Protracted withdrawal from alcohol and drugs of abuse impairs long-term potentiation of intrinsic excitability in the juxtacapsular bed nucleus of the stria terminalis.

The juxtacapsular bed nucleus of the stria terminalis (jcBNST) is activated in response to basolateral amygdala (BLA) inputs through the stria terminalis and projects back to the anterior BLA and to the central nucleus of the amygdala. Here we show a form of long-term potentiation of the intrinsic excitability (LTP-IE) of jcBNST neurons in response to high-frequency stimulation of the stria terminalis. This LTP-IE, which was characterized by a decrease in the firing threshold and increased temporal fidelity of firing, was impaired during protracted withdrawal from self-administration of alcohol, cocaine, and heroin. Such impairment was graded and was more pronounced in rats that self-administered amounts of the drugs sufficient to maintain dependence. Dysregulation of the corticotropin-releasing factor (CRF) system has been implicated in manifestation of protracted withdrawal from dependent drug use. Administration of the selective corticotropin-releasing factor receptor 1 (CRF(1)) antagonist R121919 [2,5-dimethyl-3-(6-dimethyl-4-methylpyridin-3-yl)-7-dipropylamino-pyrazolo[1,5-a]pyrimidine)], but not of the CRF(2) antagonist astressin(2)-B, normalized jcBNST LTP-IE in animals with a history of alcohol dependence; repeated, but not acute, administration of CRF itself produced a decreased jcBNST LTP-IE. Thus, changes in the intrinsic properties of jcBNST neurons mediated by chronic activation of the CRF system may contribute to the persistent emotional dysregulation associated with protracted withdrawal.

Mirtazapine treatment after conditioning with methamphetamine alters subsequent expression of place preference.

Methamphetamine (MP) is a widely abused psychostimulant. There are currently no FDA approved pharmacotherapies for the MP addict. The antidepressant, mirtazapine (Mirt) is a high affinity antagonist at several monoaminergic receptors that are affected by MP. This study evaluated the potential of Mirt as a therapeutic agent for MP addiction and described associated changes in neuronal signaling. A single pairing conditioned place preference (CPP) paradigm was utilized as a behavioral measure of MP-induced effects. Rats learned to associate unique environmental cues with the effects of 1.0 mg/kg (i.p.) MP (day 1) or saline (day 2). Mirt (5.0 mg/kg i.p.) was given in the home cage on day 3 and CPP was assessed on day 4. To evaluate signaling events that correlate with this behavior, brain tissue of these rats were dissected for immunoblot assays of extracellular signal-regulated kinase (ERK) and a transcriptional regulator, cAMP response element-binding protein (CREB) after the CPP test. During the CPP test, rats conditioned with MP spent more time in the environment associated with MP. Importantly, rats given Mirt did not express CPP. MP-induced CPP was associated with a decrease in phosphorylated CREB (pCREB) in the ventral tegmental area, and decreased phosphorylated ERK and pCREB in the nucleus accumbens and treatment with Mirt did not reverse these changes. No changes in signaling proteins were obtained from rats similarly treated with MP and Mirt, without exposure to cues of the conditioning paradigm. Overall, a post-conditioning treatment with Mirt can nullify MP-induced associative learning. However, additional studies are needed to ascertain the molecular events underlying this effect of Mirt.

CRF(1) receptor antagonists attenuate escalated cocaine self-administration in rats.

RATIONALE: Previous work suggests a role for stress-related corticotropin-releasing factor (CRF) systems in cocaine dependence. However, the involvement of activation of CRF(1) receptors in rats self-administering cocaine with extended access is unknown. OBJECTIVE: The current study examined whether CRF(1) receptor antagonist administration alters cocaine self-administration in animals given extended access. MATERIALS AND METHODS: Wistar rats (n = 32) acquired cocaine self-administration (0.66 mg/kg per infusion) in 1 h sessions for up to 11 days. Rats then were assigned to receive either daily short (1 h, ShA) or long (6 h, LgA) access to cocaine self-administration (n = 7-9 per group). Following escalation of intake, animals received one of two selective CRF(1) antagonists: antalarmin (6.3-25 mg/kg, i.p.) or N,N-bis(2-methoxyethyl)-3-(4-methoxy-2-methylphenyl)-2,5-dimethyl-pyrazolo[1,5a]pyrimidin-7-amine (MPZP; 3.6-27.5 mg/kg, s.c.). RESULTS: By day 11 of the escalation period, LgA rats increased their cocaine intake, reaching an intake level of 15.1 mg/kg, compared to 11.1 mg/kg in ShA rats, during the first hour of sessions. Antalarmin reduced cocaine self-administration at the highest dose selectively in the LgA group but not the ShA group. MPZP reduced cocaine intake both in LgA and ShA rats. However, MPZP did so at a lower dose in LgA rats than in ShA rats. Within the LgA group, MPZP decreased cocaine intake in the first 10 min (loading phase) as well as in the latter session intake (maintenance phase). CONCLUSION: The data suggest that hypersensitivity of the CRF system occurs with extended access to cocaine self-administration and that this altered CRF system may contribute to the increased motivation to self-administer cocaine that develops during psychostimulant dependence.

Effects of dose and session duration on cocaine self-administration in rats.

Previous studies showed that an extended 6-h session duration produced an increasing rate of cocaine self-administration in rats. The present study further investigated the effect of dose and session duration on cocaine self-administration. Eight groups of rats (4 doses x 2 session durations) self-administered one of four cocaine doses (0.25, 0.5, 1, and 2 mg/kg/injection) in either 1- or 6-h sessions under a fixed-ratio schedule. In another experiment, two other groups of rats self-administered 0.5 mg/kg/injection of cocaine in either 3- or 12-h sessions. Cocaine self-administration increased at all doses in 6-h sessions but not in 1-h sessions. Cocaine intake (milligram/kilogram) reached an asymptote earlier at a higher dose, but the rate of responding increased faster when the dose was lower. In ShA rats, the cocaine dose-response function was higher in rats at the two higher unit doses than at the lower doses. Cocaine self-administration increased in 6- and 12-h sessions, but not in 1- and 3-h sessions. The increase in self-administration was faster and greater in 12-h sessions than 6-h sessions. The data suggest that cocaine self-administration increases at various doses with prolonged access and that an increase in the rate of responding is positively and inversely associated with session duration and unit dose, respectively. Results also imply that cocaine intake reaches a ceiling faster at high doses even under short session duration. Therefore, high doses or prolonged access to cocaine are more likely to result in a pattern of cocaine intake that reflects compulsive use.

Extended access to nicotine self-administration leads to dependence: Circadian measures, withdrawal measures, and extinction behavior in rats.

The present study characterized nicotine intake, circadian patterns of food and water intake, precipitated somatic signs of withdrawal, and extinction of nicotine-seeking behavior in rats with 23-h access to intravenous self-administration (IVSA). Separate groups of animals were allowed access to nicotine IVSA (0.015, n = 9; 0.03, n = 14; 0.06, n = 16; mg/kg/0.1 ml infusion/s; fixed ratio 1) and trained to nosepoke for food and water 23 h/day for 40 consecutive days. Somatic signs of nicotine withdrawal were examined following saline or mecamylamine administration (1.5 mg/kg i.p.), and extinction of nicotine-seeking behavior was assessed. A dose-dependent decrease in lever responding and an increase in nicotine intake were observed, with the highest nicotine dose producing the lowest amount of lever responding and the highest amount of nicotine intake. Nicotine acutely reduced diurnal and nocturnal food intake, producing smaller and fewer meals, and an increased rate of eating. Differences in rate of nicotine intake between the light and dark phase decreased significantly, especially in rats receiving higher unit nicotine doses (0.03 and 0.06 mg/kg), along with long-term decreases in the circadian profile and amplitude of feeding. Mecamylamine precipitated robust withdrawal signs, the magnitude of which was positively correlated with the total amount of self-administered nicotine. Extinction of nicotine-seeking behavior was observed and was facilitated by removal of nicotine-associated cues. The results demonstrate that rats will self-administer nicotine to the point of producing dependence, as measured by somatic signs, resistance to extinction, and measures of food intake.

Escalation of methamphetamine self-administration in rats: a dose-effect function.

RATIONALE: The transition from stable to escalated drug intake has been demonstrated in rats self-administrating cocaine and heroin using a single dose of drug. OBJECTIVES: To investigate the prolonged exposure to methamphetamine self-administration and the effect of various training doses of methamphetamine on the changes of methamphetamine intake over a 21-day period. METHODS: Two groups of rats were trained in 1-h daily sessions of methamphetamine self-administration [0.033 mg/infusion (inf); approximately 0.066 mg/kg/inf]. Methamphetamine access was increased to 6 h in one group [Long Access (LgA)] or maintained at 1 h in another [Short Access (ShA)]. The same procedure was repeated in rats exposed to different training doses of methamphetamine (0.05, 0.1, and 0.2 mg/kg/inf). RESULTS: In LgA rats, total and first hour intake of methamphetamine significantly increased compared to ShA rats at various methamphetamine doses. LgA animals, at all doses in the second study, escalated intake to 8-9 mg/kg per 6-h session, with the most rapid escalation occurring at 3-5 days at a methamphetamine dose of 0.1 mg/kg/inf. CONCLUSIONS: The escalation of drug intake observed with extended access is produced at multiple doses of methamphetamine. The rapidity of escalation depends on the dose. Ultimately, all doses in the dose-response study engendered self-administration of the same amount of total drug in a 6-h session in the extended-access group. Results suggest that the rapidity of escalation is dependent on dose and has an upper limit of intake over a period of 21 days.

Role for hypocretin in mediating stress-induced reinstatement of cocaine-seeking behavior.

Hypocretin-1 and -2 (Hcrt-1 and Hcrt-2), also referred to as orexin-A and -B, are neuropeptides synthesized by a few thousand neurons in the lateral hypothalamus. Hypocretin-containing neurons project throughout the brain, with a prominent input to basal forebrain structures involved in motivation, reward, and stress. However, the role of hypocretins in addiction-related behaviors remains largely unexplored. Here we show that intracerebroventricular infusions of Hcrt-1 lead to a dose-related reinstatement of cocaine seeking without altering cocaine intake in rats. Hcrt-1 also dramatically elevates intracranial self-stimulation thresholds, indicating that, unlike treatments with reinforcing properties such as cocaine, Hcrt-1 negatively regulates the activity of brain reward circuitries. Hypocretin-induced reinstatement of cocaine seeking was prevented by blockade of noradrenergic and corticotropin-releasing factor systems, suggesting that Hcrt-1 reinstated drug seeking through induction of a stress-like state. Consistent with this interpretation, the selective Hcrt-1 receptor antagonist SB-334867 blocked footshock-induced reinstatement of previously extinguished cocaine-seeking behavior. These findings reveal a previously unidentified role for hypocretins in driving drug seeking through activation of stress pathways in the brain.

Nutrition knowledge and practices, and consumption of vitamin A--rich plants by rural Nepali participants and nonparticipants in a kitchen-garden program.

Food-based nutrition interventions, including kitchen gardens and nutrition education, offer a potentially sustainable approach to reducing multiple nutritional deficiencies, but they have been poorly evaluated in developing countries. In a poor region of the terai (the flat, subtropical agricultural region that borders on India) in rural Nepal, we developed and evaluated the impact of a nutrition program added to the Market Access for Rural Development (MARD) Project. The primary objective of the MARD Project was to augment household income by increasing the production of high-economic-value crops. The objective of the nutrition program was to increase vitamin A and iron intakes by promoting kitchen gardens (training, technical assistance, and seed distribution) and nutrition education. One-third of the kitchen-garden program participants also attended nutrition education or agricultural training sessions that were part of the MARD Project. The program was evaluated after 36 months by a cross-sectional nutrition survey in 430 MARD households with kitchen gardens and 389 non-MARD control households. The lack of knowledge about nutrition, including the causes, prevention, and treatment of night-blindness and anemia, was remarkable. However, compared with control households, the kitchen-gardens group had significantly more nutrition knowledge (38% vs. 13% knew one of the causes of night-blindness, and 17% vs. 3% knew one of the causes of anemia), were more likely to feed special complementary foods to infants and to preserve food, and consumed more of 16 types of home-produced micronutrient-rich vegetables and fruits. Although the cross-sectional nature of the study limits our ability to attribute these differences to the program, we observed a striking lack of nutrition knowledge in these communities, and a clear opportunity to increase the intake of vitamin A through home production of vitamin A-rich plants.