TY - JOUR
T1 - Responses and afferent pathways of superficial and deeper C1-C2 spinal cells to intrapericardial algogenic chemicals in rats
AU - Qin, Chao
AU - Chandler, Margaret J.
AU - Miller, Kenneth E.
AU - Foreman, Robert D.
PY - 2001
Y1 - 2001
N2 - Electrical stimulation of vagal afferents or cardiopulmonary sympathetic afferent fibers excites C1-C2 spinal neurons. The purposes of this study were to compare the responses of superficial (depth <0.35 mm) and deeper C1-C2 spinal neurons to noxious chemical stimulation of cardiac afferents and determine the relative contribution of vagal and sympathetic afferent pathways for transmission of noxious cardiac afferent input to C1-C2 neurons. Extracellular potentials of single C1-C2 neurons were recorded in pentobarbital anesthetized and paralyzed male rats. A catheter was placed in the pericardial sac to administer a mixture of algogenic chemicals (0.2 ml) that contained adenosine (10-3 M), bradykinin, histamine, serotonin, and prostaglandin E2 (10-5 M each). Intrapericardial chemicals changed the activity of 20/106 (19%) C1-C2 spinal neurons in the superficial laminae, whereas 76/147 (52%) deeper neurons responded to cardiac noxious input (P < 0.01). Of 96 neurons responsive to cardiac inputs, 48 (50%) were excited (E), 41 (43%) were inhibited (I), and 7 were excited/inhibited (E-I) by intrapericardial chemicals. E or I neurons responsive to intrapericardial chemicals were subdivided into two groups: short-lasting (SL) and long-lasting (LL) response patterns. In superficial gray matter, excitatory responses to cardiac inputs were more likely to be LL-E than SL-E neurons. Mechanical stimulation of the somatic field from the head, neck, and shoulder areas excited 85 of 95 (89%) C1-C2 spinal neurons that responded to intrapericardial chemicals; 31 neurons were classified as wide dynamic range, 49 were high threshold, 5 responded only to joint movement, and no neuron was classified as low threshold. For superficial neurons, 53% had small somatic fields and 21% had bilateral fields. In contrast, 31% of the deeper neurons had small somatic fields and 46% had bilateral fields. Ipsilateral cervical vagotomy interrupted cardiac noxious input to 8/30 (6 E, 2 I) neurons; sequential transection of the contralateral cervical vagus nerve (bilateral vagotomy) eliminated the responses to intrapericardial chemicals in 4/22 (3 E, 1 I) neurons. Spinal transection at C6-C7 segments to interrupt effects of sympathetic afferent input abolished responses to cardiac input in 10/10 (7 E, 3 I) neurons that still responded after bilateral vagotomy. Results of this study support the concept that C1-C2 superficial and deeper spinal neurons play a role in integrating cardiac noxious inputs that travel in both the cervical vagal and/or thoracic sympathetic afferent nerves.
AB - Electrical stimulation of vagal afferents or cardiopulmonary sympathetic afferent fibers excites C1-C2 spinal neurons. The purposes of this study were to compare the responses of superficial (depth <0.35 mm) and deeper C1-C2 spinal neurons to noxious chemical stimulation of cardiac afferents and determine the relative contribution of vagal and sympathetic afferent pathways for transmission of noxious cardiac afferent input to C1-C2 neurons. Extracellular potentials of single C1-C2 neurons were recorded in pentobarbital anesthetized and paralyzed male rats. A catheter was placed in the pericardial sac to administer a mixture of algogenic chemicals (0.2 ml) that contained adenosine (10-3 M), bradykinin, histamine, serotonin, and prostaglandin E2 (10-5 M each). Intrapericardial chemicals changed the activity of 20/106 (19%) C1-C2 spinal neurons in the superficial laminae, whereas 76/147 (52%) deeper neurons responded to cardiac noxious input (P < 0.01). Of 96 neurons responsive to cardiac inputs, 48 (50%) were excited (E), 41 (43%) were inhibited (I), and 7 were excited/inhibited (E-I) by intrapericardial chemicals. E or I neurons responsive to intrapericardial chemicals were subdivided into two groups: short-lasting (SL) and long-lasting (LL) response patterns. In superficial gray matter, excitatory responses to cardiac inputs were more likely to be LL-E than SL-E neurons. Mechanical stimulation of the somatic field from the head, neck, and shoulder areas excited 85 of 95 (89%) C1-C2 spinal neurons that responded to intrapericardial chemicals; 31 neurons were classified as wide dynamic range, 49 were high threshold, 5 responded only to joint movement, and no neuron was classified as low threshold. For superficial neurons, 53% had small somatic fields and 21% had bilateral fields. In contrast, 31% of the deeper neurons had small somatic fields and 46% had bilateral fields. Ipsilateral cervical vagotomy interrupted cardiac noxious input to 8/30 (6 E, 2 I) neurons; sequential transection of the contralateral cervical vagus nerve (bilateral vagotomy) eliminated the responses to intrapericardial chemicals in 4/22 (3 E, 1 I) neurons. Spinal transection at C6-C7 segments to interrupt effects of sympathetic afferent input abolished responses to cardiac input in 10/10 (7 E, 3 I) neurons that still responded after bilateral vagotomy. Results of this study support the concept that C1-C2 superficial and deeper spinal neurons play a role in integrating cardiac noxious inputs that travel in both the cervical vagal and/or thoracic sympathetic afferent nerves.
UR - http://www.scopus.com/inward/record.url?scp=0035065743&partnerID=8YFLogxK
U2 - 10.1152/jn.2001.85.4.1522
DO - 10.1152/jn.2001.85.4.1522
M3 - Article
C2 - 11287476
AN - SCOPUS:0035065743
SN - 0022-3077
VL - 85
SP - 1522
EP - 1532
JO - Journal of Neurophysiology
JF - Journal of Neurophysiology
IS - 4
ER -