Gabapentin fails to alter P/Q‐type Ca2+ channel‐mediated synaptic transmission in the hippocampus in vitro

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Abstract
Gabapentin (Neurontin) has been successfully used in the treatment of both epilepsy and neuropathic pain. Despite its widespread clinical use, its mechanism of action is very poorly understood. Indeed, the only protein it is known to interact with is the α2δ subunit of the voltage-gated Ca2+ channel complex. In a recent article, gabapentin was reported to inhibit synaptic transmission in the spinal cord through an inhibitory effect on presynaptic P/Q-type Ca2+ channels in both glutamatergic primary afferents and glycinergic interneuones. To examine if such inhibition of P/Q-channel-mediated synaptic transmission by gabapentin generalised to other synaptic pathways, we tested the actions of gabapentin of P/Q-type Ca2+ channel-mediated synaptic responses in the CA1 subfield of the hippocampus. We found that gabapentin was completely inactive on such synaptic responses even at 10 times the maximally effective concentration used in the spinal cord. A small (∼10%) but consistent depression of control synaptic responses was elicited by 10 μM gabapentin. No greater response was observed at a 10 times higher concentration. From these data we conclude that gabapentin is not a generic inhibitor of presynaptic P/Q-type channels and its actions at the spinal level must represent a feature of the P/Q-type channel not present in the hippocampus. Given the known interactions of this compound, the best candidate for this is the presence, subtype, or state of the α2δ subunit. Synapse 55:262–269, 2005.