Hypertonic saline and immobilization induce Fos expression in mouse brain catecholaminergic cell groups:...

The aim of the present study was to reveal stress-type dependent differences in hindbrain catecholaminergic (CA) cells and parabrachial nuclei (PBN) in the wild-type mouse. Neuronal activities were evaluated based on the incidence of Fos-labeling analyzed 60 min after injection of hypertonic saline (HS; 400 microL, 1.5 M, i.p.) or 120 min of immobilization (IMO) stress. The phenotypic nature of neurons was identified by costaining of Fos with either tyrosine hydroxylase (TH) or the neuropeptide Y (NPY) antibody. Generally, HS elicited broader Fos-staining than IMO. In comparison with IMO, HS induced more extensive Fos activation in the nucleus tractus solitarii-area postrema complex, and in TH- and NPY-positive cells in the A1 and C1 areas. Locus coeruleus (LC) cells displayed similar Fos activation after HS and IMO, and both stimuli also evoked evident TH-Fos colocalizations. Both stimuli also induced TH-Fos costainings in the A5 area. In contrast, IMO failed to activate PBN cells. The data indicate that the activity of TH and NPY hindbrain neurons responds differently to HS and IMO stress, supporting the notion that different stressors have different effects on the activity of autonomic centers.