NEUROENDOCRINE DISTURBANCES   [ back to Brain Injury 101 ]
The brain is home to the pituitary (the "master gland" of the endocrine system), the hypothalamus, the pineal and other structures which regulate mood, sleep, sex drive, aggression, hunger, thirst, blood pressure, metabolic rate, energy level, body temperature, and other basic physiological states, through production of or modulation of production of  hormones. When the brain is badly shaken or physically bounced off the bony walls inside the skull, these structures and their hormonal outputs are negatively affected, and the net result is that the body loses some of its homeostasis, its capacity to keep its vital systems in balance. Traumatic injury to the brain is accompanied by immediate, measurable hormonal changes, which can include some or all of the following: decreased  thyroid output (associated with slowed metabolism and depression), increased cortisol production (the stress hormone associated with agitation, anxiety, depression and insomnia ) and decreased testosterone (especially after severe TBI), which is associated with diminished libido. Cortisol is increased after mild and moderate TBI but decreased after severe TBI. Excess cortisol has been linked to depression in patients with Cushing's Disease and Post-Traumatic Stress Disorder.  The AMA's Essential Guide to Depression states that about 50% of all people with depression show abnormally high levels of cortisol.  This makes sense, because neuropsychologists note a surprising absence of depression in patients with severe TBI, yet cortisol is reduced below normal levels in those patients.

Low supplies of the neurotransmitter serotonin are associated with depression, anxiety, impulsive/aggressive conduct and suicide. Serotonin is produced primarily (but not exclusively) in clusters of nerve cells called the raphe nuclei distributed in structures at the back and base of the brain, i.e. the pons, midbrain and medulla. The rostral raphe nuclei in the upper pons deliver serotonin to the frontal lobes and limbic structures of the medial temporal lobes which regulate mood. It is believed that traumatic brain injury from a blow to the head can cause depression by shear-strain damage to the axonal connections which deliver serotonin from the rostral raphe nuclei to those areas. In the normal brain excess serotonin is cleared from the frontal lobes and limbic areas and brought back to the raphe nuclei at the back of the brain by SERT (the serotonin transporter system). Anti-depressant medications like Prozac and Zoloft (the SSRIs or selective serotonin reuptake inhibitors) improve depressed mood by blocking SERT,  decreasing the reacquisition of serotonin and leaving more serotonin between synapses in the frontal and medial temporal lobes.