Altered synaptic transmission in rat anterior cingulate cortex following peripheral nerve injury.
BACKGROUND
Patients with neuropathic pain present not only with persistent pain but also a complex set of additional symptoms, including mood disorders and cognitive disturbance. Given the important roles of the anterior thalamic nuclei (ATN) and anterior cingulate cortex (ACC) in the cognitive and emotional aspects of pain, investigation of the properties of ATN-ACC synapses will help us to understand the mechanisms underlying neuropathic pain.


METHODS
We studied changes in ATN-evoked ACC excitatory postsynaptic potentials (EPSPs) induced by neuropathic pain in a rat model under halothane anaesthesia.


RESULTS
Neuropathic pain caused significant suppression of EPSPs in the ACC compared with rats subjected to sham surgery. Similar to previous evidence, acute inflammatory pain induced by formalin injection into the hind paw significantly increased synaptic efficacy in the ACC compared with naive rats. Neither of the pain paradigms altered the paired-pulse responses.


CONCLUSIONS
A possible explanation for the neuropathic pain-related suppression of EPSPs is that the ACC was already sufficiently active at baseline as a result of neuropathic pain, and ATN stimulation could not further increase the already elevated level of ACC activity. This abnormal excitability of the ATN-ACC synapse may be important in understanding the mechanism underlying neuropathic pain, particularly with respect to the affective and cognitive aspects.
Tachibana
Kaori
K
Department of Anesthesiology and Critical Care Medicine, Hokkaido University Graduate School of Medicine, Sapporo, Japan. shibak@med.hokudai.ac.jp
Kato
Rui
R
Tsuruga
Kenkichi
K
Takita
Koichi
K
Hashimoto
Toshikazu
T
Morimoto
Yuji
Y
D000818:Animals; D004594:Electrophysiology; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D006179:Gyrus Cinguli / Q000503:physiopathology*; D008026:Ligation; D008297:Male; D009437:Neuralgia / Q000503:physiopathology*; D051381:Rats; D017208:Rats, Wistar; D012584:Sciatic Nerve / Q000293:injuries / Q000502:physiology; D009435:Synaptic Transmission / Q000502:physiology*