Increased synaptosomal [3H] GABA uptake in the rat brainstem after facial carrageenan injections

The aim of the present study was to quantify synaptosomal [(3)H] gamma aminobutyric acid (GABA) uptake in the rat brainstem after facial carrageenan injections. Synaptosomal preparations from the brainstem of rats that had received one or four facial carrageenan injections showed greater GABA binding on the side of the brainstem ipsilateral to the carrageenan injection than on the contralateral side when compared to saline injected controls. In contrast, no difference in GABA binding between the injected and contralateral sides was observed in the same synaptosomal preparations that had been treated with GABA uptake inhibitors NNC-711, beta-alanine, or nipecotic acid. The difference between GABA binding in the absence of the GABA uptake inhibitor and GABA binding in a portion from the same synaptosomal preparation which had been incubated with the GABA uptake inhibitor was obtained to represent [(3)H] GABA binding to GABA transporters/transporter mediated [(3)H] GABA uptake. A significantly greater GABA uptake was observed on the side of the brainstem ipsilateral to the carrageenan injection(s) than on the contralateral side. A consequence of the observed increase in GABA uptake is that it could reduce the amount of GABA in the synaptic cleft. This could influence the transmission of nociceptive input from primary afferents to secondary neurons in the spinal trigeminal nucleus and could be a contributing factor in the development of hyperalgesia after carrageenan injections or other chronic inflammatory conditions.