Substantia nigra vulnerability after a single moderate diffuse brain injury in the rat

Role of the Dopaminergic System in the Striatum and Its Association With Functional Recovery or Rehabilitation After Brain Injury

Disabilities are estimated to occur in approximately 2% of survivors of traumatic brain injury (TBI) worldwide, and disability may persist even decades after brain injury. Facilitation or modulation of functional recovery is an important goal of rehabilitation in all patients who survive severe TBI. However, this recovery tends to vary among patients because it is affected by the biological and physical characteristics of the patients; the types, doses, and application regimens of the drugs used; and clinical indications. In clinical practice, diverse dopaminergic drugs with various dosing and application procedures are used for TBI. Previous studies have shown that dopamine (DA) neurotransmission is disrupted following moderate to severe TBI and have reported beneficial effects of drugs that affect the dopaminergic system. However, the mechanisms of action of dopaminergic drugs have not been completely clarified, partly because dopaminergic receptor activation can lead to restoration of the pathway of the corticobasal ganglia after injury in brain structures with high densities of these receptors. This review aims to provide an overview of the functionality of the dopaminergic system in the striatum and its roles in functional recovery or rehabilitation after TBI.

Amantadine preserves dopamine level and attenuates depression-like behavior induced by traumatic brain injury in rats

Traumatic brain injury (TBI) often results in multiple neuropsychiatric sequelae, including cognitive, emotional, and behavioral problems. Among them, depression is a common psychiatric symptom, and links to poorer recovery. Amantadine, as an antiparkinsonian, increases dopamine release, and blocks dopamine reuptake, but has recently received attention for its effectiveness as an antidepressant. In the present study, we first induced a post-TBI depression rat model to probe the efficacy of amantadine therapy in reducing post-TBI depression. The DA concentration in the striatum of the injured rats, as well as the degeneration and apoptosis of dopaminergic neurons in the substantia nigra (SN), were checked along with the depression-like behavior. The results showed that amantadine therapy could significantly ameliorate the depression-like behavior, improving the DA level in the striatum and decreasing the degeneration and apoptosis of dopaminergic neurons in the SN. The results indicated that the anti-depression effect may result from the increase of extracellular DA concentration in the striatum and/or the indirect neuroprotection on the dopaminergic neurons in the SN. We conclude that DA plays a critical role in post-TBI depression, and that amantadine shows its potential value in anti-depression treatment for TBI.