THE EFFECTS OF LONG-TERM TREATMENT WITH THE 5-HT(1A) RECEPTOR AGONIST8-OH-DPAT AND THE 5-HT(2 1C) RECEPTOR AGONIST DOI IN THE NEONATAL RAT/

The rat pup ultrasonic call was used to study the effects of acute and long-term treatment with the 5-HT1A receptor agonist 8-hydroxy-2-(di- n-propylamino)tetralin (8-OH-DPAT) and the 5-HT2/1C receptor agonist 1 -(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) during the neonatal period. Acute administration of 8-OH-DPAT and DOI reduced the number of ultrasonic calls. The reduction induced by 8-OH-DPAT and DOI was an tagonized by the 5-HT1A antagonist )-5-fluoro-8-hy-droxy-2-(di-n-propy lamino)tetralin ((S)-UH-301) and the 5-HT2 antagonist ketanserin, resp ectively. The long-term treatments were started on postnatal day 1. On postnatal day 7, the response of the long-term DOI-treated group was clearly attenuated in comparison to that of the acute DOI-treated grou p. In contrast, no tolerance to the effect of 8-OH-DPAT was achieved a fter an analogous treatment. The data indicate that there is a diversi ty in the ontogeny of the ability to develop tolerance to 5-HT1A agoni sts in comparison to 5-HT2/1C agonists.