p-Chloroamphetamine-Enhanced Neostriatal Dopamine Exocytosis in Rats Neonatally Co-lesioned with 6-OHDA and 5,7-DHT: Relevance to Parkinson's Disease

Effects of neonatal dopaminergic lesion on oral cocaine self-administration in rats: Higher female vulnerability to cocaine consumption

The dopaminergic system is associated with cocaine-seeking behaviors, being influenced by other neurotransmitters such as GABA and deregulated by chronic cocaine self-administration. Administration of 6-hydroxydopamine (6-OHDA) to neonatal rats produces a depletion of brain dopamine, mainly, that results in behavioral alterations in adulthood. This model can be applied to better understanding of the role of the dopaminergic system in cocaine use and how its behavioral effects can modulate drug intake. Though there are well-established sex differences in the pattern of drug use, there are no published studies investigating sex-dependent effects of neonatal lesions with 6-OHDA on cocaine self-administration nor regarding GABA_A receptor (GABA_AR) subunits expression. Herein, neurotoxic lesion was induced in male and female neonatal rats by intracisternal injection of 6-OHDA at PND 4, and locomotion was evaluated before and after cocaine self-administration. Cocaine was diluted in a sweet solution (sucrose 1.5%) and offered for 27 consecutive 3-h daily sessions via a dispenser for oral intake, in an operant chamber under a fixed-ratio 1 (FR1) schedule. The 6-OHDA lesion reduced oral cocaine self-administration in male and female rats. Female rats, independent of dopaminergic condition, consumed more cocaine-containing solution than sucrose-only solution. Furthermore, as expected, 6-OHDA-lesioned animals presented a higher basal locomotor activity when compared to sham rats. We evaluated GABA_AR subunit expression and found no statistically significant differences between rats that self-administered a sucrose-only solution and those that self-administered a cocaine-containing solution. Even when the reward system is depleted, some behavioral differences remain in females, providing more data that highlight the female vulnerability to cocaine consumption.

Desipramine, commonly used as a noradrenergic neuroprotectant in 6-OHDA-lesions, leads to local functional changes in the urinary bladder and gastrointestinal tract in healthy rats

The 6-hydroxydopamine (6-OHDA) rat model is one of the most common animal models of Parkinson's disease. When experimentally inducing dopaminergic neurodegeneration in the nigrostriatal pathway using 6-OHDA, the noradrenergic reuptake inhibitor desipramine is often systemically injected in order to protect against damages to the noradrenergic system in the brain. An increasing number of studies are focusing on understanding the pathophysiological changes underlying autonomic non-motor symptoms, in particular urinary bladder and gastrointestinal dysfunctions, of the disease. Several of these studies have investigated the contractile properties and the activation of smooth muscle in the 6-OHDA rat model. Since the injection of desipramine is commonly placed in close proximity to the urinary bladder and gastrointestinal tract, in the current study we wanted to understand if the drug alone has an effect. For this, we have injected a single dose (25 mg/kg) of desipramine either intraperitonially or subcutaneously and investigated smooth muscle contractility in vitro in the urinary bladder, proximal colon and distal ileum four weeks post injection. Our data show that desipramine significantly alters smooth muscle contractility of the urinary bladder and proximal colon in healthy rats. Conclusively, we suggest, based on our data, that desipramine should be omitted when using the 6-OHDA rat model to investigate smooth muscle function in Parkinson's disease research.