Effect of acetylcholine receptors on the pain-related electrical activities in the hippocampal CA3 region of morphine-addicted rats.
OBJECTIVE
To determine the effect of acetylcholine (ACh), pilocarpine, and atropine on pain evoked responses of pain excited neurons (PEN) and pain inhibited neurons (PIN) in hippocampal CA3 region of morphine addicted rats.


METHODS
Female Wistar rats, weighing between 230-260 g were used in this study. Morphine addicted rats were generated by subcutaneous injection of increasing concentrations of morphine hydrochloride for six days. Trains of electrical impulses applied to the sciatic nerve were used as noxious stimulation and the evoked electrical activities of PEN or PIN in hippocampal CA3 area were recorded using extracellular electrophysiological recording techniques in hippocampal slices. The effect of acetylcholine receptor stimulation by ACh, the muscarinic agonist pilocarpine, and the muscarinic antagonist atropine on the pain evoked responses of pain related electrical activities was analyzed in hippocampal CA3 area of morphine addicted rats.


RESULTS
Intra-CA3 microinjection of ACh (2 μg/1 μl) or pilocarpine (2 μg/1 μl) decreased the discharge frequency and prolonged the firing latency of PEN, but increased the discharge frequency and shortened the firing inhibitory duration (ID) of PIN. The intra-CA3 administration of atropine (0.5 μg/1 μl) produced opposite effect. The peak activity of cholinergic modulators was 2 to 4 min later in morphine addicted rats compared to peak activity previously observed in normal rats.


CONCLUSIONS
ACh dependent modulation of noxious stimulation exists in hippocampal CA3 area of morphine addicted rats. Morphine treatment may shift the sensitivity of pain related neurons towards a delayed response to muscarinergic neurotransmission in hippocampal CA3 region.
Department of Neurology, Liaocheng People's Hospital, 67 Dongchang Xi Road, Liaocheng 252000, China.
Guan Zeng
GZ
Li
Department of Cadre Health Protection, Liaocheng People's Hospital, 67 Dongchang Xi Road, Liaocheng 252000, China.
Zhe Hui
ZH
Liu
Department of Neurology, Second Affiliated Hospital, Harbin Medical University, 194 Xuefu Road, Nangang District, Harbin 150081, Heilongjiang, China.
XinYa
X
Wei
Department of Neurology, Second Affiliated Hospital, Harbin Medical University, 194 Xuefu Road, Nangang District, Harbin 150081, Heilongjiang, China.
Pan
P
Zhao
Department of Neurology, Second Affiliated Hospital, Harbin Medical University, 194 Xuefu Road, Nangang District, Harbin 150081, Heilongjiang, China.
Chun Xiao
CX
Yang
Laboratory of Neural Algesia Electrophysiology, Department of Physiology, Harbin Medical University, 194 Xuefu Road, Nangang District, Harbin 150081, Heilongjiang, China.
Man Ying
MY
Xu
Hippocampal CA3; Morphine addiction; Muscarinergic Acetylcholine receptors; Pain