Behavioral effects Of 8-OH-DPAT in chronically stressed male and female rats.

The present study tested the hypothesis that chronic stress desensitizes serotonergic 5-HT(1A) receptors and alters behavioral changes following 5-HT(1A) agonist administration. Eating, acoustic startle response (ASR), and locomotor activity were measured in stressed and nonstressed male and female rats after 8-OH-DPAT administration. Stressed rats were paired and stressed by around-the-clock intermittent foot shock. Controllable stress (CS) rats could avoid/terminate shock for themselves and their yoked partners by pulling a ceiling chain, whereas their partners, the uncontrollable stress (UCS) rats, could not. Rats earned their entire daily ration of food by pressing a lever. In previous experiments, this paradigm was stressful, but not debilitating and rats continued to eat, groom, sleep, and avoid/escape greater than 99% of shock trials. Locomotor activity and ASR were measured in the present study after saline and 8-OH-DPAT administration (0.25 mg/kg, IP) before, 24 h, and 72 h after shock onset. 8-OH-DPAT only decreased food intake significantly in male and female rats after the first administration. Stress decreased food intake in both the CS and UCS rats, with UCS rats eating the least. However, the effects of stress and 8-OH-DPAT were not additive. 8-OH-DPAT significantly increased peak startle amplitude at 100 and 120 dB, and decreased latency to peak startle amplitude at 100 dB in male and female rats. In contrast, 8-OH-DPAT did not alter percent prepulse inhibition (%PPI) at 100 dB, but significantly decreased %PPI in males but not females at 120 dB. Stress did not have a consistent effect on ASR, but reduced %PPI in males, but not females. Neither stress nor 8-OH-DPAT significantly altered locomotor activity. Although the results do not show an increased sensitivity to 8-OH-DPAT in stressed rats, the unexpectedly weak effects of 8-OH-DPAT alone on the behavioral measures chosen limits the conclusions that can be drawn.