Social isolation-induced effects on male-specific courtship behaviours and dendritic architecture in associative forebrain areas in Zebra finches (Taeniopygia guttata)

Zebra finches ( Taeniopygia guttata) are highly monogamous birds that maintain lifelong pair-bonds. Females make the mate choice based on the quality of males who initiate pair-bond formation by courting the female. A mate separation-reunion paradigm can help to evaluate the adaptive value of social affiliation of male finches and their affinity to new females in absence of mated females which can manifest at a neuronal level by dendritic measures. The aim of this study was to examine behavioural and neuronal changes as a result of social isolation following pair-bonding in male zebra finches. Towards this, male zebra finches from a pair-bonded group were isolated for a period of ten days and then exposed to either the mate or a new female. Four main courtship behaviours: clumping, allopreening, nest box occupancy and directed singing were recorded and analysed. Brains were processed by a modified Golgi technique to detect changes in dendritic arborizations using the Sholl analysis. Baseline behavioural results showed an increase in clumping and nest box activity by day 10. Isolated males re-introduced with their pair-bonded females demonstrated increased nest box activity. Alternatively, isolated males exposed to new females demonstrated increased directed singing when compared to their pair-bonded state, but lower than when exposed to same female. Neuro-morphological changes assessed through quantification of dendritic intersections and branch points were observed in pallial brain areas known to be implicated in the development of social/sexual preferences, with the pair-bonded group demonstrating more branching and longer dendrites when compared to the socially-isolated group. Thus social isolation impacts both courtship behaviour and neuronal morphologies with differential responses to the pair-bonded female versus a new female.

Unusual ultrastructural findings in dendrites of pyramidal neurons in the cerebral cortex of rabies-infected mice

Previous studies using the Golgi technique have demonstrated alterations in the dendritic morphology of pyramidal neurons of the cerebral cortex of mice inoculated with the rabies virus. However, knowledge about the fine structure of dendrites in rabies infection is scarce. This work had the aim of studying the ultrastructure of dendrites in cortical pyramidal neurons of rabies-infected mice. Mice were inoculated intramuscularly with a street rabies virus of canine origin. The animals that showed an advanced stage of disease were fixed by perfusion with glutaraldehyde and paraformaldehyde. Brains were removed and cut on a vibratome to obtain coronal slices of 200 micrometers of thickness. Vibratome slices were subjected to the following treatment: postfixation, dehydration, embedding in epoxy resin and polymerization between glass slides. Ultrathin sections of oriented tissue fragments from the cerebral cortex were obtained and observed under electron microscope. The most significant ultrastructural findings were located within distal dendrites of cortical pyramidal neurons: loss of mitochondria, disorganization and loss of microtubules, formation of vacuoles interrupting the continuity of the cytoplasm and formation of myelin-like figures. These strange myelin figures, which apparently had not been reported in previous studies of rabies, were the most noticeable ultrastructural feature. They also differ from the best known myelin figures formed by concentric lamellae. The possible origin of these myelin figures as result of mitochondrial degeneration is discussed.

Unusual ultrastructural findings in dendrites of pyramidal neurons in the cerebral cortex of rabies-infected mice

Previous studies using the Golgi technique have demonstrated alterations in the dendritic morphology of pyramidal neurons of the cerebral cortex of mice inoculated with the rabies virus. However, knowledge about the fine structure of dendrites in rabies infection is scarce. This work had the aim of studying the ultrastructure of dendrites in cortical pyramidal neurons of rabies-infected mice. Mice were inoculated intramuscularly with a street rabies virus of canine origin. The animals that showed an advanced stage of disease were fixed by perfusion with glutaraldehyde and paraformaldehyde. Brains were removed and cut on a vibratome to obtain coronal slices of 200 micrometers of thickness. Vibratome slices were subjected to the following treatment: postfixation, dehydration, embedding in epoxy resin and polymerization between glass slides. Ultrathin sections of oriented tissue fragments from the cerebral cortex were obtained and observed under electron microscope. The most significant ultrastructural findings were located within distal dendrites of cortical pyramidal neurons: loss of mitochondria, disorganization and loss of microtubules, formation of vacuoles interrupting the continuity of the cytoplasm and formation of myelin-like figures. These strange myelin figures, which apparently had not been reported in previous studies of rabies, were the most noticeable ultrastructural feature. They also differ from the best known myelin figures formed by concentric lamellae. The possible origin of these myelin figures as result of mitochondrial degeneration is discussed.

Antiserum to lucifer yellow: preparation, characterization, and use for immunocytochemical localization of dye-filled retinal neurons.

We present a new method for the preparation of antisera to Lucifer Yellow, and these antisera are here shown to be particularly suitable for immunocytochemical localization of multiple dye-injected cells in large pieces of vertebrate retina. The method involves the preparation of covalent conjugates of the VS isomer of Lucifer Yellow with keyhole limpet hemocyanin (KLH) or rabbit serum albumin (RSA), and their use as immunogens in rabbits. Both carrier protein conjugates yielded robust antibody responses. Antiserum to the KLH-LY conjugate contained precipitating antibodies against LY and KLH, although activity to the latter did not interfere with immunocytochemical staining. Rabbit antiserum to the RSA-LY conjugate contained precipitating antibody only against LY. When used for immunocytochemical staining of large retinal pieces containing many LY-filled cells, both antisera yielded well-stained, darkly filled cells similar to those seen with the Golgi technique; even very fine dendritic processes of retinal ganglion cells could be followed for long distances. LY immunocytochemistry provides a useful alternative to photooxidation for the analysis of multiple dye injected cells, especially in whole mounts. This approach may also be useful for immunocytochemical identification of cells filled with LY after tissue fixation.