Myelin Sheath Development in the Maxillary Nerve of the Newborn Pig.

Myelination, the ensheathing of neuronal axons by myelin, is important for the proper function of both central and peripheral nervous systems. Various studies have investigated the quantitative parameters of myelination in certain species. Pigs are among the species of which their use as laboratory animals in neuroscience research increased the past few decades. However, there is limited data regarding the myelination process in the pig. Moreover, the maxillary nerve is crucial for Pseudorabies Virus (PrV) neuropathogenesis. In this context, a quantitative analysis of various myelination parameters of the maxillary nerve was performed, during the first 5 weeks of porcine post-natal development, the time period, which exhibits the highest interest for PrV neuropathogenesis. The evaluation was conducted in four groups of uninfected pigs, at the time of birth (group 0w), at the age of 1 week (group 1w), 3 weeks (group 3w) and 5 weeks (group 5w), using toluidine blue staining, immunofluorescence and electron microscopy. Axon and fibre diameter, perimeter and surface, myelin sheath thickness and g-ratio were measured on histological sections transverse to the longitudinal axis of the maxillary nerve. The thickness of myelin sheath was 0.76 µm for group 0w, 0.94 µm for group 1w, 0.98 µm for group 3w and 1.03 µm for group 5w. The g-ratio was 0.529, 0.540, 0.542 and 0.531 for the respective animal groups. The results of this study contribute to the understanding of the myelination process in the pig will be used for the study of PrV effects on the myelination development of newborn piglets' maxillary nerve and may shed new light to their vulnerability to the virus.

Vascular network of the rat hippocampus is not homogeneous along the septotemporal axis.

Qualitative and quantitative image analysis of hippocampal vascular bed, after transcardial perfusion of India ink, reveals significant differences among hippocampal subfields and along the septotemporal axis of the rat hippocampus. Ventral hippocampus exhibits significantly higher levels of vascularization compared to dorsal hippocampus, which, however, is characterized by significantly higher capillary density. These results may explain the selective ischemia vulnerability of hippocampus along its septotemporal axis.

Postnatal development of the dopaminergic system of the striatum in the rat.

The dopaminergic innervation of the developing caudate-putamen (patches and matrix) and nucleus accumbens (shell and core) of the rat was examined with light and electron microscope immunocytochemistry, using antibodies against dopamine. Light microscopic analysis showed, in accordance with previous studies, that early in life, dopaminergic fibers were relatively thick and present throughout the striatum. Their distribution was heterogeneous, showing dense aggregations, the so-called dopamine islands. The pattern of innervation became more uniform during the third postnatal week with most of the dopamine islands no longer detectable. For electron microscopic analysis, parts of the caudate-putamen containing dopamine islands or matrix, and of the nucleus accumbens, from the shell and the core of the nucleus, were selected. This analysis revealed that symmetrical synapses between immunoreactive profiles and unlabeled dendritic shafts predominated throughout development but, at the late stages, symmetrical axospinous synapses also became a prominent feature. These findings indicate that: (1) although the caudate-putamen and the nucleus accumbens have different connections and functions, they exhibit similar types of dopaminergic synapses, and (2) the relatively late detection of dopaminergic axospinous synapses suggests that the development of the dopaminergic system in the striatum is an active process, which parallels the morphological changes of striatal neurons and may contribute to their maturation.