Striatal dopamine release is altered by glucose and insulin during push-pull perfusion of the rat's caudate nucleus

Abstract

An individual site in the caudate-putamen complex of the unrestrained, fasted rat was tritium-labeled with 1.0 μCi of either 3H-DA or 3H-NE. The amine was microinjected in a volume of 0.5 μl through a permanently implanted 20 ga guide cannula. Then 30 min later, a push-pull cannula assembly was lowered through the guide and the labeled site was perfused with an artificial CSF solution at a rate of 25 μl/min. Each perfusion lasted for 5 min with a 10 min interval between successive perfusions. At the mid-point of a sequence of seven perfusions, one of two experimental procedures was introduced: (1) the rat was offered food pellets which were readily consumed; or (2) one of three compounds was added to the CSF perfusate: (a) 55 μg/gml of D-glucose; (b) 4 mU/μl of insulin; or (c) 10 μg/μl of 2-DG. The results showed that the efflux of 3H-DA increases as the rat feeds and during the subsequent perfusions. An immediate rise occurs in the output of the amine also when insulin is added to the perfusate; conversely, a slight suppression in 3H output is caused by glucose during its perfusion but a consistent elevation of radioactivity follows thereafter. 2-DG has no effect on the kinetics of catecholamine activity in the caudate-putamen. The patterns of release of 3H-NE are similar to those of 3H-DA under the same experimental conditions; however, the magnitude of the change is substantially attenuated. Although catecholamine activity within the caudate-putamen is usually implicated in motor control, our results support the possibility that dopamine in this structure may play a functional role in the regulation of food intake.