Castration differentially alters [3H]nisoxetine binding to norepinephrine uptake sites in olfactory bulb and frontal cortex of male rats

Abstract

In the present study, [3H]nisoxetine binding to norepinephrine (NE) uptake sites and [3H]norepinephrine uptake were investigated within olfactory bulb (OB) and frontal cortex homogenates from intact and castrated male rats. Statistically significant reductions in the number of [3H]nisoxetine binding sites (Bmax) were found in OB from the castrates, while significantly increased Bmax values were obtained in the frontal cortex. Castration also significantly altered the affinity (Kd) of [3H]nisoxetine binding in the frontal cortex, but not in the OB. Assessment of [3H]norepinephrine uptake showed that in neither brain regions were there any statistically significant differences in Km nor Vmax between the castrated and intact male rats, indicating that the basal uptake process is not changed following castration in either of these brain areas. These results demonstrate the differential effects of castration upon [3H]nisoxetine binding sites between the OB and frontal cortex. Such findings provide new evidence for one of the mechanisms by which androgens may modulate central noradrenergic activity.

In vitro binding assays using 3H nisoxetine and 3H WIN 35,428 reveal selective effects of gonadectomy and hormone replacement in adult male rats on norepinephrine but not dopamine transporter sites in the cerebral cortex

“…5, 6 A,C). These values are comparable to those previously reported for rat brain homogenates (Tejani-Butt, 1992, Vathy et al, 1997, Shang et al, 1999). Across all of the 4 and 28-day treated groups, values of ligand binding affinity for the caudate nucleus were similar to corresponding controls.…”

“…Nonetheless, as expected maximal numbers of binding sites in the controls were higher in prefrontal cortex (~135–300 fm/mg protein) than in sensorimotor cortex (~150–250 fmol/mg protein) or caudate nucleus (~100–135 fmol/mg protein, Figs. 5, 6B, D) and showed values that on average were comparable to those previously reported for rat brain homogenates (Tejani-Butt, 1992, Vathy et al, 1997, Shang et al, 1999). Visual inspection of the data further showed that for the control and experimental groups alike variance in the data was typically accounted for by single outliers in the data, that for the most part the tissue-specific values that were obtained across these groups were largely overlapping and that there were no obvious group trends in these data (Figs.…”

“…In terms of contributing to the effects of gonadectomy on cortical DA level, the NET may also be the more likely candidate than the DAT, as previous studies have also shown that this site may be hormone-sensitive. For example, maximal numbers of frontal cortical 3 H-nisoexteine binding sites have been shown to be significantly lower in male than in female rats (Vathy et al, 1997), and Kd and Bmax values for 3 H-nisoexteine binding have been shown to be significantly higher in the cortex of adult male rats that have been gonadectomized for two weeks compared to intact controls (Shang et al, 1999). Although in this study no obvious effects on maximal numbers of NET binding sites were found, consistent results were obtained regarding the ability of gonadectomy to significantly raise cortical Kd values for 3 H nisotexine that confirmed and extended previous findings in several ways.…”

Functional expression of the norepinephrine transporter in cultured rat astrocytes

“…The K m of Na + -dependent [ 3 H]NE uptake in astrocytes was only two-fold lower than that in COS-7 cells expressing the rat NET (Paczkowski et al 1999), suggesting the existence of a high-affinity NE uptake system in rat astrocytes. The V max of Na + -dependent [ 3 H]NE uptake in rat cortical astrocytes was 1.41 pmol/mg protein/min, a value very similar to that previously reported for rat cortical synaptosomes (1.63 pmol/mg protein/min reported by Shang et al 1999). Furthermore, the NE transport system in astrocytes appears to be sensitive to both Na + , and ouabain (Na + -K + ATPase inhibitor).…”

“…1999), suggesting the existence of a high‐affinity NE uptake system in rat astrocytes. The V max of Na + ‐dependent [ 3 H]NE uptake in rat cortical astrocytes was 1.41 pmol/mg protein/min, a value very similar to that previously reported for rat cortical synaptosomes (1.63 pmol/mg protein/min reported by Shang et al . 1999).…”