Figure 3. Serotonergic nerve endings (schematic drawing, upper left) in the hippocampal formation release the neurotransmitter serotonin (gray balls), which binds to its receptors, the serotonin-1 A (5-HT1A) receptors (orange). The three pseudo-color pictures demonstrate receptor binding in normal male tree shrews (left), in tree shrews that were submitted to chronic psychosocial stress (middle), and in stressed tree shrews that had received testosterone as a treatment (right). Colors indicate numbers of receptors in the different regions of the hippocampal formation: orange, high receptor numbers; yellow, moderate numbers; green, low numbers; purple, no receptors. Note that after chronic social stress receptor numbers are decreased, but that the normal receptor number is restored following testosterone treatment.
