Cocaine-induced ischemia in prefrontal cortex is associated with escalation of cocaine intake in rodents.

Cocaine-induced vasoconstriction reduces blood flow, which can jeopardize neuronal function and in the prefrontal cortex (PFC) it may contribute to compulsive cocaine intake. Here, we used integrated optical imaging in a rat self-administration and a mouse noncontingent model, to investigate whether changes in the cerebrovascular system in the PFC contribute to cocaine self-administration, and whether they recover with detoxification. In both animal models, cocaine induced severe vasoconstriction and marked reductions in cerebral blood flow (CBF) in the PFC, which were exacerbated with chronic exposure and with escalation of cocaine intake. Though there was a significant proliferation of blood vessels in areas of vasoconstriction (angiogenesis), CBF remained reduced even after 1 month of detoxification. Treatment with Nifedipine (Ca2+ antagonist and vasodilator) prevented cocaine-induced CBF decreases and neuronal Ca2+ changes in the PFC, and decreased cocaine intake and blocked reinstatement of drug seeking. These findings provide support for the hypothesis that cocaine-induced CBF reductions lead to neuronal deficits that contribute to hypofrontality and to compulsive-like cocaine intake in addiction, and document that these deficits persist at least one month after detoxification. Our preliminary data showed that nifedipine might be beneficial in preventing cocaine-induced vascular toxicity and in reducing cocaine intake and preventing relapse.

Hemodynamic and neuronal responses to cocaine differ in awake versus anesthetized animals: Optical brain imaging study.

Cocaine is a highly addictive drug with complex pharmacological effects. Most preclinical imaging studies investigating the effects of cocaine in the brain have been performed under anesthesia, which confounds findings. To tackle this problem, we used optical imaging to compare the effects of cocaine in the awake versus the anesthetized states. For this purpose, we customized an air floating mobile cage to fit the multi-wavelength spectral and laser speckle optical imaging system and implanted a multi-layer cranial window over the mouse somatosensory cortex. Results showed significant differences in neuronal activity and hemodynamics at baseline and in response to cocaine between the awake and the anesthetized states (isoflurane anesthesia). Specifically, 1) at baseline isoflurane dilated cerebral vessels, increased cerebral blood flow and depressed neuronal Ca2+ activity compared to the awake state; 2) acute cocaine (1 mg/kg iv) vasoconstricted blood vessels (arteries and veins) and decreased cerebral blood flow and oxygenated hemoglobin in the anesthetized state but not in the awake condition; 3) cocaine increased the accumulation of mean intracellular Ca2+ in neurons in the anesthetized state but not in the awake condition; and 4) in the awake state acute cocaine increased neuronal activities (increased the frequency of Ca2+ transients) and increased neuronal synchronization. We also corroborated that in the awake state cocaine also disrupted neurovascular coupling. These findings indicate that both vascular and neuronal responses to cocaine are influenced by isoflurane anesthesia, which highlights the importance of imaging awake animals when studying the effects of cocaine or other drugs in the brain.

Enhanced neuronal and blunted hemodynamic reactivity to cocaine in the prefrontal cortex following extended cocaine access: optical imaging study in anesthetized rats.

Cocaine addiction is associated with dysfunction of the prefrontal cortex (PFC), which facilitates relapse and compulsive drug taking. To assess if cocaine's effects on both neuronal and vascular activity contribute to PFC dysfunction, we used optical coherence tomography and multi-wavelength laser speckle to measure vascularization and hemodynamics and used GCaMP6f to monitor intracellular Ca2+ levels ([Ca2+ ]in ) as a marker of neuronal activity. Rats were given short (1 hour; ShA) or long (6 hours; LgA) access cocaine self-administration. As expected, LgA but not ShA rats escalated cocaine intake. In naïve rats, acute cocaine decreased oxygenated hemoglobin, increased deoxygenated hemoglobin and reduced cerebral blood flow in PFC, likely due to cocaine-induced vasoconstriction. ShA rats showed enhanced hemodynamic response and slower recovery after cocaine, versus naïve. LgA rats showed a blunted hemodynamic response, but an enhanced PFC neuronal [Ca2+ ]in increase after cocaine challenge associated with drug intake. Both ShA and LgA groups had higher vessel density, indicative of angiogenesis, presumably to compensate for cocaine's vasoconstricting effects. Cocaine self-administration modified the PFC cerebrovascular responses enhancing it in ShA and attenuating it in LgA animals. In contrast, LgA but not ShA animals showed sensitized neuronal reactivity to acute cocaine in the PFC. The opposite changes in hemodynamics (decreased) and neuronal responses (enhanced) in LgA rats indicate that these constitute distinct effects and suggest that the neuronal and not the vascular effects are associated with escalation of cocaine intake in addiction whereas its vascular effect in PFC might contribute to cognitive deficits that increase vulnerability to relapse.

Memantine Attenuates Cocaine and neuroHIV Neurotoxicity in the Medial Prefrontal Cortex.

Individuals with substance use disorder are at a higher risk of contracting HIV and progress more rapidly to AIDS as drugs of abuse, such as cocaine, potentiate the neurotoxic effects of HIV-associated proteins including, but not limited to, HIV-1 trans-activator of transcription (Tat) and the envelope protein Gp120. Neurotoxicity and neurodegeneration are hallmarks of HIV-1-associated neurocognitive disorders (HANDs), which are hypothesized to occur secondary to excitotoxicity from NMDA-induced neuronal calcium dysregulation, which could be targeted with NMDA antagonist drugs. Multiple studies have examined how Gp120 affects calcium influx and how cocaine potentiates this influx; however, they mostly focused on single cells and did not analyze effects in neuronal and vascular brain networks. Here, we utilize a custom multi-wavelength imaging platform to simultaneously study the neuronal activity (detected using genetically encoded Ca2+ indicator, GcaMP6f, expressed in neurons) and hemodynamic changes (measured by total hemoglobin and oxygenated hemoglobin within the tissue) in the prefrontal cortex (PFC) of HIV-1 Tg rats in response to cocaine and evaluate the effects of the selective NMDA antagonist drug memantine on cocaine and HIV neurotoxicity compared to those of non-HIV-1 Tg animals (controls). Our results show that memantine improved cocaine-induced deficit in cerebral blood volume while also attenuating an abnormal increase of the neuronal calcium influx and influx duration in both control rats and HIV-1 Tg rats. Cocaine-induced neuronal and hemodynamic dysregulations were significantly greater in HIV-1 Tg rats than in control rats. With memantine pretreatment, HIV-1 Tg rats showed attenuated cocaine's effects on neuronal and hemodynamic responses, with responses similar to those observed in control rats. These imaging results document an enhancement of neuronal Ca2+ influx, hypoxemia, and ischemia with cocaine in the PFC of HIV-1 Tg rats that were attenuated by memantine pretreatment. Thus, the potential utility of memantine in the treatment of HAND and of cocaine-induced neurotoxicity deserves further investigation.

Oxycodone dose-dependently imparts conditioned reinforcing properties to discrete sensory stimuli in rats.

The aim of this study was to explore the psychopharmacological characteristics of opioid-induced conditioned reinforcement using oxycodone, a potent mu-opioid receptor agonist with known abuse potential. In differed groups of rats, passive intravenous infusions of oxycodone (100 infusions/3 h×6 sessions in total; 0, 0.01, 0.05 and 0.1 mg/kg/inf) were paired with an audio-visual stimulus and, subsequently, operant responding maintained by this conditioned stimulus was tested in extinction conditions. It was found that the oxycodone-paired stimulus maintained operant responding and that this effect was dependent on the number of conditioning sessions and on the conditioning dose. Responding maintained the oxycodone-paired stimulus could also be reinstated by both foot-shock stress and by oxycodone priming (0.25 mg/kg, SC). A conditioned place preference experiment (3 drug and 3 vehicle injections over 6 days; oxycodone: 0, 0.25, 2 and 5 mg/kg, SC) confirmed that stimuli associated with lower doses of oxycodone induce conditioned approach. Finally, two control experiments performed with chlordiazepoxide ruled out an interpretation of the oxycodone data based on drug-induced amnesia, and confirmed that operant responding for a drug-conditioned stimulus is observed only when the drug possesses unconditioned reinforcing properties. Therefore, the intravenous conditioned reinforcement procedure appears a useful method to study how opioid drugs impart reinforcing value to discrete environmental stimuli.

Ca2+ channel blockade reduces cocaine's vasoconstriction and neurotoxicity in the prefrontal cortex.

Cocaine profoundly affects both cerebral blood vessels and neuronal activity in the brain. The vasoconstrictive effects of cocaine, concurrently with its effects on neuronal [Ca2+]i accumulation are likely to jeopardize neuronal tissue that in the prefrontal cortex (PFC) could contribute to impaired self-regulation and compulsive cocaine consumption. Here we used optical imaging to study the cerebrovascular and neuronal effects of acute cocaine (1 mg/kg i.v.) and to examine whether selective blockade of L-type Ca2+ channels by Nifedipine (NIF) (0.5 mg/kg i.v.) would alleviate cocaine's effects on hemodynamics (measured with cerebral blood volume, HbT), oxygenation (measured with oxygenated hemoglobin, HbO2) and neuronal [Ca2+]i, which were concomitantly measured in the PFC of naive rats. Our results show that in the PFC acute cocaine significantly reduced flow delivery (HbT), increased neuronal [Ca2+]i accumulation and profoundly reduced tissue oxygenation (HbO2) and these effects were significantly attenuated by NIF pretreatment. They also show that cocaine-induced vasoconstriction is distinct from its increase of neuronal [Ca2+]i accumulation though both of them contribute to hypoxemia and both effects were attenuated by NIF. These results provide evidence that blockade of voltage-gated L-type Ca2+ channels might be beneficial in preventing vasoconstriction and neurotoxic effects of cocaine and give support for further clinical investigations to determine their value in reducing cocaine's neurotoxicity in cocaine use disorders.

Perseveration in the presence of punishment: the effects of chronic cocaine exposure and lesions to the prefrontal cortex.

Perseveration is the repetition of a previously appropriate response in a manner, or context, which is detrimental to the individual. Although both cocaine exposure and prefrontal cortex (PFC) dysfunctions have been implicated in perseverative-like behaviours, the underlying nature of the impairments has been debated. The current study tested whether chronic cocaine exposure and PFC lesions induce perseverative-like behaviours by causing insensitivity to punishment. Food-restricted male Sprague-Dawley rats were trained to respond for sucrose on concurrent schedules of reinforcement. After initial training, rats received either a sensitizing regimen of cocaine exposure, or excitotoxic lesions to subregions of the PFC. The test of perseveration involved a choice of responding between two levers associated with fixed ratio and progressive ratio (PR) schedules. Responding on the PR lever was punished by a 1 min timeout period. It was found that, unlike control subjects, those exposed to chronic cocaine, or with lesions to the medial prefrontal cortex, were significantly slower in adapting their responding to avoid punishment. The current study provides evidence that both cocaine exposure and lesions to the prefrontal cortex can increase perseverative-like responding, although the magnitude and permanence of these effects are contingent on the nature of the task.

Effect of food restriction on cocaine locomotor sensitization in Sprague-Dawley rats: role of kappa opioid receptors.

RATIONALE: The interaction between repeated cocaine exposure and food restriction on sensitization to the stimulatory effects of cocaine has not been characterized. OBJECTIVES: To compare cocaine sensitization in rats free fed and food restricted, and begin to explore the role of the stress-responsive dynorphin/kappa opioid system. METHODS: Male rats were maintained for 10 days on two feeding conditions: free fed or food restricted (85 % of free fed weight). Test 1 of locomotor reactivity to cocaine (3, 9, or 15 mg/kg, IP) was followed by a sensitizing regimen of cocaine exposure (0 or 30 mg/kg/day × 5 days, IP), by a 10-day drug-free period, and by Test 2 of reactivity to the same cocaine dose. In a second experiment, rats received an injection of norbinaltorphimine (nor-BNI; 0, 5 or 20 mg/kg, SC) 10 days prior to each locomotion test, and plasma corticosterone (CORT) was assessed after Test 2. RESULTS: On Test 1, it was found that food restriction enhanced locomotor responses to all doses of cocaine. On Test 2, it was found that free fed and food restricted animals displayed similar sensitized responses to cocaine. This, however, was not observed in nor-BNI-treated rats. Furthermore, 20 mg/kg nor-BNI reduced both the locomotor response to cocaine on Test 2 and the effect of cocaine and food restriction on CORT plasma levels. CONCLUSIONS: These results indicate that the interaction between cocaine sensitization and food restriction is not synergistic, and that it involves activation of kappa-opioid receptors.

The effects of acute and chronic steady state methadone on memory retrieval in rats.

RATIONALE: Although widely prescribed to treat opioid addiction, little is known about the possible side effects of methadone on memory functions. OBJECTIVES: The aim of this study is to compare the effects of acute and chronic methadone on memory retrieval in rats and to explore the selectivity of possible deficits. METHODS: Administration of acute (0, 1.25, 2.5, and 5 mg/kg SC) and chronic steady state methadone (0, 10, 30, and 55 mg/kg/day SC by osmotic mini-pump) was tested on recall of three different types of information: stimulus-reward (10-arm parallel maze), stimulus-response (8-arm radial maze), and stimulus-stimulus (Barnes maze). Acute and steady state methadone doses were also compared on tests of locomotor activity and reactivity to aversive stimuli (i.e., swimming and acoustic startle). RESULTS: In the stimulus-reward task, acute methadone impaired performance as a result of severe depression of locomotion. This motor deficit, however, was modulated by the motivational valence of environmental stimulation. In fact, acute methadone did not eliminate forced swimming behavior. In the stimulus-response and stimulus-stimulus tasks, accuracy was impaired independently of direct motor deficits, but rats were hyper-reactive to aversive stimulation and, in fact, 5 mg/kg enhanced acoustic startle. Importantly, chronic steady state methadone did not affect accuracy of memory retrieval, did not depress motor or swimming activity, and did not change startle reactivity. CONCLUSION: Only acute methadone impaired accuracy and/or performance on three tests of memory retrieval. These findings in rats suggest that memory deficits reported in methadone-maintained individuals may not be directly attributable to methadone.

Excitotoxic lesions to the prefrontal cortex of Sprague-Dawley rats do not impair response matching.

Perseveration refers to maladaptive persistence of behavior outside appropriate contexts and despite negative outcomes. In humans, perseveration is a symptom of a variety of psychiatric disorders. In rats, perseveration has been observed in reversal learning tasks following lesions of the prefrontal cortex (PFC). However, the exact nature of the impairment underlying this effect remains unclear. Male Sprague-Dawley rats were trained on a novel reversal task that requires switching between two rewarded options varying in effort (concurrent fixed and progressive ratios) necessary to obtain the reward. Following initial training, bilateral lesions of the dorsal PFC, medial PFC, or orbitofrontal cortex were produced by NMDA infusions. When animals were re-tested post-surgery, no significant impairments were found. These results indicate that, in trained rats, the PFC is not necessary for selecting responses on the basis of favorable effort-to-reward contingencies.

Effects of an estrogen receptor alpha agonist on agonistic behaviour in intact and gonadectomized male and female mice.

Gonadal hormones mediate both affiliative and agonistic social interactions. Research in estrogen receptor alpha (ERα) or beta (ERß) knockout (KO) mice suggests that ERα increases and ERß decreases male aggression, while the opposite is found for female ERαKO and ERßKO mice. Using a detailed behavioural analysis of the resident-intruder test, we have shown that the ERß selective agonist WAY-200070 increased agonistic behaviours, such as aggressive grooming and pushing down a gonadectomized (gonadex) intruder, in gonadally intact but not gonadex male and female resident mice, while leaving attacks unaffected. The role of acute activation of ERα in agonistic behaviour in adult non-KO CD1 mice is presently unknown. The current study assesses the effects of the ERα selective agonist 1,3,5-tris(4-hydroxyphenyl)-4-propyl-1H-pyrazole (PPT) on the social and agonistic responses of gonadally intact and gonadex male and female CD1 mice to a gonadex, same-sex intruder. PPT had few effects in gonadally intact mice, but seems to increase sex-typical aggression (i.e., attacks in males, other dominance-related behaviours in females) in gonadex mice. In untreated mice, we confirmed our previous findings that gonadally intact males attacked the intruder more than females, but females spent more time engaged in agonistic behaviour than males. As in our previous results, we observed that gonadex mice generally show behaviour patterns more like those of the gonadally intact opposite sex, while leaving overall levels of agonistic behaviour unaffected. Taken together, our current and previous results show that exogenous activation of ERα had no effects in gonadally intact mice, but increased sex-typical agonistic behaviour in gonadex mice, while ERß had no effects in gonadex mice, but increased non-attack agonistic behaviour in gonadally intact animals. This suggests that, as in social recognition, ERα may be necessary for the activation of agonistic responses, while ERß may play a modulatory role.

Effect of acute and repeated cocaine exposure on response matching capabilities of Sprague-Dawley rats responding for sucrose on concurrent schedules of reinforcement.

Cocaine exposure impairs the ability to match responding when rewarded and non-rewarded response options are reversed. However, it is unclear whether the impairment can also be observed when two rewarded responses differing in delay or magnitude of reward are reversed. Therefore, we tested the effect of acute (Experiment 1) and repeated (Experiment 2) cocaine on response matching between options dynamically varying in reinforcement schedule. Male Sprague-Dawley rats responded on concurrent fixed ratio 25 (FR25) and variable ratio 15 (VR15) schedules for sucrose. On tests, a progressive ratio (PR) schedule replaced the VR15, creating a within-session dynamic reversal point. In Experiment 1, acute cocaine (0, 1, 3 or 15mg/kg IP) did not alter response matching. In Experiment 2, rats chronically exposed to cocaine (30mg/kg/dayx5days, IP) were tested after a 10-day withdrawal period on three sets of FR25/PR matching tasks with varying rates of PR escalation. Cocaine pre-exposure significantly increased perseverative matching errors, although repeated testing compensated the impairment. These results suggest that prior exposure to cocaine can produce perseverative behavior even when animals are required to match two well-learned and rewarded response options. The implications for addictive behaviors are discussed.

FAAH inhibitor, URB-597, promotes extinction and CB(1) antagonist, SR141716, inhibits extinction of conditioned aversion produced by naloxone-precipitated morphine withdrawal, but not extinction of conditioned preference produced by morphine in rats.

Converging evidence suggests that the endogenous cannabinoid (eCB) system is involved in extinction of learned behaviours. Using operant and classical conditioning procedures, the potential of the fatty acid amide (FAAH) inhibitor, URB-597, and the CB(1) antagonist/inverse agonist, SR141716, to promote and inhibit (respectively) extinction of learned responses previously motivated by either rewarding or aversive stimuli was investigated. In the operant conditioning procedure (Expt. 1), rats previously trained to lever press for sucrose reward were administered URB-597 (0.3 mg/kg) or the CB(1) antagonist/inverse agonist SR141716 (2.5 mg/kg) prior to each of three extinction trials. In the conditioned floor preference procedure (Expts 2a-d), rats trained to associate morphine with one of two distinctive floors were administered one of several doses of the CB(1) antagonist/inverse agonist, AM-251 (Expt 2a) or URB-597 (Expt 2b and 2d) prior to each extinction/test trial wherein a choice of both floors was presented and prior to forced exposure to each floor (Expt 2c). In the conditioned floor aversion procedure (Expt. 3), rats trained to associate a naloxone-precipitated morphine withdrawal with a floor cue were administered URB-597 or SR141716 prior to each of 24 extinction/testing trials. URB-597 did not promote and SR141716 did not reduce extinction rates for sucrose reward-induced operant responding (Expt. 1) or morphine-induced conditioned floor preference (Expts. 2a-d). In contrast, URB-597 facilitated, whereas SR141716 impaired, extinction of the conditioned floor aversion (Expt. 3). These data support previous reports that the eCB system selectively facilitates extinction of aversive memories. URB-597 may prove useful in targeting extinction of aversively motivated behaviours.