Self-administration of heroin, acetylmethadol, morphine, and methadone in rhesus monkeys.

Heroin, α-$\text{l}$-acetylmethadol (LAAM), morphine, and methadone each maintained self-administration in rhesus monkeys. The order of relative potency was heroin ≥ LAAM > morphine ≥ methadone. Total daily drug intake increased as dose per injection increased; maximum daily intake was inversely related to relative potency. At high doses, self-injection of methadone and LAAM caused stupor and/or respiratory failure in some monkeys. These toxic effects were partly or completely reversible by naloxone.     

Second-order schedules of drug injection.

Key-press responding of squirrel monkeys produced intravenous injections of cocaine under two simple types of schedule. Under a fixed ratio schedule, every 30th response produced an injection; steady responding at high rates of over one per second were maintained during each fixed-ratio component. Under a fixed-interval schedule, the first response occurring after a fixed time of 5 min produced an injection; there was a pause at the start of each interval and then progressively increasing responding until cocaine was injected at the end of the interval. Both squirrel monkeys and rhesus monkeys also were studied under second-order schedules of drug injection. Under one type of second-order schedule, studies only in squirrel monkeys, completion of each fixed-interval component produced only a 2 sec light; completion of the 10th fixed-interval component produced the brief light and an intravenous injection of cocaine. Under a second type of second-order schedule, each fixed-ratio component completed during a fixed time interval (5 or 60 min) produced only a 2-sec light; the first fixed-ratio component completed after the interval of time elapsed produced the brief light and an intravenous (squirrel monkeys) or intramuscular (rhesus monkeys) injection of cocaine. Under both types of second-order schedules, repeated sequences of responding were maintained during each session and characteristic fixed-interval or fixed-ratio patterns of responding were controlled by the brief visual stimuli.     

Effect of isradipine,a dihydropyridine-calcium antagonist on I.V. self-administration of morphine in rats

The effect of dihydropyridine calcium channel antagonist isradipine (PN 200-110) on morphine reinforcement has been investigated using i.v. self-administration test in rats. Rats were given the opportunity to self-administer a solution of morphine (1 mg/Ml, i.v.) in a 1 hr limited access paradigm (FR = 1). Within 5–7 days rats had learned to self-administer approximately 1 mg of morphine in 1 hr as evidenced by a plateau of responding. The administration of isradipine (1.2, 2.5 and 5.0 mg/kg s.c.) 90 min before the morphine self-administration session, induced dose-dependent increase in the number of morphine self-infusions with respect to basal values. This response pattern was very similar to the one observed when morphine solution was substituted by saline in trained rats not treated with isradipine. The results indicate that isradipine inhibits partially the reinforcing properties of morphine in self-administration test.     

Fewer peak trials per session facilitate acquisition of peak responding despite elimination of response rate differences

It has been shown in previous research [Kaiser, D.H., 2008. The proportion of fixed interval trials to probe trials affects acquisition of the peak procedure fixed interval timing task. Behav. Process., 77 (1), 100-108] that rats acquired peak responding sooner when fewer peak trials were presented during sessions of training with the peak procedure timing task. One potential problem with that research was that there were large differences in response rates among the groups. The present experiment attempted to examine the effect of proportion of peak trials when differences in response rate were controlled. Two groups of rats were each simultaneously tested with two versions of the peak procedure. One group was tested with 10% peak trials per session, and the other group was tested with 50% peak trials per session. For both of the groups, one of the panel lights and levers was associated with the traditional peak procedure. The other panel light and lever was associated with a similar peak procedure; however, reinforcement was provided at the end of each peak trial. This manipulation eliminated differences in response rate among the groups, however, Group 10% acquired peak responding more quickly than Group 50%, effectively replicating previous work in the absence of a response bias.     

Alteration of ethanol self-administration by naltrexone

The effect of naltrexone HC1 (NLTRX) on the reinforcing properties of ethanol (EtOH) was evaluated with intravenous self-administration (IVSA). Eight drug-naive, male, 3.5–5.0 Kg rhesus monkeys ($\text{M. mulatta}$) were selected for: spontaneous acquisition of EtOH IVSA, consumption of at least 1.0 gm/Kg/day of EtOH during daily 4 hr. IVSA test sessions, and extremely low daily variability (10%) of EtOH intake during a 30 day control period. The selected subject group received intramuscular injections of either saline (SAL) (1.0 ml) or NLTRX (1, 3, 5 mg/Kg) 30 minutes before each test session. SAL was administered for 10 consecutive days and each NLTRX dose for 15 consecutive days. SAL phases were alternated with the NLTRX phases. NLTRX pretreatment produced lower levels of EtOH IVSA than those observed during SAL pretreatment phases. The magnitude of the suppression of EtOH IVSA corresponded to the NLTRX dose and was statistically significant following both 3 mg/Kg (p<0.05) and 5 mg/Kg (p<0.01) doses. NLTRX pretreatment produced transient increases in EtOH IVSA during the first 5 days of treatment, followed by significant decreases for the next 10 days. These data suggest that the blockade of opiate receptors by NLTRX in rhesus monkeys apparently decreases the reinforcing effects of EtOH measured with IVSA techniques.     

Sensitization enhances acquisition of cocaine self-administration in female rats: Estradiol further enhances cocaine intake after acquisition

Cocaine self-administration in rodents has been used widely as a preclinical model of cocaine use in humans. In laboratory animals, estradiol enhances behavioral sensitization to cocaine and the acquisition of cocaine self-administration in female rats. The rewarding effect of cocaine has been shown to be enhanced following behavioral sensitization in male rats. This experiment examined whether behavioral sensitization to cocaine would promote cocaine-taking behavior in female rats, and whether estradiol could further modulate cocaine-taking behavior in cocaine-sensitized rats. Ovariectomized female rats were pretreated with either cocaine or saline for 4 days per week for 3 weeks. Self-administration sessions started 2 weeks after the last dose of drug. Female Sprague-Dawley rats received either estradiol or oil 30 min prior to the start of each session and self-administration was carried out 5 days per week for 4 weeks. The dose of cocaine self-administered each week was as follows (in mg/kg/infusion): week 1, 0.1; week 2, 0.1; week 3, 0.15; and week 4, 0.4. The rats that received cocaine pretreatment took fewer days to acquire cocaine self-administration and took more cocaine than rats that received saline pretreatment. Estradiol enhanced cocaine intake during the last six self-administration sessions after acquisition but did not affect acquisition of self-administration at the lowest doses of cocaine used. In conclusion, cocaine sensitization promotes the acquisition of cocaine self-administration in female rats. Furthermore, prior cocaine experience is more powerful than estradiol at enhancing acquisition, while estradiol enhances intake of cocaine after acquisition of self-administration.     

Effects of single and multiple injections of ketamine hydrochloride on serum hormone concentrations in male cynomolgus monkeys

Using simulated short- and long-term effect studies, we evaluated the effect of ketamine anesthesia on serum cortisol, testosterone, and immunoreactive luteinizing hormone (ILH) and bioactive LH (BioLH) concentrations in adult male cynomolgus monkeys. Cortisol, testosterone, and ILH were measured by use of radioimmunoassay, and BioLH was measured by use of a radioreceptor assay method. For the acute effect, the first group (eight monkeys) was given four successive intramuscular injections of ketamine (10, 5, 5, and 5 mg/kg of body weight at 0, 30, 60, and 110 min respectively). Blood samples were taken at 0, 15, 30, 45, 60, and 120 min. For the long-term effect, the second group (10 monkeys) was given a single injection of ketamine (10 mg/kg) once a week for 4 consecutive weeks. Blood samples were taken 5 to 10 min after each injection, then were used to determine the variation in hormone concentrations among the monkeys (inter-individual variation) and within each monkey (intra-individual variation). There were no statistically significant differences in serum cortisol, testosterone, ILH, and BioLH values between the first blood sample (before the ketamine injection) and sequential blood samples in monkeys of the first group. Although intra-individual variation in the hormones (i.e., hormonal change within each monkey) was not statistically significant, inter-individual variation (among the monkeys) was significantly (0.00001 < P < 0.033) different in monkeys of the second group. These results indicate that an adequate number of animals must be used to minimize animal-to-animal variability. Our results confirm that ketamine is a suitable anesthetic agent to immobilize male cynomolgus monkeys in experimental studies (short- and long-term studies) aimed at elucidating hormonal changes.     

Classical olfactory conditioning in the cockroach Periplaneta americana

We established a classical conditioning procedure for the cockroach, Periplaneta americana, by which odors were associated with reward or punishment. Cockroaches underwent differential conditioning trials in which peppermint odor was associated with sucrose solution and vanilla odor was associated with saline solution. Odor preference of cockroaches was tested by allowing them to choose between peppermint and vanilla sources. Cockroaches that had undergone one set of differential conditioning trials exhibited a significantly greater preference for peppermint odor than did untrained cockroaches. Memory formed by three sets of differential conditioning trials, with an inter-trial interval of 5 min, was retained at least 4 days after conditioning. This conditioning procedure was effective even for cockroaches that had been harnessed in plastic tubes. This study shows, for the first time in hemimetaborous insects, that both freely moving and harnessed insects are capable of forming olfactory memory by classical conditioning procedure. This procedure may be useful for future electrophysiological and pharmacological studies aimed at elucidation of neural mechanisms underlying olfactory learning and memory.     

The proportion of fixed interval trials to probe trials affects acquisition of the peak procedure fixed interval timing task

A common procedure for studying the ability of animals to time is the peak procedure. With the peak procedure, animals are first trained on a fixed interval schedule (i.e., 30s). After the animals have been well trained on the fixed interval schedule, probe trials are introduced. On probe trials, the stimulus is presented longer (i.e., 90s) and the animal does not receive reinforcement for responding. When animals are first presented with probe trials responding remains flat following the point that reinforcement normally occurs on fixed interval trials. The descending slope that eventually emerges is acquired with experience with probe trials. The present experiments manipulated the percentage of probe trials compared to FI trials across groups of rats. It was hypothesized that the descending limb of peak responding would be acquired more quickly when there were many probe trials per session as this might facilitate extinction of responding beyond the interval that reinforcement normally occurs. It was found, however, that acquisition of peak responding occurred best when there were few probe trials per session.     

Effect of negative air ions on morphine-induced changes in the latency of the tail-flick reflex

Adult male Long-Evans rats were exposed to negatively charged air ions at high concentrations (7 x 10(5)/cm3) for six days. Sham-exposed rats were treated identically except that the source of ions was not activated. At the end of the exposure, the latency of the tail-flick reflex was measured in each rat before and 30 and 60 min after an injection of morphine sulphate. The tail-flick reflex was initiated by thermal stimulation. Two heat settings were employed, the lower considered to impart a submaximal and the higher a maximal thermal stimulus. Three morphine doses were tested: 0.5, 1.0, and 1.5 mg/kg. Statistically significant differences between ion-exposed and sham-exposed rats were observed in tail-flick latencies 30 min after the administration of the two lower doses, but not after the highest dose of morphine sulphate. These differences were found at both intensities of thermal stimulation. Tail-flick latencies measured in each group prior to morphine injection were not affected by negative-ion exposure. The data indicate that exposure of rats to negative air ions tends to inhibit the action of morphine on the latency of the tail-flick reflex at morphine doses below 1.0 mg/kg.     

可卡因固定比率自身给药大鼠模型的建立

目的：建立稳定的可卡因固定比率自身给药大鼠模型,并提高其成功率。方法：16只大鼠随机分为对照组和模型组,每组8只。2组大鼠全部行右侧颈静脉长期置管术,术后第6天起进行每天2小时的自身给药训练,训练程序为固定比率的FR1程序（即大鼠触碰鼻触一次可获得药物注射一次）,模型组注射药物为浓度为5mg／ml的可卡因溶液（50μl／次）,对照组为生理盐水（50μl／次）,每次注射后20秒内为不应期,当大鼠连续3天触鼻频率最高值与最低值的差值小于均数标准差的1／4后,FR1模式下的大鼠自身给药训练成功。结果：通过8-11天训练,模型组8只SD大鼠全部形成稳定的自身给药行为,且与对照组相比,触鼻次数明显增加,P〈0．01。结论：通过静脉自身给药训练,盐酸可卡因可使大鼠建立稳定的自身给药模型：通过改善手术质量、加强术后维护,可明显提高模型成功率。     

Morphine self-administration added to food conditioning: methodological variant in rats]

Rats with permanent intra-jugular cannula are submitted to an alimentary operant reinforcement schedule with fixed ratio type FR 1, FR5, then FR 20. As a result, the animals are self administering (together with the alimentary inducer) a slow (about 5 sec) intravenous infusion of morphine (0.05 mg/kg). 20 per cent only of the experimental population exhibit a psychogenic dependance afterward. On the other hand, the animals for which morphine self-administration has been substituted to the alimentary reinforcement without respecting a transitory period combining both types of reinforcement have never shown any tendancy toward morphine self-administration. The lack of positive results could be related to the marked duration of the self-injection.     

Effects of angiotensin II and captopril on rewarding properties of morphine

The effects of captopril and Ang II on morphine-induced conditioned place preference (CPP) and morphine self-administration in male Wistar rat were investigated. In CPP experiment, injection of captopril before test significantly decreased the difference of the time spent in compartment A between pre- and post-conditioning compared to morphine group. In self- administration experiment number of active lever pressing was significantly greater than passive in morphine group. In captopril group number of active lever pressing was significantly lower than morphine group however, there was not significant difference between active and passive lever pressed number. The results showed that captopril significantly decreased morphine-induced conditional place preference and morphine self-administration but the effect of Ang II was not significant. It can be concluded that RAS may have a role in rewarding properties of morphine.     

Evidence for morphine-induced galactorrhea in male cynomolgus monkeys

We evaluated the effect of a daily injection of morphine hydrochloride on galactorrhea in male cynomolgus monkeys. Three groups of three monkeys (nine total) were used. The treatment schedule was separated into three periods: pre-treatment, treatment, and post-treatment. Each group of monkeys was subcutaneously injected daily with 1.5, 3.0, or 6.0 mg/kg (monkey weight) of morphine for 74–130 days, respectively, during the treatment period, and with saline during the pre-treatment and post-treatment periods. We then measured the prolactin (PRL) and testosterone (T) levels from weekly blood samples that were taken 20 hours after injection. No statistically significant differences in either the PRL or T level were detected throughout the treatment period. However, monkeys treated with 3.0 and 6.0 mg/kg/day showed a decrease in T level and an increase in PRL level during the early post-treatment period. Seven of the nine monkeys produced a milk-like secretion from their mammary gland (a symptom of galactorrhea) during the treatment and post-treatment periods. For several months of post-treatment period (average 6.75 months), we monitored the time-course changes in PRL and T levels in all monkeys for 10 hours after a single injection of morphine at the same dose given during the treatment period. Morphine induced a sudden increase in the PRL level (peaked within 30 minutes) and a gradual decrease in the T level (leveled off within 6.5–10 hours), and then returned to basal levels. These results indicate that morphine does not cause a long-term effect on hormonal changes and that a morphine-induced transient rise in PRL levels accompanied by a decrease in T levels can induce spontaneous galactorrhea in male cynomolgus monkeys.     

Simultaneous determination of morphine and monoamine transmitters in a single mouse brain

A simple procedure for the simultaneous determination of morphine and monoamine transmitters was developed. The procedure consisted of (1) n-butanol extraction and (2) separation and quantitative determination by means of high-performance liquid chromatography combined with electrochemical detection. The maximum intracerebral concentration (210 ± 35 ng/g wet tissue) of morphine was detected 30 min after intramuscular injection (10 mg/kg), which agreed with previous research. Noradrenaline was significantly decreased by morphine injection, while dopamine and 5-hydroxytryptamine were unchanged. However, 3-methoxytyramine, a metabolite of dopamine, was increased, suggesting that the drug increased the turnover rate of dopamine. The procedure used revealed a direct correlation between pharmacokinetics (e.g., distribution of morphine) and pharmacodynamics (e.g. changes of monoamine concentrations) of the drug in vivo.     

Speed training with body weight unloading improves walking energy cost and maximal speed in 75- to 85-year-old healthy women.

This randomized controlled study was designed to prove the hypothesis that a novel approach to high-speed interval training, based on walking on a treadmill with the use of body weight unloading (BWU), would have improved energy cost and speed of overground walking in healthy older women. Participants were randomly assigned to either the exercise group (n = 11, 79.6 +/- 3.7 yr, mean +/- SD) or the nonintervention control group (n = 11, 77.6 +/- 2.3 yr). During the first 6 wk, the exercise group performed walking interval training on the treadmill with 40% BWU at the maximal walking speed corresponding to an intensity close to heart rate at ventilatory threshold (T(vent) walking speed). Each session consisted of four sets of 5 min of walking (three 1-min periods at T(vent) walking speed, with two 1-min intervals at comfortable walking speed in between each period at T(vent) walking speed) with 1-min interval between each set. Speed was increased session by session until the end of week 6. BWU was then progressively reduced to 10% during the last 6 wk of intervention. After 12 wk, the walking energy cost per unit of distance at all self-selected overground walking speeds (slow, comfortable, and fast) was significantly reduced in the range from 18 to 21%. The exercise group showed a 13% increase in maximal walking speed and a 67% increase in mechanical power output at T(vent) after the training program. The novel "overspeed" training approach has been demonstrated to be effective in improving energy cost and speed of overground walking in healthy older women.     

Effects of long-term treatment with bovine somatotropin on follicular dynamics and subsequent oocyte and blastocyst yield in an OPU-IVF program

Fourteen Holstein-Friesian heifers between 15 and 22 months of age with normal reproductive tracts were used in an experimental set up to investigate the effect of a long term rBST-treatment on the follicular population prior to transvaginal ovum pick-up (OPU). The estrous cycle of the animals was synchronized by means of a double injection of 2 ml cloprostenol 11 days apart. The heifers were divided in 2 equal groups (n = 7) in which the animals had the same average body weight, one group receiving a weekly subcutaneous injection of 640 mg recombinantly derived bovine somatotropin (rBST) on Mondays (rBST-treatment group) and a control group, being injected with 10 ml of saline. Heifers in both groups were submitted to OPU twice a week on Mondays and Thursdays using a 5 Mhz transducer and a disposable, 55 mm long, 20-g short bevelled needle at a vacuum pressure corresponding to approximately 13 ml water/min. The experimental period lasted for 10 weeks (April to June), each animal receiving a total of 10 injections and being submitted to OPU for 20 times. Oocytes were subsequently matured and cultured in a separate drop per cow following conventional IVF procedures. A blood sample was taken on heparin immediately after each OPU session, for determination of blood progesterone concentrations to assess the influence of treatment and OPU procedure on the cow's estrous cycle. Although results show a significant increase in the total number of follicles and medium sized follicles in the rBST-treated group, no statistically significant different number of retrieved oocytes between the rBST-treated and nontreated group could be detected. The average number of retrieved oocytes per session per cow was comparable, being 6.4 for the treated and 6.0 for the control group. Additionally, the average number of blastocysts per cow per session did not differ significantly between groups, being 1.41 in the rBST-treated group and 1.53 in the control group. The number of cultured oocytes which developed to the blastocyst stage was 22% in the rBST-treated group, which was not significantly different from 25% in the control group. Repeated OPU appeared to induce a certain degree of acyclicity in both treated and nontreated animals.     

High reinforcing efficacy of nicotine in non-human primates

Although tobacco appears highly addictive in humans, there has been persistent controversy about the ability of its psychoactive ingredient nicotine to induce self-administration behavior in laboratory animals, bringing into question nicotine's role in reinforcing tobacco smoking. Because of ethical difficulties in inducing nicotine dependence in na?ve human subjects, we explored reinforcing effects of nicotine in experimentally-naive non-human primates given access to nicotine for periods of time up to two years. Five squirrel monkeys with no experimental history were allowed to intravenously self-administer nicotine by pressing one of two levers. The number of presses on the active lever needed to obtain each injection was fixed (fixed-ratio schedule) or increased progressively with successive injections during the session (progressive-ratio schedule), allowing evaluation of both reinforcing and motivational effects of nicotine under conditions of increasing response cost. Over time, a progressive shift toward high rates of responding on the active lever, but not the inactive lever, developed. The monkeys' behavior was clearly directed toward nicotine self-administration, rather than presentation of environmental stimuli associated with nicotine injection. Both schedules of reinforcement revealed a high motivation to self-administer nicotine, with monkeys continuing to press the lever when up to 600 lever-presses were needed for each injection of nicotine. Thus, nicotine, by itself, in the absence of behavioral or drug-exposure history, is a robust and highly effective reinforcer of drug-taking behavior in a non-human primate model predictive of human behavior. This supports the use of nicotinic ligands for the treatment of smokers, and this novel preclinical model offers opportunities to test future medications for the treatment of nicotine dependence.     

Introduction of a retention interval in a sustained attention task in rats: effects of a visual distracter and increasing the inter-trial interval

The impact of manipulating explicit attentional demands on working memory has not been well studied in rodents. The present experiment was designed to test the effects of incorporating a retention interval in a two-lever sustained attention task that requires discrimination of visual signals and non-signals and that has previously been shown to yield valid measures of attention in the rat. Upon establishing baseline performance, additional manipulations, including presentation of a visual distracter and increasing the length and variability of the inter-trial interval were conducted. During baseline conditions, accurate detection of signals, but not non-signals, decreased as the retention interval was increased. Presentation of a flashing houselight throughout the session eliminated delay-dependent detection of signals. Increasing the inter-trial interval improved detection of signals and decreased detection of non-signals at the longest retention interval. Finally, increasing the variability of the inter-trial interval did not have significant effects on performance above and beyond the effects of increasing the inter-trial interval. The present experiment demonstrates that manipulation of explicit attentional demands can alter working memory performance in the rat. This task may be employed to understand the neuropharmacological and neuroanatomical substrates mediating memory while attentional load is systematically varied.     

Little and often? Maintaining continued performance in an automated T-maze for mice

Operant and maze tasks in mice are limited by the small number of trials possible in a session before mice lose motivation. We hypothesized that by manipulating reward size and session length, motivation, and hence performance, would be maintained in an automated T-maze. We predicted that larger rewards and shorter sessions would improve acquisition; and smaller rewards and shorter sessions would maintain higher and less variable performance. Eighteen C57BL/6J mice (9 per sex) acquired (criterion 8/10 correct) and performed a spatial discrimination, with one of 3 reward sizes (.02, .04, or .08 g) and one of 3 session schedules (15, 30, or 45 min sessions). Each mouse had a total of 360 min of access to the maze per night, for two nights, and averaged 190 trials. Analysis used split-plot GLM with contrasts testing for linear effects. Acquisition of the discrimination was unaffected by reward size or session length/interval. After-criterion average performance improved as reward size decreased. After-criterion variability in performance was also affected. Variability increased as reward size increased. Session length/interval did not affect any outcome. We conclude that an automated maze, with suitable reward sizes, can sustain performance with low variability, at 5-10 times faster than traditional methods.