Hippocampal 5-HT7 receptors signal phosphorylation of the GluA1 subunit to facilitate AMPA receptor mediated-neurotransmission in vitro and in vivo.

BACKGROUND AND PURPOSE: The 5-HT7 receptor is a GPCR that is the target of a broad range of antidepressant and antipsychotic drugs. Various studies have demonstrated an ability of the 5-HT7 receptor to modulate glutamatergic neurotransmission and cognitive processes although the potential impact upon AMPA receptors has not been investigated directly. The purposes of the present study were to investigate a direct modulation of the GluA1 AMPA receptor subunit and determine how this might influence AMPA receptor function. EXPERIMENTAL APPROACH: The influence of pharmacological manipulation of the 5-HT7 receptor system upon phosphorylation of GluA1 subunits was assessed by Western blotting of fractionated proteins from hippocampal neurones in culture (or proteins resident at the neurone surface) and the functional impact assessed by electrophysiological recordings in rat hippocampus in vitro and in vivo. KEY RESULTS: 5-HT7 receptor activation increased cAMP and relative pCREB levels in cultures of rat hippocampal neurones along with an increase in phosphorylation (Ser845) of the GluA1 AMPA receptor subunit evident in whole neurone extracts and within the neurone surface compartment. Electrophysiological recordings in rat hippocampus demonstrated a 5-HT7 receptor-mediated increase in AMPA receptor-mediated neurotransmission in vitro and in vivo. CONCLUSIONS AND IMPLICATIONS: The 5-HT7 receptor-mediated phosphorylation of the GluA1 AMPA receptor provides a molecular mechanism consistent with the 5-HT7 receptor-mediated increase in AMPA receptor-mediated neurotransmission.

Orally bioavailable small molecule drug protects memory in Alzheimer's disease models.

Oligomers of beta-amyloid (Aß) are implicated in the early memory impairment seen in Alzheimer's disease before to the onset of discernable neurodegeneration. Here, the capacity of a novel orally bioavailable, central nervous system-penetrating small molecule 5-aryloxypyrimidine, SEN1500, to prevent cell-derived (7PA2 [conditioned medium] CM) Aß-induced deficits in synaptic plasticity and learned behavior was assessed. Biochemically, SEN1500 bound to Aß monomer and oligomers, produced a reduction in thioflavin-T fluorescence, and protected a neuronal cell line and primary cortical neurons exposed to synthetic soluble oligomeric Aß(1-42). Electrophysiologically, SEN1500 alleviated the in vitro depression of long-term potentiation induced by both synthetic Aß(1-42) and 7PA2 CM, and alleviated the in vivo depression of long-term potentiation induced by 7PA2 CM, after systemic administration. Behaviorally, oral administration of SEN1500 significantly reduced memory-related deficits in operant responding induced after intracerebroventricular injection of 7PA2 CM. SEN1500 reduced cytotoxicity, acute synaptotoxicity, and behavioral deterioration after in vitro and in vivo exposure to synthetic Aß and 7PA2 CM, and shows promise for development as a clinically viable disease-modifying Alzheimer's disease treatment.

Histamine excites neonatal rat sympathetic preganglionic neurons in vitro via activation of H1 receptors.

The role of histamine in regulating excitability of sympathetic preganglionic neurons (SPNs) and the expression of histamine receptor mRNA in SPNs was investigated using whole-cell patch-clamp electrophysiological recording techniques combined with single-cell reverse transcriptase polymerase chain reaction (RT-PCR) in transverse neonatal rat spinal cord slices. Bath application of histamine (100 microM) or the H1 receptor agonist histamine trifluoromethyl toluidide dimaleate (HTMT; 10 microM) induced membrane depolarization associated with a decrease in membrane conductance in the majority (70%) of SPNs tested, via activation of postsynaptic H1 receptors negatively coupled to one or more unidentified K+ conductances. Histamine and HTMT application also induced or increased the amplitude and/or frequency of membrane potential oscillations in electrotonically coupled SPNs. The H2 receptor agonist dimaprit (10 microM) or the H3 receptor agonist imetit (100 nM) were without significant effect on the membrane properties of SPNs. Histamine responses were sensitive to the H1 receptor antagonist triprolidine (10 microM) and the nonselective potassium channel blocker barium (1 mM) but were unaffected by the H2 receptor antagonist tiotidine (10 microM) and the H3 receptor antagonist, clobenpropit (5 microM). Single cell RT-PCR revealed mRNA expression for H1 receptors in 75% of SPNs tested, with no expression of mRNA for H2, H3, or H4 receptors. These data represent the first demonstration of H1 receptor expression in SPNs and suggest that histamine acts to regulate excitability of these neurons via a direct postsynaptic effect on H1 receptors.

Orexigen-sensitive NPY/AgRP pacemaker neurons in the hypothalamic arcuate nucleus.

The hypothalamic arcuate nucleus (ARC) integrates and responds to satiety and hunger signals and forms the origins of the central neural response to perturbations in energy balance. Here we show that rat ARC neurons containing neuropeptide Y (NPY) and agouti-related protein (AgRP), which are conditional pacemakers, are activated by orexigens and inhibited by the anorexigen leptin. We propose a neuron-specific signaling mechanism through which central and peripheral signals engage the central neural anabolic drive.

Activation and integration of bilateral GABA-mediated synaptic inputs in neonatal rat sympathetic preganglionic neurones in vitro.

The role of GABA receptors in synaptic transmission to neonatal rat sympathetic preganglionic neurones (SPNs) was investigated utilizing whole-cell patch clamp recording techniques in longitudinal and transverse spinal cord slice preparations. In the presence of glutamate receptor antagonists (NBQX, 5 microm and D-APV, 10 microm), electrical stimulation of the ipsilateral or contralateral lateral funiculi (iLF and cLF, respectively) revealed monosynaptic inhibitory postsynaptic potentials (IPSPs) in 75% and 65% of SPNs, respectively. IPSPs were sensitive to bicuculline (10 microM) in all neurones tested and reversed polarity around -55 mV, the latter indicating mediation via chloride conductances. In three neurones IPSPs evoked by stimulation of the iLF (n = 1) or cLF (n = 2) were partly sensitive to strychnine (2 microM). The expression of postsynaptic GABA(A) and GABA(B) receptors were confirmed by the sensitivity of SPNs to agonists, GABA (2 mm), muscimol (10-100 microM) or baclofen (10-100 microM), in the presence of TTX, each of which produced membrane hyperpolarization in all SPNs tested. Muscimol-induced responses were sensitive to bicuculline (1-10 microM) and SR95531 (10 microM) and baclofen-induced responses were sensitive to 2-hydroxy-saclofen (100-200 microM) and CGP55845 (200 nM). The GABA(C) receptor agonist CACA (200 microM) was without significant effect on SPNs. These results suggest that SPNs possess postsynaptic GABA(A) and GABA(B) receptors and that subsets of SPNs receive bilateral GABAergic inputs which activate GABA(A) receptors, coupled to a chloride conductance. At resting or holding potentials close to threshold either single or bursts (10-100 Hz) of IPSPs gave rise to a rebound excitation and action potential firing at the termination of the burst. This effect was mimicked by injection of small (10-20 pA) rectangular-wave current pulses, which revealed a time-dependent, Cs(+)-sensitive inward rectification and rebound excitation at the termination of the response to current injection. Synaptic activation of a rebound excitation mediated by a time-dependent inward rectification expressed intrinsically by SPNs may provide a novel mechanism enabling SPNs to be entrained to rhythms driven from the brainstem or higher centres.