Buprenorphine duration of action: mu-opioid receptor availability and pharmacokinetic and behavioral indices.

BACKGROUND: Buprenorphine (BUP) is effective in the treatment of opioid dependence when given on alternating days, probably as a result of long-lasting occupation of micro opioid receptors (microORs). This study examined the duration of action of BUP at microORs and correlations with pharmacokinetic and pharmacodynamic outcomes in 10 heroin-dependent volunteers. METHODS: Availability of microOR (measured with positron emission tomography and [(11)C]-carfentanil), plasma BUP concentration, opioid withdrawal symptoms, and blockade of hydromorphone (HYD; heroin-like agonist) effects were measured at 4, 28, 52, and 76 hours after omitting the 16 mg/d dose of BUP in a study reported elsewhere. RESULTS: Relative to heroin-dependent volunteers maintained on BUP placebo, whole-brain microOR availability was 30%, 54%, 67%, and 82% at 4, 28, 52, and 76 hours after BUP. Regions of interest showed similar effects. Plasma concentrations of BUP were time dependent, as were withdrawal symptoms, carbon dioxide sensitivity and extent of HYD blockade. Availability of microOR was also correlated with BUP plasma concentration, withdrawal symptoms, and HYD blockade. CONCLUSIONS: Together with our previous findings, it appears that microOR availability predicts changes in pharmacokinetic and pharmacodynamic measures and that about 50%-60% BUP occupancy is required for adequate withdrawal symptom suppression (in the absence of other opioids) and HYD blockade.     

Alcohol intoxication does not change [11C]cocaine pharmacokinetics in human brain and heart.

There is increasing evidence that the combined use of cocaine and alcohol produces enhanced behavioral and toxic effects. We have used PET and tracer doses of [11C]cocaine in 7 normal human volunteers to assess if the distribution and clearance of cocaine are altered by alcohol intoxication. Each subject received 2 PET studies with [11C]cocaine (3-11 micrograms), one before and one during alcohol intoxication (1 g/kg). Regions of interest included the brain (n = 3) and heart (n = 4). Arterial plasma was assayed for unchanged cocaine and for labeled cocaethylene, a metabolite of cocaine found in individuals using cocaine and alcohol in combination (Hearn et al., 1991a). Alcohol intoxication did not change uptake and clearance or the steady-state distribution volume of [11C] cocaine in brain (striatum, thalamus, and cerebellum) or in heart. Moreover, labeled cocaethylene was not detected in the 10 minute plasma sample. These results suggest that the acute enhancement of behavior and toxicity associated with the combined use of cocaine and alcohol is not due to an alteration in cocaine's organ distribution or to cocaethylene formation but may be related to an additive effect resulting from the direct actions of each of these drugs.     

Recovery of superior frontal gyrus cortical thickness and resting‐state functional connectivity in abstinent heroin users after 8 months of follow‐up

Compared with healthy controls, heroin users (HUs) show evidence of structural and functional brain alterations. However, little is known about the possibility of brain recovery after protracted heroin abstinence. The purpose of this study was to investigate whether brain recovery is possible after protracted abstinence in HUs. A total of 108 subjects with heroin addiction completed structural and functional scans, and 61 of those subjects completed 8‐month follow‐up scans. Resting‐state data and 3D‐T1 MR images were collected for all participants, first at baseline and again after 8 months. Cognitive function and craving were measured by the Trail Making Test‐A (TMT‐A) and Visual Analog Scale for Craving, respectively. The cortical thickness and resting‐state functional connectivity (RSFC) differences were then analyzed and compared between baseline and follow‐up, and correlations were obtained between neuroimaging and behavioral changes. HUs demonstrated improved cognition (shorter TMT‐A time) and reduced craving at the follow‐up (HU2) relative to baseline (HU1), and the cortical thickness in the bilateral superior frontal gyrus (SFG) was significantly greater at HU2 than at HU1. Additionally, the RSFC of the left SFG with the inferior frontal gyrus (IFG), insula, and nucleus accumbens and that of the right SFG with the IFG, insula and orbitofrontal cortex (OFC) were increased at HU2. The changes in TMT‐A time were negatively correlated with the RSFC changes between the left SFG and the bilateral IFG, the bilateral caudate, and the right insula. The changes in craving were negatively correlated with the RSFC changes between the left OFC and the bilateral SFG. Our results demonstrated that impaired frontal‐limbic neurocircuitry can be partially restored, which might enable improved cognition as well as reduced craving in substance‐abusing individuals. We provided novel scientific evidence for the partial recovery of brain circuits implicated in cognition and craving after protracted abstinence.     

Comparative PET studies of the kinetics and distribution of cocaine and cocaethylene in baboon brain.

Recent studies have suggested that cocaethylene, an active metabolite of cocaine found in blood and postmortem brain of individuals self-administering cocaine and alcohol, may play a role in the increased toxicity seen when coadministering these 2 drugs. We have used positron emission tomography (PET) and carbon-11 (t1/2:20.4 min) labeled cocaine and cocaethylene to compare the short-term kinetics of cocaine and cocaethylene in baboon brain. The regional uptake of [11C]cocaine cocaethylene in baboon brain. The regional uptake of [11C]cocaine ([11C]COC) and [11C]cocaethylene ([11C]CE), 5-8 mCi and 4-6 micrograms, in baboon brain (n = 7) were similar but clearance from whole brain (global, GL) and from striatum (SR), thalamus (TH), and cerebellum (CB) was slower for cocaethylene. Steady-state distribution volumes (DV) were not significantly different in the striatum but were greater for cocaethylene in the thalamus, cerebellum, and whole brain. Debenzoylation of cocaethylene proceeded at about one-third the rate of cocaine, as determined by in vitro incubation of labeled cocaethylene and labeled cocaine with baboon plasma and with purified horse butyryl-cholinesterase (EC 3.1.1.8). Even though the slower clearance of cocaethylene could lead to longer tissue exposures and potentially accentuated or different physiological effects relative to cocaine, the difference between the 2 drugs is not large. Thus it is more likely that the direct actions of cocaine and alcohol on some organs, rather than cocaethylene, account for this enhanced toxicity.     

Somatostatin receptors increase in the olfactory bulb of developing pups after perinatal exposure to cocaine

The effects of chronic prenatal and/or postnatal exposure to cocaine on somatostatin concentration and receptors were studied in the olfactory bulbs of rat pups at birth and at 15 days old. Wistar rats were injected subcutaneously with single daily doses of 40 mg cocaine hydrochloride/kg from days 7 to 19 of gestation, from day 7 of gestation to day 15 postpartum or from parturation to day 15 postpartum. Fetal exposure to cocaine decreased SS concentrations in the olfactory bulb of the newborn pups while prenatal-plus-postnatal exposure increased this parameter. Administration of cocaine only during lactation did not induce any change. Exposure during gestation or during nursing induced an increase in the total number of somatostatin receptors and a decrease in the affinity constant in the olfactory bulb of newborn and 15-day-old pups. These results suggest that the development of somatostatin receptors in the olfactory bulb can be altered by prenatal and/or nursing period exposure to cocaine.     

Mu-opioid receptor binding measured by [11C]carfentanil positron emission tomography is related to craving and mood in alcohol dependence.

BACKGROUND: The endogenous opioid system has been linked to alcohol dependence through animal and human studies. We investigated the relationship between alcohol craving and brain mu opioid receptors (mu-OR) in alcohol-dependent subjects. METHODS: Regional brain mu-OR binding potential (BP) was measured using [(11)C]carfentanil positron emission tomography in eight male alcohol-dependent subjects undergoing alcohol withdrawal and eight matched control subjects. Self-reported alcohol craving, withdrawal, and mood were measured. RESULTS: Lower mu-OR BP was associated with higher craving in the right dorsal lateral prefrontal cortex, the right anterior frontal cortex, and right parietal cortex. In these regions, alcoholics showed lower mean mu-OR BP compared with control subjects. Mu-OR BP in four other brain regions also correlated with craving, but there were no group differences in receptor binding potential. Mu-OR BP also correlated with depressive symptoms in five brain regions, three of which were identified in the craving analyses. CONCLUSIONS: Results show a strong functional relationship between alcohol craving, mood, and mu-OR binding in specific brain regions of recently abstinent, alcohol-dependent men.     

Overlapping patterns of brain activation to food and cocaine cues in cocaine abusers

Cocaine, through its activation of dopamine (DA) signaling, usurps pathways that process natural rewards. However, the extent to which there is overlap between the networks that process natural and drug rewards and whether DA signaling associated with cocaine abuse influences these networks have not been investigated in humans. We measured brain activation responses to food and cocaine cues with fMRI, and D2/D3 receptors in the striatum with [¹¹C]raclopride and Positron emission tomography in 20 active cocaine abusers. Compared to neutral cues, food and cocaine cues increasingly engaged cerebellum, orbitofrontal, inferior frontal, and premotor cortices and insula and disengaged cuneus and default mode network (DMN). These fMRI signals were proportional to striatal D2/D3 receptors. Surprisingly cocaine and food cues also deactivated ventral striatum and hypothalamus. Compared to food cues, cocaine cues produced lower activation in insula and postcentral gyrus, and less deactivation in hypothalamus and DMN regions. Activation in cortical regions and cerebellum increased in proportion to the valence of the cues, and activation to food cues in somatosensory and orbitofrontal cortices also increased in proportion to body mass. Longer exposure to cocaine was associated with lower activation to both cues in occipital cortex and cerebellum, which could reflect the decreases in D2/D3 receptors associated with chronicity. These findings show that cocaine cues activate similar, though not identical, pathways to those activated by food cues and that striatal D2/D3 receptors modulate these responses, suggesting that chronic cocaine exposure might influence brain sensitivity not just to drugs but also to food cues. Hum Brain Mapp, 36:120–136, 2015. © 2014 Wiley Periodicals, Inc .     

Long-term consequences of prenatal exposure to cocaine or related drugs: Effects on rat brain monoaminergic receptors

Reports from both this laboratory and others indicate that prenatal exposure of rats to cocaine can produce alterations in development, activity and responses to environmental stimuli. In order to determine a biochemical basis for these effects, radioligand receptor-binding assays for different monoaminergic receptors were performed on rat brain tissues obtained from offspring of dams treated SC with saline, cocaine (15 mg/kg b.i.d.), amitriptyline (10 mg/kg) or amfonelic acid (AFA, 1.5 mg/kg). Male rat pups were fostered by surrogate dams and one rat per litter taken at 30, 60 or 180 days postnatal for determination of striatal and prefrontal cortical D2 receptors, prefrontal cortical 5HT2 receptors, cortical alpha 1-, alpha 2-, beta 1- and beta 2-adrenoceptors. Across all drug treatments and times, the only significant change was at 30 days of age when beta 1-adrenoceptors were increased 68% in the cocaine exposed pups--a time when these rats show hyperactivity--and at 180 days postnatal when a 20% decrease in DA2 receptor Bmax was observed. Also, cortical membrane Mg(2+)-dependent Na+, K(+)-ATPase activities and basal ATPase activities were unaltered by any of the treatments at any of the times. These results suggest that few changes have occurred in monoaminergic receptor sensitivity as a result of the exposure to these drugs during gestation. The behavioral changes that are known to occur following prenatal exposure to cocaine may be due to presynaptic alterations in neurotransmitter function rather than changes in postsynaptic receptors.     

Excessive sugar intake alters binding to dopamine and mu-opioid receptors in the brain.

Palatable food stimulates neural systems implicated in drug dependence; thus sugar might have effects like a drug of abuse. Rats were given 25% glucose solution with chow for 12 h followed by 12 h of food deprivation each day. They doubled their glucose intake in 10 days and developed a pattern of excessive intake in the first hour of daily access. After 30 days, receptor binding was compared to chow-fed controls. Dopamine D-1 receptor binding increased significantly in the accumbens core and shell. In contrast, D-2 binding decreased in the dorsal striatum. Binding to dopamine transporter increased in the midbrain. Opioid mu-1 receptor binding increased significantly in the cingulate cortex, hippocampus, locus coeruleus and accumbens shell. Thus, intermittent, excessive sugar intake sensitized D-1 and mu-1 receptors much like some drugs of abuse.     

Involvement of adenosine A2A and dopamine receptors in the locomotor and sensitizing effects of cocaine

Recent data indicate that cocaine locomotor responses may be influenced by dopamine (DA) neurotransmission and adenosine neuromodulation involving the A2A receptor (A2AR). Male Wistar rats were injected with MSX-3 (1-25 mg/kg; an antagonist of A2AR), CGS 21680 (0.05-0.2 mg/kg; an agonist of A2AR), SCH 23390 (0.125-0.25 mg/kg; an antagonist of DA D1/5R), raclopride (0.1-0.8 mg/kg; an antagonist of DA D2/3R), nafadotride (0.2-0.4 mg/kg; an antagonist of DA D3R) or 7-OH-PIPAT (0.01-1 mg/kg; an agonist of DA D3R) to verify the hypothesis that adenosine A2AR and DA receptors and their antagonistic interactions may control locomotor and sensitizing effects of cocaine. In well-habituated animals, MSX-3 (5 mg/kg) increased, while raclopride (0.4-0.8 mg/kg) decreased basal locomotor activation; the other drugs were inactive. The locomotor hyperactivation induced by acute cocaine (10 mg/kg) was enhanced by MSX-3 (5-25 mg/kg) or nafadotride (0.4 mg/kg), while CGS 21680 (0.2 mg/kg), SCH 23390 (0.25 mg/kg), raclopride (0.2-0.8 mg/kg) or 7-OH-PIPAT (0.1 mg/kg) decreased this effect of cocaine. Given during the development of sensitization (in combination with 5-daily cocaine, 10 mg/kg, injections), MSX-3 (5-25 mg/kg) increased, but CGS 21680 (0.2 mg/kg) and raclopride (0.8 mg/kg) reduced the locomotor response to a cocaine challenge dose (10 mg/kg) on day 10. When injected acutely with a cocaine challenge dose (on day 10), CGS 21680 (0.2 mg/kg), raclopride (0.2-0.8 mg/kg) or 7-OH-PIPAT (1 mg/kg) reduced, while MSX-3 (5 mg/kg) or nafadotride (0.4 mg/kg) enhanced the expression of cocaine sensitization. The present results show that adenosine A2ARs and DA D3Rs exert inhibitory actions on acute locomotor responses to cocaine and on the expression of cocaine sensitization, while DA D2Rs had an opposing role in such effects. Pharmacological stimulation of adenosine A2ARs protected against both the development and expression of cocaine sensitization, which may offer a therapeutic potential of A2AR agonists in the treatment of cocaine dependence. The results suggest an antagonistic role of A2ARs in D2R-mediated cocaine actions based at least in part on the existence of A2A/D2 heteromeric receptor complexes.     

Behavioral responses to cocaine and amphetamine administration in mice lacking the dopamine D1 receptor

Cocaine and amphetamine can induce both short-term and long-term behavioral changes in rodents. The major target for these psychostimulants is thought to be the brain dopamine system. To determine whether the dopamine D1 receptor plays a crucial role in the behavioral effects of psychostimulants, we tested both the locomotor and stereotyped behaviors in D1 receptor mutant and wild-type control mice after cocaine and amphetamine treatments. We found that the overall locomotor responses of D1 receptor mutant mice to repeated cocaine administration were significantly reduced compared to those of the wild-type mice and the responses of the D1 receptor mutant mice to cocaine injections were never significantly higher than their responses to saline injections. D1 receptor mutant mice were less sensitive than the wild-type mice to acute amphetamine stimulation over a dose range even though they exhibited apparently similar behavioral responses as those of the wild-type mice after repeated amphetamine administration at the 5 mg/kg dose. Immunostaining experiments indicated that there was no detectable neurotoxicity in the nucleus accumbens in both D1 receptor mutant and wild-type mice after repeated amphetamine administration. The data suggest that the D1 receptor plays an essential role in mediating cocaine-induced behavioral changes in mice. Moreover, the D1 receptor also participates in behavioral responses induced by amphetamine administration.     

Changes in endocannabinoid contents in the brain of rats chronically exposed to nicotine,ethanol or cocaine

Despite recent data suggesting that the endocannabinoid transmission is a component of the brain reward system and plays a role in dependence/withdrawal to different habit-forming drugs, only a few studies have examined changes in endocannabinoid ligands and/or receptors in brain regions related to reinforcement processes after a chronic exposure to these drugs. Recently, we carried out a comparative analysis of the changes in cannabinoid CB(1) receptor density in several rat brain regions caused by chronic exposure to some of the most powerful habit-forming drugs. In the present study, we have extended this objective by examining changes in the brain contents of arachidonoylethanolamide (AEA) and 2-arachidonoyl-glycerol (2-AG), the endogenous ligands for cannabinoid receptors, in animals chronically exposed to cocaine, nicotine or ethanol. Results were as follows. Cocaine was the drug exhibiting the minor number of effects, with only a small, but significant, decrease in the content of 2-AG in the limbic forebrain. In contrast, chronic alcohol exposure caused a decrease in the contents of both AEA and 2-AG in the midbrain, while it increased AEA content in the limbic forebrain. This latter effect was also observed after chronic nicotine exposure together with an increase in AEA and 2-AG contents in the brainstem. In contrast, the hippocampus, the striatum and the cerebral cortex exhibited a decrease in AEA and/or 2-AG contents after chronic nicotine exposure. We also tested the effect of chronic nicotine on brain CB(1) receptors, which had not been investigated before, and found an almost complete lack of changes in mRNA levels or binding capacity for these receptors. In summary, our results, in concordance with previous data on CB(1) receptors, indicate that the three drugs tested here produce different changes in endocannabinoid transmission. Only in the case of alcohol and nicotine, we observed a common increase in AEA contents in the limbic forebrain. This observation is important considering that this region is a key area for the reinforcing properties of habit-forming drugs, which might support the involvement of endocannabinoid transmission in some specific events of the reward system activated by these drugs.     

Genetic differences in the time course for the development and persistence of the anticonvulsant effects of carbamazepine against cocaine seizures

Initial studies of the effect of chronic carbamazepine (CBZ) against cocaine-induced seizures indicated that there were genetic differences in both the time course for the development of the anticonvulsant effects of CBZ against cocaine-induced seizures and the persistence of these effects. The present studies were initiated to investigate the time course for the development and persistence of the anticonvulsant effects of chronic CBZ against cocaine seizures in BALB/cByJ, C57Bl/6J and SJL/J mice. The anticonvulsant actions of CBZ were dependent on the duration of CBZ administration, requiring 4–7 days to achieve maximal efficacy. However, once the anticonvulsant effects of CBZ were manifest, the effect persisted for up to 5 days after stopping CBZ treatment depending on the genotype. The levels of CBZ and its active epoxide metabolite were determined in plasma and brain at various time points during and after chronic CBZ treatment. The levels of CBZ and CBZ-10,11-epoxide were substantially reduced over the course of treatment in all three strains, such that the levels of the two compounds in plasma and brain could not account for the decreased susceptibility to cocaine seizures observed following chronic CBZ. These results suggest that the effects of CBZ on cocaine seizures are mediated by relatively long-term changes in one or more biological systems associated with cocaine's convulsant effects.     

In vivo imaging of neurotransmission and brain receptors in dementia.

Positron emission tomography (PET) and single photon emission tomography (SPECT) are the most sensitive techniques to study, in vivo, neurotransmitter systems in normal human brain and in diseases. These methods have been applied over the last years to explore the integrity of cholinergic, serotonergic, GABAergic, and dopaminergic systems in Alzheimer's disease (AD) and in other dementias. The results of these investigations have provided new insights into the neurotransmission involvement in these disorders. Moreover, these methods provide objective quantitative markers for monitoring the progression of disease and the effects of therapies. The pathophysiological and clinical relevance of results from these studies are reviewed and the potential role in early and differential diagnosis discussed. New emerging radiotracers/methods for future investigations of neurochemical processes are delineated.     

Distribution of cocaine recognition sites in monkey brain: I. In vitro autoradiography with [3H]CFT.

The cocaine analog [3H]CFT ([3H]WIN 35,428) was used to map and characterize cocaine recognition sites in the squirrel monkey brain by quantitative autoradiography. Coronal tissue sections were incubated with 5 nM [3H]CFT to measure total binding or with [3H]CFT in the presence of 30 microM (-)-cocaine to measure nonspecific binding. High densities of [3H]CFT binding sites were present in dopamine-rich brain regions, including the caudate nucleus, putamen, nucleus accumbens, and olfactory tubercle. In each of these regions specific binding was greater than 90% of total binding. Several additional brain regions exhibited intermediate densities of [3H]CFT binding, including the substantia nigra, the zona incerta, the amygdala, and the hypothalamus. Low, though measurable levels of binding were observed in the bed nucleus of the stria terminalis, the ventral tegmental area, the medial preoptic area, the pineal, the hippocampus, and thalamic central nuclei. Near-background levels of binding were found in white matter, cortical regions, globus pallidus, and cerebellum. The pharmacological specificity of [3H]CFT binding in various brain regions was determined in competition studies using [3H]CFT and a range of concentrations of selected monoamine uptake inhibitors. In all brain regions examined, stereoselective inhibition of [3H]CFT binding was observed for the (-) over the (+) isomer of cocaine. For other drugs tested, competition experiments indicated a rank order of potency of GBR 12909 greater than or equal to CFT greater than bupropion, suggestive of binding of [3H]CFT to elements of the dopamine transport system. The results demonstrate that although densities of [3H]CFT binding sites are highest in the caudate nucleus, putamen, and nucleus accumbens/olfactory tubercle, significant levels of binding can be detected in other brain regions that may contribute to the behavioral and physiological effects of cocaine.     

Stress-induced relapse to heroin and cocaine seeking in rats: a review

Studies in humans suggest that exposure to stress increases the probability of relapse to drug use, but until recently there has been no animal model to study the mechanisms that mediate this effect. We have developed a reinstatement procedure that allows us to study the effect of stress on relapse to drug seeking in rats. Using this procedure, we have shown that exposure to intermittent footshock stress reliably reinstates heroin and cocaine seeking after prolonged drug-free periods. In the present paper, we summarize results from several studies on stress-induced reinstatement of heroin and cocaine seeking in rats. We first assess the degree to which the phenomenon of stress-induced relapse generalizes to other stressors, to behaviors controlled by other drugs of abuse, and to behaviors controlled by non-drug reinforcers. We then review evidence from studies concerned with the neurotransmitters, the brain sites, and the neural systems involved in stress-induced reinstatement of drug seeking. Finally, we consider the mechanisms that might underlie stress-induced relapse to drug seeking and the possible implications of the findings for the treatment of relapse to drug use in humans.     

Chronic inhibition of the norepinephrine transporter in the brain participates in seizure sensitization to cocaine and local anesthetics

The involvement of chronic inhibition of monoamine transporters (MAT) in the brain with respect to sensitization to cocaine- and local anesthetic-induced seizures was studied in mice. Repeated administration of subconvulsive doses of meprylcaine as well as cocaine, both of which inhibit MAT, but not lidocaine, which does not inhibit MAT, increased seizure activity and produced sensitization to other local anesthetics. The effects of five daily treatments of monoamine transporter inhibitors on lidocaine-induced convulsions were examined 2 or 3 days after the last dose of the inhibitors. Daily treatments of GBR 12935, a specific inhibitor of dopamine uptake, significantly increased the incidence and the intensity of lidocaine-induced convulsions at 20 mg/kg and decreased the threshold of the convulsions. Daily treatments of desipramine and maprotiline, selective norepinephrine uptake inhibitors, markedly increased the incidence and intensity of lidocaine-induced convulsions, and decreased the threshold in a dose-dependent manner at between 5 and 20 mg/kg. Daily treatments of citalopram, a selective serotonin uptake inhibitor, at 10 and 20 mg/kg, produced no significant increase in the incidence or intensity of lidocaine-induced convulsions, but decreased the threshold of the convulsions. These results suggest that the chronic intermittent inhibition of monoamine uptake increases susceptibility to cocaine- and local anesthetic-induced seizures, and the norepinephrine transporter is an integral component of this sensitization.     

Regional binding to corticotropin releasing factor receptors in brain of rats exposed to chronic cocaine and cocaine withdrawal

Cocaine, as does exposure to other physiological stressors, releases brain corticotropin releasing factor (CRF), and this release habituates during the course of repeated cocaine administration in animals. Due to the many signs of anxiety and responses to stress that are produced by cocaine withdrawal in humans, the present study was designed to assess the effects of chronic cocaine and its withdrawal on regional ¹²⁵I-Tyr-oCRF binding to the CRF₁ receptor in brains of male Lewis rats. Cocaine or saline was intravenously infused for 10 days in a regimen that resembled a self-administration paradigm (1 mg/kg every 12 min for 2 h each day). Tissues were harvested either 15 min after or 10 days after the last cocaine infusion, and the brains were sectioned and prepared for CRF₁ receptor autoradiography. Compared with findings in saline controls, there was a 31% lower level of CRF binding sites in the basolateral nucleus of the amygdala immediately after the last cocaine infusion, but not 10 days later. Neuroendocrine and non-neuroendocrine mechanisms associated with CRF₁ receptors do not appear to contribute to long-term withdrawal effects. Synapse 25:272–276, 1997. © 1997 Wiley-Liss, Inc.