Afferent/efferent Projections Of The Medial Area Of Nucleus Retrofacialis And The Role Of Glycine Receptors In The Primary Respiratory Rhythm Generation In The Rat

Objectl.To illustrate the afferent/efferent projections of cells in the medial area of nucleus retrofacialis (mNRF) in the adult SD rat using retrograde/ anterograde tracing methods;2. To investigate the roles of glycine receptors in the primary respiratory rhythm generation and modulation by exploring the effects of glycine receptors agonist and antagonist on the discharge activities of inspiratory neurons in mNRF. Methods:1. Twenty-five adult SD rats of either sex,weighting 200-250g,were used in the first part of study. According to the atlas,HRP/WGA-HRP solution was microinjected with a microsyringe into mNRF unilaterally. Control:HRP solution was microinjected into the area 2mm away from mNRF. After a survival time of 48h,animals were perfused transcardially to fix the brain. The brains were removed and then frozen,sliced into 40(xm transverse sections. The sections were processed histochemically according to the tetramethylbenzidine(TMB) method. After reactions,the sections were mounted on gelatin-coated slides. HRP/WGA-HRP products were examined microscopically under bright-field illumination.2. The second part studies were performed on the in vitro brainstem slice isolated from neonatal rats (0-3 d). 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 theglass microelectrode into the mNRF of the slices. The inspiratory neurons were determined according to the temporal relationship between the neuronal discharge and the hypoglossal nerve activity. Drugs were administered by bath application and their effects on the inspiratory neuronal activity were investigated. Results:l.HRP labeled cell bodies were mainly found in AMB,NTS,Gi,raphe nuclei,PB-KF complex,spinal intermediate zone and reticular formation of medulla oblongata and pons.2.WGA-HRP labeled terminal fibers were mainly observed in AMB,NTS,intermediate zone and reticular formation of pons.S.Inspiratory/expiratory neuronal discharge activities were recorded in mNRF extracellularly.4. During the control perfusion,the peak frequency of inspiratory neurons was 28.80+2.77Hz. After application of STR,the peak frequency was increased to 38.60+4.33Hz (P<0.01). After application of Glycine,the peak frequency was decreased to 25.15+3.42Hz (P<0.05). After washout,the peak frequency was 31.76+6.80Hz. Conclusions:1 The first 2 results indicated that in the adult rats:1) There are widely anatomical connections between many respiratory related regions in brainstem and mNRF;2) These connections between many respiratory related regions in brainstem and mNRF may be involved in the adjustment of the basic respiratory rhythm generation.The other 2 results indicated that in the in vitro brainstem slice from neonatal rats:1) All subtypes of respiratory neurons located in mNEF. 2) Activation/inhibition of Glycine receptors can affect the inspiratory neuronal discharge in mNRF,which indicated that Glycine is involved in the generation and maintenance of the basic respiratory rhythm as an inhibitor.