The distribution of evoked expression of the proto-oncogene c-Fos was immunohistochemically examined in the parabrachial nucleus (PBN) of the rat after free ingestion of NaCl and some other taste solutions. C-Fos-like immunoreactive neurones (c-Fos neurones) were densely observed in the external lateral subnucleus (els), central lateral subnucleus (els), and the central part of the medial subnucleus (ms). The finding that the number of c-Fos neurones decreased dramatically in the ms after treatment of the tongue with amiloride or after dissection of the chorda tympani suggests that taste information of NaCl projects mainly to the ms. The functional significance of the els and els is discussed, and it is suggested that the els is a recipient zone for general visceral inputs and the els is concerned with palatability of the liquids ingested. The present study has proved that c-Fos immunoreactivity is a useful anatomical marker for activated neurones in the PBN during ingestive behaviour.
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