Effects of pedunculopontine tegmental nucleus lesions on responding for intravenous heroin under different schedules of reinforcement

The pedunculopontine tegmental nucleus (PPTg) is believed to play important roles in reward and learning. We examined the effect of PPTg lesions (0.5 microl of 0.1 M NMDA injected bilaterally over 10 min) on the learning of an operant response for opiate reward. In 14 adult male Long-Evans rats, bilateral lesions of the PPTg disrupted the acquisition of responding for intravenous heroin (0.1 mg/kg infused at a rate of 0.25 ml/28 sec) on a fixed ratio-1 (FR-1) schedule of reinforcement. The 12 remaining lesioned animals increased their heroin intake over the acquisition sessions but did not reach the response levels of sham-lesioned animals on the 15th and final session. The sham- and PPTg-lesioned animals that learned the FR-1 task exhibited similar patterns of responding during extinction and reacquisition sessions. When tested on a progressive ratio (PR) schedule of reinforcement, however, PPTg-lesioned animals had lower break points than sham-lesioned animals. Asymmetric lesions, which destroyed the majority of the nucleus in one hemisphere only, did not produce any behavioral deficits. Rats that were lesioned after training also did not show deficits in responding under either FR or PR schedules. These findings suggest that PPTg lesions reduce the rewarding effect of opiates but do not disrupt the ability either to learn an operant response or the response requirements of a PR schedule.     

Factors modulating the effects of teleost telencephalon ablation on retention, relearning, and extinction of instrumental avoidance behavior.

Examined the nature of avoidance behavior in a total of 65 goldfish (Carassius auratus) in 2 experiments. In Exp I, a master/yoked design was used to determine the degree to which Pavlovian conditioning would generate acquisition of a shuttle response by 24 Ss. Results indicate that the sequence of signal-shock pairings experienced by the avoidance Ss was not in this situation sufficient to explain the development of the instrumental avoidance responding. In Exp II, the effects of 3 variables on the retention and extinction of the avoidance response were studied. First, unilateral lesions of the telencephalon produced a transient deficit from which the Ss recovered to normal levels. Retention of avoidance response after bilateral telencephalon ablation was impaired and never fully recovered with additional training. Second, this deficit was reduced under higher intensities of electric shock. Overtraining on the task before the ablation had only a nonsignificant enhancing effect on retention levels. Extinction was always poorer following ablation, independent of the type of ablation, intensity of shock, degree of overtraining, and terminal retention level of performance. (52 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Increased reactivity and impaired adaptability in operant behavior of adult mice given corticosterone in infancy.

Reports 2 series of tests of the operant behavior of 29 adult Swiss Albino male mice after early corticosterone treatment, which irreversibly decreases growth and DNA synthesis in the brain. Ss, paired with littermate controls, bar-pressed on continuous reinforcement at the same rate as controls but left more food uneaten; they responded at higher rates than controls during extinction and on a fixed-ratio-64 (FR-64) schedule. On 20-sec differential reinforcement of low rate (DRL), Ss again responded at higher rates and were less successful than controls in making a transition from FR-99 to 20-sec DRL. However, naive Ss were as efficient as controls on 20-sec DRL. Thus, after early hypercorticism, adult mice are hyperresponsive when working for food and show an impaired ability to adapt to a schedule change. (22 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Facilitation of instrumental behavior by a Pavlovian appetitive conditioned stimulus.

In Exp I, 16 New Zealand white rabbits were trained to perform an instrumental head-raising response for sucrose reward. A jaw-movement CR was established to a 2-sec CS by pairing it with sucrose; a control stimulus was unpaired with sucrose. Instrumental responding maintained by a VI 40-sec schedule was enhanced during 10-sec presentations of the paired, but not the unpaired, CS. Responding on a VR 15 schedule was unaffected except on trials on which the pre-CS baseline response rate was low; in such cases the paired CS caused a long-lasting acceleration of responding. Noncontingent presentation of the sucrose reinforcer itself briefly suppressed responding but had no long-term effect. In Exp II (6 Ss), a CS that had been conditioned at a 10-sec duration produced the same pattern of effects as in Exp I, indicating that facilitation resulted from CS presentation rather than from the frustrative effects of nonreinforcement of the CS. In Exp III (16 Ss), an inhibitory CS blocked facilitation by the excitatory CS but did not itself affect instrumental responding. (53 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Shuttle-box-avoidance performance and basal corticosterone levels as a function of duration of individual housing in rats.

Examined avoidance responding and plasma corticosterone levels in Long-Evans male rats (N = 50) following 0, 30, or 50 days of individual housing. Compared to the group-housed Ss, individually housed Ss showed (a) facilitated acquisition and extinction of a shuttle-box avoidance response (p     

Pavlovian analysis of avoidance conditioning in the goldfish (Carassius auratus).

Conducted 2 experiments in which 144 and 54 goldfish, respectively, were trained in a shuttlebox with light as CS and brief shock as UCS. Performance was measured in terms of "initial response" to the CS (at least 1 crossing of the hurdle on any trial) and-where the CS was not terminated by the initial response-in terms of "multiple response" to the CS (more than 1 crossing on any trial). The level of initial responding was as high in classically conditioned Ss (shocked on every trial) as in avoidance Ss, whether or not the CS was terminated by response, but lower in control Ss, yoked with the avoidance Ss, and lower also in punished Ss (shocked only if they responded). Multiple responding was negligible in avoidance Ss, but common in classically conditioned and in punished Ss. Results can be accounted for in purely Pavlovian terms, no reference to instrumental learning being required. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of varied extinction conditions with alcoholics and social drinkers.

In a task analogous to excessive drinking behavior, 30 male alcoholics and 30 male social drinkers trained on a 100% rewarded button-pressing response received 1 of 3 extinction conditions: nonreward, simultaneous reward-punishment, and punishment only. Ss could discontinue responding at any time during the extinction phase. Alcoholics showed significantly greater resistance to extinction in the punishment and reward-punishment conditions, but not in the nonreward condition. No differences were found between groups during acquisition. Using an anticipatory punishment response model, an explanation of maladaptive operant responding in the alcoholic is suggested. (18 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dopamine receptor blockade and extinction differentially affect behavioral variability.

Dopamine (DA) neurons respond to unexpected food delivery and are inhibited during the omission of expected reward. DA receptor blockade mimics some, but not all, aspects of nonreward (extinction) conditions. It was therefore of interest to ask whether DA receptor blockade produces extinction-like increases in behavioral variability in addition to its well-known operant response-suppressing effects. In the current experiment, rats were trained drug-free on an operant task in which they pressed on a keyboard. Two of the keys led to food on a continuous reinforcement schedule. Both response rates and behavioral variability were measured. Test day administration of D? and D? antagonists SCH23390 and raclopride, like extinction, suppressed responding but, unlike extinction, did not lead to an increase in variability. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Adrenocortical response to hypertonic saline in rats with lateral hypothalamic lesions.

Used plasma corticosterone levels to assess the response to stress induced by ip injections of hypertonic saline in 27 male albino Harlan-Sprague rats with lateral hypothalamic (LH) or sham lesions. Ss with LH lesions displayed a corticosterone response equal to that of normal Ss under basal conditions, after control injections of isotonic saline, and 20 min after injection of hypertonic saline (1.5 M, 1.0 ml/100 g of body weight). The corticosterone response of Ss with LH lesions, however, was significantly less than that of normal Ss 90 min after injection of hypertonic saline when no water was available. With access to water, normal Ss displayed substantial drinking (14.5 ml/90 min), which resulted in a reduction in plasma corticosterone concentrations to a level observed after a control injection of isotonic saline, but the little water ingested by Ss with LH lesions (2.5 ml) had no effect on the pituitary-adrenal system. It is concluded that the failure of Ss with LH lesions to drink following a hydrational challenge is not the result of an exaggerated response to stress. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A "freeloading" effect: Changes in response rate following non-contingent food reward.

Trained 82 male albino rats to barpress on an operant schedule. Ss were then given noncontingent reward training with the bar removed, and retested on the barpressing response. In each of the 4 experiments, rates of responding were generally depressed following noncontingent rewards on either VI or FI schedules. Reward schedules during barpressing affected the depression effect very little. Several hypotheses were tested in the last 2 studies, but none were supported by the data. (French summary) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Extinction and retention of a classically conditioned flexor nerve response in acute spinal cat.

Conditioned adult male and female cats by pairing a mild electrical stimulus to the superficial peroneal sensory nerve (CS) with a stronger electrical stimulus to the ankle skin (UCS) of the same leg. Subsequent extinction was produced by presenting CS-alone trials. In Exp I (42 Ss), Ss given massed extinction trials showed response decrements to base levels, but Ss that received distributed extinction trials showed no decrements. In Exp II, .5-, 1-, 2-, 3-, or 4-hr intervals between acquisition and extinction produced no significant differences in the extinction data. In Exp III (20 Ss), Ss received extinction trials immediately or 30 min after acquisition trials, followed by 20 additional extinction trials 30 min later. Data indicated significant acquisition and extinction in the 10- and 20-acquisition trial groups. As in Exp II (35 Ss), varying the interval between acquisition and extinction did not produce any group differences in the extinction data. These results demonstrate that response increases produced by paired trials in the spinal preparation do not decay spontaneously over time and are not caused by sensitization effects. (23 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociation of the frustration effect and the partial reinforcement extinction effect after limbic lesions in rats.

20 male albino Wistar rats with control operations, 20 with lesions in the amygdala, and 20 with lesions in the septal area were tested in a double runway. Results show that after omission of reward in the 1st goal box on 50% of the trials, control and septal Ss showed a frustration effect. Lesions in the amygdala eliminated this effect. Subsequent tests of extinction behavior indicated that Ss with control operations and Ss with damage in the amygdala showed a partial reinforcement extinction effect whereas Ss with septal lesions did not. It is concluded that frustration effects and extinction effects have independent neural substrates. (17 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Septal lesions and incentive expectancies in rats.

Tested male albino Wistar rats with bilateral septal lesions on a multiple DRL schedule with large and small rewards. The lesion produced less efficient DRL performance under both conditions. Small rewards produced more efficient DRL responding in controls and brain-damaged Ss. A 2nd study investigated runway conditioning under immediate, delayed, and no reward. Septal lesions increased running speeds with immediate reward, maintained faster speeds during the early delayed-reward trials, but produced no differences during extinction. A 3rd experiment investigated the effects of immediate and delayed rewards on auditory discrimination learning in septal and control Ss. Brain-damaged Ss showed inferior discrimination performance with delayed rewards but not with immediate rewards. Data suggest that septal lesions alter cognitive strategies (i.e., expectancies) based on incentive characteristics. (French abstract) (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Appetitively motivated instrumental learning in SynGAP heterozygous knockout mice.

The synaptic Ras/Rap-GTPase-activating protein (SynGAP) regulates specific intracellular events following N-methyl-d-aspartate receptor (NMDAR) activation. Here, the impact of SynGAP heterozygous knockout (SG+/?) on NMDAR-dependent functions was assessed using different positive reinforcement schedules in instrumental conditioning. The knockout did not affect the temporal control of operant responding under a fixed interval (FI) schedule, but led to a putative enhancement in response vigor and/or disinhibition. When examined on differential reinforcement of low rates of response (DRL) schedules, SG+/? mice showed increased responding under DRL-4s and DRL-8s, without impairing the response efficiency (total rewards/total lever presses) because both rewarded and nonrewarded presses were elevated. Motivation was unaffected as evaluated using a progressive ratio (PR) schedule. Yet, SG+/? mice persisted in responding during extinction at the end of PR training, although an equivalent phenotype was not evident in extinction learning following FI-20s training. This extinction phenotype is therefore schedule-specific and cannot be generalized to Pavlovian conditioning. In conclusion, constitutive SynGAP reduction increases vigor in the execution of learned operant behavior without compromising its temporal control, yielding effects readily distinguishable from NMDAR blockade. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Operant and Pavlovian control of visual stimulus orienting and food-related behaviors in rats with lesions of the amygdala central nucleus.

The effects of superimposing operant reward and omission contingencies on 2 Pavlovian conditioned responses evoked by a visual conditioned stimulus paired with food were examined in rats with lesions of the amygdala central nucleus (CN). In sham-lesioned rats, the frequency of an orienting response, rearing, was increased by reward contingencies and decreased by omission contingencies, compared with yoked Pavlovian controls. In contrast, in CN-lesioned rats, rearing was not affected by either operant contingency and occurred at lower levels with Pavlovian procedures alone than in sham-lesioned rats. Nevertheless, CN-lesioned and sham-lesioned rats showed similar increases in the frequency of conditioned food-cup behavior with reward contingencies, similar decreases with omission contingencies, and similar levels of that response with Pavlovian procedures. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Violation of expectancy and frustration in early infancy.

Instrumental responses to both learning and extinction were examined in a group of infants aged 2–8 months. Eighty infants, divided equally among 4 age groups (2, 4, 6, and 8 months), participated in a contingency learning task. Forty-eight Ss received an audiovisual stimulus contingent on arm movement, and 32 Ss served as a yoked control group. Findings indicated that (a) infants in the contingent group showed a significant increase in their rate of arm pulling as a function of contingent stimulation; (b) with the cessation of stimuli during extinction, contingent subjects at all ages showed a significant increase in response rate from the learning phase; and (c) the ability to learn an instrumental response and reactivity to the violation of a learned expectancy were not related to temperament differences. The results indicate that exposure to extinction, a period in which the infant's expectancy regarding contingent outcomes is violated, produces responsivity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modulation of behavioral inhibition in appetitive extinction following manipulation of adrenal steroids in rats: Implications for involvement of the hippocampus.

Two experiments were conducted in this study, utilizing 57 male Sprague-Dawley rats. Exp I investigated the functional behavioral significance of the hormone-brain interaction in the extinction of an appetitive runway response in normal Ss and in those with lesions of the hippocampus. During extinction, half of the Ss in each group were given daily sc injections of corticosterone. While the classical retardation effect of hippocampal lesions on appetitive extinction was replicated, hormone treatment was without effect in normal or hippocampally damaged Ss. The absence of a hormone effect in normals was primarily attributed to a saturated limited-binding system operating in the normal S. Exp II tested this notion, repeating the 1st experiment, with adrenalectomized (ADX), ADX?+?corticosterone replacement, and normal groups of Ss. Adrenalectomy produced a striking facilitation of extinction, which was speculated to be the result of hyperactive inhibitory neural organ free from an inhibitory endocrine feedback. This was supported when corticosterone treatment normalized the progress of extinction in ADX Ss. (40 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Major attenuation of food reward with performance-sparing doses of pimozide in the rat.

48 male Sprague-Dawley rats were trained to leverpress for food or saccharin reward, and then tested 4 successive times under conditions of normal reward, nonreward, or pretreatment with the dopamine receptor blocker, pimozide. Normally rewarded Ss progressively slowed responding within sessions (became satiated) with food reward but not with saccharin reward. Nonrewarded Ss and pimozide-treated Ss responded vigorously at the beginning of sessions, but slowed within sessions and showed reduced willingness to respond across sessions. Normal responding in the 1st session and in the early phases of later sessions rules out significant motor impairment. Pimozide appears to attenuate selectively the rewarding quality of food for hungry rats. (French summary) (21 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential changes in noradrenaline turnover in specific regions of rat brain produced by controllable and uncontrollable shocks.

Three studies investigated the effects of the ability to avoid or escape shock (controllability) and the lack of ability to do so (uncontrollability) on noradrenergic neurons in various brain regions of 104 male Wistar rats. Brain levels of noradrenaline (NA) and its major metabolite, 3-methoxy-4-hydroxyphenylethyleneglycol sulfate (MHPG-SO?), were measured fluorometrically. Results indicate that after 3 or 6 hrs in a free operant avoidance-escape stress procedure, the experimental Ss able to avoid or escape shock showed greater increases in NA turnover (lower NA levels and higher MHPG-SO? levels) in the hypothalamus, amygdala, and thalamus than the yoked Ss unable to control the same shock. After 21 hrs of stress, yoked Ss exhibited a more marked enhancement of NA turnover in these brain regions than did experimental Ss. Once shock-controlling responses had been acquired and well established by experimental Ss, the responses of NA neurons in these Ss did not differ markedly from those in the nonshocked controls. Yoked Ss given the same repetitive sessions of uncontrollable shock displayed sustained increases in NA turnover preferentially in the hypothalamus and amygdala, compared with the experimental Ss. Results suggest that NA release in specific brain regions in the experimental "coping" rats is increased before the rats have learned the effective coping response. However, once a coping response is firmly established, NA release is reduced. (52 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociation of Pavlovian and instrumental incentive learning under dopamine antagonists.

The administration of the dopamine antagonists, pimozide and α-flupenthixol, to rats reduced Pavlovian–instrumental transfer when a conditioned stimulus (CS) that had been paired with a noncontingent food reward was tested on instrumental performance. The administration of the antagonists during Pavlovian conditioning and/or testing abolished the enhancement of instrumental performance by the CS. The effect of both antagonists on instrumental incentive learning was then examined. After training in which the rats performed 2 responses for different food rewards, they consumed 1 type food under the antagonists and the other type under vehicle during reexposure. When instrumental responding was subsequently tested in extinction, performance was unaffected by whether the rats had been reexposed to the training reward under the antagonists. These results suggest that Pavlovian and instrumental incentive learning are not mediated by a common process. (PsycINFO Database Record (c) 2010 APA, all rights reserved)