Abstract
Drug addiction has become a worldwide problem, affecting millions of people across the globe. While the majority of mechanistic studies on drug addiction have been focused on the central nervous system, including the mesolimbic dopamine system, the peripheral actions of drugs of abuse remain largely unknown. Our preliminary study found that the systemic injection of cocaine increased peripheral skin temperature. This led us to our present study, which investigated the mechanisms underlying the increase in peripheral temperature following cocaine injection. Male Sprague Dawley rats were anesthetized with pentobarbital sodium, and peripheral skin temperature measurements were taken using a thermocouple needle microprobe and an infrared thermal camera. Cocaine injection caused an acute rise in peripheral body temperature, but not core body temperature, about 10 min after injection, and the temperature increases were occluded by systemic injection of dopamine D2 receptor antagonist L741,626, but not D1 receptor antagonist SCH23390. In addition, systemic administration of bromocriptine, a dopamine D2 receptor agonist, significantly increased peripheral temperature. Infrared thermal imaging showed that the thermal increases following cocaine injection were predominantly in the distal areas of the forelimbs and hindlimbs, relative to core body temperature. Treatment with cocaine or bromocriptine decreased the size of skin blood vessels without affecting the expression of dopamine D2 receptors. These results suggest that increased peripheral temperature in skin following cocaine injection is associated with the activation of the dopamine D2 receptor.
Highlights
Cocaine addiction is a chronic, relapsing neuropsychiatric disorder characterized by compulsive risk-taking and reward-seeking behaviors
We investigated whether (1) acute administration of cocaine changes peripheral skin or core body temperature in rats, (2) the increased peripheral skin temperature following cocaine injection is prevented by pretreatment with certain dopamine receptor antagonists, (3) dopamine receptor agonists can elevate peripheral body temperature, and (4) cocaine or a dopamine D2 agonist affect the size of skin blood vessels, or the expression of dopamine D2 receptors
Peripheral body temperature over the wrist significantly and rapidly increased 10 min after cocaine injection at the higher dose of 20 mg/kg, but temperature changes were not observed at the lower dose of 10 mg/kg when compared to the values before cocaine injection or in the saline-injected group
Summary
Cocaine addiction is a chronic, relapsing neuropsychiatric disorder characterized by compulsive risk-taking and reward-seeking behaviors. Cocaine is rooted as a highly addictive psychostimulant with a wide range of effects It targets and blocks the dopamine transporter (DAT) in the mesolimbic reward system, causing a rapid increase in extracellular dopamine levels and the subsequent activation of dopamine receptors, the post-synaptic D1 receptors and the pre- and post-synaptic D2 receptors, which produces reinforcing effects that lead to cocaine abuse [3,4]. In addition to these reinforcing properties, cocaine produces systemic effects in humans, such as increased heart rate and blood pressure and respiratory depression [5,6]. It stimulates the sympathetic nervous system by inhibiting catecholamine reuptake at the sympathetic nerve terminals [8,9], and increases heart rate and blood pressure [10,11]
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