Blunted metabolic response to SKF 82958 in the mesolimbic system following preweaning cocaine treatment

Sex differences in the effects of cocaine abuse across the life span

Cocaine alters brain function from the early days of development throughout the entire life of an individual. Since the first preclinical research on cocaine sensitization was published, sex differences in response to the drug in adult rats have been noted. With the appearance of reports on "crack babies" during the 1980s, sex differences in response to prenatal (developmental) exposure have been identified in both clinical and preclinical reports. Cocaine administered during early development in the rat produces wide-spread alterations in function which depend on the timing of drug administration as well as the sex of the animal. In males, the response patterns following postnatal days (PND) 11-20 cocaine administration (equivalent to the late prenatal period in humans) are quite similar to those seen following prenatal exposure (equivalent to the first half of pregnancy in humans). There is a general decrease in dopaminergic (DA) markers and reactivity perhaps due to the uncoupling of the D1 receptor from its second messenger system. While similar changes in D1 uncoupling are seen in females, behavioral and metabolic responses to drug challenges generally show increases in DA responsivity (except adolescents) perhaps due to the activational effects of estrogen and/or decreases in serotonin (5-HT) mediated regulation of DA function. We have found that a significant factor in the hyper-responsivity of the female is the role of the testing environment and the responses to stress which can obscure underlying neurochemical dysregulation. Whether parallel factors are operational in adult males and females is currently under investigation.

Standardization of a novel blood-sampling method through the jugular vein for use in the quantified [14C] 2-deoxyglucose method

In the traditional [14C] deoxyglucose (2DG) method for the measurement of local cerebral glucose utilization (LCGU), blood samples are collected from the femoral artery. However, the placement of a femoral catheter can affect locomotor activity of the animal. We wanted to develop a new technique for blood sampling that would not interfere with the ongoing behavior. Therefore, the present report establishes a method of collecting blood samples for the 2DG method through the jugular vein. To calibrate this method, catheters were inserted in both the femoral artery and jugular vein of adult male Sprague Dawley rats. The next day, rats were injected with 2DG (125 microCi/kg) through the jugular vein. To quantify 14C in plasma, the standard method of blood collection was used for the femoral artery while syringes were used to extract blood samples from the jugular vein. We calculated the integrated specific activity of the plasma and final tissue 2DG concentrations based on Sokoloff's original equation using blood samples derived from both vessels. LCGU determined in selected brain regions was equivalent using both sampling methods. In conclusion, sampling from the jugular vein is appropriate for the quantified 2DG method and does not disrupt locomotor activity of the rat.

Preweaning cocaine exposure alters brain glucose metabolic rates following repeated amphetamine administration in the adult rat

Developmental cocaine exposure produces long-term alterations in function of many neuronal circuits. This study examined glucose metabolic rates following repeated amphetamine administration in adult male and female rats pretreated with cocaine during postnatal days (PND) 11-20. PND11-20 cocaine increased the response to amphetamine in many components of the motor system and the dorsal caudate-putamen, in particular, and decreased the metabolic response in the hypothalamus. While amphetamine alone produced widespread increases in metabolism, there were no cocaine-related effects in the mesolimbic, limbic or sensory structures. These data suggest that a brief cocaine exposure during development can alter ontogeny and result in abnormal neuronal responses to repeated psychostimulant administration in adulthood.

Correlating brain metabolism with stereotypic and locomotor behavior

Many studies have shown that developmental cocaine exposure alters brain function and behavior, the present study examined the relationship between brain metabolism and behavioral responses to drug challenge. SKF 82958, a selective D1 dopamine agonist, was administered to preweaning cocaine-exposed (50 mg/kg/day) rats and controls at 60 days of age. Deoxyglucose was administered 30 min later, during the peak behavioral response, to measure brain functional activity. Pearsonproduct-moment correlations of behavior (locomotor activity and stereotypic behavior) with rates of glucose metabolism in components of the nigrostriatal and mesolimbic circuits were analyzed. The analysis revealed that under saline-challenge conditions in control animals, rates of metabolism in mesolimbic regions are positively correlated to rates of locomotor activity, whereas in cocaine-treated rats, these correlations were absent. Following SKF challenge, a different pattern was seen; locomotor activity or stereotypic behavior was not correlated with mesolimbic or nigrostriatal metabolism, respectively, in controls but was positively correlated in cocaine-treated rats. Therefore, cocaine exposure during development enhances the coupling of metabolism in components of the mesolimbic and nigrostriatal dopamine systems with the behavioral output associated with these systems under drug-challenge conditions. This may be due to loss of inhibitory influences within the mesolimbic and nigrostriatal systems. Thus, the correlation of behavior and cerebral glucose metabolism provides a unique way of examining the effect of developmental cocaine exposure.