Electrophysiological and morphological properties of neurons in the substantia gelatinosa of the mouse trigeminal subnucleus caudalis

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Abstract
The excitability of the second order neurons within the trigeminal subnucleus caudalis underlies pain perception and processing in migraine and trigeminal neuralgia. These neurons were studied with whole-cell patch-clamp technique in slices from mouse brain stem. Electrical and morphological characteristics of 56 neurons were determined. Four categories were distinguished from electrophysiological properties: tonic (39%), phasic (34%), delayed (16%) and single spiking (11%). These categories did not show distinct morphological properties. Neurons had tetrodotoxin-sensitive sodium currents that activated and inactivated within milliseconds. They also showed a high voltage-activated, slowly inactivating calcium current: up to half of this current was blocked by ω-conotoxin GVIA (1 μM) and ω-agatoxin IVA (100–300 nM), but it was not affected by nifedipine (10 μM). Exogenously applied capsaicin (1 μM) and αβmethylene-5′-adenosine triphosphate (100 μM) elicited large amplitude, spontaneous excitatory postsynaptic currents that were blocked by capsazepine (10 μM) and 5-[(3-phenoxybenzyl)-(1,2,3,4-tetrahydro-naphthalen-1-yl)-carbamoyl]-benzene-1,2,4-tricarboxylic acid (A-317491: 10 μM), respectively. Thus, neurons of the mouse trigeminal subnucleus caudalis substantia gelatinosa exhibit N-type and P/Q-type voltage-gated calcium channels, and receive presynaptic afferents that express TRPV1 and P2X2/3 receptors. These results suggest possible therapeutic interventions, and serve as a basis for the characterization of cellular changes that may underlie trigeminal neuropathic pain.