Western diet and the weakening of the interoceptive stimulus control of appetitive behavior.

In obesogenic environments food-related external cues are thought to overwhelm internal cues that normally regulate energy intake. We investigated how this shift from external to internal stimulus control might occur. Experiment 1 showed that rats could use stimuli arising from 0 and 4h food deprivation to predict sucrose delivery.

A study of hippocampal structure-function relations along the septo-temporal axis.

This study examined structural-functional differences along the septo-temporal axis of hippocampus using radial-maze tasks that involved two different memory processes [reference memory (RM) and working memory (WM)], and the use of two kinds of information (spatial vs. nonspatial cue learning). In addition, retention of the nonspatial cue task was tested nine weeks following completion of acquisition, and the rats then underwent discrimination reversal training.

Hippocampal lesions impair retention of discriminative responding based on energy state cues.

The present research investigated the hypothesis that the hippocampus is involved with the control of appetitive behavior by interoceptive "hunger" and "satiety" signals. Rats were trained to solve a food deprivation intensity discrimination problem in which stimuli produced by 0-hr and 24-hr food deprivation served as discriminative cues for the delivery of sucrose pellets. For Group 0+, sucrose pellets were delivered at the conclusion of each 4-min session that took place under 0-hr food deprivation, whereas no pellets were delivered during sessions that took place when the rats had been food deprived for 24 hr.

Contributions of the hippocampus and medial prefrontal cortex to energy and body weight regulation.

The effects of selective ibotenate lesions of the complete hippocampus (CHip), the hippocampal ventral pole (VP), or the medial prefrontal cortex (mPFC) in male rats were assessed on several measures related to energy regulation (i.e., body weight gain, food intake, body adiposity, metabolic activity, general behavioral activity, conditioned appetitive responding).

Memory inhibition and energy regulation.

At a simple behavioral level, food intake and body weight regulation depend on one's ability to balance the tendency to seek out and consume food with the ability to suppress or inhibit those responses. Accordingly, any factor that augments the tendency to engage in food seeking and eating or that interferes with the suppression of these behaviors could produce (a) caloric intake in excess of caloric need; (b) increases in body weight leading to obesity. This paper starts with the idea that excess body weight and obesity stem from a failure or degradation of mechanisms that normally function to inhibit eating behavior.

The hippocampus and inhibitory learning: a 'Gray' area?

Gray's approach to understanding hippocampal functioning [The Neuropsychology of Anxiety: An Enquiry into the Function of the Septo-hippocampal System, 1982; The Neuropsychology of Anxiety, 2000] departs from the prevailing view of that structure as a substrate for memory. Instead, Gray and McNaughton have proposed that hippocampus is involved with a function that is more fundamental than memory, namely the resolution of conflict between competing approach and avoidance tendencies. The present paper attempts to advance this perspective by describing how the effects of selective lesions of the hippocampus on performance in both relatively simple Pavlovian conditioning tasks and in more complex radial maze problems could be a consequence of an impairment in a simple form of inhibitory learning.

Functional differentiation within the medial temporal lobe in the rat.

The structures that comprise the medial temporal lobe (MTL) have been implicated in learning and memory. The question of primary concern in the present research was whether the group of anatomically related structures (hippocampus, subiculum, presubiculum/parasubiculum, entorhinal cortex, perirhinal/postrhinal cortex) are involved in mediating a similar memory process or whether the individual structures are differentially involved in memory processes and/or in handling various types of information. A series of five experiments were carried out that involved selectively lesioning the main MTL structures and testing each animal on radial-maze tasks and procedures that provided measures of two different memory processes (reference memory, working memory) and the utilization of two kinds of information (spatial, nonspatial).

Perirhinal cortex supports delay fear conditioning to rat ultrasonic social signals.

Auditory information can reach the lateral nucleus of the amygdala (LA) through a monosynaptic thalamic projection or a polysynaptic cortical route. The polymodal input from the perirhinal cortex (PR) is a major informational gateway to the LA and nearby structures. Pretraining PR lesions impair fear conditioning to a context, but there have been no reports that they cause deficits in delay conditioning to an auditory cue.

Excitotoxic lesions of the pre- and parasubiculum disrupt the place fields of hippocampal pyramidal cells.

To determine what influence the pre- and parasubiculum regions of the hippocampal formation have on neural representations within the dorsal hippocampus, single-unit recordings were made as rats with bilateral ibotenic acid lesions centered on the former regions (n = 4) or control surgeries (n = 3) foraged freely. Spatial firing specificity was measured using an information content procedure. Cells from lesioned animals (n = 57) provided significantly less spatial information than cells from control animals (n = 44).

The effects of selective ibotenate lesions of the hippocampus on conditioned inhibition and extinction.

Previously, Solomon (1977) reported that aspiration lesions of the dorsal hippocampus in rabbits had no effect either on the acquisition of Pavlovian conditioned inhibition or on performance during a subsequent retardation test. The present experiment confirmed and extended these findings by showing that rats with ibotenate lesions of the complete hippocampus (the dorsal and ventral hippocampus and the dentate gyrus) were also unimpaired on the same types of tasks. Additional tests with the same rats showed that removing the hippocampus significantly impaired extinction of responding to a stimulus that had been previously trained with an appetitive unconditioned stimulus.

Use of excitotoxins to lesion the hippocampus: update.

Although many of the problems associated with the use of conventional lesion techniques (aspiration, electrolytic, radiofrequency) can be avoided by employing focal injections of excitotoxins, experience gained over the past 12 years has shown that considerable care must be exercised with this newer method, to limit the cell loss to the intended area or structure. Of the toxins that have been used most often to selectively destroy the cells that comprise the hippocampus, ibotenic acid (IBO) and N-methyl-D-aspartate (NMDA) have proved to be nonspecific in their effects on different cell types and these toxins do not cause seizures. In contrast, focal injections of kainate (KA) and quisqualate result in damage that centers primarily in the CA3 pyramidal cell field and hilar cells in the dentate gyrus.

A comparison of the effects of fimbria-fornix, hippocampal, or entorhinal cortex lesions on spatial reference and working memory in rats: short versus long postsurgical recovery period.

Using a radial maze task and different postoperative recovery periods, this experiment assessed and compared the reference and working memory performances of adult Long-Evans male rats subjected to entorhinal cortex, fimbria-fornix, and hippocampus lesions. Sham-operated rats were used as controls. In order to see whether the duration of the postsurgical recovery period would influence acquisition of the complex radial maze task, training began 1 month following surgery (Delay 1) for half the rats in each group, while for the other half training was started 6.

The hippocampus and motivation revisited: appetite and activity.

After reviewing the available data regarding the various effects of manipulating (e.g. lesions, chemical or electrical stimulation) the hippocampal formation, Jarrard concluded that this structure likely played a role in motivated behaviors, specifically in general behavioral activation and incentive motivation.

Contextual fear conditioning is disrupted by lesions of the subcortical, but not entorhinal, connections to the hippocampus.

Recent studies have questioned the importance of the entorhinal cortex (ERC) for normal hippocampal function. For example, fibre-sparing ERC lesions have been found to have no effect on spatial learning in the watermaze. There is also doubt as to the importance of the ERC for contextual fear conditioning, with previous studies having yielded conflicting results.

The role of the entorhinal cortex in two forms of spatial learning and memory.

It is generally acknowledged that the rodent hippocampus plays an important role in spatial learning and memory. The importance of the entorhinal cortex (ERC), an area that is closely interconnected anatomically with the hippocampus, in these forms of learning is less clear cut. Recent studies using selective, fibre-sparing cytotoxic lesions have generated conflicting results, with some studies showing that spatial learning can proceed normally without the ERC, suggesting that this area is not required for normal hippocampal function.

Retrograde amnesia and consolidation: anatomical and lesion considerations.

The four papers in this issue of Hippocampus dealing with retrograde amnesia, together with relevant animal studies in the literature, are reviewed from the perspective of the anatomical location of the lesion and extent of damage to the brain. In order to evaluate the underlying damage in these and related prospective experimental studies, it is necessary to consider both the lesion techniques that were used as well as the care with which the resulting damage was determined. Both temporally graded and flat, ungraded retrograde amnesia have been reported, as well a lack of effects, following damage to structures in the medial temporal area.

Excitotoxic lesions of the pre- and parasubiculum disrupt object recognition and spatial memory processes.

Rats with bilateral ibotenic acid lesions centered on the pre- and parasubiculum and control rats were tested in a series of spatial memory and object recognition memory tasks. Lesioned rats were severely impaired relative to controls in both the reference and working memory versions of the water maze task and displayed a delay-dependent deficit in a delayed nonmatch to place procedure conducted in the T-maze. Lesioned rats also displayed reduced exploration in a novel environment, and performance was altered in an object recognition procedure as compared with the control group.

Reconsideration of the role of the hippocampus in learned inhibition.

The purpose of this article is to reconsider the role of the hippocampus in learning tasks that require suppression or prevention of memories or responses. This type of learning has generally been referred to as inhibitory learning. Although early theories proposed that the hippocampus was important for inhibitory learning, these ideas have generally fallen out of favor.

Selective lesions of the entorhinal cortex, the hippocampus, or the fimbria-fornix in rats: a comparison of effects on spontaneous and amphetamine-induced locomotion.

Using adult Long-Evans male rats, this experiment compared spontaneous (assessed 15 days and 4.5 months after surgery) and amphetamine-induced (assessed from 4.5 months after surgery onwards; 1 mg/kg, i.

Hippocampectomized rats are impaired in homing by path integration.

Theoretical, behavioral, and electrophysiologic evidence suggests that the hippocampal formation may play a role in path integration, a form of spatial navigation in which an animal can return to a starting point by integrating self-movement cues generated on its outward journey. The present study examined whether the hippocampus (Ammon's horn and the dentate gyrus) is involved in this form of spatial behavior. Control rats and rats with selective ibotenic acid lesions of the hippocampus were tested in a foraging task in which they retrieved large food pellets from an open field, which when found, they carried to a refuge for consumption.

Effects of ibotenate hippocampal and extrahippocampal destruction on delayed-match and -nonmatch-to-sample behavior in rats.

The effects of ibotenate lesions of the hippocampus (HIPP) or hippocampus plus collateral damage to extrahippocampal structures (HCX) were investigated in rats trained to criterion on spatial versions of either a delayed-match (DMS) or delayed-nonmatch-to-sample (DNMS) task. After recovery from surgery, animals were retrained at "0" sec delays, then assessed at 0-30 sec delays for 15 d, retrained again at 0 sec delays, and retested for another 25 d on 0-30 sec delays. Pretrained HIPP-lesioned animals showed marked delay-dependent deficits in both tasks that never recovered.

Fimbria-fornix vs selective hippocampal lesions in rats: effects on locomotor activity and spatial learning and memory.

The behavioral effects of interrupting the axons that pass in the fimbria and dorsal fornix were compared with the effects of selective removal of the cells that comprise the hippocampus with ibotenic acid. Starting 4.5 months after surgery, lesioned and control rats were (i) trained in both the Morris water maze and the eight-arm radial maze using protocols that placed an emphasis on either working memory (WM) or reference memory (RM) and (ii) tested for locomotor activity in the home cage.

Behaviors and neurodegeneration induced by two blockers of K+ channels, the mast cell degranulating peptide and Dendrotoxin I.

Both the Mast Cell Degranulating (MCD) peptide and Dendrotoxin I (DTX(I)), two blockers of fast activation and slowly inactivating K+ channels, induced epileptiform seizures and brain damage after intracerebroventricular injection (200 pmol) in Sprague-Dawley rats. A considerable variation in the response of the rats was observed for each toxin. The neurodegeneration included the hippocampal formation, subiculum, septum, amygdala, and the cerebellum for both toxins, and the neocortex and anterior thalamic nuclei exclusively for DTX(I) treatment.

Effects of postoperative housing conditions on functional recovery in rats with lesions of the hippocampus, subiculum, or entorhinal cortex.

In order to study the effects of differential housing conditions on recovery from damage to different components of the hippocampal formation, 85 rats received bilateral lesions of the hippocampus, entorhinal cortex, or subiculum or sham surgery and then were housed for 30 days in either an enriched environment or an impoverished environment. Rats were subsequently tested on a battery of tasks for assessing locomotor activity in their home cage, reactivity to novelty, spatial working and reference memory in the Morris water maze, and learning in the Hebb-Williams maze. Rats with the hippocampus removed showed impairments in most of the tasks we used (home-cage and novelty-induced locomotor activity, water maze, and Hebb-Williams maze).

Facilitation of conditioned odor aversion by entorhinal cortex lesions in the rat.

This study examined the role of the entorhinal cortex (EC) in conditioned odor aversion learning (COA). Lateral EC lesions did not impair but rather facilitated COA. In the experiments the delay separating the odor cue presentation from the subsequent toxicosis was varied during acquisition.