Dendritic right/left asymmetries in the neurons of the human hippocampal formation: a quantitative Golgi study

OBJECTIVE: To search for right/left asymmetries in the dendritic trees of the neuronal populations and in the cell-free layer volumes of the human hipoccampal formation. METHOD: In necropsic material obtained from six male individuals we performed a quantitative Golgi study of the dendritic trees of dentate granules, CA3 and CA1 pyramidal neurons and a volumetric analysis of dentate gyrus molecular layer, strata oriens plus alveus and strata lacunosum-moleculare plus radiatum of CA3 and CA1 fields. RESULTS: We found inter-hemispheric asymmetries in the dendrites trees of all neurons, reaching the significant level in the number of granule cells dendritic segments (higher in the left than in the right hemisphere), dendritic branching density of CA3 pyramidal cells and mean dendritic length of CA1 apical terminal segments (higher in the right than in the opposite side). No volumetric differences were observed. CONCLUSION: This study points to different anatomical patterns of connectivity in the hippocampal formations of both hemispheres which may underlie functional asymmetries.

OBJETIVO: Pesquisar a existência de assimetrias direita/esquerda nas arborizações dendríticas neuronais e nos volumes das camadas não celulares da formação do hipocampo humano. MÉTODO: Efectuamos estudo quantitativo Golgi das arborizações dendríticas dos grânulos da fascia denteada e das células piramidais de CA3 e CA1, e uma análise estereológica dos volumes da camada molecular da fascia denteada, do strata oriens + alveus e do strata lacunosum-moleculare + radiatum de CA3 e de CA1 em material necrópsico colhido em 6 indivíduos do sexo masculino. RESULTADOS: Encontrámos assimetrias inter-hemisféricas nas arborizações dendríticas de todos os neurónios, significativas no número de segmentos dendríticos das células granulares (maior à esquerda do que à direita) na densidade de ramificação dendrítica das pirâmides de CA3 e no comprimento dendrítico médio dos segmentos apicais terminais das pirâmides de CA1 (maiores à direita do que à esquerda). Não encontramos diferenças volumétricas. CONCLUSÃO: Estes resultados alertam para diferentes padrões anatómicos de conectividade nas formações do hipocampo de ambos os hemisférios que podem fundamentar assimetrias funcionais.

Dendritic right/left asymmetries in the neurons of the human hippocampal formation: a quantitative Golgi study.

OBJECTIVE: To search for right/left asymmetries in the dendritic trees of the neuronal populations and in the cell-free layer volumes of the human hipoccampal formation. METHOD: In necropsic material obtained from six male individuals we performed a quantitative Golgi study of the dendritic trees of dentate granules, CA3 and CA1 pyramidal neurons and a volumetric analysis of dentate gyrus molecular layer, strata oriens plus alveus and strata lacunosum-moleculare plus radiatum of CA3 and CA1 fields. RESULTS: We found inter-hemispheric asymmetries in the dendrites trees of all neurons, reaching the significant level in the number of granule cells dendritic segments (higher in the left than in the right hemisphere), dendritic branching density of CA3 pyramidal cells and mean dendritic length of CA1 apical terminal segments (higher in the right than in the opposite side). No volumetric differences were observed. CONCLUSION: This study points to different anatomical patterns of connectivity in the hippocampal formations of both hemispheres which may underlie functional asymmetries.

Prolonged alcohol intake leads to irreversible loss of vasopressin and oxytocin neurons in the paraventricular nucleus of the hypothalamus.

Previous data revealed that numerous neurons in the supraoptic nucleus degenerate after prolonged ethanol exposure, and that the surviving neurons increase their activity in order to prevent dramatic changes in water metabolism. Conversely, excess alcohol does not induce cell death in the suprachiasmatic nucleus, but leads to depression of neuropeptide synthesis that is further aggravated by withdrawal. The aim of the present study is to characterize the effects of prolonged ethanol exposure on the magnocellular neurons of the paraventricular nucleus (PVN) in order to establish whether or not magnocellular neurons display a common pattern of reaction to excess alcohol, irrespective of the hypothalamic cell group they belong. Using conventional histological techniques, immunohistochemistry and in situ hybridization, the structural organization and the synthesis and expression of vasopressin (VP) and oxytocin (OXT) in the magnocellular component of the PVN were studied under normal conditions and following chronic ethanol treatment (6 or 10 months) and withdrawal (4 months after 6 months of alcohol intake). After ethanol treatment, there was a marked decrease in the number of VP- and OXT-immunoreactive magnocellular neurons that was attributable to cell death. The surviving neurons were hypertrophied and the VP and OXT mRNA levels in the PVN unchanged. Withdrawal did not alter the number of VP- and OXT-producing neurons or the gene expression of these peptides. These results substantiate the view that after prolonged ethanol exposure numerous neurons of the hypothalamic magnocellular system degenerate, but the mRNA levels of VP and OXT are not decreased due to compensatory changes undergone by the surviving neurons.