Stimulation of Acetylcholine Release and Pharmacological Potentiation of Cholinergic Transmission Affect Cholinergic Receptor Expression Differently during Visual Conditioning

Abstract

Cholinergic stimulation coupled with visual conditioning enhances the visual acuity and cortical responses in the primary visual cortex. To determine which cholinergic receptors are involved in these processes, qRT-PCR was used. Two modes of cholinergic enhancement were tested: a phasic increase of acetylcholine release by an electrical stimulation of the basal forebrain cholinergic nucleus projecting to the visual cortex, or a tonic pharmacological potentiation of the cholinergic transmission by the acetylcholine esterase inhibitor, donepezil. A daily visual exposure to sine-wave gratings (training) was paired with the cholinergic enhancement, up to 14 days. qRT-PCR was performed at rest, 10 min, one week or two weeks of visual/cholinergic training with samples of the visual and somatosensory cortices, and the BF for determining mRNA expression of muscarinic receptor subtypes (m1, m2, m3, m4, m5), nicotinic receptor subunits (α3, α4, α7, β2, β4), and NMDA receptors, GAD65 and ChAT, as indexes of cortical plasticity. A Kruskal–Wallis test showed a modulation of the expression in the visual cortex of m2, m3, m4, m5, α7, β4, NMDA and GAD65, but only β4 within the basal forebrain and none of these mRNA within the somatosensory cortex. The two modes of cholinergic enhancement induced different effects on mRNA expression, related to the number of visual conditioning sessions and receptor specificity. This study suggests that the combination of cholinergic enhancement and visual conditioning is specific to the visual cortex and varies between phasic or tonic manipulation of acetylcholine levels.