FOS and Hypoglycemia: Using c-Fos immunocytochemistry combined with in situ hybridizations of HDC mRNA, researchers find that different subregions of histaminergic neurons act differently when facing different stress situations: restraint, insulin-induced hypoglycaemia and foot shock can cause specific activation of histaminergic E4 and E5 subgroup; some neurons of the E1, E2, E3 were activated after restraint stress and no c-Fos change in either hyperosmotic stimulus or injection of bacterial lipopolysaccharide [78].