The effects of orbital frontal cortex damage on the modulation of defensive responses by rats in playful and nonplayful social contexts.

In a series of 3 experiments on rats, 2 hypotheses were tested: (a) that damage to the orbital frontal cortex (OFC) would alter the socially relevant context for executing defensive responses but not their performance and (b) that damage done to the OFC in early infancy would produce more deficits in social behavior than similar damage occurring in adulthood. Bilateral or unilateral OFC damage in adult males did not impair their ability to defend themselves during play fighting and when protecting their food but did impair their ability to modify the pattern of defense in response to different partners. Rats that sustained bilateral damage at 3 days of age not only had deficits in partner-related modulation of defense but also exhibited hyperactivity in their play. The findings thus supported the proposed hypotheses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of the medial prefrontal cortex in the play fighting of rats.

Although decorticated rats are able to engage in play, their play is abnormal in three ways. First, decorticates do not display the normal, age-related shifts in defensive strategies during development. Second, decorticates do not modify their defensive tactics in response to the social identity of their partners. Third, decorticates display a global shift in defensive tactics from more complex to less complex strategies. It has been shown that lesions of the motor cortex (MC) selectively produce the abnormal developmental effects on play, and that lesions of the orbitofrontal cortex (OFC) selectively produce the deficits in behavioral discrimination between social partners. In the current set of experiments, we demonstrate that lesions of the medial prefrontal cortex (mPFC) produce the shift from more complex to less complex defensive tactics, while leaving intact the age-related and partner-related modulation of defensive strategies. Thus, we have evidence for a triple dissociation of function between the MC, the OFC, and the mPFC with respect to social play behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of cortical serotonin in anxiety and locomotor activity in Wistar rats.

The brain's serotonergic system is known to play an important role in the modulation of anxiety. While the role of serotonin (5-HT) in subcortical structures is well investigated, little is known about the function of cortical 5-HT. The present series of studies used local injections of the serotonergic neurotoxin, 5,7-dihydroxytryptamine (5,7-DHT), into the medial prefrontal cortex (mPFC), entorhinal cortex (EC), or occipital cortex (OccC) of rats to chronically reduce 5-HT neurotransmission in these brain areas. The animals were tested for anxiety-like behavior on the elevated plus-maze and open field. An 82% depletion of 5-HT from the mPFC increased anxiety-like behavior, while no general motor effects were evident. In contrast, a 63% 5-HT-depletion of the EC or a 78% 5-HT-depletion of the OccC did not have any effects on emotional or exploratory behaviors. These findings are in line with a proposed role of 5-HT in the mPFC in the modulation of anxiety- and stress-mediated behavior and demonstrate a functional differentiation between different cortical 5-HT projections. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Tactile stimulation during development attenuates amphetamine sensitization and structurally reorganizes prefrontal cortex and striatum in a sex-dependent manner.

This study investigated the effect of postnatal tactile stimulation (TS) on juvenile behavior, adult amphetamine (AMPH) sensitization, and the interaction of TS and AMPH on prefrontal cortical (PFC) thickness and striatum size. Pups received TS by stroking daily with a feather duster from birth till weaning and were tested, as juveniles, in behavioral tasks including open field locomotion, elevated maze, novel object recognition, and play fighting behavior. Development and persistence of drug-induced behavioral sensitization was tested by chronic AMPH administration and challenge, respectively. PFC thickness and striatum size were assessed from serial brain sections. The findings showed that TS rats spent less time with novel objects on first exposure but open field locomotion and elevated plus maze tasks were not affected substantially. TS reduced the frequency of play fighting and enhanced evasion in response to a playful attack, but only in males. The probability of complete rotation defense, leading to a supine posture during play, was reduced in both sexes. AMPH administration resulted in gradual increase in behavioral sensitization that persisted at least for 2 weeks. However, TS rats exhibited attenuated AMPH sensitization compared to sex-matched controls. Neuroanatomically, AMPH reduced the PFC thickness in control females but enlarged the posterior striatum in control males. TS experience blocked these effects. In summary, TS during development modulated the response to novel objects and altered social behaviors and attenuated AMPH-induced behavioral sensitization by preventing drug-induced structural alteration in the PFC and the striatum, brain regions implicated in drug abuse. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

Play fighting between kindling-prone (fast) and kindling-resistant (slow) rats.

Differences in the play behavior of 2 strains of rats suggest that different components of play fighting can be modified independently. The development of play fighting in cross-strain pairs of familiar and unfamiliar rats was examined to determine whether interacting with a noncongruent pairmate would alter the pattern of play typical for each strain. In both strains, changes in play fighting were observed throughout development, but partner identity appeared to influence play fighting in different ways depending on age. These data suggest that some components of play may be more impervious to changes in social environment than other components. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Purkinje Cell Loss by OX7-Saporin Impairs Excitatory and Inhibitory Eyeblink Conditioning.

Cerebellar cortical contributions to eyeblink conditioned excitation have been examined extensively. In contrast, very little evidence exists concerning the role of the cerebellar cortex in eyeblink conditioned inhibition. In the current study, rats were given intraventricular infusions of the immunotoxin OX7-saporin to selectively destroy Purkinje cells throughout the cerebellar cortex following excitatory conditioning. After a 2-week postinfusion period, the rats were given reacquisition training. After reacquiring excitatory conditioning, the rats were trained in a feature-negative discrimination procedure to establish conditioned inhibition. Rats treated with OX7-saporin showed impaired reacquisition of excitatory conditioning and acquisition of conditioned inhibition. The results suggest that Purkinje cells play important, but different, roles in conditioned excitation and inhibition in rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A threshold and continuum of injury during active stretch of rabbit skeletal muscle

Play fighting by juvenile rats involves playful attacks directed at the partner's nape, where successful contact leads to gentle rubbing of the snout into the nape area. In addition, the recipient of such contact may defend the nape by adopting tactics of playful defense. The two most common defensive tactics in the juvenile period are evasion, where the recipient swerves or leaps away and facing defense involving rotation to supine, where the attacker is faced and its further attempts to contact the nape are blocked. An unresolved issue is whether the nape contact itself or defense by the recipient alone or in combination with nape contact, are involved in rewarding play fighting. In this study, drug-induced non-playful partners were used to test the 'motivation' for play fighting when only playful nape contact was possible. In drug-trials compared to baseline and saline trials, both neonatally androgenized females (high players) and control, oil-treated, females (low players), decreased the frequency of launching nape attacks. These results suggest that nape contact alone, in the absence of defense by the recipient, is not sufficient reinforcement for such playful activity, irrespective of the initial playfulness of the subjects. However, while nape attacks decrease, other forms of social contact, such as anogenital investigation and climbing over the partner (i.e., crawl overs), increase in frequency. These results suggest that non-playful partners are not neutral targets for normal rats. Rather, the 'non-normal' behavior of the drugged target may affect the subjects' behavior in such a way as to reduce their playfulness for reasons other than reduced reinforcement for play.     

Emotional behavior in feral cats with ablations of prefrontal cortex and subsequent lesions in amygdala.

Bilateral ablations of gyrus proreus in 6 cats did not significantly alter either the intensity or the pattern of flight behavior during confrontation with a human. The scores for defense behavior were reduced in only 2 Ss. Subsequent lesions in the rostral part of the basolateral nuclei of amygdala reduced flight and transiently decreased defense scores in all Ss. It is concluded that the prefrontal cortex does not seem necessary for the flight and defense responding observed in feral cats. The role of amygdala in the regulation of these behaviors is confirmed. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Orbital frontal cortex ablations of rock squirrels (Spermophilus variegatus) disinhibit innate antisnake behavior.

The antisnake behavior of rock squirrels (Spermophilus variegatus) was examined to determine the role of the orbital frontal cortex in regulating physiological arousal and behavioral excitability during encounters with a rattlesnake predator. Rock squirrels with orbital frontal cortex ablations and shamsurgery control squirrels were presented with a caged rattlesnake pre- and postsurgery. Orbital frontal cortex ablations had no substantial effect on the expression of gross motor behavior in dealing with the rattlesnake, but they augmented the speed of snake recognition and clearly disinhibited sympathetic arousal as manifested by increased tail piloerection and tail-flagging activity, which is a specific antisnake behavior. Natural selection from snakes has probably shaped the neural organization of the orbital frontal cortex to afford adaptive behavioral flexibility during snake encounters. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Unilateral cortical lesions and paw preferences in cats.

Conducted 3 experiments to examine the effects of unilateral cortical lesions on the paw preferences of a total of 30 laboratory-reared mongrel and 3 Siamese 6-146 mo. old cats. Results show that paw preferences were reversed by ablations of the sensorimotor cortex contralateral to the preferred paw. These shifts in manual preferences remained constant throughout several mo. of postoperative testing. Ss with lesions in sensorimotor cortex, tested only after the acute effects of the cortical lesion subsided, showed a permanent reversal in their responses on object-displacement tasks, but not on simpler retrieval tasks. Extensive ablations of the posterior cortex, alone or in combination with section of the corpus callosum, had no significant effect upon paw preferences when the sensorimotor cortex was spared. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of bilateral lesions of auditory cortex in mice on the acoustic startle response

The acoustic startle response (ASR) was used to investigate the effects of auditory cortical lesions on a brain stem-mediated auditory behavior. The ASRs were obtained longitudinally from young adult C57BL/6J mice before bilateral ablation of auditory cortex, 1 day after ablation, and 1 month later. Control mice received lesions of nonauditory cortex. For some mice, averaged brain stem-evoked responses (ABR) were obtained, and these indicated no effects of lesions on auditory sensitivity. One month after surgery, mice with auditory cortex ablations were statistically indistinguishable from controls on all suprathreshold measures of ASR. However, 1 day after ablation of auditory cortex, experimental animals (but not controls) exhibited a change in ASR amplitude (but not threshold or latency). When a noise burst of 80 dB SPL was used to elicit the ASR, the amplitude was diminished, but with a 110 dB stimulus, amplitude was enhanced. The findings can be interpreted in one of two ways: temporary interference with modulation of the ASR normally performed by auditory cortex; or a general effect of auditory cortex ablation on brain stem auditory circuits not specific to the ASR. In any event, if auditory cortex plays a modulatory role with regard to the ASR, it is apparently nonessential and/or readily compensated for after ablation.     

Comparison of emotional responses in monkeys with rhinal cortex or amygdala lesions.

Four emotionally arousing stimuli were used to probe the behavior of monkeys with bilateral ablations of the entorhinal and perirhinal cortex. The monkeys' behavioral changes were then contrasted with those observed earlier (M. Meunier, J. Bachevalier, E. A. Murray, L. Málková, & M. Mishkin, 1999) in monkeys with either neurotoxic or aspiration lesions of the neighboring amygdala. Rhinal cortex ablations yielded several subtle behavioral changes but none of them resembled any of the disorders typically seen after amygdalectomies. The changes produced by rhinal damage took mainly the form of heightened defensiveness and attenuated submission and approach responses, that is, just the opposite of some of the most distinctive symptoms following amygdala damage. These findings raise the possibility that the rhinal cortex and amygdala have distinct, interactive functions in normal behavioral adaptation to affective stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Movement-associated neural excitation as a factor in spatial representational memory in rats.

The hypothesis that rats require an attentionlike function arising from integration of exteroceptive and movement-related excitation during the information phase of representational memory–dependent discriminations is proposed. Experiments 1A and 1B (both behavioral) demonstrated the crucial importance of movement-related excitation (angle of turn at T-maze choice point). Experiment 2 showed that, contrary to plausible expectations, ablation of putative posterior parietal association cortex only mildly affected memory. This finding agrees with the notion of a nonspecific mass action–equipotential effect of ablations in nondifferentiated cortex on memory rather than the specific effects resulting from dorsolateral prefrontal ablations in primates. Instead, it is proposed from previous data (e.g., K. M. Heilman et al, 1987) that the hippocampus integrates movement-related and exteroceptive excitations necessary for representational memory, which is largely restricted to spatial attributes in rats. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Cortical Responses in Rats Predict Perceptual Sensitivities to Complex Sounds.

The common assumption that perceptual sensitivities are related to neural representations of sensory stimuli has seldom been directly demonstrated. The authors analyzed the similarity of spike trains evoked by complex sounds in the rat auditory cortex and related cortical responses to performance in an auditory task. Rats initially learned to identify 2 highly different periodic, frequency-modulated sounds and then were tested with increasingly similar sounds. Rats correctly classified most novel sounds; their accuracy was negatively correlated with acoustic similarity. Rats discriminated novel sounds with slower modulation more accurately than sounds with faster modulation. This asymmetry was consistent with similarities in cortical representations of the sounds, demonstrating that perceptual sensitivities to complex sounds can be predicted from the cortical responses they evoke. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociating the role of the parietal cortex and dorsal hippocampus for spatial information processing.

Dorsal hippocampus, parietal cortex, and control lesioned rats were tested on both a metric and topological task. The metric task consisted of 2 different objects placed 68 cm apart on a cheese board. After habituation, the objects were moved to a separation of 38 cm on Day 1 and to a separation of 98 cm on Day 2. The topological task consisted of 4 different objects placed in a square orientation. After habituation, the first 2 objects were switched, and after the rats habituated to that change, the back 2 objects were switched. This was repeated on a different day with 4 new objects. The data suggest that the hippocampus is necessary for metric representations, whereas the parietal cortex is necessary for topological representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Sex and social play in juvenile rats (Rattus norvegicus).

Four experiments were conducted to examine the effects of pretest social isolation, sex of the social stimulus, and test cage familiarity on sex differences in play fighting in 156 juvenile Long-Evans rats. Reliable sex differences were found only when Ss were tested after 6 days of isolation in undisturbed cages (Exp III). In contrast to weak sex effects, pretest isolation and test cage familiarity were robust variables influencing levels of play fighting in juveniles of both sexes. Results are discussed in reference to procedural differences among experimental approaches that have examined sex differences in social play. It is suggested that social investigatory behavior and play behavior appear to be reciprocally related. Hence, the sex difference in social play is accompanied by an apparent reversal in the sex effect seen with social investigation. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of lesions in the amygdala, periamygdaloid cortex, and stria terminalis on aggressive behaviors in rats.

In 3 experiments, with a total of 113 male albino Sprague-Dawley rats, it was found that small lesions in the periamygdaloid cortex, cortical amygdaloid nucleus, or bed nuclei of the stria terminalis reduced or eliminated attacks and signs of dominance in fights which were generated by isolated housing and the omission of food reward. The same lesions had little or no effect on pain-induced or reflexive "fighting" or on mouse-killing. Small lesions in the lateral or central amygdaloid nuclei significantly inhibited pain-induced "aggression," but did not modify attack behavior or dominance in fights that occurred in situations not involving painful stimulation. These lesions also did not alter mouse-killing behavior. Results suggest that the periamygdaloid cortex and cortical amygdaloid nucleus, as well as the stria terminalis, may be part of a neural system which influences intraspecies aggression in male rats. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Brain regional neuropeptide changes resulting from social defeat.

Past work has demonstrated robust brain changes in cholecystokinin (CCK-8) following social defeat. Here the authors analyzed brain regional, CCK-8, substance P, corticotropin releasing factor (CRF), and neuropeptide Y levels in adult male Long-Evans rats defeated in a resident-intruder social aggression paradigm, as indexed by elevated bites received, freezing, and emission of 20-kHz calls. Brains harvested 6 hr after social defeat were dissected into 12 regions (olfactory bulbs, 3 cortical regions [frontal cortex, cortex above the basal ganglia, cortex above the diencephalon], caudate-putamen, basal forebrain, hypothalamus, hippocampus, thalamus, tectum, tegmentum, and lower brain stem). Neuropeptide radioimmunoassays demonstrated the following statistically significant regional changes in defeated rats as compared with nondefeated rats: CCK-8 was reduced in frontal cortex and cortex overlying diencephalon, the olfactory bulbs, caudate-putamen, hippocampus, tectum, and lower brainstem. Neuropeptide Y was elevated in the caudate-putamen. Substance P was elevated in the cortex over the basal ganglia and decreased in basal forebrain. CRF was diminished in the hippocampus. The results highlight more robust CCK modulation by social defeat as compared with 3 other neuropeptide systems involved in brain emotional regulation. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Posterior extramarginal cortex and visual learning by cats.

Reports results of 3 experiments with a total of 59 mongrel and 11 Siamese cats. Extensive ablations of posterior cortex which spared the primary visual areas severely impaired visual pattern discrimination, detour learning, and spatial reversal performance. Lesions in the posterior ecto- and suprasylvian gyri (EP) produced significant deficits in learning multiple object discrimination problems, repeated reversals on spatial or visual cues, and successive visual discriminations. Ss with cortical ablations that did not invade the EP region but did cause damage to the optic radiations were not impaired in reversal learning and were deficient in successive discriminations only when tested with nonsalient cues. Thus, some of the defects shown by EP cats are qualitatively different from the losses in cats with damage to the geniculostriate system. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Motor cortex injury has different behavioral and anatomical effects in early and late adolescence.

Although there are many studies investigating the effects of early cortical injury on brain and behavioral development in laboratory animals, there are virtually no studies examining the effects of cortical injury in adolescence. The purpose of present study was to investigate the effects of unilateral motor cortex lesion received in early and late adolescence periods (Postnatal days 35 and 55 [P35, P55]) on spontaneous neural reorganization and behavioral recovery in adulthood. Rats were given unilateral motor cortex lesions at P35 or P55 and their motor behaviors were compared to sham controls in adulthood. The results of behavioral tests (skilled reaching, postural asymmetry, sunflower seed manipulation, forepaw inhibition in swimming) revealed that rats with P35 lesions had significant functional deficits whereas the rats with P55 lesions showed nearly complete recovery. Golgi-Cox analysis of pyramidal neurons showed bilateral hypertrophy of dendritic fields in the remaining sensorimotor cortex in P55 but not P35 rat brains. Thus, there appears to be an age-related pattern of morphological and behavioral changes in response to cortical injury in the early and late adolescent periods leading to better functional recovery from later injuries, much as is seen in human children. (PsycINFO Database Record (c) 2010 APA, all rights reserved)