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Biomedical subjects

J P Aggleton

Publications and source records attributed to J P Aggleton.

At least 109 records · Page 6Linked to original sources
PubMed1987

Effects of scopolamine and physostigmine on recognition memory in monkeys with ibotenic-acid lesions of the nucleus basalis of Meynert.

Monkeys with bilateral ibotenic-acid lesions of the nucleus basalis of Meynert, an area rich in cholinergic neurons that innervate the cerebral cortex, were compared with unoperated control monkeys on a recognition memory task. Although animals with large lesions had substantial reductions of cortical choline acetyltransferase activity, none showed impairment in the task. Lesion effects were observed, however, when performance was assessed following administration of a muscarinic receptor blocker (scopolamine) or a cholinesterase inhibitor (physostigmine). Although scopolamine produced dose-related impairments in both groups, this effect was greater in the experimental animals. Conversely, whereas physostigmine produced modest improvement in performance in the control group, no such improvement was observed in the experimental animals. The altered sensitivity to the mnemonic effects of cholinergic agents in the experimental group suggests that the cholinergic neurons of the nucleus basalis of Meynert contribute to recognition memory.

Acetylcholinesterase↗
PubMed1987

A comparison between the connections of the amygdala and hippocampus with the basal forebrain in the macaque.

Autoradiographic experiments indicated that the amygdala projects to division Ch3 and Ch4 of the basal forebrain (nomenclature from Mesulam et al. 1983) and the olfactory tubercle. The heaviest of these amygdaloid outputs arose from the lateral basal, accessory basal, central, and medial amygdaloid nuclei, each with a slightly different pattern of distribution from that of the other. Injections of the retrograde tracer horseradish peroxidase (HRP) into the amygdala revealed dense reciprocal projections arising from region Ch4, especially from subdivisions Ch4al, Ch4iv, and Ch4p. The other basal forebrain regions, by contrast, provided very little input to the amygdala. Hippocampal efferents terminated densely in the medial (Ch1), lateral and dorsal septum, and in region Ch2. Hippocampal efferents terminated less densely in restricted portions of the olfactory tubercle and in Ch4. Experiments in which the fornix was transected showed that all of these hippocampal projections to the basal forebrain ran through the fornix. The hippocampal output to the septum, which was the heaviest projection of those examined, appears to have a crude topographic arrangement. Little overlap was observed between the terminal zones of the amygdaloid and hippocampal projections to the basal forebrain, indicating yet again the independence of the amygdaloid and hippocampal systems that has been demonstrated in other regions of the forebrain, such as the thalamus and cerebral cortex.

Amygdala↗
PubMed1986

The origin, course, and termination of the hippocampothalamic projections in the macaque.

The projections from the hippocampal formation to the thalamus were investigated with both anterograde and retrograde tracers. Horseradish peroxidase was injected into medial and midline thalamic sites in six cases, and tritiated amino acids were injected into the hippocampal formation in nine others, five of which had prior transections of the fornix. Only the subicular and entorhinal cortices were found to project to the thalamus. From the subicular cortex, dense bilateral projections were traced through the fornix to the anterior nuclei, while lighter fornical projections terminated in other rostral midline sites, including the nuclei reuniens, centralis latocellularis, and paraventricularis. These projections arose predominantly from the polymorphic cells which are located in the deepest cellular layers of the subiculum and prosubiculum. In addition, the subicular cortex was found to project to the nucleus lateralis dorsalis. The latter projection, which showed evidence of a crude topographic organization, ran either through the fornix or, unlike the other subicular efferents, through the sublenticular limb of the internal capsule to form part of the temporopulvinar bundle of Arnold. The nonfornical projection to the nucleus lateralis dorsalis passed through the medial pulvinar, where there was some additional termination. Few, if any, projections from the entorhinal cortex to the thalamus travelled in the fornix. Rather, the entorhinal efferents were carried in the inferior thalamic peduncle to the magnocellular portion of the nucleus medialis dorsalis, and in the internal capsule and bundle of Arnold to the medial pulvinar and the nucleus lateralis dorsalis.

Afferent Pathways↗
PubMed1986

A description of the amygdalo-hippocampal interconnections in the macaque monkey.

The interconnections between the amygdala and the hippocampal formation were investigated in the macaque monkey using anterograde tracers. The hippocampal inputs to the amygdala arose from the subicular and entorhinal cortices and passed through the angular bundle to terminate principally in the medial basal and lateral basal nuclei, with lighter termination in the lateral nucleus, the periamygdaloid cortex, and the cortical-transition area. The majority of these amygdaloid inputs arose from the rostral hippocampal formation although there was equivocal evidence of an additional projection from the caudal hippocampus to the central nucleus. Projections arose from many of the amygdaloid nuclei to terminate in the molecular layer of the amygdalo-hippocampal area and the adjacent stratum moleculare of the uncal portion of the hippocampus. The accessory basal, lateral basal, and medial basal nuclei also projected to the most rostral portions of the stratum moleculare of fields CA1-3, the heaviest termination occurring in field CA3. Additional projections from the basal nuclei terminated in the prosubiculum, presubiculum, and parasubiculum. The heaviest entorhinal inputs arose from the accessory basal and lateral nuclei and terminated in layers I, II, and III of areas 28b, 28i, and the prorhinal cortex. The major amygdaloid input to the perirhinal cortex arose from the lateral basal nucleus.

Amygdala↗
PubMed1986

The effects of hippocampal lesions upon spatial and non-spatial tests of working memory.

A series of experiments examined the proposal that the primary effect of hippocampal damage in rats is to disrupt working memory. Although extensive hippocampal lesions produced a severe impairment in forced-choice alternation--a test of spatial working memory--the same lesions did not impair the acquisition of a non-spatial test of working memory--delayed non-matching-to-sample. This test of object recognition required the rats to select that arm in a Y-maze which contained unfamiliar stimuli. Rats with hippocampal lesions were able to learn and perform this task at normal rates, even with retention delays of as long as 60 s. Two additional experiments helped confirm that the animals had indeed learnt a non-spatial test of working memory. The final experiment examined whether hippocampal lesions resulted in an increased sensitivity to proactive interference. It was found that repetition of test stimuli within a session, which increased interference, did attenuate recognition performance but there was no evidence that the animals with hippocampal lesions were differentially affected.

Animals↗
PubMed1986

Memory impairments caused by experimental thalamic lesions in monkeys.

A series of experiments examined the effects of selective diencephalic lesions upon object recognition in the cynomolgus monkey (Macaca fascicularis). In the first experiment it was found that extensive lesions of the medial thalamus (MT) produced a severe deficit in both relearning the recognition task and subsequently performing with retention intervals longer than 10 sec. Additional experiments showed that more selective lesions in either the anterior medial thalamus (AMT), the posterior medial thalamus (PMT), or the medial mamillary nucleus (MB) only produced mild recognition memory impairments. It is argued that a combination of damage is required to produce the severe memory impairments observed in cases of global diencephalic amnesia.

Alcohol Amnestic Disorder↗
PubMed1985

A description of intra-amygdaloid connections in old world monkeys.

The intrinsic amygdaloid connections of the cynomolgus monkey were investigated using the autoradiographic method. Additional evidence concerning the origin of some intra-amygdaloid connections was provided by a series of rhesus monkeys with injections of horseradish peroxidase (HRP) in the amygdaloid complex. The experiments indicated that each of the major amygdaloid nuclei possesses a unique, organized set of intrinsic projections. Furthermore, there were large differences in the magnitude of the internal connections arising from or terminating in the various nuclei. The heaviest intrinsic projections arose from the lateral and basal nuclei while the central, medial, cortical, and accessory basal nuclei received the greatest number of these afferents. Thus, there was a clear trend for the bulk of these connections to run dorsally and medially within the amygdala. One important function of these intrinsic connections may be the integration of afferent sensory information from the various association areas which project to the amygdala.

Amygdala↗
PubMed1985

Mamillary-body lesions and visual recognition in monkeys.

Cynomolgus monkeys with complete bilateral destruction of the medial mamillary nucleus exhibited little, if any, deficit in object recognition, although they did show evidence of impairment in spatial memory. The pattern of effects thus resembled that found previously after either hippocampal ablations or transections of the fornix and suggests that, like such damage, mamillary-body damage alone is insufficient to produce the global amnesia attributed to it in clinical cases.

Amnesia↗
PubMed1985

X-ray localization of limbic structures in the cynomolgus monkey (Macaca fascicularis).

The anterior/posterior (AP) and dorsal/ventral positions of 3 subcortical structures, the amygdala, the mamillary bodies, and the anterior commissure, were estimated with respect to the skull in a series of cynomolgus monkeys (Macaca fascicularis). The distance from the external auditory meatus, from which stereotaxic coordinates are typically derived, to these structures was found to be highly variable. In contrast, radiography revealed that a skull landmark which forms part of the sphenoid bone lies at a remarkably constant distance from these 3 structures. The posterior clinoid process also proved to be a more accurate reference point than the auditory meatus, although it was less reliable than the sphenoid landmark. It is proposed that the position of the sphenoid bone could be used to localize a wide range of limbic and basal forebrain structures.

Amygdala↗
PubMed1984

Projections of the amygdala to the thalamus in the cynomolgus monkey.

The projections of the amygdala to the thalamus in cynomolgus monkeys (Macaca fascicularis) were studied with both anterograde and retrograde axonal tracing techniques. Horseradish peroxidase (HRP) was injected into medial and midline thalamic sites in five animals, and tritiated amino acids were injected into selected amygdaloid regions in a total of 13 hemispheres in ten animals. The findings from the two types of tracer experiments demonstrated the origins, course, and terminal pattern of amygdaloid projections to two thalamic nuclei--medialis dorsalis (MD) and reuniens. Almost all of the amygdaloid nuclei contribute projections to MD, though the greatest proportion arise from the basal group and terminate in discrete, interlocking patches within the medial, magnocellular portion of MD. In addition to this major projection, the central and medial amygdaloid nuclei send a lighter projection to the lateral portion of nucleus reuniens. The amygdalothalamic projections took a variety of routes out of the amygdala before the large majority joined the inferior thalamic peduncle and entered the rostral head of the thalamus where they turned caudally toward their targets. A small number of amygdalothalamic fibers may also run in the stria terminalis.

Amygdala↗
PubMed1983

Memory impairments following restricted medial thalamic lesions in monkeys.

Thalamic contributions to memory were assessed in monkeys with lesions placed in the medial portions of either the anterior or posterior thalamus (AMT and PMT, respectively). Both lesions produced a moderate impairment in a test of object recognition memory. Furthermore, all three animals in the PMT group and two out of the three in the AMT group were moderately impaired on a test of object-reward associative memory. Comparison of these results with those of a previous study in which the AMT and PMT regions were removed jointly (Aggleton and Mishkin 1983) suggests that damage in either region can induce a memory loss but that combined damage to both is required to produce a full-blown amnesia.

Alcohol Amnestic Disorder↗
PubMed1983

Visual recognition impairment following medial thalamic lesions in monkeys.

Monkeys with surgical lesions which removed the medial portions of the medial and anterior thalamic nuclei were markedly impaired on a test of object recognition. The same animals were able to learn visual pattern discriminations and a spatial delayed response task at a normal rate. These findings indicate that lesions in the medial thalamus produce a selective impairment in visual recognition memory in monkeys and, consequently, may provide an experimental model for human "diencephalic amnesia".

Animals↗
PubMed1982

An assessment of the reinforcing properties of foods after amygdaloid lesions in rhesus monkeys.

The reinforcing strengths of foods were assessed in rhesus monkeys before and after bilateral radio-frequency lesions of the lateral amygdala (n = 4), basolateral amygdala (n = 4), and total amygdala (n = 3). None of these lesions altered preoperative preferences between three highly palatable foods. Moreover, the lesions had no discernible effect on the animals' responses to different food rewards as measured by a progressive ratio schedule, although performance on this schedule proved sensitive to the size and type of food reward and to the degree of deprivation. The results suggest that amygdalectomy leaves a normal appreciation of at least this one class of rewards, foods. The dietary changes typically seen after amygdalectomy, such as meat eating, which were also observed in the same animals, probably reflect a loss of neophobia.

Amygdala↗
PubMed1981

Stereotaxic surgery under X-ray guidance in the rhesus monkey, with special reference to the amygdala.

The anterior/posterior (AP) positions of three subcortical regions; the amygdala, supra-optic nucleus of the hypothalamus and mammillary bodies, were estimated with respect to the skull in 35 rhesus monkeys (Macaca mulatta). The distances from the external auditory meatus, from which stereotaxic coordinates are typically derived, to these subcortical nuclei were found to be highly variable. In contrast the posterior tip of the sphenoid bone, which was visualized on lateral radiographs, provided a landmark at a remarkably constant AP distance from these nuclei. This landmark was used to guide a series of a amygdaloid lesions and injections. The accuracy of these operations strongly suggested that the posterior tip of the sphenoid bone could be used to predict not only the AP but also the height of the amygdala. It is proposed that this radiographic technique could be applied to other hypothalamic and basal forebrain regions.

Amygdala↗
PubMed1981

Syndrome produced by lesions of the amygdala in monkeys (Macaca mulatta).

Behavioral effects of subtotal amygdaloid lesions were investigated in an attempt to dissociate some of the abnormalities seen after total amygdalectomy. Twelve monkeys received bilateral stereotaxic lesions centered in the basolateral amygdala, lateral amygdala, dorsal amygdala, or the temporal white matter lying adjacent to the lateral amygdala. These monkeys were compared with others with control operations. The control monkeys then received total amygdaloid lesions (AMX). The AMX monkeys exhibited the typical amygdaloid syndrome of hypoemotionality, meat eating, coprophagia, and excessive exploration. In contrast, the monkeys with subtotal amygdaloid lesions would not eat meat or feces, though they were more willing than control monkeys to investigate inanimate objects. Although minor changes in affect were observed, the extreme emotional changes seen after total amygdalectomy were found only in the monkey with the largest subtotal lesion. Only those animals that were hypoemotional showed a deficit in learning successive reversals of an object discrimination. This close association suggests that both the hypoemotionality and the successive reversal deficit arise from the same underlying dysfunction.

Amygdala↗
PubMed1980

Cortical and subcortical afferents to the amygdala of the rhesus monkey (Macaca mulatta).

The afferent projections to the primate amygdala were studied using horseradish peroxidase. The potential advantages of this technique are discussed compared with those previously used to determine amygdaloid afferents. The findings indicate that certain agranular or dysgranular cortical regions may project directly to the amygdala: in particular, the orbital frontal cortex, anterior cingulate gyrus, subcallosal gyrus, temporal pole and anterior insula. These projections probably terminate predominantly in either the lateral or accessory basal nuclei. Other cortical projections from the inferotemporal and superior temporal gyri are described. Evidence was found for a heavy projection from the superior temporal sulcus to the lateral nucleus. Subcortical afferents were found from the hypothalamus, substantia innominata, diagonal band, thalamus, periaqueductal central gray, peripeduncular nucleus and from a band of cells extending medially from the peripeduncular nucleus to the midline, just ventral to the thalamus. In the thalamus, labelled cells were restricted to the non-specific nuclei, and were common in the rostral midline nuclei. No projection was observed from the dorsomedial nucleus of the thalamus. We discuss the implications of these results for interpreting the functions of the amygdala.

Afferent Pathways↗