Effects of kainic acid lesions in rat ventral lateral geniculate nucleus upon field potentials of the superior colliculus: correlation between morphological and physiological observations.
Morphological and physiological effects of kainic acid (KA) lesions in rat ventral lateral geniculate nucleus (LGV) were studied 1.5 and 6 h after KA injection. Morphological changes were examined mainly by electron micrographs. At 1.5 h after KA injection dendrites were dilated and some vacuolations occurred in both dendrites and perikarya including geniculotectal relay neurons while axons were completely intact and cell organelles almost remained intact. Six h after KA injection dendrites and cell bodies were massively dilated with degeneration of cell organelles accompanied by sparse cytoplasm and deformed chromatin in the nucleus. However, almost all presynaptic axons, mainly retinogeniculate fibers, still remained intact. The electron micrographs demonstrate that destruction occurred first in dendrites, next in cell bodies and finally axons were likely to be affected. These morphological changes induced by KA are compatible with physiological effects which were assessed by the field response of the superior colliculus (SC) evoked by stimulation of the optic chiasm. During 1.5-2 h after KA injection all components of the SC response, the presynaptic and postsynaptic negative-positive waves were enhanced. The enhancement of the SC response may be correlated with morphological changes in terms of excitatory action of KA resulting in facilitation of geniculotectal transmission. Six h after KA injection postsynaptic negative-positive waves gradually declined in amplitude while the presynaptic wave returned to control level. The late suppression of postsynaptic components of the SC response may be attributable to a marked loss of geniculotectal transmission resulting from destruction of geniculotectal relay neurons by KA.
Nagata
T
T
Department of Physiology, Hyogo College of Medicine, Japan.
Tsukamoto
Y
Y
Matsuno
K
K
Hayashi
Y
Y
D000200:Action Potentials; D000818:Animals; D005829:Geniculate Bodies / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D007608:Kainic Acid; D008845:Microinjections; D008854:Microscopy, Electron; D051381:Rats; D013477:Superior Colliculi / Q000502:physiology* / Q000648:ultrastructure; D014795:Visual Pathways / Q000502:physiology*
D007608:Kainic Acid