Sensory Fibers of the Pelvic Nerve Innervating the Rat's Urinary Bladder

2000 ◽  
Vol 84 (4) ◽  
pp. 1924-1933 ◽  
Author(s):  
V. K. Shea ◽  
R. Cai ◽  
B. Crepps ◽  
J. L. Mason ◽  
E. R. Perl
Keyword(s):  
Urinary Bladder ◽  
Conduction Velocity ◽  
Receptive Fields ◽  
The Body ◽  
Sensory Innervation ◽  
Pelvic Nerve ◽  
Ureterovesical Junction ◽  
Bladder Filling ◽  
Afferent Fibers ◽  
Conduction Velocities

Much attention has been given to the pelvic nerve afferent innervation of the urinary bladder; however, reports differ considerably in descriptions of afferent receptor types, their conduction velocities, and their potential roles in bladder reflexes and sensation. The present study was undertaken to do a relatively unbiased sampling of bladder afferent fibers of the pelvic nerve in adult female rats. The search stimulus for units to be studied was electrical stimulation of both the bladder nerves and the pelvic nerve. Single-unit activity of 100 L6 dorsal root fibers, activated by both pelvic and bladder nerve stimulation, was analyzed. Sixty-five units had C-fiber and 35 units had Aδ-fiber conduction velocities. Receptive characteristics were established by direct mechanical stimulation, filling of the bladder with 0.9% NaCl at a physiological speed and by filling the bladder with solutions containing capsaicin, potassium, or turpentine oil. The majority (61) of these fibers were unambiguously excited by bladder filling with 0.9% NaCl and were classified as mechanoreceptors. All mechanoreceptors with receptive fields on the body of the bladder had low pressure thresholds (≤10 mmHg). Receptive fields of units with higher thresholds were near the ureterovesical junction, on the base of the bladder or could not be found. Neither thresholds nor suprathreshold responses could be related to conduction velocity. Bladder compliance and mechanoreceptor thresholds were influenced by the stage of the estrous cycle: both were lowest in proestrous rats and highest in metaestrous rats. Mechanoreceptors innervating the body of the bladder and the region near the ureterovesical junction showed two patterns of responsiveness to slow bladder filling. One group of units exhibited increasing activity with increasing pressure up to 40 mmHg, while the other group showed a peak in activity at pressures below 40 mmHg followed by a plateau or decrease in activity with increasing pressure. It is proposed that differences in stimulus transduction relate to the different response patterns. Thirty-nine units failed to respond to bladder filling. Eight of these were excited by intravesical potassium or capsaicin and were classified as chemoreceptors. The remaining 31 units were not excited by any stimulus tested. Chemoreceptors and unexcited units had both Aδ and C afferent fibers. We conclude that the pelvic nerve sensory innervation of the rat bladder is complex, may be sensitive to hormonal status, and that the properties of individual sensory receptors are not related in an obvious manner to the conduction velocity of their fibers.

Mechanosensitive properties of pelvic nerve afferent fibers innervating the urinary bladder of the rat

1994 ◽  
Vol 72 (5) ◽  
pp. 2420-2430 ◽  
Author(s):  
J. N. Sengupta ◽  
G. F. Gebhart
Keyword(s):  
Acetic Acid ◽  
Urinary Bladder ◽  
Conduction Velocity ◽  
Regression Line ◽  
High Threshold ◽  
Pelvic Nerve ◽  
Distribution Profile ◽  
Stimulus Response ◽  
C Fibers ◽  
Afferent Fibers

1. Single-unit activity was recorded from S1 dorsal root afferent fibers in pentobarbital-anesthetized rats. In 25 experiments, 245 afferent fibers were identified by electrical stimulation of the pelvic nerve. Fifty-two percent were C fibers (conduction velocity: 1.70 +/- 0.04 m/s; mean +/- SE) and 48% were A delta-fibers (conduction velocity: 11.07 +/- 0.95 m/s). 2. Of 245 pelvic nerve afferent fibers, 92 (38%) responded to noxious urinary bladder distension (UBD; 80 mmHg); 57 of these fibers were C fibers and 35 were A delta-fibers. Forty-four fibers responded to colorectal distension (CRD; 80 mmHg); 32 were C fibers and 12 were A delta-fibers. A total of 39 fibers were identified in the anal mucosa; 3 were C fibers and 36 were A delta-fibers. Seventy fibers (28%) in these experiments were unresponsive to either UBD or CRD or to probing of the anal mucosa; 32 were unmyelinated C fibers and 38 were A delta-fibers. 3. Reproducibility of responses to repeated UBD (80 mmHg, 20 s; 8 trials at 4-min intervals) was tested in 10 fibers. In nine fibers, responses to repeated distension did not change; one fiber exhibited a progressive decrease in response magnitude after the third trial. 4. Of the 92 afferent fibers that responded to UBD, 45 were further characterized for responses to graded intensities of UBD. Forty fibers had some resting activity (1.7 +/- 0.3 impulses/s) and five fibers exhibited no ongoing activity. The response to UBD adapted slowly during the 20-s period of phasic UBD or during slow isotonic filling of the bladder. 5. The stimulus-response function (SRF) of fibers (n = 45) to graded UBD was monotonic < or = 80 mmHg. Thresholds for responses were determined after extrapolation of the least-squares linear regression line to the ordinate, and varied between 0 and 45 mmHg. The frequency distribution profile of thresholds revealed two populations of pelvic nerve afferent fibers in the urinary bladder: a larger group (n = 36) of low-threshold (LT) fibers (5.7 +/- 1.0 mmHg) and a smaller group (n = 9) of high-threshold (HT) fibers (34 +/- 2.5 mmHg). 6. Responses of four LT fibers to graded UBD were tested before and 30 min after instillation of 0.5 ml of 0.5% acetic acid (pH 3) into the bladder. The mean threshold for response of these fibers before instillation of acetic acid (9.4 +/- 3.1 mmHg) more than doubled (to 22.3 +/- 6.7 mmHg) after instillation of acetic acid.(ABSTRACT TRUNCATED AT 400 WORDS)

scholarly journals Cystitis increases colorectal afferent sensitivity in the mouse

2009 ◽  
Vol 297 (6) ◽  
pp. G1250-G1258 ◽  
Author(s):  
Pablo Rodolfo Brumovsky ◽  
Bin Feng ◽  
Linjing Xu ◽  
Carly Jane McCarthy ◽  
G. F. Gebhart
Keyword(s):  
Urinary Bladder ◽  
Treated Group ◽  
Mechanical Sensitivity ◽  
Pelvic Nerve ◽  
Treatment Groups ◽  
Colon Inflammation ◽  
Afferent Fibers ◽  
Peripheral Mechanism ◽  
Inflammatory Soup

Studies in humans and rodents suggest that colon inflammation promotes urinary bladder hypersensitivity and, conversely, that cystitis contributes to colon hypersensitivity, events referred to as cross-organ sensitization. To investigate a potential peripheral mechanism, we examined whether cystitis alters the sensitivity of pelvic nerve colorectal afferents. Male C57BL/6 mice were treated with cyclophosphamide (CYP) or saline, and the mechanosensitive properties of single afferent fibers innervating the colorectum were studied with an in vitro preparation. In addition, mechanosensitive receptive endings were exposed to an inflammatory soup (IS) to study sensitization. Urinary bladder mechanosensitive afferents were also tested. We found that baseline responses of stretch-sensitive colorectal afferents did not differ between treatment groups. Whereas IS excited a proportion of colorectal afferents CYP treatment did not alter the magnitude of this response. However, the number of stretch-sensitive fibers excited by IS was increased relative to saline-treated mice. Responses to IS were not altered by CYP treatment, but the proportion of IS-responsive fibers was increased relative to saline-treated mice. In bladder, IS application increased responses of muscular afferents to stretch, although no differences were detected between saline- and CYP-treated mice. In contrast, their chemosensitivity to IS was decreased in the CYP-treated group. Histological examination revealed no changes in colorectum and modest edema and infiltration in the urinary bladder of CYP-treated mice. In conclusion, CYP treatment increased mechanical sensitivity of colorectal muscular afferents and increased the proportion of chemosensitive colorectal afferents. These data support a peripheral contribution to cross-organ sensitization of pelvic organs.

Response and receptive-field properties of spinomesencephalic tract cells in the cat

1986 ◽  
Vol 55 (1) ◽  
pp. 76-96 ◽  
Author(s):  
R. P. Yezierski ◽  
R. H. Schwartz
Keyword(s):  
Spinal Cord ◽  
Receptive Field ◽  
Dynamic Range ◽  
Receptive Fields ◽  
The Body ◽  
Noxious Stimulation ◽  
Primary Afferent ◽  
Receptive Field Properties ◽  
Afferent Fibers ◽  
Primary Afferent Fibers

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.

Characteristics of spinoreticular and spinothalamic neurons with renal input

1987 ◽  
Vol 58 (3) ◽  
pp. 480-495 ◽  
Author(s):  
W. S. Ammons
Keyword(s):  
Conduction Velocity ◽  
Dynamic Range ◽  
Receptive Fields ◽  
High Threshold ◽  
Wide Dynamic Range ◽  
Left Flank ◽  
Conduction Velocities ◽  
C Fiber ◽  
Medial Geniculate ◽  
Somatic Receptive Fields

Spinoreticular (SRT) and spinothalamic (STT) neurons were studied for responses to renal and somatic stimuli in 34 cats that were anesthetized with alpha-chloralose. SRT cells were antidromically activated from the medial medullary reticular formation near the gigantocellular tegmental field contralateral (35 cells), ipsilateral (15 cells), or both contralateral and ipsilateral (11 cells) to the recording site. Collision tests showed that activation from two electrodes resulted from stimulation of separate axonal branches and not from current spread. Twenty STT cells were activated from the spinothalamic tract just medial to the medial geniculate nucleus. SRT cells were located in laminae I, V, VII, and VIII of the T12-L2 segments. Most cells were located in lamina VII. STT cells were found in laminae I, V, and VII. The axons of 12 SRT cells were located in the ventrolateral or ventral quadrants of the upper cervical spinal cord. Antidromic conduction velocities of SRT cells averaged 48.7 +/- 3.7 m/s. No differences in conduction velocity were found between cells projecting to different reticular sites. In addition conduction velocity did not vary with the type of somatic or renal input. Antidromic conduction velocities of STT cells averaged 46.4 +/- 4.7 m/s. Renal nerve stimulation excited 58 and inhibited 3 SRT cells. All 20 STT cells were excited. Thirty SRT cells were excited only by A-delta input, 26 received both A-delta- and C-fiber inputs, and 2 cells received only C-fiber input. Ten STT cells received A-delta input only and 10 received both A-delta- and C-fiber inputs. All cells with renal input also received somatic input. Thirty-six SRT cells (59%) were classified as high threshold, 12 (20%) as wide dynamic range, and 10 (16%) as deep. Ten STT cells were classified as high threshold and 10 as wide dynamic range. Somatic receptive fields of STT cells were usually simple and invariably included the left flank region, although many of the fields extended to the left hindlimb or abdomen. Eighteen of the 20 were restricted to the ipsilateral side. In contrast, somatic receptive fields of SRT cells were primarily bilateral (71%). While all but two receptive fields included the left flank area, most extended to one or both hindlimbs, the abdomen, or the right flank. Inhibitory receptive fields were found for 33% of the SRT cells and 20% of the STT cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Activity-dependent sensory signal processing in mechanically responsive slowly conducting meningeal afferents

2014 ◽  
Vol 112 (12) ◽  
pp. 3077-3085 ◽  
Author(s):  
Michael Uebner ◽  
Richard W. Carr ◽  
Karl Messlinger ◽  
Roberto De Col
Keyword(s):  
Action Potential ◽  
Conduction Velocity ◽  
Receptive Fields ◽  
Low Frequency ◽  
Mechanical Stimulus ◽  
Mechanical Stimuli ◽  
Action Potential Firing ◽  
Afferent Fibers ◽  
Custom Made ◽  
Activity Dependent

Activity-dependent processes in slowly conducting afferents have been shown to modulate conduction and receptive properties, but it is not known how the frequency of action potential firing determines the responses of such fibers to mechanical stimulation. We examined the responses of slowly conducting meningeal afferents to mechanical stimuli and the influence of preceding action potential activity. In hemisected rat heads with adhering cranial dura mater, recordings were made from meningeal nerves. Dural receptive fields of mechanically sensitive afferent fibers were stimulated with a custom-made electromechanostimulator. Sinusoidal mechanical stimuli of different stimulus durations and amplitudes were applied to produce either high-frequency (phasic) or low-frequency (tonic) discharges. Most fibers showed slowing of their axonal conduction velocity on electrically evoked activity at ≥2 Hz. In this state, the peak firing frequency of phasic responses to a 250-ms mechanical stimulus was significantly reduced compared with control. In contrast, the frequency of tonic responses induced by mechanical stimuli of >500 ms did not change. In a rare subtype of afferents, which showed conduction velocity speeding during activity, an increase in the phasic responses to mechanical stimuli was observed. Depending on the axonal properties of the afferent fibers, encoding of phasic components of mechanical stimuli is altered according to the immediate firing history. Preceding activity in mechanoreceptors slowing their conduction velocity seems to provide a form of low-pass filtering of action potential discharges predominantly reducing the phasic component. This may improve discrimination between harmless and potentially harmful mechanical stimuli in normal tissue.

Effects of Opioids on Mechanosensitive Pelvic Nerve Afferent Fibers Innervating the Urinary Bladder of the Rat

1997 ◽  
Vol 77 (3) ◽  
pp. 1566-1580 ◽  
Author(s):  
X. Su ◽  
J. N. Sengupta ◽  
G. F. Gebhart
Keyword(s):  
Urinary Bladder ◽  
Opioid Receptor ◽  
Dorsal Root ◽  
Mustard Oil ◽  
Pelvic Nerve ◽  
Receptor Agonists ◽  
C Fibers ◽  
Afferent Fibers ◽  
Δ Opioid Receptor ◽  
Opioid Receptor Agonists

Su, X., J. N. Sengupta, and G. F. Gebhart. Effects of opioids on mechanosensitive pelvic nerve afferent fibers innervating the urinary bladder of the rat. J. Neurophysiol. 77: 1566–1580, 1997. A total of 443 pelvic nerve afferent fibers in the L6 dorsal root of the rat were identified by electrical stimulation of the pelvic nerve; 319 (72%) were myelinated Aδ fibers with a mean conduction velocity (CV) of 11.8 m/s and 124 (28%) were unmyelinated C fibers with mean CV of 1.9 m/s. Two hundred fifty-two fibers (57%) responded to noxious urinary bladder distension (UBD; 80 mmHg); 108 were C fibers (mean CV: 1.9 m/s) and 144 were Aδ fibers (mean CV: 8.2 m/s). Forty-nine UBD-sensitive fibers were further characterized; all gave monotonic increases in firing to increasing distending pressures. Thirty-six fibers (73%) had a low-threshold (LT) for response (mean: 6 mmHg) and 13 fibers (27%) had high-thresholds (HT) for response (mean: 32 mmHg). Responses of 15 fibers to graded UBD (11 LT and 4 HT) were tested before and after instillation of 0.5 ml of 30% xylenes ( n = 11) or 5% mustard oil ( n = 4) into the bladder. The mean resting activity of 13 fibers significantly increased, and 7 fibers exhibited sensitization of responses to graded UBD 30 min after xylenes or mustard oil instillation. All 4 HT fibers were sensitized; 3 of the 11 LT fibers were sensitized (i.e., gave increased responses to UBD). The effects of opioid receptor agonists were tested on responses to noxious UBD (80 mmHg). Cumulative intraaterial doses of μ-opioid receptor agonists (morphine, 8 mg/kg, and fentanyl, 300 μg/kg) and of δ-opioid receptor agonists (DPDPE, 300 μg/kg, and SNC-80, 300 μg/kg) did not affect responses to noxious UBD. In contrast, cumulative 16 mg/kg intraarterial doses of the κ-opioid receptor agonists U50,488H, U69,593 and U62,066 dose-dependently attenuated responses to noxious UBD. There were no differences in the dose-response relationships of these drugs on afferent fibers from untreated and xylenes- or mustard oil-treated urinary bladder. These results reveal that there is a greater proportion of UBD-sensitive fibers in the L6 dorsal root (57%) than in the S1 dorsal root of the rat (38%; a previous study). The attenuation of responses to UBD by κ, but not μ or δ opioid receptor agonists suggests a potential use for peripherally acting κ opioid receptor agonists in the control of urinary bladder pain.

Pressure, volume, and chemosensitivity in afferent innervation of urinary bladder in rats

1997 ◽  
Vol 272 (2) ◽  
pp. R695-R703 ◽  
Author(s):  
N. G. Moss ◽  
W. W. Harrington ◽  
M. S. Tucker
Keyword(s):  
Filling Rate ◽  
Similar Extent ◽  
Pelvic Nerve ◽  
Nerve Activity ◽  
Hypogastric Nerve ◽  
Bladder Filling ◽  
Afferent Nerves ◽  
Pressure Threshold ◽  
Afferent Fibers ◽  
Afferent Innervation

Bladder afferent nerve activity was recorded from the pelvic and hypogastric nerves of rats anesthetized with pentobarbital sodium. Bladder filling with isotonic NaCl at a rate of 250 microl/min excited multiunit afferent activity in the hypogastric nerve by 190 +/- 38% over background at a pressure of 30 mmHg, whereas 150 meq/l KCl at the same filling rate excited hypogastric nerve activity by 498 +/- 103% (P < 0.0001). This difference was localized to a group of chemosensitive fibers that are excited by bladder filling with KCl in a concentration-dependent fashion but are insensitive to bladder filling with NaCl. Bladder filling with 200 meq/l KCl at different filling rates caused a bursting pattern of discharge in these fibers at consistent bladder volumes but with a pressure threshold that increased proportionately with filling rate. Other hypogastric bladder afferent fibers were activated to a similar extent by NaCl and KCl solutions. Chemoreceptive bladder afferent fibers were rare in the pelvic nerve (1 of 15 units), and multiunit preparations showed comparable excitations during bladder filling with NaCl and KCl solutions. The bursting activation of bladder chemoreceptive afferent nerves in hypogastric nerves could signal noxious overdistension and/or inflammation of the bladder.

A thalamic terminus of the lateral cervical nucleus: the lateral division of the posterior nuclear group

1986 ◽  
Vol 56 (6) ◽  
pp. 1498-1520 ◽  
Author(s):  
R. S. Metherate ◽  
D. C. da Costa ◽  
P. Herron ◽  
R. W. Dykes
Keyword(s):  
Receptive Fields ◽  
Frontal Plane ◽  
Dorsal Column ◽  
Excitatory Input ◽  
The Body ◽  
Dorsal Column Nuclei ◽  
Posterior Thalamus ◽  
Afferent Fibers ◽  
Lateral Cervical Nucleus ◽  
Nuclear Group

The submodality and receptive field properties of single units in the lateral cervical nucleus (LCN) of barbiturate anesthetized cats were studied with glass microelectrodes. In other experiments, a region of the posterior thalamus containing neurons with properties comparable to those seen in the LCN was examined with tungsten microelectrodes. The responses of most units in the LCN reflected a major input from large myelinated afferent fibers innervating guard hairs but no input from Pacinian afferent fibers. The large size of the receptive fields indicated that excitatory input converged selectively from afferent fibers serving hairs over large areas of the body. In the posterior thalamus rapidly adapting neurons characterized by very large receptive fields and driven by the movement of guard hairs were observed to a region identified histologically as the rostral extension of the lateral division of the posterior nuclear group (POl). Caudally this region was located immediately adjacent to the dorsolateral part of the ventroposterior inferior nucleus (VPI). In more rostral parts of the thalamus it was located more dorsally and the ventroposterior lateral nucleus intervened between it and the VPI. This region was less than 1 mm wide in the frontal plane but extended rostrocaudally for several millimeters. Horseradish peroxidase injected into the region of the VPI and the POl labeled many cells in the LCN and the caudal pole of the dorsal column nuclei demonstrating that neurons in the LCN relay information to this part of the thalamus. These data, plus previous experiments showing that the VPI receives a major projection from the caudal poles of the dorsal column nuclei, suggest that the rostral portion of the POl receives an important afferent supply from the LCN. The responses of neurons in the POl appear to arise from specific classes of sensory receptors and cannot be considered less precise or more primitive than responses observed in the ventroposterior nucleus of the thalamus.

Representation of the urinary bladder in the lateral thalamus of the cat

1993 ◽  
Vol 70 (2) ◽  
pp. 482-491 ◽  
Author(s):  
J. Bruggemann ◽  
C. Vahle-Hinz ◽  
K. D. Kniffki
Keyword(s):  
Urinary Bladder ◽  
Receptive Fields ◽  
The Body ◽  
Intravesical Pressure ◽  
Thalamic Neurons ◽  
Electrolytic Lesions ◽  
Low Threshold ◽  
Excitatory Responses ◽  
Ventral Posterolateral Nucleus ◽  
Alpha Chloralose

1. In alpha-chloralose-anesthetized cats the region surrounding the ventral posterolateral nucleus (VPL) of the thalamus was investigated to locate foci with input from the urinary bladder stimulated by application of intravesical pressure. The locations of the recording sites were verified in Nissl-stained histological sections with reference to electrolytic lesions. 2. Of the 23 visceroceptive thalamic neurons identified, 4 (17%) were located in the periphery of the VPL (VPLp) and 19 (83%) in the lateral and dorsal aspects of the posterior complex (POl and POd, respectively) adjoining VPLp. 3. The neurons responded to noxious intensities of intravesical pressure in the range of 50-100 mmHg. Excitatory responses were elicited in 8 (35%) neurons, "inhibitory" responses in 13 (57%) neurons, and 2 (9%) neurons responded with an increase and a decrease of their discharge to subsequent stimuli. 4. Of the 22 visceroceptive thalamic neurons tested for this parameter, 73% had low-threshold cutaneous receptive fields (RFs). These were located in the region of the lower back, the hip, the thigh, and the proximal tail (12 PO neurons), or covered the entire postcranial contralateral part of the body (3 PO neurons). For only one of the VPLp neurons, a somatic RF was found and this was located on the distal tail. The neurons responded to tap stimuli applied at a low repetition rate. None of the 11 neurons tested with noxious pinching of the skin was activated by this kind of stimulus. 5. It is concluded that the cat's lateral thalamic region, around but not within VPL proper, contains neurons that play a role in the processing of information about noxious events in the urinary bladder. A comparison with results from experiments in the monkey indicates differences in the organization of the visceroceptive systems between both species, regarding the thalamic localization of visceroceptive neurons, the occurrence of convergent low-threshold somatic RFs, and the association of excitatory and inhibitory effects of urinary bladder stimulation with the location of somatic RFs.

Physiological properties of primary sensory neurons appropriately and inappropriately innervating skin in the adult rat

1991 ◽  
Vol 66 (4) ◽  
pp. 1205-1217 ◽  
Author(s):  
G. R. Lewin ◽  
S. B. McMahon
Keyword(s):  
Receptive Field ◽  
Conduction Velocity ◽  
Sensory Neurons ◽  
Receptive Fields ◽  
Muscle Afferents ◽  
High Threshold ◽  
Distal Stump ◽  
Myelinated Fibers ◽  
Conduction Velocities ◽  
Low Threshold

1. We have studied the physiology of sensory neurons innervating skin of the rat hindlimb, in three groups of animals: 1) normal animals; 2) animals in which the sural nerve (Sn) had regenerated to its original cutaneous target; and 3) animals in which the gastrocnemius muscle nerve (Gn) had previously been cut and cross anastomosed with the distal stump of the cut Sn so that its axons regenerated to a foreign target, skin. 2. Single-unit recordings were made from 222 afferents in normal, intact animals. They had conduction velocities of 0.5-53.1 m/s. The conduction velocity distribution had distinct peaks at approximately 37.5, 2.5, and 1.25 m/s, presumably corresponding to A alpha beta-, A delta-, and C-fiber populations. Eighty-two percent of the characterized myelinated fibers had low-threshold mechanosensitive receptive fields, whereas 16% were high threshold, and only 2% appeared to have no receptive field. The very large majority of low-threshold mechanosensitive receptive fields (87%) were rapidly adapting hair follicle afferents. 3. In animals with regenerated Sn, 308 afferents were recorded with conduction velocities of 0.4-58.8 m/s. However, the mean conduction velocity was lower than in control animals (P less than 0.05), and only one peak, at 27.5 m/s, was apparent for myelinated fibers. Eighty-six percent of myelinated fibers were low-threshold mechanosensitive afferents, 8.5% were high-threshold mechanoreceptors (HTMRs), and 5.5% appeared to have no receptive fields. Fewer low-threshold mechanoreceptors (LTMRs; compared with controls) were activated by hair movement (63 vs. 87%). Most of the remainder appeared to be field receptors (which were therefore more commonly observed here than in normal animals). 4. In animals in which the Gn had regenerated to skin, 430 afferents were recorded. These had conduction velocities ranging from 0.6 to 71.4 m/s, and again only one peak was apparent in the myelinated conduction velocity histogram, at approximately 17.5 m/s. Of the myelinated fibers, 79% had low-threshold mechanosensitive receptive fields in skin and 10% high-threshold mechanosensitive receptive fields. The remaining 11% apparently had no receptive field (cf. 5.5% in regenerated Sn). In contrast to normal or regrown sural afferents, only 58% of low-threshold gastrocnemius afferents in skin were rapidly adapting. Of the 42% slowly adapting afferents, many surprisingly responded to hair movement. Thus some gastrocnemius afferents seemed to have retained the adaptation properties characteristic of muscle afferents. Also surprisingly, given that the Gn contains fewer fibers than the Sn, receptive-field areas were not significantly different from regrown or normal sural fibers.(ABSTRACT TRUNCATED AT 400 WORDS)

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