Methodology for coupling local application of dopamine and other chemicals with rapid in vivo electrochemical recordings in freely-moving rats.

Methodology is presented for constructing and using an electrode/microcannulae assembly that allows in vivo electrochemical measurements coupled with local application of dopamine (DA) and other chemicals in the unanesthetized freely-moving rat. Rats were implanted with a voltammetric electrode constructed of a carbon fiber sealed in fused silica tubing attached to a pair of stainless steel guide cannulae, into which fused silica injection cannulae were inserted for local application of DA and other chemicals. Precise delivery of nanoliter volumes was accomplished using a syringe drive combined with a fluid swivel to deliver the solutions to the injection cannulae. A newly-designed miniature potentiostat connected to a commutator via a modular telephone jack assembly allowed for high-speed chronoamperometric electrochemical recordings in freely-moving rats. Initial experiments characterized the in vitro electrochemical recording characteristics of the voltammetric electrode. In vivo studies were also carried out to study clearance of locally-applied DA and of potassium-evoked endogenous DA in the striatum and nucleus accumbens of freely-moving rats. In addition, the effects of chloral hydrate anesthesia on DA clearance signals in the nucleus accumbens were investigated. Moreover, the stability and reproducibility of this recording technique for measuring exogenous DA clearance was verified over a period of 5 days. Finally, the concurrent effects of systemic cocaine injection on DA uptake in nucleus accumbens and locomotor activity were examined. These studies support the conclusion that the methodology described herein allows for rapid chronoamperometric electrochemical recordings in freely-moving rats with precise microapplications of DA and other chemicals combined with concurrent measures of animal behavior.

Effects of the calcium channel blocker nimodipine on nicotine-induced locomotion in rats.

The effects of nimodipine, an L-type calcium channel antagonist, on nicotine-induced locomotor activity were investigated in drug-naive rats. Nicotine (0.4 mg/kg i.p.) produced significant increases in locomotion following acute administration. However, when rats were given injections of nimodipine (5, 10, or 20 mg/kg i.p.) 1 h prior to the test drug, nicotine-induced locomotor activity was altered. Nimodipine 5 mg did not significantly block locomotor activity produced by nicotine. In contrast, pretreatment with 10 and 20 mg nimodipine significantly blocked nicotine-induced locomotor activity. These findings clearly indicate that nicotine-induced locomotion is altered by nimodipine in a dose-dependent fashion. Results further suggest that the effect of nicotine on locomotion is calcium-dependent.

Nicotine effects on dopamine clearance in rat nucleus accumbens.

In vivo voltammetry was used to measure the clearance to exogenously applied dopamine (DA) in the nucleus accumbens following acute systemic nicotine administration in urethane-anesthetized rats. The IVEC-5 system was used for continuous in vivo electrochemical measurements. A finite amount of DA was pressure-ejected (25-100 nl, 200 microM barrel concentration) at 5-min intervals from micropipettes (tip diameter, 10-15 microns) positioned 250 +/- 50 microns from the recording electrode. The peak DA concentration after each DA ejection was significantly decreased in rats following nicotine, but not in rats given saline. In addition, when mecamylamine was administered 20 min before nicotine it clearly antagonized nicotine effects. These results suggest that nicotine may actually facilitate DA transporter systems within the nucleus accumbens.

Nicotine enhances dopamine clearance in rat nucleus accumbens.

1. Adult male rats were urethane-anesthetized and prepared for acute in-vivo voltammetric recording in the nucleus accumbens. 2. Small amounts of 200 uM dopamine were pressure ejected near the tip of the recording electrode at 5-min intervals, while the peak concentration and time course of dopamine clearance were measured voltammetrically. 3. After stable peak amplitudes were established, nicotine (0.4 mg/kg) was injected systemically. 4. Dopamine peak amplitudes decreased following nicotine injection, presumably due to enhanced dopamine reuptake.

Acute and chronic nicotine effects on measures of activity in rats: a multivariate analysis.

Nicotine has been reported to increase or decrease measures of activity in rats, including locomotor activity and rearing. Nicotine dose and repeated exposure to nicotine are known to be important factors in determining the effects on locomotor behavior. Less information has been gathered on rearing and other measures of activity. Rats were tested repeatedly, once per day, in Digiscan automated activity analyzers that reported 19 measures of activity. Each rat was given the same drug and dose each day, either saline or 0.1, 0.2, or 0.4 mg/kg nicotine. The 19 measures were combined or modified to produce 14 measures that were examined using factor analysis to help select the most independent measures. Four measures were selected to describe the effects of dose and to compare day 1 results with day 5 results. Total distance moved was increased in a dose-related fashion and was greater on day 5 than on day 1. Rearing was increased at low doses and decreased at high doses on both days. Stereotypy was increased approximately the same amount by all three doses, and was greater on day 5 than on day 1. Center time was increased by the highest dose on both days. These results once again point out the influences of repeated testing and repeated nicotine exposure on behavior. They may also help to clarify why some studies have reported that both ambulation and rearing are increased after nicotine whereas others find opposite effects.

Acute tolerance to the locomotor stimulant effects of nicotine in the rat.

Studies of peripheral nicotinic receptors have revealed that, after an initial agonist action, the receptors remain inhibited either through continued depolarization blockade due to continued presence of the agonist or through a brief inactivation of the receptor following its activation. If a similar phenomenon occurs at central nervous system nicotinic receptors, then behavioral responses to nicotine should exhibit an acute tolerance (tachyphylaxis). Groups of rats were given either saline or 0.2 mg/kg nicotine injections at 20-min intervals in photocell activity cages. A progressive decline in the locomotor responsiveness to nicotine was observed. The time course of this acute tolerance was observed in other rats given initial 0.2 mg/kg nicotine injections followed at differing time intervals by second 0.2 mg/kg nicotine test injections. The secondary antagonism to nicotine's locomotor stimulant effects was maximal at 45-60 min and recovered by 90-120 min. The locomotor response to 0.2 mg/kg nicotine test injections was observed in other rats following exposure to 1.8 mg/kg nicotine, and the behavioral response was attenuated for more than 5 h.

Chronic voluntary nicotine drinking enhances nicotine palatability in rats.

The response of rats to nicotine solutions was examined with the brief-exposure, taste reactivity test and a two-bottle, 24-hr preference test. In Experiment 1, naive nondeprived rats were administered intraoral infusions (0.8 ml infused during 1 min) of distilled water and 1 microgram/ml, 5 micrograms/ml, 10 micrograms/ml, 25 micrograms/ml, 50 micrograms/ml, and 100 micrograms/ml nicotine. The oral motor, taste reactivity (TR) responses of the rats were recorded during the infusion. Nicotine solutions up to a concentration of 50 micrograms/ml elicited a number of ingestive TR responses similar to that by water. Ingestive responses significantly decreased and aversive TR responses significantly increased in response to 100 micrograms/ml nicotine. On the basis of these results, two-bottle preferences for water versus 1 microgram/ml, 5 micrograms/ml, and 0 microgram/ml (water control group) nicotine were measured in three groups of naive rats. Rats initially showed an equal preference for 0 microgram/ml and 1 microgram/ml nicotine. After 16 days of exposure, however, rats developed a significant preference for 1 microgram/ml nicotine. The preference ratio for 5 micrograms/ml nicotine significantly increased during the experiment, but the preference ratio remained significantly less than that for 1 microgram/ml and 0 microgram/ml nicotine solutions. Last, TR responses elicited by intraoral infusions of 1 microgram/ml and 5 micrograms/ml nicotine were then measured in these rats having had the two-bottle experience. Rats showing a two-bottle preference for the 1 microgram/ml nicotine solution displayed significantly more ingestive TR responses to 1 microgram/ml and 5 micrograms/ml nicotine than did the control rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Nicotine induced locomotor activity in rats: the role of Pavlovian conditioning.

Rats repeatedly exposed to small doses of nicotine will demonstrate a significant augmentation of locomotor activity in response to a subsequent test dose of nicotine. A sensitization of brain tissue is hypothesized to account for this effect but Pavlovian conditioning might also be a major factor. Therefore the present study assessed the possible role of Pavlovian conditioning in this nicotine effect. Two experiments were conducted. In the first, subjects were administered either saline or nicotine in either their home cages or in activity test cages for five days. All subjects were then tested in the activity test cages on day six. In the second experiment rats were administered either nicotine or saline in the presence of a complex stimulus and later tested for response to nicotine alone and the complex stimulus alone. Results from these experiments indicate that Pavlovian conditioning does not play a major role in nicotine's effect on locomotor activity.

Chronic nicotine and locomotor activity: influences of exposure dose and test dose.

Repeated exposure to nicotine increases both the number of central nicotinic receptors and the behavioral stimulant effect of nicotine. In the present experiments, the behavioral response to nicotine was examined in photocell activity cages. Groups of rats were tested using doses from 0.1 to 1.6 mg/kg both before and after all rats were exposed for 5 days to a common dose of 0.2 mg/kg/day. Prior to the 5-day exposure, there was a dose-related stimulant response to nicotine, with a maximum response seen at 0.4 mg/kg. After the 5-day exposure, the dose-effect curve was shifted upward, so that greater stimulation was produced at each test dose of nicotine. Other groups of rats were exposed for 5 days to doses of nicotine ranging from 0.01 to 0.30 mg/kg/day. On the 6th day all rats received a common test dose of 0.2 mg/kg and their response was measured in the activity cages. In animals exposed to 0.01 mg/kg/day, the test day response was not different from saline controls, but the groups exposed to higher doses showed increased stimulation in response to the common test dose. Measurements of nicotinic receptor binding using [3H]-acetylcholine found increased binding in groups receiving 0.03 mg/kg/day or more, but not in the group that received 0.01 mg/kg/day. The correspondence between the doses that increase behavioral stimulant reactions to nicotine and the doses that increase nicotinic binding suggest that increased receptor numbers may be responsible for the increased behavioral stimulation. However, rats given high doses (1.6 mg/kg, twice per day) did not show increased behavioral stimulation to a test dose of 0.2 mg/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

The effects of d-amphetamine, alpha-flupenthixol, and mesolimbic dopamine depletion on a test of attentional switching in the rat.

A test of attentional switching was devised for the rat in which it obtained sucrose reinforcement by an appropriate nose-poke response that discriminated which of two visual events terminated first, in a specially designed chamber. The effect of mesolimbic dopamine depletion (to 20% of control values) produced by infusions of 6-hydroxydopamine (6-OHDA) into the nucleus accumbens (N. Acc) on stable discrimination was measured alone and in the presence of a range of doses of d-amphetamine (0.4-2.3 mg/kg IP). The 6-OHDA lesion of the N. Acc impaired postoperative performance transiently by reducing choice accuracy and slowing response latency. By post-operative days 12-16, however, performance recovered to control levels and was not differentially affected by a manipulation of task difficulty. d-Amphetamine produced dose-dependent performance impairments, which were antagonised by the 6-OHDA treatment. In a second group of N. Acc lesioned rats, the neuroleptic alpha-flupenthixol (0.1-1.0 mg/kg) led to fewer trials being completed and longer latencies than in the sham-operated control group. The results are discussed in terms of the possible attentional mechanisms underlying the d-amphetamine-induced disruption of performance mediated by the N. Acc and of the implications for psychopathology resulting from possible dysfunction of this region.

Exposure to nicotine enhances the behavioral stimulant effect of nicotine and increases binding of [3H]acetylcholine to nicotinic receptors.

Rats were given daily injections of nicotine sulfate in doses ranging from 0.1 to 0.4 mg/kg. The behavioral effect of these injections was measured as locomotor activity in photocell cages. Repeated administration of the same dose to each rat resulted in an enhancement of the stimulant effect of nicotine. This enhanced behavioral effect was quite pronounced within 5 days of repeated injection. Tissue from the cerebral cortex of these rats, exposed to nicotine for 5 days, was assayed for binding of [3H]acetylcholine to nicotinic receptors. These relatively small doses of nicotine resulted in 18-26% increases in cortical nicotinic receptors, compared to saline-treated rats. Rats exposed to 0.2 mg/kg of nicotine for 5 days and then given saline for 7 days still showed an enhanced behavioral response to nicotine on the eighth day after exposure, and nicotinic binding in the cortex was still elevated. However, 21 days after exposure to nicotine both the behavioral response to nicotine and the binding values had returned to the same values as those of saline-treated rats. These data imply that increased binding of [3H]acetylcholine to nicotinic sites and the enhanced behavioral effect of nicotine are functionally linked.

Brain norepinephrine depleting lesions selectively enhance behavioral responsiveness to novelty.

The noradrenergic innervation of the forebrain by cells from the locus coeruleus (LC) was interrupted by either electrolytic lesions of the LC or 6-hydroxydopamine (6-OHDA) lesions of the dorsal noradrenergic bundle (DB). Animals so treated were then tested in a modified open field test designed to measure responsiveness to environmental novelty and also tested for food consumption in their home cages. In addition, DB lesioned animals were tested in photocell activity cages for both their initial locomotor response to the novel cages as well as their activity level after habituation. The DB lesioned animals were also tested for rates of acquisition and extinction of an operant response. The DB lesion produced no deficits in either the acquisition or the extinction of a food rewarded operant response. The DB lesion did reduce the initial amount of locomotor activity in response to introduction to the activity cages but did not alter the rate of habituation of the locomotor response nor the "basal" level of activity at the end of two hr of exposure. Neither lesion affected the amount of food eaten by 24 hr-fasted animals in their home cages during the first 15 min. When fasted prior to being given access to food in a novel open field, however, both lesions resulted in decreased food consumption and decreased amounts eaten per approach to the food pedestal. The DB lesion, but not the LC lesion, resulted in decreased rearing and grooming in this setting.(ABSTRACT TRUNCATED AT 250 WORDS)

Taste and nicotine as determinants of voluntary tobacco use by hamsters.

Syrian hamsters consumed a commercial chewing tobacco in daily amounts equivalent to 2.6% of their body weights, even though food and water were always available. Daily intake increased gradually to this level over a period of 4 months. Commercial tobaccos contain a variety of flavoring agents, including sugars. Moistened, unflavored tobacco was consumed in much smaller amounts than the commercial tobacco. Addition of sucrose to the unflavored tobacco produced a concentration-dependent increase in daily consumption. Addition of nicotine to the drinking water did not affect daily fluid intake or food consumption, but produced a selective, dose-related decrease in consumption of the commercial tobacco. These results indicate interactive roles for taste and nicotine in controlling the daily, voluntary, high-level use of tobacco by hamsters.

Enhanced behavioral response to nicotine in an animal model of Alzheimer's disease.

Three groups of rats received either kainic acid or vehicle in the ventral pallidum or no operation, and were then tested in photocell activity cages following recovery from surgery. Locomotor activity was measured following injections of saline, nicotine (0.1, 0.2, 0.4 mg/kg) or d-amphetamine (0.5, 1.0 mg/kg). The lesioned rats showed an enhanced locomotor response after injections of nicotine compared with sham operated or unoperated controls. In contrast, both lesioned and control rats showed increased activity after amphetamine; this effect was not influenced by the lesion. Since these lesions are known to produce neurochemical and cellular changes resembling those seen in human Alzheimer's disease, this increased response to nicotine might also be found in Alzheimer's patients and serve as the basis for a diagnostic test.

Changes in locomotor response to beta-endorphin microinfusion during and after opiate abstinence syndrome--a proposal for a model of the onset of mania.

Beta-Endorphin (0.3 or 0.6 nanomoles) was infused into the A10-ventral tegmental area (VTA) of male Wistar rats previously treated for 6 days with either morphine sulfate or lactose via subcutaneously implanted silastic pellets. Beta-Endorphin microinfusions occurred at 24 and 96 hours after pellets were removed. Profound changes in locomotor response to beta-endorphin were found, with morphine-pretreated rats showing a spontaneous switch from hyporesponsiveness to hyperresponsiveness over 72 hours, compared to lactose-pretreated controls. These findings may reflect on current biochemical theories regarding the "switch" process in bipolar affective disease. The data can be viewed within a heuristic model of receptor changes which may underlie the transition from depression to mania.

Drug effects on discrimination performance at two levels of stimulus control.

The effects of several doses of d-amphetamine, chlordiazepoxide (CDP), chlorpromazine (CPZ), LSD, pentobarbital, and scopolamine were examined in rats trained to respond to the brighter of two keys. On each of the 100 trials during a daily session, the rat pressed the key that was brighter (correct key) and received a food pellet, or pressed the incorrect key and terminated the trial without food, or pressed neither key for 10s, allowing the trial to terminate. Within a session, trials were mixed randomly such that on 50 trials the incorrect key was not lit (easy trials) and on 50 trials the incorrect key was dimly lit (difficult trials). Amphetamine (0.5-2.0 mg/kg) reduced percent correct responses, with a greater effect on difficult than on easy trials. CDP (4.0-16.0 mg/kg) and pentobarbital (2.0-16.0 mg/kg) reduced percent correct responses on the difficult trials at the highest doses tested. Scopolamine (0.12-1.0 mg/kg) reduced both percent correct (more so on the difficult trials) and percent of trials on which a response was made, in a dose-related fashion. CPZ (1.0-4.0 mg/kg) reduced trial responding at 2.0 and 4.0 mg/kg and reduced percent correct on the difficult trials at 4.0 mg/kg. LSD (0.08-0.32 mg/kg) did not significantly alter behavior in this study.

Pentobarbital, promazine, d-amphetamine, and scopolamine effects on behavior under multiple and primed schedules of reinforcement.

Pigeons responded under compound fixed-interval (FI) fixed-ratio (FR) schedules of food presentation. Distinctive discrimininative stimuli were either continuously present during each component schedule (multiple FI FR) or were present only for a brief period at the beginning of each component (primed FI FR). Similar rates and patterns of responding were maintained under the multiple and primed schedules. Pentobarbital, scopolamine, and d-amphetamine decreased FR responding, but promazine had little effect at the doses studied. d-Amphetamine and promazine increased FI responding at certain doses, pentobarbital had little effect, and scopolamine decreased responding. There were no systematic differences in the effects of drugs under the multiple and primed schedules, in spite of the differences in discriminative stimuli under the conditions.

LSD and d-amphetamine effects on fixed interval responding in the rat.

Food-deprived rats were trained to press a key which produced a food pellet for the first press after 3 min had elapsed (FI 3 min). Daily sessions consisted of 10 such intervals. Graded doses of LSD (0.04 - 1.28 mg/kg) and a d-amphetamine (0.5 - 2.0 mg/kg) were given 30 min before sessions. LSD produced a decrease in response rate at doses of 0.32 mg/kg and above, but did not disrupt the typical FI pattern of responding except at the highest dose (1.28 mg/kg). Amphetamine did not significantly alter the overall response rate, but caused a dose-related disruption of the FI response pattern, with previously low response rates increased more than higher rates, and occasional decreases in the previously highest rates. The experiment was repeated using the same rats responding on a multiple FIFR schedule. The presence of a 2000 Hz tone signalled FR periods; the tone was absent during FI periods. During the FR components, a pellet was produced after 30 responses had been emitted. The FI components were unchanged. LSD (0.08 - 0.32 mg/kg) again produced decreases in FI rate without altering the pattern, and amphetamine again altered the FI pattern without significantly changing overall rate.