The antiepileptic agent gabapentin (Neurontin) possesses anxiolytic-like and antinociceptive actions that are reversed byd-serine

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Abstract
This report describes the activity of the antiepileptic agent gabapentin (Neurontin) in animal models predictive of anxiolysis and analgesia. Gabapentin displayed anxiolytic-like action in the rat conflict test, the mouse light/dark box and the rat elevated X-maze with respective minimum effective doses (MEDs) of 3, 10 and 30 mg/kg. Furthermore, gabapentin also induced behavioural changes suggestive of anxiolysis in the marmoset human threat test with a MED of 30 mg/kg. In the rat formalin test of tonic nociception, gabapentin dose-dependently (30–300 mg/kg) and selectively blocked the late phase with a MED of 100 mg/kg. However, it failed to block carrageenan-induced paw oedema. The intracerebroventricular (ICV) administration of the glycine/NMDA receptor agonistd-Serine, dose-dependently (10–100 μg/animal) reversed the antinociceptive action of gabapentin (200 mg/kg, SC).d-Serine (30 μg/animal, ICV) also reversed the anxiolytic-like effects (in the light/dark box and the rat elevated X-maze) of gabapentin (30 mg/kg). In contrast,l-Serine (100 μg, ICV) failed to block the antinociceptive action of gabapentin. The antinociceptive action of (+)-HA-966 (25 mg/kg, SC), a partial agonist at the glycine/NMDA receptor, was reversed byd-Serine (100 μg/animal, ICV). However,d-Serine (100 μg/animal, ICV) failed to affect the antinociceptive action of a competitive NMDA receptor antagonist CGS 19755 (3 mg/kg, SC). Gabapentin has negligible affinity for the strychnine insensitive [3H]glycine binding site. This indicates that the interaction between gabapentin andd-Serine may not involve the NMDA receptor complex. Gabapentin may represent a novel type of anxiolytic and analgesic agent.