Mechanisms of M1 muscarinic receptor-mediated up-regulation of neuronal nitric oxide synthase in N1E-115 neuroblastoma cells

The prelimbic cortex muscarinic M₃ receptor-nitric oxide-guanylyl cyclase pathway modulates cardiovascular responses in rats

The prelimbic cortex (PL), a limbic structure, sends projections to areas involved in the control of cardiovascular responses. Stimulation of the PL with acetylcholine (ACh) evokes depressor and tachycardiac responses mediated by local PL muscarinic receptors. Early studies demonstrated that stimulation of muscarinic receptors induced nitric oxide (NO) synthesis and cyclic guanosine cyclic monophosphate (cGMP) formation. Hence, this study investigates which PL muscarinic receptor subtype is involved in the cardiovascular response induced by ACh and tests the hypothesis that cardiovascular responses caused by muscarinic receptor stimulation in the PL are mediated by local NO and cGMP formation. PL pretreatment with J104129 (an M3 receptor antagonist) blocked the depressor and tachycardiac response evoked by injection of ACh into the PL. Pretreatment with either pirenzepine (an M1 receptor antagonist) or AF-DX 116 (an M2 and M4 receptor antagonist) did not affect cardiovascular responses evoked by ACh. Moreover, similarly to the antagonism of PL M3 receptors, pretreatment with N(ω)-propyl-L-arginine (an inhibitor of neuronal NO synthase), carboxy-PTIO(S)-3-carboxy-4-hydroxyphenylglicine (an NO scavenger), or 1H-[1,2,4]oxadiazolol-[4,3-a]quinoxalin-1-one (a guanylate cyclase inhibitor) blocked both the depressor and the tachycardiac response evoked by ACh. The current results demonstrate that cardiovascular responses evoked by microinjection of ACh into the PL are mediated by local activation of the M3 receptor-NO-guanylate cyclase pathway.

The effect of nNOS inhibitors on toxin-induced cell death in dopaminergic cell lines depends on the extent of enzyme expression

Nitric oxide is linked with neurodegeneration in Parkinson's disease (PD) through the involvement of both inducible (iNOS) and neuronal nitric oxide synthase (nNOS). While non-selective NOS inhibitors are neuroprotective, the role of nNOS has not been determined using selective NOS inhibitors. The present study investigated the neuroprotective effect of selective iNOS and nNOS inhibitors on MPP(+)- and MG-132-induced cell death in cell lines with differing levels of nNOS expression. Inhibition of endogenously expressed nNOS by 7-NI and ARR17477 enhanced the toxicity of MPP(+) and MG-132 in N1E-115 cells, whereas in transfected SH-SY5Y cells overexpressing nNOS, ARR17477 and 7-NI protected against MPP(+)- and MG-132-induced cell death. In contrast, inhibition of iNOS by 1400W was ineffective in preventing MPP(+) and MG-132 toxicity in these cell lines. These results suggest a dual role for NOS in dopaminergic cell viability. nNOS is protective against toxic insult when produced endogenously. When nNOS is overexpressed, it becomes neurotoxic to cells suggesting that inhibition of nNOS may be a promising strategy to prevent cell death in PD.

Hippocampal GABAergic synapses possess the molecular machinery for retrograde nitric oxide signaling

Nitric oxide (NO) plays an important role in synaptic plasticity as a retrograde messenger at glutamatergic synapses. Here we describe that, in hippocampal pyramidal cells, neuronal nitric oxide synthase (nNOS) is also associated with the postsynaptic active zones of GABAergic symmetrical synapses terminating on their somata, dendrites, and axon initial segments in both mice and rats. The NO receptor nitric oxide-sensitive guanylyl cyclase (NOsGC) is present in the brain in two functional subunit compositions: alpha1beta1 and alpha2beta1. The beta1 subunit is expressed in both pyramidal cells and interneurons in the hippocampus. Using immunohistochemistry and in situ hybridization methods, we describe that the alpha1 subunit is detectable only in interneurons, which are always positive for beta1 subunit as well; however, pyramidal cells are labeled only for beta1 and alpha2 subunits. With double-immunofluorescent staining, we also found that most cholecystokinin- and parvalbumin-positive and smaller proportion of the somatostatin- and nNOS-positive interneurons are alpha1 subunit positive. We also found that the alpha1 subunit is present in parvalbumin- and cholecystokinin-positive interneuron terminals that establish synapses on somata, dendrites, or axon initial segments. Our results demonstrate that NOsGC, composed of alpha1beta1 subunits, is selectively expressed in different types of interneurons and is present in their presynaptic GABAergic terminals, in which it may serve as a receptor for NO produced postsynaptically by nNOS in the very same synapse.