Retractable Lever Research Articles

Dietary additives and the acquisition of cocaine self-administration in rats.

The effects of dietary caffeine and the amount and palatability of food on the acquisition of cocaine (0.2 mg/kg) self-administration were examined. Using an autoshaping procedure, seven groups of 13 rats each were trained to press a lever resulting in a cocaine (0.2 mg/kg infusion under a fixed-ratio 1 (FR 1) schedule. One group had ad libitum access to caffeine- (0.2% w/w) admixed food. Three groups had access to 10 g, 20 g or ad lib food each day. Another three groups had the same three amounts of ground food with powdered saccharin (0.2% w/w) added. During daily 6-h autoshaping sessions, ten infusions were delivered each hour under a random-time 90-s schedule after a brief (15 s) extension of a retractable lever. These were followed by 6-h self-administration sessions, when the lever remained extended and cocaine infusions were available under an FR 1 schedule. The acquisition criterion was self-administration of a mean of 100 infusions over 5 days. Cocaine self-administration was accelerated in the caffeine group compared to the regular chow group. However, by 30 days nearly the same percentage of rats in the caffeine and regular food groups met the acquisition criterion. In the other six groups, as the amount of food increased, the rate of acquisition and percentage of rats per group meeting the acquisition criterion decreased. In the ad lib group, acquisition was further reduced when saccharin was added to food. In summary, dietary caffeine accelerated acquisition and a greater amount and increased palatability of food independently interfered with acquisition of cocaine self-administration in rats.

Lesions of the frontal cortex, hippocampus, and intralaminar thalamic nuclei have distinct effects on remembering in rats.

Lesions of the intralaminar thalamic nuclei (ILn), the medial wall (MW) area of prefrontal cortex, and the hippocampus were compared and found to have distinct effects on delayed matching-to-sample (DMS) and delayed non-matching-to-sample (DNMS) tasks based on different types of stimulus cues. Hippocampal lesions impaired DNMS trained in a radial arm maze but had little effect on DMS trained with retractable levers or olfactory DNMS. MW lesions affected the DMS task but had limited effects on olfactory DNMS and radial arm maze DNMS. ILn lesions resulted in a more generalized pattern of impairment for radial maze tasks and (in previous studies) for the DMS and olfactory DNMS tasks. Only the hippocampal lesion was associated with a delay-dependent impairment. It is argued that ILn lesions disrupt remembering through their effects on the recurrent, feedback pathways that link functionally related areas of the basal ganglia and cortex.

Cocaine impairs acquisition of an autoshaped lever-touch response.

The effects of daily peripheral (IP) post-session injection of cocaine on the development of an autoshaped lever-touch response in rats were investigated. Male Sprague-Dawley rats received ten daily pairings of a retractable lever (conditioned stimulus; CS) and food delivery (unconditioned stimulus; UCS). Food delivery occurred if the subjects contacted the extended lever within 10 s, or, if the subjects failed to contact the lever, at the end of the 10-s stimulus interval. These contingencies resulted in increased lever-touch responses over 10 days of conditioning. Cocaine (5.6-19.0 mg/kg) impaired development of the lever-touch response, as compared to saline-treated control subjects. Because the injections were given immediately after each conditioning session, we suggest that cocaine affects the neural processes involved in consolidation. Three additional control experiments support this suggestion. The effect of cocaine on lever-touch acquisition was time-dependent as daily injection of cocaine (5.6 mg/kg) 3 h after each conditioning session did not affect lever-touch acquisition. In addition, the effect of cocaine was dependent upon the explicit pairing of lever extension (CS) and food delivery (UCS) as immediate post-session cocaine (5.6 mg/kg) administration did not alter responding when the presentation of both the CS and the UCS was uncorrelated. Cocaine (5.6 mg/kg) administered to subjects previously trained to a performance criterion did not affect lever-touch responding, indicating that cocaine administration (5.6 mg/kg) impairs the development, but not the maintenance, of autoshaped lever-touch responding. In contrast, the highest dose of cocaine tested, 19.0 mg/kg, did decrease lever-touch responding in well-trained subjects, indicating that post-session administration of higher doses of cocaine can produce aversive effects that may affect both the acquisition and maintenance of appetitively motivated behavior in the rat. The relative contributions of the instrumental and classical associations inherent in the autoshaping procedure were investigated by altering response contingencies. Rats showed no evidence of learning the lever-touch response when lever insertion and food delivery were positively correlated, and no explicit response contingency was present (classical conditioning); further, cocaine-treated subjects did not differ from saline-treated subjects. However, cocaine did impair lever-touch responding in the instrumental version of the task. Taken together, these results show that the post-session administration of cocaine can impair the acquisition of a multi-trial, multi-session appetitively motivated response.

Pyrogens Specifically Disrupt the Acquisition of a Task Involving Cognitive Processing in the Rat

In addition to changes in body temperature and other metabolic and physiological responses corresponding to immune activation, pyrogens can induce profound behavioral changes referred to collectively as sickness behavior. One feature of sickness behavior, sometimes reported in clinical settings, but rarely exposed to experimental analysis, is depressed cognitive functioning. The present series of five experiments sought to demonstrate the existence of specific cognitive deficits in rats, independently of any confounding performance effects of pyrogen injections. The behavioral task used, called autoshaping, consisted of presenting hungry Wistar rats with a stimulus (introduction of a retractable lever) that predicted food delivery. Control rats quickly learned to press the lever, although this response does not influence the probability of food delivery. When pyrogens (250 μ/kg lipopolysaccharide, 4 μg/rat interleukin-1 β, or 300 mg/rat yeast) were injected to rats during acquisition of this task, they severely disrupted acquisition while the pyrogen was active. The same treatments were, however, without effect on performance when injected later, when performance had stabilized. II is argued that these results demonstrate specific, performance-independent effects of pyrogens on the cognitive processes needed for the acquisition of this task. The results are discussed in terms of the relationship between these effects and the cytokines induced in the brain by pyrogens, and in terms of the exact nature of the cognitive process likely to be affected.

Effects of toluene inhalation on detection of auditory signals in rats

Inhalation of organic solvents can affect vigilance and reaction time in humans. An animal model of vigilance was designed to assess the effects of toluene on these processes. Adult male Long-Evans rats were trained to detect auditory signals (20-msec increases in the intensity of white noise). Two to 4 s after each signal (or blank period), two retractable levers were inserted into the test chamber. A press on one lever after a signal and on the other lever after a blank resulted in the delivery of food. Signal detection analysis showed that sensitivity (Sensitivity Index, SI) and response bias (Responsivity Index, RI) increased with signal intensity, indicating that loud signals were more detectable than soft signals and that the animals' criterion for responding “signal” increased with signal intensity. Response latency for correct choices was faster for signal trials than for blank trials. Toluene vapor was added to the airstream of these chambers at concentrations of 0, 1000, 1500, or 2000 ppm, either 10 or 30 min before testing and for the duration of each 1-h test. In air, SI increased across the duration of the test; this within-session improvement was reversed by toluene. RI did not change in air; it was decreased by toluene at the beginning of each exposure session, returned to the control level during exposure to 1000 and 1500 ppm toluene and exceeded air control after 40 min exposure to 2000 ppm toluene. Latency increased monotonically across toluene concentrations and time on test. Neither signal intensity nor the duration of toluene exposure before testing altered these effects of toluene. SI, RI, and latency baselines were recovered after toluene exposure indicating that no persistent effects of toluene were detectable. This conclusion was supported by data from other rats showing that toluene exposure (2000 ppm for 2 h/day for 4 consecutive days) did not affect auditory thresholds, as determined by reflex modification of an acoustic startle response using a 16 kHz tone as a prepulse stimulus, 7 or 17 days after exposure to toluene. Finally, rats tested immediately or 20 min after exposure to 0, 1000, 1500, or 2000 ppm toluene were not affected by the vapor, indicating that the impairment observed during toluene inhalation did not persist beyond the period of exposure.

A failed attempt to autoshape leverpressing in horses

In this paper, we describe a study in which we attempted to autoshape three horses to make a leverpress response. This study was motivated by observations made during earlier studies (Dougherty & Lewis, 1991b, 1992) in which we observed horses directing consummatory behaviors toward stimuli signaling the availability of reinforcers. The procedure was similar to that of other autoshaping procedures. Horses received forward conditioning trials in which stimuli (an illuminated panel and a retractable response lever) were periodically presented together for 10 sec and followed by a grain reinforcer. Each horse’s stall served as an experimental chamber. A response panel was positioned in the stall’s doorway, and a computer located nearby controlled and monitored experimental events. Each day, for 14 days, 100 stimulus-reinforcer pairings were presented. Despite 1,400 stimuli-reinforcer presentations, none of the horses were autoshaped. A few possible reasons for these results are discussed.

Autoshaping i.v. cocaine self-administration in rats: effects of nondrug alternative reinforcers on acquisition.

The purpose of this experiment was to examine the effects of a nondrug alternative reinforcer and feeding conditions on the acquisition of cocaine self-administration. Rats were autoshaped to press a lever that resulted in a 0.2 mg/kg i.v. cocaine infusion. Responses on the lever were monitored during six consecutive autoshaping sessions that occurred each day. A retractable lever was inserted into the operant chamber on a random time 60 s schedule 10 times per session for six sessions that began each hour. Each day the six autoshaping sessions were followed by a 6-h cocaine self-administration session. During self-administration the lever remained extended, and each response on the lever resulted in a cocaine infusion (0.2 mg/kg). The criterion for acquisition of cocaine-reinforced behavior was met when there were 5 consecutive days during which the mean number of infusions during the 6-h self-administration session was at least 100. This procedure was repeated daily until the criterion was met or 30 days elapsed. The rats were also trained to respond on lick-operated automatic drinking devices that delivered 0.05 ml water or a glucose and saccharin solution (G + S) contingent upon each lick response. Five groups of 12-14 rats were compared. The first four groups constituted a 2 x 2 factorial design whereby either G + S or water was available in the home cage for 3 weeks before autoshaping began and G + S or water was available in the operant chamber during autoshaping. These groups were limited to 20 g food per day and all had free access to water.(ABSTRACT TRUNCATED AT 250 WORDS)

SEQUENCES OF SPACED RESPONSES: BEHAVIORAL UNITS AND THE ROLE OF CONTIGUITY

Sequences of temporally spaced responses were reinforced to investigate the effects of delay of reinforcement on the formation of functional behavioral units. In Experiment 1, rats' two- and three-response demarcated sequences of left and right lever presses were reinforced such that different response distributions would occur depending on whether the sequences themselves or individual responses were functional units. The matching law could thus be obeyed either by individual responses or by sequences, but not by both; intermediate results were possible. Both regular (nonretractable) and retractable levers were used; the retractable levers precluded the occurrence of insufficiently spaced responses. At a minimum interresponse time of 5 s for regular levers and 7 s for retractable ones, matching results were intermediate, with greater evidence of sequence conditionability in the two-response sequences than in the three-response sequences. In Experiment 2, the required minimum interresponse spacing for two-response retractable-lever sequences was varied in an attempt to locate the sequence matching threshold. This attempt was unsuccessful, but the sequences (instead of individual responses) more closely obeyed the matching law. In the shortest spaced condition, conditional probability data on Lag 1 sequence emission order showed marked, highly similar patterning for all rats, indicating sequential control of the sequences. Post hoc definition of the behavioral unit in these studies is ambiguous. Although reinforcement contiguity was important, aspects of the results could support both molar- and molecular-level interpretations.

Food deprivation enhances both autoshaping and autoshaping impairment by a latent inhibition procedure

The influence of food deprivation on acquisition of autoshaped operant behavior was measured. In one study separate groups of young, male rats that were deprived to 75%, 80%, 85%, 90%, and 95% of ad lib weight were subjected to an autoshaping procedure in which a 6 s delay was interposed between lever retraction (which occurred when rats made a lever touch, or automatically after 15 s) and food pellet delivery. In a second study, groups of rats were deprived to 80% or 90% of ad lib weight prior to testing in a latent inhibition variation of the same autoshaping procedure. This was done to determine if greater food deprivation would enhance learning which, because of the latent inhibition manipulation, is manifest as less lever-directed behavior. Greater food deprivation was associated both with fast acquisition of autoshaped lever responding and with more reliable failure to increase lever responding in the latent inhibition paradigm. Thus, increasing food deprivation was associated with enhanced acquisition regardless of whether the required performance was an increase or a failure to increase the same behavior, indicating a specific effect on learning.

Pharmacological studies of a rat spatial delayed nonmatch‐to‐sample task as an animal model of dementia

AbstractA variation of the delayed nonmatch‐to‐sample task in rats has recently been described in which the spatial positions of retractable levers are used as the sample and response cues. The pharmacology of this task has been investigated, with the aim of developing models relevant to the search for compounds active in dementia, particularly Alzheimer's disease. Scopolamine and atropine decreased the accuracy of responding. This was attenuated by physostigmine and THA. Mecamylamine, 8‐OH DPAT, CPP, MK‐801, and pentobarbital all produced marked accuracy deficits. Diazepam and sodium valproate affected accuracy rather less. Subthreshold doses of mecamylamine and scopolamine given together produced a significant accuracy deficit. All the drugs tested decreased the total trials performed. Prior satiation experiments demonstrated that this rate decrease in itself did not necessarily cause the decrease in accuracy. CPP and MK‐801 appeared to produce the largest decrease in accuracy, with the least effect on rate. This selectivity, combined with the emerging role of the NMDA receptor complex in learning, memory, and dementia, encourages the development of this model or similar models in the search for compounds with the potential to treat dementia.

Opposing effects of vasopressin on matching versus non-matching to position: further evidence for response, not memory, modulation

Rats were trained on either of two related variants of an operant memory task. In the matching to position (MTP) task, one of two retractable response levers appeared, at random, as the sample. A response caused the lever to retract and this was followed by a delay (0-32 s) interval, during which the subjects had to approach and respond at the magazine tray. Both levers were then presented and the rat had to respond, for food reward, to the one which had appeared as the sample. A second group of rats learned non-matching to position (NMTP). This task was very similar to MTP, with one crucial difference: here, the subject had to respond to the lever which had not appeared as the sample. Both groups of rats learned their respective tasks rapidly, performance depending on the delay interval as expected. They were then injected, peripherally, with different doses of arginine-vasopressin (AVP: 0-25 micrograms/kg), a peptide which others have argued improves mnemonic performance. There was evidence to suggest that MTP performance was improved by AVP; on the other hand, NMTP performance appeared to be disrupted. It is suggested that AVP induces a bias towards responding on one side of the two lever test chamber. In other words, it affects motor or motivational, not mnemonic mechanisms.

Effects of nicotine, oxotremorine and 9-amino 1,2,3,4- tetrahydroacridine (tacrine) on matching and non matching to position in rats: no evidence for mnemonic enhancement

Groups of rats were trained on one of two variants of an operant memory task which allows strength of memory (accuracy), bias and response rates to be measured directly. In matching to position (MTP), one of two retractable response levers appeared at random as the sample. A response caused the lever to retract and this was followed by a delay (0-64 s) interval, during which the rat had to approach, and respond at, the magazine tray. Both levers were then presented and the rat had to respond to the lever which had most recently appeared as the sample, for food reward. A second group of rats learned non-matching to position (NMTP). In this task, rats had to respond to the lever which had not appeared as the sample.The subjects were then divided into subgroups and injected, peripherally and prior to test, with one of three cholinergic drugs. These were nicotine (NIC: 0-0.3 mg/kg), oxotremorine (OXO: 0-0.3 mg/kg) and 9-amino 1,2,3,4-tetrahydroacridine (tacrine, THA: 0-3.0 mg/kg). NIC had a delay-independent disruptive effect on accuracy, but only in the non-matching version, and it did not affect rate of responding. OXO and THA had no effect on accuracy, but adversely affected response latencies and rates.The results suggest that these drugs do not affect memory mechanisms; instead, and at the doses used, certain types of bias may be induced (NIC) and general responsiveness altered (OXO and THA).

Modelling working and reference memory in rats

A model of working and reference memory in rats is described, based on a discrete-trial operant procedure with concurrent components of spatial matching (for working memory) and nonspatial discrimination (for reference memory). On each trial in the matching component, rats received food for pressing one of two retractable levers after a delay if that lever had been presented in the prior sample phase of the trial. On each trial in the discrimination component, food was delivered if the rat pressed a lever illuminated by a cue light after the delay interval. The model was tested with scopolamine (0.10 to 0.56 mg/kg, ip), which reduced matching accuracy in a dose-related manner. Linear slope and intercept estimates of retention gradients showed that intercepts declined and slopes remained unchanged with increasing scopolamine dose. In contrast, scopolamine had no significant effect on nonspatial discrimination accuracy, indicating a relative insensitivity of reference memory to cholinergic blockade. Because the matching component involved spatial cues and the discrimination component did not, a second group of rats was trained to discriminate between the spatial locations of two levers, to compare the effects of scopolamine on spatial and nonspatial discriminations. Scopolamine at the same doses caused a small, consistent decrease in spatial discrimination accuracy, suggesting that spatial discrimination was more sensitive to disruption by scopolamine than was nonspatial discrimination. The combined delayed matching-to-position/nonspatial discrimination procedure appears to provide a useful technique for characterizing mnemonic effects of drugs and toxicants in rats.

ラットの遅延弁別反応による記憶に対する薬物効果の検索

Delayed discrimination experiments were conducted to examine drug effects on memory in rats. Three kinds of experimental situations: a Y-maze, an operant chamber with two retractable levers, and an operant chamber with two fixed levers were used. A discriminative stimulus light either on the left or the right side of a stimulus panel was presented for a brief period in each situation. After a certain delay time following extinguishment of the light, a choice response to the previously lighted side was termed as a correct choice. Scopolamine at 0.015-0.06 mg/kg, s.c., decreased the correct choice ratio in trials with a delay time of 0 sec in the Y-maze situation and in trials with longer delay times in the operant chamber situations. Nicotine at 0.06-1 mg/kg, s.c., decreased the correct choice ratio in trials with a delay time of 0-4 sec in the Y-maze situation, a delay time of 4 sec in the retractable-lever operant chamber situation, and a delay time of 0.1 sec in the fixed-lever operant chamber situation. Using this delayed discrimination procedure, drug effects on the relationship between delay time and correct choice ratio were observed. From these results, the present procedure was found to be useful for the evaluation of drug effects on memory in rats.

Signal-directed behavior in the rat: Interactions between the nature of the CS and the nature of the UCS

Two experiments are described, which involved the investigation of interactions between the nature of the conditioned stimulus (CS) and the nature of the unconditioned stimulus (UCS) in producing signal-centered behavior. In Experiment 1, rats received response-independent heat reinforcement in a cold environment. For some groups, this heat UCS was signaled by presentations of a standard aluminum retractable lever; for other groups, it was signaled by a retractable lever covered in acrylic fur (furry lever CS). Only the subjects that received the furry lever CS paired with heat exhibited differential CS-contact behavior, when compared with unpaired, aluminum lever, and warm control subjects. In Experiment 2, hungry rats received pairings of either an aluminum or a furry lever with food (UCS). When compared with unpaired controls, only the subjects that received the aluminum lever paired with food showed differential signal-directed behavior; the subjects receiving the furry lever CS did not show differential contact with the CS, but instead exhibited differential food tray entry behavior during CS presentation. In the two studies, the signal-directed behavior exhibited by subjects resembled either thermoregulatory or feeding behaviors characteristic of rats. The results suggest that signal-directed behavior is determined by a complex interaction between the ecological relevance of the CS and the nature of the UCS—an interaction that can best be described in terms of a behavior systems model of conditioned responding.

Naloxone administration impairs autoshaped learning

Effects of naloxone on acquisition of autoshaped behavior were investigated. Rats deprived to 85% of free-feeding weights were trained to touch a retractable lever; delivery of a food pellet occurred on every trial following lever retraction. The lever was retracted immediately if a touch occurred within 15 s, or automatically after 15 s. Analyses were conducted on number and latencies of touches of the extended lever, nose-pokes (touches) directed at the retracted lever during intertrial intervals (a measure less constrained by ceiling effects than extended lever touches), and unconditioned exploratory rearing activity, measured as touches of a metal strip mounted above the grid floor of the apparatus. In an initial experiment, male Sprague-Dawley rats were given saline or naloxone (2.0 mg/kg, ip) 5 min before a training session of 12 trials. Two days later they were tested, in the absence of drug, in a session of 36 (three blocks of 12) trials. Naloxone depressed training levels of lever responding, in addition to slowing acquisition rate. No effect of naloxone was observed on rearing activity. Previous work showed that injection of saline 5 min before behavioral testing increases the rate of autoshaping compared to injections 30 min before (Messing & Sparber, 1984). Thus, effects of naloxone on acquisition of lever-directed behaviors may have been confounded by behavioral depressant effects and/or by an injection effect such a short time before testing. In a second experiment naloxone (0.5 or 2.0 mg/kg) was injected after five of seven training sessions (12 trials each) to male and female rats. A 6-s delay of reinforcement was inserted between lever retraction and food delivery, slowing acquisition rates and providing the opportunity to test the effects of naloxone throughout a multiple-session task. The low dose retarded acquisition of extended lever touching in both sexes; both doses retarded acquisition of interim lever touching in males. Thus, in some circumstances, post-training naloxone administration may impair learning. The results support the notion that low doses of naloxone may have agonist activity.

Effects of delay, intertrial interval, delay behavior and trimethyltin on spatial delayed response in rats

Working memory was modeled in rats using a delayed response task with spatial location as the discriminative cue. Rats received food for pressing 1 of 2 retractable levers in the choice phase of a trial if that lever had been presented in the prior sample phase of that trial. When delays of 0–20 sec were imposed between sample and choice, choice accuracy declined with increasing delay. With short intertrial intervals (ITIs), choice accuracy decreased more at long delays than at short delays, showing that interference from previous trials impaired memory but not discrimination. Rats emitted overt mediating responses during delay by pressing the levers in the retracted position. However, the frequency of delay presses was low (<2/trial in all rats) and neither their frequency nor accuracy was related to choice accuracy. Resetting the delay interval for each delay press did not significantly alter choice response accuracy. Trimethyltin (TMT), 7 mg/kg IV, reduced the choice accuracy of one rat to chance levels at all delays; two other rats were affected transiently. TMT reduced choice accuracy during weeks 1 and 4 postinjection, with significant effects on the linear slope and intercept of the mean retention gradient during week 4. TMT did not affect responses to the retracted levers during delays. TMT treatment also elevated levels of glial fibrillary acidic protein (GFAP) in the CNS, measured 4 weeks after treatment. Hippocampal GFAP correlated highly with the reduction in choice accuracy during week 1 ( r = −.903) and week 4 ( r = −.797) postTMT. GFAP levels also correlated significantly with TMT-induced changes in the slopes and intercepts of the retention gradients for individual animals at both times after treatment. The delay and ITI effects suggest that the task adequately assessed working memory. The lack of effect of delay presses on choice accuracy suggests that these overt mediating responses did not differentially affect choice responding. The preferential disruption of choice accuracy at long delays by TMT indicates that the compound impaired the retention of spatial information over time, supporting the view that time-dependent processes are particularly vulnerable to this lesion. This spatial delayed response task thus provides a practical analytical tool for the characterization of memory deficits following exposure to neurotoxicants.

Actions of nicotine on the acquisition of an autoshaped lever-touch response in rats.

Experimentally naive male, Sprague-Dawley rats maintained at 85% of their original body weight were trained to touch a retractable lever that was presented on a random interval 48-s schedule. The lever retracted when touched or after 15 s had elapsed, and one 45 mg food pellet was delivered simultaneously with lever retraction or after an 8-s delay. Rats received ten daily sessions each consisting of ten lever presentations. Nicotine (0.25-0.8 mg/kg SC) administration, either 15 min prior to (pre-session) or immediately after (post-session) the daily autoshaping sessions, caused a significant dose-related impairment of acquisition with the post-session injections having the greater effect. Low doses of nicotine (0.025-0.1 mg/kg SC) had little effect on acquisition when injected pre-session or post-session. Injections of 0.45 mg/kg nicotine either immediately (t = 0) or at +5 min after the daily sessions impaired acquisition of the lever-touch response. Nicotine injected at +15, +30, +60, or +120 min had no effect on acquisition. A single intraventricular injection of the ganglionic blocker chlorisondamine (5 micrograms) 2 weeks prior to autoshaping blocked the impairment produced by 0.45 mg/kg nicotine. Post-session injections of nicotine did not alter the lever-touch behavior of well-trained animals, but suppressed responding in animals that were partially trained. Thus, nicotine-induced impairment of the autoshaped lever-touch response is dose dependent, centrally mediated, occurs within 5 min of a SC injection, and may interfere with post-training consolidation processes.

Studies on desglycinamide arginine vasopressin and scopolamine in a modified/lever-touch autoshaping model of learning/memory in rats

Vasopressin administration has been reported to improve acquisition and retard extinction of both conditioned avoidance and food-reinforced behavioral tasks. In the present experiment the effects of a vasopressin analog (DGAVP) and scopolamine (SCOP) were tested in an autoshaped lever-touch model of learning and memory. Rats were food-deprived to 80% of original body weights and tested in modular cages which contained a retractable lever that was presented on a random interval 48 sec schedule. The lever retracted after 15 sec or when it was touched, at which time one 45 mg food pellet was delivered. Subcutaneous injection of 10 μg/kg DGAVP 1 hr prior to acquisition and extinction sessions did not alter responding compared to saline controls. DGAVP at doses of 10, 20, and 30 μg/kg also failed to affect responding in a more difficult task which included an 8 sec delay between lever retraction and reinforcement. Homozygous Brattleboro rats, which are deficient in vasopressin, did not differ from normal heterozygous littermates in the acquisition of the lever-touch response. Intraperitoneal injection of SCOP (0.1–0.8 mg/kg) 30 min prior to testing caused a dose-related impairment of acquisition compared to saline controls, but did not alter responding in animals which had previously acquired the lever-touch response. These data suggest that manipulations of vasopressin do not affect, while SCOP impairs, the acquisition of a positively reinforced lever-touch response in rats.

Single unit activity in cat prefrontal and parietal cortex during performance of a symmetrically reinforced go-no go task.

Relationships between the performance in a symmetrically reinforced go-no go task and cellular firing patterns in prefrontal and parietal association areas of the neocortex were studied in six cats. During recordings, animals lay in a box, with their heads fixed to a stereotaxic frame, and performed an auditory go-no go task by pressing a retractable lever in front of them. Units obtained were classified into eight types according to the correlation of their activity changes with aspects of the task and/or with sensory stimuli. These types were (poly-) sensory, reward related, EMG-related, EOG-related, event-related, movement-initiating, expressing expectancy or novelty, and nonspecific or task-unrelated active units. Between the two recording areas a considerable degree of similarity was obtained in unit firing patterns. It was concluded that within the cerebral cortex, and especially within its association areas, a considerable functional overlap exists, that neurons may be involved in the processing of several and rather different phenomena, and that the processing of information at this level of the brain is generally done via widespread, interwoven neuronal nets so that only the average network activity, but not that of a particular, single neuron, represents a stimulus or an event.