Ecgonine methyl ester, a major cocaine metabolite, causes cerebral vasodilation in neonatal sheep

Effects of ecgonine methyl ester on cognition in scopolamine-impaired and aged rats

RATIONALE

Searches for antidotes to cocaine, and for cognition enhancers potentially applicable to Alzheimer's disease, have revealed a novel regulatory site on nicotinic acetylcholine receptors. In the presence of an agonist, inhibitors binding to this site changed the ion channel equilibrium from the open-channel form towards the closed form. Other, related, molecules could bind to the site without changing the equilibrium. These latter compounds were predicted to displace the inhibitors without affecting receptor function per se. These compounds alleviated the inhibition. One of them is ecgonine methyl ester (EME), which is generally described as inactive, but this work suggested a beneficial effect on cognition.

OBJECTIVE

This in vivo study tested for cognitive enhancement by EME in scopolamine-impaired, and aged, rats.

METHODS

Memory was the primary endpoint, but thigmotaxis became an important secondary endpoint in the light of observations made during the study. Impaired cognition was pharmacologically induced by scopolamine in young rats, and spontaneously present in aged rats. Learning ability before and after administration of EME was tested in Morris water maze protocols. Concentrations of EME in the brain and plasma were analyzed by gas chromatography-mass spectrometry.

RESULTS

A single dose of EME reversed scopolamine impairment, indicating involvement of acetylcholine receptors. Longer-term treatment improved cognition in aged rats, with enhanced rates of learning in the absence of an exogenous cognition-impairing compound. Impairment returned with a new challenge; the improvement could be re-established with continued dosing. EME also reversed thigmotaxis seen in aged rats; thigmotaxis is believed to indicate anxiety. The concentrations of EME in the brain proved adequate drug exposure.

CONCLUSIONS

Since other investigators have shown cognition impairment caused by cocaine in aged rats, this work shows that cocaine and EME have opposite effects in Morris water maze models. EME might induce cognitive enhancement and relief of anxiety in cocaine-impaired humans, and in other cognitive disorders.

Chronic prenatal exposure to cocaine alters cerebrovascular responses in newborn pigs

Maternal cocaine abuse may increase the incidence of perinatal asphyxia. In nonexposed asphyxiated neonates, decreased cerebrospinal fluid (CSF) cAMP concentrations are associated with poor neurological outcome. On the other hand, cocaine increases central nervous system (CNS) cAMP. Therefore, we hypothesized that in utero cocaine exposure may increase brain cAMP and thereby preserve cerebrovascular responses to cAMP-dependent stimuli following asphyxia. Pregnant pigs received either cocaine (1 mg/kg, i.v.) twice weekly during the last trimester or normal saline vehicle (sham-control) and were allowed to deliver vaginally at term. Cranial windows were implanted in the newborn pigs within the first week of life and used to collect CSF for cAMP determinations and to assess changes in pial arteriolar diameters (PAD). In the first part of the study, pial arteriolar responses to different vasodilator and vasoconstrictor stimuli were evaluated in piglets prior to asphyxia (n = 20). In newborn pigs exposed to cocaine, cerebrovascular responses to hypercapnia and norepinephrine were significantly exaggerated compared to controls. Then, piglets were randomly selected for the second part of the study that involved prolonged asphyxia (n = 12). In cocaine-exposed but not sham-control piglets, CSF cAMP increased markedly during asphyxia. In the sham piglets, but not the cocaine-exposed piglets, CSF cAMP fell progressively below the baseline during recovery. Cerebrovascular reactivity to cAMP-dependent stimuli (hypercapnia and isoproterenol) was preserved during recovery from asphyxia in the cocaine-exposed piglets but significantly attenuated in the sham controls. We conclude that piglets with chronic prenatal exposure to cocaine show exaggerated cerebrovascular responses to vasogenic stimuli and preserved cAMP-dependent cerebral vasoreactivity following asphyxia.

Ecgonine Methyl Ester Protects Against Cocaine Lethality in Mice

BACKGROUND

Plasma cholinesterase (PChE) metabolizes cocaine to ecgonine methyl ester (EME). Limited data demonstrate that EME is a mild vasodilator. Exogenous PChE protects against cocaine-induced seizures and lethality. It is unclear whether this protective effect results from enhanced degradation of cocaine, the loss of active metabolites (benzoylecgonine, norcocaine), or the production of a beneficial metabolite (EME). This study was designed to further investigate the pharmacologic effects of EME.

METHODS

All experiments used female ICR Swiss albino mice weighing 20-30 grams. Mice were acclimated to 12 h alternating light-dark cycles and given food and water ad libitum. Using a randomized, blinded protocol, 80 mice were then pretreated with either IP EME (50 mg/kg) in a 0.9% sodium chloride solution or an equal volume of 0.9% sodium chloride solution as control. Five minutes later, all animals received 126 mg/kg of cocaine IP and were observed for seizures and death. Fatality was compared using a Fisher's exact test, and the time to seizures and death were compared using a Mann-Whitney U statistic.

RESULTS

Pretreatment with EME increased survival following cocaine (9/40 vs. 2/40, for EME vs. control, respectively, p<0.05). The median times to seizure and death for both groups were 2.0 vs. 1.5 min (p>0.05), and 4.5 vs. 4.6 min (p>0.05) (EME vs. control for seizures and death, respectively).

CONCLUSION

In this animal model, EME is protective against cocaine lethality. This effect is consistent with the previously described vasodilatory effects of EME. Further studies are indicated to determine whether the increase in EME produced by exogenous PChE administration contributes to the benefits that occur when PChE is given to cocaine-poisoned animals.

Central and autonomic system signs with in utero drug exposure

AIMS

To determine risk for central nervous system/autonomic nervous system (CNS/ANS) signs following in utero cocaine and opiate exposure.

METHODS

A multisite study was designed to determine outcomes of in utero cocaine and opiate exposure. A total of 11 811 maternal/infant dyads were enrolled. Drug exposed (EXP) infants were identified by maternal self report of cocaine or opiate use or by meconium testing. Of 1185 EXP, meconium analysis confirmed exposure in 717 to cocaine (CO) only, 100 to opiates (OP), and 92 to opiates plus cocaine (OP+CO); 276 had insufficient or no meconium to confirm maternal self report. Negative exposure history was confirmed in 7442 by meconium analysis and unconfirmed in 3184. Examiners masked to exposure status, assessed each enrolled infant. Using generalised estimating equations, adjusted odds ratios (OR) and 95% confidence intervals (CI) were estimated for manifesting a constellation of CNS/ANS outcomes and for each sign associated with cocaine and opiate exposure.

RESULTS

Prevalence of CNS/ANS signs was low in CO, and highest in OP+CO. Signs were significantly related to one another. After controlling for confounders, CO was associated with increased risk of manifesting a constellation of CNS/ANS outcomes, OR (95% CI): 1.7 (1.2 to 2.2), independent of OP effect, OR (95% CI): 2.8 (2.1 to 3.7). OP+CO had additive effects, OR (95% CI): 4.8 (2.9 to 7.9). Smoking also increased the risk for the constellation of CNS/ANS signs, OR (95% CI) of 1.3 (1.04 to 1.55) and 1.4 (1.2 to 1.6), respectively, for use of less than half a pack per day and half a pack per day or more.

CONCLUSION

Cocaine or opiate exposure increases the risk for manifesting a constellation of CNS/ANS outcomes.

Effects of cocaine and cocaine metabolites on cardiovascular function in squirrel monkeys

The effects of cocaine and the cocaine metabolites norcocaine, ecgonine methyl ester, benzoylecgonine and cocaethylene were evaluated in conscious squirrel monkeys for their effects on blood pressure and heart rate. Norcocaine, ecgonine methyl ester and benzoylecgonine are produced in vivo following cocaine use. Cocaethylene is produced in vivo following concurrent cocaine and alcohol use. Increases in both blood pressure and heart rate were observed following cocaine doses of 0.3-3.0 mg/kg. Ecgonine methyl ester and benzoylecgonine had no effect on either parameter up to doses of 10.0 mg/kg. Norcocaine increased blood pressure, but was less potent than cocaine. Norcocaine did not affect heart rate at doses up to 3.0 mg/kg. In contrast to the other metabolites, cocaethylene increased blood pressure and heart rate similarly to cocaine. These results suggest that ecgonine methyl ester and benzoylecgonine are devoid of cardiovascular effects at doses comparable to cocaine and would not be expected to contribute to cocaine's overall cardiovascular effects. Norcocaine's effect on blood pressure might contribute to the cardiovascular effects of cocaine, but this metabolite is produced only at low levels in vivo. The one metabolite that might be expected to contribute to cocaine's overall cardiovascular effect is cocaethylene, although the degree of this contribution is not clear.

A prospective comparison of developmental outcome of children with in utero cocaine exposure and controls using the Battelle Developmental Inventory

Children with in utero cocaine exposure may be at risk for adverse neurodevelopmental outcome. To evaluate such outcome in young children, we administered the Battelle Developmental Inventory (BDI) to a group of inner-city children with (COC) and without (CON) in utero cocaine exposure at ages 3 and 5 years. Sixty-five COC and 68 CON, similar at age of testing, were evaluated at both time points by examiners masked to child group status. Both groups scored poorly and worsened over time. Although Total BDI raw scores were lower in the COC group than in the CON group at 3 years, this difference was related to postnatal environmental factors, caregiver (p = .022), and home environment (p = .010), not to in utero cocaine exposure (p = .88). At 5 years, the Total BDI score was related to the home environment (p < .001) but not to the caregiver (p = .36) or in utero cocaine exposure (p = .83). We conclude that inner-city children are at risk for adverse developmental outcome regardless of in utero cocaine exposure.

Comparison of cerebrovascular effects of intravenous cocaine injection in fetal, newborn, and adult sheep

Cocaine may cause stroke, intracranial hemorrhage, seizures, and neurobehavioral abnormalities in fetuses, newborns, and adults, and there could be developmental and/or species differences in mechanisms for these cocaine-induced cerebrovascular effects. To evaluate developmental differences in responses to cocaine, we compared the cerebrovascular and metabolic responses to a 2 mg/kg iv cocaine dose in unanesthetized fetal (n = 8, previously reported, direct fetal injection), newborn (n = 6), and adult (n = 12) sheep. We measured cerebral blood flow, mean arterial blood pressure, and arterial and venous O(2) content, and we calculated cerebral O(2) consumption and cerebral vascular resistance at baseline and at 30 s and at 5, 15, and 60 min after cocaine injection. Cerebral blood flow increased 5 min after injection in the fetus and newborn, but not until 15 min in the adult. In the fetus, cocaine caused a transient cerebral vasoconstriction at 30 s; in all three groups, cocaine caused cerebral vasodilation, which was delayed in the adult. Cerebral metabolic O(2) consumption increased 5 min after injection in the fetus and newborn, but not until 15 min after injection in the adult. Arterial O(2) content decreased 5 min after injection in the fetus and 15 min after injection in the adult. We speculate that clinical differences in response to cocaine injection may be explained, in part, by these developmental differences in the cerebrovascular and metabolic responses to cocaine.

Propranolol blocks cocaine-induced cerebral vasodilation in newborn sheep

OBJECTIVE

The objective of this study was to test the hypothesis that cocaine-induced cerebral vasodilation in newborn sheep is mediated via beta-adrenergic receptor activation.

DESIGN

The cerebral effects of a single intravenous injection of cocaine (4 mg/kg) given 30 mins after pretreatment with propranolol (1 mg/kg) were studied and compared with the results from a previous study using an identical cocaine protocol without propranolol pretreatment.

SUBJECTS

Seven chronically catheterized, unanesthetized newborn sheep (6 +/- 1 days old).

MEASUREMENTS

Cerebral blood flow using radiolabeled microspheres, mean arterial blood pressure (MAP), heart rate, and cerebral arterial and venous oxygen content were measured at baseline, after administration of propranolol, and 0.5, 5, 15, and 60 mins after cocaine injection. Cerebrovascular resistance was calculated as the MAP divided by the cerebral blood flow.

MAIN RESULTS

Propranolol injection alone caused no systemic or cerebral physiologic changes other than an 11 +/- 2% (mean +/- SEM) decrease in heart rate, which was sustained after cocaine injection. In contrast to previous studies showing cerebral vasodilation (25% decrease in cerebrovascular resistance) and acute hypertension (57% increase in MAP) 30 secs after cocaine injection, there were no changes in cerebrovascular resistance after cocaine injection and after propranolol pretreatment and there was only a 23 +/- 7% increase in MAP 30 secs after injection, with a return to baseline by 15 mins. Cocaine and norepinephrine levels were similar to those previously reported in the newborn sheep after an injection of 4 mg/kg cocaine.

CONCLUSION

Propranolol blocks cocaine-induced cerebral vasodilation and blunts the acute hypertension in newborn sheep, suggesting that cocaine's cerebrovascular effects in the developing brain are mediated, at least in part, by beta-adrenergic receptor activation.