Mode of [14C] 2-deoxy-D-glucose uptake into retrosplenial cortex and other memory-related structures of the monkey during a delayed response

Multiple potential mechanisms of graft action is not a new idea

It is well established that neural grafts can exert functional effects on the host animal by a multiplicity of different mechanisms – by diffuse release of trophic molecules, neurohormones, and deficient neurotransmitters, as well as by growth and reformation of neural circuits. Our challenge is to understand how these different mechanisms complement each other.

Grafts and the art of mind's reconstruction

The use of neural transplantation to alleviate cognitive deficits is still in its infancy. We have an inadequate understanding of the deficits induced by different types of brain damage and their homologies in animal models against which to assess graft-induced recovery, and of the ways in which graft growth and function are influenced by factors within the host brain and the environment in which the host is operating. Further, use of fetal tissue may only be a transitory phase in the search for appropriate donor sources. Nevertheless, findings from our laboratory and elsewhere have made aprima faciecase for successful cognitive reconstruction by graft methods.

Studying restoration of brain function with fetal tissue grafts: Optimal models

We concur that basic research on the use of CNS grafts is needed. Two important model systems for functional studies of grafts are ignored by Stein & Glasier. In the first, reproductive function is restored in hypogonadal mice by transplantation of GnRH-synthesizing neurons. In the second, circadian rhythmicity is restored by transplantation of the suprachiasmatic nucleus.

Gene replacement therapy in the CNS: A view from the retina

Gene replacement therapy holds great promise in the treatment of many genetic CNS disorders. This commentary discusses the feasibility of gene replacement therapy in the unique context of the retina, with regard to: (1) the genetics of retinal neoplasia and degeneration, (2) available gene transfer technology, and (3) potential gene delivery vehicles.

The limitations of central nervous systemdirected gene transfer

Complementation and correction of a genetic defect with CNS manifestations lags behind gene therapy for inherited disorders affecting other organ systems because of shortcomings in delivery vehicles and access to the CNS. The effects of improvements in viral and nonviral vectors, coupled with the development of delivery strategies designed to transfer genetic material thoughout the CNS are being investigated by a number of laboratories in efforts to overcome these problems.

CNS transplant utility may surive even their hasty clinical application

Neural cell transplants have been introduced in clinical practice during the last decade with mixed results, encouraged by success with simple animal models. This commentary is a reminder that although the ideas and techniques of transplantation appear simple, the variables involved in host-transplant integration still require further study. The field may benefit from a concerted, multidisciplinary approach.

Are fetal brain tissue grafts necessary for the treatment of brain damage?

Despite some clinical promise, using fetal transplants for degenerative and traumatic brain injury remains controversial and a number of issues need further attention. This response reexamines a number of questions. Issues addressed include: temporal factors relating to neural grafting, the role of behavioral experience in graft outcome, and the relationship of rebuilding of neural circuitry to functional recovery. Also discussed are organization and type of transplanted tissue, the “trophic hypothesis” of transplant viability, and whether transplants are really needed to obtain functional recovery after brain damage.

Transplantation, plasticity, and the aging host

Neural transplantation as a recovery strategy for neuro-degenerative diseases in humans has used mainly grafting following acute denervation strategies in young adult hosts. Our work in aged mice and rats demonstrates an age-related increase in susceptibility to oxidative damage from neurotoxins, a remarkably poor recovery of C57BL/6 mice from MPTP insult with transplantation and growth factors, even at 12 months of age, and diminished plasticity of host neurons. We believe that extrapolation of data from young adult animal models to aged humans without thorough investigation of transplantation and host response inagedrecipients is scientifically and ethically inappropriate.

Lack of effect of lesions in the anterior cingulate cortex and retrosplenial cortex on certain tests of spatial memory in the rat

The effects of cytotoxic lesions in either the anterior cingulate cortex or the retrosplenial cortex were compared with those of fornix lesions on three tests of spatial memory. Two of the tasks, delayed nonmatching-to-position and spatial reversal learning, were tested in an automated apparatus. The third task, forced alternation, was tested in a T-maze. Neither anterior cingulate nor retrosplenial cortex damage produced any significant impairment on the three tasks. In contrast, rats with fornix lesions (hippocampal system damage) were markedly impaired on all three tasks. The results, which were considered in the light of proposals for a hippocampal--anterior thalamic--cingulate system that is important for spatial memory, suggest that neither of the cingulate regions involved in this study form a critical subcomponent of this proposed system. It is therefore assumed that the cingulate cortices are only critical for certain classes of spatial problem. It is also suggested that in some previous studies the effects of inadvertent damage to the cingulum bundle may have contributed to the apparent effects of cingulate lesions.

Efferent projections from the anterior thalamic nuclei to the cingulate cortex in the rat

The organization of projections from the anterior thalamic nuclei to the cingulate cortex was analyzed in the rat by the anterograde transport of Phaseolus vulgaris-leucoagglutinin. The rostral part of the anteromedial nucleus projects to layers I, V and VI of the anterior cingulate areas 1 and 2, layers I and III of the ventral orbital area, layers I, V and VI of area 29D of the retrosplenial area, and layers I and V of the caudal part of the retrosplenial granular and agranular areas. In contrast, the caudal part of the anteromedial nucleus projects to layer V of the frontal area 2, and layers I and V of the rostral part of the retrosplenial granular and agranular areas. The interanteromedial nucleus projects to layers I, III and V of the frontal area 2, layer V of the agranular insular area, and layers I, V and VI of area 29D. The anteroventral nucleus projects to layers I and IV of the retrosplenial granular area, whereas the anterodorsal nucleus projects to layers I, III and IV of the same area. Projections from the anteroventral and anterodorsal nuclei were, furthermore, organized such that their ventral parts project to the rostral part of the retrosplenial granular area, whereas their dorsal parts project to the more caudal part. The results suggest that the anterior thalamic nuclei project to more widespread areas and laminae of the cingulate cortex than was previously assumed. The projections are organized such that the anteromedial and interanteromedial nuclei project to layer I and the deep layers of the anterior cingulate and retrosplenial cortex, whereas the anteroventral and anterodorsal nuclei project to the superficial layers of the retrosplenial cortex. These thalamocortical projections may play important roles in behavioral learning such as discriminative avoidance behavior.

Connections of the retrosplenial dysgranular cortex in the rat

Although the retrosplenial dysgranular cortex (Rdg) is situated both physically and connectionally between the hippocampal formation and the neocortex, few studies have focused on the connections of Rdg. The present study employs retrograde and anterograde anatomical tracing methods to delineate the connections of Rdg. Each projection to Rdg terminates in distinct layers of the cortex. The thalamic projections to Rdg originate in the anterior (primarily the anteromedial), lateral (primarily the laterodorsal), and reuniens nuclei. Those from the anteromedial nucleus terminate predominantely in layers I and IV-VI, whereas the axons arising from the laterodorsal nucleus have a dense terminal plexus in layers I and III-IV. The cortical projections to Rdg originate primarily in the infraradiata, retrosplenial, postsubicular, and areas 17 and 18b cortices. The projections arising from visual areas 18b and 17 predominantly terminate in layer I of Rdg, axons from contralateral Rdg form a dense terminal plexus in layers I-IV, with a smaller number of terminals in layers V and VI, afferents from postsubiculum terminate in layers I and III-V, and the projection from infraradiata cortex terminates in layers I and V-VI. The efferent projections from Rdg are widespread. The major cortical projections from Rdg are to infraradiata, retrosplenial granular, area 18b, and postsubicular cortices. Subcortical projections from Rdg terminate primarily in the ipsilateral caudate and lateral thalamic nuclei and bilaterally in the anterior thalamic nuclei. The efferent projections from Rdg are topographically organized. Rostral Rdg projects to the dorsal infraradiata cortex and the rostral postsubiculum, while caudal Rdg axons terminate predominantely in the ventral infraradiata and the caudal postsubicular cortices. Caudal but not rostral Rdg projects to areas 17 and 18b of the cortex. The Rdg projections to the lateral and anterior nuclei also are organized along the rostral-caudal axis. Together, these data suggest that Rdg integrates thalamic, hippocampal, and neocortical information.

Connections between the retrosplenial cortex and the hippocampal formation in the rat: a review

The retrosplenial cortex is situated at the crossroads between the hippocampal formation and many areas of the neocortex, but few studies have examined the connections between the hippocampal formation and the retrosplenial cortex in detail. Each subdivision of the retrosplenial cortex projects to a discrete terminal field in the hippocampal formation. The retrosplenial dysgranular cortex (Rdg) projects to the postsubiculum, caudal parts of parasubiculum, caudal and lateral parts of the entorhinal cortex, and the perirhinal cortex. The retrosplenial granular b cortex (Rgb) projects only to the postsubiculum, but the retrosplenial granular a cortex (Rga) projects to the postsubiculu, rostral presubiculum, parasubiculum, and caudal medial entorhinal cortex. Reciprocating projections from the hippocampal formation to Rdg originate in septal parts of CA1, postsubiculum, and caudal parts of the entorhinal cortex, but these are only sparse projections. In contrast, Rgb and Rga receive dense projections from the hippocampal formation. The hippocampal projection to Rgb originates in area CA1, dorsal (septal) subiculum, and post-subiculum. Conversely, Rga is innervated by ventral (temporal) subiculum and postsubiculum. Further, the connections between the retrosplenial cortex and the hippocampal formation are topographically organized. Rostral retrosplenial cortex is connected primarily to the septal (rostrodorsal) hippocampal formation, while caudal parts of the retrosplenial cortex are connected with temporal (caudoventral) areas of the hippocampal formation. Together, the elaborate connections between the retrosplenial cortex and the hippocampal formation suggest that this projection provides an important pathway by which the hippocampus affects learning, memory, and emotional behavior.

Time-dependent sequential increases in [14C]2-deoxyglucose uptake in subcortical and cortical structures during memory consolidation of an operant training in mice

Previous results have suggested that memory processing may involve the sequential activation of subcortical and cortical structures. To study this phenomenon, we have examined the immediate (15 min) and delayed (220 min) metabolic changes produced in BALB/c mice by a partial training session in a bar-pressing appetitive task, using the [14C]-2-deoxyglucose (2-DG) relative glucose uptake method. These relative metabolic changes were compared to the ones produced in several control groups: untrained animals, sham-conditioned animals, overtrained animals, and animals forced to walk on a moving belt (immediate and delayed condition). Animals were given a single intrajugular injection (5 microCi) of 2-DG either 5 min before or 3 h (delayed condition) after the second training session. Forty minutes after the 2-DG injection, the animals were sacrificed and their brains processed for autoradiography. At the 15-min delay, a large 2-DG labeling increase was found in partially trained animals for various subcortical areas (septum, diagonal band, hippocampus, thalamus, and mammillary bodies) while a much smaller increase was found in four cortical areas (frontal, cingulate, parietal, and sensory motor cortices). At the 220-min delay, we observed a large 2-DG labeling increase in cortical (frontal, pyriform, and cingulate cortices) and subicular areas while a moderate 2-DG labeling increase was observed in entorhinal cortex and the diagonal band. These results show that, shortly after training, subcortical structures are preferentially activated while cortical structures are much less activated. Three hours later, at a time when retention performances have been shown to improve spontaneously in the same strain of mice and in the same task, cortical structures are highly activated.

Connections of the retrosplenial granular a cortex in the rat

Although the retrosplenial granular a cortex (Rga) is situated in a critical position between the hippocampal formation and the neocortex, few studies have examined its connections. The present experiments use both retrograde and anterograde tracing techniques to characterize the afferent and efferent connections of Rga. Cortical projections to Rga originate in the ipsilateral area infraradiata, the retrosplenial agranular and granular b cortices, the ventral subiculum, and the contralateral Rga. Subcortical projections originate in the claustrum, the diagonal band of Broca, the thalamus, the midbrain raphe nuclei, and the locus coeruleus. The thalamic projections to Rga originate mainly in the anterodorsal (AD) and laterodorsal (LD) nuclei with sparse projections arising in the anteroventral (AV) and reuniens nuclei. Each projection to Rga terminates in distinct layers of the cortex. The thalamic projection from AD terminates primarily in layers I, III, and IV of Rga, whereas the axons arising from the LD nucleus have a dense terminal plexus only in layer 1. The projections arising from the subiculum end predominantly in layer II, whereas the postsubiculum projects to layers I and III-V. Axons from the contralateral Rga form a dense terminal plexus in layers IV and V, with a smaller number of terminals in layers I and VI. Rga projects ipsilaterally to the AV and LD nuclei of the thalamus and to the anterior cingulate, retrosplenial agranular,a and postsubicular cortices. Contralaterally it projects to the retrosplenial agranular and Rga cortices. Rga projections to the thalamus terminate ipsilaterally in the dorsal part of LD and bilaterally in AV. Together, these data suggest that Rga integrates thalamic with limbic information.

Laminar distribution of neuron degeneration in posterior cingulate cortex in Alzheimer's disease

The laminar distribution of neuron losses in posterior cingulate cortex were evaluated in 25 clinically and neuropathologically diagnosed cases of dementia of the Alzheimer type (DAT). The layer of maximal neuron loss in area 23a for each DAT case was determined by comparison with mean neuron densities for each layer of 17 neurologically intact control cases. The DAT cases were separated into five classes: class 1, 12% of all DAT cases, no or less than 40% neuron loss in any layer; class 2, 24%, maximal neuron losses in layers II or III; class 3, 28%, losses mainly in layer IV; class 4, 12%, losses mainly in layers V or VI; class 5, 24%, severe losses in all layers. An analysis of large and small neurons showed that in class 2 there was an equal loss of both in layer IIIa--b, in class 3 mostly small neurons were lost in layer IV, in class 4 mostly large neurons were lost in layers III, IV and V, while in class 5 there was no selectivity. The age of disease onset and length of the disease were the same for all classes, although classes 4 and 5 tended to have an earlier onset. No measures of thioflavin S-stained neuritic plaque (NP) or neurofibrillary tangle (NFT) density discriminated among these classes. In 64% of all DAT cases there was a progressive shift in NFT from ventral area 30 where most were in layer II to areas 23a--b where there was a balance between those in superficial and deep layers to dorsal area 23c where most were in layers V and VI.(ABSTRACT TRUNCATED AT 250 WORDS)