Associative effects of US preexposure: Modulation of conditioned responding by an excitatory training context.

Conducted 2 experiments with 120 naive Sprague-Dawley rats to examine factors that contribute to retarded emergence of conditioned responding to a conditioned stimulus/stimuli (CS) trained in a context in which unsignaled unconditioned stimulus/stimuli (UCS) had previously been administered. In both experiments, water-deprived Ss were used in a conditioned lick suppression task to measure the conditioned response (CR) elicitation potential of the CS and the training context. From Exp I, it was determined that nonreinforced exposure to the excitatory context after UCS preexposure and prior to CS–UCS pairings in that context eliminated the CR deficit observed on a subsequent test of the CS. From Exp II, it was determined that the recovery induced by contextual deflation after CS training was specific to deflation of the context in which the CS was trained as opposed to another excitatory context. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Rats given dopamine-depleting brain lesions as neonates are subsensitive to dopaminergic antagonists as adults.

Notes that extensive damage to central dopamine (DA)-containing neurons produces akinesia and sensory neglect when the lesions are made in adult rats. Similar behavioral impairments occur when dopaminergic function is disrupted temporarily by DA receptor blocking agents, and brain-damaged rats are particularly sensitive to the effects of those drugs. The present 2 experiments, with 67 male Sprague-Dawley rat pups, are thought to offer a contrast to these accepted findings that central DA-containing neurons are critical to the initiation of voluntary movement. After near-total destruction of the dopaminergic neurons in 3-day-old rats, there were no conspicuous behavioral dysfunctions at any time during the subsequent 5–8 mo, even when Ss received large intraperitoneal doses of the DA receptor blocking agents haloperidol (.2–2.0 mg/kg) and fluphenazine HCl (1 mg/kg). Findings suggest that some other neuronal system had replaced the absent dopaminergic neurons in the central control of movement. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Striatal synaptophysin levels are not indicative of dopaminergic supersensitivity

Recent evidence suggests that behavioral supersensitivity to dopamine (DA) agonists observed in chronic neuroleptic-treated animals might be related to changes in synaptic morphology and density. The aim of this study was to test this hypothesis using Western blotting to determine the striatal synaptophysin levels in rats chronically treated with haloperidol followed by sub-acute administration of a DA agonist. Chronic haloperidol treatment (1 mg/kg/day for 21 days) produced an 88% increase in striatal synaptophysin levels and a 73% increase in apomorphine-induced stereotypes. Sub-acute administration of the DA D-1 receptor agonist SKF38393 (10 mg/kg/day for 5 days) or the DA D-2 receptor agonist quinpirole (1 mg/kg/day for 5 days) did not modify the haloperidol-induced increase in striatal synaptophysin levels. However, sub-acute administration of SKF38393 attenuated (62%) haloperidol-induced stereotypies. We conclude that there is no direct relationship between stereotyped behavior and synaptophysin levels indicating that striatal synaptophysin levels are not a good marker of dopaminergic supersensitivity.     

Latent inhibition experiments with goldfish (Carassius auratus).

Examined evidence of latent inhibition in a series of experiments with goldfish. In Exp I, 12 Ss were given nonreinforced preexposure to a color that subsequently predicted shock in an activity conditioning situation; their performance did not differ from that of 12 control Ss preexposed to a markedly different color. In Exp II, 12 Ss given nonreinforced preexposure to a tone and an unstimulated control group of 12 Ss were trained in an appetitive situation, with the tone serving either as a conditioned excitor or as a conditioned inhibitor. Preexposure had significant effect in the conditioned excitation training, but it reduced the level of responding both to the positive stimulus and to the negative compound in the conditioned inhibition training. In Exps III and IV, classical aversive conditioning was studied in the shuttle box. In Exp III, excitatory conditioning to a color was found to be impaired (relative to the performance of nonpreexposed control Ss) as much by nonreinforced preexposure to the training color as by nonreinforced preexposure to a markedly different color; substantial variation in amount of preexposure was without significant effect. In the conditioned inhibition training of Exp IV, 12 Ss with nonreinforced preexposure responded less than did 12 unstimulated control Ss, both to the positive stimulus and to the negative compound. Results demonstrate that the effect of preexposure on goldfish is their reduction of general responsiveness or level of arousal. (47 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spontaneous configuring in conditioned flavor aversion.

Four experiments with 202 rats investigated spontaneous configuring, using the conditioned flavor-aversion paradigm. In Exp I, extended training of a 2-flavor compound stimulus did not produce spontaneous differentiation of conditioned responding to that compound and its elements. In Exp II, it was found that extended nonreinforced exposure to a compound stimulus generated spontaneous element–compound differentiation when the elements were later conditioned. Ss that received extended preexposure to the compound showed less conditioned responding to the compound than to either of its elements. However, Ss that had not received preexposure to the compound showed greater conditioned responding to the compound than to either of its elements (summation). In Exp III, nonreinforced preexposure to a compound stimulus prior to minimal reinforced compound training produced spontaneous compound–element differentiation, but extended reinforced compound training eliminated that differentiation. In Exp IV, extended partial reinforcement training with a compound produced differentiation of the compound from its elements. Implications of these data for the mechanisms responsible for spontaneous configuring, and for the summation assumptions common to most learning theories, are discussed. (38 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Phantom auditory sensation in rats: An animal model for tinnitus.

To measure tinnitus induced by sodium salicylate injections, 84 rats were used in a conditioned suppression paradigm. In Exp 1, Ss were trained with a conditioned stimulus/stimuli (CS) consisting of the offset of a continuous background noise. One group began salicylate injections before Pavlovian training, a 2nd group started injections after training, and a control group received daily saline injections. Resistance to extinction was profound when injections started before training but minimal when initiated after training, suggesting that salicylate-induced effects acquired differential conditioned value. In Exp 2, salicylate treatments were mimicked by substituting a 7 kHz tone in place of respective injections, resulting in effects equivalent to salicylate-induced behavior. A 3rd experiment included a 3 kHz CS, and again replicated the salicylate findings. In Exp 4, we decreased the motivational level, and the sequential relation between salicylate-induced effects and suppression training was retained. Findings support the demonstration of phantom auditory sensations in animals. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Pavlovian second-order conditioned analgesia.

Three experiments, with 118 Sprague-Dawley rats, assessed conditioned analgesia in a Pavlovian 2nd-order conditioning procedure by using inhibition of responding to thermal stimulation as an index of pain sensitivity. In Exp I, Ss receiving 2nd-order conditioning showed longer response latencies during a test of pain sensitivity in the presence of the 2nd-order conditioned stimulus (CS) than Ss receiving appropriate control procedures. Exp II found that extinction of the 1st-order CS had no effect on established 2nd-order conditioned analgesia. Exp III evaluated the effects of post 2nd-order conditioning pairings of subcutaneous morphine sulfate (10–20 mg/kg) and the shock unconditioned stimulus/stimuli (UCS). Ss receiving paired morphine–shock presentations showed significantly shorter response latencies during a hot-plate test of pain sensitivity in the presence of the 2nd-order CS than did Ss receiving various control procedures; 2nd-order analgesia was attenuated. Data extend the associative account of conditioned analgesia to 2nd-order conditioning situations and are discussed in terms of the mediation of both 1st- and 2nd-order analgesia by an association between the CS and a representation or expectancy of the UCS, which may directly activate endogenous pain inhibition systems. (52 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The reward value of light increment under supranormal and subnormal arousal.

2 Experiments, with 80 male Wistar rats each, studied the effects of methamphetamine and pentobarbital, respectively, on the reward value of light increment, alternating training days with test days to separate learning effects from performance effects. During the 1st wk. of Exp. I, if injected on training days with saline solution, Ss trained with light increment performed more responses on test days than Ss trained without light increment but, if injected with methamphetamine, Ss trained with light increment performed fewer responses. During the 2nd wk., training with light increment became relatively more effective for those trained under 2 or 3 mg/kg of methamphetamine but less effective in Ss with 0 or 1 mg/kg. In Exp. II, the difference in number of test-day responses between Ss trained with and without light increment decreased when pentobarbital injections (5, 10, 15, or 20 mg/kg) were administered on training days. In both experiments, more responses were performed on training days by Ss receiving light increments, and the number of responses varied inversely with doses of drugs. Results complement previous findings and indicating that the reward value of an indifferent stimulus depends on an interaction between the arousal value of the stimulus and arousal level of the organism. (French summary) (18 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Flavor-illness aversions: Gustatory neocortex ablations disrupt taste but not taste-potentiated odor cues.

Two studies evaluated the contribution of the gustatory neocortex (GN) to the potentiation of odor by taste during illness-induced aversions in 130 male Sprague-Dawley rats. In Exp I, Ss lacking GN and controls were given an odor, a taste, or an odor–taste compound cue followed by intragastric gavage of LiCl. Prior to conditioning, neophobia for flavored solutions was absent in Ss with GN lesions. After pairing with LiCl, GN Ss developed normal conditioned odor aversions, whereas conditioned taste aversions were attenuated or totally blocked. Potentiation of odor by taste after compound conditioning was evident in both control and GN Ss. In Exp II, normal Ss were given compound conditioning to induce potentiated odor aversions and then given GN lesions prior to tests with the odor and taste components. Taste aversion retention was totally disrupted by GN ablation; potentiated odor aversions were retained by both groups, although the GN group extinguished faster. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus generalization of suppression in rats following aversively motivated instrumental or Pavlovian training.

Following 100 or 300 avoidance training trials in Exp I, a total of 60 Holtzman male albino rats and their yoked Pavlovian counterparts were tested for generalization of lick suppression along the frequency dimension of the avoidance conditioned stimulus. Gradients of stimulus control were evident after 300 instrumental avoidance training trials, and additional intradimensional Pavlovian discrimination training further sharpened the gradients. After 100 trials, the yoked Pavlovian Ss suppressed more than their instrumental counterparts. However, with increased Pavlovian training, flatter gradients with decreased suppression were obtained. Results from Exp II, using 12 Ss, revealed that, whereas Pavlovian experience decreased suppression to the tone, Ss suppressed drinking in the presence of static, environmental cues. Data from both experiments support interpretations that stress the role of response control over environmental events. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Directional responses to sounds in young gerbils (Meriones unguiculatus).

Conducted 3 experiments to determine the ability of infant gerbils to approach an auditory stimulus. In Exp I, 48 16–23 day old Ss were tested in a circular apparatus with a central start area and a movable sound source located at 1 of 8 positions around the perimeter. Stimuli included high- and low-intensity presentations of a tape-recorded gerbil social call, a broad-band white noise stimulus, and a no-stimulus control condition. Ss showed a strong tendency to approach the low-intensity social call and a less pronounced tendency to approach the white noise. In Exp II, 24 16–23 day old Ss were tested in the same apparatus with or without ear blocks to determine the role of binaural cues in directional approach responding. The tendency to approach a low-intensity vocalization was disrupted by obstruction of one ear but not by blocking both ears. Thus, binaural balance was shown to be important for early sound localization. In Exp III, using 6 12–27 day old Ss, the tendency to approach a social call was compared at 12–25, 16–29, 20–23, and 24–27 days after birth. Approach responses were first seen at 16–29 days of age. The responses continued at 20–23 days of age but began to wane at 24–27 days of age. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Haloperidol attenuates rewarding and aversively conditioned suppression of saccharin solution intake: Reevaluation of the anhedonia hypothesis of dopamine blocking.

The dopamine (DA) antagonist, haloperidol, affected the conditioned suppression of a saccharin solution intake (the conditioned stimulus, CS) induced by amphetamine (AMPH) and lithium chloride (LiCl) unconditioned stimuli (USs). Four experiments showed that (a) haloperidol by itself did not reduce saccharin solution intake. (b) When haloperidol was injected between the CS and the US, the conditioned suppression was attenuated; however, (c) this did not occur when haloperidol was injected after the US, indicating that haloperidol affected the perception of the US. (d) This attenuation was found with both rewarding AMPH and aversive LiCl treatments, indicating that the valence of the US was unimportant. Thus, the so-called "anhedonia response" might be due to weakening of US impact. A general salient-stimulus hypothesis was proposed, with the anhedonia hypothesis of DA blocking as its subset. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Learning in the rat: Effect of early experience with an unsolvable problem.

Assigned 120 female Sprague-Dawley rats to 7 groups receiving no training or training on a solvable or unsolvable visual discrimination task. After 20 days, Ss were compared with controls on a solvable discrimination, selected problems from the Hebb-Williams test of animal intelligence, and a multiple-unit maze providing spatial cues. Highly consistent choice of 1 aspect of the stimulus situation was found during the unsolvable phase of the study. A learning deficit was found at the time the Ss were experiencing solvable problems. The deficit found after 20 days and in situations differing in nature from the unsolvable problem is interpreted as a lasting generalized learning deficit. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hippocampus and trace conditioning of the rabbit's classically conditioned nictitating membrane response.

In 2 experiments, 36 New Zealand albino rabbits received classical conditioning of the nictitating membrane response in a trace conditioning paradigm. In this paradigm, a 250-msec tone conditioned stimulus (CS) occurred, after which there was a 500-msec period of time in which no stimuli occurred (the trace interval), followed by a 100-msec air-puff unconditioned stimulus (UCS). In Exp I, lesions of the hippocampus or cingulate/retrosplenial cortex (CRC) disrupted acquisition of the long-latency or adaptive conditioned response (CR) relative to unoperated controls and Ss that received neocortical lesions that spared the CRC. When Ss with hippocampal or CRC lesions were switched to a standard delay paradigm in which the CS and UCS were contiguous in time, they acquired in about the same number of trials as naive Ss. In Exp II, multiple-unit activity in area CA1 of the hippocampus was examined during acquisition of the trace CR. Ss had a 500-msec trace interval (Group T-500), received explicitly unpaired presentations of the CS and UCS, or underwent conditioning with a 2-sec trace interval. Group T-500 acquired the CR in about 500 trials. Early in training, there was a substantial increase in neuronal activity in the hippocampus that began during the CS and persisted through the trace interval. Later in conditioning as CRs emerged, the activity shifted to later in the trace interval and formed a model of the amplitude–time course of the behavioral CR. (65 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Epinephrine-induced learning under anesthesia: Retention performance at several training–testing intervals.

While under deep barbiturate anesthesia, 58 male Sprague-Dawley rats received a series of 10 classical conditioning trials in which white noise was paired with intramuscular shock. The anesthetized Ss received subcutaneous injections of saline or epinephrine bitartrate (.1 mg/kg) prior to the training trials. Independent sets of Ss were tested for retention performance 2, 7, or 15 days after training. In these test trials, a conditioned suppression measure was used in which the white noise was turned on while the Ss were drinking. Results indicate that the Ss that had received saline while trained under anesthesia exhibited no evidence of later retention. Ss that had received epinephrine injections prior to training under anesthesia suppressed their drinking in the presence of the white noise when tested 2 or 7, but not 15, days later. Findings demonstrate that epinephrine can enable learning under anesthesia and that forgetting occurs within 15 days. (7 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Overshadowing effects in the stimulus control of morphine analgesic tolerance.

Attempted to replicate previous demonstrations of classical conditioning of morphine analgesic tolerance and to determine whether stimulus overshadowing effects might explain previous conflicting findings. In Exp I, 8 groups of male Sprague-Dawley rats received a series of 10 morphine (5 mg/kg) and/or saline injections, differing only with respect to the contingency between a compound visual-auditory CS and the substance injected. When tested for analgesic responding to morphine in the presence of the compound CS, only those groups for which the CS and morphine injections were paired during the acquisition sequence evidenced tolerance. In Exp II, tolerant Ss were tested in the presence of 1 component of the compound CS. When a loud tone (85 db) was used in the compound, less analgesic tolerance was elicited later by the weaker visual stimulus alone. This differential stimulus control of the analgesic response suggests that overshadowing may contribute to failures to replicate conditioned morphine tolerance. It is possible that internal morphine-produced stimuli may overshadow external cues. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Temporal dynamics of the rabbit's nictitating membrane response in serial compound conditioned stimuli.

Two experiments, with 88 female albino rabbits, investigated conditioning of the nictitating membrane response to a reinforced serial compound stimulus. The serial compound was composed of a 400-msec CS (CSA), a trace interval of at least 2 sec, and a brief 2nd CS (CSB) prior to the UCS. The CSB duration was either 150, 250, or 400 msec in Exp I, and the CSB duration in Exp II was 400 msec. Exp I compared serial compound training to an "uncoupled" condition, which contained intermixed CSA–UCS trials and CSB–UCS trials. Exp II compared serial compound training with uncoupled training, 2nd-order conditioning (CSA–CSB/CSB–UCS), trace conditioning (CSA–UCS), and generalization testing that entailed CSB–UCS training and unreinforced tests with CSA. The serial compound, uncoupled, and 2nd-order conditioning procedures all produced high levels of responding during CSA, but only the reinforced serial compound procedure yielded an appreciable likelihood of CR initiation during the trace interval between CSA and CSB. The CRs during the trace interval were temporally distinct from the CRs during CSA and did not appear to be belated CRs to CSA itself. Results are discussed in connection with stimulus selection phenomena, for example, overshadowing and potentiation of toxicosis conditioning. (46 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Opioid receptors in the midbrain periaqueductal gray regulate prediction errors during Pavlovian fear conditioning.

The authors used a within-subject blocking design to study the role of ventrolateral periaqueductal gray (v1PAG) opioid receptors in regulating prediction errors during Pavlovian fear conditioning. In Stage I, the authors trained rats to fear conditioned stimulus (CS) A by pairing it with shock. In Stage II, CSA and CSB were copresented and followed with shock. Two novel stimuli, CSC and CSD, were also copresented and followed with shock in Stage II. CSA blocked fear from accruing to CSB. Blocking was prevented by systemic pretreatment with naloxone. Blocking was also prevented in a dose-dependent and neuroanatomically specific fashion by vlPAG infusions of the μ-opioid receptor antagonist CTAP. These experiments show that v1PAG μ-opioid receptors contribute to Pavlovian fear learning by regulating predictive error. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lesions of the amygdala, but not of the cerebellum or red nucleus, block conditioned fear as measured with the potentiated startle paradigm.

In Exp I, 97 male Sprague-Dawley albino rats were given 10 light–shock pairings on 2 successive days. At 24–48 hrs following training, groups of Ss received bilateral transection of the cerebellar peduncles, bilateral lesions of the red nucleus (which receives most of the cerebellar efferents), or bilateral lesions of the central nucleus of the amygdala. Controls were sham operated. At 3–4 days after surgery, Ss were tested for potentiated startle (PS [increased acoustic startle in the presence of the light previously paired with shock]). PS was blocked by lesions of the central nucleus of the amygdala but not by transection of the cerebellar peduncles or lesions of the red nucleus. Exp II, in which a visual prepulse test was used with 14 Ss, indicated that the blockade of PS observed in Ss with amygdala lesions could not be attributed to optic tract damage. Exp III, with 20 Ss, demonstrated that the absence of potentiation in Ss with amygdala lesions was not simply due to a lowered startle level ceiling, because these Ss could show increased startle with increased stimulus intensity and with administration of intraperitoneal strychnine, (0.75 mg/kg), a drug that increases startle. Results are consistent with the hypothesis that the amygdala is involved in fear conditioning. (64 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neuromuscular blocking drugs and heart rate changes after direct nerve stimulation and during classical conditioning in cats.

2 experiments investigated cardiovascular responses to several common neuromuscular blocking compounds. Exp I, employing 16 male cats, assessed ganglionic transmission in sympathetic and parasympathetic systems controlling heart rate and blood pressure after dextrotubocurarine chloride (TC), dimethyl dextrotubocurarine iodide (DTI), succinylcholine chloride (SC), or saline. Cardiovascular responses to sympathetic stimulation were essentially unaffected at drug levels that blocked evoked electromyograms; however, vagally evoked bradycardia and corresponding blood pressure decrease were blocked by TC and reduced by DTI and SC. Exp II compared heart responses of 12 male cats under the same blocking compounds during differential classical aversive conditioning. Differential conditioned responses and unconditioned responses occurred under DTI, less under SC, but not under TC. However, Ss trained under TC and tested under DTI showed differential conditioned responses. (18 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)