Roles of PLCβ, PIP2 , and GIRK channels in arginine vasopressin-elicited excitation of CA1 pyramidal neurons

Arginine vasopressin activates serotonergic neurons in the dorsal raphe nucleus during neonatal development in vitro and in vivo

Birth stress is a risk factor for psychiatric disorders and associated with exaggerated release of the stress hormone arginine vasopressin (AVP) into circulation and in the brain. In perinatal hippocampus, AVP activates GABAergic interneurons which leads to suppression of spontaneous network events and suggests a protective function of AVP on cortical networks during birth. However, the role of AVP in developing subcortical networks is not known. Here we tested the effect of AVP on the dorsal raphe nucleus (DRN) 5-hydroxytryptamine (5-HT, serotonin) system in male and female neonatal rats, since early 5-HT homeostasis is critical for the development of cortical brain regions and emotional behaviors. We show that AVP is strongly excitatory in neonatal DRN: it increases excitatory synaptic inputs of 5-HT neurons via V1A receptors in vitro and promotes their action potential firing through a combination of its effect on glutamatergic synaptic transmission and a direct effect on the excitability of these neurons. Furthermore, we identified two major firing patterns of neonatal 5-HT neurons in vivo, tonic regular firing and low frequency oscillations of regular spike trains and confirmed that these neurons are also activated by AVP in vivo. Finally, we show that the sparse vasopressinergic innervation in neonatal DRN originates exclusively from cell groups in medial amygdala and bed nucleus of stria terminalis. Hyperactivation of the neonatal 5-HT system by AVP during birth stress may impact its own functional development and affect the maturation of cortical target regions, which may increase the risk for psychiatric conditions later on.

Ionic mechanisms involved in arginine vasopressin-mediated excitation of auditory cortical and thalamic neurons

The axons containing arginine vasopressin (AVP) from the hypothalamus innervate a variety of structures including the cerebral cortex, thalamus, hippocampus and amygdala. A plethora amount of evidence indicates that activation of the V1a subtype of the vasopressin receptors facilitates anxiety-like and fear responses. As an essential structure involved in fear and anxiety responses, the amygdala, especially the lateral nucleus of amygdala (LA), receives glutamatergic innervations from the auditory cortex and auditory thalamus where high density of V1a receptors have been detected. However, the roles and mechanisms of AVP in these two important areas have not been determined, which prevents the understanding of the mechanisms whereby V1a activation augments anxiety and fear responses. Here, we used coronal brain slices and studied the effects of AVP on neuronal activities of the auditory cortical and thalamic neurons. Our results indicate that activation of V1a receptors excited both auditory cortical and thalamic neurons. In the auditory cortical neurons, AVP increased neuronal excitability by depressing multiple subtypes of inwardly rectifying K+ (Kir) channels including the Kir2 subfamily, the ATP-sensitive K+ channels and the G protein-gated inwardly rectifying K+ (GIRK) channels, whereas activation of V1a receptors excited the auditory thalamic neurons by depressing the Kir2 subfamily of the Kir channels as well as activating the hyperpolarization-activated cyclic nucleotide-gated (HCN) channels and a persistent Na+ channel. Our results may help explain the roles of V1a receptors in facilitating fear and anxiety responses. Categories: Cell Physiology.

Arginine vasopressin effects on membrane potentials of preoptic area temperature-sensitive and -insensitive neurons in rat hypothalamic tissue slices

Arginine vasopressin (AVP) plays a hypothermic regulatory role in thermoregulation and is an important endogenous mediator in this mechanism. In the preoptic area (POA), AVP increases the spontaneous firing and thermosensitivity of warm-sensitive neurons and decreases those of cold-sensitive and temperature-insensitive neurons. Because POA neurons play a crucial role in precise thermoregulatory responses, these findings indicate that there is an association between the hypothermia and changes in the firing activity of AVP-induced POA neurons. However, the electrophysiological mechanisms by which AVP controls this firing activity remain unclear. Therefore, in the present study, using in vitro hypothalamic brain slices and whole-cell recordings, we elucidated the membrane potential responses of temperature-sensitive and -insensitive POA neurons to identify the applications of AVP or V_1a vasopressin receptor antagonists. By monitoring changes in the resting potential and membrane potential thermosensitivity of the neurons before and during experimental perfusion, we observed that AVP increased the changes in the resting potential of 50% of temperature-insensitive neurons but reduced them in others. These changes are because AVP enhances the membrane potential thermosensitivity of nearly 50% of the temperature-insensitive neurons. On the other hand, AVP changes both the resting potential and membrane potential thermosensitivity of temperature-sensitive neurons, with no differences between the warm- and cold-sensitive neurons. Before and during AVP or V_1a vasopressin receptor antagonist perfusion, no correlation was observed between changes in the thermosensitivity and membrane potential of all neurons. Furthermore, no correlation was observed between the thermosensitivity and membrane potential thermosensitivity of the neurons during experimental perfusion. In the present study, we found that AVP induction did not result in any changes in resting potential, which is unique to temperature-sensitive neurons. The study results suggest that AVP-induced changes in the firing activity and firing rate thermosensitivity of POA neurons are not controlled by resting potentials.

Arginine Vasopressin, Synaptic Plasticity, and Brain Networks

The arginine vasopressin (AVP), a neurohypophysial hormone, is synthesized within specific sites of the central nervous system and axonally transported to multiple areas, acting as a neurotransmitter/ neuromodulator. In this context, AVP acts primarily through vasopressin receptors A and B and is involved in regulating complex social and cognition behaviors and basic autonomic function. Many earlier studies have shown that AVP as a neuromodulator affects synaptic plasticity. This review updates our current understanding of the underlying molecular mechanisms by which AVP affects synaptic plasticity. Moreover, we discuss AVP modulatory effects on event-related potentials and blood oxygen level-dependent responses in specific brain structures, and AVP effects on the network level oscillatory activity. We aimed at providing an overview of the AVP effects on the brain from the synaptic to the network level.

Anti-stress Effect of Octopus Cephalotocin in Rats

Cephalotocin is a bioactivity-regulating peptide expressed in octopus (Octopus vulgaris). The peptide sequence of cephalotocin is very similar to the peptide sequence of mammalian vasopressin, and cephalotocin has been proposed to mainly activate arginine vasopressin 1b receptor (Avpr1b) in the brain. However, the effects of cephalotocin on mammalian behavior have not been studied. In the current study, cephalotocin significantly reduced both the frequency and amplitude of spontaneous excitatory postsynaptic currents (sEPSCs) recorded from not only cultured neuronal cells from postnatal Sprague–Dawley (SD) rats but also hippocampal slices from 4-week-old male C57BL/6 mice. Intraperitoneal (IP) injection did not affect the open field behaviors of C57BL/6 mice. Cephalotocin was directly infused into the hippocampus because the normalized Avpr1b staining intensity divided by the DAPI staining intensity indicated that Avpr1b expression tended to be high in the hippocampus. A hippocampal infusion of 1 mg/kg cephalotocin via an implanted cannula exerted an anti-stress effect, significantly reducing the immobility time in the tail suspension test (TST). The present results provide evidence that the effects of cephalotocin on the activity of hippocampal neurons are related to ameliorating stress, suggesting that cephalotocin may be developed as an anti-stress biomodulator that functions by affecting the brain.