Hippocampus and dentate gyrus of the Cebus monkey: architectonic and stereological study.

Behavioral, electrophysiological, and anatomical assays of non-human primates have provided substantial evidence that the hippocampus and dentate gyrus are essential for memory consolidation. However, a single anatomical and stereological investigation of these regions has been done in New World primates to complement those assays. The aim of the present study was to describe the cyto-, myelo-, and histochemical architecture of the hippocampus and dentate gyrus, and to use the optical fractionator method to estimate the number of neurons in the hippocampal pyramidal and granular neurons in the dentate gyrus of the Cebus monkey. NeuN immunolabeling, lectin histochemical staining with Wisteria floribunda agglutinin (WFA), enzyme-histochemical detection of NADPH-diaphorase activity and Gallyas silver staining were used to define the layers and limits of the hippocampal fields and dentate gyrus. A comparative analysis of capuchin (Cebus apella) and Rhesus (Macaca mulatta) monkeys revealed similar structural organization of these regions but significant differences in the regional distribution of neurons. C. apella were found to have 1.3 times fewer pyramidal and 3.5 times fewer granular neurons than M. mulatta. Taken together the architectonic and stereological data of the present study suggest that hippocampal and dentate gyrus neural networks in the C. apella and M. mulatta may contribute to hippocampal-dentate gyrus-dependent tasks in different proportions.

Three dimensional morphometric analyses of axon terminals early changes induced by methylmercury intoxication in the adult cat striate cortex.

The aim of the present report is to investigate in detail morphometric changes of axon terminals of area 17 of adult cat induced by methylmercury intoxication. Six adult male cats (Felix catus), with 12 h day-light cycle and ad libitum water and food regimen, received a single dose of MeHgCl (6.4 mg/kg) dissolved in milk, whereas control subjects (n=6) received only milk. After 30 days, biocytin iontophoretic injections were done into the area 17, (Horsley-Clark coordinates between AP 3.0-6.0) on the crown of the lateral gyrus, near the border with area 18. MeHg and inorganic Hg (Hgi) concentrations were measured in the brain parenchyma of intoxicated cats and corresponded on average to 1.39+/-0.3 and 6.79+/-0.6 ppm (mean+/-s.e.m.) respectively. Twenty four hours after iontophoresis, aldehyde fixed brain sections (200 microm thick), were processed to reveal biocytin labeled terminals. Axonal microscopic 3D reconstructions using Neurolucida software (Microbright Systems Inc.) allowed estimations of boutons, branching points and segment densities for each terminal. Cluster analysis of morphometric axonal features from control and intoxicated group revealed, two distinct axon families (Type I and II) as described elsewhere. Total density values of boutons, branching points and segment densities of intoxicated group, decreased 81, 59 and 91% respectively, as compared to the control group (ANOVA two-way, Bonferroni a priori test p<0.05). Altered axonal morphology associated with MeHg, appeared early in the disease (30 days after contamination), revealing new aspects of the neuronal pathology of the methylmercury intoxication in the visual cortex.