Modulation of the Acetylcholine System in the Superior Cervical Ganglion of Rat: Effects of GABA and Hypoglossal Nerve Implantation After In Vivo GABA Treatment

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Abstract
GABA was applied to the superior cervical ganglion (SCG) of CFY rats in vitro and in vivo, with or without implantation of a hypoglossal nerve, to evaluate the effects of these experimental interventions on the acetylcholine (ACh) system, which mainly serves the synaptic transmission of the preganglionic input. Long-lasting GABA microinfusion into the SCG in vivo apparently resulted in a functional denervation. This treatment reduced the acetylcholinesterase (AChE; EC 3.1.1.7) activity by 30% (P < 0.01) and transiently increased the number of nicotinic ACh receptors, but had no significant effect on the choline acetyltransferase (acetyl-coenzyme A:choline-O-acetyl-transferase; EC 2.3.1.6) activity, the ACh level or the number of muscarinic ACh receptors. The relative amounts of the different molecular forms of AChE did not change under these conditions. In vivo GABA application to the SCG with a hypoglossal nerve implanted in the presence of intact preganglionic afferent synapses exerted a significant modulatory effect on the AChE activity and its molecular forms. The hyperinnervation of the ganglia led to increases in the AChE activity (to 142.5%, P < 0.01) and the 16S molecular form (to 200% P < 0.01). Apparently, in vivo GABA microinfusion and GABA treatment in the presence of additional cholinergic synapses has a modulatory effect on the elements of the ACh system in the SCG of CFY rats.