Background: The trigeminal subnucleus caudalis (Vc) plays a critical role in transmission and modulation of nociceptive afferent inputs, and exhibits a similar layer construction to the spinal dorsal horn. However, afferent inputs enter the brainstem and project to a separately located nucleus. It has previously been difficult to record responses of the Vc to afferent fiber activation in a brainstem slice preparation. The aim of the present study was to establish a novel brainstem slice preparation method to study trigeminal nociceptive transmission mechanisms.
New method: Thirty adult 6-7-week-old C57/BL6J male mice were included in the study. Obliquely sliced brainstem sections at a thickness of 600 mu m, which included the Vc and the root entry zone to the brainstem, were prepared. The Vc response to electrical stimulation of afferent fibers was observed as a change in intracellular calcium concentration by fluorescence intensity response.
Results: Electrical stimulation of afferent inputs to the trigeminal nerve increased fluorescent intensity in the Vc, which was completely diminished by tetrodotoxin and significantly suppressed by the AMPA/kainate antagonist CNQX (paired t-test, P<0.001), although the non-competitive NMDA antagonist (+)-MK801 maleate resulted in no changes. These results suggested a glutamate receptor-mediated response.
Comparison with existing methods/conclusion: This brainstem slice preparation will be useful for investigating nociceptive transmission mechanisms of the trigeminal nerve. (C) 2017 The Authors. Published by Elsevier B.V.