The Excitation and Depression of Mammalian Cortical Neurones by Amino Acids

Abstract

Amino acids related to L-glutamic and y-amino-n-butyric acid have been administered electrophoretically, and by pressure ejection, into the extraneuronal environment of single neurones in the pericruciate cortex of cats anaesthetized with allobarbitone or allobarbitone-urethane. Acidic amino acids related to glutamic acid, particularly N-methyl-D-aspartic acid, excited cortical neurones. Neutral amino acids related to y-amino-n-butyric acid, particularly 3-amino-1-propanesulphonic acid, depressed cortical neurones. Some of the depressants blocked the antidromic invasion of Betz cells by pyramidal volleys. There are no essential differences between the sensitivities of cortical and spinal neurones towards locally administered amino acids. A transmitter function of such amino acids within the mammalian central nervous system is considered unlikely.When ejected electrophoretically from glass micropipettes, many acidic amino acids related to glutamic acid excite neurones in the feline spinal cord (Curtis,

Cardiovascular function is altered by picomole injections of glutamate into rat medulla

“…This is unlikely since a given response could be reproduced 4-5 times in rapid succession with no noticeable decrease in the response. Also, the magnitude of the response was both volume (0.2-10 nl) and concentration (l-10 mM) dependent and did not show a biphasic component suggestive of depolarization blockade (Crawford and Curtis, 1964). In addition, blockade of local neuronal discharge by lidocaine did not mimic the effects of Glu.…”

“…First, pressure injection artifacts are possible, but they are ruled out by the absence of effects of equivalent or larger volumes of saline or an antagonist. Second, depolarization block is a potential problem (Crawford and Curtis, 1964;Engberg et al, 1979a, b). This is unlikely since a given response could be reproduced 4-5 times in rapid succession with no noticeable decrease in the response.…”

The effect of microiontophoretically applied vasopressin and oxytocin on single neurones in the septum and dorsal hippocampus of the rat

“…However, the peptide-induced responses differed from the Glu-evoked responses in at least one aspect. Inc~eazing the G]u-expelling currcz~t frequently led to a decrease in the extracellu|a~'ly recorde0, spike amplitude and firing rate of neurones, presumably as a result of 'dei)olarization b!Gck ~ [4]. In a~l but two neurones, tNs decrease in amplitude was never observed during application of AVP or OXT even when the peptides were ejected with the maxima ~, current (260 hA) for at least 3 mi~_ (not shown)° When AVP and OXT were tested on the same neurotics, approximately one-third (n = 13) of the neuroues responded to both F,eptid~ with excitatP3m Twenty of the remaining neurones were excited by either AVP or OXT.…”

Quantitative studies on some antagonists of N‐methyl D‐aspartate in slices of rat cerebral cortex

“…For our present purposes we decided to use a preparation of cerebral cortex, since it has long been known that virtually all cortical neurones are excited by L-glutamate and other amino acids (Krnjevic & Phillis, 1963;Crawford & Curtis, 1964). We set out to prepare a slice of brain tissue containing cortical efferents which could be placed in a two-compartment bath so that the depolarization of individual neurones by L-glutamate could be recorded as a population response.…”