Characterization of responses of T2-T4 spinal cord neurons to esophageal distension in the rat

1993 ◽  
Vol 69 (3) ◽  
pp. 868-883 ◽  
Author(s):  
I. Euchner-Wamser ◽  
J. N. Sengupta ◽  
G. F. Gebhart ◽  
S. T. Meller

1. Three hundred fifty neurons in the T2-T4 spinal segments of 38 intact, pentobarbital sodium-anesthetized, pancuronium-paralyzed male rats were examined for somatic receptive fields and responses to midthoracic esophageal distension (ED). Recordings were made at a depth of 0.1–1.45 mm from the dorsal spinal cord surface and from the midline to approximately 1.0 mm lateral. 2. Fifty-six of the 350 total neurons (16%) responded to ED, produced by air inflation of a latex balloon (0.5–1.5 ml). Most of these 56 neurons (84%) were excited by ED, and all except one were excited at a short latency (< 2 s) to stimulus onset. The response to ED in about one-half of all excited neurons terminated abruptly with termination of the stimulus; the other neurons exhibited an afterdischarge of 5 to > 80 s. Repeated ED at a constant intensity (1.25 ml, 30 s every 6 min) produced stable and reproducible responses of neurons excited by ED. Twenty-one percent of neurons that responded to ED were antidromically invaded from the spinomedullary junction. 3. Graded ED (0.5–1.5 ml, 30 s every 6 min) produced linear and accelerating stimulus-response functions in the 29 neurons tested. The mean threshold for distension, determined with a least-squares regression analysis, was extrapolated to near 0.5 ml of distending volume, and no difference in response threshold was found between neuronal groups with or without after-discharge. 4. The spontaneous activity of 7 of the 56 neurons (12.5%) that responded to ED was inhibited by the stimulus. Stimulus-response functions for four neurons inhibited by ED were intensity dependent. The spontaneous activity of these neurons was inhibited to a mean of 24.5% of the prestimulus control by 1.25 ml ED. 5. Two neurons of the total sample of 56 (3.5%) responded to ED (1.50 ml) in a biphasic excitatory-inhibitory manner. The excitatory component of excitatory-inhibitory neurons encoded the intensity of ED; the inhibitory component during the second half of ED was apparent only at greater distending volumes (1.25–1.5 ml). 6. Somatic receptive fields were found for 303/350 neurons, and 98% were located on the thorax and proximal forearm (all ipsilateral). Five neurons in T2–T4 spinal segments had their cutaneous receptive fields located on caudal parts of the body (tail, hindleg, scrotum).(ABSTRACT TRUNCATED AT 400 WORDS)

1985 ◽  
Vol 53 (4) ◽  
pp. 1059-1078 ◽  
Author(s):  
C. N. Honda

One hundred and sixty extracellularly and intracellularly recorded unitary discharges from the sacral or caudal spinal segments of 30 anemically decerebrated cats were studied to examine the effects of somatic and visceral afferent stimulation on neurons near the central canal (CC). The recorded unitary activity was histologically verified (by dye marks or horseradish peroxidase, HRP) as having come from the gray matter surrounding the CC that approximates Rexed's lamina X. In the absence of intentional stimulation or apparent injury by the recording electrode, 62% of the units exhibited ongoing discharges. Each unit was tested for responses to the stimulation of somatic (cutaneous and subcutaneous) and visceral (bladder and colon) structures. Seventy-six (48%) of the units responded exclusively to the stimulation of somatic receptive fields, and 10 (6%) of the units were selectively responsive to stimulation of the pelvic viscera. The activity of the remaining 74 (46%) was influenced by activity in both somatic and visceral afferent fibers. Eighteen of the 160 neurons were intracellularly marked with HRP. Based on perikaryal size and dendritic extent, it was possible to divide these cells into two partially overlapping groups. One group consisted of seven neurons with small to medium-sized perikarya, dendritic arbors largely restricted to the gray matter surrounding the CC, and small, singular somatic receptive fields. The second group comprised 11 cells with medium to large-sized soma and dendrites extending out of lamina X. These larger neurons usually possessed multiple, widely distributed somatic receptive fields. The principal finding of the present study is that in the sacral spinal cord many cells near the CC receive primary afferent inputs converging from a wide range of receptor types in somatic and visceral structures. Such neurons are capable of integrating afferent information from somatic structures on both sides of the body with information originating in pelvic viscera and midline regions such as the genitals.


1987 ◽  
Vol 57 (6) ◽  
pp. 1867-1892 ◽  
Author(s):  
T. J. Ness ◽  
G. F. Gebhart

The cutaneous receptive fields, long ascending projections, and responses to colorectal distension (20-100 mmHg) and tail movement of 252 neurons in spinal segments L6-S1 were characterized in pentobarbital- or halothane-N2O anesthetized, physiologically intact male rats. Seventeen additional neurons were studied in spinalized rats. Neurons studied were located within 0.5 mm of the midline at depths 0.2-1.4 mm from the spinal cord dorsum and included the area immediately dorsal and lateral to the central canal. Colorectal distension and/or antidromic invasion from the contralateral ventral quadrant of the cervical spinal cord were used as search stimuli. One hundred seventeen neurons responded to noxious colorectal distension; many had long ascending projections and convergent somatic input from deep joint receptors, ipsilateral perianal/scrotal cutaneous receptive fields, or both. Stimulus-response functions (SRFs) of 45 neurons to graded colorectal distension were linear, allowing extrapolation of threshold distending pressures to neuronal response. Neurons responsive to colorectal distension were subdivided into four classes based on their initial response colorectal distension (75-80 mmHg, 20 s). Short-latency abrupt (SL-A) neurons were excited at short latency by colorectal distension; activity abruptly returned to base line following termination of distension. Most SL-A neurons had long ascending projections, convergent somatic receptive fields, and 4/6 tested were excited by bradykinin administered intraarterially. The threshold distending pressure, estimated from the SRFs of 19 SL-A neurons, extrapolated to 2.7 mmHg. Short-latency sustained (SL-S) neurons were also excited at short latency by colorectal distension, but responses were sustained for 4–120 s following termination of distension. Most SL-S neurons had long ascending projections, convergent somatic receptive fields, and 18/20 tested were excited by intraarterial bradykinin. The threshold distending pressure, estimated from the SRFs of 20 SL-A neurons, extrapolated to 17.0 mmHg. Long-latency (LL) neurons were excited by colorectal distension at long latency following the onset of distension. No LL neurons had demonstrable long ascending projections, and few had convergent excitatory somatic fields. Three of five LL neurons were excited by intraarterial bradykinin. The threshold distending pressure, estimated from the SRFs of six LL neurons, extrapolated to 9.8 mmHg. Inhibited (INHIB) neurons were spontaneously active and were inhibited by colorectal distension.(ABSTRACT TRUNCATED AT 400 WORDS)


1993 ◽  
Vol 69 (2) ◽  
pp. 557-568 ◽  
Author(s):  
K. J. Berkley ◽  
G. Guilbaud ◽  
J. M. Benoist ◽  
M. Gautron

1. Previous studies in the rat and other species have shown that neurons in and near the ventrobasal complex (VB) can be activated by various visceral as well as somatic stimuli. 2. This study examined the responses of 84 single neurons in and near the rostral 2/3 of VB in 19 adult female rats in estrus to mechanical stimulation of the skin (brush, pressure, noxious pinch) and 4 different visceral stimuli, as follows: distension of both uterine horns, mechanical probing of the vagina, gentle pressure against the cervix, and distension of the colon. The rats were studied while under moderate gaseous anesthesia (33% O2-67% N2O + 0.5% halothane) and paralyzed (pancuronium bromide). 3. Of 77 neurons tested with both somatic and visceral stimuli, 70 were responsive to one type and/or the other. Responses to somatic stimuli were immediate with brief afterdischarges to the pinch stimuli. In contrast, responses to visceral stimuli were delayed an average of 9 s with long afterdischarges averaging 2 min. Most viscerally responsive neurons (74%) had somatic receptive fields, often (44%) to noxious pinch. 4. Of the 70 responsive neurons, 43 (61%) responded to 1 or more of the 4 visceral stimuli, primarily with excitation. Most of these 43 neurons (71%) were responsive to uterine distension, whereas fewer responded to stimulation of the cervix (45%), vagina (29%), or colon (34%). 5. Viscerally responsive neurons were preferentially located in regions bordering or near VB. Only 6 of 22 neurons within the core of VB (27%) responded to visceral stimuli, in contrast with 37 of 48 neurons bordering or near VB (77%). 6. The six viscerally responsive neurons within VB all had somatic receptive fields located primarily on the caudal part of the body and were responsive to only one or two of the four visceral stimuli, usually the uterus. The 37 viscerally responsive neurons bordering or near VB were of 3 types. Neurons of the first type (n = 15) were scattered throughout the areas bordering VB and responded to both somatic and visceral stimuli much like VB neurons, except that they showed more visceral convergence. Neurons of the second type (n = 11) were concentrated at the rostral and dorsal borders of VB and responded only to visceral stimuli, mainly the uterus. Neurons of the third type (n = 11) were concentrated ventrally and had very complex, long-lasting and history-dependent response characteristics to both visceral and somatic stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)


1986 ◽  
Vol 55 (1) ◽  
pp. 76-96 ◽  
Author(s):  
R. P. Yezierski ◽  
R. H. Schwartz

Recordings were made from 90 identified spinomesencephalic tract (SMT) cells in the lumbosacral spinal cord of cats anesthetized with alpha-chloralose and pentobarbital sodium. Recording sites were located in laminae I-VIII. Antidromic stimulation sites were located in different regions of the rostral and caudal midbrain including the periaqueductal gray, midbrain reticular formation, and the deep layers of the superior colliculus. Twelve SMT cells were antidromically activated from more than one midbrain level or from sites in the medial thalamus. The mean conduction velocity for the population of cells sampled was 45.2 +/- 21.4 m/s. Cells were categorized based on their responses to graded intensities of mechanical stimuli and the location of excitatory and/or inhibitory receptive fields. Four major categories of cells were encountered: wide dynamic range (WDR); high threshold (HT); deep/tap; and nonresponsive. WDR and HT cells had excitatory and/or inhibitory receptive fields restricted to the ipsilateral hindlimb or extending to other parts of the body including the tail, forelimbs, and face. Some cells had long afterdischarges following noxious stimulation, whereas others had high rates of background activity that was depressed by nonnoxious and noxious stimuli. Deep/tap cells received convergent input from muscle, joint, or visceral primary afferent fibers. The placement of mechanical lesions at different rostrocaudal levels of the cervical spinal cord provided information related to the spinal trajectory of SMT axons. Six axons were located contralateral to the recording electrode in the ventrolateral/medial or lateral funiculi while two were located in the ventrolateral funiculus of the ipsilateral spinal cord. Stimulation at sites used to antidromically activate SMT cells resulted in the inhibition of background and evoked responses for 22 of 25 cells tested. Inhibitory effects were observed on responses evoked by low/high intensity cutaneous stimuli and by the activation of joint or muscle primary afferent fibers. Based on the response and receptive-field properties of SMT cells it is suggested that the SMT may have an important role in somatosensory mechanisms, particularly those related to nociception.


2003 ◽  
Vol 90 (5) ◽  
pp. 3161-3167 ◽  
Author(s):  
P. V. Zelenin ◽  
E. L. Pavlova ◽  
S. Grillner ◽  
G. N. Orlovsky ◽  
T. G. Deliagina

In the lamprey (a lower vertebrate), motor commands from the brain to the spinal cord are transmitted through the reticulospinal (RS) and vestibulospinal (VS) pathways. The axons of larger RS neurons reach the most caudal of approximately 100 spinal segments, whereas the VS pathway does not descend below the 15th segment. This study was carried out to compare functional projections of RS and VS neurons in the rostral spinal segments that the neurons innervate together. To reveal these projections, individual RS or VS neurons were stimulated, and the responses of different groups of spinal motoneurons were recorded in ventral root branches to dorsal and ventral parts of myotomes. The responses were detected using a spike-triggered averaging technique on the background of ongoing motoneuronal activity. Individual RS and VS neurons exerted uniform effects on segmental motor output within this rostral part of the spinal cord. The effects of VS neurons on different groups of motoneurons were weaker and less diverse than those of RS neurons. The results indicate that VS neurons are able to elicit a flexion of the rostral part of the body and to turn the head in different planes without affecting more caudal parts. By contrast, larger RS neurons can elicit head movement only together with movement of a considerable part of the body and thus seem to be responsible for formation of gross motor synergies.


1984 ◽  
Vol 51 (3) ◽  
pp. 467-480 ◽  
Author(s):  
W. D. Willis ◽  
K. D. Gerhart ◽  
W. S. Willcockson ◽  
R. P. Yezierski ◽  
T. K. Wilcox ◽  
...  

Recordings were made from 132 raphe- and reticulospinal tract neurons in the medial part of the lower brain stem in 32 anesthetized monkeys. Recording sites were in the nucleus raphe magnus, the rostral nucleus raphe obscurus, and the reticular formation adjacent to the raphe. The neurons were identified by antidromic activation from the upper lumbar spinal cord. Of the population sampled, 83 cells were activated antidromically from the left dorsal lateral funiculus (DLF), 32 from the right DLF, and 17 from both sides. The mean latency for antidromic activation was 8.2 +/- 7.1 ms, corresponding to a mean conduction velocity of 22.8 m/s. No conduction velocities characteristic of unmyelinated axons were observed. Collision tests indicated that raphe-spinal axons that bifurcated to descend in both DLFs branched within the spinal cord. The effects of stimulation in the periaqueductal gray (PAG) or adjacent midbrain reticular formation were tested on 102 spinally projecting neurons in the medial medulla. Of these, 60 cells were excited, 9 cells were inhibited, 8 showed mixed excitation and inhibition, and 25 cells were unaffected. The mean latency for excitation was 11.6 ms and for inhibition, 17.8 ms. Threshold for excitation of raphe- and reticulospinal neurons ranged from 50 to 400 microA. Raphe- and reticulospinal tract cells could often (31/46 cells tested) be excited following stimulation in the ventral posterior lateral nucleus of the thalamus. The mean latency of excitation was 35.6 ms (range, 6-112 ms). Receptive fields could be demonstrated for 80 raphe- and reticulospinal cells, while 48 neurons possessed no demonstrable cutaneous receptive field. Most cells had large excitatory receptive fields, often encompassing the surface of the entire body and face. Some neurons had complex excitatory and inhibitory receptive fields, whereas other cells had large inhibitory receptive fields over much of the surface of the body and face. For most cells (52/55) with excitatory receptive fields, the only effective stimuli were noxious mechanical or noxious heat stimuli. Nonnoxious mechanical stimuli, such as brushing the skin, were capable of activating only a few (3/55) raphe- and reticulospinal neurons, and these were more effectively excited by noxious stimuli.(ABSTRACT TRUNCATED AT 400 WORDS)


2002 ◽  
Vol 87 (1) ◽  
pp. 103-112 ◽  
Author(s):  
Volker Neugebauer ◽  
Weidong Li

Pain has a strong emotional dimension, and the amygdala plays a key role in emotionality. The processing of nociceptive mechanical and thermal information was studied in individual neurons of the central nucleus of the amygdala, the target of the spino-parabrachio-amygdaloid pain pathway and a major output nucleus of the amygdala. This study is the first to characterize nociceptive amygdala neurons with input from deep tissue, particularly the knee joint. In 46 anesthetized rats, extracellular single-unit recordings were made from 119 central amygdala neurons that were activated orthodromically by electrical stimulation in the lateral pontine parabrachial area and were tested for receptive fields in the knee joints. Responses to brief mechanical stimulation of joints, muscles, and skin and to cutaneous thermal stimuli were recorded. Receptive-field sizes and thresholds were mapped and stimulus-response functions constructed. Neurons in the central nucleus of the amygdala with excitatory input from the knee joint ( n = 62) typically had large symmetrical receptive fields in both hindlimbs or in all four extremities and responded exclusively or preferentially to noxious mechanical stimulation of deep tissue ( n = 58). Noxious mechanical stimulation of the skin excited 30 of these neurons; noxious heat activated 21 neurons. Stimulus-response data were best fitted by a sigmoid nonlinear regression model rather than by a monotonically increasing linear function. Another 15 neurons were inhibited by noxious mechanical stimulation of the knee joint and other deep tissue. Fifteen neurons had no receptive field in the knee but responded to noxious stimulation of other body areas; 27 nonresponsive neurons were not activated by natural somesthetic stimulation. Our data suggest that excitation is the predominant effect of brief painful stimulation of somatic tissue on the population of central amygdala neurons with knee joint input. Their large symmetrical receptive fields and sigmoid rather than monotonically increasing linear stimulus-response functions suggest a role of nociceptive central amygdala neurons in other than sensory-discriminative aspects of pain.


1951 ◽  
Vol 7 (3) ◽  
pp. 271-279 ◽  
Author(s):  
J. T. EAYRS

The growth of the body and central nervous system and the emergence of stereotyped behaviour have been studied in male and female rats during the first 24 days of life. The effects of daily injections of equine gonadotrophin on these measures have also been investigated. The weight of the body and of the central nervous system was significantly less in the female than in the male. The daily administration of 10 i.u. of equine gonadotrophin was without effect on either. The movements of the trunk and limbs concerned in the body-righting reflex became coordinated more slowly in the gonadotrophin-injected animals than in their litter-mate controls. At 15 days old, male rats were able to right in mid-air more successfully than litter-mate females. The placing reflex appeared earlier in the male than in the female. Its appearance was accelerated in the females given gonadotrophin, but not in the males. In the ventral funiculus of the spinal cord of 24-day-old experimental animals, the axis cylinders occupied more space relative to that occupied by myelin than did those of the controls. The total amount of myelin present was unchanged. There was no sex difference in the progress of myelination in the spinal cord. The significance of these findings in relation to the secretion of sex hormones is discussed. It is suggested that the secretion of androgen may be responsible for an acceleration of nervous maturation.


1988 ◽  
Vol 60 (4) ◽  
pp. 1419-1438 ◽  
Author(s):  
T. J. Ness ◽  
G. F. Gebhart

1. One-hundred thirty-two neurons responsive to colorectal distension in the dorsal horn of the T13-L2 spinal segments of 35 spinalized and 7 intact, deeply pentobarbital-sodium-anesthetized rats were characterized for convergent cutaneous receptive fields, long ascending projections and responses to the intra-arterial administration of the algesic peptide bradykinin. All but 9 neurons had an identifiable excitatory cutaneous receptive field; all receptive fields were located on the lower abdomen, flank, and dorsal body surface. Electrical stimulation in the cutaneous fields of 28 neurons demonstrated that neurons responsive to colorectal distension receive afferent information carried by A- and C-fibers. Stimulus-response functions (SRFs) of 52 neurons excited by graded colorectal distension (20-100 mmHg, 20 s) were monotonic and accelerating, allowing extrapolation of threshold distending pressures to neuronal response. Neurons were subdivided into four classes based upon their response to an 80-mmHg, 20-s colorectal distension search stimulus. 2. Short-latency abrupt [SL-A] neurons (spinalized, n = 46; intact, n = 9) were excited at short latency; activity abruptly returned to base line on termination of distension. Six of 9 neurons in intact rats had long ascending projections as demonstrated by antidromic invasion from the contralateral, ventrolateral caudal medulla. Responses of SL-A neurons to colorectal distension were significantly greater in spinalized than in intact rats. Fifty-three of 55 SL-A neurons had convergent excitatory cutaneous receptive fields and most were responsive to both noxious and nonnoxious stimuli. Ten of 13 neurons tested were excited by intra-arterial bradykinin. The threshold distending pressure, determined from the SRFs of 29 neurons in both the spinalized and intact states, extrapolated to near 0 mmHg. 3. Short-latency sustained (SL-S) neurons (spinalized, n = 31; intact, n = 11) were also excited at short latency in response to colorectal distension, but responses were sustained for 4-50 s following termination of the distending stimulus. Nine of 11 SL-S neurons in intact rats had long ascending projections. All 42 SL-S neurons were spontaneously active and 41 of 42 had convergent excitatory cutaneous receptive fields, excited exclusively by noxious stimuli (n = 29) or excited by both noxious and nonnoxious stimuli (n = 12). Responses to colorectal distension and spontaneous activity were significantly greater in spinalized rats. Twelve of 12 neurons tested were excited by intra-arterial bradykinin.(ABSTRACT TRUNCATED AT 400 WORDS)


Author(s):  
Stephen R. Humble

Devor and Wall, in a pioneering electrophysiological study, examined the change in somatic receptive fields in the dorsal horn of the spinal cord after nerve injury. Rather than the anticipated loss of an area of electrophysiological perception, the system demonstrated ‘plasticity’ whereby novel receptive fields, remote to the corresponding area of damage, were evident. The authors postulated that this neuroplasticity occurred via a hitherto undefined spinal mechanism, which lead to an explosion of interest and research to elucidate the mechanisms of central plasticity. In this truly landmark paper, the idea of the nervous system being an inherently ‘hard-wired’ structure was made redundant and the concept of neuroplasticity was given robust form.


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