Mechanoreceptive and nociceptive responses in the central nervous system of goldfish (Carassius auratus) and trout (Oncorhynchus mykiss).

UNLABELLED: Nociceptive responses to a repetitive pin-prod stimulus in goldfish and trout were assessed. Single unit recordings were taken from the spinal cord, cerebellum, tectum, and telencephalon. Neuronal responses were elicited in all these regions of the central nervous system in both species of fish during brush (mechanoceptive) and pin-prod (nociceptive) stimuli. In addition, in trout, a heated prod stimulus was used. Mechanoreceptive and nociceptive neuronal responses to various stimuli were elicited in all regions, and responses were detected as far as the telencephalon in both species. In goldfish, a noxious stimulus produced greater neuronal activity than a mechanoreceptive stimulus. This was not found in trout. The accurate setting of timed prods allowed the latency of the response to be calculated in all regions. From these data, conduction velocities suggested that A delta and C fibers were activated; both fiber groups previously have been shown to be involved in nociception in fish. This study has shown that there is neuronal activity in all brain areas including the telencephalon, suggesting a nociceptive pathway from the periphery to the higher central nervous system of fish. PERSPECTIVE: This study presents novel data on telencephalic activity in fish after noxious stimulation and demonstrates the potential for pain perception in lower vertebrates. Not only is this of an evolutionary significance, but it also adds to the controversial argument about whether fish perceive pain.