Effect of acetylcholine on the discharge of presympathetic neurons of the rostral ventrolateral medulla of rats 3

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1 468, Dec. 2000, 52 (6) : Acta Physiologica Sinica 3, 1 3 3,,, (, ; 1, ) :, (ACh) (RVLM) RVLM 35, ACh ( P < 0105), 22 M (ATR) ( P < 0105) ACh ; 7 6 (ACh N 1 N 2 ) (ACh N 1 ) ACh, RVLM M : ; ; ; ; : Q425 Effect of acetylcholine on the discharge of presympathetic neurons of the rostral ventrolateral medulla of rats 3 WANG Wei2Zhong, WANG Xue2Mei 1, RONG Wei2Fang, WANGJi2Jiang, YUAN Wen2Jun 3 3 ( Department of Physiology, Second Military Medical University, Shanghai ; 1 Training Center of Health Personnel, Hefei ) Abstract : Effect of acetylcholine (ACh) on presympathetic neurons of the rostral ventrolateral medulla ( RVLM) was studied by extracellular recording technique and microiontophoresis in urethane2anaesthetized rats. Spontaneous discharges of 35 presympathetic neurons of RVLM were recorded. All the neurons showed increased discharge by microiontophoresis of ACh dose2 dependently with the increase of iontophoretic current. In 22 units microiontophoresis of atropine decreased the baseline discharge rate and completely blocked the ex2 citatory effect of ACh on these neurons, while in the remaining 7 and 6 neurons microiontophoresis of d2tubocu2 rarine (d2tc) and hexamethonium (C 6 ) respectively had no effect and did not block the action of ACh. The above finding suggests that presympathetic neurons of RVLM receive a tonic excitatory cholinergic input mediat2 ed by M receptors. Key words : rostral ventrolateral medulla ; presympathetic neurons ; extracellular recording ; microionto2 phoresis ; acetylcholine ( rostral ventrolateral medulla,, [1,2 ] RVLM) RVLM RVLM ( (acety2, presympathetic neurons), lcholine, ACh), ; RVLM ; ACh Received Accepted Project supported by National Basic Program (No. G ) of China and the Research Foundation for Medical Sciences of PLA (the 9th Five2Year Program No. 96M072) 3 3 Corresponding author. Tel : ; E2mail :

2 6 : 469, ACh RVLM [3,4 ] [6, 113 RVLM ] RVLM (1) AN [5 ], (Nihon Kohden, SEN27103) AN ACh ( 200 s, 5 ms, 3, 1 Hz), ACh ma, RVLM, AN ( RVLM 1A) ; (2) SD ( g), 60 mg/ kg,,,, (Narishige), 1 % (10 mg/ kg, 3 mg/ kg), (10 12 ml/ kg, / min), 20 % ( 1 g/ kg, 10 min, ), ( aortic nerve, AN),,,, 1 2,, AN, CO 2 4 % 5 %, ,, 2 % ( pontamine sky blue, PSB)2015 mol/ L, 3 5 m, 4 10 M : 011 mol/ L (glutamate, Glu, ph 618) 011 mol/ L ACh (ph 615) 2 mol/ L NaCl, 011 mol/ L (at2 (10 g/ kg), ( 1 B) ; (3) R ropine, ATR, ph 618) 011 mol/ L ( d2 1. RVLM tubocurarine, d2tc, ph 618) 011 mol/ L Fig1 1. Electrophysiological identification of presympathetic neu2 rons in the RVLM. A. Inhibition of ongoing activity by short train (hexamethonium, C 6, ph 619) pulse stimulation of aortic nerve (indicated by a filled triangle) M (obex), RVLM The recording is a summation of 300 sweeps. Bin width = 1 ms. B. Inhibition of ongoing activity by intravenous injection of ( mm, mm, phenylephrine (10 g/ kg, marked by an open triangle), which mm), elevated blood pressure. Bin width = 1 s. C. R2wave (of ECG) (Nihon Kohden, MEZ28210) ( triggered average of blood pressure pulse and neural activity. The recording is a summation of 300 sweeps. Bin width = 1 ms. D Hz) 2 ( The constant onset latency of action potentials ( marked by an, TAWA294) open circle) evoked by spinal cord stimulation ( marked by a filled circle)., 1 ms,

3 470 Acta Physiol. Sin. 52, 50 m, Pax2 ( inos and Watson [8 ], 1 C) ; (4), ( ), 2 ( ( 2) mm, mm), 116, : 012 ms, ma, 115 Hz ( 1 D), t, P < ( ), ( 117 Glu ACh ATR d2tc C 6 Sig2, MIS9400) ma Glu, ATR ACh d2tc C 6 RVLM, Glu (0 60 na),, 211 ACh RVLM, ;, RVLM 35, [7 ],, / s ( / s, n = 35), 1 min, na ACh, 2 min, 1 10 s, ( P < (8 na, ), 0105) ( P < 0101) / s ( P 115 RVLM < 0101), 2811 % 8010 % % 35 PSB ( 1, 3A), ( - 15 A, 10 min), 100 ml 10 %, 20 % 2 ACh, 300 ml, 10 %, 2. RVLM Fig1 2. Location of the recorded neurons in the RVLM. Recording sites (marked by black circles) of presympathetic neurons plotted on each cross section through the rat medulla mm rostral to the obex. Amb, neucleus ambiguus ; IO, inferior oli2 vary nucleus ; LPGi, lateral paragigantocellular nucleus ; Py, pyramidal tract ; RF, retrofacial nucleus ; RVL, nucleus reticularis rostroventrolateralis ; Sp5O, spinal trigeminal tract nucleus, oral.

4 6 : ACh RVLM Table 1. Effects of microiontophoresis of ACh and its receptor blockers on the discharge of presympathetic n neurons in the RVLM Control Spikes/ s (change : %) 30 na 60 na 90 na ACh ( %) ( %) ( %) 3 3 Atropine ( %) ( %) ( %) 3 3 d2tc ( %) ( %) ( %) C ( %) ( %) ( %) 3 3 P < 0105, 3 P < 0101 vs control. 212 M ACh ACh 22 ACh (60 na) RVLM RVLM 7515 % ; 22 RVLM ( 90 na 1 2 min / s, n = 22), na ACh (60 na), ACh RVLM ATR, ( P < 315 % ( P > 0105), 0105) ( P < 0101) / s ( P < 0101), 2011 % 3415 % 4816 % ( 1, ACh ( 3 C) 213 N 1 N 2 ACh ACh 3 B), RVLM 7 6 RVLM ( / s), na d2tc C 6,, ( P > 0105, n = 7) / s ( P > 0105, n = 6) ( 1) ; 90 na d2tc C min ACh (60 na), ACh ACh RVLM Fig1 3. Responses of presympathetic neurons in the RVLM to microiontophoretic application of ACh or ATR. A. Excitatory ef2 fects of presympathetic neurons during repeated microiontophoretic application of ACh. B. Inhibition of ongoing activity of the neu2 ron during repeated microiontophoretic application of ATR. C. ATR completely blocked the excitatory effect induced by mi2 croiontophoresis of ACh on the presympathetic neuron. Saline = 2 mol/ L NaCl. Bin width = 1 s in A, B and C. 4. d2tc C 6 RVLM Fig1 4. Responses of presympathetic neurons in the RVLM to microiontophoretic application of d2tc or C 6. A. The discharge of presympathetic neuron was not affected by microiontophoretic application of d2tc, and the excitatory effect of ACh on the neu2 rons was not blocked by d2tc. B. Microiontophoretic application of C 6 did not change the baseline discharge of the presympathetic neurons and did not block the excitatory effect of ACh on presym2 pathetic neurons. Sal = control, Bin = 1 s in both A and B.

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