New learning and memory related pathways among the hippocampus, the amygdala and the ventromedial region of the striatum in rats.

BACKGROUND: The hippocampus, central amygdaloid nucleus and the ventromedial region (marginal division) of the striatum have been reported to be involved in the mechanism of learning and memory. This study aimed elucidating anatomical and functional connections among these brain areas during learning and memory. RESULTS: In the first part of this study, the c-Fos protein was used to explore functional connections among these structures. Chemical stimulation of either hippocampus or central amygdaloid nucleus results in dense expression of c-Fos protein in nuclei of neurons in the marginal division of the striatum, indicating that the hippocampus and the central amygdaloid nucleus might be functionally connected with the marginal division. In the second part of the study, the cholera toxin subunit B-horseradish peroxidase was injected into the central amygdaloid nucleus to observe anatomical connections among them. The retrogradely transported conjugated horseradish peroxidase was observed in neurons of both the marginal division and dorsal part of the hippocampus following the injection. Hence, neural fibers from both the marginal division and the hippocampus directly projected to the central amygdaloid nucleus. CONCLUSION: The results implicated potential new functional and structural pathways through these brain areas during the process of learning and memory. The pathways ran from ventromedial portion (the marginal division) of the striatum to the central amygdaloid nucleus and then to the hippocampus before going back to the marginal division of the striatum. Two smaller circuits were between the marginal division and the central amygdaloid nucleus, and between the central amygdaloid nucleus and the hippocampus. These connections have added new dimensions of neural networks of learning and memory, and might be involved in the pathogenesis of dementia and Alzheimer disease.

[Functional connection between the marginal division and hippocampus in rats].

OBJECTIVE: To investigate the functional connection between the marginal division of the striatum and hippocampus, a brain region that play a vital role in learning and memory. METHODS: Morphological localization of functional activity of the nervous system was employed. Kainic acid (0.01%) was stereotaxically injected into the hippocampus as a chemical stimulus, and immunohistochemistry method was used to show the expression of c-Fos in rat brain. RESULTS: c-Fos was intensely expressed in the hippocampus, amygdaloid nucleus, the bed nucleus of the stria terminals and cerebral cortex; in the striatum, a stretch in the marginal division where c-Fos-positive nuclei congregated was observed, while c-Fos expression was scarcely detectable in the caudate putamen and globus pallidus. CONCLUSION: Functional connection exists between the marginal division and hippocampus in rats.