Neural Correlates Of Acute Morphine Injection In Feline: A Manganese-enhanced MRI Study

Calcium ion (Ca²⁺) is an important substrate for neurotransmission, which plays an essential role in neural function. Biologically divalent manganese ion (Mn²⁺) is an analog to Ca²⁺, which can enter neurons via voltage-gated Ca²⁺ channels and be transported through neuronal microtubule system.In addition, Mn²⁺ is paramagnetic and can be used as contrast agent in magnetic resonance imaging(MRI). Therefore, manganese-enhanced magnetic resonance imaging(MEMRI) is an ever-growing technique for functional and molecular imaging of specific biological processes which has found wide applications in neuronal tracts tracing, delineation of fine cerebral neuroarchitecture and studying brain activities etc.Objective In this dissertation, we realized MEMRI technology in our laboratory, and applied this technology to develop the animals'brain function activity, to determine the value of locate the encephalic region correlated with acute morphine-induced by MEMRI and further to determine the correlation of morphine effects and calcium overloading. Accordingly, the study was carried out on the neural correlation and allocation.Method Based on experimental evidence and taking into account the availability, water solubility, redox properties, toxicity, suitability and relaxitivity of the manganese compounds, 120mM MnCl2 was selected for use in MEMRI. Sixteen male adult cats(2-3kg)were divided into two groups at random, morphine-induced group and control group. The adult cats were anaesthetized with anesthesia respirator and the internal arteria carotis(ICA)was catheterized after tracheal intubation. Then the cats were sent into the MRI room, carrying on the scanning. Meanwhile according to the dosage of 1ml/kg +1ml, inject 120mM MnCl2 deionized water iso-osmotic solution through Micro-pump into the right the ICA catheter. Animals first underwent a continuous MnCl2 infusion for 30 min. Bolus injection of hyperosmolar(25%)mannitol was delivered through the right ICA catheter 20 min after the initiation of MnCl2 infusion.About 20 minutes after the cessation of MnCl2 infusion, animals received either morphine or saline, and the scan continued for another 75 min. Adopt software package of AFNI(Analysis of Functional NeuroImages)to deal with MRI data and statistical analysis. A fractional signal enhancement map was generated to identify regions that exhibited significant signal increases during Mn²⁺infusion. Signal change due to Mn²⁺ infusion was calculated. Results After MnCl2 infusion, the signal whithin cats'brain parenchyma in control group and morphine-induced group has no change over time. A gradual signal enhancement was seen in the muscles of the head and the ventricular,and the enhancement rate of these two districts were 23%,45% respectively, and they had no significant differences with the control group (P>0.05). The signal little enhancement(approximately 15%)within brain parenchyma were not observed until by mannitol administration, and they had no significant differences with the control group(P>0.05). Many brain structures exhibited signal enhancement following acute morphine administration included prefrontal (PFC), cingulate cortex, hippocampus and basal ganglia(approximately 28 % )and they had significant differences with the control group (P<0.05⁰.01).Whereas the ventricle and muscle signal decreased after the cessation of Mn²⁺ infusion, consistent with its known rapid washout from tissue.Regions significantly activated by morphine included the right prefrontal (PFC), cingulate cortex,basal ganglia and occipital lobe.Conclusion The prefrontal (PFC), cingulate cortex, basal ganglia and occipital lobe are the correlated encephalic regions of acute morphine-induction. MEMRI can play an important role in allocation and revealing onset mechanism of acute morphine-induction. The results of our studies indicate that MEMRI is a useful tool to study changes in brain activities and neuronal tracts induced by pathological conditions, and may provide new opportunities for understanding the neurobiology of drug addiction.