Groleau_2015_J.Vis_15_30

The muscarinic and nicotinic transmissions in the primary visual cortex (V1) are involved in the enhancement of specific visual stimuli as well as long-term modifications of the neuronal processing, in regards to perceptual learning. We investigated the involvement of the different cholinergic receptors subtypes underlying this long-term functional plasticity using RT-PCR and recording of visual evoked potentials (VEPs). Perceptual learning-like test was performed by exposing awaken rats to a visual stimulation (VS) - a sinusoidal grating (30 degrees , 0.12cpd) - for 10min/day during 14days. This VS was provided alone or coupled to an electrical stimulation of the basal forebrain which sends cholinergic projections to V1 (HDB/VS) or paired with a cholinesterase inhibitor (donepezil, 1mg/kg injected 30min prior to visual exposure) to enhance cholinergic transmission in V1 (DONEP/VS). One week after the last training session, VEPs were recorded and the cortices encompassing V1 were collected to determine the expression level of mRNA of muscarinic (M1-5) and nicotinic (alpha/beta) receptors sub-units by RT-PCR. VS coupled to pharmacological or electrical stimulation of the cholinergic system produced a significant enhancement of the cortical response, as shown by VEP recordings. Two weeks of VS treatment alone caused an increase of the expression of M3 and M5 mRNA suggesting an increase of their production and activity during long-term visual stimulation. In the HDB/VS group, alpha3 sub-unit was decreased suggesting its involvement in phasic cholinergic stimulation. The DONEP/VS treatment presented a decrease in the expression of M2, suggesting a down regulation of mRNA synthesis. This could indicate an increased cortico-cortical inhibition, as M2 receptors are located massively on the GABAergic neurons. Therefore, even with similar functional enhancement, the cholinergic receptors regulation differs between an electrical and a pharmacological treatment. These results are crucial for determining which receptors are the most involved in the pharmacological cholinergic stimulation to enhance visual perception. Meeting abstract presented at VSS 2015.