Behavioral effects of psychomotor stimulants in rats with dorsal or ventral subiculum lesions: Locomotion, cocaine self-administration, and prepulse inhibition of startle.

Compelling evidence suggests a primary role for the mesoaccumbens dopaminergic pathway in the behavioral effects of amphetamine and cocaine, but the roles of other projections to the accumbens, including those arising in the hippocampal formation, are less clear. The authors evaluated the effects of discrete excitotoxic lesions of either the dorsal or ventral subiculum on the locomotor activating, reinforcing, and sensorimotor gating-disruptive effects of psychomotor stimulant drugs. Whereas dorsal subiculum-lesioned rats were hyperactive in tests of exploratory locomotion and startle reactivity, ventral subiculum-lesioned rats exhibited an attenuated locomotor response to amphetamine, moderately impaired acquisition of cocaine self-administration, and reduced levels of prepulse inhibition of startle. These 2 behavioral profiles overlap considerably with those previously observed in rats with lesions of the rostrodorsal and caudomedial accumbens, respectively, and suggest that projections from dorsal subiculum to accumbens core and ventral subiculum to accumbens shell exert distinct influences on behavioral responses that are amplified by psychomotor stimulant drugs. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Spatial learning impairment parallels the magnitude of dorsal hippocampal lesions, but is hardly present following ventral lesions

The hippocampus plays an essential role in spatial learning. To investigate whether the whole structure is equally important, we compared the effects of variously sized and localized hippocampal aspiration lesions on spatial learning in a Morris water maze. The volume of all hippocampal lesions was determined. Dorsal hippocampal lesions consistently impaired spatial learning more than equally large ventral lesions. The dorsal lesions had to be larger than 20% of the total hippocampal volume to prolong final escape latencies. The acquisition rate and precision on a probe test without platform were sensitive to even smaller dorsal lesions. The degree of impairment correlated with the lesion volume. In contrast, the lesions of the ventral half of the hippocampus spared both the rate and the precision of learning unless nearly all of the ventral half was removed. There was no significant effect of the location (dorsal or ventral) of damage to the overlying neocortex only. In conclusion, the dorsal half of the hippocampus appears more important for spatial learning than the ventral half. The spatial learning ability seems related to the amount of damaged dorsal hippocampal tissue, with a threshold at about 20% of the total hippocampal volume, under which normal learning can occur.     

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)     

Performance on spatial working memory tasks after dorsal or ventral hippocampal lesions and adjacent damage to the subiculum.

Rats with excitotoxic lesions of the dorsal or ventral hippocampus and control rats were trained on 2 spatial working memory tasks: the standard version of the radial maze with 8 baited arms and the nonmatching-to-place procedure in the T maze. Dorsal lesions produced deficits in both tasks, whereas ventral lesions did not affect learning in either of them. A volumetric analysis of subicular damage showed that dorsal hippocampal lesions caused a deficit in the nonmatching-to-place only when accompanied by damage to the dorsal subiculum; on the other hand, lesions to the dorsal hippocampus impaired performance in the radial-arm maze regardless of the extent of subicular damage. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociating context and space within the hippocampus: Effects of complete, dorsal, and ventral excitotoxic hippocampal lesions on conditioned freezing and spatial learning.

Rats with complete excitotoxic hippocampal lesions or selective damage to the dorsal or ventral hippocampus were compared with controls on measures of contextually conditioned freezing in a signaled shock procedure and on a spatial water-maze task. Complete and ventral lesions produced equivalent, significant anterograde deficits in conditioned freezing relative to both dorsal lesions and controls. Complete hippocampal lesions impaired water-maze performance; in contrast, ventral lesions improved performance relative to the dorsal group, which was itself unexpectedly unimpaired relative to controls. Thus, the partial lesion effects seen in the 2 tasks never resembled each other. Anterograde impairments in contextual freezing and spatial learning do not share a common underlying neural basis; complete and ventral lesions may induce anterograde contextual freezing impairments by enhancing locomotor activity under conditions of mild stress. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of differential hippocampal lesions and pre- and postoperative training on extinction.

Examined resistance to extinction of a food-motivated response in a total of 78 male albino Wistar rats with sham operations or bilateral dorsal hippocampal, ventral hippocampal, or combined dorsal and ventral hippocampal lesions in 2 experiments. Surgery occurred either before or after acquisition of the to-be-extinguished response. Ss with combined hippocampal lesions showed greater resistance to extinction than controls if acquisition occurred preoperatively, but less resistance if acquisition occurred postoperatively. Ss with ventral hippocampal lesions were affected in a similar manner but to a lesser degree by differential prior experience. In contrast, dorsal hippocampal-lesioned Ss exhibited no change in approach latency during extinction, irrespective of the timing of surgery. It is suggested that both ventral and combined hippocampal lesions interfere with the changing of an established approach "set." (French summary) (16 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Amygdala and Ventral Hippocampus Contribute Differentially to Mechanisms of Fear and Anxiety.

Cytotoxic ventral hippocampal lesions produced anxiolytic effects on 4 ethologically based, unconditioned tests of anxiety in the rat (hyponeophagia, black/white 2-compartment box test, a successive alleys test that represents a modified version of the elevated plus-maze, and a social interaction test). Dorsal hippocampal lesions did not produce anxiolytic effects on these tests, suggesting a distinct specialization of function within the hippocampus. Furthermore, the effects of ventral hippocampal lesions were also distinct from those of amygdala lesions. This suggests that the effects of ventral hippocampal lesions are not simply due to direct or indirect effects on the amygdala, and that these 2 brain areas contribute differentially to a brain system (or systems) associated with the processing of fearful and/or anxiogenic stimuli. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Double dissociation of function within the hippocampus: Spatial memory and hyponeophagia.

Complete and dorsal hippocampal lesions impaired spatial performance on 2 working memory tasks: rewarded alternation on the T maze and matching to position in the water maze. In contrast, ventral hippocampal lesions had no effect on these tasks, even when task difficulty was increased by the introduction of delays. Ventral lesions did resemble complete lesions in reducing anxiety in 3 commonly used tests of anxiety (social interaction, plus-maze, and hyponeophagia). Dorsal lesions also appeared to be anxiolytic in the social interaction and plus-maze tests, but they did not affect hyponeophagia. Complete- and dorsal-lesioned rats displayed hyperactivity, whereas ventral-lesioned rats did not. These results show a double dissociation between dorsal and ventral hippocampal lesions (hyponeophagia vs. spatial memory), suggesting differentiation of function along the septotemporal axis of this structure. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Some behavioral effects of transecting ventral or dorsal fiber connections of the septum of the rat.

Compared the behavioral effects of large electrolytic lesions in the septal area with those of knife cuts that severed the ventral or dorsal connections of this structure, using 37 adult male albino Sprague-Dawley rats in each of 6 experiments. Ss with septal lesions lost weight and were transiently hyperdipsic. Ventral cuts produced similar effects, but dorsal cuts did not. All 3 operations decreased the latency to eat in a novel environment, increased the intake of sweetened milk, enhanced acquisition of a food-rewarded running response, and facilitated acquisition of a shuttle-box avoidance response. The lesion, but neither of the knife cuts, reduced the effects of punishment and impaired the acquisition of a 1-way avoidance response. (57 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Double dissociation of function within the hippocampus: A comparison of dorsal, ventral, and complete hippocampal cytotoxic lesions.

Rats with complete cytotoxic hippocampal lesions exhibited spatial memory impairments in both the water maze and elevated T maze. They were hyperactive in photocell cages; swam faster in the water maze; and were less efficient on a nonspatial, differential reinforcement of low rates (DRL) task. Performance on both spatial tasks was also impaired by selective dorsal but not ventral lesions; swim speed was increased by ventral but not dorsal lesions. Both partial lesions caused a comparable reduction in DRL efficiency, although these effects were smaller than those of complete lesions. Neither partial lesion induced hyperactivity when rats were tested in photocell cages, although both complete and ventral lesion groups showed increased activity after footshock in other studies (Richmond et al., see record 1999-01985-006). These results demonstrate possible functional dissociations along the septotemporal axis of the hippocampus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

"Acquisition of a complex place task in rats with selective ibotenate lesions of hippocampal formation: Combined lesions of subiculum and entorthinal cortex versus hippocampus": Correction.

Reports an error in "Acquisition of a complex place task in rats with selective ibotenate lesions of hippocampal formation: Combined lesions of subiculum and entorhinal cortex versus hippocampus" by John-Paul Bouffard and Leonard E. Jarrard (Behavioral Neuroscience, 1988[Dec], Vol 102[6], 828-834). This article's corresponding plate appears on page 995. The information should read, "Plate A. Photomicrographs of horizontal, cresyl violet stained sections at dorsal, middle, and ventral levels of the brain for an unoperated control rat (left), an animal from the Subiculum + Entorhinal lesion group (middle), and a rat from the hippocampus group (right)." (The following abstract of the original article appeared in record 1989-28756-001.) The effects of isolating the hippocampus from its neocortical inputs and outputs by damaging the deep layers of entorhinal cortex and subiculum were compared with direct removal of the hippocampus using acquisition of a complex radial maze task. A series of eight problems (four out of eight arms being correct) were learned under either massed (45 s) or distributed (10 min) practice conditions, thus varying contextual information. Performance of rats with subiculum/entorhinal cortex lesions was similar to that of controls in all aspects of the radial maze task; whereas animals with hippocampal lesions were impaired on nearly all dependent measures. Although the effects of varying the intertrial interval were generally small, distributed practice did serve to facilitate the performance of hippocampal rats in terms of working memory. These findings are discussed as they related to recent theorizing in the area. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transfer Effects and Conditional Learning in Rats With Selective Lesions of Medial Septal/Diagonal Band Cholinergic Neurons.

The authors examined visual-spatial conditional learning with automated touchscreen tasks in male Long-Evans rats with selective lesions of medial septal/vertical limb of diagonal band (MS/VDB) cholinergic neurons produced by 192 IgG-saporin. Performance on a conditional task, in which 1 of 2 centrally displayed stimuli directed the rat to respond to an illuminated panel on the left or right, depended on training history: Control rats with experience on other visual tasks performed better than MS/VDB-lesioned rats with similar training histories, whereas this effect was reversed in naive rats. This difference appears to reflect transfer effects present in the control rats that are absent in the MS/VDB-lesioned rats. These findings may suggest that MS/VDB cholinergic neurons play a particular role in the transfer of behavioral experience and flexibility of application of behavioral rules in memory, rather than a role in conditional learning per se. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of regional striatal lesions on motor, motivational, and executive aspects of progressive-ratio performance in rats.

The striatum is implicated in response selection and performance, the dorsal striatum in sensorimotor control and habit learning, and the ventral striatum in motivation and rewarded behaviors. Ventral striatal lesions produce performance changes on food-reinforced, progressive-ratio (PR) schedules, but the effects of dorsal striatal lesions on this task are not known. In this study, neither medial nor lateral dorsal striatal lesions produced deficits on the main motivational indices of PR performance. In contrast, significant impairments were observed in motoric or "executive" aspects of performance. Motivationally related manipulations of the task (food deprivation and reward magnitude) produced some subtle lesion-specific changes in behavior on these motoric or executive aspects of performance. Findings are discussed in relation to the roles of the dorsal and ventral striatum in reward-related behaviors. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Hippocampal Lesions Modulate Both Associative and Nonassociative Priming.

In associative priming, rats are more likely to orient to a visual stimulus whose memory has not been recently activated (V1) than to one whose memory has been recently activated (V2). However, rats with excitotoxic hippocampal lesions are more likely to orient to the primed V2 than to the unprimed V1. This study investigated the influence of hippocampal lesions on nonassociative priming. Rats received presentations of 2 visual stimuli, V1 and V2, that had been presented more (V2, primed) or less (V1, unprimed) recently. Control rats oriented to V1 rather than to V2, whereas hippocampal rats oriented to V2 rather than to V1. These results parallel those observed in an associative priming procedure and thereby suggest that the role of the hippocampus in priming is general. (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)     

Hormonal dissociation of limbic lesion effects on shuttle box avoidance in rats.

In a study with a total of 57 male albino Holtzman-derived rats, Ss with septal or hippocampal lesions showed facilitated acquisition of a shuttle box avoidance response compared to normal controls. Ss with septal lesions were also highly resistant to extinction compared with normal Ss. When the same lesion effects were examined in hypophysectomized Ss, the Ss with septal lesions continued to show facilitated performance, and Ss with hippocampal lesions performed no differently than nonoperated controls. These findings are consistent with the hypothesis that the facilitated avoidance performance found in rats with hippocampal lesions is attributable to lesion-induced changes in hypophyseal activity, but similar changes induced by septal lesions are not. (16 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dissociating the roles of dorsal and ventral CA1 for the temporal processing of spatial locations, visual objects, and odors.

The differential contributions of the dorsal and ventral hippocampus for learning and memory have long been of interest. The present experiments were designed to evaluate the contributions of dorsal CA1 and ventral CA1 for temporal processing. Animals were run on three temporal ordering paradigms: one with visual objects, one with olfactory stimuli, and one with spatial locations. Animals with lesions to dorsal CA1 showed deficits for the temporal ordering of visual objects relative to control animals, and deficits for the temporal ordering of spatial locations relative to control and ventral CA1 lesioned animals. Animals with lesions to ventral CA1 showed deficits for the temporal ordering of olfactory information relative to control and dorsal CA1 lesioned animals, and a mild deficit for the temporal ordering of visual objects relative to control animals, but not as severe as those shown by the dorsal CA1 lesioned animals. These data suggest that dorsal CA1 and ventral CA1 contribute to temporal ordering processes, and that dorsal CA1 and ventral CA1 are dissociable for temporal ordering based upon the nature of the information that is processed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fornix Lesions Impair Context-Related Cingulothalamic Neuronal Patterns and Concurrent Discrimination Learning in Rabbits (Oryctolagus cuniculus).

Cingulothalamic neurons develop topographic patterns of cue-elicited neuronal activity during discrimination learning. These patterns are context-related and are degraded by hippocampal lesions, suggesting that hippocampal modulation of cingulothalamic activity results in the expression of the patterns, which could promote the retrieval of context-appropriate responses and memories. This hypothesis was tested by training rabbits (Oryctolagus cuniculus) with fornix lesions concurrently on two discrimination tasks (approach and avoidance) in different contexts. Because the same conditioned stimuli were used for both tasks, contextual information was critical for overcoming intertask interference during concurrent task acquisition. The lesions degraded the topographic patterns and significantly impaired concurrent learning, suggesting that hippocampal-cingulothalamic interactions and the resulting topographic patterns are critical for processing contextual information needed to defeat interference. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lesions of the Dorsal Hippocampus Block Trace Fear Conditioned Potentiation of Startle.

Several studies show that the hippocampus is critical for the memories mediating trace and contextual fear conditioning. This study investigates whether N-methyl-D-aspartate-induced lesions of the dorsal hippocampus made prior to training affect context fear conditioning and trace fear conditioning measured with the fear-potentiated startle. Pretraining excitotoxic lesions of the dorsal hippocampus blocked acquisition of trace fear conditioning to a tone stimulus but did not affect context fear conditioning. These data indicate that without a dorsal hippocampus rats are unable to acquire trace conditioning but can acquire contextual fear when fear is measured by potentiation of the startle response. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effects of hippocampal and fimbria–fornix lesions on prepulse inhibition.

The present experiments tested the effects of conventional (dorsal aspiration and electrolytic) and excitotoxic (N-methyl-{d}-aspartate [NMDA]) hippocampal lesions and fimbria-fornix (FF) transection on prepulse inhibition (PPI) of startle response and on open-field activity. Activity was increased by FF transection and by conventional but not excitotoxic hippocampal lesions; complete NMDA lesion increased amphetamine-induced activity. Whereas dorsal hippocampal aspiration lesion disrupted PPI, the phenomenon was not affected by dorsal hippocampal. electrolytic lesion, partial or complete excitotoxic (NMDA) hippocampal lesions, or complete FF transection, which interrupted the cholinergic input to the hippocampus as well as the hippocampal-subicular input to the nucleus accumbens. Systemic apomorphine disrupted PPI in both FF-transected rats and their controls. It is suggested that the hippocampus is essential for PPI disruption rather than for PPI expression. (PsycINFO Database Record (c) 2010 APA, all rights reserved)