Effects of aging on morphine withdrawal in the rat.

Little is known about the effects of aging on the process of opiate dependence and withdrawal in the rat. The present study was undertaken to quantitate naloxone-precipitated opiate withdrawal in young (3-4 months old) and aged (24 month old) Long-Evan female rats. Following addiction to morphine, young and aged rats were evaluated for tail skin temperature (TST), rectal temperature (Tr), behavior, rhinorrhea, lacrimation, salivation, and diarrhea in response to naloxone administration. Young rats showed the expected TST increase and Tr decline in response to withdrawal. By contrast, aged rats showed two distinct TST response subgroups. The majority of aged rats showed an exaggerated TST response to naloxone, while some aged rats failed to exhibit any TST response to withdrawal. This latter subgroup showed significantly lower basal Tr than either the young rats or the aged-responders. The behavioral activating effects of opiate withdrawal were blunted in aged rats, and these old animals showed a marked decline in rhinorrhea, lacrimation, and salivation during withdrawal. The diarrheal response during withdrawal was not substantially different between the two groups. Collectively, these data indicate that aged female rats exhibit markedly different responses to opiate withdrawal than do their young counterparts.