future areas of investigation.

Species, sex and individual differences in the vasotocin/vasopressin system: relationship to neurochemical signaling in the social behavior neural network

Arginine-vasotocin (AVT)/arginine vasopressin (AVP) are members of the AVP/oxytocin (OT) superfamily of peptides that are involved in the regulation of social behavior, social cognition and emotion. Comparative studies have revealed that AVT/AVP and their receptors are found throughout the "social behavior neural network (SBNN)" and display the properties expected from a signaling system that controls social behavior (i.e., species, sex and individual differences and modulation by gonadal hormones and social factors). Neurochemical signaling within the SBNN likely involves a complex combination of synaptic mechanisms that co-release multiple chemical signals (e.g., classical neurotransmitters and AVT/AVP as well as other peptides) and non-synaptic mechanisms (i.e., volume transmission). Crosstalk between AVP/OT peptides and receptors within the SBNN is likely. A better understanding of the functional properties of neurochemical signaling in the SBNN will allow for a more refined examination of the relationships between this peptide system and species, sex and individual differences in sociality.

Evolution of time-keeping mechanisms: early emergence and adaptation to photoperiod

Virtually all species have developed cellular oscillations and mechanisms that synchronize these cellular oscillations to environmental cycles. Such environmental cycles in biotic (e.g. food availability and predation risk) or abiotic (e.g. temperature and light) factors may occur on a daily, annual or tidal time scale. Internal timing mechanisms may facilitate behavioural or physiological adaptation to such changes in environmental conditions. These timing mechanisms commonly involve an internal molecular oscillator (a 'clock') that is synchronized ('entrained') to the environmental cycle by receptor mechanisms responding to relevant environmental signals ('Zeitgeber', i.e. German for time-giver). To understand the evolution of such timing mechanisms, we have to understand the mechanisms leading to selective advantage. Although major advances have been made in our understanding of the physiological and molecular mechanisms driving internal cycles (proximate questions), studies identifying mechanisms of natural selection on clock systems (ultimate questions) are rather limited. Here, we discuss the selective advantage of a circadian system and how its adaptation to day length variation may have a functional role in optimizing seasonal timing. We discuss various cases where selective advantages of circadian timing mechanisms have been shown and cases where temporarily loss of circadian timing may cause selective advantage. We suggest an explanation for why a circadian timing system has emerged in primitive life forms like cyanobacteria and we evaluate a possible molecular mechanism that enabled these bacteria to adapt to seasonal variation in day length. We further discuss how the role of the circadian system in photoperiodic time measurement may explain differential selection pressures on circadian period when species are exposed to changing climatic conditions (e.g. global warming) or when they expand their geographical range to different latitudes or altitudes.

Endogenous peptide discovery of the rat circadian clock: a focused study of the suprachiasmatic nucleus by ultrahigh performance tandem mass spectrometry

Understanding how a small brain region, the suprachiasmatic nucleus (SCN), can synchronize the body's circadian rhythms is an ongoing research area. This important time-keeping system requires a complex suite of peptide hormones and transmitters that remain incompletely characterized. Here, capillary liquid chromatography and FTMS have been coupled with tailored software for the analysis of endogenous peptides present in the SCN of the rat brain. After ex vivo processing of brain slices, peptide extraction, identification, and characterization from tandem FTMS data with <5-ppm mass accuracy produced a hyperconfident list of 102 endogenous peptides, including 33 previously unidentified peptides, and 12 peptides that were post-translationally modified with amidation, phosphorylation, pyroglutamylation, or acetylation. This characterization of endogenous peptides from the SCN will aid in understanding the molecular mechanisms that mediate rhythmic behaviors in mammals.

Characterization of the oxytocin system regulating affiliative behavior in female prairie voles

Oxytocin regulates partner preference formation and alloparental behavior in the socially monogamous prairie vole (Microtus ochrogaster) by activating oxytocin receptors in the nucleus accumbens of females. Mating facilitates partner preference formation, and oxytocin-immunoreactive fibers in the nucleus accumbens have been described in prairie voles. However, there has been no direct evidence of oxytocin release in the nucleus accumbens during sociosexual interactions, and the origin of the oxytocin fibers is unknown. Here we show for the first time that extracellular concentrations of oxytocin are increased in the nucleus accumbens of female prairie vole during unrestricted interactions with a male. We further show that the distribution of oxytocin-immunoreactive fibers in the nucleus accumbens is conserved in voles, mice and rats, despite remarkable species differences in oxytocin receptor binding in the region. Using a combination of site-specific and peripheral infusions of the retrograde tracer Fluorogold, we demonstrate that the nucleus accumbens oxytocin-immunoreactive fibers likely originate from paraventricular and supraoptic hypothalamic neurons. This distribution of retrogradely labeled neurons is consistent with the hypothesis that striatal oxytocin fibers arise from collaterals of magnocellular neurons of the neurohypophysial system. If correct, this may serve to coordinate peripheral and central release of oxytocin with appropriate behavioral responses associated with reproduction, including pair bonding after mating, and maternal responsiveness following parturition and during lactation.

Mass spectrometry-based discovery of circadian peptides

A significant challenge to understanding dynamic and heterogeneous brain systems lies in the chemical complexity of secreted intercellular messengers that change rapidly with space and time. Two solid-phase extraction collection strategies are presented that relate time and location of peptide release with mass spectrometric characterization. Here, complex suites of peptide-based cell-to-cell signaling molecules are characterized from the mammalian suprachiasmatic nucleus (SCN), site of the master circadian clock. Observed SCN releasates are peptide rich and demonstrate the co-release of established circadian neuropeptides and peptides with unknown roles in circadian rhythms. Additionally, the content of SCN releasate is stimulation specific. Stimulation paradigms reported to alter clock timing, including electrical stimulation of the retinohypothalamic tract, produce releasate mass spectra that are notably different from the spectra of compounds secreted endogenously over the course of the 24-h cycle. In addition to established SCN peptides, we report the presence of proSAAS peptides in releasates. One of these peptides, little SAAS, exhibits robust retinohypothalamic tract-stimulated release from the SCN, and exogenous application of little SAAS induces a phase delay consistent with light-mediated cues regulating circadian timing. These mass spectrometry-based analyses provide a new perspective on peptidergic signaling within the SCN and demonstrate that the integration of secreted compounds with information relating time and location of release generates new insights into intercellular signaling in the brain.

Serotonin and the neuroendocrine regulation of the hypothalamic--pituitary-adrenal axis in health and disease

Serotonin (5-hydroxytryptamine, 5-HT)-containing neurons in the midbrain directly innervate corticotropin-releasing hormone (CRH)-containing cells located in paraventricular nucleus of the hypothalamus. Serotonergic inputs into the paraventricular nucleus mediate the release of CRH, leading to the release of adrenocorticotropin, which triggers glucocorticoid secretion from the adrenal cortex. 5-HT1A and 5-HT2A receptors are the main receptors mediating the serotonergic stimulation of the hypothalamic-pituitary-adrenal axis. In turn, both CRH and glucocorticoids have multiple and complex effects on the serotonergic neurons. Therefore, these two systems are interwoven and communicate closely. The intimate relationship between serotonin and the hypothalamic-pituitary-adrenal axis is of great importance in normal physiology such as circadian rhythm and stress, as well as pathophysiological disorders such as depression, anxiety, eating disorders, and chronic fatigue.

Neuroendocrine pharmacology of stress

Exposure to hostile conditions initiates responses organized to enhance the probability of survival. These coordinated responses, known as stress responses, are composed of alterations in behavior, autonomic function and the secretion of multiple hormones. The activation of the renin-angiotensin system and the hypothalamic-pituitary-adrenocortical axis plays a pivotal role in the stress response. Neuroendocrine components activated by stressors include the increased secretion of epinephrine and norepinephrine from the sympathetic nervous system and adrenal medulla, the release of corticotropin-releasing factor (CRF) and vasopressin from parvicellular neurons into the portal circulation, and seconds later, the secretion of pituitary adrenocorticotropin (ACTH), leading to secretion of glucocorticoids by the adrenal gland. Corticotropin-releasing factor coordinates the endocrine, autonomic, behavioral and immune responses to stress and also acts as a neurotransmitter or neuromodulator in the amygdala, dorsal raphe nucleus, hippocampus and locus coeruleus, to integrate brain multi-system responses to stress. This review discussed the role of classical mediators of the stress response, such as corticotropin-releasing factor, vasopressin, serotonin (5-hydroxytryptamine or 5-HT) and catecholamines. Also discussed are the roles of other neuropeptides/neuromodulators involved in the stress response that have previously received little attention, such as substance P, vasoactive intestinal polypeptide, neuropeptide Y and cholecystokinin. Anxiolytic drugs of the benzodiazepine class and other drugs that affect catecholamine, GABA(A), histamine and serotonin receptors have been used to attenuate the neuroendocrine response to stressors. The neuroendocrine information for these drugs is still incomplete; however, they are a new class of potential antidepressant and anxiolytic drugs that offer new therapeutic approaches to treating anxiety disorders. The studies described in this review suggest that multiple brain mechanisms are responsible for the regulation of each hormone and that not all hormones are regulated by the same neural circuits. In particular, the renin-angiotensin system seems to be regulated by different brain mechanisms than the hypothalamic-pituitary-adrenal system. This could be an important survival mechanism to ensure that dysfunction of one neurotransmitter system will not endanger the appropriate secretion of hormones during exposure to adverse conditions. The measurement of several hormones to examine the mechanisms underlying the stress response and the effects of drugs and lesions on these responses can provide insight into the nature and location of brain circuits and neurotransmitter receptors involved in anxiety and stress.

Vasopressin in the brain of a desert hibernator, the jerboa (Jaculus orientalis): presence of sexual dimorphism and seasonal variation

The distribution of vasopressin innervation in the brain of the jerboa (Jaculus orientalis) was investigated, with special attention to sex differences and seasonal variations. Vasopressin perikarya were observed in the paraventricular and supraoptic nuclei, the suprachiasmatic nucleus, the periventricular nucleus, the medial preoptic area, the bed nucleus of the stria terminalis, and the medial amygdaloid nucleus. In addition, vasopressin cell bodies were observed in the ventral retrochiasmatic area. After treatment with colchicine, vasopressin perikarya were also observed around the organum vasculosum laminae terminalis, in the medial diagonal band of Broca, and in the dorsal medial preoptic nucleus. Vasopressin fibers were also found to be more widespread in the jerboa brain than in other rodents. Fibers were observed in the medial diagonal band of Broca, the stria medullaris, the tuber cinerum, the area postrema, the medial vestibular nucleus, and the dorsal motor nucleus of the vagus. Sexual dimorphism and seasonal variation in vasopressin immunoreactivity were observed in areas that not only showed a testosterone-dependent vasopressin innervation in other rodents but also in the paratenial and mediodorsal thalamic nuclei, the tuber cinerum, the supramammillary complex, the zona incerta, the interpeduncular complex, and the dorsal and medial raphe nuclei. A denser vasopressin innervation was observed in spring/summer (sexual active period) than in autumn. Numerous brain structures contained vasopressin receptors (cerebral cortex, hypothalamus, substantia nigra, dentate gyrus, thalamic nuclei, superior colliculus, dorsal cochlear nucleus, and cerebellum); no sex- or season-related differences were observed. These data indicate a high level of vasopressin in the jerboa brain, which may reflect an adaptation to its harsh bioclimatic environment.

Colocalization of calbindin-D28k with vasopressin in hypothalamic cells of the rat: a double-labeling immunofluorescence study

By use of a double-labeling immunofluorescence method, we examined whether vasopressin-containing cells possess a calcium-binding protein, calbindin-D28k, in the hypothalamus of the rat. Subpopulations of vasopressin-containing cells varied in their ability to possess calbindin-D28k immunoreactivity in different regions. In the supraoptic nucleus, most vasopressin-immunoreactive cells were also stained for calbindin-D28k. By contrast, in the magnocellular part of the hypothalamic paraventricular nucleus, all vasopressin-labeled cells lacked calbindin-D28k. In the suprachiasmatic nucleus, no calbindin-D28k was found in vasopressin-stained cells. This study shows a further characterization of vasopressin-containing cells of the rat hypothalamus.

Vasopressinergic innervation of the mouse suprachiasmatic nucleus: an immuno-electron microscopic analysis

Attempts are being made to unravel the local circuitry of the suprachiasmatic nucleus, with a view toward eventually correlating specific neuronal systems with circadian events. Hence, the vasopressinergic innervation of this nucleus in the laboratory mouse has been analyzed immunocytochemically at the light and electron microscopical levels. Monoclonal antineurophysin and polyclonal antivasopressin were used on aldehyde-fixed brains. Serial vibratome sections of the appropriate forebrain region were prepared for pre-embedding immunoperoxidase staining and/or postembedding immunogold labeling. Immunoreactive somata, processes, varicosities, and synaptic terminals were found throughout the suprachiasmatic nucleus, their ratio and density varying at different locations. The predominant type of vasopressinergic soma was ovoid to rounded (7-10 microns), containing secretory granules (85-120 nm), a large proportion of which were immunoreactive. Axon terminals, both nonimmunoreactive and immunoreactive, impinged upon vasopressinergic somata and processes, often displaying synaptic specializations. Vasopressinergic terminals, containing secretory granules and microvesicles, were found throughout the nucleus, particularly within the dorsomedial neuropil. These labeled terminals varied in size (0.4-3.4 microns 2) and shape, ranging from compact boutons to pleomorphic profiles, some deeply indented by postsynaptic spines, either dendritic or somatic. Approximately 65% of the vasopressin-containing terminals were axodendritic and 30% axosomatic; about 5% appeared to be axoaxonic. At least a quarter of all vasopressinergic synaptic terminals were axospinous. Other forms of interneuronal contact involving vasopressinergic elements (somata, dendrites) included extensive membrane to membrane appositional sites, and multiple puncta adhaerentia. The versatility of interconnections between vasopressin-containing neurons in the mouse suprachiasmatic nucleus suggests a highly active and coordinated network, which contributes substantially to local intranuclear circuitry. In addition, a dense efferent vasopressinergic output is directed dorsally towards the periventricular hypothalamus, where direct associations may be established with diverse hypothalamic neuroendocrine systems.

Vasopressin mRNA in the suprachiasmatic nuclei: daily regulation of polyadenylate tail length

Daily variation has been found in the length of the polyadenylate tail attached to vasopressin messenger RNA in the suprachiasmatic nuclei, which is the location of an endogenous circadian pacemaker in mammals. No such variation was found in the supraoptic or paraventricular nuclei. This variation in the length of the polyadenylate tail may underlie the circadian rhythm of vasopressin peptide levels in cerebrospinal fluid and is a unique example of a daily rhythm in messenger RNA structure.

Localization of vasopressin-, vasoactive intestinal polypeptide-, peptide histidine isoleucine- and somatostatin-mRNA in rat suprachiasmatic nucleus

Messenger RNAs (mRNA) coding for vasoactive intestinal polypeptide (VIP), peptide histidine isoleucine (PHI), somatostatin and vasopressin were localized in the suprachiasmatic nucleus (SCN) of the rat hypothalamus using in situ hybridization histochemistry. Specific mRNA coding for each of these peptides was distributed in areas coextensive with the immunohistochemical localization of the appropriate peptide. The autoradiographic signal produced with probes to VIP and PHI created dense concentrations of silver grains over neuronal perikarya in the ventrolateral SCN, and the coextensive distribution of both VIP- and PHI-mRNAs suggests that both peptides are synthesized within the same neurons. The distribution of somatostatin-mRNA was distinct from the of VIP and PHI. Labeled neurons are observed at the interface of the two SCN subdivisions and the distribution of these neurons is identical to those shown to contain somatostatin immunoreactivity. Vasopressin-mRNA is also differentially concentrated within neurons in the dorsomedial subdivision of the SCN in an area that is coextensive with vasopressin-immunoreactive perikarya. The discrete pattern of hybridization for each of these mRNAs indicates that each of these peptides are synthesized in SCN neurons and reaffirms the differential distribution of each of these chemically defined cell populations within cytoarchitecturally distinct subdivisions of the nucleus.

In vivo metabolic activity of the suprachiasmatic nuclei: non-uniform intranuclear distribution of 14C-labeled deoxyglucose uptake

Anatomical techniques have shown that the suprachiasmatic nuclei (SCN) are organized into distinct dorsomedial and ventrolateral subdivisions. As a functional correlate to this morphological organization, the intranuclear distribution of SCN glucose utilization was mapped using the autoradiographic 14C-labeled deoxyglucose method. In nocturnal rats and diurnal squirrel monkeys injected with the tracer during the light portion of the light-dark cycle, the middle of the SCN was metabolically more active than its rostral or caudal ends. No obvious dorsomedial/ventrolateral parcellation of SCN functional activity was disclosed. The rostrocaudal metabolic contour persisted unchanged in the absence of external light and resembled the 3-dimensional shape of the SCN (the highest metabolic activity was generally found at the largest cross-sectional area). This result is discussed with respect to its implications for the generation of circadian rhythmicity by the endogenous pacemaker in the SCN.

Efferent projections of the suprachiasmatic nucleus: II. Studies using retrograde transport of fluorescent dyes and simultaneous peptide immunohistochemistry in the rat

In a previous study (Watts et al., '87) we reexamined the projections of the suprachiasmatic nucleus (SCh) with the PHA-L method and found that they could be divided conveniently into six groups of fibers. By far the densest projection ends just dorsal to the SCh in a comma-shaped region designated the "subparaventricular zone," although some fibers continue on through the paraventricular nucleus of the hypothalamus to end in the overlying midline thalamus, and others continue on to end in the dorsomedial nucleus, the region around the ventromedial nucleus, and the posterior hypothalamic area. Other relatively sparse projections from the SCh were also described to the preoptic region, lateral septal nucleus, parataenial and paraventricular nuclei of the thalamus, and ventral lateral geniculate nucleus. In addition, the same method was used to show that the subparaventricular zone projects in turn massively to these same regions, as well as back to the SCh itself and to the periaqueductal gray. The present series of experiments was designed to confirm these observations with retrograde tracer injections and to investigate the cellular and possible neurotransmitter organization of the major projections from the SCh and subparaventricular zone with a combined retrograde tracer-immunohistochemical method. For this, the distribution of neuronal cell bodies within the SCh that stain with antisera to vasopressin, vasoactive intestinal polypeptide (VIP), corticotropin-releasing factor, bombesin, substance P, neurotensin, somatostatin, thyrotropin-releasing hormone, and angiotensin II was described in detail first. Then the distribution of retrogradely labeled neurons that were also stained for one or another of these peptides was described after injections of true blue, or in some cases SITS, into the regions of the subparaventricular zone, the paraventricular and parataenial nuclei of the thalamus, the ventromedial nucleus, the dorsomedial nucleus, and the periaqueductal gray. The results confirm previous immunohistochemical and anterograde tracing studies and in addition indicate that cells in dorsal as well as ventral parts of the SCh project to each of the terminal fields examined, as do many cells in surrounding areas, including the subparaventricular zone. Our results also suggest that, at the very least, vasopressin-, VIP-, and neurotensin-stained cells in the SCh project to the subparaventricular zone, midline thalamus, and dorsomedial nucleus, and that the vasopressin and VIP-stained fiber systems are partially segregated at the level of the subparaventricular zone.(ABSTRACT TRUNCATED AT 400 WORDS)

Ultrastructural localization of GABA in the supraoptic nucleus and neural lobe

Antibodies directed against the neurotransmitter gamma-aminobutyric acid (GABA) enabled the ultrastructural localization of GABA in conventional glutaraldehyde fixed and osmium postfixed material of the rat supraoptic nucleus and neural lobe. GABA was visualized using immunogold postembedding staining in axonal profiles that terminate on dendrites, axons or cell bodies throughout the supraoptic nucleus. The optimum ultrastructural preservation made possible the visualization of GABA terminals, also in the neural lobe. Here GABA axons were found to terminate synaptically on pituicytes and axonal profiles containing large dense core vesicles. These results emphasize, from an anatomical point of view, the potency of GABA to influence, as a transmitter, the release of vasopressin and oxytocin, both at the level of the cell body and of the neural lobe.

Synaptic relationships between neurons containing vasopressin, gastrin-releasing peptide, vasoactive intestinal polypeptide, and glutamate decarboxylase immunoreactivity in the suprachiasmatic nucleus: dual ultrastructural immunocytochemistry with gold-substituted silver peroxidase

In order to examine the morphological substrates for neuronal connections between cells of the hypothalamic suprachiasmatic nucleus (SCN) that contain immunoreactivity for different neurotransmitters, a double ultrastructural immunocytochemical analysis was used. For double immunostaining, the first neuroactive substance antigen was labeled with gold-substituted silver-intensified peroxidase (GSSP), which results in a granular gold deposit of high electron and light opacity. The second antigen was labeled with peroxidase and a diaminobenzidine chromagen. The GSSP reaction product greatly increased the visibility of immunoreactive structures, with both light and electron microscopy. Intensification with the GSSP method worked at all depths of thick tissue sections as determined with analysis of immunostained sections cut perpendicular to their flat surface, and with analysis of thick 80-micron sections of brain tissue into which horseradish peroxidase (HRP) has been microinjected. On a nitrocellulose dot-blot comparison of different substrates for HRP, the GSSP intensification compared favorably with tetramethylbenzidine, but unlike tetramethylbenzidine, the GSSP was stable in a wide range of buffers. In addition to diaminobenzidine, the GSSP reaction was used to intensify and stabilize both the Hanker-Yates reagent and tetramethylbenzidine on the nitrocellulose model system. Through the use of the GSSP reaction, five new synaptic relationships in the suprachiasmatic nucleus were revealed. By increasing the sensitivity of the peroxidase method by silver-gold intensification, immunoreaction product could be found in dendrites at a greater distance from the perikaryon than in nonintensified material. Because of this greater sensitivity, the neuroactive substance contained in the cell of origin of a dendrite could sometimes be identified. Boutons immunoreactive for vasopressin-associated neurophysin were found to make synaptic contact with postsynaptic dendrites that also contained vasopressin-neurophysin immunoreactivity. Similarly, boutons containing gastrin-releasing peptide immunoreactivity made synaptic contact with cells also exhibiting gastrin-releasing peptide immunoreactivity. Neurons stained with GSSP reaction product could be easily discriminated from those containing only HRP-precipitated diaminobenzidine, allowing the simultaneous use of these two markers in the same 30-micron tissue section and subsequently in ultrathin sections for electron microscopy.(ABSTRACT TRUNCATED AT 400 WORDS)

Gamma-aminobutyrate, gastrin releasing peptide, serotonin, somatostatin, and vasopressin: ultrastructural immunocytochemical localization in presynaptic axons in the suprachiasmatic nucleus

An ultrastructural immunocytochemical study was undertaken to identify neuroactive substances contained in presynaptic boutons in the hypothalamic suprachiasmatic nucleus. Axonal boutons containing immunoreactive gamma-aminobutyrate, glutamate decarboxylase, neurophysin/vasopressin, gastrin releasing peptide/bombesin, somatostatin and serotonin were localized within the hypothalamic suprachiasmatic nucleus with pre-embedding peroxidase immunostaining. Synaptic contacts were found between boutons containing each of these substances and postsynaptic structures. While some variation in synaptic morphology existed, most of the immunoreactive contacts were of the symmetrical type. Previous work has indicated that neuroactive peptides may be found in highest concentrations in dense-core vesicles, to examine the subcellular localization of the amino acid inhibitory transmitter gamma-aminobutyrate, ultrastructural immunocytochemistry with pre-embedding peroxidase was compared with post-embedding immunocytochemistry with colloidal gold. Ultracryothin sections were also used for ultrastructural localization of gamma-aminobutyrate and glutamate decarboxylase immunoreactivity. Both gamma-aminobutyrate and glutamate decarboxylase immunoreactivity were found throughout the cytoplasm of immunoreactive boutons when pre-embedding peroxidase was used; with post-embedding colloidal gold immunostaining, label was found over areas containing small clear vesicles, and over mitochondria of immunoreactive axons. At the dilutions used in this study, strongly immunoreactive gamma-aminobutyrate dendrites, boutons forming asymmetrical synapses, and cell bodies were not found. Differences between pre-embedding and post-embedding immunostaining may be due to antigen and label diffusion caused by mild fixation and membrane damage necessary for antisera penetration during pre-embedding immunostaining. These results suggest that gamma-aminobutyrate, gastrin releasing peptide, somatostatin and vasopressin are contained in axons making contact with neurons of the suprachiasmatic nucleus, and may function as neurotransmitters here. Since all of these substances can also be localized in perikarya within the suprachiasmatic nucleus, there is a strong possibility that at least some of the axons containing immunoreactivity for each of these substances may be involved in local circuit interactions between neurons within the suprachiasmatic nucleus.

Neurotransmitters of the hypothalamic suprachiasmatic nucleus: immunocytochemical analysis of 25 neuronal antigens

An immunocytochemical analysis with 33 antisera was undertaken to investigate the localization of 25 different neurotransmitter-related antigens in the hypothalamic suprachiasmatic nucleus in the rat. To obtain estimates of relative densities of immunoreactive axons a stereological approach was used involving counting of intersections of immunoreactive axons with a superimposed semi-circle test grid. All neurotransmitter-related antigens found in perikarya within the suprachiasmatic nucleus, including those stained with antisera against bombesin, gastrin-releasing peptide, neurophysin, vasopressin, somatostatin, gamma-aminobutyrate, glutamate decarboxylase and vasoactive intestinal polypeptide were also found in axons within the nucleus. A greater number of these immunoreactive axons was found within the nucleus than in the adjacent anterior hypothalamus. The size of all immunoreactive axons in the suprachiasmatic nucleus was consistently small; immunoreactive axons were found ramifying widely in the nucleus, often ending with terminal boutons near perikarya immunoreactive for the same antigen. All neurotransmitter-related substances found in perikarya of the suprachiasmatic nucleus were also found in axons crossing over the midline to innervate the contralateral nucleus, providing an anatomical substrate for a high degree of communication between the paired nuclei. Axons immunoreactive for other putative transmitters including serotonin arising outside the nucleus were also found in high densities within the nucleus and crossing over the midline between the nuclei. Immunoreactivity for some transmitters was found in axons of similar densities within and outside the nucleus, including antisera against tyrosine hydroxylase; a small number of dopamine beta-hydroxylase and a few phenylethanolamine N-methyltransferase-immunoreactive axons were found in the SCN, suggesting that dopamine, norepinephrine and epinephrine may occur in a limited number of axons in the nucleus. Small numbers of axons immunoreactive with antisera raised against cholecystokinin, prolactin, substance P, thyrotropin-releasing hormone and choline acetyltransferase were found within the suprachiasmatic nucleus. Axons immunoreactive for luteinizing hormone-releasing hormone, adrenocorticotropic hormone, alpha-melanocyte-stimulating hormone and neurotensin were rarely found within the suprachiasmatic nucleus; axons immunoreactive for luteinizing hormone-releasing hormone, adrenocorticotropic hormone, cholecystokinin and tyrosine hydroxylase were found in both horizontal and coronal sections in the area between the left and right suprachiasmatic nuclei.(ABSTRACT TRUNCATED AT 400 WORDS)

Vasopressin neuron survival in neonatal Brattleboro rats; critical factors in graft development and innervation of the host brain

Previously it was found that grafts of supraoptic plus paraventricular areas from 19-day-old foetal normal rats survived in the third ventricle of the brain of 4- to 6-day-old, vasopressin-deficient Brattleboro pups, but could not alleviate their polyuria. In the present series, factors important in graft development were analysed. Again using day-19 fetuses as donors, anterohypothalamus grafts as well as grafts placed near a crushed median eminence survived relatively poorly, but showed the presence of vasopressin neurons immunocytochemically one month post-grafting. Homotopic grafting in the supraoptic nucleus, however, even failed to show surviving vasopressin neurons. Graft survival was improved by the use of donor tissue of fetuses younger than day 19. Parvocellular vasopressin cells were frequently seen, organized into clusters resembling the normal suprachiasmatic nucleus. However, magnocellular neurons, as normally seen in supraoptic and paraventricular nuclei, only survived grafting when taken between days 11 and 15 of fetal age. It was concluded that only immature vasopressin neurons survived grafting under the condition employed. Magnocellular neurons had a limited fiber outgrowth into the host brain and median eminence. Most large neurons only stained with non-specific neurophysin antiserum, not with specific vasopressin-associated neurophysin antiserum. Thin fibers of the parvocellular vasopressin neurons provided only occasional and sparse innervation of the host median eminence and lateral septum (one case), but several examples of massive fiber bundles running dorsally from graft into host brain were observed. These fibers terminated in the thalamic periventricular area, a nucleus that is normally innervated by the vasopressin neurons of the suprachiasmatic nucleus. The failure of the grafts to provide adequate vasopressinergic innervation of the host median eminence probably explains why none of the nearly 200 Brattleboro neonates operated upon showed any sign of relief of their diabetes insipidus. It suggests, however, that the present procedures might be useful in restoring central vasopressinergic functions in the developing Brattleboro rat.

The dopaminergic innervation of the supraoptic and paraventricular nucleus. A light and electron microscopical study

An antiserum that has been raised against glutaraldehyde-conjugated dopamine was used to demonstrate specifically dopamine in the rat hypothalamus. This dopamine antiserum permitted an optimal fixation with glutaraldehyde and therefore enabled the simultaneous light and electron microscopic immunocytochemical localization of dopamine. It was demonstrated that the paraventricular and supraoptic nuclei of the hypothalamus were innervated by thin dopaminergic fibers, in contrast to the suprachiasmatic nucleus, which hardly received any dopaminergic input. Ultrastructural observations revealed that the dopamine fibers terminated synaptically on the magnocellular neurons and their processes. It is concluded that the present results may explain the effect of centrally injected dopamine on vasopressin and oxytocin release. In the dopamine-containing terminals the reaction product was frequently observed in 90 nm dense core vesicles and around clear vesicles.

Influence of environmental light-dark cycle and enucleation on activity of suprachiasmatic neurons in slice preparations

The influence of environmental light-dark cycle (LD) and bilateral enucleation on single neuronal activity in the suprachiasmatic nucleus (SCN) was examined using a hypothalamic slice preparation. Firstly, we reconfirmed previous results that the discharge rate in slices taken from animals kept on normal LD was higher during the light than during the dark period. Secondly, the day time discharge rate in the ventrolateral part of the SCN was decreased by bilateral enucleation and DD housing, while in the dorsomedial part it was unaffected. Thirdly, LL housing suppressed the discharge rates in both parts during the day and night periods. The present results suggest that the dorsomedial part of the SCN is more important in regulation of the circadian rhythm of SCN neuronal activity than the ventrolateral.

A daily vasopressin rhythm in rat cerebrospinal fluid

Cerebrospinal fluid (CSF) was serially withdrawn in individual, unanesthetized, unrestrained rats and assayed for vasopressin using a sensitive and specific radioimmunoassay. A prominent daily rhythm in the CSF concentrations of this peptide was found under diurnal lighting conditions. Low levels during the dark period alternated with high values during the light period; the rhythm appeared to anticipate the artificial 'dawn' and 'dusk' by a few hours. An 8-h phase shift in diurnal lighting caused a corresponding phase shift in the CSF rhythm. In addition, the rhythm persisted for at least 10 days in the absence of periodic environmental lighting cues in animals blinded by bilateral orbital enucleation; the rhythm was disrupted after 10 days of constant light. Blood vasopressin concentrations did not show a daily rhythm. Our results indicate that the daily vasopressin rhythm in rodent CSF is endogenously generated and that its phase is synchronized to the environmental light-dark cycle.

Comparison of the temporal profiles of vasopressin and oxytocin in the cerebrospinal fluid of the cat, monkey and rat

The temporal profiles of oxytocin were examined in the cerebrospinal fluid (CSF) of the cat and rat. Unlike the marked daily rhythm of oxytocin concentrations recently described in the CSF of the rhesus monkey, no daily rhythm of the peptide was evident in the CSF of either the cat or rat. The apparent species specificity of the CSF oxytocin profiles among these mammals is contrasted with the consistent expression of a daily rhythm of arginine-vasopressin in the CSF of each of the three species.

Horseradish peroxidase: a tool for study of the neuroendocrine cell and other peptide-secreting cells

The versatility of horseradish peroxidase is its usefulness both as an antigenic marker and as a probe molecule. We have demonstrated in the neuroendocrine cell that an HRP-bound antibody offers a high order of resolution for determining in which cellular compartment an antigen is located and where it is not. When native peroxidase is applied as an intracellular probe, it labels organelles associated with endocytosis in retrograde axonal transport and with the lysosomal system in both retrograde and orthograde axonal transport. The investigation that remains is the application of lectin-bound HRP to determine the pathways of membrane flow at the time when the neuroendocrine cell is stimulated to synthesize, transport, and secrete its peptide. For example, we are interested to know (1) whether internalized axon terminal membrane tagged with wheat germ agglutinin-HRP is channeled to all Golgi saccules engaged in the production of secretory granules in salt stimulated supraoptic neurons; and (2) if internalized cell membrane of the supraoptic cell body is tagged with wheat germ agglutinin-HRP and channeled to GERL, will this membrane be transferred from GERL to secretory granules, lysosomes in the cell body and axon, the axonal endoplasmic reticulum, and to autophagic/crinophagic vacuoles in axon terminals of salt-stressed supraoptic neurons? These additional studies should provide a more comprehensive, morphological picture of membrane flow in a neuroendocrine cell that is responding to the metabolic demands placed upon it.

Oxytocin, vasopressin, and estrogen-stimulated neurophysin: daily patterns of concentration in cerebrospinal fluid

The concentrations of oxytocin, arginine vasopressin, and estrogen stimulated neurophysin in cerebrospinal fluid of monkeys showed a daily fluctuation with high concentrations occurring during the light period. The patterns of oxytocin and estrogen-stimulated neurophysin in the cerebrospinal fluid were not observed in the plasma nor were they altered after the administration of a dose of estradiol that increased concentrations of estrogen-stimulated neurophysin in plasma. The disassociation between these cerebrospinal fluid and plasma patterns and values suggests that the secretory activity of neurons that release estrogen-stimulated neurophysin and oxytocin into the cerebrospinal fluid is controlled by mechanisms different from those that control their release into the plasma.

Oxytocin biotransformation in the rat limbic brain: characterization of peptidase activities and significance in the formation of oxytocin fragments

The enzymatic conversion of oxytocin by brain peptidases has been studied. Oxytocin was incubated with synaptosomal plasma membranes (SPM) isolated from the rat brain. Qualitative studies using a microdansylation technique revealed two types of oxytocin converting peptidases, e.g. aminopeptidase and C-terminal cleaving peptidase activities. Both enzyme activities were quantitated using [14C]oxytocin labeled at either the tyrosine-2 or the glycinamide-9 residue. Radiolabeled products were separated by high-voltage paper electrophoresis or high-pressure liquid chromatography. The aminopeptidase activity was optimally active at pH 6.9 with a Michaelis constant (Km) of 6.1 x 10(-5) M. The pH optimum of the C-terminal cleaving peptidase activity was pH 6.0 with Km = 1.3 x 10(-5) M. Subcellularly, highest amino-peptidase activities were associated with SPM, synaptosomal and microsomal preparations, while the C-terminal cleaving peptidase prevailed in the cytosol and mitochondrial fractions. The regional distribution of both peptidases showed differences between several brain areas and indicated the medial basal hypothalamus as a locus of high oxytocin biotransformation. In the course of this investigation an oxytocin fragment of unknown structure was detected in the digests and its accumulation was studied together with the determination of peptidase activities. It is suggested that the SPM-associated peptidases may have a role in the modulation of oxytocin action in the brain.

Identification of parvocellular vasopressin and neurophysin neurons in the suprachiasmatic nucleus of a variety of mammals including primates

The presence of parvocellular vasopressin- and neurophysin-containing neurons in the suprachiasmatic nucleus (SCN) was investigated in 13 mammalian species representing six mammalian orders (marsupials, rodents, lagomorphs, artiodactyls, carnivores, and primates), using specific antisera to vasopressin and neurophysin in the unlabelled antibody=enzyme immunoperoxidase method. In all mammals examined, including man, parvocellular vasopressin and neurophysin neurons were found in the SCN. Only a portion of SCN neurons contain vasopressin and neurophysin, the number varying with species. Cell counts comparing the number of immunoreactive to Nissl-stained neurons showed averages of 17% immunopositive neurons in the rat SCN, and 31% in the human SCN. No oxytocin-containing SCN neurons were observed. These findings suggest that parvocellular vasopressin and neurophysin neurons are widely represented in mammals.

Cytodifferentiation of the supraoptic nucleus correlated with vasopressin synthesis in the rat

This study demonstrates that neurons in the supraoptic nucleus attain many of the prerequisites for functional activity prior to birth. Immunoassayable vasopressin (VP) was detected in the hypothalamo-neurohypophyseal system (HNS) of the rat as early as 17 days post-coitus (dpc). Vasopressin concentrations increased 3--6-fold daily from an average of 21 pg/animal on 17 dpc to 5984 pg/animal at 21 dpc. The daily increases were highly significant (P less than 0.001). Between 21 dpc and the morning of the day of birth on 22 dpc, a further significant increase (P less than 0.05) occurred to a mean level of 9672 pg VP/animal. Birth usually occurred on the afternoon of the 22nd day. Parturition did not seem to deplete VP stores in the HNS. Differentiation of the magnocellular neurons in the supraoptic nucleus closely paralleled the appearance and increases in VP. It was first possible to dintinguish a supraopic nucleus in the 17 dpc rat and to identify dense core granules in the developing neurons of the nucleus. Cytodifferentiation of the magnocellular neurons was essentially complete by 21 dpc. Synaptic contacts could not be found on the soma and dendrites of the supraoptic neurons until 21 dpc and were extremely rare throughout the period examined.