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 a nd the frontoparietal cortex, under both basal conditions and followin g tactile stimulation. Additionally, the effects of including two diff erent concentrations (0.05 mu M and 0.5 mu M) of a cholinesterase inhi bitor (neostigmine) in the perfusion fluid were assessed. Basal levels of acetylcholine (i.e. during non-stimulated sessions) were similar i n medial prefrontal and frontoparietal areas. Tactile stimulation reli ably increased acetylcholine efflux in a similar fashion (up to 140% i ncrease above baseline) in both cortical areas studied. Predictably, t he higher concentration of neostigmine (0.5 mu M) increased basal acet ylcholine efflux by about 150% from levels observed with the lower neo stigmine concentration (0.05 I.IM), but the concentration of local neo stigmine had no effect oil either the magnitude or the duration of the increased acetylcholine efflux following tactile stimulation. These r esults suggest that the pattern of acetylcholine release may be compar able in different areas of the cortex, supporting the idea that cholin ergic projections from the basal forebrain to the cortex represent a g lobally regulated system. Furthermore, while the inclusion of neostigm ine in perfusion fluid must be taken into account when interpreting ac etylcholine efflux data, it appears that concentrations of up to 0.5 m u M do not interfere fundamentally with the lability of cortical acety lcholine efflux in response to behavioural stimulation. (C) 1998 IBRO. Published by Elsevier Science Ltd.