5-HT receptor activation produces rapid antidepressant-like effects in rodents.

Ketamine is noted for its rapid onset antidepressant response and effectiveness in patients with treatment resistant depression. While most research has focused on glutamatergic mechanisms, recent studies show that antidepressant-like effects in rodents are dependent upon the serotonergic (5-HT) system and suggest a potential contribution of the 5-HT receptor. In this study we utilized CP-94253 to examine whether 5-HT receptor agonism produces rapid and sustained antidepressant-like effects, focusing on rodent models and treatment approaches commonly used to demonstrate the differentiated response to ketamine.

Cell-Type-Specific Expression Pattern of Proton-Sensing Receptors and Channels in Pituitary Gland.

In mammalian cells, extracellular protons act as orthosteric and allosteric ligands for multiple receptors and channels. The aim of this study is to identify proton sensors in the rat pituitary gland. qRT-PCR analysis indicated the expression of G-protein-coupled receptor 68 gene (Gpr68) and acid-sensing ion channel (ASIC) genes Asic1, Asic2, and Asic4 in anterior pituitary cells and Asic1 and Asic2 in immortalized GH3 pituitary cells.

Enhanced tonic inhibition influences the hypnotic and amnestic actions of the intravenous anesthetics etomidate and propofol.

Intravenous anesthetics exert a component of their actions via potentiating inhibitory neurotransmission mediated by γ-aminobutyric type-A receptors (GABAARs). Phasic and tonic inhibition is mediated by distinct populations of GABAARs, with the majority of phasic inhibition by subtypes composed of α1-3βγ2 subunits, whereas tonic inhibition is dependent on subtypes assembled from α4-6βδ subunits. To explore the contribution that these distinct forms of inhibition play in mediating intravenous anesthesia, we have used mice in which tyrosine residues 365/7 within the γ2 subunit are mutated to phenyalanines (Y365/7F).

Dependence of the excitability of pituitary cells on cyclic nucleotides.

Cyclic 3',5'-adenosine monophosphate and cyclic 3',5'-guanosine monophosphate are intracellular (second) messengers that are produced from the nucleotide triphosphates by a family of enzymes consisting of adenylyl and guanylyl cyclases. These enzymes are involved in a broad array of signal transduction pathways mediated by the cyclic nucleotide monophosphates and their kinases, which control multiple aspects of cell function through the phosphorylation of protein substrates. We review the findings and working hypotheses on the role of the cyclic nucleotides and their kinases in the control of electrical activity of the endocrine pituitary cells and the plasma membrane channels involved in this process.

Activity-dependent phosphorylation of GABAA receptors regulates receptor insertion and tonic current.

The expression of GABA(A) receptors and the efficacy of GABAergic neurotransmission are subject to adaptive compensatory regulation as a result of changes in neuronal activity. Here, we show that activation of L-type voltage-gated Ca(2+) channels (VGCCs) leads to Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) phosphorylation of S383 within the β3 subunit of the GABA(A) receptor. Consequently, this results in rapid insertion of GABA(A) receptors at the cell surface and enhanced tonic current.

Dependence of spontaneous electrical activity and basal prolactin release on nonselective cation channels in pituitary lactotrophs.

All secretory anterior pituitary cells fire action potentials spontaneously and exhibit a high resting cation conductance, but the channels involved in the background permeability have not been identified. In cultured lactotrophs and immortalized GH(3) cells, replacement of extracellular Na(+) with large organic cations, but not blockade of voltage-gated Na(+) influx, led to an instantaneous hyperpolarization of cell membranes that was associated with a cessation of spontaneous firing. When cells were clamped at -50 mV, which was close to the resting membrane potential in these cells, replacement of bath Na(+) with organic cations resulted in an outward-like current, reflecting an inhibition of the inward holding membrane current and indicating loss of a background-depolarizing conductance.

The expression and role of hyperpolarization-activated and cyclic nucleotide-gated channels in endocrine anterior pituitary cells.

Pituitary cells fire action potentials independently of external stimuli, and such spontaneous electrical activity is modulated by a large variety of hypothalamic and intrapituitary agonists. Here, we focused on the potential role of hyperpolarization-activated and cyclic nucleotide-gated (HCN) channels in electrical activity of cultured rat anterior pituitary cells. Quantitative RT-PCR analysis showed higher level of expression of mRNA transcripts for HCN2 and HCN3 subunits and lower expression of HCN1 and HCN4 subunits in these cells.

The residence time of GABA(A)Rs at inhibitory synapses is determined by direct binding of the receptor α1 subunit to gephyrin.

The majority of fast synaptic inhibition in the brain is mediated by benzodiazepine-sensitive α1-subunit-containing GABA type A receptors (GABA(A)Rs); however, our knowledge of the mechanisms neurons use to regulate their synaptic accumulation is rudimentary. Using immunoprecipitation, we demonstrate that GABA(A)Rs and gephyrin are intimately associated at inhibitory synapses in cultured rat neurons. In vitro we reveal that the E-domain of gephyrin directly binds to the α1 subunit with an affinity of ∼20 μm, mediated by residues 360-375 within the intracellular domain of this receptor subunit.

Cyclin E constrains Cdk5 activity to regulate synaptic plasticity and memory formation.

Cyclin E is a component of the core cell cycle machinery, and it drives cell proliferation by regulating entry and progression of cells through the DNA synthesis phase. Cyclin E expression is normally restricted to proliferating cells. However, high levels of cyclin E are expressed in the adult brain.

Role of nonselective cation channels in spontaneous and protein kinase A-stimulated calcium signaling in pituitary cells.

Several receptors linked to the adenylyl cyclase signaling pathway stimulate electrical activity and calcium influx in endocrine pituitary cells, and a role for an unidentified sodium-conducting channel in this process has been proposed. Here we show that forskolin dose-dependently increases cAMP production and facilitates calcium influx in about 30% of rat and mouse pituitary cells at its maximal concentration. The stimulatory effect of forskolin on calcium influx was lost in cells with inhibited PKA (cAMP-dependent protein kinase) and in cells that were haploinsufficient for the main PKA regulatory subunit but was preserved in cells that were also haploinsufficient for the main PKA catalytic subunit.

Dependence of multidrug resistance protein-mediated cyclic nucleotide efflux on the background sodium conductance.

Anterior pituitary cells fire action potentials and release cyclic nucleotides both spontaneously and in response to agonist stimulation, but the relationship between electrical activity and cyclic nucleotide efflux has not been studied. In these cells, a tetrodotoxin-resistant background N(+) conductance is critical for firing of action potentials, and multidrug resistance proteins (MRPs) MRP4 and MRP5 contribute to cyclic nucleotide efflux. Here, we show that abolition of the background Na(+) conductance in rat pituitary cells by complete or partial replacement of extracellular Na(+) with organic cations or sucrose induced a rapid and reversible hyperpolarization of cell membranes and inhibition of action potential firing, accompanied by a rapid inhibition of cyclic nucleotide efflux.

Cloning and functional identification of novel endothelin receptor type A isoforms in pituitary.

Mammalian endothelin (ET) receptors, termed ET(A)R and ET(B)R, are derived from two intron-containing genes and the functional splice variants of ET(B)R but not ET(A)R have been identified. Here, we report about the isolation of cDNAs of ET(A)R transcripts from rat anterior pituitary, which are generated by alternative RNA splicing. Deletion of exon 2 and insertion of fragments from intron 1 and 2 accounted for formation of three misplaced proteins, whereas the insertion of a fragment from intron 6 resulted in generation of a functional plasma membrane receptor, termed ET(A)R-C13.

ZD7288 inhibits exocytosis in an HCN-independent manner and downstream of voltage-gated calcium influx in pituitary lactotrophs.

Pituitary lactotrophs fire action potentials spontaneously and the associated voltage-gated calcium influx is sufficient to maintain high prolactin release. Here we studied the role of hyperpolarization-activated cation channels in pacemaking activity, calcium signaling, and prolactin secretion in these cells. A slowly developing and hyperpolarization-activated inward current was identified but only in a fraction of lactotrophs.

Dependence of hyperpolarisation-activated cyclic nucleotide-gated channel activity on basal cyclic adenosine monophosphate production in spontaneously firing GH3 cells.

The hyperpolarisation-activated cyclic nucleotide-gated (HCN) channels play a distinct role in the control of membrane excitability in spontaneously active cardiac and neuronal cells. Here, we studied the expression and role of HCN channels in pacemaking activity, Ca(2+) signalling, and prolactin secretion in GH(3) immortalised pituitary cells. Reverse transcriptase-polymerase chain reaction analysis revealed the presence of mRNA transcripts for HCN2, HCN3 and HCN4 subunits in these cells.

Dependence of electrical activity and calcium influx-controlled prolactin release on adenylyl cyclase signaling pathway in pituitary lactotrophs.

Pituitary lactotrophs in vitro fire extracellular Ca2+-dependent action potentials spontaneously through still unidentified pacemaking channels, and the associated voltage-gated Ca2+influx (VGCI) is sufficient to maintain basal prolactin (PRL) secretion high and steady. Numerous plasma membrane channels have been characterized in these cells, but the mechanism underlying their pacemaking activity is still not known. Here we studied the relevance of cyclic nucleotide signaling pathways in control of pacemaking, VGCI, and PRL release.

Carboxyl-terminal splicing enhances physical interactions between the cytoplasmic tails of purinergic P2X receptors.

Purinergic P2X receptors are ion-conducting channels composed of three subunits, each having two transmembrane domains and intracellular amino (N) and carboxyl (C) termini. Although alternative splicing extensively modifies the C-terminal sequences of P2X subunits, the direct influence of such post-transcriptional modifications on receptor architecture and function remains poorly understood. In this study, we focused on mouse pituitary P2X2 receptors.

Circadian rhythmicity in AVP secretion and GABAergic synaptic transmission in the rat suprachiasmatic nucleus.

A variety of physiological and behavioral functions exhibit circadian changes and these circadian rhythms are driven by oscillatory expression of clock genes in the suprachiasmatic nuclei (SCN). It is still unknown how this molecular clockwork is controlled by extracellular neurohormones and neurotransmitters and which membrane receptors undergo circadian modulation. Circadian rhythm can be measured as a secretion of arginine vasopressin (AVP) in organotypic SCN culture for several weeks.

Characterization of neuromuscular transmission in mice with progressive motoneuronopathy.

Progressive motoneuronopathy (PMN) is an autosomal recessive mouse disease, which is characterized by the development of hind limbs paralysis rapidly progressing to the anterior parts of the body, muscular atrophy, respiratory depression, and death at 6-7 postnatal weeks. Here, we recorded the resting membrane potential (RMP), spontaneous miniature endplate potentials (MEPPs), and quantum content of endplate potentials (EPP) at the diaphragm muscle fibers in controls and PMN mice aged 18 to 43 days. In control animals, there was a progressive increase in RMP, MEPP frequency and EPP quantum content, as well as a decrease in mean MEPP amplitude.

Recovery of Ins(1,4,5)-trisphosphate-dependent calcium signaling in neonatal gonadotrophs.

Pituitary gonadotrophs express non-desensitizing gonadotropin-releasing hormone (GnRH) receptors and their activations leads to inositol 1,4,5-trisphosphate (InsP3)-dependent Ca2+ mobilization. When added in physiological concentration range GnRH induces baseline Ca2+ oscillations, whereas in higher concentrations it induces a prolonged spike response accompanied with non-oscillatory or oscillatory plateau response. Here, we studied the recovery of calcium signaling during repetitive stimulation with short (10-30 s) GnRH pulses and variable interpulse intervals in neonatal gonadotrophs perfused with Ca2+/Na+ -containing, Ca2+ -deficient/Na+ -containing, and Ca2+ -containing/Na+ -deficient media.

Melatonin action in neonatal gonadotrophs.

Neonatal pituitary cells express MT1 and MT2 subtype of melatonin receptors that are coupled to pertussis toxin-sensitive G proteins. Their activation by melatonin leads to a decrease in cAMP production and activity of protein kinase A, and attenuation of gonadotropin-releasing hormone (GnRH)-induced gonadotropin secretion. Single cell calcium and electrophysiological recordings have revealed that a reduction in gonadotropin release results from melatonin-induced inhibition of GnRH-stimulated calcium signaling.

Day-night variations in zinc sensitivity of GABAA receptor-channels in rat suprachiasmatic nucleus.

In the suprachiasmatic nucleus (SCN), electrical activity, secretion, and other cellular functions undergo profound rhythm during day-night cycle due to oscillatory expression of clock gene constituents. Although SCN is enriched with gamma-aminobutyric acid (GABA)-ergic neurons, it is unknown whether there are circadian changes in the GABAA receptor expression and/or function. Here we investigated the possible daily variations in zinc sensitivity of GABAA channels in rat SCN neurons maintained in brain slices.