Eur J Anat, 5 (3): 119-132 (2001)

Localization of excitatory amino acid and neuropeptide markers in neurons of the subicular complex projecting to the retrosplenial granular cortex of the rat

Gonzalo-Ruiz A., Bayona I.

Laboratory of Neuroanatomy, Inst. of Neurosci. of Castilla/Leon, University of Valladolid, C/ Nicolas Rabal, 17, 42003 Soria, Spain

ABSTRACT Retrograde labelling was combined with immunohistochemistry to localize neurons containing glutamate and different neuropeptides such as neurotensin, leu-enkephalin, and substance P-like immunoreactivity in the projection pathways from the presubiculum and subiculum to the retrosplenial granular cortex of the rat. Injections of horseradish peroxidase conjugated to subunit B of cholera toxin (CT-HRP) into the retrosplenial granular cortex labelled large numbers of neurons in the presubiculum. A significant number of retrogradely-labelled neurons was seen in the dorsal subiculum, whereas small numbers of CT-HRP-labelled neurons were also found in the ventral subiculum. In the presubiculum, 90-95% of the CT-HRP-labelled neurons (30-32 per section) were also immunoreactive for glutamate, and small numbers of retrogradely-labelled neurons also displayed neurotensin-, leu-enkephalin- or substance P-immunoreactivity. In the subiculum, approximately 90-95% of the CT-HRP-labelled neurons (19-20 per section) were also immunoreactive for glutamate, and a significant number of retrogradely-labelled neurons (70-75%, 14-15 per section) also displayed neurotensin immunoreactivity. In addition, small numbers of CT-HRP-labelled neurons in the subiculum were immunoreactive for leu-enkephalin or substance P. These results suggest that the complexity of the neurotransmitter(s)/neuromodulator(s) of the subicular projections to the retrosplenial granular cortex of the rat should be taken into account when considering the mechanisms of the retrosplenial cortical neurons thought to play a role in memory.

Keywords: 4 aminobutyric acid, cholera toxin B subunit, excitatory amino acid, glutamic acid, horseradish peroxidase, leucine enkephalin, neuropeptide, neurotensin, neurotransmitter, substance P, animal tissue, article, cingulate gyrus, controlled study, female, hippocampus, histochemistry, immunohistochemistry, limbic system, male, nerve cell, nonhuman, rat, subiculum