The combined results obtained are compatible with the view that in a genetic model of depression using the FSL rat strain, alterations may develop in the agonist regulation of the density of FGFR1-5-HT1A heteroreceptor complexes located in the dorsal raphe and in the CA2-CA3 areas of the dorsal hippocampus. The gene discussed is FGFR1; the disease is major depressive disorder.