Contributions of raphe-cortical and thalamocortical axons to the transient somatotopic pattern of serotonin immunoreactivity in rat cortex.
Two experiments were carried out to evaluate the relative contributions of thalamocortical and raphe-cortical fibers to the transient somatotopically organized pattern of serotonin (5-HT) immunoreactivity that appears in the primary somatosensory cortex (SI) of rats during the first 2 weeks of life. In the first experiment, the specific 5-HT uptake inhibitors, fluoxetine and paroxetine, were administered systemically, animals were killed 3, 6, or 12 h later, and cortices evaluated for 5-HT immunoreactivity. Fluoxetine treatment had no appreciable effect on the density of 5-HT immunoreactivity in the cortex. Paroxetine treatment caused a reduction in 5-HT immunoreactivity which was maximal 6 h after administration. Examination of the cortices of these animals revealed a loss of very fine dust-like 5-HT immunoreactivity, but a vibrissae-related pattern remained visible in thicker fibers. In a second experiment, raphe-cortical fibers were destroyed by systemic administration of 5,7-dihydroxytryptamine on the day of birth. Six days after this manipulation, 5-HT was applied directly to the cortex in vivo and the animals were then killed and cortices processed to demonstrate 5-HT immunoreactivity. The cortices of these rats revealed a fine dust-like immunoreactivity organized in a somatotopic pattern, but only very few 5-HT-positive axons. The results of these experiments suggest that both raphe-cortical axons and thalamocortical fibers contribute to the patterned 5-HT immunoreactivity observed in SI of perinatal rats.
Bennett-Clarke
C A
CA
Department of Anatomy and Neurobiology, Medical College of Ohio, Toledo 43699, USA.
Chiaia
N L
NL
Rhoades
R W
RW
D000344:Afferent Pathways / Q000033:anatomy & histology / Q000187:drug effects; D000818:Animals; D000831:Animals, Newborn; D001369:Axons / Q000187:drug effects / Q000648:ultrastructure*; D001931:Brain Mapping; D002540:Cerebral Cortex / Q000033:anatomy & histology* / Q000187:drug effects; D005260:Female; D005473:Fluoxetine / Q000494:pharmacology; D007124:Immunoenzyme Techniques; D008297:Male; D017374:Paroxetine / Q000494:pharmacology; D011903:Raphe Nuclei / Q000033:anatomy & histology* / Q000187:drug effects; D051381:Rats; D011985:Receptors, Serotonin / Q000187:drug effects / Q000648:ultrastructure; D012701:Serotonin / Q000502:physiology*; D017367:Selective Serotonin Reuptake Inhibitors / Q000494:pharmacology; D012867:Skin / Q000294:innervation*; D013003:Somatosensory Cortex / Q000033:anatomy & histology* / Q000187:drug effects; D013787:Thalamic Nuclei / Q000033:anatomy & histology* / Q000187:drug effects
D005473:Fluoxetine; D017374:Paroxetine; D011985:Receptors, Serotonin; D012701:Serotonin; D017367:Selective Serotonin Reuptake Inhibitors