CHOLINERGIC ACTIVATION IN FRONTAL-CORTEX AND NUCLEUS-ACCUMBENS RELATED TO BASIC BEHAVIORAL MANIPULATIONS - HANDLING, AND THE ROLE OF POST-HANDLING EXPERIENCE
Cm. Thiel et al., CHOLINERGIC ACTIVATION IN FRONTAL-CORTEX AND NUCLEUS-ACCUMBENS RELATED TO BASIC BEHAVIORAL MANIPULATIONS - HANDLING, AND THE ROLE OF POST-HANDLING EXPERIENCE, Brain research, 812(1-2), 1998, pp. 121-132
The present experiment is part of a series of studies designed to inve
stigate cerebral cholinergic activity during basic behavioral testing
procedures. Using in vivo microdialysis, we monitored extracellular ac
etylcholine levels in rats which were picked up manually (termed handl
ing) and exposed to an open field, or animals which were picked up and
returned to their home cage. These procedures were repeated on two co
nsecutive days. In the lateral precentral area of the frontal cortex,
both procedures increased cholinergic activity. However, on the 1 st d
ay of testing, the degree of cholinergic activation was of even greate
r magnitude in animals which were returned to the home cage after hand
ling than in animals which were exposed to a novel open field. This ne
urochemical pattern was dissociated from behavioral indices of activat
ion, since rearing and locomotor activity were more pronounced in the
open field than in the home cage. In the nucleus accumbens core and sh
ell, where extracellular acetylcholine is provided by cholinergic inte
rneurons, we also found cholinergic activation on both days of testing
. However, unlike the frontal cortex, there were no substantial neuroc
hemical differences between animals which were exposed to the open fie
ld after handling vs. those which were returned to their home cage. To
gether, our data suggest that a simple interaction Like handling provi
des a significant stimulus for the animal to which cholinergic activit
y responds in several forebrain areas. Here, frontal cortical acetylch
oline appears to be especially sensitive, with a pattern of activation
which is dependent on post-handling experience. These results are dis
cussed with respect to their possible functional implications, and the
role of handling as an experimental factor. Since handling is part of
many neurobehavioral procedures, handling-induced changes can interac
t with the imposed independent variables under investigation, such as
post-trial pharmacological manipulations, requiring consideration in t
he interpretation of any experiment employing handling of the subjects
. (C) 1998 Elsevier Science B.V. All rights reserved.