Neonatally elevated serotonin levels alter terminal arbors of individual retinal ganglion cells in superior colliculus of hamsters.

Previous studies from this laboratory showed that sprouting of serotoninergic (5-HT) axons in the hamster's superior colliculus (SC), induced by a single subcutaneous injection of 5,7-dihydroxytryptamine (5,7-DHT) at birth (postnatal day 0 [P-0]), resulted in an increased terminal distribution of the uncrossed retinocollicular projection that was not associated with any changes in the number or distribution of ipsilaterally projecting retinal ganglion cells. The present study was undertaken to determine what effect this manipulation had on the terminal arbors of such axons. Retinocollicular axons of normal and 5,7-DHT-treated animals were anterogradely labeled with small intraretinal injections of the lipophilic dye 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (DiI) on P-16.

The cortical vibrissae representation is normal in transgenic mice lacking the 5-HT(1B) receptor.

Recent studies have suggested that 5-HT may modulate thalamocortical development in somatosensory cortex (S-I) of rats and mice, and that the 5-HT(1B) receptor may play a critical role in this process. Analysis of CO-stained sections through lamina IV of S-I in perinatal and adult 5-HT(1B) knockout mice revealed a normal vibrissae-related pattern, indicating that activation of the 5-HT(1B) receptor is not necessary for the normal development of the vibrissae representation in S-I.

Organization of the corticotectal projection in hamsters with neonatally elevated levels of serotonin in the superior colliculus.

A previous study from this laboratory showed that elevated serotonin (5-HT) levels in the hamsters superior colliculus (SC), induced by a single subcutaneous injection of 5,7-dihydroxytryptamine (5,7-DHT) at birth, resulted in an abnormally widespread distribution of the uncrossed retinotectal projection. The present study investigated whether the corticotectal projection in such animals was altered. Adult normal and 5,7-DHT-treated hamsters were injected with horseradish peroxidase (HRP) into occipital cortex and processed for anterograde tracing of corticotectal terminals in the SC.

Augmentation of serotonin in the developing superior colliculus alters the normal development of the uncrossed retinotectal projection.

A previous study from this laboratory showed that sprouting of serotoninergic axons in the hamster's superior colliculus (SC) induced by a single subcutaneous injection of 5,7-dihydroxytryptamine (5,7-DHT) at birth (postnatal day 0; P-0) resulted in an abnormal terminal distribution of the uncrossed retinotectal projection. The present study provided further evidence to support the role of increased 5-HT levels within the SC in this phenomenon. Slow-release polymer (ELVAX) chips impregnated with serotonin (5-HT) were placed over the SC on either P-1 or P-3, and retinotectal projections were assessed via anterograde transport of horseradish peroxidase when animals reached P > 18.