Selective facilitation of the serotonin1B receptor causes disorganization of thalamic afferents and barrels in somatosensory cortex of rat

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Abstract
Alteration of serotonin (5‐HT) levels influences developing thalamocortical afferents (TCAs) in primary somatosensory cortex (SI) of rats and mice. The 5‐HT1B receptor, present on TCAs during the first postnatal week, may be involved in these effects. The present study asked whether administration of 5‐nonyloxytriptamine (NNT), a selective 5‐HT1B receptor agonist, affects TCA organization in rat SI. Littermates were injected five times daily (5×/day), with either 0.1 mg/kg NNT or vehicle from birth to postnatal day 6 (P‐6). Animals were killed on P‐6, and their brains were processed for high‐performance liquid chromatography (HPLC), cytochrome oxidase (CO) histochemistry, cresyl violet, or demonstration of TCAs by placement of 1,1′‐dioctadecyl‐3,3,3′′,3′‐tetra‐methylindocarbocyanine perchlorate (Di‐I) on thalamocortical radiations. At P‐6, NNT treatment decreased 5‐HT levels slightly compared with controls, although this difference was not statistically significant. In NNT‐treated rats, the Di‐I‐labeled vibrissae‐related pattern showed a range of effects, from fusion of patches related to mystacial vibrissae in treated animals to a less distinct vibrissae‐related pattern in SI barrelfield compared with controls. Staining for CO and Nissl stain in layer IV of SI showed a similar range of abnormalities. These results indicate that the agonist action of NNT at the 5‐HT1B receptor causes TCA disorganization in rat barrel field cortex in the absence of elevated 5‐HT. J. Comp. Neurol. 425:130–138, 2000.

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