Nisoxetine Binding Research Articles

Effect of repeated novel stressors on depressive behavior and brain norepinephrine receptor system in Sprague-Dawley and Wistar Kyoto (WKY) rats

This study compared the effects of repeated novel stressors on ‘depressive behaviors’, defined by the forced-swim and open-field tests, in Sprague-Dawley (S-D) and Wistar Kyoto (WKY) rats. Since stress appears to alter brain norepinephrine (NE) activity, this study also investigated the effects of the stressors on β-adrenoceptors (β-ARs), α 2-adrenoceptors ( α 2-ARs ) and NE transporter (NET) sites in S-D and WKY rats. Stress did not alter 125I-iodopindolol ( 125I-PIN) binding to β-ARs, nor [ 3H]idazoxan ([ 3H]IDAZ) binding to α 2-ARs in S-D rats, compared to non-stressed controls. However, WKY-stressed rats showed a significant reduction in 125I-IPIN binding to β-ARs in the cortex, hippocampus, amygdala and hypothalamus, and a reduction in [ 3H]IDAZ binding to α 2-ARs in the amygdala. [ 3H]nisoxetine ([ 3H]NIS) binding to NET sites in WKY-stressed rats was also reduced in the cortex, hippocampus and amygdala. When both strains were compared, the most surprising finding was a significantly higher density of NET sites in the hippocampus and amygdala in WKY rats compared to S-D rats. The results of this study indicate that stress, not only exacerbates depressive behavior in WKY rats, but also selectively alters β-ARs, α 2-ARs and NET sites in limbic brain regions. Thus, the WKY strain may serve as a useful animal model for depressive behavior and for the investigation of novel antidepressant drugs.

RTI-4793-14, a new ligand with high affinity and selectivity for the (+)-MK801-insensitive [3H]1-]1-(2-thienyl)cyclohexyl]piperidine binding site (PCP site 2) of guinea pig brain.

[3H]TCP, an analog of the dissociative anesthetic phencyclidine (PCP), binds with high affinity to two sites in guinea pig brain membranes, one that is MK-801 sensitive and one that is not. The MK-801-sensitive site (PCP site 1) is associated with NMDA receptors, whereas the MK-801-insensitive site (PCP site 2) may be associated with biogenic amine transporters (BAT). Although several "BAT ligands" are known that bind selectively to PCP site 2 and not to PCP site 1 (such as indatraline), these compounds have low affinity for site 2 (Ki values > 1 microM). Here we demonstrate that the novel pyrrole RTI-4793-14 is a selective, high affinity ligand for PCP site 2. We determined the IC50 values of RTI-4793-14 and several reference compounds [PCP, (+)-MK801 and indatraline] for PCP site 1 (assayed with [3H](+)-MK801), PCP site 2 (assayed with [3H]TCP in the presence of 500 nM (+)-MK801) and a variety of BAT-related measures ([3H]CFT binding to the DA transporter, [3H]nisoxetine binding to the norepinephrine transporter, [3H]dopamine uptake, [3H]serotonin uptake). In addition, we determined the ability of RTI-4793-14 to block NMDA responses in cultured hippocampal neurons under voltage clamp. (+)-MK801 had high affinity for PCP site 1 (4.6 nM) and potently inhibited NMDA-induced responses, but was much less potent in the BAT-related measures (IC50 s > 10 microM). PCP had high affinity at PCP site 1 (IC50 = 92 nM) and PCP site 2 (IC50 = 117 nM), and was moderately potent in all BAT-related measures except [3H]nisoxetine binding.(ABSTRACT TRUNCATED AT 250 WORDS)

Norepinephrine transporter sites are decreased in the locus coeruleus in Alzheimer's disease

The present study determined whether [ 3H]nisoxetine binding to norepinephrine transporter sites would be altered uniformly througout the locus coeruleus in Alzheimer's disease. A significant decrease ( P < 0.01) in [ 3H]nisoxetine binding was seen in the mid and caudal regions but not in the rostral region of the locus coeruleus. The loss of [ 3H]nisoxetine binding to norepinephrine transporter sites may be attributed to a loss of norepinephrine transporter sites located on terminals of noradrenergic neurons in the locus coeruleus in Alzheimer's disease.

Effect of age on [ 3H]nisoxetine binding to uptake sites for norepinephrine in the locus coeruleus of humans

[3H]Nisoxetine ([3H]NIS) was used to measure uptake sites for norepinephrine (NE) in the locus coeruleus (LC) of humans. Regression analysis demonstrated an inverse correlation between age and the binding of [3H]NIS to NE uptake sites in the LC (r = -0.6; P less than 0.01). Since considerable cell loss has been reported to occur with age in the human LC, the decreased binding of [3H]NIS probably reflects loss of LC cells rather than a down-regulation of these sites.

3H]Nisoxetine: a new radioligand for norepinephrine uptake sites in brain

[ 3H]Nisoxetine binds with high affinity (K d = 0.7 nM) and selectivity to a homogenous population of sites associated with the uptake of norepinephrine. Specific [ 3H]nisoxetine binding to rat cortical homogenates was saturable, sodium-dependent and averaged 90% of total binding at its K d concentration. Pretreatment with the neurotoxin DSP-4 resulted in 95% decrease in binding. [ 3H]Nisoxetine exhibits superior properties to radioligands previously used and appears to be the radioligand of choice for studies involving uptake sites for norepinephrine.

Highly selective vagotomy.

Dysregulation of dopamine neurotransmission has been linked to the development of human immunodeficiency virus (HIV)-associated neurocognitive disorder (HAND). To investigate the mechanisms underlying this phenomenon, this study used an inducible HIV-1 transactivator of transcription (Tat) transgenic (iTat-tg) mouse model, which demonstrates brain-specific Tat expression induced by administration of doxycycline. We found that induction of Tat expression in the iTat-tg mice for either 7 or 14 days resulted in a decrease (∼30%) in the <i>V</i>_max of [³H]dopamine uptake via both the dopamine transporter (DAT) and norepinephrine transporter (NET) in the prefrontal cortex (PFC), which was comparable to the magnitude (∼35%) of the decrease in <i>B</i>_max for [³H]WIN 35,428 and [³H]nisoxetine binding to DAT and NET, respectively. The decreased <i>V</i>_max was not accompanied by a reduction of total or plasma membrane expression of DAT and NET. Consistent with the decreased <i>V</i>_max for DAT and NET in the PFC, the current study also found an increase in the tissue content of DA and dihydroxyphenylacetic acid in the PFC of iTat-tg mice after 7 days’ administration of doxycycline. Electrophysiological recordings in layer V pyramidal neurons of the prelimbic cortex from iTat-tg mice found a significant reduction in action potential firing, which was not sensitive to selective inhibitors for DAT and NET, respectively. These findings provide a molecular basis for using the iTat-tg mouse model in the studies of NeuroHIV. Determining the mechanistic basis underlying the interaction between Tat and DAT/NET may reveal novel therapeutic possibilities for preventing the increase in comorbid conditions as well as HAND. <h3>SIGNIFICANCE STATEMENT</h3> Human immunodeficiency virus (HIV)-1 infection disrupts dopaminergic neurotransmission, leading to HIV-associated neurocognitive disorders (HANDs). Based on our in vitro and in vivo studies, dopamine uptake via both dopamine and norepinephrine transporters is decreased in the prefrontal cortex of HIV-1 Tat transgenic mice, which is consistent with the increased dopamine and dihydroxyphenylacetic acid contents in this brain region. Thus, these plasma membrane transporters are an important potential target for therapeutic intervention for patients with HAND.