Differential cannabinoid-induced electrophysiological effects in rat ventral tegmentum

Cannabinoids are known to exert mainly excitatory effects on dopaminergic cells of the ventral tegmental area (VTA). We have utilized an in vivo multiple-single unit electrophysiological approach to assess different neuronal contributions that may ultimately lead to excitation in this area. Baseline neuron recordings, using low impedance microwires, showed a variety of waveforms with a wide range of durations (0.8–3.2 ms). In the first experiment systemic injection of the potent cannabinoid agonist HU210 (100 μg/kg, i.p.) led predominantly to an increase in firing rate (~214%, compared to pre-drug) in slowly firing cells with broad action potentials, possibly driven by a majority of presumed dopaminergic neurons ( n = 31). However, the firing rate of some units was either unaffected (