A peculiar pattern of temporal involvement of rat perirhinal cortex in memory processing.

By means of the fully reversible tetrodotoxin inactivation technique, perirhinal cortex (PC) mnemonic function was investigated in rats trained to a passive avoidance response (PAR). It was shown that PC functional integrity is necessary during PAR acquisition, during late and very late consolidation (from 24 hr up to 192 hr after the training session), and during retrieval. An unexpected finding was that the PC was not involved in the early consolidation period. Thus the PC may play a relatively simple relay or connective role during acquisition, but its very late and very long consolidative involvement may indicate a peculiar function in consolidation and possibly in the storage of the PAR engram. The results are discussed in terms of the mnemonic characteristics of other neural sites (amygdala, hippocampus, and entorhinal cortex) involved in the same learning process. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Parallel involvement of perirhinal and lateral entorhinal cortex in the polysynaptic activation of hippocampus by olfactory inputs

BACKGROUND AND AIMS OF THE STUDY: There is a need for a replacement cardiac valve constructed from non-immunogenic materials but incorporating living, and preferably autologous, cells. The object of this study was to colonize freeze-dried porcine valve leaflets with human fibroblasts and vascular endothelial cells. METHODS: Porcine pulmonary valve leaflets were freeze-dried to produce a porous matrix having communicating cavities of appropriate dimensions for fibroblast repopulation. Cultured human fibroblasts and vascular endothelial cells that had been cryopreserved by standard methods were added to freeze-dried leaflets. Following culture at 37 degrees C, the leaflets were examined by confocal scanning microscopy and transmission electron microscopy. RESULTS: Mechanical perforation of the leaflet surface permitted colonization of the freeze-dried matrix by fibroblasts; under the conditions we studied, the cell density did not reach physiologic levels but those cells that were present were well attached and metabolically active. Gentle cotton abrasion of the surface of the freeze-dried leaflets provided a suitable substrate for endothelial cell attachment and confluence was achieved in 10 days. Leaflets were perforated, cultured with human fibroblasts for 10 days, then gently rubbed with a cotton bud and cultured for a further 10 days with human endothelial cells. The endothelial cells formed a confluent layer on the surface and viable fibroblasts were present within the substance of the leaflet. CONCLUSION: Although these results are preliminary, they demonstrate the basic feasibility of this approach to the production of xenogeneic valves that contain the patient's own cells.     

Learning and transfer of object—reward associations and the role of the perirhinal cortex.

Perirhinal cortex ablation has previously been shown only to impair new postoperative object discrimination learning with large stimulus set sizes (≥40 problems). In this study, 3 cynomolgus monkeys (Macaca fascicularis) with bilateral perirhinal cortex ablations were impaired relative to 3 normal controls on concurrent discrimination learning tasks with only 10 problems with the objects presented in different orientations in each trial to increase the demands placed on object identification. This supports the hypothesis that perirhinal cortex damage impairs the ability to identify multiple individual objects. Fewer errors were made to digitized images of objects than toward real objects. Both groups subsequently transferred specific object-reward associations from real objects to digitized images of the respective objects and vice versa, providing evidence that cynomolgus monkeys can recognize photographic representations of objects with experience. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of muscarinic blockade in perirhinal cortex during visual recognition

Stimulus recognition in monkeys is severely impaired by destruction or dysfunction of the perirhinal cortex and also by systemic administration of the cholinergic-muscarinic receptor blocker, scopolamine. These two effects are shown here to be linked: Stimulus recognition was found to be significantly impaired after bilateral microinjection of scopolamine directly into the perirhinal cortex, but not after equivalent injections into the laterally adjacent visual area TE or into the dentate gyrus of the overlying hippocampal formation. The results suggest that the formation of stimulus memories depends critically on cholinergic-muscarinic activation of the perirhinal area, providing a new clue to how stimulus representations are stored.     

Role of the perirhinal cortex in rats' conditioned taste aversion response memorization.

The role of the perirhinal cortex (PC) in conditioned taste aversion (CTA) learning was investigated in Long-Evans rats. CTA was induced by the intraperitoneal administration of LiCl 60 min after saccharin-sweetened water drinking. The PC was reversibly inactivated by the stereotaxic administration of tetrodotoxin (TTX) 60 min before saccharin drinking, immediately after saccharin drinking (Experiment 1), 6 or 24 hr after LiCl administration (Experiment 2), and 60 min before CTA retrieval testing (Experiment 3). Only pre-saccharin drinking PC inactivation disrupted CTA. Thus, PC integrity is necessary only during the earliest phases of CTA mnemonic processing, that is, taste information acquisition and early gustatory memory elaboration. The results are discussed in relation to PC connectivity and PC temporal involvement in the memorization process of other aversive responses. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Patterns of Fos expression in the amygdala and ventral perirhinal cortex induced by training in an olfactory fear conditioning paradigm.

The activation of amygdaloid nuclei, the ventral perirhinal cortex (vPRh), and several other brain areas in the rat during the acquisition and expression of olfactory fear conditioning was assessed through Fos immunocytochemistry in 3 separate experiments. The results of Experiment 1 suggest that olfactory and somatosensory inputs may functionally converge in the anterior region of the medial nucleus (aMe). The results of Experiment 2 indicate that the aMe exhibited significantly greater Fos-like immunoreactivity (FLI) in subjects acquiring conditioned stimulus–unconditioned stimulus associations than in those presented with the same olfactory and somatosensory stimuli in a manner that precluded acquisition. The results of Experiment 3 indicate that the vPRh appeared to exhibit learning-related increases in FLI during the expression of previously acquired associations. Collectively, these data suggest that the aMe and vPRh may be critically involved in different aspects of olfactory fear conditioning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

A crucial role of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid subtype of glutamate receptors in piriform and perirhinal cortex for the initiation and propagation of limbic motor seizures

The role of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptors in the initiation and propagation of limbic motor seizures in rats was examined by the intracerebral and systemic administration of 2,3-dihydroxy-6-nitro-7-sulfamoyl-benzo (f) quinoxaline (NBQX), a selective antagonist of the AMPA subtype of glutamate receptor. Limbic motor seizures were evoked focally by the application of the gamma-aminobutyric acid receptor antagonist, bicuculline, into area tempestas, an epileptogenic site in the deep anterior piriform cortex. Before eliciting seizures, NBQX was applied focally into either 1) area tempestas or 2) perirhinal or posterior piriform cortex ipsilateral to the area tempestas from which seizures were evoked. In addition, pretreatment with i.p. NBQX was evaluated for anticonvulsant actions against area tempestas-evoked clonic or systemically evoked tonic seizures. In all conditions, a dose-dependent decrease in the severity of seizures was obtained with NBQX. With focal intracerebral administration, a dose of 500 pmol of NBQX consistently protected against limbic motor seizures, with partial protection achieved with 100 pmol. After i.p. administration, 2.5 and 5.0 mg/kg significantly protected the rats from both limbic motor seizures and tonic extensor seizures. No overt disturbance of spontaneous behavior was associated with the anticonvulsant doses of NBQX. Moreover, both forebrain substrates of limbic motor seizures and hindbrain substrates of tonic extensor seizures were highly susceptible to disruption by NBQX. The results indicate that AMPA subtype of glutamate receptors are crucial mediators of seizure propagation via perirhinal and piriform cortics.     

A generalized expression for lag-time in the gas-phase permeation of hollow tubes

A generalized expression for the nonsteady state parameter, lag-time, has been obtained from Fick’s second law for gas-phase transport through hollow, cylindrical membranes. This generalized expression is simplified for three limiting cases of practical interest: 1) diffusion controlled transport, 2) phase boundary reaction control at the inlet surface, and 3) phase boundary reaction control at the outlet surface. In all three cases the lagtime expressions were found to be inversely proportional only to the diffusion coefficient and functionally dependent on the membrane radii. Finally, the lag-time expressions were applied to experimentally obtained lag-time data for α-phase titanium and α-phase iron. Formerly with NASA-Ames Research Center, Materials Science Branch.     

A generalized expression for lag-time in the gas-phase permeation of hollow tubes

A generalized expression for the nonsteady state parameter, lag-time, has been obtained from Fick’s second law for gas-phase transport through hollow, cylindrical membranes. This generalized expression is simplified for three limiting cases of practical interest: 1) diffusion controlled transport, 2) phase boundary reaction control at the inlet surface, and 3) phase boundary reaction control at the outlet surface. In all three cases the lagtime expressions were found to be inversely proportional only to the diffusion coefficient and functionally dependent on the membrane radii. Finally, the lag-time expressions were applied to experimentally obtained lag-time data for α-phase titanium and α-phase iron.     

Familiarity-based stimulus generalization of conditioned suppression in rats is dependent on the perirhinal cortex.

We report that bilateral, excitoxic lesions of the perirhinal cortex attenuate rats' familiarity-based stimulus generalization. After surgery, rats were preexposed either to 2 auditory stimuli (A and B) or to only 1 auditory stimulus (B). Following preexposure, all rats received pairings of A and a footshock before assessment of generalized responding (conditioned suppression) to B. Sham rats' generalization was greater when preexposure was to both A and B than when preexposure was to B only. That pattern was abolished in lesioned rats, though no general deficiency was found in other measures of auditory processing. Our findings suggest that the perirhinal cortex is required for rats to encode familiarity as part of stimulus representations. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Memory impairment on a delayed non-matching-to-position task after lesions of the perirhinal cortex in the rat.

Previous research conducted in monkeys and rats has established that the perirhinal cortex is critically involved in object- or stimulus-recognition memory, whereas other research suggests this region may contribute to memory for object discriminations. These findings do not rule out the possibility that the perirhinal cortex plays a more general role in memory. The present experiment addressed whether selective lesions of the perirhinal cortex would result in a delay-dependent deficit on a test of memory that did not involve stimulus recognition or object memory. Rats with bilateral perirhinal lesions were tested on a delayed non-matching-to-position task. Lesions of the perirhinal cortex did not interfere with acquisition or performance at short (0–4 s)-delay intervals, but lesions did impair performance at longer delays. It is suggested that the perirhinal cortex is involved in maintaining representations of trial-specific information over time. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lesions of the perirhinal cortex do not impair integration of visual and geometric information in rats.

Rats with lesions of the perirhinal cortex and a control group were required to find a platform in 1 corner of a white rectangle and in the reflection of this corner in a black rectangle. Test trials revealed that these groups were able to integrate information regarding the shape of the pool and the color of its walls (black or white) to identify the correct location of the platform. A clear effect of the perirhinal cortex lesions was, however, revealed using an object recognition task that involved the spontaneous exploration of novel objects. The results challenge the view that the perirhinal cortex enables rats to solve discriminations involving feature ambiguity. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Lesions of rat perirhinal cortex exacerbate the memory deficit observed following damage to the fimbria-fornix.

Rats that had received bilateral lesions of the perirhinal cortex, fimbria-fornix, combined lesions of both these structures, or sham operations were tested on an object-guided delayed non-match-to-sample task. Perirhinal lesioned and fimbria-fornix lesioned rats were moderately impaired when delay intervals of 30 s or more were introduced between the sample and test phases of the experiment. Animals with combined lesions displayed a considerably greater impairment than animals with lesions of either structure alone. The combined lesioned animals were severely impaired in the initial acquisition of the task and displayed a profound memory deficit at delay intervals of greater than 4 s. These results emphasize the importance of the perirhinal cortex to memory function and suggest that the perirhinal cortex and the hippocampal formation may function interactively in the execution of memory processes. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Excitotoxic lesions centered on perirhinal cortex produce delay-dependent deficits in a test of spatial memory

The purpose of the study was to assess developments in the theory of mind suggested by changes in the organization of cognitive verb extensions during the elementary school years. Adults and 3rd- and 5th-grade children were provided with a set of mental activity scenarios and were asked to select the best verbs from a list of cognitive verbs that might apply to each scenario. Changes in organization were assessed by examining overlapping uses of cognitive verbs in different contexts. There were 3 major changes with development: (a) the understanding of the role of memory in input functions increased, (b) the interrelatedness of memory- and comprehension-related verbs increased, and (c) the importance of cognitive certainty and uncertainty engaged by constructive processing verbs increased. Together, these findings suggest that a constructivist theory of mind develops in later childhood.     

Brain self-stimulation: direct evidence for the involvement of dopamine in the prefrontal cortex

Rats were trained to self-stimulate the medial prefrontal cortex, a region rich in dopaminergic terminals. After the region adjacent to the electrode site was labeled with [14C]dopamine, it was perfused repeatedly by means of push-pull cannulas. Electrical stimulation of this cortical area in six animals enhanced the release of dopamine and its associated metabolites in nine of 16 experiments. Thus in vivo evidence is provided that dopamine is involved in the brain self-stimulation mechanism within the frontal cortex.     

Methods for whole-cell recording from visually preselected neurons of perirhinal cortex in brain slices from young and aging rats

Consideration of the individual, his or her needs, and what he or she hopes to gain through surgery is of primary importance in determining a surgical plan for the rheumatoid patient. Nevertheless, procedures undertaken to save life or prevent neurologic demise must, of course, take precedence. Alleviation of pain and correction of disabling deformity take next priority. Many other considerations go into the formulation of the list of surgical priorities. A full understanding of these considerations and a well-integrated team approach to the rheumatoid patient provide the best chance for optimal outcome following surgery.     

The effects of neurotoxic lesions of the perirhinal cortex combined to fornix transection on object recognition memory in the rat

The effects of lesions centred in the perirhinal cortex region (Prh) or in both the perirhinal cortex region and the fornix (Prh + Fx) were assessed in two different working memory tasks, one spatial the other nonspatial. For the spatial task the rats were tested in an eight arm radial maze, using a standard procedure in which they were rewarded for avoiding previously visited arms. The Prh + Fx, but not the Prh, rats produced significantly more errors (re-entries) and these started significantly earlier in each session when compared with a surgical control group. The nonspatial task was a test of spontaneous object recognition in which rats were tested on their ability to discriminate between a familiar and a novel object. For the initial tests the Prh group failed to discriminate between the objects, but the Prh + Fx group showed a clear preference for the novel object. Observation of the test showed, however, that the Prh + Fx group were spending a greater length of time initially exploring the sample (familiar) object. When the amount of exposure to the sample object was limited to either 20 or 40 s (i.e. was the same for all three groups), the Prh + Fx group now failed to discriminate between the two objects. This change was especially evident for shorter sample duration (20 s). The Prh group did, however, show an amelioration of their deficit with this further testing. The present results support previous dissociation between spatial and nonspatial working memory, and indicate that there may be some recovery of function following perirhinal cortical damage.     

Lesions of the perirhinal cortex interfere with conditioned excitation but not with conditioned inhibition of fear.

Posttraining lesions of the perirhinal cortex (Prh) have been shown to interfere with the expression of fear. This study assessed whether Prh lesions would also disrupt the inhibition of fear as measured with conditioned inhibition of fear-potentiated startle. Following light + shock, noise→ light-no shock conditioned-inhibition training, rats were given Prh lesions. The lesions interfered with the expression of fear-potentiated startle to the light. To assess whether conditioned inhibition was affected, the rats were given light + retraining without additional noise→ light - training. The noise-conditioned inhibitor retained its ability to inhibit fear-potentiated startle to the retrained light. These results suggest that the areas of the Prh that are essential for the initial expression of conditioned fear are not important for the expression of conditioned inhibition of fear. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

The effect of excitotoxic lesions centered on the perirhinal cortex in two versions of the radial arm maze task.

Rats with bilateral ibotenic acid lesions centered on the perirhinal cortex and sham-operated controls were tested in 2 versions of a spatially guided radial arm maze task. Lesioned rats made significantly more errors and required more sessions to reach criterion relative to controls in the standard radial maze task. When they were tested in a delayed nonmatch to sample version of this task, lesioned rats made more errors during the predelay phase and at both the 30-s and 10-min delays of the postdelay phase. These findings provide further support for the hypothesis that the role of the perirhinal cortex in object recognition memory may include reference to some spatial aspect of the environment. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Transient memory impairment in monkeys with bilateral lesions of the entorhinal cortex

Performance on five behavioral tasks was assessed post-operatively in Macaca fascicularis monkeys prepared with bilateral lesions of the entorhinal cortex (E group). Three of the tasks were also readministered 9-14 months after surgery. Initial learning of the delayed nonmatching-to-sample (DNMS) task was impaired in the E animals relative to unoperated control monkeys. On the delay portion of DNMS, the performance of E animals was nearly at control levels at short delays (up to 60 sec) but was impaired at 10 min and 40 min retention intervals. On the retest of DNMS, the E animals performed normally at all retention intervals. The E animals were unimpaired on the four other memory tasks. Neuroanatomical studies revealed a significant transverse expansion of the terminal field of the perirhinal cortical projection in the CA1 region of the hippocampus. Compared to unlesioned, anatomical control monkeys, the transverse length of the perirhinal terminal field in CA1 increased approximately 70% in the E monkeys. Although this was a striking morphological alteration, it is not known whether the sprouting of this projection influenced the behavioral recovery. The results of these studies suggest that the entorhinal cortex may normally participate in the learning and performance of tasks that are dependent on the medial temporal lobe memory system. However, recovery of normal DNMS performance demonstrates that the entorhinal cortex is not, by itself, essential for learning and performance of such tasks.