T. Kamishita et al., METABOTROPIC GLUTAMATE RECEPTORS AND VISUAL CORTICAL SYNAPTIC PLASTICITY, Canadian journal of physiology and pharmacology, 73(9), 1995, pp. 1312-1322
Two forms of use-dependent synaptic plasticity, called long-term poten
tiation (LTP) and long-term depression (LTD), can be elicited in the v
isual cortex following different paradigms of electrophysiological sti
mulation. These neurobiological phenomena often are considered as nece
ssary components of models for the alteration in function of the nervo
us system that must occur at some level for the establishment and (or)
maintenance of memory engrams, for learning processes, or for the con
solidation of active neural connections and regression of inactive con
tacts in thr developing brain. It has been postulated that for LTP and
LTD to be produced in the hippocampus, activation of a particular sub
type of excitatory amino acid receptor, the metabotropic receptor, is
a critical requirement. Only recently has it become possible to test t
his hypothesis directly, as a new compound, (+/-)-alpha-methyl-4-carbo
xyphenylglycine (MCPG), has been introduced and the suggestion made th
at it selectively antagonizes the metabotropic receptor. This substanc
e has been tested in the present study on responses recorded from slic
es of rat visual cortex and has been found both to block the activatio
n of the metabotropic receptor and to interfere selectively with the f
orm of synaptic plasticity called LTD. It thus appears from the experi
ments reported in this paper as though the metabotropic receptor subty
pe that is blocked by MCPG is required for the expression of LTD but n
ot for the expression of LTP, in the visual cortex of adult rats.