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M Sarter

Publications and source records attributed to M Sarter.

121 records · Page 7Linked to original sources
PubMed1985

Reversal learning in senescent rats.

The ability of old (24 months) and young (3 months) male rats to reverse a previously acquired discrimination was compared in 5 experiments. The old rats did not need more trials to learn a position habit in a T-maze to obtain water reward, but required more trials to reverse the position habit. The old rats showed a similar deficit in a second, but not in subsequent reversals of the position habit. In a second experiment, old rats were slower in learning to operate one of two levers in an operant chamber to obtain food reward on a CRF schedule, but by the session prior to reaching criterion for acquisition they showed response rates similar to the young animals. When the rats were required to operate the alternative lever to obtain reward, the young rats emitted 70% of their responses during the first reversal session on the newly-correct lever, but the old rats only 35%. Nevertheless, the groups were similar in the number of sessions required to reach a criterion of 95% of responses on the correct lever. In 3 subsequent reversals, old and young rats did not differ nor were there differences in the number of responses in 4 extinction sessions in the rats which had received reversal training. In experiment 3 with old and young rats which had received only acquisition training, old rats emitted fewer responses than young animals during extinction. From these experiments it was hypothesized that the apparent difficulty of old rats in learning a reversal task was due to the low probability of their emitting spontaneously a novel or previously unrewarded response, and not to a difficulty in forming a new association. This hypothesis was tested in two further experiments in which rats were required to learn a brightness discrimination in a T-maze. Old and young rats which had learned and reversed position habits in the T-maze in experiment 1, did not differ in either acquisition or reversal of the brightness discrimination, suggesting that old rats do not differ from young animals in reversal tasks when the motor response requirements for the task are already within the animals' behavioural repertoire. Consistent with this hypothesis, naive old rats were slower than young rats in acquiring a similar brightness discrimination but did not differ in the reversal task.

Aging↗
PubMed1985

The amygdala's role in human mnemonic processing.

The possible role played by the human amygdaloid complex in the processing of mnemonic information is examined. First, evidence is reviewed from case reports in which amygdaloid damage occurred due to surgical intervention or pathological or age-related changes. Then, studies are evaluated in which the amygdala was stimulated or in which electrical potentials were recorded from it. Based on this survey an hypothesis on the possible involvement of the amygdala in mnemonic information processing is proposed. In essence, it is argued that the human amygdala is responsible for activating or reactivating those mnemonic events which are of an emotional significance for the subjects' life history and that this (re-)activation is performed by charging sensory information with appropriate emotional cues. Supportive evidence for this hypothesis is given based on human case reports, on studies in animals in which information processing was determined following amygdaloid lesions, and on evidence of neuroanatomical connections of the primate amygdala.

Adult↗
PubMed1985

Involvement of the amygdala in learning and memory: a critical review, with emphasis on anatomical relations.

The amygdala has been attributed with a considerable number of very diverse functions. Its involvement in learning and memory, though, has found increased attention. Following a short description of the connections of the amygdala and its critical neurotransmitters, studies are reviewed here in which the amygdala's activity was manipulated or observed by different methods (lesions, electrical brain stimulation, neurochemical intra-amygdaloid injections, single-unit recordings). Some of the major conclusions resulting from this data analysis indicate an advantage in performing subtotal amygdaloid lesions over an amygdalectomy, a point of view that is especially supported by the heterogeneous anatomical connections of different amygdaloid nuclei. Thereafter, an evaluation is made of different tasks with respect to their discriminative sensitivity to amygdaloid manipulations. Some species-specific differences in performing certain tasks after amygdaloid injuries are discussed in relation to the different expansion of amygdalo-cortical connections in higher and less highly encephalized species. Finally, some general assumptions are made on the specific role of each of the amygdaloid nuclei during the mnemonic processes attributed to the amygdala. It is concluded that emotionally significant information is encoded and can be retrieved on the basis of the structures and connections of the basolateral limbic circuit.

Amygdala↗
PubMed1985

Collateralization in the mammalian nervous system.

After reviewing the loci of origin for neurons with collateralized axons, some hypotheses on their distribution in the mammalian nervous system, on their functional contributions and on their significance in the course of encephalization are discussed. In principle, the distribution of collateralized neurons seems to be restricted to anatomical circuits subserving unspecific activation of forebrain regions and controlling body balance and movements. Concerning the limbic system, a minor degree of collateralization seems to exist only in less encephalized species. Based on a number of anatomical and functional arguments, it is assumed that the significance of collateralization fades in the course of encephalization.

Animals↗
PubMed1984

Afferents to the ventral tegmental nucleus of Gudden in the mouse, rat, and cat.

Afferents to the ventral tegmental nucleus of Gudden (VT) were investigated in mice, rats, and cats. Unilateral and bilateral injections or iontophoretical applications of horseradish peroxidase (HRP) were made into the region of the VT. The entire cerebrum was then screened for labeled neurons. Following injections situated principally within the VT, in all three species many retrogradely labeled neurons were observed in the mamillary bodies and the lateral habenular nuclei. Fewer labeled cells were observed in the prefrontal cortex, the basal forebrain, various hypothalamic nuclei, the interpeduncular nucleus, nucleus of the posterior commissure, nucleus of Darkschewitsch and interstitial nucleus of Cajal, vestibular nucleus, and nucleus praepositus hypoglossi. Scant but consistent labeling occurred in the cingular, retrosplenial, and insular cortices, within the medial forebrain bundle, fields of Forel, zona incerta, ventral tegmental area of Tsai, substantia nigra, pretectal area, periaqueductal gray, dorsal tegmental nucleus, locus ceruleus, and raphe complex. Our results show a high similarity in the distribution of afferent connections converging on the VT of mice, rats, and cats. They indicate furthermore that the VT is reached by a variety of cortical and subcortical afferents, which belong either to the limbic system or to brain stem regions related to motor, sensory, and autonomic functions. It is suggested that the VT subserves as a midbrain core structure of the limbic system, which is responsible for the transfer of motor, sensory, and autonomic informations arising within the brain stem to limbic forebrain structures.

Animals↗
PubMed1984

Collateral innervation of the medial and lateral prefrontal cortex by amygdaloid, thalamic, and brain-stem neurons.

The distribution of the afferents to the rat's prefrontal cortex originating in the thalamic mediodorsal nucleus and the amygdala was investigated with two fluorescent tracers. Special emphasis was laid on detecting the loci of neurons which project via axonal collaterals into both lateral and medial portions of the prefrontal cortex. It was found that a high number of neurons of the anterior portion of the basolateral amygdaloid nucleus terminate via collaterals in both the medial and lateral subfields of the prefrontal cortex. On the other hand, only a small number of mediodorsal thalamic cells were found to project to both sides of the prefrontal hemisphere via bifurcating axonal collaterals. These cells were situated exclusively in the lateral part of the medial segment of the mediodorsal nucleus. The majority of both thalamic and amygdaloid neurons with bifurcating axons originate from subregions whose cells innervate primarily the medial prefrontal cortex. In brain-stem, neurons of the nucleus raphé dorsalis also project via collaterals to the medial and lateral prefrontal regions. Furthermore, neurons of the dorsal and ventral premamillary nuclei, the lateral mamillary nucleus, the ventral tegmental area of Tsai, and the ventral tegmental nucleus of Gudden were found to project to the medial prefrontal cortex. Our results indicate a differential collateral organization of thalamic and amygdaloid afferents to prefrontal cortical fields. The anterior basolateral amygdala (which innervates via collaterals both the medial and lateral prefrontal subfields) may add a common input to either subfield, such as information on the significance of incoming stimuli to the animal's behavior, while the mediodorsal nucleus (whose segments are principally connected to only one prefrontal subfield) may add segment-specific information, for example, of a spatial-cognitive nature for the lateral segment and of an emotional nature for the central and medial segments. The existence of a basolateral limbic circuit, composed of the amygdala, the thalamic mediodorsal nucleus, and the prefrontal cortex, is confirmed and knowledge on its interconnectivity is extended. From an anatomical point of view these data provide arguments for both unitary and diverging functions of the prefrontal cortex.

Amygdala↗
PubMed1983

Reduced resistance to progressive extinction in senescent rats: a neuroanatomical and behavioral study.

The behavior of senescent rats and mature-young rats was compared in a learning task which consisted of the acquisition of a visual discrimination task, its reversal, the induction of a progressively increasing extinction, relearning and, finally, a complete extinction training. It was found that young and old rats were statistically indistinguishable during all parts of the task, except the progressively increasing extinction. Here, the senescent animals made a significantly higher number of errors than the mature-young ones. Neuroanatomically, ventricular dilation, commissural changes and neuronal loss were observed in senescent rats. The significantly reduced number of neurons in the medial nucleus of the amygdala in old rats compared to young was not directly related to the changed behavior in the progressively increasing extinction part of the visual discrimination task. Based on the anatomical connections of the amygdala and its possible functions in learning and memory, the hypothesis is made that the medial amygdaloid nucleus is involved in the learning of changing response-reinforcement contingencies.

Age Factors↗
PubMed1983

Convergence of basolateral amygdaloid and mediodorsal thalamic projections in different areas of the frontal cortex in the rat.

The extent of convergence of mediodorsal thalamic and amygdalar afferents on the rat's frontal cortex was studied by tracing retrogradely labeled cells following injections of horseradish peroxidase (HRP). HRP was applied iontophoretically in extremely small injections throughout all areas of the frontal cortex. The following organization was revealed: Converging inputs from the mediodorsal nucleus and the amygdala are observed in the posterior parts of the pre- and infralimbic areas, in the posterior half of the dorsal and ventral agranular insular areas and in the lateral and dorsal precentral areas. Both mediodorsal and amygdaloid afferents reach the dorsal tip of the frontal cortex. Only the mediodorsal afferents were found to terminate in the anterior parts of the pre- and infralimbic areas and in the anterior part of the dorsal division of the anterior cingulate area and in the medial precentral area. On the lateral side of the hemisphere the anterior halves of the dorsal and ventral agranular insular areas receive mediodorsal afferents. Amygdaloid, but not mediodorsal afferents, were found following injections into the more posterior parts of the lateral precentral area. These results are discussed with respect to the extent of the prefrontal cortex in the rat and its definability as a target area of subcortical nuclei. Functional aspects of the anatomical convergence of connections within the so-called basolateral limbic circuit are outlined.

Afferent Pathways↗
PubMed1983

Interhemispheric nigrostriatal projections in the rat: bifurcating nigral projections and loci of crossing in the diencephalon.

The organization of interhemispheric nigrostriatal projections in the rat was studied with (1) a double labeling technique combined with a histofluorescence method for monoamines and with (2) horseradish-peroxidase (HRP) as a tracer. Each animal received an injection of Fast Blue (FB) into the caudate nucleus (NC) of one hemisphere and an injection of Nuclear Yellow (NY) into the NC of the other hemisphere. Brains were processed according to the sucrose-potassium phosphate-glyoxylic acid (SPG) method in order to identify monoaminergic neurons. About 5% of the neurons which were labeled by either of the tracers in the substantia nigra (SN) ipsilateral to the injection site were also labeled in the contralateral SN. Most of these interhemispherically projecting SN-neurons were monoaminergic. A small number of neurons in either SN was labeled with both fluorescent tracers. This suggests that bifurcating, monoaminergic neurons in the SN project to both NC. In the second experiment, rats received a unilateral injection of HRP into NC. After a survival time of several hours the animals were perfused and the brains were processed using benzidine-dihydrochloride. Fibers crossing the hemisphere were found within the massa intermedia of the thalamus and within the inferior thalamic peduncle. The results are discussed with respect to a possible functional role of interhemispheric nigrostriatal connections.

Animals↗
PubMedDate not supplied

Vitamin E deprivation in rats: some behavioral and histochemical observations.

Rats deprived of vitamin E from age of 4 weeks were tested in four independent behavioral experiments and compared with a group fed a control diet. During a 14-minute session in a hole-board, no differences in the level and the course of habituation of parameters of activity and exploration were found. A second group of animals was trained in an automatically controlled six-arm radial tunnel maze. Although no differences were found in various activity measurements, the deprived animals showed a slightly impaired spatial concept formation during 8 acquisition sessions. Testing their relearning ability of the same maze 18 days later, the vitamin E deprived animals showed a significant impairment. In a third experiment, animals were trained 16 days in the same maze configuration and at day 17 they were exposed to the mirror image of the radial maze. Both groups mastered this reversal with an increased level of activity but without differences in patrolling efficiency. In a fourth behavioral experiment, the effects of scopolamine on deprived animals were examined. Compared to the controls, the vitamin E deprived animals were relatively insensitive to the effects of scopolamine. Autofluorescent neuronal lipofuscin accumulation was found especially in the hippocampus (CA3) of vitamin E deprived animals. Based on these results, the usefulness of vitamin E deprivation as an animal model for accelerated normal aging is discussed.

Aging↗
PubMedDate not supplied

Toward modeling age-related changes of attentional abilities in rats: simple and choice reaction time tasks and vigilance.

Fischer-344 rats aged 4, 12, or 18 months were trained in a simple or choice reaction time task (SRTT; CRTT). Animals were required to detect a brief (50 ms), rarely, and unpredictably occurring signal that was presented either at the central panel light (SRTT) or above one of the two levers (CRTT). Animals reported detection by pressing either lever (SRTT) or the cued lever (CRTT) within 3 s. False alarm rates were obtained from a nonsignal 3-s bin. In comparison to younger animals, 18-month-old animals showed a reduced signal detectability, and this effect did not interact with practice. These results suggest that age affected vigilance and practice did not attenuate this effect. The benzodiazepine receptor agonist chlordiazepoxide (at subsedative doses; 1, 3, and 5 mg/kg) and the beta-carboline ZK 93 426 (1, 3, and 5 mg/kg) failed to affect signal detectability. Scopolamine HBr and MBr impaired detectability and responsivity to a similar extent. However, scopolamine MBr, unlike the tertiary compound, failed to affect response accuracy in the CRTT. It is speculated that the failure of chlordiazepoxide to affect performance was related to low processing demands of both tasks. Although these behavioral models show good face validity, they do not allow determination of the major components of attentional processes (perceptual sensitivity, response criterion, processing capacity). Animal behavioral paradigms that allow determination of such components are required for the investigation of the neuronal basis of age-related changes in attentional abilities.

Aging↗
PubMedDate not supplied

Potassium, but not atropine-stimulated cortical acetylcholine efflux, is reduced in aged rats.

Using in vivo microdialysis, cortical acetylcholine (ACh) efflux was measured in freely moving Brown Norway/Fischer 344 F1 rats, aged 4 or 22 months. The effects of local, intracortical perfusion of atropine (1.0 or 100.0 microM) via the dialysis probe were compared to local K+ (100.0 mM) stimulation in the presence of elevated extracellular Ca2+ (2.5 mM). Basal cortical ACh efflux in aged rats was similar to that of young animals. Administration of atropine (1.0 or 100.0 microM) via the cortical dialysis probe substantially increased cortical ACh efflux, but did not differentially stimulate ACh efflux in young and aged rats. In contrast, ACh efflux stimulated locally with K+ and Ca2+ was significantly reduced in aged rats relative to young adults. The implications of the dissociable effects of K(+)-depolarization and muscarinic blockade for local regulation of cortical ACh efflux in aged animals are discussed.

Acetylcholine↗