EFFECT OF SEROTONIN DEPLETION ON VIBRISSA-RELATED PATTERNS OF THALAMIC AFFERENTS IN THE RATS SOMATOSENSORY CORTEX

To investigate the role of 5-HT in the development of the somatosensor y cortex, this amine was depleted in newborn (P-0) rats with a single subcutaneous injection of the toxin 5,7-dihydroxytryptamine (5,7-DHT) and thalamocortical organization was assayed by application of the car bocyanine dye Di-l to the thalamocortical radiations or ventrobasal th alamus, or by staining cortical sections for AChE or cytochrome oxidas e (CO). High-performance liquid chromatographic analysis of cortices f rom animals killed on P-6 or P>60 demonstrated that 5,7-DHT treatment resulted in 85.04 +/- 12.6% and 72.5 +/- 1.5% reductions in cortical 5 -HT, respectively. Alternate cortices from the brains of animals kille d on P-6 processed for 5-HT immunoreactivity demonstrated a complete a bsence of the vibrissa-related pattern of immunoreactivity and only a small number of coarse immunoreactive axons. The 85% depletion of 5-HT did not alter the somatotopic organization of thalamocortical afferen ts in animals killed on P-6 or P>60, but it did cause 30.5 +/- 7.3% an d 19.1 +/- 3.7% reductions in the cross-sectional areas of the patches of thalamocortical afferents corresponding to the long mystacial vibr issae (p < 0.05). These reductions were not associated with significan t reductions in either brain or cortical weight or with decreases in t he dimensions of the thalamic representation of the vibrissa follicles . These results indicate that 5-HT plays a significant role in the dev elopment of the thalamic innervation of the primary somatosensory cort ex.