Ivan Divac

Magnocellular nuclei of the basal forebrain project to neocortex, brain stem, and olfactory bulb. Review of some functional correlates

Horseradish peroxidase was injected into the neocortex of squirrel monkeys, rats, tree shrews and one opossum, in the brain stem of one squirrel monkey and rats, and in the olfactory bulb, the corpus vitreum or the vascular system of rats. Following the cortical, brain stem and bulbar injections labeled cells were found (predominatly ipsilaterally) in the magnocellular nuclei of the basal forebrain: nucleus of the diagonal band, the magnocellular preoptic nucleus and nucleus basalis. These nuclei may, therefore, be classified together hodologically as well as cytologically and histochemically. The number of labeled cells was proportional to the size of the injected region. It is uncertain whether the same cells project to all target regions. Large labeled cells were found scattered among pallidal and entopeduncular neurons in rats with cortical or brain stem injections. These neurons may be the equivalent to the nucleus basalis in other species.

Subcortical projections to the prefrontal cortex in the rat as revealed by the horseradish peroxidase technique

Abstract The sources and distribution of subcortical afferents to the anterior neocortex were investigated in the rat using the horseradish peroxidase technique. Injections into the prefrontal cortex labelled, in addition to the mediodorsal thalamic nucleus, neurons in a total of fifteen subcortical nuclei, distributed in the basal telencephalon, claustrum, amygdala, thalamus, subthalamus, hypothalamus, mesencephalon and pons. Of these, the projections from the zona incerta, the lateroposterior thalamic nucleus, and the parabrachial region of the caudal mesencephalon to the prefrontal cortex have not previously been described. Different parts of the mediodorsal thalamic nucleus project to different areas of the frontal cortex. Thus, horseradish peroxidase injections in the most ventral pregenual part of the medial cortex labelled predominantly neurons in the medial anterior and dorsomedial posterior parts of the mediodorsal nucleus; injections into the more dorsal pregenual area labelled only neurons in the lateral and ventral parts of the nucleus; injections placed supragenually labelled neurons in the dorsolateral posterior part of the nucleus; and injections into the dorsal bank of the anterior rhinal sulcus labelled neurons in the centromedial part of the nucleus. Several other subcortical nuclei had projections overlapping with that of the mediodorsal thalamic nucleus. Five different types of such overlap were distinguished: (1) cell groups labelled after horseradish peroxidase injections into one of the subfields of the projection area of the mediodorsal nucleus (defined as the prefrontal cortex), but not outside this area (parataenial nucleus of the thalamus); (2) cell groups labelled both after injection into a subfield of the projection area of the mediodorsal nucleus and after injections in a restricted area outside this area (anteromedial, ventral and laterposterior thalamic nuclei); (3) cell groups labelled after injections into all subfields of the mediodorsal nucleus projection area, but not outside this area (ventral tegmental area, basolateral nucleus of amygdala); (4) cell groups labelled after injections into any area of the anterior neocortex, including the mediodorsal nucleus projection area (parabrachial neurons of the posterior mesencephalon); (5) cell groups labelled after all neocortical injections investigated (claustrum, magnocellular nuclei of the basal forebrain, lateral hypothalamus, zona incerta, intralaminar thalamic nuclei, nuclei raphe dorsalis and centralis superior, and locus coeruleus). We can draw the following conclusions from these and related findings. First, because of the apparent overlap of projections of the mediodorsal, the anteromedial and ventral thalamic nuclei in the rat, parts of the prefrontal cortex can also be called ‘cingulate’ and ‘premotor’. Second, on the basis of projections from parts of the mediodorsal nucleus, the prefrontal cortex of the rat can be subdivided into areas corresponding to those in other species. Third, the neocortex receives afferents from a large number of subcortical cell groups outside the thalamus, distributed from the telencephalon to the pons; however, the prefrontal cortex seems to be the only neocortical area innervated by the ventral tegmental area and amygdala. Finally, neither the prefrontal cortex nor the mediodorsal thalamic nucleus receives afferents from regions directly involved in sensory and motor functions.

Selective ablations within the prefrontal cortex of the rat and performance of delayed alternation

Ablations of the pregenual area of the anteromedial prefrontal cortex produced a significantly larger impairment in delayed alternation than did removal of the supragenual area. Both ablations caused significant impairments as compared with lesions of the posteromedial cortex. Only one of four rats with ablations of the dorsal bank and lip of the anterior part of the rhinal sulcus was impaired. The results indicate than in the rat, as in the monkey and dog, one part of the prefrontal cortex is particularly involved in mediation of delayed alternation.

The Prefrontal 'Cortex' in the Pigeon

In3 pigeons ablation of the posterodorsolateral neostriatum impaired delayed alternation without affecting visual discrimination. In mammals the same selective deficit is produced by lesions in the prefrontal system. The presently ablated neostriatal region resembles the mammalian prefrontal cortex also by being richly innervated with dopaminergic fibers. This region is clearly separated from paleostriatum augmentatum and archistriatum which also have a strong dopaminergic innervation. The presence of a prefrontal cortex-like formation in a bird species raises the possibility that all higher vertebrates are equipped with this neural device.

“Cognitive” Functions of the Neostriatum

Publisher Summary This chapter highlights the cognitive functions of the neostriatum (NS). The NS seems to take part in mediating a phylogenetically widespread, supramodal function, which is largely independent of response topography and which is operative under a rather well-defined range of circumstances. The chapter reviews tsources of the information to be processed by the NS, the nature of local NS processing, and psychological analysis of this innominate function. Studies in several species have shown that only a limited portion of NS is of critical importance for delayed response-type tasks. The focal NS region is the recipient of information from that subdivision of the prefrontal cortex, which is the neocortical center for the same class of behavior and probably also from the mediodorsal thalamic nucleus. The electrophysiological and neurochemical basis for NS involvement in delayed response tasks is insufficiently investigated, and the available evidence does not particularly illuminate the fate, within the NS, of the information arriving from the frontal lobes.

Spontaneous alternation in rats with lesions in the frontal lobes: An extension of the frontal lobe syndrome

Bilateral lesions in the anteromedial neocortex or the associated part of the neostriatum abolished spontaneous alternation in rats; removal of the suprarhinal strip did not. The classical deficit of spatial choice following frontal-lobe injury is not an artifact of the learning paradigm, but can be extended to unconditioned behavior. Furthermore, the impairment is not restricted to food-reinforced or massed responses. The response-guiding role of the frontal lobe is of such wide generality in the laboratory that it can be expected to operate in the animal’s usual environment as well.

The prefrontal “cortex” in the pigeon catecholamine histofluorescence

The prefrontal cortex of mammals is densely innervated with dopaminergic fibers. We report a comparable, dense network of catecholamine (probably dopamine)-containing fluorescent fibers in the posterodorsolateral neostriatum of the pigeon. This region is clearly separable from paleostriatum augmentatum, lobus parolfactorius, posterior archistriatum, posteromedial corticoid and septum, all of which also show strong catecholamine fluorescence. Parallel biochemical, anatomical and neurobehavioral data support the suggestion that posterodorsolateral neostriatum in the pigeon may be comparable to the mammalian prefrontal cortex. Thus the telencephalic tissue represented as the prefrontal cortex in mammals and the posterodorsolateral neostriatum in the pigeon, may turn out to be a phylogenetically ancient neural device.

The prefrontal ‘cortex’ in the pigeon. Biochemical evidence☆

Concentrations of dopamine and noradrenaline were determined in 6 regions of the telencephalon and in the cerebellum of the pigeon. Noradrenaline was rather evenly distributed. A significant variation was found of the dopamine-noradrenaline ratio (DA:NA), a measure which makes it possible to distinguish dopamine found in dopaminergic fibers from dopamine which is precursor of noradrenaline. The highest ratio was found in the anteroventromedial region (containing the presumed homologue of the mammalian neostriatum), and the next highest in the posteroventrolateral region (containing the archistriatum). Like in mammals, the lowest concentration of the non-precursor dopamine in the pigeon brain seems to be contained in the cerebellum. Among the regions which show physiological and anatomical similarities with the mammalian cerebral cortex, the DA:NA ratio was significantly higher in the posterodorsolateral, than in the posterodorsomedial and anterodorsomedial regions. The two dorsomedial regions contain the equivalents of the hippocampus and sensory cortical areas of mammals. The strong dopamine innervation of the posterodorsolateral region is comparable to that of the mammalian prefrontal cortex.

The prefrontral cortex of the cat: Anatomical subdivisions based on retrograde labeling of cells in the mediodorsal thalamic nucleus

SummaryDifferent areas of the frontal cortex of the cat were injected with small amounts of horseradish peroxidase. The regions of labeled cells in the mediodorsal nucleus of the thalamus (MD) were related to the injected areas. Distinct relations between subdivisions of MD and of the prefrontal cortex were established: a rather large central sector of MD projects to the gyrus proreus and to the anterior parts of the gyri sigmoideus, rectus, and frontalis. A narrow lateral band of anterior MD neurons projects predominantly to an area on both sides of the sulcus praesylvius, whereas a postero-lateral band sends fibers to a region on the ventral anterior sylvian gyrus. The area between the presylvian sulcus and the sylvian gyrus is apparently free of MD afferents, but not of other thalamic afferents. A fourth sector of MD, situated dorsomedially, projects to the middle parts of the gyri rectus and frontalis. And a fifth sector, located ventrally to the dorsomedial MD sector, projects to the ventral part of the gyrus rectus. The established subfields of MD and of the prefrontal cortex are discussed with respect to previous anatomical research in the cat.

NOS neurones lie near branchings of cortical arteriolae

We show that numerous neurones labelled for NADPH-diaphorase, which synthetize nitric oxide, lie near branching points of the arteriolae which descend through the cerebral cortex from its pial surface. This spatial relationship suggests the possibility of neural control of cortical blood flow by the NADPH-diaphorase neurones, possibly mediated by the rapid action of nitric oxide.