Graphs illustrating the effects of Days 1 and 2 swim stress on numbers of c-Fos-immunoreactive (ir) serotonergic neurons in subregions of the dorsal raphe nucleus (DR). Graphs display the effects of either home cage control (HC) conditions or a 15 minute swim stress exposure at 19 °C or 25 °C on Day 1 on cellular responses to subsequent exposure to either HC conditions or a 5 min swim stress exposure at 25 °C on Day 2. Graphs display the effects of treatment on the numbers of c-Fos-immunoreactive (ir)/tryptophan hydroxylase (Tph)-ir neurons following swim stress on Day 2 (HC or 25 °C 5 minute swim) within different subdivisions of the dorsal raphe nucleus (DR). Open bars represent mean values for numbers of Tph-ir neurons, closed bars represent mean values for numbers of c-Fos-ir/Tph-ir neurons. * p < 0.05 vs Day 2 home cage (HC) control conditions under the same Day 1 condition, ** p < 0.01 vs Day 2 home cage (HC) control conditions under the same Day 1 condition, *** p < 0.001 vs Day 2 home cage (HC) control conditions under the same Day 1 condition, a p < 0.05 vs HC/25; Fisher’s protected least significant difference (LSD) test. Abbreviations: DRD, dorsal raphe nucleus, dorsal part; DRVL/VLPAG, dorsal raphe nucleus, ventrolateral part/ventrolateral periaqueductal gray; DRI, dorsal raphe nucleus, interfascicular part.