Objective: To explore the underlying electrophysiological mechanism of depression induced by chronic pain in dopaminergic neurons in midbrain ventral tegmental area (VTA) of rats.
Methods: Twenty-four healthy adult rats were divided into two groups randomly(n=12):12 rats formed the sham group by exposing the spared nerve, and another 12 rats were served as the spared nerve injury (SNI)group by branchedness sciatic nerve injury surgery. The mechanical allodynia test were detected on the day of 3, 7, 14, 28, 42 and 56 after surgery, and the depressive-like behaviors such as open-field test, sucrose preference and forcedswim test were detected at the same time. Then we used the Multichannel Acquisition Processor (MAP) system to record the firing activity of neurons in VTA in both Sham rats and SNI rats.
Results: ①Comparing to sham rats, the paw withdrawalmechanical threshold of SNI rats was decreased significantly (P< 0.01);② According to depression-related behavioral test, SNI rats showed significant difference in open field text, sucrose preference, focus swim text comparing with Sham rats (P< 0.01);③ The firing rate and burst activity of dopaminergic neuronsin midbrain VTA are increased in depression rats compare to sham rats(P<0.05).
Conclusions: Chronic pain could induce depression, and the increase of spontaneous firing rate of dopaminergic neurons in midbrain VTA might be contribute to the depression induced by the chronic neuropathic pain.
Keywords: chronic neuropathic pain; depression; dopaminergic neurons; rat; spontaneous firing.