Accumulating evidence confirms that the exposure of neonatal rats to maternal separation (MS) can significantly alter individual processes of postnatal neurogenesis in the olfactory neurogenic region -the subventricular zone (SVZ) and the rostral migratory stream (RMS). To establish the stressful influence of MS on postnatal neurogenesis we have investigated whether altered olfactory environment caused by short-term MS induces expression of Fos protein in the SVZ/RMS and in the olfactory

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... l area -anterior olfactory nucleus (AON) of neonatal rats. Pups were separated from mothers for 2 hours at the postnatal days 7, 14 and 21. Immunohistochemically labeled Fos protein was assessed. Our results revealed that single exposure to MS is a stressful event that selectively and in age-dependent manner stimulates cellular activity in the SVZ and AON. A few Fos + cells were found in the SVZ of P21 control animals and MS significantly increased their number. This suggests that some SVZ cells are included in the circuitry, which is activated by MS and that these cells have complete equipment for the Fos signal transduction. MS significantly increased the number of Fos + cells in the AON in all age stages examined suggesting that its effect is mediated by olfaction.