Reduction by gabapentin of K+-evoked release of [3H]-glutamate from the caudal trigeminal nucleus of the streptozotocin-treated rat

Recently, we showed that gabapentin can inhibit a facilitatory effect of substance P (SP) on K+-evoked glutamate release in rat trigeminal slices (Maneuf et al., 2001), and we have now examined the effect of gabapentin on glutamate release in the trigeminal slice from the streptozotocin (STZ)-treated rat. 1 At 4 weeks following STZ treatment (50 mg kg(-1) i.p.), blood glucose was increased in the majority of cases, compared to the control level. All the treated animals showed a significant degree (P<0.001) of tactile allodynia (assessed using von Frey filaments) that did not appear to correlate with blood glucose levels. 2 In this study, we demonstrated that, after STZ treatment, 30 μM gabapentin reduced K+-evoked release of [H-3]-glutamate in either normal (11 mm) or high (30 mM) glucose conditions by 24 and 22%, respectively. In the normal rat, gabapentin (up to 100 μM) is ordinarily unable to affect release of glutamate from the trigeminal slice. 3 The uptake of glutamate in Sp5C punches from streptozotocin-treated rats was reduced under normal glucose conditions (41.7% of control), whereas high glucose restored uptake to normal (84.7% of control). 4 The addition of 1 μM substance P potentiated the evoked release of glutamate in both normal (40% increase) and high glucose (28%), and this was blocked by gabapentin (30 μM) in both conditions. It is interesting to speculate that this ability of gabapentin to reduce the release of glutamate in the trigeminal nucleus after streptozotocin treatment may be of relevance to the antihyperalgesic-allodynic actions of the drug.