Neostriatal Regions Research Articles

Prefrontal system in the rat visualized by means of labeled deoxyglucose--further evidence for functional heterogeneity of the neostriatum.

An epileptic focus was formed in the anteromedial part of the prefrontal cortex in rats by means of intracortical injection of penicillin, and radioactively labeled deoxyglucose was immediately injected intravenously. Auto-radiograms revealed that, in addition to the injected cortical area, a number of formations increased their consumption of deoxyglucose. The labeled formations were the posterior medial and perirhinal cortical areas, the anteromedial part of the neostriatum, the anterior and intermediodorsal part of globus pallidus, the entopeduncular nucleus, the reticular portion of the substantia nigra, the claustrum, and the basolateral nucleus of amygdala. In addition, several thalamic nuclei were activated, including the entire parataenial, paraventricular, anteromedial, and axial nuclei, as well as distinct parts of the mediodorsal and lateral nuclei and, in the instances of spread of cortical activity to the dorsal surface, of the ventral nucleus. In some animals, activation of the ventral tegmental area of Tsai was also found. All these formations have previously been shown by neuro anatomical techniques to be directly connected with the anteromedial cortex of the neostriatum. Some of them were included in the "prefrontal system." The present findings, in agreement with earlier neurobehavioral studies, indicate that, in the rat, the anteromedial part of the neostriatum, but not other neostriatal regions, is functionally related to the anteromedial part of the prefrontal cortex. The present and earlier similar studies suggest that the mammalian forebrain contains a number of "systems," each of which consists of a neocortical area and a set of associated subcortical sites.

Behavioral and anatomical consequences of small intrastriatal injections of kainic acid in the rat

The effects of bilateral injections of kainic acid into the anteromedial neostriatal region were examined behaviorally and anatomically in two groups of rats. Behaviorally, kainic acid injections resulted in a severe impairment of delayed alternation retention, while the ability for visual discrimination remained unaffected. Anatomically it was found that axons traversing the injected area remain able to transport horseradish peroxidase. Furthermore, histological examinations of the injected regions revealed a heavy loss of neurons and a decrease of histochemical staining for specific acetylcholinesterase. Silver impregnation showed slightly disorganized, but continuous, axons in bundles of the capsula interna. On the other hand, the axonal network throughout the neuropil of the injected area was markedly diminished. No conspicuous change was found in myelin staining or in the intensity or catecholamine fluorescence. The anatomical results suggest that kainic acid appears to affect only perikarya of the neostriatum and the axons originating from these perikarya, whereas passing axons seem to remain intact. Thus, the observed behavioral impairment must be attributed to changes in the neostriatum itself. It is concluded that the neostriatum has ‘complex’ or ‘cognitive’ functions and that some mental symptoms in Huntington's chorea may be attributed to a dysfunction of this part of the brain.