| Abstract: | By use of various histochemical techniques, it was shown that both DA and non-DA cells in the VTA project to the NAc. Of these VTA-NAc output cells, the great majority were DA-containing cells. A small number of non-DA cells were encountered most frequently in the lateral part of the VTA. Correspondingly, two distinct groups of neurons, types I and II, could be identified by antidromic stimulation of the NAc. Several lines of evidence suggest that type I cells are DA-containing neurons. The evidence may be summarized as follows: 1. (1) type I cells had a slow-bursting or regular firing pattern, slow discharge rate and wide spike duration which appears to be identical to the characteristics of DA neurons originally described by Bunney et al.16; 2. (2) the great majority of these cells could be activated antidromically by stimulation of the NAc; 3. (3) the conduction velocity and absolute refractory period of type I cells are consistent with unmyelinated fine DA fibers; 4. (4) injection of 6-OHDA, but not 5,7-DHT directly in the MFB blocked antidromic responses of these cells; 5. (5) they were extremely sensitive to intravenously administered DA agonist apomorphine (ID50 = 7 μg/kg); and 6. (6) direct fluorescence histochemical examination of serial sections from brains of animals in which type I cells have been identified by antidromic stimulation of the NAc showed that type I cells are most likely catecholamine-containi ng neurons. By contrast, type II cells possessed an entirely different spectrum of physiological characteristics; in addition, they showed no consistent response to apomorphine and their antidromic responses to stimulation of the NAc were not affected by 6-OHDA. It is concluded that (1) VTA output neurons consist of both DA and nonDA neurons, and (2) identified types I and II neurons in the VTA by antidromic stimulation of the NAc are DA and non-DA cells, respectively.
Author Keywords: dopamine neurons; non-dopamine neurons; ventral tegmental area; antidromic stimulation; nucleus accumbens; histofluorescence; apomorphine; 6-hydroxy-dopamine |
