Participation of the GABAergic system on the glutamate release of synaptosomes from animals with Experimental autoimmune encephalomyelitis (EAE).
Recent reports have showed a deficit in expression of proteins associated with GABAergic neurotransmission in neocortex of patients with Multiple sclerosis (MS). It had been described that the activation of GABAA receptors led to an inhibition of glutamate release. Recently we found in synaptosomes from rat cerebral cortex that the glutamate release was decreased during the development of EAE, the animal model of MS. In order to evaluate the events that may affect neuronal function in EAE synaptosomes, we analyzed the participation of the GABAergic system on the glutamate release. For this, synaptosomes from control (CFA) and EAE rats were incubated in the presence of GABA followed by the addition of 4AP to trigger neurotransmitter release. The glutamate release was unaffected in GABA-incubated synaptosomes from EAE animals. However, in synaptosomes from CFA rats, this release was decreased. To confirm that this diminution was indeed mediated by GABAA receptors, we incubated synaptosomes with a GABAA antagonist, prior to the addition of GABA. The inhibition of glutamate release by GABA in CFA synaptosomes was abolished by the antagonist. Also GABAA R density was measured ex vivo in neocortex cerebral synaptosomes by 3[H]-flunitrazepam binding assay. The Bmax in synaptosomes from EAE rats was 591 fmol/mg proteins, whereas the Bmax in CFA synaptosomes was 1101 fmol/mg proteins. Ours results suggest that the diminution of the flunitrazepam sensitive GABAA R density could explain the observed failure of the GABAergic regulation on the glutamate release of synaptosomes from EAE rats.
Recent reports have showed a deficit in expression of proteins associated with GABAergic neurotransmission in neocortex of patients with Multiple sclerosis (MS). It had been described that the activation of GABAA receptors led to an inhibition of glutamate release. Recently we found in synaptosomes from rat cerebral cortex that the glutamate release was decreased during the development of EAE, the animal model of MS. In order to evaluate the events that may affect neuronal function in EAE synaptosomes, we analyzed the participation of the GABAergic system on the glutamate release. For this, synaptosomes from control (CFA) and EAE rats were incubated in the presence of GABA followed by the addition of 4AP to trigger neurotransmitter release. The glutamate release was unaffected in GABA-incubated synaptosomes from EAE animals. However, in synaptosomes from CFA rats, this release was decreased. To confirm that this diminution was indeed mediated by GABAA receptors, we incubated synaptosomes with a GABAA antagonist, prior to the addition of GABA. The inhibition of glutamate release by GABA in CFA synaptosomes was abolished by the antagonist. Also GABAA R density was measured ex vivo in neocortex cerebral synaptosomes by 3[H]-flunitrazepam binding assay. The Bmax in synaptosomes from EAE rats was 591 fmol/mg proteins, whereas the Bmax in CFA synaptosomes was 1101 fmol/mg proteins. Ours results suggest that the diminution of the flunitrazepam sensitive GABAA R density could explain the observed failure of the GABAergic regulation on the glutamate release of synaptosomes from EAE rats.
