Study On Distribution Of Respiratory Neurons In The In Vitro Brainstem Slice From Neonatal Rat And Mechanisms Of The Primary Respiratory Rhythm Generation

sABSTRACT?Study on distribution of respiratory neurons in the in vitro brainstem slice from neonatal rat and mechanisms of the primaryrespiratory rhythm generationObject1. To illustrate the distribution of different subtypes of respiratory neurons in the brainstem slices isolated from neonatal rats by simultaneous recording of respiratory neurons discharge and hypoglossal nerve activity; 2. To test the hypothesis that the medial area of nucleus retrofacialis (mNRF) may be the kernel site for primary respiratory rhythmogenesis by comparing the anatomical location of respiratory neurons with the mNRF. 3. To investigate the roles of non-NMDA receptors in the respiratory rhythm generation and modulation by exploring the effects of non-NMDA receptors agonist and antagonist on the activities of respiratory neurons.Methods:The present studies were performed on the in vitro brainstem slice isolated from neonatal rats. The respiratory activity was monitored by suction electrode applied on the central end of hypoglossal nerve and the respiratory neuronal discharges were recorded extracellularly by inserting the glass microelectrode into the ventral part of the slices. The respiratory neurons were classified into several subtypes with reference to the temporal relationship between the neuronal discharge and the hypoglossal nerve activity. The distributional status of different types of respiratory neurons were constructed by their distances from the midline, obex and the ventral surface of medullary slices. Drugs were administered by bath application and their effects on the respiratory neuronal activity were investigated.Results:51.In the present study, a total of 429 neuronal units with spontaneousdischarge were recorded. Out of them there were 326 respiratory neuronsand l03 non-respiratory neurons;2. The respiratory neurons were grossly classified into inspiratory neuronsand expiratory neurons with the reference to the temporal relationshipbetween the neuronal discharge and hyPoglossa1 nerve activity Moreovef,the inspiratory neurons were further classified into pre-insPiratory neuronsand early inspiratory neurons as we1l as late inspiratory neurons based ontheir temporal discharge pattems.3. On the other hand, the exPiratory neurons were then classified into threesubtyPes listed as throughout expiratory neurons, biphasic expiratoryneurons and late expiratory neurons.4. A1l the respiratory neurons were distributed and imrningled as a coluninalong the nucleus ambiguus. The inspiratory neurons, howevef, werelocated a little more caudal1y in comparison with the relatively rostrallocation of the expiratory neurons.5. SubtyPes of inspiratory or expiratory neurons showed no conspicuousdifference in the spatial distribution.6. During the control perfusion, the peak frequency of biphasic expiratoryneuronal discharge was 39.75 l 5.43Hz. After bathing aPPlication of KAfor 5 minutes, an agonist of non-N'MDA recePtors, the peak frequencywere increased to 55. l4 t l0.l7Hz and the whole discharge pattems wereelevated. These effects were idriited by administration of DNQX.7.After aPplication of KA, the peak discharge frequency of inspiratoryneurons were increased from 4l.0l l l.l0 Hz to 50.70 t l.43 Hz.MeanWile, the discharge pattems in the middle inspiratory phase wereelevated. In contrast, the discharge pattems in the early and late phaseexhibited no conspicuous changes. The KA excitatory effects could bereversed by ensuing aPplication of DNQX.Conclusions:These results indicated that in the l'n vitrO brainstem slice from6neonatal rats: 1) There were several subtypes of respiratory neurons with different discharge patterns and they were mingled as a column along the nucleus ambiguus; 2) The anatomical localization of respiratory neurons overlapped the structure of mNRF, which suggested the important role of mNRF in the primary respiratory rhythm generation in mammals; 3) Similar to the in vivo situation, Pr...