Serotonergic neuronal activity in the dorsal raphe nucleus of selectively bred alcohol-preferring and alcohol-nonpreferring rats and unselected Wistar rats

Background: Selectively-bred alcohol-preferring (P) rats have fewer serotonin (5-HT) neurons in the dorsal raphe nucleus (DRN) than do alcohol-nonpreferring (NP) rats. The present study was designed to test the hypothesis that the remaining 5-HT neurons in P rats compensated for their reduced number by increasing neuronal activity. Methods: Spontaneous activity was recorded from single-spiking and bursting 5-HT neurons in the DRN of unanesthetized paralyzed, alcohol-naive P, NP, and Wistar rats. Firing frequencies, the percentages of action potentials in bursts, and the percentages of bursting neurons were evaluated. Results: There were no significant differences among the three groups of rats in any of the parameters measured. Power analyses were performed on preliminary data to determine the sample sizes necessaIy for detection of significant differences. The mean firing frequencies of single-spiking 5-HT neurons averaged 1.8 (37 neurons), 1.7 (17 neurons), and 1.8 (41 neurons) spikes per second in P, NP, and Wistar rats, respectively. For bursting 5-HT neurons, the percentages of action potentials in bursts for P, NP, and Wistar rats were 55.0% (24 neurons), 49.7% (18 neurons), and 55.1% (21 neurons). The mean percentages of bursting 5-HT neurons encountered per electrode penetration were 44% for P rats (n = 28), 44% fur NP rats (n = 14), and 34% for Wistar rats (n = 26). Conclusions: The results indicate that the sample of 5-HT neurons recorded in the DRN of P rats had nor compensated for a reduced number by altering neuronal activity.