The effects of 8-OH-DPAT and (+/-)-pindolol on isolation-induced ultrasonic vocalizations in 3-, 10-, and 14-day-old rats

It has been established that administration of 5-HT1A agonists attenuates t he I ate of isolation-induced ultrasonic vocalizations (USV) in IO-day-old rat pups. In this study we extended these findings by examining the effects of administration of the serotonergic IA receptor agonist, 8-hydroxy-2-(di -n-propylamino)tetralin (8-OH-DPAT), and mixed 5-HT1A antagonist/beta adren ergic antagonist, (+/-)-pindolol, in 3-, 10-, and 14-day-old rat pups in or der to assess the effect of these drugs fr om a developmental perspective. At all three ages, 8-OH-DPAT significantly reduced the rate of isolation-in duced USV. While only the highest dose (1.0 mg/kg) of 8-OH-DPAT administere d to the 10- and 14-day-olds significantly reduced the rate of vocalization , both the 0.1 - and 1.0-mg/kg doses significantly attenuated the vocalizat ion rate in the 3-day-olds. Pindolol administration did not alter the rate of USV at any age nor did it block the quieting effect that generally occur s when an anesthetized littermate is placed with the isolated pup. We concl ude that 8-OH-DPAT is effective as early as 3 days of age in the quieting o f isolation-induced USV and that the regional age-dependent development of 5-HT1A receptors and projections are important factors in the observed diff erential sensitivity to 8-OH-DPAT administration during development. (C) 19 99 John Wiley & Sons, Inc.