Castration increases nisoxetine-evoked norepinephrine levels in vivo within the olfactory bulb of male rats.

In the present experiment we compared differences in extracellular norepinephrine levels in vivo within the olfactory bulb of intact and castrated male rats following infusion of the norepinephrine transport inhibitors, nisoxetine and tomoxetine. With this approach it was possible to assess whether dynamic changes in in vivo norepinephrine transporter function occur as a function of the gonadal state of the animal. Norepinephrine levels following infusion of nisoxetine were significantly increased in castrated compared with intact male rats. While a similar trend was present in response to tomoxetine infusion, these differences failed to achieve a statistically significant difference. These results demonstrate that castration of male rats alters norepinephrine transporter function within the olfactory bulbs. The increased extracellular levels of norepinephrine in response to agents which inhibit transporter function suggest that castration reduces transporter activity. Such effects have important implications not only with regard to processes involving the norepinephrine system in the olfactory bulb but also to the generalized sites and mechanisms by which gonadal steroid hormones modulate central nervous system functions.