A light and electron microscopic analysis of the convergent retinal and visual cortical projections to the nucleus of the optic tract (NOT) in the pigmented rat.
It is generally known that the nucleus of the optic tract (NOT) subserves visuomotor relations between the retina and preoculomotor structures as the only subcortical pathway mediating optokinetic responses (OKR) in mammals. We have examined the projections from the retina and visual cortical areas (areas 17, 18a and 18b) to NOT using tracers (wheat germ agglutinin-conjugated horseradish peroxidase, WGA-HRP and cholera toxin B subunit, CTB) in order to clarify how these two different functional inputs to OKR are organized. CTB injection into the vitreous body resulted in anterograde label almost exclusively in the contralateral NOT. Ultrastructually, the size of the retinal axon terminals was small (up to 0.7 micron in diameter), contained round synaptic vesicles and pale mitochondria, and made asymmetrical synaptic contacts with both GABA-positive and GABA-negative NOT neurons. Visual cortical area 17 and the transitional area between area 17 and 18a, or between area 17 and 18b projected their axons to the ipsilateral NOT. Ultrastructually, the size of the cortical axon terminals was small (up to 0.5 micron in diameter), contained round synaptic vesicles, and made asymmetrical synaptic contacts only with GABAnegative NOT neurons. With light and electron microscopical observation, there was a considerable overlap in the cortico-NOT and retino-NOT projection pattern: GABA-negative (presumably NOT projection) neurons simultaneously receive input from both cortical and retinal terminals. From these results, it seems reasonable to postulate that inputs from visual cortical areas in the pigmented rat cooperate with those from the retina in controlling OKR.
Shintani
T
T
Department of Neurobiology and Anatomy, Niigata University, School of Medicine, Japan.
Hoshino
K
K
Meguro
R
R
Kaiya
T
T
Norita
M
M
D000818:Animals; D002772:Cholera Toxin; D003712:Dendrites / Q000648:ultrastructure; D008854:Microscopy, Electron; D017120:Nystagmus, Optokinetic / Q000502:physiology; D017729:Presynaptic Terminals / Q000648:ultrastructure; D051381:Rats; D020318:Rats, Long-Evans; D012165:Retinal Ganglion Cells / Q000737:chemistry / Q000502:physiology / Q000648:ultrastructure*; D016610:Tissue Embedding; D014793:Visual Cortex / Q000737:chemistry / Q000166:cytology* / Q000502:physiology; D014795:Visual Pathways / Q000166:cytology* / Q000502:physiology; D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; D005680:gamma-Aminobutyric Acid / Q000032:analysis
D018998:Wheat Germ Agglutinin-Horseradish Peroxidase Conjugate; D005680:gamma-Aminobutyric Acid; D002772:Cholera Toxin