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Although originally cloned from rat brain, the P2X[sub 7] receptor has only recently been localized in neurones, and functional responses mediated by these neuronal P2X[sub 7] receptors (P2X[sub 7]R) are largely unknown. Here we studied the effect of P2X[sub 7]R activation on the release of neurotransmitters from superfused rat hippocampal slices. ATP (1-30 mM) and other ATP analogues elicited concentration-dependent [³H]GABA outflow, with the following rank order of potency: benzoylbenzoylATP (BzATP) > ATP > ADP. PPADS, the non-selective P2-receptor antagonist (3-30 µM), Brilliant blue G (1-100 nM) the P2X[sub 7]-selective antagonist and Zn[sup 2+] (0.1-30 µM) inhibited, whereas lack of Mg[sup 2+] potentiated the response by ATP. In situ hybridization revealed that P2X[sub 7]R mRNA is expressed in the neurones of the cell body layers in the hippocampus. P2X[sub 7]R immunoreactivity was found in excitatory synaptic terminals in CA1 and CA3 region targeting the dendrites of pyramidal cells and parvalbumin labelled structures. ATP (3-30 µM) and BzATP (0.6-6 µM) elicited concentration-dependent [[sup 14]C]glutamate efflux, and blockade of the kainate receptor-mediated transmission by CNQX (10-100 µM) and gadolinium (100 µM), decreased ATP evoked [³H]GABA efflux. The Na[sup +] channel blocker TTX (1 µM), low temperature (12°C), and the GABA uptake blocker nipecotic acid (1 mM) prevented ATP-induced [³H]GABA efflux. Brilliant blue G and PPADS also reduced electrical field stimulation-induced [³H]GABA efflux. In conclusion, P2X[sub 7]Rs are localized to the excitatory terminals in the hippocampus, and their activation regulates the release of glutamate and GABA from themselves and from their target cells. [ABSTRACT FROM AUTHOR]

Release of distinct cellular cargoes in response to specific stimuli is a process fundamental to all higher eukaryotes and controlled by the regulated secretory pathway (RSP). However, the mechanism by which genes involved in the RSP are selectively expressed, leading to the establishment and appropriate functioning of regulated secretion remaining largely unknown. Using the rat pheochromocytoma cell line PC12, we provide evidence that, by controlling expression of many genes involved in the RSP, the transcriptional repressor REST can regulate this pathway and hence the neurosecretory phenotype. Introduction of REST transgenes into PC12 cells leads to the repression of many genes, the products of which are involved in regulated secretion. Moreover, chromatin immunoprecipitation assays show that many of the repressed genes recruit the recombinant REST protein to RE1 sites within their promoters and abrogation of REST function leads to reactivation of these transcripts. In addition to the observed transcriptional effects, PC12 cells expressing REST have fewer secretory granules and a reduction in the ability to store and release noradrenaline. Furthermore, an important trigger for synaptic release, influx of calcium through voltage-operated calcium channels, is compromised. This is the first demonstration of a transcription factor that directly controls expression of many major components of the RSP and provides further insight into the function of REST.

Development of the nervous system is accompanied by expansion and differentiation of the neuronal progenitors within the embryonic neuroepithelium. Although the role of growth factors in this process is well documented, there is increasing evidence for a role of neurotransmitters. Acetylcholine is known to exert many actions on developing neural cells, but its potential role in neurogenesis is unclear. Here, we show that the M1 muscarinic acetylcholine receptor is expressed in the neuroepithelium of the rat forebrain, where it is found on both nestin+ progenitor cells and TuJ1+ newly differentiated neurons. Furthermore, transcription is governed, at least in part, by regulatory cis elements that are also responsible for driving transcription in neuroblastoma cells. This represents the first demonstration of M1 receptors on neuronal progenitor cells and supports the notion that M1 muscarinic receptors may play a role in development of the nervous system prior to the onset of synaptogenesis and their subsequent role in neurotransmission.

Although originally cloned from rat brain, the P2X7 receptor has only recently been localized in neurones, and functional responses mediated by these neuronal P2X7 receptors (P2X7 R) are largely unknown. Here we studied the effect of P2X7 R activation on the release of neurotransmitters from superfused rat hippocampal slices. ATP (1-30 mm) and other ATP analogues elicited concentration-dependent [3 H]GABA outflow, with the following rank order of potency: benzoylbenzoylATP (BzATP) > ATP > ADP. PPADS, the non-selective P2-receptor antagonist (3-30 microm), Brilliant blue G (1-100 nm) the P2X7 -selective antagonist and Zn2+ (0.1-30 microm) inhibited, whereas lack of Mg2+ potentiated the response by ATP. In situ hybridization revealed that P2X7 R mRNA is expressed in the neurones of the cell body layers in the hippocampus. P2X7 R immunoreactivity was found in excitatory synaptic terminals in CA1 and CA3 region targeting the dendrites of pyramidal cells and parvalbumin labelled structures. ATP (3-30 microm) and BzATP (0.6-6 microm) elicited concentration-dependent [14 C]glutamate efflux, and blockade of the kainate receptor-mediated transmission by CNQX (10-100 microm) and gadolinium (100 microm), decreased ATP evoked [3 H]GABA efflux. The Na+ channel blocker TTX (1 microm), low temperature (12 degrees C), and the GABA uptake blocker nipecotic acid (1 mm) prevented ATP-induced [3 H]GABA efflux. Brilliant blue G and PPADS also reduced electrical field stimulation-induced [3 H]GABA efflux. In conclusion, P2X7 Rs are localized to the excitatory terminals in the hippocampus, and their activation regulates the release of glutamate and GABA from themselves and from their target cells.