MK-801, phencyclidine (PCP), and PCP-like drugs increase burst firing in rat A10 dopamine neurons: comparison to competitive NMDA antagonists.

Extracellular single-unit recordings were used to assess the effects of PCP and PCP-like drugs (MK-801 and TCP) on the burst firing of ventral tegmental A10 dopamine neurons in the rat. The effects of these noncompetitive N-methyl-D-aspartate (NMDA) receptor antagonists were compared to the potent and competitive NMDA antagonists CGS 19755 and (+/-)CPP, and to BTCP, a PCP-derivative possessing little affinity for the PCP binding site within the ion channel gated by NMDA. PCP, MK-801, and TCP produced dose-dependent increases in the firing rate, which were accompanied by increases in the amount of burst activity, the number of action potentials within a burst, and the conversion of nonbursty cells to bursty. However, the coefficient of variation, a measure of the regularity of firing, was not significantly altered. These predominately excitatory effects contrast with the inhibition of firing, decrease in bursting, and regularization of pattern produced by BTCP. CGS 197555 and (+/-)CPP failed to alter any of the measured parameters. Thus, the increase in firing rate and amount of burst activity of dopamine neurons produced by PCP and PCP-like drugs, and the resultant hyperdopaminergia within the mesolimbic-mesocortical regions, could underlie the psychotomimetic properties of these compounds. Moreover, this effect would not appear to be related to a loss of activity at the NMDA recognition site, as evidenced by the lack of effect of the competitive NMDA antagonists.