Effects of local cholinesterase inhibition on acetylcholine release assessed simultaneously in prefrontal and frontoparietal cortex

To investigate whether acetylcholine is released in a similar fashion in different regions of the cortex, in vivo microdialysis was used to measure acetylcholine efflux simultaneously in the medial prefrontal and the frontoparietal cortex, under both basal conditions and following tactile stimulation. Additionally, the effects of including two different concentrations (0.05 mu M and 0.5 mu M) of a cholinesterase inhibitor (neostigmine) in the perfusion fluid were assessed. Basal levels of acetylcholine (i.e. during non-stimulated sessions) were similar in medial prefrontal and frontoparietal areas. Tactile stimulation reliably increased acetylcholine efflux in a similar fashion (up to 140% increase above baseline) in both cortical areas studied. Predictably, the higher concentration of neostigmine (0.5 mu M) increased basal acetylcholine efflux by about 150% from levels observed with the lower neostigmine concentration (0.05 I.IM), but the concentration of local neostigmine had no effect oil either the magnitude or the duration of the increased acetylcholine efflux following tactile stimulation. These results suggest that the pattern of acetylcholine release may be comparable in different areas of the cortex, supporting the idea that cholinergic projections from the basal forebrain to the cortex represent a globally regulated system. Furthermore, while the inclusion of neostigmine in perfusion fluid must be taken into account when interpreting acetylcholine efflux data, it appears that concentrations of up to 0.5 mu M do not interfere fundamentally with the lability of cortical acetylcholine efflux in response to behavioural stimulation. (C) 1998 IBRO. Published by Elsevier Science Ltd.