Dissociable effects of selective lesions to hippocampal subsystems on exploratory behavior, contextual learning, and spatial learning.

Rats received excitotoxic lesions of different subsystems within the hippocampal system--either the hippocampus proper (cornu ammonis and dentate gyrus; hippocampal lesions) or the entorhinal cortex-subicular region (entorhinal lesions). Subsequently, their activity in an operant chamber was monitored both before and after footshock had been delivered (Experiment 1). Rats with hippocampal lesions showed enhanced activity before the delivery of footshock and reduced freezing after the delivery of shock. Rats with entorhinal lesions showed control levels of activity before the delivery of footshock and control levels of freezing after the delivery of footshock. Both types of lesion impaired spatial learning in a water maze (Experiment 2). These results suggest that the deficits arising from damage to the hippocampal system in contextual and spatial learning have different origins. (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)     

Double dissociation of effects on learning of medial versus lateral hyperstriatal lesions in pigeons.

Three experiments examined the effects of medial and lateral hyperstriatal lesions in two groups of pigeons. In Experiment 1, both hyperstriatal groups were impaired, relative to unoperated and operated control groups, in postoperative performance of preoperatively acquired serial reversal of both spatial and visual discriminations. The deficits of the two hyperstriatal groups appeared both quantitatively and qualitatively similar. Experiment 2 found that performance of spatial reversals was disrupted in the medial, but not in the lateral, hyperstriatal group by a long intertrial interval. Experiment 3 found that acquisition of simultaneous matching-to-sample was disrupted by lateral, but not by medial, hyperstriatal lesions; the lateral group also showed a lower rate of response to the sample stimulus than any of the other groups. Implications of these findings for current theories of hyperstriatal function are discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Impairments in negative patterning, but not simple discrimination learning, in rats with 192 IgG-saporin lesions of the nucleus basalis magnocellularis.

Rats with 192 IgG-saporin lesions of the nucleus basalis magnocellularis (NBM) and sham-operated rats were trained in either a simple discrimination paradigm assessing simple association learning or a negative patterning paradigm assessing configural association learning. In the simple discrimination task, rats were reinforced for responding to a light but were not reinforced for responding to a tone. In the negative patterning discrimination task, rats were reinforced for responding to either a light or a tone presented alone but were not reinforced for responding to both stimuli presented simultaneously. Simple discrimination learning was not affected, whereas acquisition of negative patterning was impaired by NBM lesions. Impaired configural association learning may reflect a loss in the ability of rats with NBM lesions to attend to multiple sensory stimuli or to cope with conflicting response strategies. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Influence of acute and repeated interleukin-2 administration on spatial learning, locomotor activity, exploratory behaviors, and anxiety.

Interleukin-2 (IL-2), released from activated T cells, influences central neurochemical functioning, and IL-2 immunotherapy in cancer patients may provoke neuropsychiatric and cognitive disturbances. In this study, acute, systemic IL-2 did not influence Morris water-maze performance in mice. In contrast, chronic IL-2 impaired performance when the position of the escape platform varied over days but was without effect when the platform position was fixed. These effects could not be attributed to illness, because IL-1β, which induces marked malaise, did not influence water-maze performance. Chronic IL-2 produced modest reductions in exploration and approach to a novel stimulus, effects not seen after acute treatment, but did not influence spontaneous alternation performance or behavior in an elevated plus-maze test. Thus, repeated IL-2 may influence spatial working memory without affecting habituation/ attentional processes or anxiety. (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)     

Independent effects of age and nucleus basalis magnocellularis lesion: Maze learning, cortical neurochemistry, and morphometry.

Assessed the effects of age and lesion of the cholinergic nucleus basalis magnocellularis (NBm) behaviorally, morphologically, and biochemically. Groups consisted of rats lesioned 1 mo before testing, rats lesioned 13 mo before testing, and their respective age-matched controls. Both age and lesion independently induced behavioral deficits in performance on 2 water maze tasks. The combined effect of these 2 factors produced behavioral deficits equal to the sum of the individual impairments. NBm lesion produced a 28% decrease in anterior cortical choline acetyltransferase activity and a 20% decrease in synaptophysin immunoreactivity in the neocortex that was stable over a 12-mo period. Neither neuritic plaque nor neurofibrillary-tanglelike structures were found in the brains of 18-mo-old control rats, nor were they found in NBm-lesioned rats examined 15 mo postlesion. There was an age-related decrease in homovanillic acid levels in both control and NBm groups, which suggests a decrease in dopamine turnover. These results show a lack of biochemical and behavioral recovery after NBm lesion and suggest that the effects of age on behavior are independent of NBm-cortical dysfunction. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Habituation of startle response, lick suppression, and exploratory behavior in rats with hippocampal lesions.

34 male albino Holtzman rats with bilateral hippocampal lesions (HLs) and 22 controls with neocortical lesions (NLs) were compared on the habituation of lick suppression and startle response. Ss with HLs showed no consistent differences from controls on any measure within these 2 response systems. Ss with HLs showed significant retention of habituation over periods of 24 hrs and 21 days. Experimental and control differences were not revealed when stimulation was presented on a 1-sec interstimulus interval. None of these results varied with the extent of the HLs, which ranged from relatively small lesions restricted to the dorsal hippocampus to large lesions that damaged the hippocampus in its dorsal, posterior, and ventral aspects. In contrast to the startle response and lick suppression results, HLs significantly disrupted Y-maze exploratory behavior, and the disruption was directly related to the extent of hippocampal damage. Data suggest that the hippocampus is not involved in any important way in the control of either short- or long-term habituation of elicited, reflex-like behaviors but is importantly involved in the control of emitted, exploratory behaviors. (39 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of nucleus basalis magnocellularis lesions in Long-Evans hooded rats on two learning set formation tasks, delayed matching-to-sample learning, and open-field activity.

Rats with quisqualic acid lesions of the nucleus basalis magnocellularis (nBM) and control rats were compared in discrimination reversal learning set (DRLS) and olfactory discrimination learning set (ODLS) tasks, a delayed matching-to-sample task (DMTS), and open-field activity. Evidence of learning set formation was seen to control rats but not in nBM-lesioned rats in the DRLS and ODLS tasks. Better-than-chance performances were seen for both groups in open-field activity. These findings suggest that the nBM is important for higher cognitive processing such as "learning to learn" and thus is important for a complex form of reference memory. In addition, perseverational, working memory, and attentional deficits could not explain learning set impariment after nBM lesions. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Short-term versus long-term effects of adrenal hormones on behaviors.

Hypothesizes that short-term exposures to stress facilitate performances of serially repetitive, overlearned tasks and impair performances of perceptual restructuring tasks, while long-term exposures to stress produce the opposite behavioral effects. These effects are attributed, in part, to the length of exposure of the central nervous system to stress-elicited adrenal hormones (epinephrine and cortisol). Short-term exposures are believed to induce states of central adrenergic dominance that favor performances of serially repetitive, overlearned tasks at the expense of perceptual restructuring tasks. Longer exposures are thought to result in a shift to central cholinergic dominance that favors the opposite pattern of performances. A physiological model is presented that accounts for the shift from central adrenergic to central cholinergic dominance. Experimental procedures derived from the model promote the reversal of some of the behavioral and physiological effects of a long-term stressor. (5 p ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of septal, preoptic, and habenula ablations on thirst-motivated behaviors in rats.

Two experiments used a total of 59 male Sprague-Dawley rats. Bilateral septal lesions dramatically enhanced barpressing rates generated under progressive ratio schedules of reinforcement. This increased barpressing was dependent on deprivation level but independent of the type of deprivation (i.e., food or water). Equivalent effects on barpressing were observed in Ss with bilateral medial forebrain bundle lesions at the level of the lateral preoptic area. Septal lesions, medial forebrain bundle lesions, and habenula lesions did not result in a hyperreactivity to bitter quinine solutions. Hyperreactivity to quinine was observed only in Ss with medial preoptic lesions. This medial preoptic lesion also impaired operant responding for water on a progressive ratio schedule of reinforcement. It is suggested that the medial preoptic lesion produced a deficit in thirst-motivated behavior. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of dorsal versus ventral hippocampal, total hippocampal, and parietal cortex lesions on memory for allocentric distance in rats.

To test for the contribution of the parietal cortex and hippocampus to memory for allocentric spatial cues, the authors trained rats on a go/no-go task that required the rat to remember the distance between two visual cues. Total hippocampal lesions impaired working-memory representation for allocentric distance, whereas parietal cortex lesions resulted in only a transient impairment. In a second experiment, neither hippocampal nor parietal cortex lesions impaired allocentric distance discrimination. A third experiment showed that both the dorsal and ventral areas of the hippocampal formation must be destroyed to impair working memory for allocentric distance information. There appears to be a dissociation between the hippocampus and parietal cortex in mediating memory for allocentric distance information. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Early postnatal X-irradiation of the hippocampus and discrimination learning in adult rats.

Trained Long-Evans rats with X-irradiation produced degranulation of the hippocampal dentate gyrus in the acquisition and reversal of simultaneous visual and tactile discriminations in a T-maze in 3 experiments. The experiments employed the same treatment, apparatus, and procedure but varied in task difficulty. In the brightness and roughness discriminations, the irradiated Ss were not handicapped in acquiring or reversing discriminations of low or low-moderate task difficulty. However, these Ss were handicapped in acquiring and reversing discriminations of moderate and high task difficulty. In a Black/White discrimination in which the stimuli were restricted to the goal-arm walls, the irradiated Ss were handicapped in the acquisition (low task difficulty) and reversal (moderate task difficulty) phases of the task. Results suggest that the irradiated Ss were not handicapped when the noticeability of the stimuli was high, irrespective of modality used, but were handicapped when the noticeability of the stimuli was low. Results are consistent with the hypothesis that rats with hippocampal damage are inattentive due to hyperactivity. (36 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Neurotrophic effects of BDNF and CNTF, alone and in combination, on postnatal day 5 rat acoustic ganglion neurons

The effects of encapsulating bovine hemoglobin (BHb) in the bicontinuous cubic phase formed by monooleoylglycerol and water was investigated with Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction. Cubic phase was formed in the presence of 1-10 wt% BHb. Studies using X-ray diffraction reveal that at 0.5-2.5 wt% BHb, the cubic phase structure is characterized by the double diamond lattice (Pn3m). At 2.5-5 wt% BHb, coexistence of two cubic phase structures, Pn3m and the gyroid lattice (Ia3d), was observed while at BHb, concentrations higher than 5 wt% the gyroid structure persists. FTIR shows there is an increase in intensity of the free nu C = O (1745 cm-1) and a corresponding decrease in the intensity of the hydrogen bonded nu C = O (1720 cm-1) as the BHb concentration is increased. The nu C-O-CO peak shifts from 1183 cm-1 to 1181 cm-1 as the concentration of BHb raised from 2.5 to 10 wt% indicating BHb may induce subtle changes in the interfacial region of cubic phase monoolein. The bandwidth of the nu asCH2 stretch (2926 cm-1) increased in the presence of 5 wt% BHb compared to samples with 2.5 or 10 wt% BHb. The increase in frequency of the nu sCH2 stretch (2854 cm-1) induced by increasing temperature 20 to 60 degrees C was dampened when BHb was present compared to samples heated in isotonic buffer. Analysis of the amide I band at 1650 cm-1 showed that the secondary structure of BHb is not affected by encapsulation in monoolein. In vitro release studies showed that 45% of the entrapped BHb was released after 144 h at 37 degrees C. The porous nature of bulk cubic phase was further demonstrated by diffusion of K2Fe(CN)6 and conversion of 73% of the oxyhemoglobin to methemoglobin after 1 h. These results suggest that the cubic phase may be useful for encapsulation of Hb as a red cell substitute and for the encapsulation and delivery of other bioactive agents.     

Collateral behaviors and the DRL deficit of rats with septal lesions.

Trained a total of 31 male Long-Evans hooded normal and septally-lesioned rats to lever press for food on a DRL 20-sec schedule in either a conventional operant chamber or 1 containing wood blocks and cardboard strips. The DRL behavior of normals trained in modified chambers was most efficient, and that of Ss with septal lesions trained in conventional chambers was least efficient. After 35 hr. of training, normals tested in conventional chambers and Ss with septal lesions tested in modified chambers did not differ significantly. Ss chewed the blocks and cardboard, and prevention of these collateral behaviors reduced DRL efficiency. Results show that colalteral behaviors facilitate the development of efficient DRL behavior and indicate that the DRL deficit of rats with septal lesions can be modified. (17 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of substantia nigra and caudate nucleus lesions on avoidance learning in rats.

Compared to 21 operated and 14 nonoperated controls, 36 male Sprague-Dawley albino rats with small bilateral lesions in the anteroventral caudate nucleus or the rostral substantia nigra were significantly impaired in the acquisition of 1-way active avoidance, passive avoidance requiring the inhibition of the previously acquired 1-way response, and shuttle-box avoidance. Ss with nigral lesions took significantly more trials to criterion than Ss with caudate lesions on 1-way avoidance. Results are considered in terms of the intimate anatomical and neurochemical relationships between these structures, and a circuit of structures involved in avoidance learning is suggested. (34 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Differential effects of prefrontal cortex ablation in neonatal, juvenile, and young adult rats.

Long-Evans hooded rats sustaining lesions in the medial (MF) or the orbital (OF) prefrontal cortex at various ages (10, 25, 40, or 60 days postnatally) were tested as adults on a series of behavioral tasks that are known to be sensitive to such lesions in adults. On spatial alternation learning, both the 40- and 60-day MF Ss were seriously impaired, whereas neither the 10- nor the 25-day MF Ss differed from controls. On a hoarding task, 25- and 60-day MF Ss hoarded less food than either controls or 10-day MF Ss. Lesions of OF cortex in males at 40 or 60 days significantly increased running-wheel activity; OF lesions in both sexes at 25 days of age or later decreased the rate of continuous reinforcement reacquisition relative to controls, whereas 10-day OF Ss did not differ from controls on either task. Thus, Ss with lesions of either frontal area at 10 days of age showed complete behavioral sparing on all measures. The effects of lesions at later ages varied with the behavioral task employed and with lesion locus. Although the 10-day Ss received a somewhat longer postoperative recovery interval than most of the later operates, these results cannot be explained on the basis of recovery time alone. (34 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Physiological and behavioral effects of acute ethanol hangover in juvenile, adolescent, and adult rats.

This study examined differential responding of juvenile, adolescent, and adult rats after intoxication from an acute alcohol challenge. Experiment 1 generated blood ethanol curves for subjects 25, 35, or 110 days postnatal, after doses of 2.0 or 4.0 g/kg, assessing elimination rates and time of drug clearance. Experiment 2 compared ethanol's initial hypothermic and delayed hyperthermic effect across age by 48-hr temperature measurement with telemetry. At clearance or 24 hr after alcohol exposure, Experiment 3 tested subjects for changes in acoustic startle reactivity and ultrasonic vocalization (USV). Younger rats showed an absent or reduced tendency for residual hyperthermia, and adults showed alterations in USV observed as aftereffects of intoxication, despite greater initial blood alcohol levels and ethanol hypothermia in the former. The lesser ethanol hangover effects in weanlings and adolescents may be due in part to faster ethanol elimination at these ages compared with adults. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Prefrontal cortex and caudate nucleus in conditional associative learning: Dissociated effects of selective brain lesions in rats.

Rats with lesions to prefrontal cortex (PFC) or caudate nucleus (CN) were compared on tests of conditional associative learning (CAL) that placed varying demands on conditional rule learning and working-with-memory operations that are essential for response selection. Damage to either structure impaired performance, but the respective deficits resulted from disruption of different processes. CN lesions produced a consistent learning deficit that was thought to reflect a basic impairment in forming stimulus-response (S-R) associations. The behavior of PFC rats was more variable and depended on task requirements. When S-R learning or response selection was relatively easy, the PFC was not critical. However, when either component was made more difficult, thus requiring the contribution of strategic processes, PFC damage produced profound impairments. In addition to clarifying the roles of the PFC and CN in CAL, the results provide further evidence that multiple brain regions participate in relatively simple behavioral tasks and that their respective contributions can be dissociated. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Anxiolytic effects of cytotoxic hippocampal lesions in rats.

Rats with cytotoxic lesions of the hippocampus were given 3 anxiety tests: social interaction with a novel rat, the elevated zero-maze (a modification of the plus-maze), and hyponeophagia (eating familiar and novel foods in a novel place). Marked anxiolytic effects were seen in the social interaction and hyponeophagia tests, but not on the zero-maze. These results confirm and extend previous experiments that used traditional lesion techniques. The zero-maze result was consistent with other experiments using the plus-maze, in which intrahippocampal administrations of pharmacological agents were not anxiolytic, although variability in ethological tests may also be a factor. As the hyponeophagia test used an elevated apparatus, as in the zero- and plus-mazes, the lack of a lesion effect in the zero-maze was unlikely to have been due to an inability to relieve height-induced anxiety. (PsycINFO Database Record (c) 2010 APA, all rights reserved)