Discovery of novel selective hypotensive vasopressin peptides that exhibit little or no functional interactions with known oxytocin/vasopressin receptors

1. Arginine-vasopressin (VP) has both vasoconstricting and vasodilating action. We report here the discovery of four novel selective hypotensive VP analogues: d(CH2)5[D-Tyr(Et)2,Arg3,Val4]AVP; d(CH2)5[D-Tyr(Et)2,Lys3,Val4]AVP and their iodinatable Tyr-NH2(9) analogues. 2. Bioassays in rats for activities characteristic of neurohypophysial peptides showed that the four VP peptides possessed little or no V1a, V2 or oxytocin (OT) receptor agonistic or antagonistic activities. 3. In anaesthetized rats, these peptides (0.05-0.10 mg kg(-1) i.v.) elicited a marked fall in arterial blood pressure. 4. Blockade of cholinoceptors, adrenoceptors and bradykinin B2 receptors, and inhibition of prostaglandin synthesis had little effect on their vasodepressor action. 5. Classical V1a, V2 and OT receptor antagonists did not block the vasodepressor response. 6. L-NAME, 0.2 mg kg(-1) min(-1), markedly suppressed the hypotensive response to ACh but not the vasodepressor response to the hypotensive VP peptides. However, the duration of the vasodepressor response was shortened. Very high doses of L-NAME attenuated both the vasodepressor response and the duration of action. 7. These findings indicate that the vasodepressor action of these VP peptides is independent of the peripheral autonomic, bradykinin and PG systems and is not mediated by the known classical OT/VP receptors. NO does not appear to have an important role in their vasodepressor action. 8. The discovery of these novel VP peptides could lead to the development of new tools for the investigation of the complex cardiovascular actions of VP and the introduction of a new class of hypotensive agents. The two iodinatable hypotensive VP peptides could be radiolabelled as potential markers for the localization of the receptor system involved.

Functions of the hypophysis-gonad and hypophysis-adrenal cortex systems during repeated administration of gonadotropin-releasing hormone in the postnatal period

The effects of multiple doses of gonadotropin-releasing hormone (luliberin, LH-RH) on the functional activity of the hypophysis--gonad and hypophysis--adrenal cortex systems were studied in young hamadril baboons of different ages. After six doses (given on alternate days) of LH-RH, radioimmunoassays were used to determine blood concentrations of testosterone, dihydrotestosterone, cortisol, 11-deoxycortisol, and luteinizing hormone. A reduction in the stimulatory effect of luliberin on the luteinizing hormone level in male hamadril baboons aged one year was seen after repeated doses. There was no tendency for the stimulatory effect of LH-RH on the accompanying increase in the testosterone level to decrease. Doses of LH-RH did not alter blood cortisol levels in animals aged two years, but led to increases in cortisol in one-year-old animals. Repeated doses of LH-RH to young male hamadril baboons produced changes in adrenal steroidogenesis, with reductions in the blood corticosterone, 11-deoxycortisol, and dihydrotestosterone levels.

Ultramicroanalysis of peptide profiles in biological samples using MALDI mass spectrometry

In the past few years, matrix-assisted laser desorption/ionization (MALDI) mass spectrometry has emerged as a powerful tool for the direct analysis of peptide profiles contained in single neuroendocrine cells, tissue biopsies, as well as in releasates (after a simple sample clean-up). These studies were performed in both invertebrate (the pond snail) and vertebrate (xenopus and rat) species. The present article provides an overview of these data with a special emphasis on the sample handling required for each application.

Identification and neuroanatomical distribution of immunoreactivity for mammalian gonadotropin-releasing hormone (mGnRH) in the brain and neural hypophyseal lobe of the toad Bufo arenarum

The presence and distribution of gonadotropin-releasing hormone (GnRH) in sexually mature specimens of Bufo arenarum was studied by reverse phase/high performance liquid chromatography (RP-HPLC) combined with radioimmunoassay and immunocytochemistry. The analysis of brain extracts with RP-HPLC followed by radioimmunoassay with PBL#45 antiserum showed the presence of only one peak with immunoreactivity for GnRH (ir-GnRH) having the chromatographic and immunological characteristics of mammalian GnRH (mGnRH). This peak was further analyzed with two mGnRH-specific antisera, EL-15 and m1076, yielding serial dilution displacement curves parallel to those obtained with the mGnRH synthetic standard. Immunocytochemical results with the monoclonal antibody LRH13 showed the presence of a terminal nerve-septo-preoptic system with neurons and fibers distributed from the olfactory bulb, septal area, and anterior preoptic area toward the hypothalamus and hypophyseal neural lobe. The main group of ir-GnRH fibers and neurons was identified in the anterior preoptic area. These neurons appear to be the origin of fibers that, after surrounding the preoptic recess, border the dorsal surface of the optic chiasma, extend through the infundibulum, traverse the external layer of the median eminence, and end in the pars nervosa.

Effects of depolarization evoked Na+ influx on intracellular Na+ concentration at neurosecretory nerve endings

Electrophysiological measurements of voltage-dependent Na+ influx using patch-clamp methodology were combined with optical monitoring of the free intracellular Na+ concentration in isolated rat neurohypophysial nerve endings to determine the relationship between Na+ influx generated by repetitive stimulation and change in [Na+]i. Application of step depolarizations under voltage-clamp-evoked tetrodotoxin-sensitive inward currents that were dependent upon extracellular Na+ and that exhibited rapid activation and inactivation properties. These characteristics substantiated the evoked current as a voltage-dependent Na+ current. Application of stimulus trains consisting of step depolarizations that mimick in frequency and duration those of action potentials were found to result in increases in [Na+]i. The induced change in [Na+]i was found to be related to the frequency and period of stimulation. Changes in [Na+]i were greatest at frequencies of 40 Hz and gave maximal changes with 30 s of continuous stimulation of approximately 2.4 mM. Sodium influx expressed as a molar quantity resulted in a nearly directly proportional increase in [Na+]i during the initial period of stimulation at low Na+ loads. When expressed as a charge density (pC/microm2) Na+ influx was found to increase with smaller diameter nerve endings as did the rate of change in [Na+]i in response to applied repetitive step depolarizations. Repetitive step depolarizations which simulate impulse activity that invade neuroendocrine nerve endings in vivo in response to physiological demand for hormone secretion resulted in an increased [Na+]i. It is postulated that this increased [Na+]i may provide a modulatory influence on the secretory response indirectly via alteration of intracellular calcium regulation or, perhaps, via a direct action on the secretory mechanism.

ATP-evoked increases in [Ca2+]i and peptide release from rat isolated neurohypophysial terminals via a P2X2 purinoceptor

1. The effect of externally applied ATP on cytosolic free Ca2+ concentration ([Ca2+]i) was tested in single isolated rat neurohypophysial nerve terminals by fura-2 imaging. The release of vasopressin (AVP) and oxytocin (OT) upon ATP stimulation was also studied from a population of terminals using specific radioimmunoassays. 2. ATP evoked a sustained [Ca2+]i increase, which was dose dependent in the 1-100 microM range (EC50 = 4.8 microM). This effect was observed in only approximately 40 % of the terminals. 3. Interestingly, ATP, in the same range (EC50 = 8.6 microM), evoked AVP, but no significant OT, release from these terminals. 4. Both the [Ca2+]i increase and AVP release induced by ATP were highly and reversibly inhibited by suramin, suggesting the involvement of a P2 purinergic receptor in the ATP-induced responses. Pyridoxal-5-phosphate-6-azophenyl-2',4'-disulphonic acid (PPADS), another P2 purinergic receptor antagonist, strongly reduced the ATP-induced [Ca2+]i response. 5. To further characterize the receptor, different agonists were tested, with the following efficacy: ATP = 2-methylthio-ATP > ATP-gamma-S > alpha, beta-methylene-ATP > ADP. The compounds adenosine, AMP, beta, gamma-methylene-ATP and UTP were ineffective. 6. The ATP-dependent [Ca2+]i increase was dependent on extracellular Ca2+ concentration ([Ca2+]o). Fluorescence-quenching experiments with Mn2+ showed that externally applied ATP triggered a Mn2+ influx. The ATP-induced [Ca2+]i increase and AVP release were independent of and additive to a K+-induced response, in addition to being insensitive to Cd2+. The ATP-induced [Ca2+]i increase was strongly reduced in the presence of Gd3+. These results suggest that the observed [Ca2+]i increases were elicited by Ca2+ entry through a P2X channel receptor rather than via a voltage-dependent Ca2+ channel. 7. We propose that ATP, co-released with neuropeptides, could act as a paracrine-autocrine messenger, stimulating, via Ca2+ entry through a P2X2 receptor, the secretion of AVP, in particular, from neurohypophysial nerve terminals.

Evidence for diverse pathways of hypophysiotropic hormone transport in mammals

Comparative studies of mammalian hypothalamic-pituitary relationships have revealed striking variations in hypophysiotropic systems and in portal vascular architecture. Immunocytochemical studies indicate that mammalian GnRH, GHRH and somatostatin systems can project to all portions of the neurohypophysis (median eminence, infundibular stem and pituitary neural lobe). In rats, primary secretion sites are located within the median eminence and upper infundibular stem, whereas in bats, most projections extend into the lower infundibular stem and pituitary neural lobe. In ferrets and monkeys, sites of secretion appear to extend throughout the neurohypophysis, from median eminence to proximal neural lobe. In this review, these interspecific differences are examined in light of observed structural variations in portal vascular systems. Correlations suggest that hypophysiotropic hormones can be delivered to target cells in the pars distalis by diverse routes, with some species relying more heavily on long and others on short portal transport. These patterns may have important functional implications with respect to regulatory mechanisms operating within the hypothalamic-pituitary complex.

Tanycytes and pituicytes: morphological and functional aspects of neuroglial interaction

The hypothalamo-hypophyseal system is supplied with two types of specialized glial cells that interact in neuroendocrine functional dynamics: the tanycytes and the pituicytes. Tanycytes are the dominating glial cells within the median eminence. Similar to radial glia, they extend from the floor of the third ventricle to the neurohemal surface of the median eminence. Pituicytes, as specialized astrocytes, are the main glial cells of the neural lobe. They are in intimate contact with the perivascular space of the sinusoidal vessels. Morphological similarities between the two cell types focus on their interaction with terminal branches of hypothalamic neurons in both regions of the neurohypophysis, the median eminence and the neural lobe. Release of hypothalamic hormones is apparently influenced by pituicytes and tanycytes. For instance, both types of cells are capable of closing or opening the access to the vessels. Thereby, in contrast to the "blood-brain-barrier" function of astrocytes, pituicytes and tanycytes display "brain-blood-barrier" functions. Pituicytes are characterized by the expression of specific membrane-bound receptors for opioids, vasopressin, and beta-adrenoceptors, indicating that they receive input by numerous neuroactive substances. Integration of these incoming signals may result in a regulation of neurosecretion, especially by morphological changes and by modulation of extracellular ion concentrations. Comparable modulatory mechanisms of tanycytes have not yet been elucidated in a convincing manner. Besides possible regulatory functions, tanycytes are considered to possess guiding functions for hypothalamic axons and to be involved in transport mechanisms between ventricle and blood vessels of the portal system.

Involvement of extracellular and intracellular calcium sources in TRH-induced alpha-MSH secretion from frog melanotrope cells

The stimulatory effect of thyrotropin-releasing hormone (TRH) on alpha-melanocyte stimulating hormone (MSH) secretion from the frog pars intermedia is mediated through the phospholipase C (PLC) pathway but requires extracellular Ca2+. The aim of the present study was to investigate the respective contribution of extracellular and intracellular Ca2+ in the action of TRH on cytosolic calcium concentration ([Ca2+]i) and alpha-MSH release. In normal conditions, TRH (10(-7) M; 5 s) evoked two types of Ca2+ responses: in 63% of the cells, TRH caused a sustained and biphasic increase in [Ca2+]i while in 37% of the cells, TRH only induced a transient response. In the presence of EGTA or Ni2+, the stimulatory effect of TRH on [Ca2+]i and alpha-MSH secretion was totally suppressed. Nifedipine (10(-6) M) reduced by approximately 50% the amplitude of the two types of Ca2+ responses whereas omega-conotoxin GVIA (10(-7) M) suppressed the plateau-phase of the sustained response indicating that the activation of L-type Ca2+-channels (LCC) is required for initiation of the Ca2+ response while N-type Ca2+-channels (NCC) are involved in the second phase of the response. Paradoxically, neither nifedipine nor omega-conotoxin GVIA had any effect on TRH-induced alpha-MSH secretion. The PLC inhibitor U-73122 (10(-6) M) significantly reduced the transient increase in [Ca2+]i and totally suppressed the sustained phase of the Ca2+ response but had no effect on TRH-induced alpha-MSH secretion. The stimulatory effect of TRH on PLC activity was not effected by nifedipine and omega-conotoxin GVIA but was abolished in Ca2+-free medium. Ryanodine had no effect on the TRH-induced stimulation of [Ca2+]i and alpha-MSH secretion. Concomitant administration of nifedipine/omega-conotoxin GVIA or U-73122/omega-conotoxin GVIA markedly reduced the response to TRH but did not affect TRH-evoked alpha-MSH release. In contrast, concomitant administration of U-73122 and nifedipine significantly reduced the effect of TRH on both [Ca2+]i and alpha-MSH release. Taken together, these data indicate that, in melanotrope cells, activation of TRH receptors induces an initial Ca2+ influx through nifedipine- and omega-conotoxin-insensitive, Ni2+-sensitive Ca2+-channels which subsequently activates LCC and causes Ca2+ mobilization from intracellular pools by enhancing PLC activity. Activation of the PLC causes Ca2+ entry through NCC which is responsible for the plateau-phase of sustained Ca2+ response. Although nifedipine and U-73122, separately used, were devoid of effect on secretory response, Ca2+ entry through LCC and mobilization of intracellular Ca2+ are both involved in TRH-evoked alpha-MSH release because only one source of Ca2+ is sufficient for inducing maximal hormone release. In contrast, the Ca2+ influx through NCC does not contribute to TRH-induced alpha-MSH secretion.

Dopamine D4 receptor mediated inhibition of potassium current in neurohypophysial nerve terminals

Dopamine influences the release of neurohypophysial peptides in vivo. However, the extent to which this effect is caused by a direct dopaminergic action within the neurohypophysis remains unclear. With use of the patch-clamp technique on thin slices of rat posterior pituitary glands, we now provide evidence that dopaminergic agonists inhibit potassium current (IK) in neurohypophysial nerve terminals. Superfusion with the dopamine receptor agonist, (+/-)-2-(N-phenylethyl-N-propyl)-amino-5-hydroxytetralin (PPHT), causes a reversible inhibition of whole-terminal IK under voltage clamp. This effect is concentration-dependent, with a maximal inhibition of 40 +/- 5% and an EC50 of 1.8 +/- 1.0 microM. It can be blocked with either a nonselective D2-like antagonist (100 microM eticlopride) or with the highly selective D4 antagonist, RBI-257 (10 microM). U101958 (a derivative of RBI-257) exhibits agonist activity similar to PPHT. Neither SKF 38393 (a D1/D5 agonist) nor quinpirole (a D2/D3 agonist) had any effect on whole-terminal IK in this preparation. Kinetic analysis demonstrated that the amplitude of both the rapidly and slowly inactivating phases of neurohypophysial IK are reduced by D4 receptor activation. These two separate current components have previously been shown to represent current through two distinct potassium channels, an A-current channel and a high-conductance Ca++-activated K+ channel. Thus, both channel types can be modulated by D4 receptors. This effect is likely to enhance the release of neurohypophysial peptides in vivo.

Membrane excitability and secretion from peptidergic nerve terminals

1. Thin slices of the posterior pituitary can be used as a preparation for the study of biophysical mechanisms underlying neuropeptide secretion. Patch-clamp techniques in this preparation have revealed the properties of ion channels that control the excitability of the nerve terminal membrane and have clarified the relation between Ca2+ and exocytosis. 2. Repetitive electrical activity at high frequencies broadens action potentials to allow more Ca2+ entry and thus enhance exocytosis. Action potential broadening results from the inactivation of a voltage-dependent K+ channel. 3. When repetitive electrical activity is sustained, secretion is depressed. This depression can be attributed in part to action potential failure caused by the opening of a Ca(2+)-activated K+ channel. This channel can be modulated by protein kinases, phosphatases, and G-proteins. 4. The inhibitory neurotransmitter GABA activates a GABAA receptor in the nerve terminal membrane. The gating of the associated Cl- channel depolarizes the membrane slightly to inactivate voltage-gated Na+ channels and block action potential propagation. 5. The response of the nerve terminal GABAA receptor is enhanced by neuroactive steroids and this can potentiate the inhibition of neurosecretion by GABA. The action of neurosteroids at this site could play a role in changes in neuropeptide secretion associated with reproductive transitions. 6. Ca2+ channels in the nerve terminal membrane are inactivated by sustained depolarization and by trains of brief pulses. Ca2+ entry promotes Ca2+ channel inactivation during trains by inhibiting the recovery of Ca2+ channels from inactivation. The inactivation of Ca2+ channels can play a role in defining the optimal frequency and train duration for evoking neuropeptide secretion. 7. Measurements of membrane capacitance in peptidergic nerve terminals have revealed rapid exocytosis and endocytosis evoked by Ca2+ entry through voltage-gated Ca2+ channels. Exocytosis is too rapid to account for the delays in neuropeptide secretion evoked by trains of action potentials. Endocytosis sets in rapidly after exocytosis with a time course comparable to that of the rapid endocytosis observed in nerve terminals at rapid synapses. Our results support the finding in rapid synaptic nerve terminals that endocytosis is inhibited by intracellular Ca2+. Multiple pools of vesicles were revealed, and these pools may reflect different stages in the mobilization and release of neuropeptide.

The effect of posterior lobe extract, adrenalin, and pilocarpine on the response of the thyroid gland to the thyreoactivator hormone of the anterior lobe of the hypophysis

The studies reported here were directed toward ascertaining in a variety of organisms whether or not any of the three lobes of the pituitary gland affected thyroid activity. We documented a thyroid stimulating action of the anterior lobe of the pituitary gland extract that was not shared in by either the intermediate or posterior lobes. Pilocarpine first depressed the stimulating action of the pituitary extract but, after the fifth injection, it accentuated the response of the thyroid gland to the pituitary extract.

Afferents of the lamprey striatum with special reference to the dopaminergic system: a combined tracing and immunohistochemical study

The origin of afferents to the striatum in lamprey (Lampetra fluviatilis) was studied by using fluorescein-coupled dextran-amines (FDA). Injection of FDA into the striatum retrogradely labeled several cell populations in the forebrain and the rostral rhombencephalon. No retrograde labeled cells were seen in the mesencephalon. A dopamine-specific antiserum was used to determined the distribution of dopaminergic perikarya and fibers. Many dopamine-immunoreactive (DA-ir) fibers were present throughout the brain, but the highest density of labeled fibers was in the mediobasal prosencephalon, especially in the striatum, the lateral hypothalamic area, and the neurohypophysis. Most DA-ir cells were located in the mediobasal diencephalon (preoptic region, nucleus commissurae postopticae, hypothalamus, and nucleus tuberculi posterioris). In the mesencephalon, only a few immunopositive cells were observed in the tectum opticum. In the rhombencephalon, DA-ir cells were observed in the isthmic region, dorsally to the descending trigeminal tract, and caudally to the posterior rhombencephalic reticular nucleus. The rostralmost spinal cord received many descending DA-ir fibers from the brainstem. Along the spinal cord, DA-ir neurons were also found, some of which projected to the medioventral surface, forming a prominent plexus. On the basis of double-labeling experiments, it is shown that the dopaminergic input to the striatum originates from the nucleus tuberculi posterioris. Thus, the striatum receives inputs from different structures, including a strong dopaminergic innervation from the diencephalon. Much of the dopaminergic system in Lampetra fluviatilis is basically similar to that seen in some teleosts, but it presents differences with other anamniote (elasmobranch) as well as amniote groups.

Puberty influences expression of phospholipid hydroperoxide glutathione peroxidase (GPX4) in rat testis: probable hypophysis regulation of the enzyme in male reproductive tract

Mammalian spermatozoa are unusually rich in polyunsaturated fatty acids, a property that predisposes them to the deleterious effects of oxygen free radicals. Mouse and human spermatozoa utilize glutathione peroxidase, (GPX), to inactivate oxygen free radicals. In the GPX super-family there is the enzyme phospholipid hydroperoxide glutathione peroxidase (GPX4) that specifically protects membrane phospholipids against peroxidation. GPX4 is present, primarily, in testis where its enzymatic activity seems to be present only after puberty. In order to clarify this question we utilized total RNA from rat testis, liver and lung to carry out cDNA synthesis and the following RT-PCR amplification of cDNA products by using specific primers of rat liver sequence. RT-PCR products of the expected size for GPX4 (525 bp) were obtained from the three tissues. At last, these fragments were submitted to sequencing analysis. Here we demonstrate that the sequence analysis of rat testis GPX4 coding region is identical to that of rat liver and lung; however puberty influences the expression pattern of rat testis GPX4. In fact Northern blot analysis of total RNA from normal and pre-puberal hypophysectomized rats demonstrates the absence of a specific GPX4 mRNA in total RNA from pre-puberal hypophysectomized rat testis; on the other hand this specific transcript is present in both normal rat testis and liver and in pre-puberal hypophysectomized rat liver. Expression pattern of GPX4 is very low in lung both in post-puberal and pre-puberal hypophysectomized rats. Therefore hypophysis could regulate GPX4 transcript in rat testis.

Oxytocin and prolactin suppress cortisol responses to acute stress in both lactating and non-lactating sheep

Cortisol response to stress appears to differ between lactating and non-lactating animals. Lactating (14 d post partum) and non-lactating sheep were fitted with probes so that drugs and hormones could be infused directly into the posterior pituitary and paraventricular nucleus of the hypothalamus. The animals were also fitted with instruments to allow monitoring of heart rate, body temperature and blood cortisol levels. Their reactions to a source of acute stress (a barking dog) were then followed, with or without drug and hormone manipulation. Results in both lactating and non-lactating animals indicated shortcomings in the use of cortisol as a stress indicator. Infusing prolactin and oxytocin into either the posterior pituitary or the paraventricular nucleus of the hypothalamus suppressed cortisol responsiveness to stress in both lactating and non-lactating animals (the latter to a greater extent). In the absence of drugs, lactating animals had a slightly higher basal level of cortisol and a lower cortisol response to stress than their non-lactating counterparts. Despite suppression of cortisol responses, with or without drugs, other indicators of stress still changed with the presence of a barking dog, suggesting the complexity of control involved in stress responses.

Modulation of NCAM polysialylation is associated with morphofunctional modifications in the hypothalamo-neurohypophysial system during lactation

Post-transcriptional modification of the neural cell adhesion molecule (NCAM) by polysialic acid significantly decreases NCAM adhesiveness and more generally modifies cell-cell interactions. Polysialic acid-NCAM (PSA-NCAM) is mainly expressed in the developing nervous system. In the adult, its expression is restricted to regions that retain morphological plasticity, such as the hypothalamo-neurohypophysial system during lactation in rats. Since cell-cell interactions and synaptic contacts in the hypothalamo-neurohypophysial system are greatly increased during lactation, we examined whether PSA-NCAM expression is modified during this period. Immunohistochemistry and immunoblotting showed that, compared with virgin rats, PSA-NCAM dramatically decreased during lactation in both the supraoptic nuclei and the neurohypophysis, and returned to its initial level only after weaning. This decrease was progressive and became significant only at the end of the first week of lactation. By contrast, modifications in the level of NCAM protein or changes in the splicing pattern of NCAM mRNAs could not be detected. The decline in polysialic acid on the NCAM molecule could strengthen membrane appositions, thereby stabilizing the newly established synapses and neurohaemal contacts in the hypothalamo-neurohypophysial system that accompany the increased neuronal activity that occurs during lactation. We also studied the regulation of the phosphorylated microtubule-associated protein-1B (MAP1B-P), whose distribution pattern largely overlaps with that of PSA-NCAM in the adult brain. Expression of MAP1B-P was greatly increased during lactation in the hypothalamic axons projecting into the neurohypophysis. Thus, the expression patterns of both PSA-NCAM and MAP1B-P may reflect the permanent structural plasticity characterizing the hypothalamo-neurohypophysial system in the adult.

Role of Q-type Ca2+ channels in vasopressin secretion from neurohypophysial terminals of the rat

1. The nerve endings of rat neurohypophyses were acutely dissociated and a combination of pharmacological, biophysical and biochemical techniques was used to determine which classes of Ca2+ channels on these central nervous system (CNS) terminals contribute functionally to arginine vasopressin (AVP) and oxytocin (OT) secretion. 2. Purified neurohypophysial plasma membranes not only had a single high-affinity binding site for the N-channel-specific omega-conopeptide MVIIA, but also a distinct high-affinity site for another omega-conopeptide (MVIIC), which affects both N- and P/Q-channels. 3. Neurohypophysial terminals exhibited, besides L- and N-type currents, another component of the Ca2+ current that was only blocked by low concentrations of MVIIC or by high concentrations of omega-AgaIVA, a P/Q-channel-selective spider toxin. 4. This Ca2+ current component had pharmacological and biophysical properties similar to those described for the fast-inactivating form of the P/Q-channel class, suggesting that in the neurohypophysial terminals this current is mediated by a 'Q'-type channel. 5. Pharmacological additivity studies showed that this Q-component contributed to rises in intraterminal Ca2+ concentration ([Ca2+]i) in only half of the terminals tested. 6. Furthermore, the non-L- and non-N-component of Ca(2+)-dependent AVP release, but not OT release, was effectively abolished by the same blockers of Q-type current. 7. Thus Q-channels are present on a subset of the neurohypophysial terminals where, in combination with N- and L-channels, they control AVP but not OT peptide neurosecretion.

Central nervous system actions of oxytocin and modulation of behavior in humans

The posterior pituitary hormone oxytocin has modulatory effects on neural functioning that are significant to the regulation of behavior. Basic research in animals has established the importance of oxytocin in affiliation, including mating, pair bonding and parenting behaviors. It is also an important regulator of feeding, grooming and responses to stress. The actions of oxytocin in the brain are regulated by gonadal steroid hormones, particularly estrogen. Oxytocin might also influence normal behavior in humans, and dysfunctions in the oxytocin system might be involved in the etiology and expression of neuropsychiatric disorders.