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J N Rawlins

Publications and source records attributed to J N Rawlins.

104 records · Page 6Linked to original sources
PubMed1982

The septo-hippocampal system and cognitive mapping.

Rats were trained on a rewarded alternation task, run as a spatial working memory task on an elevated T-maze. Experiment 1 tested the effects of fornix-fimbria (FOFI) lesions on the acquisition, and of medial septal (MS) lesions on the acquisition and retention of this task, when the rats had to use information provided by being forced to run to a selected goal arm. The FOFI lesion produced an enduring impairment; the MS rats showed a severe impairment initially, but subsequently showed some behavioural recovery, when tested in acquisition or in retention. Experiment 2 similarly tested the effects of lateral septal (LS) lesions on acquisition of the task, and found an impairment which again showed signs of recovery with further testing. Experiment 3 was a transfer test conducted on the rats which had shown recovery in Experiments 1 and 2. The rats were now forced to use information provided by simply being placed on a selected goal arm. Both control animals and lesion animals showed identical choice accuracy, lower than that seen in Experiments 1 and 2. Experiment 4 tested acquisition of the task used in Experiment 3, and acquisition of a task in which the rat had to use information provided by running to the goal arm via a different route. Control rats again performed poorly, and scarcely differed from MS rats. It was concluded that rats have difficulty in using information about 'places', and that controls and lesion rats learn the tasks in the same way. The implications for 'cognitive mapping' hypotheses are discussed.

Animals↗
PubMed1982

Medial septal area lesions disrupt theta rhythm and cholinergic staining in medial entorhinal cortex and produce impaired radial arm maze behavior in rats.

This study was designed to determine (1) which brain area paces the theta rhythm in the medial entorhinal cortex (MEC) of rats and (2) the extent to which the behavioral effects of lesions in the medial septal area (MSA), which disrupt the cholinesterase-related pathway to the hippocampal formation, resemble the effects previously reported to result from fimbria-fornix lesions. MSA lesions abolished or decreased theta rhythm in dorsal hippocampus (DHPC) and MEC; acetylcholinesterase (AChE) staining was depleted or diminished in all of the hippocampus and entorhinal cortex. Rats with MSA lesions were impaired on acquisition of a radial arm maze task. Unilateral fimbria lesions left theta rhythm and AChE staining essentially unaltered in ipsilateral DHPC and MEC but depleted AChE in ipsilateral ventral hippocampus (VHPC) and ventral lateral entorhinal cortex (LEC). A lesion of the dorsal fornix at the level of the hippocampal flexure left ipsilateral DHPC theta rhythm and AChE stain unaltered while causing a substantial reduction in theta rhythm and depletion of AChE in ipsilateral MEC. AChE staining was complete in VHPC and LEC. These results suggest tha MSA paces MEC theta rhythm and that the presumed cholinergic projection which mediates this function travels in the dorsal fornix. The fimbria carries a presumed cholinergic projection to ventral LEC. Rats with MSA lesions can learn a radial arm maze task, unlike rats with fimbria-fornix lesions, but they learn significantly slower than normal rats.

Acetylcholinesterase↗
PubMed1980

The effects of hippocampectomy and of fimbria section upon the partial reinforcement extinction effect in rats.

Rats were trained to run in an alley for food reward given on every trial (continuous reinforcement, CR) or on a random 50% of trials (partial reinforcement, PR) and were then extinguished. Sham-operated controls showed the usual partial reinforcement extinction effect (PREE), i.e., PR-trained animals were more resistant to extinction than CR-trained animals. The PREE was abolished by hippocampectomy, which increased resistance to extinction in CR-trained rats and decreased it in PR-trained rats. Bilateral fimbria section had no effect on resistance to extinction in either condition. These results are discussed in the light of theories of hippocampal function and the anatomy of septohippocampal connections.

Animals↗
PubMed1980

The effects of chlordiazepoxide HCl administration upon punishment and conditioned suppression in the rat.

Rats were trained to lever press for sucrose on a random interval (RI) 64-s schedule. During a 55 min session there were four 3 min "intrusion periods" signalled by a flashing house-light. In experiment 1 there were two groups matched for baseline response rate. During the intrusion periods one group received response-independent footshock on an independent RI 64 schedule; the other group received response-contingent shock on this schedule. Shock intensity was varied for each rat to match degree of response suppression between the two groups. Chlordiazepoxide HCl (CDP) in doses 0.5-5 mg/kg alleviated response suppression equally in both groups. Experiment II followed the same procedure, except that all animals had the same shock intensity, producing greater response suppression in the response-contingent shock groups. CDP alleviated response suppression more in the response-contingent shock groups, significantly so at 5 mg/kg, nonsignificantly at 1 mg/kg. These results suggest that previous reports that CDP differentially alleviates the response suppression produced by response-contingent shock are an artefact of rate dependency.

Animals↗
PubMed1980

Dorsal periaqueductal gray punishment, septal lesions and the mode of action of minor tranquilizers.

In order to study the role of the septo-hippocampal system and the dorsal periaqueductal gray (DPAG) substance in punished behavior and in the action of minor tranquilizers, two groups of rats were trained to lever press on a continuous reinforcement schedule of food presentation. In one group, every response was subsequently punished by foot-shock delivery; in the other, by brief electrical stimulation of the DPAG of the mesencephalon. In both groups response rats were reduced to less than 10% of pre-punishment rates, but not completely supressed. Response rates did not significantly differ between the two groups, either before or after the introduction of punishment. Septal lesions significantly increased responding in the animals punished by foot-shock, but did not affect responding suppressed by DPAG stimulation. Injection of chlordiazepoxide (5mg/kg,IP) significantly increased punished responding in both groups of rats, before as well as after the septal lesion. Before the septal lesion was made, responding suppressed by foot-shock was significantly more released by chlordiazepoxide than responding punished by DPAG stimulation. These results suggest that in punishment tests using foot-shock, both a behavioral inhibitory system, including the septo-hippocampal structures and an aversive or punishment system, including the DPAG substance, act together to produce response suppression. Both these systems would be depressed by minor tranquilizers in order to cause their anti-punishment and perhaps their anti-anxiety action as well.

Animals↗
PubMed1979

Septo-hippocampal connections and the hippocampal theta rhythm.

Recordings were made of spontaneous hippocampal theta activity in free-moving rats, before and after a variety of lesions. Three recording sites were used to monitor activity in the dorsal hippocampus, the ventral hippocampus, or close to the site of the hippocampal flexure. Electrolytic lesions were made in the medial septal area or the dorso-lateral septal area; surgical transections were made of the fimbria or dorso-medial area of the fornix. Following lesions restricted to the medial septal area, theta was abolished throughout the hippocampus; after lesions restricted to the dorso-lateral septal area theta was retained. Fimbria lesions abolished it in the dorsal, but not the ventral, hippocampus. In some subjects the hippocampal formation was subsequently stained for cholinesterase: cholinesterase staining loss was generally associated with theta loss, but this was not clear at the flexure recording site. It was confirmed that theta is dependent upon the integrity of the medial septal area. It was concluded that damage to hippocampal afferents from the septum does abolish theta, while damaging the feedback efferents does not.

Animals↗
PubMed1979

Hippocampal theta in rats under urethane: generators and phase relations.

Recordings were made from the directly visualized dorsal hippocampus of urethane-anesthetized rats with silver ball and tungsten microelectrodes. Theta of about 5 c/sec was elicited by reticular stimulation and was located in two broad strata in and subjacent to CA1. A superficial generator yielded 200-250 microV theta from the alveus, stratum oriens and stratum pyramidale; a null-theta and phase-reversal point was located in stratum radiatum; a deep generator yielded 300-500 microV theta in stratum lacunosum-moleculare of the hippocampus and distal stratum moleculare of the dentate gyrus, with maximum amplitude near the fissure. No theta was found in CA3. Cross-correlation analyses between generators yielded coefficients on the order of -0.80 while within a generator--especially the deep one--coefficients could reach +0.95. Phase analyses showed the two generators were about 180 degrees out of phase, with the deep generator leading. Septotemporal movement along the upper generator yielded no phase shifts; similar movement along the deep generator showed slight lead ing in septal portions. Subiculofimbrial movement in both generators showed a complex pattern of phase shifts: generally, subicular sites led fimbrial sites, but an inversion of 10 degrees-20 degrees occurred in the millimeter anterior to the center of the hippocampus. Anatomical, phase and other datal led to consideration of a possible retrohippocampal role in supplementing the well-known pacemaker in the medial septum.

Anesthesia, General↗
PubMed1977

Lamellar organisation in the rat hippocampus.

A series of experiments was conducted in the urethane anaesthetised rat to determine the organisation of some hippocampal pathways in this species, using stimulating and recording microelectrodes to elicit and record pupulation spikes. It was found that the mossy fibres, alvear fibres and perforant path were clearly arranged in a lamellar fashion. Lamellar organisation could not be demonstrated for the afferents in the stratum radiatum which include the Schaffer collaterals. It was concluded that hippocampal organisation in this species essentially resembles that in the rabbit and cat.

Animals↗
PubMed1977

The role of the septo-hippocampal system and its noradrenergic afferents in behavioural responses to none-reward.

Our experiments were designed with two purposes: (i) to examine the effects on one behaviour of differing interventions in the septo-hippocampal system; (ii) to compare these effects with those of minor tranquillizers. The behaviour studied (in rats) is extinction in the alley after continuous (CRF) or partial (PRF) reinforcement. Minor tranquillizers and large septal lesions produce three effects: (1) resistance to extinction is increased after CRF; (2) resistance to extinction is decreased after PRF; (3) the partial reinforcement extinction effect (PREE) is abolished. Small septal lesions fractionate this syndrome: either effect (1) or an actual increase in the size of the PREE is produced by medial septal lesions abolishing hippocampal theta; effects (2) and (3), but not (1), are produced by lateral septal lesions sparing theta. Dorso-medial fornix section, abolishing theta, reproduces the effects of medial septal lesions. Fimbrial section, sparing theta, reproduces some of the effects of lateral septal lesions. Minor tranquillizers produce a rise in the threshold for septal driving of hippocampal theta specifically at 7.7 Hz. This effect is reproduced by blockade of noradrenergic transmission or destruction of the dorsal noradrenergic bundle with 6-hydroxydopamine. This lesion reproduces all three behavioural changes listed above. These results suggest a model for the role of the septo-hippocampal system and its noradrenergic inputs in the PREE. This model is compared with other approaches to the septo-hippocampal system.

Afferent Pathways↗