Single retinal ganglion cells sending axon collaterals bilaterally to the lateral geniculate nuclei and superior colliculi in the rat

S240

15-22

NORADRENERGIC CORTEX.

Physiology, Brain

CONTROL

TETSUYA

Akita University,

OF THE

School of Medicine,

microdialysis

was

RELEASE

SHIROKAWA

carried

out

AND

OF GABA TETSURO

IN THE

KITTEN

OGAWA,

VISUAL

Department

of

Akita 010, Japan.

in order

to examine

the

role

of endogenouslexogenous

noradrenaline (NA) on the release of GABA in the kitten visual cortex. We hypothesized that the cortical GABAergic system is involved in the ocular dominance plasticity, which is enhanced by the cortical infusion of NA under the acute experimental was infused through two different that 1) infusion of NA through dependent

manner, however,

(“1 mm), the spontaneous

condition

(Imamura

ways; one is through

the dialysis

and Kasamatsu, 1991). In the present a dialysis probe, the other via a cannula.

probe suppressed

the spontaneous

2) when NA was infused via the cannula

GABA release

was enhanced

release

We found of GABA in a dose-

which was implanted

during NA infusion,

study, NA

near the probe

3) visually-evoked

release

of

GABA was also modulated during NA infusion. These results suggest that 1) the NA system regulates intercolumn inhibition mediated by the cortical GABAergic network, 2) the enhanced GABA release may play a role in the ocular dominance

plasticity that is induced by NA infusion.

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LOCALIZATION OF SYNAPTIC ACTIVITY OF VERTICAL AND HORIZONTAL CONNECTIONS WITHIN lTHE RAT VISUAL CORTEX. TOMOMI ICHINOSE' and TAKAYUKI MURAKOSHI1. Departments of Pharmacoloav and Anesthesioloov, Facultv of Medicine, Tokyo Medical & Dental Universitv. l-5-45 Yushima, Bunkyo-ku, Tok-qo, 113 Japan.

Cortical neurons receive synaptic inputs through both the vertical and the horizontal pathways. We investigated the localization of these synaptic inputs onto the visual cortical neurons. Postsynaptic potentials (PSPs) were recorded from pyramidal neurons of the supra- and infragranular layers of coronal slices (400 pm thick) prepared from rats (4-7-week-old) under nembutal anesthesia. PSPs were evoked by stimulation to the underlying white matter (vertical input) or to the gray matter at 0.5-l mm distance in the same layer as the recording site (hogizontal input). Aft9 eliminating the synaptic transmissions by perfusion with low Ca (0.1 mM) and h$h Mg (6 mM) medium, it was possible to recover the PSPs by focal application of Ca with a pressure puff prior to the electrical stimulation. 2+Byapplying to various locations relative to the recording cell, hot spots of the Ca sensitivity were mapped with a resolution of ca. 100-200 pm. The hot spots of the horizontal as well as the vertical inputs were found at the area close to the soma but not at the area more basal from the cell, suggesting the coincidence with the neuro q+'s dendritic arborization. PSPs of the horizontal inputs were well recovered by a Ca -puff also at the lateral of the soma on the stimulating side but very weakly on the opposite side.

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SINGLE RETINAL GANGLION CELLS SENDING AXON COLLATERALS BILATERALLY TO THE LATERALGENICULATE NUCLEI AND SUPERIOR COLLICULI INTHE RAT YASUKOKONDO', MASAHIKO TAKADAz& NOBORU MIZUNO*, Departments of2MorphologicalBrain Science and tOphthalmologv, Faculty of Medicine, Kyoto University, Kyoto 606-01, Japan Employing fluorescent retrograde double/triple labeling, we examined whether single retinal ganglion cells project bilaterally to the lateral geniculate nuclei (LGN) and superior colliculi (SC) in the rat. After separate injections of Fast Blue (FB) and Diamidino Yellow (DY) respectively into the right and left LGN, many retrogradely-labeled cells were distributed all over the retina contralateral to each injection. Cells labeled with one tracer injected into the ipsilateral LGN were found mainly in the lower-temporal retinal region; some of them were further labeled with the other tracer injected into the contralateral LGN. The vast majority of these double-labeled cells were of large type (more than 20 pm in diameter). Similar results were obtained after separate injections of FB and DY respectively into the right and left SC, or respectively into the right SC and left LGN. After separate injections of three fluorescent retrograde tracers, FB, DY and rhodamine-B-isothiocyanate, respectively into the bilateral LGN and unilateral SC, or respectively into the unilateral LGN and bilateral SC, a number of cells triple-labeled with all tracers were localized in the lower-temporal retinal region; most of them were also of large type. The present data indicate that some retinal ganglion cells of the rat project bilaterally to the LGN or/and SC by way of axon collaterals; they are primarily large cells corresponding probably to Y cells in the cat retina, and are distributed in the lower-temporal retinal region. Since the lower-temporal region of the rat retina represents binocular vision, the bilaterally projecting ganglion cells may play important roles in stereoscopic vision.