Interactive effects of testosterone and superior cervical ganglionectomy on attraction thresholds to volatile urinary odors in gonadectomized mice.

Volatile urinary odors contribute to mate recognition in mice after their detection by the main olfactory epithelium (MOE). We used a habituation/dishabitution task to ask whether the capacity of gonadectomized mice of both sexes to detect and investigate decreasing concentrations of volatile urinary odors from either breeding males or estrous females is modulated by administering androgen or estrogen and if so, whether any effects of these sex steroids are altered by disrupting the sympathetic innervation of the MOE via bilateral superior cervical ganglionectomy (SCGx). In tests given, beginning 51 days after gonadectomy without steroid treatment both male and female subjects detected even the lowest concentrations (1:120 and 1:160 dilutions by volume) of male urinary odors, provided they were SCGx as opposed to sham operated. In subsequent tests given after estradiol benzoate (EB) followed later by 5alpha-dihydrotestosterone (DHT) treatments, neither male nor female subjects detected low concentrations of male urinary odors regardless of whether or not their SCG's were intact. Administration of testosterone (T) prior to a final series of tests restored the ability of gonadectomized subjects of both sexes to detect low concentrations of male urinary odors regardless of their SCG status. This suggests that T, but not its neural metabolites estradiol, or DHT, facilitates responsiveness to low concentrations of male odors in mice of both sexes. In tests given 51 days after gonadectomy without steroid treatment most male and female subjects readily detected the three highest concentrations of estrous female urinary odors whereas SCGx males and females failed to detect the lowest concentrations of these odors. After treatment with EB and then with DHT, gonadectomized mice of both sexes generally failed to detect the three lowest concentrations of estrous female urinary odors regardless of their SCG status. After T treatment; however, subjects of both sexes again detected most dilutions of estrous female urine, provided their SCG's were intact. Again, these results suggest that T, but not estradiol or DHT, facilitates responsiveness to estrous female urinary odors. Provided such an activational effect of T is present, sympathetic, noradrenergic inputs to the MOE may enhance odorant contrast, as previously suggested [Nat. Neurosci. 2 (1999) 106], by reducing the responsiveness of olfactory neurons to low (1:120 and 1:160 dilutions) concentrations of some biologically significant odorants (e.g. male urinary odors) while facilitating their responsiveness to low to moderate (1:80 dilution) concentrations of others (e.g. estrous female urinary odors).

Glutamate and dopamine in nucleus accumbens core and shell: sequence learning versus performance.

This study sought to determine whether neurochemical changes associated with chronic postweaning lead (Pb) exposure, namely, enhanced dopamine (DA) activity and/or blockade of NMDA function in nucleus accumbens (NAC), underlie the learning impairments also associated with this Pb regimen, and whether core or shell subregions of nucleus accumbens would be more important to such effects. If so, then mimicking these neurochemical changes in normal (control) rats should reproduce these Pb-induced learning impairments. For this purpose, the effects of DA (20-80 microg), the non-competitive NMDA antagonist MK-801 (1.0-2.5 microg) or DA+MK-801 (40+1.0, 80+2.5 microg) were infused in core or shell of nucleus accumbens in normal rats and effects on a multiple schedule of repeated learning (RL) and performance (P) evaluated. In core, MK-801 mimicked the effects of Pb exposure, selectively reducing RL accuracy with no corresponding changes in P accuracy, an effect derived from an increased frequency of perseverative errors. DA produced non-specific changes, reducing accuracy levels in RL and P components. Accuracy and rate effects of DA could be reversed by concurrent administration of the higher MK-801 dose. In shell, MK-801, primarily the lower dose, reduced accuracy in both the RL and P components, while DA did not produce any systematic effects. Collectively, these results point to a greater importance of core as compared to shell in the mediation of learning of spatial sequences, and suggest that inhibition of glutamatergic NMDA function may play a critical role in the selective learning impairments associated with chronic low level Pb exposure.