Effects of excitant amino acids on acoustic responses of inferior colliculus neurons.
Iontophoretic application of the excitant amino acids (EAAs), glutamate, aspartate and N-methyl-D-aspartate (NMDA) resulted in increased acoustically evoked and spontaneous firing of most neurons in the central nucleus of inferior colliculus (ICC). The excitatory effects of these EAAs were blocked by simultaneous application of EAA antagonists which selectively block the NMDA receptor subtype, 2-amino-5-phosphonovalerate or D-alpha-aminoadipate and to a lesser extent with non-selective EAA antagonists, such as glutamic acid diethylester. Application of NMDA receptor-selective EAA antagonists alone greatly reduced the firing of most ICC neurons examined, but non-selective EAA antagonists either increased or produced little change in firing of most ICC neurons examined. In this and previous studies cholinergic agonists were found to increase the firing of ICC neurons, but the cholinergic agonists were less effective in exciting ICC neurons than EAA agonists. Cholinergic antagonists in a previous study were considerably less effective in inhibiting the discharge of ICC neurons than were the EAA antagonists in the present study. These results, in conjunction with previous neurochemical and anatomical localization studies, support a possible role of an EAA as a candidate for afferent excitatory transmitter in neurons of the inferior colliculus.
Faingold
C L
CL
Department of Pharmacology, Southern Illinois University, School of Medicine, Springfield 62794-9230.
Hoffmann
W E
WE
Caspary
D M
DM
D015763:2-Amino-5-phosphonovalerate; D000200:Action Potentials / Q000187:drug effects; D000818:Animals; D001224:Aspartic Acid / Q000031:analogs & derivatives* / Q000037:antagonists & inhibitors / Q000494:pharmacology* / Q000502:physiology; D005971:Glutamates / Q000494:pharmacology* / Q000502:physiology; D018698:Glutamic Acid; D007245:Inferior Colliculi / Q000187:drug effects / Q000502:physiology*; D016202:N-Methylaspartate; D010277:Parasympathomimetics / Q000494:pharmacology; D051381:Rats; D011919:Rats, Inbred Strains; D014633:Valine / Q000031:analogs & derivatives / Q000494:pharmacology
D005971:Glutamates; D010277:Parasympathomimetics; D001224:Aspartic Acid; D018698:Glutamic Acid; D016202:N-Methylaspartate; D015763:2-Amino-5-phosphonovalerate; D014633:Valine