Subclinical neurological and neurovascular deficits in cocaine dependence. Gender and psychosocial considerations

Chronic cocaine exposure alters carbon dioxide reactivity but does not affect cerebral blood flow autoregulation in anesthetized dogs

BACKGROUND

Cocaine use is common in trauma victims. Consequently, understanding how cocaine alters normal physiology is important to providing appropriate medical care for these patients. This study was designed to identify how chronic cocaine exposure alters cerebrovascular physiology.

METHODS

Ten dogs (seven experimental, three control) were studied. Transcranial Doppler was used to measure CO2 reactivity and autoregulation of cerebral blood flow velocity (CBFvel). Measurements were made in anesthetized animals (0.6% or 1.8% isoflurane in oxygen and intravenous fentanyl) at baseline before cocaine exposure and then at weekly intervals for 4 weeks. During the 4-week study period, cocaine was administered intravenously four times per day.

RESULTS

Cocaine did not alter autoregulation of CBFvel in response to changes in mean arterial pressure. However, cocaine markedly impaired CO2 reactivity in three of the seven animals. In this subset of animals, increasing Paco2 decreased CBFvel, which is consistent with vasoconstriction rather than vasodilation.

CONCLUSION

Chronic cocaine exposure does not alter autoregulation of CBFvel but does alter CO2 reactivity in a subset of susceptible animals. If confirmed in humans, these findings have implications for traumatic brain injury patients who are chronic cocaine users. Specifically, the findings suggest that hyperventilation could exacerbate intracranial hypertension in a subset of these patients.

GBR12909 attenuates amphetamine-induced striatal dopamine release as measured by [(11)C]raclopride continuous infusion PET scans

Major neurochemical effects of methamphetamine include release of dopamine (DA), serotonin (5-HT), and norepinephrine (NE) via a carrier-mediated exchange mechanism. Preclinical research supports the hypothesis that elevations of mesolimbic DA mediate the addictive and reinforcing effects of methamphetamine and amphetamine. This hypothesis has not been adequately tested in humans. Previous in vivo rodent microdialysis demonstrated that the high affinity DA uptake inhibitor, GBR12909, attenuates cocaine- and amphetamine-induced increases in mesolimbic DA. The present study determined the ability of GBR12909 to attenuate amphetamine-induced increases in striatal DA as measured by [(11)C]raclopride continuous infusion positron emission tomography (PET) scans in two Papio anubis baboons. [(11)C]Raclopride was given in a continuous infusion paradigm resulting in a flat volume of distribution vs. time for up to 45 min postinjection. At that time, a 1.5 mg/kg amphetamine i.v. bolus was administered which caused a significant (30.3%) reduction in the volume of distribution (V(3)"). The percent reduction in the volume of distribution and, hence, a measure of the intrasynaptic DA release ranged between 22-41%. GBR12909 (1 mg/kg, slow i.v. infusion) was administered 90 min before the administration of the radiotracer. The comparison of the volume of distribution before and after administration of GBR12909 showed that GBR12909 inhibited amphetamine-induced DA release by 74%. These experiments suggest that GBR12909 is an important prototypical medication to test the hypothesis that stimulant-induced euphoria is mediated by DA and, if the DA hypothesis is correct, a potential treatment agent for cocaine and methamphetamine abuse. Furthermore, this quantitative approach demonstrates a way of testing various treatment medications, including other forms of GBR12909 such as a decanoate derivative.