5-HT 1A, 5-HT 1B and 5-HT 2 receptor agonists induce differential behavioral responses in preweanling rat pups

Abstract

Preweanling (postnatal day 17–18) Sprague-Dawley rat pups were tested in both the absence and presence of milk following administration of various doses of the 5-HT 1A agonists 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) or ipsapirone, the 5-HT 1B agonist 1-(3-chlorophenyl)piperazine (mCPP) or the 5-HT 2 agonist 1-(2,5-dimethoxy-4- iodo-phenyl)-2-aminopropane (DOI). 8-OH-DPAT decreased mouthing while ipsapirone, mCPP and DOI had no effect upon this behavior. However, all four agonists significantly decreased grooming. Both 8-OH-DPAT and mCPP produced alterations in limb positioning, with 8-OH-DPAT administration resulting in a poor control of the hindlimbs and mCPP inducing a hindlimb straddle position. These functional responses to 5-HT 1A, 5-HT 1B and 5-HT 2 agonists in preweanling pups vary from those observed previously in neonates. For instances, whereas inhibitory effects of 5-HT 1A stimulation on mouthing are observed in both neonatal and preweanling pups, facilitory effects of 5-HT 1B and 5-HT 2 stimulation are only seen in neonates. These ontogenetic alterations may be related to the previously reported ontogenetic reversal in the effect of serotonergic activation upon mouthing and suckling that occurs during the neonatal to weanling age period.