In the 3 May
D3 receptors are expressed mainly in an area of the brain known as the shell of the nucleus accumbens. Neurons from the ventral tegmental area (VTA), which produce both dopamine and BDNF, connect to neurons of the nucleus accumbens. Guillin
In the rat model dopamine-releasing neurons on only one side of the brain are damaged and when these rats were injected with levodopa (the precursor of dopamine), the expression of both the D3 receptor and the BDNF receptor TrkB increased. The injection caused the animals to turn away from the side of damage (levodopa-induced rotations) and this correlated with a higher activation of D3 receptors on the side of the damage. With repeated injections, this behaviour became more pronounced. The behavioural sensitisation and associated upregulation of D3 receptors was reduced when a BDNF antagonist was infused into the brain.
This suggests that BDNF is responsible for behavioural sensitisation to levodopa and might explain the abnormal movements seen in Parkinson's patients on long-term treatment with levodopa.