Effect Of Nimodipine On Rhythmical Respiration Discharge Activities Via CAMP Pathway In Vitro In Medullary Slice From Neonatal Rats

Background Respiration is the term for the exchange of oxygen from the environment for carbon dioxide from the body’s cells, which plays an important role in human physical activities. Nimodipine, an L-type calcium channel blocker, acts by inhibiton of the flux of the calcium ions into cells and promotes the release of intracellular calcium ions, leading to a decrease in intracellular calcium ions. It has high lipid solubility with ready access to the blood-brain barrier (BBB), and decrease neuron calcium overload in central nervous system. It has been used as a prophylactic and therapeutic agent for intracranial hemorrhage associated with cerebral vasospasm, migraine, vertigo symptom, and depression and so on. However, the effect of nimodipine on medullary respiratory center had never been reported. At present study, we investigated the effect of nimodipine on respiratory--related rhythmic discharge activity (RRDA) of neonatal rat and its mechanism.Objective To investigate the effect nimodipine on RRDA of in vitro brainstem slice of neonatal rat and to determine whether nimodipine induced RRDA of in vitro brainstem slice of neonatal rat via cAMP pathway, which provides the evidence for the clinical therapy of bulbar respiratory center’s diseases.Methods1. Firstly, medullary slices in vitro isolated from neonatal rats were prepared, and then these preparations were perfused by artificial cerebrospinal fluid (ACSF) supplemented with 0,0.025,0.05,0.1 and 0.2 μM nimodipine to investigated the effect of different concentrations of nimodipine on RRDA.2. Secondly, the preparations were perfused by ACSF supplemented with 0.05 μM nimodipine,10 μM 3-isobutyl-l-methylxanthine (IBMX, a nonspecific inhibitor of phosphodiesterase), an 5μM clonidine (a a2-adrenergic agonist), a combination of 0.05 uM nimodipine and 10 μIB MX and a combination of 0.05 μM nimodipine and 5 μM clonidine to investigate the effect of these drugs on RRDA of preparations.3. Finally, medullary slices in vitro were prepared, and then medial region of nucleus retrofacialis (mNRF) were cut off. Medullary slices were perfused by ACSF supplemented with 0.05μM nimodipine,10 μM 3-isobutyl-l-methylxanthine (IBMX, a nonspecific inhibitor of phosphodiesterase), an 5 μM clonidine (a a2-adrenergic agonist), a combination of 0.05 μM nimodipine and 10 μM IBMX and a combination of 0.05 μM nimodipine and 5 μM clonidine for 20 min to investigate the effect of these drugs on RRDA of preparations, and yield of cAMP in region of mNRF was determined.Results1. Compared with those of control group,0.025 μM of nimodipine led to a decrease of level of respiratory cycle (RC), while 0.05 μM of nimodipine decreased of the levels of both RC and inspiratory time (TI). However, addition of a higher dose of nimodipine (0.1 and 0.2 μM) induced epileptiform discharges.2. Compared with those of control group, addition of IBMX and nimodipine individually or in combination led to an increase in the discharge of preparations, while addition of clonidine led to a decrease. A combination of nimodipine and clonidine did not affect the discharge of preparations. Additionally, there was not obvious statistically difference of the discharge between IBMX or nimodipine-treated groups and control group, and between IBMX or nimodipine-treated groups and IBMX/nimodipine-treated groups.3. Compared with those of control group, addition of IBMX and nimodipine individually or in combination led to an increase in levels of cAMP of preparations, while the addition of clonidine led to a decrease. A combination of nimodipine and clonidine did not affect cAMP levels of preparations statistically. Additionally, there was not obvious difference of cAMP levels among the addition of IBMX and nimodipine individually or in combination.ConclusionA certain concentration nimodipine induced the excitation of RRDA of in vitro brainstem slice of neonatal rat. Experiments of neurological electrophysiology and enzyme-linked immunosorbent assay (ELISA) indicated that nimodipine possibly induced the excitation of RRDA of in vitro medullary slice preparations via cAMP pathway.