Neuro-immune interactions in the dove brain

Abstract

Mast cells (MC) are of hematopoetic origin. Connective tissue type MCs are able to function in IgE dependent and independent fashion, change their phenotype according to the tissue environment. They are able to enter the brain under normal physiological conditions, and move into this compact tissue made of neurons. In doves MCs are found only in the medial habenula (MH) and their number is changing according to the amount of sex steroids in the body. MCs are able to synthesize and store a great variety of biologically active compounds, like transmitters, neuromodulators and hormones. They are able to secrete GnRH. With the aid of electron microscopy we were able to describe MC-neuron interactions between GnRH-positive MCs and neurons. Piecemeal degranulation (secretory vesicles budding off swollen and active granules) seems to be a very efficient type of communication between MCs and surrounding neurons. Different types of granular and vesicular transports are seen between GnRH-immunoreactive MCs and neurons in the MH of doves. Sometimes whole granules are visible in the neuronal cytoplasm, in other cases exocytotic vesicles empty materials of MC origin. Thus MCs might modulate neuronal functions. Double staining experiments with IP3-receptor (IP3R), Ryanodine-receptor (RyR) and serotonin antibodies showed active MC population in the habenula. Light IP3R-labeling was present in 64-97% of the cells, few granules were labeled in 7-10% of MCs, while strong immunoreactivity was visible in 1-2% of TB stained cells. No immunoreactivity was visible in 28-73% of MCs. According to cell counts, light RyR-positivity appeared in 27-52%, few granules were immunoreactive in 4-19%, while strong immunopositivity was found only in one animal. In this case 22% of MCs were strongly RyR-positive. No staining was registered in 44-73% of MCs. Double staining with 5HT and these receptor markers proved that indeed only a part of MCs is actively secreting. Resting cells with only 5HT-immunopositivity are often visible. The activational state of MCs is changing at higher estrogen/testosterone level, thus with the secretion of neuromodulators they might alter sexual and parental behavior of the animals.