Amino Acids in the Visual System

In order to characterize the transmitters in the optic nerve, we have monitored the release of amino acids from tissue slices of the supenor colliculus (SC). The levels of aspartate, glutamate, GABA, taurine, and p-alanine in the perfusate increased during depolarization with either 56 mM potassium (Fig 4) or veratri-dine. This increased release was Ca-dependent (Note not for taurine) and tetr odotoxin-sensitive (Sandberg and Jacobson, 1981). 

In parallel, dialysates were collected m vivo from the lateral geniculate nucleus of the cat with a closed dialysis sampling probe see below) (Sandberg and Lindstrom, 1983) An attached electrode was used for recording and stimulation. Local electrical stimulation evoked a pronounced efflux of aspartate, glutamate, GABA, and taunne (Fig. 5). 

In order to localize the origin of the release, we performed perfusion and depolarization experiments on SC tissue slices after degeneration of the optic nerve terminals (Sandberg and Corazzi, 1983). The Ca-dependent release of neuroactive amino acids was, however, unchanged, which implies that the major transmitter of the optic nerve is not an easily detectable primary amine 

Brain Diafysis—Amino Acids in the Extracelluiar Fluid of the Uving Animal 

As a closed perfusion system may be precalibrated to give actual levels of free amino acids, the composition in the extracellular fluid may be compared with that in the cerebrospinal fluid (CSF, Hamberger et al., 1983 1985). A comparison between the hippocampus extracellular fluid and the cisternal fluid in albino rabbits showed good agreement with respect to taunne, valine, leucine, isoleucine, and phenylalanine, whereas the concentrations of ex- 

---