Running-wheel avoidance behavior following septal area lesions in rats.

Studied acquisition of a running-wheel avoidance response in 52 male Wistar rats with (a) septal lesions, (b) septal and postcommissural fornix lesions, or (c) septal, postcommissural fornix, and anterior thalamic damage. Ss with lesions confined to the septum were deficient in acquiring the avoidance response compared with both normal Ss and Ss with the more posterior lesions. Ss sustaining combined septal-fornical and septal-fornical-thalamic lesions did not differ from normal Ss or from each other in their acquisition scores. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Discrimination of emitted behavior following septal area lesions in rats.

Conducted 4 experiments with a total of 57 Long-Evans rats to investigate the behavioral consequences of septal lesions on acquisition, retention, and tracking performance on a 2-bar ratio schedule of reinforcement. This schedule requires S to monitor its amount of emitted behavior and match this information with reinforcement contingencies of the schedule for adaptive and efficient performance. On schedules requiring only a moderate amount of response output, septal lesions led to stereotyped and maladaptive performance. However, on very stringent schedules requiring a large amount of response output, septal lesions led to adaptive, and even enhanced, performance relative to operated controls (n = 26). Results suggest that septal lesions do not impair the sensory discrimination of emitted behavior but act differentially on numerous psychological dispositions vital for 2-bar ratio schedule performance. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Medial septal lesions disrupt spatial, but not nonspatial, working memory in rats.

In Exp 1, rats with small medial septal lesions were less able than were control rats to remember the location of the arm of a Y maze they had been forced to enter on the preceding sample run. Moreover, as the retention interval between the sample and choice runs on this spatial delayed nonmatching-to-sample (DNMTS) task was increased to 1 and 2 min, the magnitude of the deficit increased. In contrast, these same lesioned rats were not deficient in Exp 2 in their ability to remember the object they had encountered in the straight alley on the sample run. In fact, when the retention interval was increased to 1 min on this nonspatial DNMTS task, the rats with medial septal lesions were more accurate than were the controls. This pattern of results did not appear to be due to task difficulty, recovery of function, or sequence of training. Rather, these results indicate that damage to the septohippocampal system disrupts spatial working memory more than it disrupts nonspatial working memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Deficient passive and one-way active avoidance acquisition following medial forebrain bundle lesions in rats.

In 3 experiments with 93 Long-Evans male hooded rats, cathodal electrolytic lesions of the medial forebrain bundle (MFB) at posterior hypothalamic levels produced a mild, transient hypodipsia and lowered jump thresholds to footshock. Lesions produced marked deficits in passive avoidance performance in a paradigm that paired discrete, linearly incrementing footshock intensities with contact of a water spout following 48 hrs of water deprivation. Injections of levo-dextro-5-hydroxytryptophan (75 mg g, ip), the immediate metabolic precursor of serotonin, had no effect on the passive avoidance performance of either experimental or operated control Ss. Lesions of the MFB also resulted in deficient acquisition in a 1-trial step-through passive avoidance paradigm not using motivation to drink and caused a severe acquisition deficit in a 1-way active avoidance task. Lesions of the septal nuclei produced lowered jump thresholds but did not affect acquisition in the 1st passive avoidance task. Results are interpreted as indicating a lesion-induced deficiency in fear learning, independent of the serotonergic functions of the MFB. (45 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Exploratory behavior and reaction to novelty in rats: Effects of medial and lateral septal lesions.

This study was carried out to investigate whether medial septal (MS) or lateral septal (LS) lesions may differentially affect rats' ability to react to novelty or environmental change. Three types of task were used based on various sets of stimuli: visual and tactile, olfactory only, and visual only. The results showed that MS and LS lesions reduced preference for novelty, with different effects. The MS group displayed decreased exploration of both neutral and novel objects, whereas the LS group exhibited increased exploration of the objects compared with the control group. A reduced level of locomotor and rearing activity was initially seen among the MS animals. These results were compared with previous findings of behavioral changes after regional hippocampal perforant path lesions in the same test as used in this study. The comparisons imply that disruption of septal input to the hippocampal formation produces cognitive deficits different from those seen after disruption of entorhinal input. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Defensive behaviors in rats following septal and septal-amygdala lesions.

Results of 2 experiments, utilizing 88 male albino Wistar rats, indicated that septal damage produced hyperdefensiveness rather than attack behavior or general hyperreactivity. Further division of this group indicated that damage to sites anterior and ventral to the septal area, sites previously implicated in the "septal syndrome," produced maximal effect on these behaviors. When amygdala lesions were combined with septal damage, enhanced defensive responding was almost eliminated. Results also indicate that amygdaloid mechanisms are involved in the regulation of conspecific defensive behaviors. (19 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stimulus perseveration and choice behavior in rats with septal lesions.

Conducted 3 experiments to test a total of 56 Sprague-Dawley rats with lesions in the septal area and 45 controls for spontaneous-alternation behavior under various stimulus conditions. Ss with septal lesions exhibited perseveration to olfactory and visual cues presented either alone or in conjunction. This behavior was largely independent of response or spatial contingencies. Placement of the olfactory and visual cues in opposition eliminated the perseverative responding of these Ss. Normal controls exhibited the expected spontaneous-alternation behavior which was largely independent of the olfactory and visual contingencies. Results are discussed in terms of the role of the septum in the utilization of stimulus cues. (28 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lowered response to postingestive cues following septal lesions in rats.

Conducted 3 experiments with a total of 36 male albino Sprague-Dawley rats and 54 male albino Carworth CFE rats. Ss with septal lesions were tested in a variety of consummatory situations (e.g., solution intake, direct stomach loads preceding pellet intake, and stomach preloads preceding glucose intake). The lesions resulted in exaggerated responding to taste factors and a decrease in responsivity to postingestive cues relative to control Ss. Results support the view that the septum is an important link in the feeding circuit. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The role of hyperdipsia in aggression following septal lesions in rats.

Lesions of the septum in animal Ss are known to produce an increase in aggressiveness and an increase in water intake. A series of 5 experiments with 120 female Sprague-Dawley rats examined the possibility that aggression is secondary to hyperdipsia. When Ss with septal lesions were restricted to preoperative levels of water intake, aggression scores declined significantly. When Ss without lesions were preloaded with either water or saline, aggression increased. Neither decreased shock threshold nor increased cell hydration provided a full explanation for the results. It is suggested that the aversive nature of the stomach turgescence caused by increased water intake may be an additional mediating factor in septal aggression. (31 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Persistent depression of rearing behavior in rats after extensive septal lesions.

Conducted 5 experiments with a total of 77 male albino Holtzman rats. Extensive septal lesions produced a persistent (76 days) reduction in rearing behavior which was not directly attributable to altered deprivation states, emotionality, activity levels, or competing behaviors and which occurred in familiar as well as various novel testing environments. Changes in visual, olfactory, or conspecific stimuli ameliorated or had no effect on the lesion effect. Results indicate that the septal area is importantly involved in normal rearing behavior and that lesion-induced alterations in responsiveness to some forms of stimulation may play a modulatory role in reduced rearing. It is also suggested that the septal area may constitute a portion of a neural system responsible for the initiation of this form of response. (28 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The relation of feeding and activity following septal lesions in rats.

The patterns of intake of liquid diet (Exp I) and water (Exp II) were recorded in 12 female Long-Evans diet-deprived rats with septal lesions and 13 neurologically intact controls during the 1st hr of diet access. The occurrences of grooming, resting/sleeping, and exploring were also recorded. Findings show that both groups consumed similar amounts of diet in 1 meal during the 1-hr diet access period. Controls consumed the meal in 1 prolonged bout of eating, while lesioned Ss consumed the meal in numerous small bouts of eating. Lesioned Ss were active for longer periods, exhibiting continuous alternation of brief bouts of eating, drinking, exploring, and resting throughout the meal. In tests in which water was not available during the diet access period, both groups increased their intrameal bout size, but lesioned Ss still showed much smaller bouts of ingestion than did controls. Data suggest that the small-bout pattern of ingestion may reflect a general disruption in the control of behavioral sequences, rather than processes uniquely related to the regulation of eating or drinking. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Septal lesions potentiate freezing behavior to contextual but not to phasic conditioned stimuli in rats.

The effects on freezing behavior elicited by contextual and phasic conditioned stimuli (CSs) were examined in rats with septal lesions. Two wks after surgery, blocks of 2 conditioning trials consisting of a tone (10 kHz, 75 dB, 20 sec) paired with a footshock (500 msec, 0.5 mA) were presented on 2 consecutive days. Tone-alone trials were presented each day thereafter until extinction criterion was met. Septal lesions were found to potentiate the freezing response elicited by contextual stimuli but had no effect on freezing elicited by the phasic CS. The septum thus appears to be involved in the acquisition and/or expression of defensive behaviors elicited by contextual stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Visual evoked potentials during appetitive behavior after septal lesions in rats.

Analyzed averaged visual evoked responses (VERs) at the cortex to flashes used as probe stimuli during different phases of fixed-ratio barpressing for sucrose, using 5 lesioned and 7 nonlesioned male Holtzman rats. Results reveal changes in late components (including after-discharge responses) of VERs of septal preparations that would suggest enhanced electrophysiological arousal to appetitive conditions. The brain-damaged Ss also displayed heightened electrophysiological reactivity to conditions of frustration instituted by intermittent withholding of reinforcement. These dysfunctions were related to the reduced distractibility to trains of extraneous stimuli shown by septal preparations during appetitive behavior. It is suggested that impairment in inhibitory modulation of arousal mechanisms is related to augmentation in behavioral response tendencies often displayed by septal preparations. (41 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Factors underlying deficient passive-avoidance behavior by rats with septal lesions.

Analyzed passive-avoidance behavior in male Holtzman rats (N = 83) with septal lesions in 5 experiments. Results reveal 2 independent sources of the deficit in retention of passive-avoidance responding. One factor, increased responsiveness to positive reinforcement, caused a persistent deficit in passive-avoidance retention which could not be alleviated by previous training on a different passive-avoidance task. A 2nd factor, described as a temporary defect in response inhibition, produced a transient deficit in passive-avoidance retention which could be alleviated by prior training on another passive-avoidance task or continued testing on the same task. (25 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Disruption of appetite but not hunger or satiety following small lesions in the amygdala of rats.

In 5 experiments, discretely localized lesions were made in the amygdala of adult male albino Sprague Dawley rats to examine how specifically they might alter various measures of feeding behavior. Behavioral tests included spontaneous intake and body weight regulation, reactivity to saccharin and quinine solutions, conditioned taste aversion, the feeding response to food deprivation, the response to glucose gavage, and the response to dietary amino acid imbalance. Lesions in virtually all regions of the amygdala disrupted feeding behavior in some respect, but alterations in specific tasks were associated only with highly circumscribed brain damage. Body weight regulation, spontaneous food and water intake, and the responses to glucose gavage and long-term food deprivation were not altered by lesions in the amygdala. Results provide evidence that in the rat, the amygdala may play a greater role in appetite than in hunger or satiety. In particular, amygdaloid nuclei may participate in maintaining a negative bias in the reactivity to all appetitive stimuli. (64 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Context- but not familiarity-dependent forms of object recognition are impaired following excitotoxic hippocampal lesions in rats.

Dual-process models of recognition memory in animals propose that recognition memory is supported by two independent processes that reflect the operation of distinct brain structures: a familiarity process that operates independently of the hippocampus and a context-dependent (episodic) memory process that is dependent on the hippocampus. A novel variant of an object recognition procedure was used to examine this proposal. Healthy rats showed a preference for exploring a novel object rather than a familiar object: a familiarity-dependent recognition effect. They also showed a preference for exploring a familiar object that was presented in a different spatiotemporal context rather than a familiar object that was presented either in a different spatial or temporal context: a context-dependent form of recognition that is sensitive to "what" object has been presented "where" and "when." Rats with excitotoxic hippocampal lesions showed the familiarity-dependent but not the context-dependent form of recognition. The results provide support for dual-process theories of recognition memory. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Role of pituitary-adrenocortical system in mediating avoidance behavior of rats with septal lesions.

3 experiments with a total of 186 male Sprague-Dawley rats examined the hypothesis that the effects of septal lesions and systemic injections of scopolamine on avoidance acquisition could be attributed to the effects of either of these treatments on ACTH secretion. Septal lesions and scopolamine facilitated 2-way conditioned avoidance response acquisition, and the lesions retarded passive avoidance acquisition. However, neither the injections of dexamethasone, a synthetic glucocorticoid which inhibited ACTH secretion as did septal lesions, nor injections of ACTH which mimicked the facilitatory effects of scopolamine on basal ACTH secretion, affected avoidance in these paradigms. Thus, the main hypothesis was not supported. The finding that scopolamine did not affect passive avoidance indicates that a cholinergic system may not be involved in mediating the suppressive effects of punishment. (26 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of dexamethasone on affective behavior and adrenal reactivity following septal lesions in the rat.

Dexamethasone blockade of ACTH secretion from the pituitary gland did not alter the characteristic appearance or duration of the septal syndrome in male Wistar rats observed at 2, 9, and 16 days postoperatively. Despite the lack of a behavioral effect dexamethasone blocked the normal plasma corticosterone response to the stimulus of behavior rating in all groups studied. In the absence of dexamethasone, Ss with a septal lesion had a 65% greater corticosterone level 15 min. following the behavior rating than nonlesion Ss 2 days after surgery and an average increase of 35% over the 3 postoperative observation times of 2, 9, and 16 days. Results provide evidence that, in addition to the adrenal, the pituitary-adrenal axis is not essential for disturbance of affective behavior following septal ablation. (34 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Object exploration, habituation, and response to a spatial change in rats following septal or medial frontal cortical damage.

Normal rats and rats sustaining septal or medial frontal cortex lesions were compared in experiments dealing with object exploration, habituation, and reaction to novelty (measured by renewed exploration following a spatial change). Normal rats exhibited high levels of initial exploratory activity which decreased over time. Folowing a spatial change, they reinvestigated both the displaced object and the nondisplaced ones. Frontal animals were similar to normal subjects with respect to their initial exploratory level and habituation pattern. However, frontal rats reexplored only the displaced object and completely neglected the nondisplaced ones. In contrast, the behavioral pattern displayed by septal rats was markedly different from that of normal and frontal animals. Septal rats had lower levels of initial exploratory activity, did not habituate over time, and failed to react to either displaced or nondisplaced objects. These results show that although the septo-hippocampal complex and the medial frontal cortex may share some common function in spatially organized behaviors, both structures have unique roles. Some hypotheses about the possible basic processes subtended by the septal area or the medial frontal cortex are briefly mentioned and discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Clonidine blocks acquisition but not expression of conditioned opiate withdrawal in rats

Previous studies in rodents have reported that clonidine, an alpha 2-adrenergic receptor agonist, attenuated conditioned aversions to naloxone-precipitated opiate withdrawal when administered prior to each withdrawal conditioning episode. The current study was designed to determine whether clonidine could modify the expression of previously established conditioned place aversions and conditioned suppression of operant responding. Dose- and time-dependent effects of clonidine on activity and suppression of operant responding for food identified appropriate treatment parameters for subsequent studies in which rats rendered dependent on opiates through implantation of morphine pellets were tested for: (1) conditioned place aversion; and (2) conditioned suppression of operant responding for food (fixed ratio-15 schedule), in a paradigm wherein rats received four pairings of naloxone with a distinct tone and odor stimulus. Clonidine dose-dependently blocked the acquisition of both conditioned behaviors when administered prior to naloxone on each conditioning trial, but was ineffective in blocking the expression of these conditioned withdrawal signs when administered prior to the test session.