A new subcutaneously-implantable reservoir for sustained release of nicotine in the rat

Chronic nicotine reverses working memory deficits caused by lesions of the fimbria or medial basalocortical projection

Nicotine has been found in a variety of studies to improve performance in memory tasks. This study was conducted to determine if chronic nicotine administration is useful in counteracting the working memory deficits seen after lesions of the fimbria or the medial basalocortical projection. Rats were trained to asymptotic performance on a working memory version of the radial-arm maze. Then, they were given knife cut lesions of the fimbria or the medial basalocortical projection or underwent sham surgeries. At the time of surgery, rats in each treatment group were implanted with either nicotine-containing or placebo glass and Silastic pellets. Rats with fimbria or basalocortical lesions showed a significant decline in working memory performance. Chronic nicotine significantly improved choice accuracy in both lesioned and unlesioned rats. Nicotine treatment restored performance of the lesioned rats to control levels. These data show that in addition to improving memory performance in normal rats, nicotine can counteract lesion-induced memory impairments. Nicotine also may be useful for treatment of disease-related memory impairments such as seen in Alzheimer's disease.

Persistence of chronic nicotine-induced cognitive facilitation

Nicotine has been found in a variety of species and behavioral paradigms to improve memory performance. The beneficial effect of nicotine has been seen after both acute and chronic administration. Interestingly, improved performance has been seen 24 h after acute injection and for at least 2 weeks after chronic administration. However, it is not clear from previous studies whether the persistence of the improved performance represents a true carryover of the drug effect or is due to the behavioral experience while under nicotine's effect. The current study was conducted to determine whether the facilitating effect of nicotine on learning and memory performance could be seen after withdrawal even if there was no behavioral training during the period of chronic nicotine administration. Rats were administered nicotine chronically for 3 weeks but were not tested during that time. Starting 1 week after withdrawal they were trained on a working memory paradigm in an eight-arm radial maze. The nicotine-treated rats started out at control-like levels of performance, but showed significantly faster learning as detected by three different measures of choice accuracy. By the final phase of testing the control subjects had caught up with the nicotine-treated rats. After the acquisition phase, acute challenges with the nicotinic and muscarinic antagonists, mecamylamine and scopolamine, did not elicit any differential effects in the nicotine-treated and control groups. The current study demonstrated that nicotine-induced cognitive facilitation persists for at least 4 weeks after withdrawal and does not depend upon behavioral test experience under the influence of the drug. The mechanism for this persisting effect is not currently understood.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic nicotine treatment changes differentially the effects of acute nicotine on the three main dopamine metabolites in mouse striatum

The effect of chronic treatment with nicotine on striatal dopamine metabolism was studied in mice by measuring the striatal concentrations of dopamine and its metabolites 3-methoxytyramine (3-MT), 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA). (-)-Nicotine was administered for 7 days using subcutaneously implanted nicotine releasing reservoirs. The release of nicotine was confirmed by measuring nicotine and cotinine concentrations in the plasma. To study the possible tolerance induced by chronic nicotine treatment, acute challenge doses of (-)-nicotine (either 3 mg/kg given once or 1 mg/kg repeated 4 times at 30 min intervals) were given to mice on the 7th day after the implantation. At an ambient temperature of 20-22 degrees C, acute nicotine treatment induced marked hypothermia (-5.2 to -6.7 degrees C) in both chronic nicotine treated and control mice, an effect that was prevented by elevating the ambient temperature to 32-34 degrees C. Chronic nicotine treatment did not per se alter striatal dopamine metabolism. Acute nicotine administration altered the striatal dopamine metabolism in a temperature-dependent manner. In mice kept at 20-22 degrees C, the DOPAC concentration rose slightly but concentrations of 3-MT and HVA fell, indicating a decrease in the release of dopamine. In contrast, in mice kept at 32-34 degrees C the DOPAC and HVA concentrations were clearly elevated by acute nicotine, whereas the concentration of 3-MT was not altered. In these normothermic mice chronic nicotine pretreatment did not alter the effects induced by acutely administered nicotine.(ABSTRACT TRUNCATED AT 250 WORDS)

Chronic nicotine and withdrawal effects on radial-arm maze performance in rats

Rats were tested for choice accuracy in an eight-arm radial maze during and after chronic administration of nicotine via subcutaneously implanted glass and Silastic capsules. Nicotine administration significantly improved choice accuracy relative to controls. The effect gradually became apparent over the first 2 weeks of exposure and persisted through the third week. Surprisingly, the significant facilitation of the nicotine-treated rats relative to controls continued for 2 weeks after the end of nicotine administration. No effects of nicotine were seen on choice latency or the strategy to make adjacent arm entries.

Chronic nicotine induces a specific appetite for sucrose in rats

Thirty female albino rats were implanted with subcutaneous pellets releasing nicotine or amphetamine in order to study the effects of chronic pharmacological treatment on food intake and body weight. The pellets were removed after tolerance (a decrease in anorectic properties of the drugs) had developed. Nicotine administration produced a specific appetite for sucrose both during and following treatment (p less than 0.05).

A device for the sustained release of nicotine in the mouse

A subcutaneously-implantable reservoir for the sustained release of nicotine in mice is described. The device, dubbed INRm to differentiate it from an earlier Implantable Nicotine Reservoir for Rats (INRr), is a small glass cup sealed with Silastic polymer. Three sizes are described, which release 0.75-2.05 mg of nicotine per 24 hours. When implanted into mature CD-1 female mice, the largest device produces blood nicotine levels of 445 ng/ml, which remain relatively stable for at least 19 days. These blood nicotine levels produce no weight loss and minimal body temperature reduction over the time period of testing. INRms, like the INRr, are nontoxic, reproducible, inexpensive, and adaptable for behavioral, pharmacological, and toxicological studies of nicotine in mice.

Behavioral effects of acute hexamethonium in rats chronically intoxicated with nicotine

To investigate the effects of chronic nicotine administration on feeding behavior, hexamethonium, a nicotinic blocker with mainly peripheral actions, was acutely given to rats during and after chronic nicotine administration. Nicotine decreased both the time spent investigating the food and the amount of food consumed. It also decreased the time spent rearing and grooming and increased the time spent resting. These behaviors returned to control levels after nicotine withdrawal. During nicotine administration, 10 mg/kg of hexamethonium increased the amount of time the nicotine-treated rats spent investigating the food but did not change the amount of food actually eaten. These data show that predominantly peripheral nicotinic blockade can partially alleviate the effects of chronic nicotine administration of feeding behavior, suggesting that at least some of the effects of nicotine on feeding are peripheral. The finding that the investigational and consummatory aspects of feeding behavior can be pharmacologically differentiated implies that some aspects of their neural control may be distinct.

Chronic nicotine and withdrawal effects on body weight and food and water consumption in female rats

Female rats were used to examine the effects of chronic nicotine administration and withdrawal on food and water consumption and body weight. Rats with chronic nicotine pellet implants consumed significantly less food and water than controls for the first five days and then gradually returned to control levels of consumption. The lowest level of body weight was reached on day 9 after which there was a slow return to control weights by day 21. When the nicotine pellets were removed from the short-term exposure group on day 14, they showed significant hyperphagia and hyperdipsia and a very rapid weight gain for the next several days, which clearly outpaced the recovery of weight in the long-term nicotine exposure group. These results show that in female rats changes in weight during chronic nicotine administration and withdrawal are accompanied by changes in rates of consumption. In addition, nicotine withdrawal can cause hyperphagia and hyperdipsia even though levels of consumption had previously returned to control levels and even though the route of nicotine administration was not oral.

Ethanol intake increases during continuous administration of amphetamine and nicotine, but not several other drugs

Groups of rats, acclimated to drinking both water and 10% v/v ethanol were implanted with a variety of slow-release devices containing d-amphetamine (d-amp), nicotine, caffeine, phencyclidine (PCP), secobarbital, LSD, mescaline or haloperidol. Ethanol intake was elevated only during treatment with d-amp or nicotine; none of the other drugs affected ethanol consumption even though the amounts of all drugs released were pharmacologically sufficient to affect behavior. Nicotine treated rats were not simply seeking calories provided by the EtOH solution, since nicotine treatment did not enhance intake of a distinctively flavored solution isocaloric to 10% ethanol. These results support a self-medication model of ethanol intake.