Nikethamide affects inspiratory neuron discharge in the nucleus retrofacialis medial region in brain slices from neonatal rats

BACKGROUND： Nikethamide, a respiratory center stimulant, is widely used in China. However, its effects on the central nervous system and medullary respiratory center remain poorly understood. OBJECTIVE： To investigate the influence of nikethamide on inspiratory neuron discharge in the medial region of the nucleus retrofacialis in neonatal rats, based on the observations addressing rhythmic respiratory discharge generated by the basic medullary respiratory center and various respiration neuron discharges in brain slices. DESIGN, TIME AND SETTING： A controlled, observational study utilizing in vitro neuroelectrophysiology was performed at the Department of Physiology in Southern Medical University between September and December in 2007. MATERIALS： Nikethamide was purchased from Sigma, USA; BL-420E biological signal collection and manaclement system was provided by Chengdu TME Technology, China.METHODS： Isolated medulla-spinal cord preparations were collected from neonatal Sprague Dawley rats, aged 1-3 days. Tissues were divided to include the medial region of the nucleus retrofacialis, ventral respiratory, and dorsal respiratory groups. Subsequently, modified Kreb＇s solution and 5 μg/mL nikethamide-containing modified Kreb＇s solution were consecutively perfused into the medial region of the nucleus retrofacialis in neonatal rat brain slices. MAIN OUTCOME MEASURES： Hypoglossal nerve root respiratory-related rhythmic discharge activities and inspiratory neuron discharges were recorded with an adsorption electrode and microelectrode. RESULTS Nikethamide resulted in prolonged inspiratory neuron discharge time, shortened respiratory cycle and expiratory time. Nikethamide intervention resulted in enhanced integral amplitude of some inspiratory neurons with no changes in discharge frequency or increased discharge frequency in remaining inspiratory neurons with no changes in integral amplitude. CONCLUSION： Nikethamide excites inspiratory neurons in the basic rhythmic respiration and medullary respiratory center, in addition to increased inspiratory neuron and neural network excitability.

Effects of microinjection of morphine and naloxone into the medial area of nucleus retrofacialis on respiration in rats

Experiments were performed on SD rats. The animals were anesthetized with urethane (1. 0 g/kg, i. p. ). The diaphragmatic electric activity and intratracheal pressure were monitored. Morphine (4 mg/kg, i. v. ) caused marked respiratory inhibition. The respiratory frequency (RF), integrated diaphragmatic electric activity (IDEA) and diaphragmatic minute activity (DMA) were decreased. The respiratory depression effect of morphine was almost completely eliminated by pretreatment with naloxone injected into the medial areas of the nucleus retrofacialis (mNRF). Bilateral microinjection of morphine (5 μg) into mNRF might result in apnea in all animals. This effect could be fully prevented by injection of naloxone into mNRF in advance. The results suggest that there might be morphine receptors in the mNRF and they might play an important role in the respiratory inhibition induced by systemic administration of morphine.

大鼠延髓呼吸性神经元向脊髓膈运动神经元投射的实验观察

目的观察大鼠延髓呼吸性神经元向脊髓膈运动神经元的直接投射。方法 2 5只Wistar大鼠分为 3组 :脊髓定位组(5只 )、延髓投射组 (15只 )和对照组 (5只 )。运用辣根过氧化物酶 (HRP)逆追踪法 ,于脊髓定位组膈神经干注入HRP ,确定膈运动神经元在脊髓中的位置 ,然后延髓投射组于逆行性标记细胞位置 ,对照组于脊髓后角分别注入HRP ,观察延髓呼吸性神经元的标记情况。结果在脊髓定位组的注射同侧观察到 ,C3 —C5节段的前角中间部出现逆行性标记细胞 ,为典型的前角运动神经元。在延髓投射组观察到 ,逆行性标识神经元出现在延髓疑后核和面后核的腹内侧部。对照组在上述位置未见标识神经元。结论大鼠膈运动神经元位于C3 -C5节段 。