Clorgyline-induced modification of behavioral sensitization to quinpirole: effects on local cerebral glucose utilization

A dose-response study of separate and combined effects of the serotonin agonist 8-OH-DPAT and the dopamine agonist quinpirole on locomotor sensitization, cross-sensitization, and conditioned activity

Chronic treatment with the dopamine D2/D3 agonist, quinpirole, or the serotonin 1A agonist, 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT), induces behavioral sensitization. It is not known whether both drugs produce sensitization through a shared mechanism. Here, we examine whether quinpirole and 8-OH-DPAT show cross-sensitization and impact sensitization, as would be expected from shared mechanisms. Male rats (N=208) were assigned randomly to 16 groups formed by crossing four doses of quinpirole (0, 0.03125, 0.0625, or 0.125 mg/kg) with four doses of 8-OH-DPAT (0, 0.03125, 0.625, or 0.125 mg/kg). After a course of 10 drug treatments administered twice per week in locomotor activity chambers, all groups were challenged on separate tests with quinpirole (0.1 mg/kg), 8-OH-DPAT (0.1 mg/kg), or saline, and locomotor activity was evaluated. Challenge tests with quinpirole and 8-OHDPAT showed no cross-sensitization between the drugs. Chronic quinpirole (0.125 mg/kg) administration induced a sensitized quinpirole response that was attenuated dose-dependently by chronic 8-OH-DPAT cotreatment. Cotreatment with quinpirole (0.0625 mg/kg) and 8-OH-DPAT (all doses) induced quinpirole sensitization. Chronic 8-OH-DPAT (0.125 mg/kg) induced a sensitized 8-OHDPAT response that was prevented by chronic cotreatment with the lowest but not the highest dose of quinpirole. Cotreatment with 8-OHDPAT (0.0625) and quinpirole (0.125 mg/kg) induced sensitization to 8-OH-DPAT. The saline challenge test showed elevated locomotor activity in chronic quinpirole (0.125 mg/kg) and 8-OHDPAT (0.0625, 0.125 mg/kg) alone groups, and in seven of nine cotreated groups. The absence of cross-sensitization suggests separate mechanisms of sensitization to quinpirole and 8-OH-DPAT. Cotreatment effects suggest that induction of sensitization can be modulated by serotonin 1A and D2/D3 activity.

High-frequency stimulation of the nucleus accumbens core and shell reduces quinpirole-induced compulsive checking in rats

Electrical deep brain stimulation (DBS) is currently studied in the treatment of therapy-refractory obsessive compulsive disorders (OCDs). The variety of targeted brain areas and the inconsistency in demonstrating anti-compulsive effects, however, highlight the need for better mapping of brain regions in which stimulation may produce beneficial effects in OCD. Such a goal may be advanced by the assessment of DBS in appropriate animal models of OCD. Currently available data on DBS of the nucleus accumbens (NAc) on OCD-like behavior in rat models of OCD are contradictory and partly in contrast to clinical data and theoretical hypotheses about how the NAc might be pathophysiologically involved in the manifestation of OCD. Consequently, the present study investigates the effects of DBS of the NAc core and shell in a quinpirole rat model of OCD. The study demonstrates that electrical modulation of NAc core and shell activity via DBS reduces quinpirole-induced compulsive checking behavior in rats. We therefore conclude that both, the NAc core and shell constitute potential target structures in the treatment of OCD.

Altered nicotinamide adenine dinucleotide (NADH) fluorescence in dt sz mutant hamsters reflects differences in striatal metabolism between severe and mild dystonia

The dt(sz) mutant hamster represents a unique rodent model of idiopathic paroxysmal dystonia. Previous data, collected post-mortem or in anesthetized hamsters under basal conditions, indicated the critical involvement of enhanced striatal neuronal activity. To assess the importance of an enhanced striatal neuronal activity directly during a dystonic episode, continuous monitoring of changes in brain metabolism and therefore neuronal activity indirectly in awake, freely moving animals is necessary. Determination of CNS metabolism by NADH measurement by laser-induced fluorescence spectroscopy in conscious dt(sz) and nondystonic control hamsters revealed reversible decreased NADH fluorescence during dystonic episodes. The degree of change corresponded to the severity of dystonia. This study represents the first application of this innovative method in freely moving animals exhibiting a movement disorder. Our data clearly confirm that the expression of paroxysmal dystonia in dt(sz) mutant hamsters is associated with enhanced striatal neuronal activity and further underscore the versatile application of NADH fluorescence measurements in neuroscience.

Altered dopamine D2-like receptor binding in rats with behavioral sensitization to quinpirole: effects of pre-treatment with Ro 41-1049

Repeated treatment with the dopamine D2/D3 receptor agonist quinpirole produces a sensitized behavioral response in rats manifested as an increase in locomotor activity. Pre-treatment with certain monoamine oxidase inhibitors, such as Ro 41-1049 [N-(2-aminomethyl)-5-(3-fluorophenyl)-4-thiazolecarboxamide HCl], changes the sensitized response from locomotion to stationary, self-directed mouthing. In this study, the effects of quinpirole sensitization, with and without pre-treatment with Ro 41-1049, were determined on dopamine D2-like receptors in the nucleus accumbens and the striatum. Long-Evans rats were pre-treated with Ro 41-1049 (1 mg/kg) 90 min prior to administration of quinpirole (0.5 mg/kg, 8 injections, every 3-4 days). Dopamine D2-like receptor binding was determined 3 days after the last injection by ex vivo radioligand assays using [3H]spiperone and [3H]quinpirole. Densities of [3H]spiperone- and [3H]quinpirole-labeled sites were both increased 32% in the nucleus accumbens of rats with demonstrated locomotor sensitization to quinpirole. In contrast, the density of dopamine D2-like receptors in quinpirole-sensitized rats pre-treated with Ro 41-1049 was not different from saline controls. These findings support the involvement of alterations in dopamine D2-like receptors in the development of locomotor sensitization to quinpirole and suggest that modification of these alterations in dopamine D2-like receptors contributes to the change from sensitized locomotion to mouthing observed when rats are pre-treated with Ro 41-1049.

Inhibition of monoamine oxidase A promotes secretory differentiation in basal prostatic epithelial cells

Monoamine oxidase A (MAO-A) expression is associated with high-grade prostate cancer. Immunohistochemistry showed that MAO-A is also expressed in the basal epithelial cells of normal prostate glands. Using cultured primary prostatic epithelial cells as a model, we showed that MAO-A prevents basal epithelial cells from differentiating into secretory cells. Under differentiation-promoting conditions, clorgyline, an irreversible MAO-A inhibitor, induced secretory cell-like morphology and repressed expression of cytokeratin 14, a basal cell marker. More importantly, clorgyline induced mRNA and protein expression of androgen receptor (AR), a hallmark of secretory epithelial cells. In clorgyline-treated cells, androgen induced luciferase activity controlled by the promoter of prostate-specific antigen, an AR target gene, in a dose-dependent manner. This activity was blocked by the AR antagonist Casodex, showing that AR is functional. In turn, androgen decreased MAO-A expression in clorgyline-treated, secretory-like cells. Our results demonstrated that cultured basal epithelial cells have the potential to differentiate into secretory cells, and that inhibition of MAO-A is a key factor in promoting this process. Increased expression of MAO-A in high-grade prostate cancer may be an important contributor to its de-differentiated phenotype, raising the possibility that MAO-A inhibition may restore differentiation and reverse the aggressive behavior of high-grade cancer.

High frequency stimulation and temporary inactivation of the subthalamic nucleus reduce quinpirole-induced compulsive checking behavior in rats

Obsessive-compulsive disorder (OCD) represents a highly prevalent and impairing psychiatric disorder. Functional and structural imaging studies implicate the involvement of basal ganglia-thalamo-cortical circuits in the pathophysiology of this disorder. In patients remaining resistant to pharmaco- and behavioral therapy, modulation of these circuits may consequently reverse clinical symptoms. High frequency stimulation (HFS) of the subthalamic nucleus (STN), an important station of the basal ganglia-thalamo-cortical circuits, has been reported to reduce obsessive-compulsive symptoms in a few Parkinson's disease patients with comorbid OCD. The present study tested the effects of bilateral HFS of the STN and of bilateral pharmacological inactivation of the STN (via intracranial administration of the GABA agonist muscimol) on checking behavior in the quinpirole rat model of OCD. We demonstrate that both HFS and pharmacological inactivation of the STN reduce quinpirole-induced compulsive checking behavior. We conclude that functional inhibition of the STN can alleviate compulsive checking, and suggest the STN as a potential target structure for HFS in the treatment of OCD.

Basal local cerebral glucose utilization is not altered after behavioral sensitization to quinpirole

Sensitization to psychostimulants results in a behavioral response of a greater magnitude than that produced by a given single dose. Previously, we have shown that sensitization to the D(2)/D(3) dopamine receptor agonist quinpirole produces alterations in quinpirole-stimulated local cerebral glucose utilization (LCGU) in ventral striatal and limbic cortical regions. To determine whether basal neuronal activity is altered in the sensitized animal, this study examined the effects of a sensitizing course of quinpirole on basal neuronal activity using the [(14)C]-2-deoxyglucose (2-DG) method in rats with verified sensitization. Adult, male Long-Evans rats (n = 7 or 10/group) were subjected to 10 injections of quinpirole (0.5 mg/kg, s.c.) or saline administered every 3rd day. Sensitization was verified on the basis of locomotor activity. The 2-DG procedure was performed in freely moving rats 3 days after the last quinpirole injection. LCGU was determined by quantitative autoradiography. No alterations in basal LCGU were detected in quinpirole-sensitized rats compared to those treated with saline. The present finding suggests that either the basal activity of very discrete populations of neurons is affected by sensitization to quinpirole that are not likely to be detected by the 2-DG method, or that the neurobiological changes that result in the sensitized behavioral response affect only stimulated, but not basal, neuronal activity.