Calretinin-, neurocalcin-, and parvalbumin-immunoreactive elements in the olfactory bulb of the hedgehog (Erinaceus europaeus)

The distribution pattern and morphology of calretinin-, neurocalcin-, and p arvalbumin-immunoreactive neurons were studied in the main and accessory ol factory bulbs of the hedgehog. The detection of these markers was carried o ut by using monoclonal or polyclonal antibodies and the avidin-biotin-immun operoxidase method. Specific neuronal populations mere positive for these c alcium-binding proteins in the hedgehog olfactory bulb, revealing both simi larities to and differences from the data reported in the olfactory bulb of rodent species. The distribution pattern of each calcium-binding protein s tudied in the accessory olfactory bulb was highly similar to that described in other macrosmatic species. However, in the main olfactory bulb, the mar kers analyzed were expressed in similar interneuronal populations as they a re in the rodent olfactory bulb, whereas cell groups categorized as project ing neurons demonstrated striking differences in the expression of these ca lcium-binding proteins. These results suggest that the expression of calciu m-binding proteins in a given brain region is not a constant feature among species despite a similar organization but that different factors could inf luence their expression. Thus, the accessory olfactory system involved in t he processing of specific and similar olfactory cues among species demonstr ates a more constant organization among species. By contrast, the functiona lly important role of the main olfactory system in the hedgehog is accompan ied by a more complex organization, which is reflected in an increased dive rsity of calcium-buffering systems. J. Comp. Neurol. 429:554-570, 2001. (C) 2001 Wiley-Liss, Inc.