RESUMEN
In nucleus tractus solitarii-dorsal vagal nucleus slices prepared from young adult rats (180-260 g) 10(-3) M L-glutamate and 10(-5) M baclofen caused a 2-3-fold increase of field stimulation-induced [3H]-norepinephrine release without affecting the resting release. In slices prepared from rats treated neonatally with monosodium glutamate neither L-glutamate nor baclofen had any effect on stimulation-induced norepinephrine release, tested between postnatal days 74-99 (350-530 g). In untreated littermates used in the same period (460-580 g) L-glutamate was fully effective whereas baclofen was ineffective. The tritium content in tissue extracts did not differ significantly in the three experimental groups. It is concluded that i) the loss of GABA(B) receptor-mediated disinhibitory stimulation of norepinephrine release is an age-related phenomenon and ii) neonatal monosodium glutamate treatment causes a damage in the local neural circuitry characterized by the loss of glutamate receptor-mediated mechanism that stimulates the release of norepinephrine.