Abstract
The basal forebrain cholinergic system is involved in attentional processes through its projections to the prefrontal cortex (PFC) and the primary visual cortex (V1). It has been suggested that visual-induced cholinergic activation of V1 may exert a permissive and/or restrictive role for the thalamocortical inputs. However, it is not known if visual stimulation may elicit a cholinergic activation of high order brain areas in absence of attentional need. In the present study, we measured the effects of pattern visual stimulation on the release of acetylcholine (ACh) using in vivo microdialysis technique in V1 and PFC in the anesthetized rat. Moreover, we used retrograde track-tracing to determine whether the cholinergic neurons projecting to the V1 or PFC established reciprocal anatomical links.
Eleven male Long Evans rats (300–350g) were anesthetized (urethan, 1g/kg). An horizontal grating (contrast 90%, 0.08c/d, 3.4Hz) was displayed on a computer screen lateral to the animal. The contralateral V1 and the ipsilateral PFC were perfused (2.5 l/min) with ringer through a microdialysis probe. Intracerebral pressure injection of 2% Diamino Yellow or 2% Fast Blue saline solution were performed within the PFC or V1.
Pattern visual stimulation elicited significant (F(2,20) = 4.08, p<0.04) increase in ACh release in V1 ranging from 20 to 114%. The visual stimulus also produced long-term effect by increasing the basal level of ACh release in V1. Level of ACh release in the PFC cortex were not significantly (F(2,14)=0.4,ns) changed during the stimulation. Cholinergic BF neurons projecting to PFC or V1 established anatomical relationships within the BF.
Altogether, these results indicate that only specific BF cholinergic neurons respond to visual stimulation, which suggests a differential involvement of cholinergic projections in the integration of sensory stimuli.