Effects of Elevated Serotonin Levels on Patterns of GAP-43 Expression During Barrel Development in Rat Somatosensory Cortex
Elevating cortical serotonin (5-HT) in rats with clorgyline, a monoamine oxidase A (MAOA) inhibitor, from postnatal day (P-) 0 to P-6 delays the organization of thalamocortical afferent fibers into a vibrissae-related pattern in the somatosensory cortex (S-I). Despite continued elevation of cortical 5-HT, the thalamocortical fibers form a characteristic vibrissae pattern of barrels in layer IV of S-I by P-8. The growth-associated protein, GAP-43, is transiently expressed in developing S-I cortex of rats in a vibrissae related pattern until P-7. After P-7, GAP-43 expression is reduced in the barrel centers and increased in the septa. The present study evaluated the effect of elevated 5-HT levels on the distribution of GAP-43 immunoreactivity in S-I. We employed 5-HT immunocytochemistry and 1,1’-dioctadecyl-3,3,3”,3’- tetramethylindocarbocyanine perchlorate (DiI) labeling of thalamic radiations to confirm a “barrelless” phenotype in P-6 clorgyline-treated animals and a recovered barrel pattern in treated animals allowed to survive until P-8 and P-10. GAP-43 immunocytochemistry was used to evaluate the cortical distribution of this protein in similarly treated littermates. Continuous inhibition of MAOA from P-0 to P-6 resulted in a corresponding loss of the GAP-43 vibrissae-related pattern at P-6. Despite continued elevation of cortical 5-HT until P-8 and P-10, the characteristic vibrissae-complementary pattern of GAP-43 emerged with expression concentrated in the septa and rows. GAP-43 vibrissae-related thalamocortical axon pattern never appeared in the clorgyline-treated animals. Thus, while elevated 5-HT delays development of a vibrissae-related pattern of thalamocortical afferents, it does not appear to alter the time when a GAP-43 vibrissae-related complementary pattern emerges.
School:University of Toledo Health Science Campus
School Location:USA - Ohio
Source Type:Master's Thesis
Keywords:somatosensory cortex gap 43 barrels rat serotonin clorgyline
Date of Publication:01/01/2005