Effects of alterations of the vibrissae-related organization of thalamocortical axons upon the organization and outgrowth of intracortical connections in the barrelfield of the rat.
Previous studies have shown that intracortical projections in layer IV of the vibrissae representation of primary somatosensory cortex (S-I) are arrayed in a pattern complementary to that of thalamocortical axons (TCAs). Elevation of cortical serotonin (5-HT) in rats during the first postnatal week results in a transient disruption of the vibrissae-related pattern of TCAs and layer IV neurons in S-I. The present study examines the influence of elevated cortical 5-HT levels and the attendant loss of vibrissae-related TCA clusters on the organization of S-I intracortical connections. Cortical 5-HT was elevated in neonatal rats via chronic injections of clorgyline from birth until P-6. Animals were euthanized on P-6 or allowed to survive an additional 4 days without further clorgyline treatment. Distributions of TCAs and intracortical axons were assessed via application of 1,1'-dioctadecyl-3,3,3',3'-tetramethylindocarbocyanine perchlorate (Di-I) and 4-(4-(dihexadecylamino)styryl)-N-methylpyridinium iodide (Di-A) to the thalamic radiations and directly into the cortical barrelfield, respectively. Chronic administration of clorgyline resulted in a loss of the vibrissae-related organization of TCAs in layer IV of S-I. There was also a loss of the complementary pattern of intracortical projections in layer IV of this region. Discontinuation of clorgyline treatment resulted in a return of the vibrissae-related pattern of TCAs as well as the complementary pattern of intracortical projections. These results are consistent with the conclusion that the normal organization of intracortical projections in this region of S-I depends on the presence of the orderly array of TCAs.
Lane
Richard D
RD
Department of Anatomy and Neurobiology, Medical College of Ohio, Toledo 43614-5804, USA. rlane@mco.edu
Rizk
Tallat
T
Chiaia
Nicolas L
NL
Mooney
Richard D
RD
Rhoades
Robert W
RW
D000818:Animals; D001369:Axons / Q000378:metabolism / Q000502:physiology; D002352:Carrier Proteins / Q000378:metabolism; D003010:Clorgyline / Q000494:pharmacology; D004396:Coloring Agents; D007091:Image Processing, Computer-Assisted; D008562:Membrane Glycoproteins / Q000378:metabolism; D026901:Membrane Transport Proteins; D008856:Microscopy, Fluorescence; D008996:Monoamine Oxidase Inhibitors / Q000494:pharmacology; D009419:Nerve Tissue Proteins; D009434:Neural Pathways / Q000378:metabolism / Q000502:physiology; D017729:Presynaptic Terminals / Q000502:physiology; D051381:Rats; D017207:Rats, Sprague-Dawley; D044302:Receptor, Serotonin, 5-HT1B; D011985:Receptors, Serotonin / Q000378:metabolism; D012701:Serotonin / Q000378:metabolism; D050486:Serotonin Plasma Membrane Transport Proteins; D013003:Somatosensory Cortex / Q000378:metabolism / Q000502:physiology*; D013788:Thalamus / Q000502:physiology*; D014738:Vibrissae / Q000294:innervation* / Q000502:physiology
D002352:Carrier Proteins; D004396:Coloring Agents; D008562:Membrane Glycoproteins; D026901:Membrane Transport Proteins; D008996:Monoamine Oxidase Inhibitors; D009419:Nerve Tissue Proteins; D044302:Receptor, Serotonin, 5-HT1B; D011985:Receptors, Serotonin; D050486:Serotonin Plasma Membrane Transport Proteins; C493232:Slc6a4 protein, rat; D012701:Serotonin; D003010:Clorgyline