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Biomedical subjects

R D Foreman

Publications and source records attributed to R D Foreman.

At least 109 records · Page 6Linked to original sources
PubMed1982

Fastigial nucleus stimulation and excitatory spinal sympathetic activity in dog.

To locate the cerebellar-activated descending sympathetic pathways in the dog the fastigial nucleus (FN) was electrically stimulated in chloralose-anesthetized dogs while recording from sympathetic preganglionic neurons. Physiological interventions included lesions in the dorsolateral funiculus (DLF) of the spinal cord, myelotomy, arterial pressure changes, bilateral occlusion of the carotid arteries, and administration of clonidine. Multiunit activity at the T2 on T3 white ramus communicans was recorded on-line during rest and FN stimulation. Descending sympathetic activity (averaging 3.5 m/s) in the DLF was increased in response to FN stimulation but was significantly reduced by ipsilateral and eliminated by bilateral FN lesions. When testing for the effects of baroreceptor reflexes on the sympathetic pathway phenylephrine-induced hypertension decreased, but moderate hemorrhage increased the amount of preganglionic activity at rest and during FN stimulation. During hypertension and simultaneous carotid artery occlusion the amount of sympathetic activity that could be evoked was comparable to that evoked during normotensive states. Clonidine (IV) reduced the FN sympathoexcitation, but direct stimulation of the DLF indicated that clonidine had sympathoinhibitory activity at both medullary and spinal sites. In summary, rostral FN primarily excited ipsilateral descending sympathetic pathways in DLF, and this sympathoexcitation was partially inhibited by baroreceptor intervention.

Animals↗
PubMed1982

Responses of thoracic spinothalamic neurons to intracardiac injection of bradykinin in the monkey.

Bradykinin stimulates afferent fibers arising in the heart and may be involved in the mediation of anginal pain and the pain associated with myocardial infarction. The sensation of pain requires that noxious information reach the brain. The purpose of the present study was to determine whether the spinothalamic tract is involved in transmitting noxious information from the heart to the brain. Bradykinin was injected (0.3-3.5 micrograms/kg) into the heart via a catheter in the left atrium while we recorded from single spinothalamic cells in the C8 to T5 spinal segments. Thirty-one of 41 cells responded to bradykinin. The responses of 12 cells were characterized by both an increase in discharge rate and entrainment of cell activity with the cardiac cycle. Eighteen cells responded with only an increased rate, and one cell exhibited only entrainment of cell activity with the cardiac cycle. The mean onset of increased cell activity occurred 15 seconds following drug injection, and the average duration of the response was 54 seconds. Thirty cells increased their mean discharge rate from 11 +/- 2.5 to 29 +/- 4.4 spikes/second. Thus, some spinothalamic cells probably received input from both mechanosensitive and chemosensitive afferents. Tachyphylaxis to repeated doses of bradykinin was observed in 41% of cells. Cells responding to bradykinin had a spontaneous discharge rate that was significantly greater than that of nonresponding cells. Cells did not require input from C-fiber afferents to respond to bradykinin. No statistically significant relationships were found among anatomical locations (laminae and segments) and responses to bradykinin, although cells in lamina I seemed to be less responsive than more ventrally located cells. We conclude that the spinothalamic tract may be involved in the sensation of cardiac pain.

Afferent Pathways↗
PubMed1981

Descending inhibition of spinal neurons in the cardiopulmonary region by electrical stimulation of vagal afferent nerves.

Neurons in the left upper thoracic spinal cord of cats anesthetized with chloralose and relaxed with succinylcholine were activated by electrical stimulation of sympathetic chains or by pinching of the skin. Most neurons were spontaneously active, and 22 of the 51 neurons studied were antidromically activated from the spinomedullary junction, demonstrating their projection to higher centers. Stimulation of the central cut ends of either cervical vagus resulted in inhibition of firing in 26 neurons, acceleration in 6 neurons, both effects in 2 neurons, and no effect in the remaining 17 neurons. The parameters of stimulation determined whether inhibition of facilitation was produced in the two neurons that showed either effect. Two spinal neurons were fired by vagal stimulation with latencies of 16 and 20 msec. Activity in vagal afferent fibers is believed to impinge upon brain stem structures that have been shown by others to cause descending inhibition (and facilitation) of spinothalamic and spinoreticular neurons. This would provide a mechanism for modulation of sensory information from the cardiopulmonary region.

Adrenergic Fibers↗
PubMed1981

Responses of spinothalamic tract cells in the thoracic spinal cord of the monkey to cutaneous and visceral inputs.

Somatovisceral convergence was demonstrated in recordings from 15 of 16 spinothalamic tract cells in the lower thoracic spinal cords of anesthetized monkeys. Inputs were produced by mechanical (or sometimes electrical) stimulation of the skin over the lower trunk and by electrical stimulation of the greater splanchnic nerve through a buried electrode. The volley in the greater splanchnic nerve was monitored using a buried electrode on the sympathetic chain. Spinothalamic tract cells could be excited by activity in A delta and C fibers, but no effects produced by A beta fibers were noted. In some cases inhibitory effects were observed due to movement of hair on the trunk, and inhibitory interactions could be demonstrated between cutaneous and visceral afferent volleys.

Animals↗
PubMed1981

Convergence of cutaneous and pelvic visceral nociceptive inputs onto primate spinothalamic neurons.

The responses of 66 primate spinothalamic neurons to natural stimulation the the urinary bladder and testicle were studied with extracellular recording techniques in order to elucidate the neural basis for referral of visceral pain. Thirty-eight out of 53 cells located at the thoraco-lumbar junction or in sacral segments responded to noxious cutaneous stimuli, and 84% of these also exhibited phasic and/or tonic excitatory responses to distension of the urinary bladder. Seventeen out of 20 of these units, all located at the thoraco-lumbar junction, were excited by compression of the ipsilateral testicle. The response was graded with the compressive force. Excitatory responses to noxious heat and an irritant chemical (KC1) applied to the exposed testicular surface were also observed. Twelve sacral units having inputs from deep receptor of the tail exhibited mixed excitatory and inhibitory responses to bladder distension. A further 2 cells located at the thoracolumbar junction responded only to cutaneous tactile stimuli, and 13 cells located at the lumbosacral enlargement were tonically inhibited by bladder distension. It is concluded that spinothalamic neurons that convey nociceptive input from the skin may also respond to noxious visceral stimuli. Such viscero-somatic convergence provides a neural substrate for the phenomenon of cutaneous referral of visceral pain.

Animals↗
PubMed1980

Effects of coronary artery occlusion on thoracic spinal neurons receiving viscerosomatic inputs.

Action potentials of single cells in the gray matter of the T2 to T4 spinal segments of chloralose-anesthetized cats were recorded during occlusion of the anterior descending branch of the left coronary artery. Only cells responding both to visceral and somatic afferent inputs were examined. In 53% of the cells the discharge frequency was unaffected by coronary artery occlusion (CAO). The remaining 47% could be classified by four response patterns: 1) in 18% frequency increased immediately following the onset of CAO; 2) in 22%, frequency increased 13.6 +/- 3.3 (SE) s after CAO and the increased frequency usually was associated with changes in the configuration of the electrocardiogram; 3) in 3%, frequency increased at the onset of CAO and then increased more approximately 11 s later; 4) in 4%, inhibition of spontaneous activity occurred during CAO. A noxious pinch applied to the somatic receptive field maximally excited 94% and inhibited 6% of the cells. Since viscerosomatic convergence provides a basis for referred pain, these cells could potentially be involved with transmission of nociceptive information to regions of the brain that integrate pain sensations.

Action Potentials↗
PubMed1980

Neural control of the heart during arrhythmias and exercise.

Involvement of neural activity during cardiovascular adjustments and during arrhythmias can be determined by comparing the results of cardiovascular changes after lesions are made in nuclei or pathways of the central nervous system or ablations of ganglia or nerves are made in the peripheral nervous system. The neural effects can be exaggerated if these systems are forced to perform at higher levels during a stressful situation. The purpose of this presentation is to discuss the responsiveness of the cardiovascular system after left or right stellate ganglionectomy and after lesions are made in the fastigial nucleus of the cerebellum in dogs stressed with submaximal exercise. These dogs are implanted with instruments that are designed to measure cardiovascular responses. Hypotheses for potential neural mechanisms are generated from the results of chronic animal studies, and these mechanisms are tested in anesthetized dogs and cats. Electrical stimulation of ascending and descending pathways in the central nervous system and stimulations such as coronary occlusion and mechanical probing are used to activate neural mechanisms in the anesthetized state. A general schema concerning the results of our studies provides further information about our approach to understanding the physiological role that the central nervous system may exert on the cardiovascular system during stress.

Afferent Pathways↗
PubMed1979

Field potentials and excitation of primate spinothalamic neurones in response to volleys in muscle afferents.

1. In anesthetized monkeys, stimulation of muscle afferents results in a sequence of cord dorsum potentials. These include a group I volley followed by several negative potentials called here the NI, NII and NIII waves. 2. Evidence based on the effects of graded stimulus strengths, measurements of latencies, and the results of anodal blockade of large muscle afferents indicate that the NI, NII and NIII waves are evoked, respectively, by group I, II and III muscle afferents. 3. The NII and NIII waves appear to be confined to the lumbosacral enlargement when evoked by hind limb muscle afferents. However, the group I volley and NI wave can be detected at least as far rostrally as L 3. 4. The NII and NIII waves were mapped in the depth of the cord. The maxima for these waves were found in the neck of the dorsal horn. The waves reversed to become positive in the ventral horn. 5. Using graded electrical stimulation of muscle nerves it was possible to demonstrate that a few spinothalamic tract neurones could be activated monosynaptically by group I volleys; other spinothalamic cells may have been activated polysynaptically by group I volleys. The lack of any substantial excitation of spinothalamic neurones by intra-arterial injections of succinylcholine suggests that these group I actions may have been due to group Ib afferents from Golgi tendon organs. 6. The most potent excitation of spinothalamic tract cells was due to the action of middle sized and small muscle afferents. Evidence was obtained for an excitatory action of group II, III and IV afferents. There was a good correlation between the effects of graded stimulation in evoking discharges in separate bursts associated with the arrival of volleys in group II and group III afferents and the generation of the NII and NIII waves. 7. Some spinothalamic neurones, including several located in lamina I, were unaffected by the muscle afferent volleys used. It is suggested that such neurones might help to signal well localized pain, whereas the cells which respond to a variety of cutaneous and muscle afferents might be involved in signalling poorly localized pain which is subject to referral.

Animals↗
PubMed1979

Effects of mechanical and chemical stimulation of fine muscle afferents upon primate spinothalamic tract cells.

1. Injections of algesic chemicals were made into the arterial circulation of the triceps surae muscles in anaesthetized monkeys. 2. The responses of a sample of primary muscle afferents suggest that what is known about the activation of muscle afferents in the cat by algesic agents applies also to the monkey. One exception to this is the activation of many group I afferents by KCl in the monkey, but not in the cat. 3. Many spinothalamic tract cells were powerfully excited by the intra-arterial injection of algesic chemicals (bradykinin, 5-hydroxytryptamine (5-HT), KCl) in preparations in which the hind limb was denervated except for the nerves to the triceps surae muscles. The excitatory action of bradykinin had a slower time course than did that of 5-HT or KCl. 4. A number of the spinothalamic tract cells which failed to respond to chemical activation of muscle afferents were located in lamina I of the spinal cord. 5. Repeated injections of bradykinin produced similar responses, whereas the effects of 5-HT injections showed marked tachyphylaxis. 6. No evidence was obtained that activation of muscle spindle afferents by succinylcholine injections resulted in the excitation of spinothalamic tract neurones in the population sampled. 7. Injections of hypertonic NaCl into muscle or tendon produced a prolonged excitation of many spinothalamic tract cells. 8. It is concluded that a substantial proportion of primate spinothalamic tract cells receive a convergent input from cutaneous and muscle receptors. The muscle receptors involved appear to include primary afferents of group III and IV calibre. The possibility is suggested that such cells could play a role in the production of poorly localized pain.

Animals↗
PubMed1978

Categories of axons in the inferior cardiac nerve of the cat.

Myelinated and unmyelinated axons in the inferior cardiac nerve of the cat were examined to determine how many axons were (1) sensory, (2) preganglionic sympathetic, and (3) postganglionic sympathetic. In one group of cats, a segment was removed from the middle of the inferior cardiac nerve as a control, and the proximal and distal stumps of the nerve were examined one week later. In another group of cats, the control segment of nerve was removed and the first thoracic white ramus communicans and sympathetic trunk were cut proximal to the stellate ganglion, followed in one week by examination of the proximal and distal stumps of the inferior cardiac nerve. In still another group of cats, the first five thoracic spinal nerves were cut just distal to the dorsal root ganglion. The counts of myelinated and unmyelinated axons after these surgical procedures indicated that, in the cat inferior cardiac nerve, all or almost all of the approximately 30,000 unmyelinated axons and 10 percent of the myelinated axons are postganglionic sympathetic fibers, and that approximately 90 percent of the myelinated axons are sensory.

Animals↗
PubMed1977

Spinal cord potentials evoked by cutaneous afferents in the monkey.

1. Negative intermediary cord potentials and the equivalent field potentials were recorded from the surface or within the monkey lumbosacral spinal cord in response to stimulation of myelinated afferent fibers in cutaneous or mixed nerves of the hindlimb. 2. Cord potentials resembling the N1 and N2 potentials described in the cat spinal cord were found but, in addition, activation of small myelinated fibers produced a later potential named here the N3-wave. By use of a subtraction technique, it is estimated that the N3-wave has a latency of 11.4 (+/- 3.5 SD) ms from the time of arrival of the volley in the largest affs at 9 (+/- 3) ms after its onset, and the wave lasts 23 (+/- 5.7) ms. 3. The N3-wave is not lost following spinal cord transection, but may instead be enhanced. It is thus due to neural circuitry intrinsic to the lumbosacral spinal cord. 4. The longitudinal distribution of the N3-wave is similar to that of the N1- and N2-waves. 5. The field potential associated with the N3-wave and recorded from within the spinal cord has two negative foci in some animals: near the dorsalmost part of the dorsal horn and in an area equivalent to Rexed's laminae IV-VI. The field potential reverses in sign in the ventral horn. 6. The N3-wave is evoked by Adelta fibers. This was shown by grading the stimulus strength, by measuring the conduction delay for producing the wave when stimuli are applied either proximally or distally on the sural nerve, and by showing that the N3-wave persists when the Aalphabeta fibers are anodally blocked. 7. There is often a late burst discharge in spinal neurons, including spinothalamic tract neurons, which can be attributed to Adelta fibers and which corresponds in time to the N3-wave. 8. It is proposed that the N3-wave can be used as a monitor of the central effects of Adelta fibers in the spinal cord.

Animals↗
PubMed1976

Fiber analysis of the feline inferior cardiac sympathetic nerve.

The left inferior cardiac nerves of nine adult cats were examined with the electron microscope. Electrical recordings were also made from four of these nerves. Most of the nerves contained between 25,000 and 40,000 unmyelinated fibers and 30 to 150 myelinated fibers. The diameters of the unmyelinated fibers ranged from 0.1 mu to 1.8 mu with mean diameters ranging from 0.47 to 0.78 mu in the various nerves. The myelinated fibers ranged in diameter from 1 mu to 9 mu with a mean difference of approximately 3 mu. Electrical recordings showed two peaks in both the C fiber and the Adelta fiber compound action potentials. Conduction velocities of the two C fiber peaks were approximately 0.7 and 0.9 m/sec. The two groups of A delta fibers had conduction velocities of approximately 7 and 16 m/sec.

Animals↗
PubMed1976

Effect of dorsal root section on the arrhythmias associated with coronary occlusion.

In anesthetized vagotomized dogs and cats the circumflex and/or the anterior descending coronary artery were briefly occluded (5-90 s), and ectopic beats occurring during the occlusion and for 60 s following release were counted. When arrhythmias were regularly produced for a given occlusion, the dorsal roots from C8 to T5 were transected and the occlusions were repeated. Dorsal root section produced minor changes in heart rate and blood pressure. Dogs and cats did not differ in their responses. Dorsal root section was performed in eight animals and decreased the absolute number of ectopic beats by 63 +/- 19% compared to control values (P less than 0.05). In four animals the effect on ectopic beats produced by repeated occlusions without dorsal root section was investigated and found to be increased by 35 +/- 24% compared to contrl values. Most of the somatic afferents contained in the dorsal roots were damaged by the surgical preparation. Therefore, repeated occlusions and interruption of somatic afferents do not appear to have influenced our results. The arrhythmogenic interaction between the local effects of myocardial ischemia and the sympathetic activity, whose outlow contained in the ventral roots remained intact, was still possible after dorsal root section and this explains why ectopic beats were reduced but not almost suppressed as is usually the case after bilateral stellectomy. We conclude that dorsal root section reduces the number of ectopic beats associated with short-lasting coronary artery occlusions and that the most likely mechanism is the interruption of the cardiocardiac sympathetic reflex which depends upon afferent fibers running through the dorsal roots.

Animals↗