Age-related changes in deterministic behaviors of nociceptive firing of rat dorsal horn neurons.

To demonstrate the age-related changes in the dynamics of the nociceptive discharge of dorsal horn nociceptive neurons, the nonlinear prediction method was used to quantify the degree of deterministic behavior within the interspike interval series of tissue injury-induced firing of spinal nociceptive neurons in anesthetized adult young (3-4 months) and aged (>22 months) rats. Subcutaneous bee venom injection induced long-term discharge of spinal wide dynamic range (WDR) neurons in both groups. However, the nociceptive discharge of single WDR neurons in the aged group showed higher determinism when compared with the adult young rats. This result suggests that the dynamics of single nociceptive neurons may not remain constant throughout the life span, and this age-associated change may be an underlying mechanism for various pain manifestations in the elderly population.