Immunocytochemical evidence for in vitro release of glutamate and GABA from separate nerve terminal populations in the rat pontine nuclei.
A quantitative electron microscopic immunocytochemical method was used to study the synaptic handling of glutamate and GABA in slice preparations from the rat pontine nuclei. Slices were subjected to a depolarizing stimulus (55 mM K+, 20 min) in the presence of a physiological or low Ca(2+)-concentration. Depolarization at physiological [Ca2+] evoked a depletion of glutamate-like immunoreactivity from nerve terminals that contain round vesicles and establish asymmetric synaptic contacts. When depolarization was induced in the presence of only 0.1 mM Ca2+ (10 mM Mg2+ added), the loss of glutamate was significantly reduced or abolished, indicative of a Ca(2+)-dependent component of glutamate release. By means of a double-labeling immunocytochemical method we could identify a population of nerve terminals that displayed strong GABA-like immunoreactivity, and a level of glutamate-like immunoreactivity that was low but yet clearly above background level. This type of terminal contains elongated or pleomorphic vesicles and establishes symmetric synaptic contacts. In these terminals, depolarization evoked a Ca(2+)-dependent depletion of GABA-like immunoreactivity, but failed to change the level of glutamate-like immunoreactivity. The present study demonstrates that two different types of nerve terminal in the rat pontine nuclei contain releasable pools of glutamate and GABA, respectively, and that the GABA-releasing terminals also contain a non-releasable pool of glutamate. The glutamate of the latter pool could act as precursor of GABA.
Aas
J E
JE
Department of Anatomy, University of Oslo, Norway.
Laake
J H
JH
Brodal
P
P
Ottersen
O P
OP
D000818:Animals; D001369:Axons / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D002118:Calcium / Q000494:pharmacology; D005971:Glutamates / Q000032:analysis / Q000378:metabolism*; D018698:Glutamic Acid; D066298:In Vitro Techniques; D008274:Magnesium / Q000494:pharmacology; D008297:Male; D016253:Microscopy, Immunoelectron / Q000379:methods; D009411:Nerve Endings / Q000502:physiology* / Q000648:ultrastructure; D011149:Pons / Q000502:physiology* / Q000648:ultrastructure; D011188:Potassium / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D013569:Synapses / Q000187:drug effects / Q000502:physiology* / Q000648:ultrastructure; D005680:gamma-Aminobutyric Acid / Q000032:analysis / Q000378:metabolism*
D005971:Glutamates; D018698:Glutamic Acid; D005680:gamma-Aminobutyric Acid; D008274:Magnesium; D011188:Potassium; D002118:Calcium