Histamine excites neonatal rat sympathetic preganglionic neurons in vitro via activation of H-1 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 mu M) or the H-1 receptor agonist histamine trifluoromethyl toluidide dimaleate (HTMT; 10 mu M) induced membrane depolarization associated with a decrease in membrane conductance in the majority (70%) of SPNs tested, via activation of postsynaptic H-1 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 H-2 receptor agonist dimaprit (10 mu M) or the H-3 receptor agonist imetit (100 nM) were without significant effect on the membrane properties of SPNs. Histamine responses were sensitive to the H-1 receptor antagonist triprolidine (10 mu M) and the nonselective potassium channel blocker barium (1 mM) but were unaffected by the H-2 receptor antagonist tiotidine (10 mu M) and the H-3 receptor antagonist, clobenpropit (5 mu M). Single cell RT-PCR revealed mRNA expression for H-1 receptors in 75% of SPNs tested, with no expression of mRNA for H-2, H-3, or H-4 receptors. These data represent the first demonstration of H-1 receptor expression in SPNs and suggest that histamine acts to regulate excitability of these neurons via a direct postsynaptic effect on H-1 receptors

Electrophysiological, pharmacological and molecular profile of the transient outward rectifying conductance in rat sympathetic preganglionic neurons in vitro

Transient outward rectifying conductances or A-like conductances in sympathetic preganglionic neurons (SPN) are prolonged, lasting for hundreds of milliseconds to seconds and are thought to play a key role in the regulation of SPN firing frequency. Here, a multidisciplinary electrophysiological, pharmacological and molecular single-cell rt-PCR approach was used to investigate the kinetics, pharmacological profile and putative K(+) channel subunits underlying the transient outward rectifying conductance expressed in SPN. SPN expressed a 4-aminopyridine (4-AP) sensitive transient outward rectification with significantly longer decay kinetics than reported for many other central neurons. The conductance and corresponding current in voltage-clamp conditions was also sensitive to the Kv4.2 and Kv4.3 blocker phrixotoxin-2 (1-10 mu M) and the blocker of rapidly inactivating Kv channels, pandinotoxin-K alpha (50 nM). The conductance and corresponding current was only weakly sensitive to the Kv1 channel blocker tityustoxin-K alpha and insensitive to dendrotoxin I (200 nM) and the Kv3.4 channel blocker BDS-II (1 mu M). Single-cell RT-PCR revealed mRNA expression for the alpha-subunits Kv4.1 and Kv4.3 in the majority and Kv1.5 in less than half of SPN. mRNA for accessory beta-subunits was detected for Kv beta 2 in all SPN with differential expression of mRNA for KChIP1, Kv beta 1 and Kv beta 3 and the peptidase homologue DPP6. These data together suggest that the transient outwardly rectifying conductance in SPN is mediated by members of the Kv4 subfamily (Kv4.1 and Kv4.3) in association with the beta-subunit Kv beta 2. Differential expression of the accessory beta subunits, which may act to modulate channel density and kinetics in SPN, may underlie the prolonged and variable time-course of this conductance in these neurons. (c) 2011 IBRO. Published by Elsevier Ltd. All rights reserved

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

Oligomers of beta-amyloid (Aβ) 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) Aβ-induced deficits in synaptic plasticity and learned behavior was assessed. Biochemically, SEN1500 bound to Aβ 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 Aβ1–42. Electrophysiologically, SEN1500 alleviated the in vitro depression of long-term potentiation induced by both synthetic Aβ1–42 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 Aβ and 7PA2 CM, and shows promise for development as a clinically viable disease-modifying Alzheimer's disease treatment