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)     

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)     

Medial Septal Lesions Mimic Effects of Both Selective Dorsal and Ventral Hippocampal Lesions.

Electrolytic medial septal (MS) lesions, which depleted acetylcholinesterase staining in both dorsal and ventral hippocampus, produced a constellation of behaviors, combining aspects of both selective dorsal and ventral hippocampal lesion effects. MS lesions impaired spatial working memory on the T maze, thus resembling the effects of dorsal hippocampal lesions. In addition, MS lesions reduced anxiety during successive alleys (a modified form of the elevated plus-maze), social interaction, and hyponeophagia tests. MS lesions also reduced postshock freezing. These effects more closely resemble those of ventral hippocampal lesions. Therefore, the effects of electrolytic MS lesions derive from the resulting combined deafferentation of dorsal and ventral hippocampal regions, suggesting that previously reported effects of cytotoxic dorsal hippocampal lesions are unlikely to be due to a demyelination of fibers of passage coursing through the septal pole. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Disruption of spatial but not object-recognition memory by neurotoxic lesions of the dorsal hippocampus in rats.

Ischemia-induced cell loss in the CA1 region of the dorsal hippocampus results in severe deficits on delayed non-matching-to-sample (DNMS), whereas hippocampectomy produces little or no impairment, suggesting that partial hippocampal damage is more detrimental to DNMS performance than total ablation. To test this hypothesis, rats with or without preoperative DNMS training were given partial cytotoxic lesions of the dorsal hippocampus. When tested, neither group displayed any DNMS deficits despite widespread cell loss in the CA1 and other regions of the dorsal hippocampus. In the final experiments, rats tested previously on DNMS were found to be impaired on the Morris water maze. The finding that partial hippocampal lesions disrupt spatial memory while leaving object-recognition memory intact indicates a specialized role for the hippocampus in mnemonic processes. (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)     

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)     

Monkeys with rhinal cortex damage or neurotoxic hippocampal lesions are impaired on spatial scene learning and object reversals

Rhesus monkeys (Macaca mulatta) with lesions of the rhinal cortex or parahippocampal gyrus (made by aspiration) or hippocampus (made with ibotenic acid) and unoperated controls were tested on object discrimination and reversal, place discrimination and reversal, and spatial scene learning to determine the contribution of these temporal lobe structures to these forms of learning and memory. Rhinal cortex lesions produced a severe deficit in object reversal learning; hippocampal lesions produced a milder deficit. Monkeys with rhinal cortex removals and those with hippocampal lesions were equally impaired on spatial scene learning. None of the lesions impaired place discrimination or reversal. These results argue against the idea that the mnemonic contributions of the rhinal cortex and hippocampus are limited to object and spatial domains, respectively.     

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)     

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)     

Lymphomas of the urinary tract

Lesioning the ventral hippocampus of neonatal rats has been proposed as an experimental model of schizophrenia. This lesion causes a syndrome of hyperresponsivity to the stimulant effects of amphetamine, impaired grooming and disrupted social interactions, effects that emerge during adolescence, much like schizophrenia. Persisting cognitive effects of neonatal ventral hippocampal lesions were assessed in the current study, because the hippocampus is critically important for a variety of cognitive functions and cognitive impairment and because it is an important feature of schizophrenia. Spatial learning and working memory were assessed in the radial-arm maze, which is sensitive to the adverse effects of hippocampal lesions made in adults. Lesioned rats showed pronounced deficits in radial-arm maze choice accuracy that persisted throughout training. Deficits were seen during the prepubertal period as well as in adulthood. Even though the lesioned rats performed more poorly, they were significantly less sensitive to the amnestic effects of the nicotinic antagonist mecamylamine and the muscarinic antagonist scopolamine. No significant effects of nicotine or amphetamine were seen in either the lesioned or control groups. The long-lasting deficits in spatial learning and working memory resulting from neonatal ventral hippocampal lesions show that, unlike frontal cortical lesions during the same age, the effects of hippocampal lesions are not overcome during development. The resistance to the amnestic effects of nicotinic and muscarinic acetylcholine (ACh) antagonists suggests that the hippocampus is a critical site for the action of these drugs. Neonatal hippocampal lesions may provide a good model of the cognitive impairments of schizophrenia and may be useful to assess novel drug effects to counteract the cognitive deficits in schizophrenia.     

Dorsal hippocampal lesions impair blocking but not latent inhibition of taste aversion learning in rats.

The aim of the present experiments was to study the effect of nonselective electrolytic lesions of the rat dorsal hippocampus on 2 learning phenomena: the L. J. Kamin (1969) blocking effect and latent inhibition of taste aversion learning. Bilateral dorsal hippocampal lesions selectively impaired blocking induced by 1 saccharin-lithium chloride pairing previous to 1 serial compound (saccharin–cider vinegar)–lithium pairing, but lesions had no effect on latent inhibition of a saline aversion, induced by 6 saline preexposures, in the same group of animals. Moreover, dorsal hippocampal lesions did not affect latent inhibition of saccharin-conditioned aversion induced by 1 or 6 preexposures. It is argued that blocking and latent inhibition of taste aversion learning do not share a common neural mechanism. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Fimbrial lesions and sensory preconditioning.

Examined the effects of fimbrial and cortical lesions on sensory preconditioning in 36 New Zealand albino rabbits. Damage to the cortex or the fimbria had no apparent effect on the acquisition of CRs. However, fimbrial lesions virtually abolished the effects of preconditioning, whereas cortical lesions had no significant effect. Because fimbrial damage disrupts hippocampal output, findings indicate that the hippocampus is vital to learning functions other than spatial cognition or working memory. Results are considered to be most compatible with the idea that the hippocampus is involved in "marking" biologically important portions of the temporal environment. A temporal mapping system involving the hippocampus may be critical to the formation of an association between the 2 conditional stimuli in sensory preconditioning. (24 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Newborn organ weight and spontaneous hypertension: recombinant inbred strain study

This study investigated the effects of neonatal hippocampal ablation on the development of spatial learning and memory abilities in rats. Newborn rats sustained bilateral electrolytic lesions of the hippocampus or were sham-operated on postnatal day 1 (PN1). At PN20-25, PN50-55, or PN90-95, separate groups of rats were tested in a Morris water maze on a visible "cue" condition (visible platform in a fixed location of the maze), a spatial "place" condition (submerged platform in a fixed location), or a no-contingency "random" condition (submerged platform in a random location). Rats were tested for 6 consecutive days, with 12 acquisition trials and 1 retention (probe) trial per day. During acquisition trials, the rat's latency to escape the maze was recorded. During retention trials (last trial for each day, no escape platform available), the total time the rat spent in the probe quadrant was recorded. Data from rats with hippocampal lesions tested as infants (PN20-25) or as adults (PN50-55 and PN90-95) converged across measures to reveal that 1) spatial (place) memory deficits were evident throughout developmental testing, suggesting that the deficits in spatial memory were long-lasting, if not permanent, and 2) behavioral performance measures under the spatial (place) condition were significantly correlated with total volume of hippocampal tissue damage, and with volume of damage to the right and anterior hippocampal regions. These results support the hypothesis that hippocampal integrity is important for the normal development of spatial learning and memory functions, and show that other brain structures do not assume hippocampal-spatial memory functions when the hippocampus is damaged during the neonatal period (even when testing is not begun until adulthood). Thus, neonatal hippocampal damage in rats may serve as a rodent model for assessing treatment strategies (e.g., pharmacological) relevant to human perinatal brain injury and developmental disabilities within the learning and memory realm.     

Effects of dorsal and ventral vertical lobe electrolytic lesions on spatial learning and locomotor activity in Sepia officinalis.

This study aims to analyze the effects of electrolytic lesion, restricted to either the ventral or the dorsal parts of the vertical lobe (VL), on the behavior of cuttlefish (Sepia officinalis). Two behavioral tests were performed on sham-operated and lesioned cuttlefish: assessment of locomotor activity in an open field and determination of spatial learning abilities in a T maze. The results showed that ventral lesions of the VL led to marked impairment in the acquisition of spatial learning, whereas dorsal lesions of the VL increased locomotor activity in the open field and impaired long-term retention of spatial learning. This study establishes for the first time the existence of distinct functions in the ventral and the dorsal parts of the VL in cephalopods. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Locomotor, avoidance, and maze behavior in rats with selective disruption of hippocampal output.

Investigated behavioral correlates of selective disruption of hippocampal output in a series of 5 experiments. A total of 136 male albino Moll-Wistar rats were used as Ss. In 2 experiments an attempt was made through behavioral investigation to determine whether the CA1 neurons project to the fimbria or to the subiculum. Results support recent views that the subiculum is the recipient of CA1 axons. Disruption of the CA1 output in the dorsal hippocampus of Ss produced increased open-field activity, whereas passive avoidance and spontaneous alternation behaviors remained unchanged. No differentiation was obtained between CA1 damage and neocortical lesions in maze learning. Blocking of the fimbrial CA3 output from the dorsal hippocampus improved passive avoidance performance and impaired active avoidance performance, whereas open-field and spontaneous alternation behaviors were unaffected. Interruptions of the CA3 output from the ventral hippocampus improved active avoidance performance and reduced spontaneous alternation behavior. Open-field behavior and passive avoidance performance remained unchanged. Total fimbrial sections increased open-field activity, improved passive and active avoidance, and reduced spontaneous alternation. Results are discussed in terms of functional differentiation between the CA1 and CA3 of the dorsal hippocampus aknd in terms of functional in the fimbrial CA3 output from the dorsal and ventral hippocampus. (56 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Dorsal hippocampus, CA3, and CA1 lesions disrupt temporal sequence completion.

An experiment was designed to evaluate effects of dorsal hippocampus, dorsal CA3a,b, dorsal CA1, and control lesions on performance of a temporal sequence task. Rats were trained on a sequential learning task involving six spatial locations on a radial 8-arm maze. After initial training followed by surgery, it was found that all lesioned animals were able to remember the sequence. To test temporal sequence completion, rats were started at different positions in the sequence and expected to complete the remainder of the sequence. The results indicate that control rats had no difficulty completing the sequence, regardless of starting point. In contrast, rats with dorsal hippocampus and dorsal CA3a,b lesions made errors by always returning to the first position in the sequence, regardless of which start position was used, whereas rats with dorsal CA1 lesions made random errors in the process of completing the sequence and did not appear to remember the serial order of the spatial sequence. This suggests that the dorsal hippocampus, and specifically the dorsal CA3 in conjunction with CA1, may be involved in temporal pattern completion processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of transplantation of fetal hippocampal or hindbrain tissue into the brains of adult rats with hippocampal lesions on water maze acquisition.

Rats were given bilateral aspiration lesions of the hippocampus. Some of these rats then received bilateral transplants of fetal hippocampal or dorsal ventricular ridge tissue that was dissected from embryonic rat brains at 16 or 17 days of gestation. The remaining rats with hippocampal lesions did not receive fetal brain transplants. Rats with neocortical aspiration lesions, but without transplants, and rats without brain damage were also included in the study. All of the rats were trained to find a submerged platform in a Morris water maze. Rats with the fetal brain transplants were more impaired in some measures of maze learning than were rats with hippocampal lesions only. The results indicate that transplants of fetal brain tissue are not always associated with recovery of behavioral function after brain damage and may even increase a lesion-induced behavioral impairment in tasks that require complex cognitive functioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Selective hippocampal lesions abolish the contextual specificity of latent inhibition and conditioning.

The contextual specificity of the CR and latent inhibition (LI) was examined in rats with selective hippocampal lesions. Acquisition of the CR to a novel CS was equally rapid in control and hippocampal rats (Exps 1 and 2), and CS preexposure disrupted acquisition (i.e., produced LI) to an equal extent in both groups (Exp 2). In control Ss, however, the CR established in one context transferred incompletely to a 2nd context (Exp 1), and LI was attenuated when CS preexposure and conditioning occurred in different contexts (Exp 3). This context specificity of the CR and LI was not apparent in hippocampal rats; the CR and LI transferred readily from one context to another. In addition, hippocampal rats were impaired in a spatial learning task (Exp 2) but were unimpaired in learning a Pavlovian contextual discrimination (Exp 3). Results suggest that a common contextual retrieval process underlies the contextual dependence of the CR and of LI and that this process is mediated by the hippocampus. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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)     

"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)