The Functional Connection Between The Supraoptic Nucleus And The Cardiovascular-related Neurons In Rostral Ventrolateral Medulla Of Rats

Objective: In anesthetized rats,to explore whether the direct or indirect pathways exist between supraoptic nucleus(SON)and rostral ventrolateral medulla(RVLM)neurons,the changes of the single-unit discharges of RVLM neurons and other peripheral physiological indicators were observed before and after stimulation of SON.The possibility of the vasopressin(VP)connection existing between SON and RVLM was further analyzed.It can provide a new theoretical basis for elucidating the central regulatory mechanism of cardiovascular function.Methods: Healthy adult male Sprague-Dawley rats(250~300g)were anesthetized with intraperitoneal injection of urethare(700mg/kg)and ?-chloralose(35mg/kg),and were fixed on the stereotactic apparatus.The single-unit discharges of RVLM neurons,BP,ECG,respiratory muscle electromyogram and body temperature were simultaneously recorded by using Powerlab multi-channel recording system and A-M Systems stimulator and amplifier system.To analyze whether the functional connection existed between SON and RVLM neurons,the metal stimulation electrode was putted in SON nucleus,and the changes of single-unit discharges of RVLM neurons and other peripheral physiological indicators were observed before and after stimulation of SON.In order to further analyze the possibility of the association by the VP connection between SON and RVLM,the VP receptor(V1a)blocker SR49059 was microinjected into RVLM nucleus,then the changes of single-unit discharges of RVLM neurons and other peripheral physiological indicators were observed by stimulating SON before and after administration.Results:1.The simultaneous recording technique of the cardiovascular center and cardiovascular functions:Twenty-three spontaneous unit discharges were recorded in 18 rats,containing 16 continuous discharges and 7 periodical burst discharges.Between two types of discharge groups,the discharges of RVLM neurons,BP,heart rate variability(HRV)(LF/HF),heart rate,body temperature,systolic blood pressure,diastolic blood pressure,mean arterial pressure and respiratory muscle electromyogram discharge had no significant difference,only the respiratory muscle electromyogram amplitude was significantly different(P<0.05).When the blood pressure increased,it was observed that the single-unit discharges of RVLM neurons were inhibited obviously.The peripheral physiological indicators changed accordingly when RVLM neurons discharge activity changed because of the stimulating on rat tail.2.The effect of electrical stimulation of SON on single-unit discharges of RVLM neurons and peripheral physiological indicators:Nineteen spontaneous unit discharges of RVLM neurons were recorded from 18 rats.After electrical stimulation(200?A,0.2ms,100 Hz,0.2s)to SON,the discharge frequency of 10 RVLM neuron units decreased significantly(P<0.05),discharge amplitude decreased,corresponding mean arterial pressure increased(P<0.05),heart rate and respiratory rate had a decreasing trend.However,discharge frequency in 9 RVLM neuron units increased obviously(P<0.05),and other indicators had no significant difference.3.The effect of microinjection of SR49059 into RVLM nucleus:Before pretreatment by microinjecting SR49059 into RVLM,it was observed that the discharge frequency of 9 RVLM neuron units decreased significantly(P<0.05),discharge amplitude decreased,heart rate had a decreasing trend,and other indicators had no significant difference after 200?A electrical stimulation to SON.After pretreatment by microinjecting SR49059 into RVLM,the discharge frequency and amplitude of RVLM neuron units both had an increasing trend;other indicators had no significant difference.When electrical stimulation was applied immediately after injection of SR49059,all indicators had no significant difference before and after stimulation.When electrical stimulation of SON was applied after microinjection of SR49059 for 10 min,the frequency and amplitude of single-unit discharges of RVLM neurons had no obvious decline,and other indicators had no significant difference.After 400?A electrical stimulation to SON,it was also observed that the discharge frequency and amplitude of RVLM neuron units had a decreasing trend,heart rate and LF/HF had a decreasing trend,and other indicators had no significant difference.Similarly,after pretreatment by microinjecting SR49059 into RVLM,the discharge frequency and amplitude of RVLM neuron units both had an increasing trend;other indicators had no significant difference.When electrical stimulation was applied immediately after injection of SR49059,all indicators had no significant difference.When electrical stimulation of SON was applied after microinjection of SR49059 for 10 min,the frequency and amplitude of single-unit discharges of RVLM neurons were observed to decrease,but no significant changes were observed in other parameters.Conclusions:(1)The technique of simultaneous recording in peripheral physiological parameters and single-unit discharges of cardiovascular central neurons was established,which is suitable for the study of the interaction between different levels of cardiovascular center,and interaction between the cardiovascular central and cardiovascular peripheral activities.(2)After stimulating the SON,there are different effects,manifested as inhibitory or excitatory effects,on different cardiovascular related neurons in the RVLM,and corresponding changes also showed on physiological functions.The results indicate that direct or indirect functional connection may exist between SON and RVLM,and the pathway may be involved in regulating the cardiovascular activities.(3)After microinjecting VP receptor antagonist SR49059 into RVLM nucleus,the inhibitory effect of SON stimulation on the discharges of RVLM neurons was attenuated,suggesting that VP may be involved in the functional connection of the pathway.