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SEROTONERGIC MODULATION OF THE ACOUSTIC STARTLE RESPONSE IN RATS DURING PREWEANING DEVELOPMENT
Citation:
Sheets, L., L. Cook, AND L.W. Reiter. SEROTONERGIC MODULATION OF THE ACOUSTIC STARTLE RESPONSE IN RATS DURING PREWEANING DEVELOPMENT. U.S. Environmental Protection Agency, Washington, D.C., EPA/600/J-89/337 (NTIS PB90201674).
Description:
The involvement of serotonin (5-HT) in modulating the acoustic startle response (ASR) is well established in adult rats, but (5-HT) involvement during the preweaning period, when 5-HT neurons undergo extensive development, has not previously been described. Three 5-HT2 receptor subtypes are reported to modulate the ASR in adult rats: 5-HT- and 5-HT'2 receptor agonists facilitate the ASR, whereas 5-HT1B agonists decrease the response. n the present study, the effects of 5-HT agonists and generalized 5-HT depletion on the ASR were studied in preweaning animals, using independent groups of Long-Evans rats tested on postnatal day (PHO) 13. 17 and 21. -Hydroxy-2-(d-in-propylamino) tetralin (80HDPAT, 62-1000 ug/kg), a 5-HT1A receptor agonist, and 5-methoxy-N,N-dimethyl tryptamine (Me0DHT, 2-4 mg/kg), a nonselective 5-HT agonist, had no effect on PND 13 and then increased the ASR on PND 17 and 21. he 5-HT2 receptor antagonists cyproheptadine (5 mg/kg) and ketanserin (5 mg/kg) blocked the effect of Me0DMT at both ages, providing some evidence that Me0DMT increased the ASR through 5-HT2 receptors. -(m-Chlorophenyl) piperazine (mCPP, 1-5 sg/kg), a 5-HT 1B had no effect on ASR amplitude on PND 13 or 17 and then produced a dose-related decrease in the response on PND 21. eneralized depletion of 5-HT by 8O-90% in whole-brain and spinal cord, using p-chlorophenylalanine (P, 300 mg/kg 24 hr prior to testing), did not alter ASR amplitude at any age. hese results support the development of 5-HT facilitation and inhibition of the ASR during the third postnatal week. -HT involvement in facilitating (5-HT1A and 5-HT2) developed earlier than inhibition (5-HT1B). he PCPA to increase the ASR in preweaning rats tends to indicate that 5-HT tonic inhibition has not developed by PND 21. he results with PCPA are inconclusive, however, since there is some discrepancy regarding the effect of PCPA on the ASR in adult rats.