Distribution and mRNA Expression of nAChRs in the Rat S1 and M1 Cortices After Electrical Stimulation of the Basal Forebrain.

Abstract

To study the changes in the distribution of and the transcriptional levels associated with α4- and α7-subtype nicotinic acetylcholine receptors (nAChRs) in the primary somatosensory (S1) and motor (M1) cortices of rats after electrical stimulation of the basal forebrain (BF). Immunofluorescence (IF) analyses were performed on brain sections from 20 rats (experimental groups: controls, contralateral, and ipsilateral to BF stimulation). The nAChR receptor complexes were labeled with antibodies and counted (N) in the cortical layers of the hindlimb representation (S1HL), barrel field (S1BF), and M1. To determine the relative transcriptional mRNA levels, qRT-PCR was performed with tissue from the associated brain regions of 14 different animals in two groups, controls and BF stimulation. For all three tested brain regions, N and D (density) of the α7-subtype nAChR increased in both ipsilateral and contralateral hemispheres after BF stimulation. There was no change in N and D of the α4 subtype. Regardless of BF stimulation, N of both subtypes was lower in M1 compared to S1HL and S1BF, and D was highest in layers II-IV. BF stimulation had no significant effect on the relative mRNA levels of both receptor subtypes. The results show an upregulation of the α7-subtype nAChR as a result of BF stimulation, based on receptor-complex counts on IF images. However, this change was not reflected in mRNA levels, which suggest post-translational modifications. Overall, this study suggests structural changes from the effects of cholinergic projections to the somatosensory and motor cortices.