Mittler, Taliah. Dose- and rate-dependent effects of cocaine on striatal neurons related to licking. Retrieved from https://doi.org/doi:10.7282/T3DJ5FZ5
DescriptionTo examine the role of striatal mechanisms in cocaine-induced stereotyped licking, the activity of lick-related neurons in the ventrolateral striatum of awake, freely moving rats engaged in licking was recorded before and after cocaine administration (0, 5, 10 and 20 mg/kg). Relative to zero dose, cocaine reduced lick duration and increased interlick interval, particularly at the high dose, but did not affect licking rhythm. Stereotyped licking was induced only by the high dose, evident by an increase in the number of licks in the absence of water delivery. Firing rates (FR) of striatal neurons phasically related to licking were compared between matched licks before and after injection, minimizing any influence of sensorimotor variables on changes in firing. Both increases and decreases in average FR were observed post-drug, exhibiting a dose-dependent pattern that strongly depended on pre-drug FR. At the middle and high doses relative to the zero dose group, the average FR of slow firing neurons were increased by cocaine, resulting from a general elevation of movement-related FR. By contrast, fast firing neurons showed decreased average FR only in the high dose group, with reduced FR across the entire range for these neurons. Additionally, without any drug present (prior to drug injection) FR were positively related to the strength of the correlation of FR with lick duration. Changes in behavioral correlations were demonstrated over time with no drug present (for slow firing neurons), and following cocaine administration (for slow firing neurons at all doses, and for fast firing neurons only at the high dose). Thus, differences were observed between slow and fast firing neurons in drug effects on FR, in the strength of their behavioral correlations and with respect to changes in their behavioral correlations, suggesting that fast firing neurons may be more strongly involved in the processing of movement parameters. These findings suggest that at the high dose, increased phasic activity of slow firing striatal neurons and simultaneously reduced phasic activity of fast firing striatal neurons may contribute, respectively, to the continual initiation of stereotypic movements and the absence of longer, more global movements.