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)     

Habituation of the shortening reflex in the medicinal leech.

Conducted 3 experiments in which the shortening reflex was elicited in 46 food-sated leeches (Hirudo medicinalis) by light flashes delivered at 20-sec intervals over a 40-trial session. In Exp I, the reflex was enhanced if Ss were stored at 5-7° C rather than 20° C. Short-term (within sessions) habituation was readily observed. In Exp II, dishabituation could be produced by a single electric shock at Trial 30. However, in Exp III, the shock also enhanced responding when delivered before Trial 1 (sensitization). No long-term (between-sessions) habituation occurred over 6 consecutive days of testing in Exp I; on the contrary, responding gradually increased. It is suggested that the simplicity of these short-term processes in leeches makes them particularly suitable for electrophysiological investigations into the neural basis of habituation and sensitization. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Attenuation of "acute" habituation by scopolamine in the black-tailed prairie dog (Cynomys ludovicianus).

Tested and confirmed the hypothesis that scopolamine attenuates habituation occurring within a training session as well as that occurring between training sessions. Subcutaneous scopolamine injections (.5 mg/kg) reduced spontaneous wheel running in 8 female prairie dogs. The same dosage did not affect the threshold for wheel running induced by electrical brain stimulation (EBS) in 6 Ss in Exp II. Exp III (n = 6) demonstrated that EBS-induced running declined during a 10-min stimulation period and indicated that the decline was habituative since the response was repeatedly dishabituated. In Exp IV .5 mg/kg of scopolamine reduced habituation of EBS-induced wheel running during 10-min sessions with the 6 Ss used in Exp II. (22 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Plasticity of the acoustic startle response in the acutely decerebrate rat.

In 4 experiments, plasticity of the acoustic startle reflex was measured in male albino Sprague-Dawley rats in which a complete transection between the forebrain and midbrain was made. During a period from 60 to 100 min after surgery, startle amplitude in the transected Ss was relatively stable and comparable with that of controls (anesthetized with halothane and placed in a stereotaxic instrument). During this period the transection did not alter the temporal recovery process (with intervals of 2, 4, 8, or 16 sec) or auditory prepulse inhibition (with intervals of 25, 50, 100, 500, or 1,000 msec) or the normal reduction in startle caused by high levels of background noise. The transection did prevent the normal increase in startle caused by moderate levels of background noise and eliminated within-session habituation. The effect on habituation was particularly noticeable since the curves of the transected and nontransected Ss actually crossed. Results are dicussed in terms of how the transection procedure can be used to evaluate various hypotheses about underlying mechanisms of startle plasticity. (50 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Short-term and long-term habituation of the acoustic startle response in chronic decerebrate rats.

13 chronic decerebrate male albino rats, maintained in good condition for 31–84 postoperative days, showed significant within-session habituation of the acoustic startle response. However, they showed no habituation over days under conditions that produced significant response deficits in controls. The decerebrates' stimulus-provoked response deficits may have endured for up to 40 min between sessions, and they were apparently more than normally susceptible to stimulus-provoked sensitization. Data are consistent with models that assume that the mechanisms for short-term habituation are intrinsic to the stimulus-response (S–R) pathway in the lower brain stem. On the other hand, relatively permanent long-term habituation of the acoustic startle response must be mediated by extrinsic mechanisms rostral to the S–R pathway that superimpose an inhibitory influence on that pathway. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus-produced reflex inhibition in the rat during induction of and recovery from barbiturate anesthesia.

Reported 3 experiments which show that the inhibitory effect of a preliminary stimulus on the acoustic startle reflex was disrupted during the induction of sodium pentobarbital (40 mg/kg) in a total of 50 male Holtzman rats. In Exp I (n = 35) and II (n = 8), Ss were injected with the barbiturate, and a startle stimulus was presented either alone or preceded by a white noise burst. Results show that (a) stimulus inhibition was present immediately after injection, (b) was lost during a phase of hyperreactivity which accompanied induction of the anesthesia, and (c) recovered as reactivity diminished in the anesthetic state. Exp III showed that inhibition recovered during an intervening stage prior to complete areflexia and that this recovery revealed that the earlier and later inhibitory failure cannot be ascribed to a drug-dependent degradation in a hypothetical inhibitory system. It was suggested that the expression of reflex inhibition depends on the balanced interplay of excitatory and inhibitory processes which are differentially sensitive to drug intake. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of long-term sensitization on long-term habituation of the acoustic startle response in rats: Central gray lesions, preexposure, and extinction.

The relation between long-term decrements of the acoustic startle response in rats and the development of freezing behavior during habituation training was examined. Freezing behavior developed over the initial trials of habituation training, and the rate of long-term response decrements was found to be inversely related to the development of freezing. Manipulations (neurological or behavioral) that either reduced the level of freezing or retarded its development promoted startle response decrements. In Experiment 1, rats receiving electrolytic lesions of the ventrolateral periaqueductal gray demonstrated both accelerated long-term startle response decrements and retarded development of freezing behavior. In Experiment 2, preexposure to the startle apparatus (i.e., latent inhibition) accelerated long-term startle decrements and inhibited development of freezing. In Experiment 3, exposure to the startle apparatus following initial habituation training (i.e., extinction) reduced both freezing behavior and startle response amplitudes. The results are discussed in terms of the influence of Pavlovian fear conditioning on long-term habituation of the acoustic startle response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of contextual change on latent inhibition and on the habituation of an orienting response.

In Exp I, using 20 female hooded Lister rats, the habituation of the orienting response (OR) shown by Ss to a discrete visual stimulus (a 10-sec light) in a given training context (A) was monitored. Dishabituation occurred, in that the OR returned to its initial level, when the light was presented in a different and novel context (B). In Exp II, 24 female rats received 2 sessions/day, one in each of the 2 contexts. For experimental Ss, the light was presented in Context A until the OR habituated. In the test phase, the light was presented in Context B, but the OR was not restored, suggesting that the dishabituation seen in Exp I depended on the absolute novelty of Context B. In Exp III, Ss from Exp II were required to form a light–food association in both contexts. Slow learning was observed in Ss trained with the familiar light in Context A, but learning proceeded normally with the familiar light in Context B. Thus, a context change that failed to produce dishabituation was enough to prevent the occurrence of a latent inhibition effect. (35 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some sources of variation in the bar-pressing versus freeloading phenomenon in rats.

Gave 40 albino rats a choice between barpressing for food or taking it freely from a dish. In Exp I Ss were given 3 days of free-food training and 6 days of barpress training before the choice. In Exp II the number of prechoice bar presses was varied within the choice sessions, and in Exp. III the choice sessions were extended over 10 days. In all 3 experiments the mean number of pellets obtained via bar pressing was over 70%. In Exp IV and V the amount of time spent and the number of pellets obtained in freeloading and barpressing were equalized. In both studies Ss greatly preferred to freeload. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Habituation of the acoustic startle response in rats after lesions in the mesencephalic reticular formation or in the inferior colliculus.

Extensive damage to the mesencephalic reticular formation (MRF) in 24 male albino rats altered long-term habituation of the acoustic startle response without disrupting short-term habituation. The MRF lesions did not alter initial startle amplitudes, but the Ss with lesions were unable to attain as low a long-term asymptote of habituation as could 21 control Ss. Subsequent manipulation of stimulus intensity and interstimulus interval revealed no differences in short-term habituation between the 2 groups. Large lesions to the inferior colliculus (IC) of 22 Ss did not disrupt long-term habituation of the acoustic startle response, but these Ss were unable to suppress responding as much as controls to intense stimuli presented rapidly. The deficits in long-term habituation following MRF lesions suggest a disruption of an extrinsic, inhibitory mechanism of habituation. The deficits following IC lesions could have been due either to a disruption of a short-term habituation mechanism or to an increase in response sensitization produced by the lesions. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of mesencephalic reticular formation lesions on habituation of startle and lick suppression responses in the rat.

In 2 experiments with 43 male albino Holtzman rats, extensive damage to the mesencephalic reticular formation (MRF) altered long-term habituation of the acoustic startle response without disrupting short-term habituation. Ss with MRF lesions, although initially neither more nor less responsive than controls, could not attain as low a long-term asymptote of habituation as could control Ss with repeated presentations of an auditory stimulus. Changing the quality of the auditory stimulus abolished the asymptotic difference in responsiveness. With repeated presentations of the 2nd auditory stimulus, control Ss again reached a significantly lower long-term habituation asymptote than did Ss with MRF lesions. The course of long-term habituation for the 2 groups suggested a disruption of an extrinsic, inhibitory habituation process by the lesions. The effects of MRF lesions were specific to the acoustic startle response. Control Ss and those with lesions showed comparable response levels, short-term habituation, and long-term habituation of the lick suppression response. Responsiveness and habituation to tactile stimuli were comparable for the 2 groups on both lick suppression and startle response measures. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lack of task specificity and absence of posttraining effects of atropine on learning.

Three experiments, with 91 male Lister rats, examined the effect of the cholinergic antagonist atropine on the acquisition of learning tasks known to be sensitive or insensitive to impairment by hippocampal lesions, on the retention of performance acquired in the absence of the drug, and on memory consolidation immediately after daily training trials. In Exp I, intraperitoneal atropine sulfate (10 or 50 mg/kg) injected 30 min prior to training severely impaired learning of both spatial and nonspatial discrimination tasks when compared with saline or atropine methylnitrate (50 mg/kg). In Exp II, atropine sulfate (50 mg/kg) also impaired spatial discrimination accuracy in Ss previously trained to asymptote under drug-free conditions. These deficits were not due to either peripheral drug effects of gross sensorimotor impairments. In Exp III, daily posttraining injections of atropine sulfate (50 mg/kg) failed to influence either learning or subsequent retention of place navigation in Ss trained to find a single hidden escape platform. The data confirm that profound learning deficits occur when training is conducted under atropine but offer no support to the hypotheses that cholinergic neurons play an important role in memory consolidation or other posttraining processes. Results demonstrate dissimilarities between the behavioral impairments induced by cholinergic blockade and hippocampal lesions under appropriate test regimes. (50 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of prior exposure on conditioned taste aversion in the rat: Androgen- and estrogen-dependent events.

Studied the effects of preexposure and gonadal hormone manipulation on the extinction of a conditioned taste aversion in 198 male Sprague-Dawley rats. In Exp I, Ss were given 1 prior exposure to sucrose at some selected time (Days 4, 2, or 1) before a 2nd exposure (Day 0) to sucrose and a LiCl injection, or they were given only a single exposure (Day 0). Under single exposure, castrated Ss extinguished the aversion faster than either testosterone-treated castrated Ss or sham-operated Ss. In Exp II, estradiol, dihydrotestosterone, and testosterone were studied by using only a Day 1 preexposure condition. The testosterone-treated group maintained the aversion for the longest period, followed by dihydrotestosterone-treated, sham, castrated, and estradiol-treated groups. In Exp III, estradiol was administered alone or in combination with 2 doses of dihydrotestosterone. Findings indicate that the outcome of behavior was dependent on the ratio of estradiol to dihydrotestosterone, with variations in this ratio resulting in fast (estrogen effect) to slow (androgen effect) rates of extinction. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Habituation, prepulse inhibition, fear conditioning, and drug modulation of the acoustically elicited pinna reflex in rats.

A reliable component of the acoustic startle response in animals is a flexion of the ears, the pinna reflex (PR). The present investigation attempted to develop a preparation and apparatus suitable for analyzing the PR in the awake rat. A 2nd goal was to examine the PR under behavioral and pharmacological conditions known to affect other response systems, such as whole-body startle, and determine whether the PR is a valid model for analyzing behavioral plasticity. The amplitude of the PR in 17 spinally transected male Sprague-Dawley rats was directly related to stimulus intensity and exhibited short-term habituation, prepulse inhibition, and enhancement by prior fear conditioning. PR amplitude increased following intraperitoneal administration of strychnine HCl (0.75 mg/kg) and was decreased following clonidine HCl (40 μg/kg). It is concluded that this preparation and response system are valid for studying various forms of behavioral modification. Findings are discussed in terms of the potential utility of this response system in investigating the cellular correlates of behavioral plasticity in mammals. (30 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Potentiation of the acoustic startle response by a conditioned stimulus paired with acoustic startle stimulus in rats.

The hypothesis that the standard acoustic startle habituation paradigm contains the elements of Pavlovian fear conditioning was tested. In a potentiated startle response paradigm, a startle stimulus and a light conditioned stimulus (CS) were paired. A startle stimulus then was tested alone or following the CS. Freezing behavior was measured to index conditioned fear. The startle response was potentiated on CS trials, and rats froze more in CS than in non-CS periods. In Experiment 1, response to a previously habituated, weak startle stimulus was potentiated. In Experiment 2, response to the same stimulus used as the unconditioned stimulus (US) in training was potentiated. This CS-potentiated response retarded the course of response decrements over training sessions as compared with an explicitly unpaired control group. Conditioned fear is a standard feature of this habituation paradigm, serves to potentiate the startle response, and provides an associative dimension lacking in the habituation process per se. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Habituation to shock and learned persistence in preweanling, juvenile, and adult rats.

In Exp I, a prolonged shock-habituation treatment given between runway acquisition and simple extinction promoted persistence in both preweanling and juvenile Holtzman rats. Exp II showed even stronger persistence effects in a punished-extinction test given after shock treatment, the effects being stronger in preweanlings than in juveniles. Exp III demonstrated that shock treatment at infant-to-preweanling age resulted in increased persistence that survived a 42-day retention interval in a nonreward extinction test. Exp IV demonstrated habituation to shock in preweanlings and juveniles in terms of recovery of suppression of milk intake in the shock situation and, compared with controls, in terms of reduced latency to eat in a punished-reward test at several retention intervals. Exp V showed that the strength of persistence to approach in a runway reflected the presumed degree of habituation in 70-day-old Ss. (33 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cache recovery and spatial memory in Clark's nutcrackers (Nucifraga columbiana).

Clark's nutcrackers cache pine seeds and recover them months later. Four experiments with 5 nutcrackers tested their ability to relocate their caches when the cache sites were selected by the experimenters. During Exp I, Ss had 18 cache sites available during each of 3 caching sessions, followed 10 days later by 4 recovery sessions. Recovery performance was above chance, and there were frequent revisits to previously emptied cache sites. During Exp II, hunger level (manipulated by prefeeding) had no effect on recovery accuracy. During Exp III, Ss were released into the experimental room with no seeds present. Probing behavior was directed at the old cache sites of Exp I and especially of Exp II. During Exp IV, the number of holes available during caching sessions had no effect on the accuracy of 3 of the 4 Ss. Findings suggest that spatial memory is a primary mechanism by which nutcrackers locate their caches. (30 ref) (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Effects of overtraining and high activation on bar pressing of rats tested under water deprivation.

Trained 2 groups of 9 male albino Sprague-Dawley rats each in a Skinner box under 24 hrs of water deprivation; Group 1 received 15 daily training sessions, Group 2 30 sessions. In Exp II, 4 groups (9 Ss each) were also trained in a Skinner box but under different conditions of water deprivation (24, 36, 48, and 60 hrs, respectively). In both experiments, the relationship between performance and activation was evaluated by submitting each group to successive and independent conditions of water deprivation (24, 36, 48, 60, and 72 hrs). Heart rate was used as an index of activation during training and during the test phase. Overtraining (Exp I) and high activation during training (Exp II) prevented the drop in performance usually observed under high levels of activation. (20 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sexual differentiation of play behavior in the ferret.

Three experiments examined the endocrine mechanisms responsible for sex differences in prepubertal play behavior of ferrets. In Exp I, 6 gonadally intact adolescent males exhibited higher levels of "stand-over" behavior than 6 females did in tests between 63 and 123 days of age with gonadally intact female partners of the same age. In Exp II, with 69 Ss, those Ss exposed to androgen or to ovarian steroids over Days 5–20 of postnatal life subsequently exhibited significantly higher levels of stand-over behavior in tests with females than did control females gonadectomized on Day 5 and not given steroids. None of the Ss in Exp II exhibited levels of stand-over behavior comparable to those of the gonadally intact males in Exp I. In Exp III, with 36 Ss, males gonadectomized and implanted subcutaneously with testosterone capsules on Day 70 and tested with females at 84–96 days of age exhibited levels of stand-over behavior comparable to those observed in Exp I in gonadally intact males of the same age (Weeks 12–24). Males gonadectomized on Day 70 and given no hormone at testing exhibited significantly lower levels of this behavior. Significantly lower levels were also exhibited by males gonadectomized on Day 35 and females gonadectomized on Day 70, regardless of whether they were tested with testosterone present after Day 70. Sex differences in the expression of prepubertal play behavior of ferrets apparently result from differential exposure of males and females to androgen over an extended postnatal period. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transient sex differences in the between-sessions but not in the within-session memory underlying an active place avoidance task in weanling rats.

Spatial abilities were tested in male and female rats by training them to avoid an area in which there was a mild footshock while the arena rotated at 1 revolution/minute. The to-be-avoided area was stable in the coordinates of the room, so extramaze landmarks had to be used for accurate navigation, as the rotation made intramaze cues and substrate-based path integration useless for the avoidance. From Postnatal Day (PD) 19, rats were trained for 22 consecutive days. When the shock area was the same across sessions male rats reached optimal performance on PDs 23–24, 10 days before female rats, but when the location of the shock changed daily there were no sex differences. The results indicate that there are separate memory components underlying spatial competence: a within-session component that develops similarly in male and female rats and a between-sessions component that lasts at least 24 hr and appears earlier in male than in female rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)