Figure 4.

Neurotensin-evoked excitation of DAergic neurons occurs independently of astrocyte activation. A, Graph representing the proportion of astrocytes that demonstrate an increase in [Ca²⁺]_i in response to NT (100 nm). Whereas a response was obtained in a significant proportion of primary mesencephalic astrocytes in culture, this was almost never observed in purified astrocyte cultures initially grown in flasks. B, Comparison of the NT-evoked enhancement in firing rate in DAergic neurons when grown together with responsive (open circles) (n = 7) or nonresponsive (dark squares) astrocytes (n = 10). The time course of the change in firing rate over time is expressed as a difference score (delta) representing the variation in average firing rate within 15 sec bins compared with the average firing rate within the eight initial bins acquired before peptide application. Basal firing rate was, on average, 0.40 ± 0.05 Hz in neurons grown on responsive astrocytes and 1.05 ± 0.05 in neurons grown on nonresponsive astrocytes. NT was used at 100 nm.