Histological and ultrastructural changes in the rat brain following systemic administration of picolinic acid

Picolinic acid was administered intraperitoneally in a dose of 30, 60, or 100 mmol, once every 24 h for 8 days. Histologically, under normal conditions as well as when picolinic acid was administered in a dose of 30 mmol the brain formations exhibited characteristic features. When picolinic acid was administered in a dose of 60 mmol or 100 mmol, the alterations were profound and developed selectively in hippocampus, being much less intense in the substantia nigra and striatum. In such cases, injuries of neuronal cell bodies were accompanied by symptoms of spongiosis. Within the hippocampus, the neuronal cell body injury was selectively restricted to the hilar and CA3 regions of stratum pyramidale. Tissue spongiosis was more intense at the granular layer, particularly within the hilus and in the mossy fiber area at CA3. Histochemically, a variable intensity of the reaction of succinic and alpha-glycerophosphate dehydrogenases was demonstrated. A decrease in their activities was observed in areas where the neuronal cell body injuries and spongiosis took place. No changes in the Ca-ATP-ase activity in brain formation after picolinic acid treatment were observed. Ultrastructurally, the changes within substantia nigra were manifested by neuronal cell bodies of the dark type and dendritic degenerations. Also less damaged neuronal cell bodies were seen. They were swollen, depleted of polyribosomes with dilated elements of RER and altered mitochondria. Some of the dendritic profiles were swollen with lucent cytoplasm. Most of the boutons in synaptic contact zones were unchanged. Most presynaptic terminals which were in junction with dark dendrites were swollen with or without crystal-like aggregates of synaptic vesicles.