BACKGROUND: Very few studies have addressed neuronal injury in cerebral vasospasm and subarachnoid hemorrhage (SAH), and the role of neurotransmitters in the regulation of extracellular signal-regulated kinase 1/2 (ERK1/2) expression following SAH.OBJECTIVE: To analyze neurotransmitter regulation of ERK1/2 expression through the use of signal transduction, and to investigate cerebral injury mechanisms following SAH.DESIGN, TIME AND SETTING: A completely randomized grouping and controlled animal experiment was performed at the Experimental Center of Medical College of Xi'an Jiaotong University from March to December 2008.MATERIALS: Extracellular signal-regulated ERK1/2 polyclonal antibody and streptavidin-peroxidase method kits were purchased from Beijing Biosynthesis Biotechnology,China; DAB kit was purchased from Zhongshan Golden Bridge Biotechnology, China; TUNEL kit was purchased from Promega, USA.METHODS: A total of 114 male, Sprague Dawley rats, aged 55-63 days old, were randomly assigned to five groups: SAH (n = 30), saline control (n = 30), puncture control (n = 30), normal control (n = 6), and neurotransmitter-treated (n = 18). The SAH model was established by twice injecting blood through the cisterna magna. The neurotransmitters-treated group was subdivided into three groups according to drugs injected into the lateral cerebral ventricle: acetylcholine chloride, norepinephrine, and saline, with six animals in each group.MAIN OUTCOME MEASURES: Rats from the SAH, saline control, and puncture control groups were respectively sacrificed at 6,12, and 24 hours, as well as 3 and 5 days, with six rats at each time point. The normal control group rats were sacrificed at 6 hours, and the neurotransmitter group rats were sacrificed 3 days following neurotransmitter injection. Morphological cellular changes were observed by hematoxylin and eosin staining. Immunohistochemical SP method was used to detect expression of ERK1/2 in the cortex, and cortical apoptosis was detected using the TUNEL method.RESULTS: Neural tissue edema, apoptosis, and necrosis occurred in the cortex of the SAH group.ERK1/2-positive cells were first observed at 6 hours, peaked at 12 hours following SAH in the cortex,and gradually decreased thereafter. Cellular apoptosis was observed in the cortex at 6 hours and peaked at 24 hours following SAH. ERK1/2 distribution in the brain overlapped apoptotic cells to a great degree. The number of ERK1/2-positive and apoptotic cells was significantly greater in the SAH group compared with the three control groups (P< 0.05). Compared to the number of ERK1/2-positive cells in the saline-treated group, acetylcholine chloride treatment resulted in decreased ERK1/2 expression and apoptosis (P< 0.05). Norepinephrine resulted in increased ERK1/2 expression, but there was no significance in apoptosis compared to the saline-treated group (P>0.05).CONCLUSION: Apoptosis was observed early in the rat cortex following SAH. In addition, ERK1/2 was expressed earlier than apoptosis. Acetylcholine chloride treatment resulted in decreased numbers of apoptotic cells following SAH, possibly by down-regulating ERK1/2 expression.