Biomedical subjects

Robert D Foreman

Publications and source records attributed to Robert D Foreman.

41 records · Page 3Linked to original sources

PubMed1995

Phrenic afferent input excites C1-C2 spinal neurons in rats.

Effects of electrical stimulation of the ipsilateral phrenic nerve above the heart were determined on cells in the C1-C2 spinal cord segments of 27 rats anesthetized with pentobarbital. Forty-five cells that responded to this stimulus were included in this study. These cells then were examined at the same stimulus parameters for effects of stimulating the ipsilateral phrenic nerve below the heart, the contralateral phrenic nerve above the heart, and/or the left (ipsilateral) cervical vagus nerve. Ipsilateral phrenic nerve stimulation below the heart had no effect on 20 of 20 cells tested. Seven of 16 cells tested for effects of contralateral phrenic nerve stimulation above the heart were excited and activity of 9 cells was unaffected. Activity changes and activation latencies were not significantly different in the 7 cells excited by both ipsilateral and contralateral phrenic nerve stimulation. Thirty-seven of 45 cells excited by ipsilateral phrenic nerve stimulation also were excited by stimulation of the left cervical (ipsilateral) vagus nerve. The mean increase in cell activity was significantly greater following vagal nerve stimulation compared to phrenic nerve stimulation, and mean activation latency was significantly longer for vagal stimulation. Excitatory receptive somatic fields were classified for 35 cells. Somatic field locations for most cells (80%) included the ipsilateral neck and jaw. Activity of 26 cells was increased by both noxious pinch and brushing the hair, activity of 6 cells was increased only by noxious pinch, and activity of 3 cells was increased only by brushing the hair. Results of this study indicate that there are afferent fibers in the phrenic nerve above the heart, but not below the heart, that excite cells in the C1-C2 segments of the spinal cord. Most cells also were excited by noxious stimuli applied to their somatic receptive fields. Thus, the phrenic nerve may provide a pathway for referral of pain to the neck and jaw from thoracic structures.

Afferent Pathways↗

PubMed1994

Decreased activity of spontaneous and noxiously evoked dorsal horn cells during transcutaneous electrical nerve stimulation (TENS).

The purpose of this study was to examine the effects of TENS application to somatic receptive fields on spontaneous and noxiously evoked dorsal horn cell activity in alpha-chloralose-anesthetized cat. Carbon-filament microelectrodes were used to record extracellular action potentials from 83 spontaneously discharging cells. Using a commercial TENS unit (Medtronic Eclipse Model 7723), spontaneous cell activity was decreased in 54% (65%) of the cells. Twenty-five (30%) did not respond and 4 (5%) increased activity. It was also shown that for 36 cells which were evoked with either manual pinch (19 cells) or manual clamp (17 cells), cell activity decreased during TENS application. This study shows that dorsal horn neurons which can potentially transmit noxious information to supraspinal levels, can have their cell activity decreased during TENS application to somatic receptive fields. This is consistent with the concept of the 'gate control theory of pain' in that less noxious information would be involved in the pain perception process.

Anesthesia↗

PubMed1992

Vagal afferent fibers excite upper cervical neurons and inhibit activity of lumbar spinal cord neurons in the rat.

Effects of electrical stimulation of the cervical vagus nerve were determined in cervical or lumbar spinal neurons in 27 rats anesthetized with pentobarbital. Ipsilateral cervical vagus stimulation (ICVS) increased activity of 44 neurons in the C1 segment. At the same stimulation parameters, contralateral cervical vagus stimulation (CCVS) either increased, decreased or did not affect activity of C1 neurons that were excited by ICVS. For C1 cells excited by both ICVS and CCVS, the mean latency for activation was significantly longer for CCVS than for ICVS, and ICVS produced a greater degree of excitation than CCVS. In segments C2-C6, 16 of 18 neurons were excited by ICVS and 2 were inhibited. However, CCVS did not excite the C2-C6 neurons but either inhibited or did not affect activity. In 6 cervical cells, a CCVS conditioning stimulus reduced the level of excitation by ICVS (test stimulus). Transection of the C2 or C3 dorsal roots did not significantly affect the excitatory vagal input to C1 cells. Excitatory somatic receptive fields were classified for 60 cervical spinal cells that responded to vagal stimulation. Most (87%) cells were excited by noxious pinch; 29 were wide dynamic range (WDR) cells and 21 were high threshold cells. In contrast to upper cervical neurons, spinothalamic tract (STT) and spinal cells in lumbar segments were not excited by ICVS or CCVS at the stimulation parameters used in this study, but were primarily inhibited by vagal stimulation. Results of this study showed that a group of cells in upper cervical segments were excited by vagal afferents. This excitatory vagal input reaches the C1 segment primarily via an ipsilateral, supraspinal route.

Afferent Pathways↗

PubMed1992

Viscerosomatic convergence onto feline spinal neurons from esophagus, heart and somatic fields: effects of inflammation.

One objective of this study was to examine a mechanism for the inability of patients to distinguish esophageal pain from cardiac pain. Patients with esophageal disease and angina pectoris often perceive pain as originating from the same somatic fields. Another objective was to compare the effect of esophageal distension between animals with a non-inflamed or with an inflamed esophagus. For this study in anesthetized cats, we recorded extracellular action potentials from T2-T7 spinal neurons that responded to intraluminal distension of an untreated or a turpentine-inflamed distal esophagus. Threshold distension volumes were compared between these 2 groups of animals. Neurons also were examined for effects of intracardiac bradykinin injection and somatic stimuli. Results showed that spinal neurons responded to a smaller threshold distension volume when cells in animals with an inflamed distal esophagus were compared to cells in animals with a non-inflamed distal esophagus. Spinal neurons that received input from the distal esophagus also received convergent input from the heart and somatic fields. Our data supported the hypotheses that (1) referred pain from the distal esophagus resulted from activation of the same spinal neurons by visceral and somatic input, (2) pain originating from the distal esophagus and heart might be difficult to distinguish because of viscerosomatic and viscerovisceral convergence onto the same spinal neurons, and (3) an inflamed distal esophagus might be more sensitive to distension than a non-inflamed esophagus.

Afferent Pathways↗

PubMed1991

Effects of vagal afferent stimulation on cervical spinothalamic tract neurons in monkeys.

The purpose of this study was to determine if electrical stimulation of vagal afferents inhibited activity of primate spinothalamic tract (STT) neurons located in cervical segments of the spinal cord. Previous studies show vagal inhibition of STT neurons in more caudal segments of the cord, which receive visceral spinal inputs and somatic inputs from proximal body regions. We hypothesized that activation of vagal afferents would inhibit cervical STT neurons that were excited by cardiopulmonary sympathetic afferents and not inhibit those cells inhibited or unaffected by this visceral input. Because visceral pain is referred to proximal somatic fields, we also hypothesized that STT neurons with excitatory somatic fields confined to distal areas would not be inhibited by vagal stimulation. In 42 cervical STT neurons, we found no difference in effects of vagal stimulation between cells excited or not excited by stimulation of cardiopulmonary sympathetic afferents. Responses to vagal stimulation also were the same for cervical STT cells with proximal or distal somatic fields. Furthermore, there was no difference in the inhibitory effects of vagal stimulation in cervical as compared to thoracic STT neurons. We concluded that vagal afferent stimulation causes a general inhibitory effect at all levels of the spinal cord on neurons which transmit nociceptive information.

Animals↗