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Biomedical subjects

F Cervero

Publications and source records attributed to F Cervero.

At least 73 records · Page 4Linked to original sources
PubMed1988

An electrophysiological and anatomical study of intestinal afferent fibres in the rat.

1. The afferent innervation of the distal ileum has been examined in normal rats and in rats treated at birth with capsaicin. Electrophysiological recordings were made using an in vitro preparation of distal ileum and its associated mesenteric nerves. The fibre composition of the mesenteric nerves was examined by electron microscopy and the numbers of primary afferent fibres innervating a segment of distal ileum was estimated using retrograde tracing. 2. Recordings were made from 120 single afferent units all of which showed some degree of background activity. The conduction velocities of sixty-seven afferent units were estimated, and all were found to be in the C-fibre range (less than 2 m/s). Eighty-two units were sufficiently studied to allow their classification according to whether they responded to mechanical stimuli (M units), chemical stimuli (Ch units) or both mechanical and chemical stimuli (MCh units). In control rats 85.5% were classified as MCh units, 11.9% as M units and 2.6% as Ch units. In capsaicin-treated rats six single and three multi-units were MCh and one multi-unit was classified as an M recording. 3. The effects of intraluminal distension were investigated in sixty-seven units which were classified according to whether or not they adapted during the distension. About half the total units were classified as rapidly adapting, the other half were slowly adapting. This distribution was similar for the MCh-units, but of the eight M units tested, seven adapted during distension. The distension thresholds were tested in thirty units, of which twenty-eight responded at thresholds below 18 mmHg. There were no differences in the thresholds of units from control and capsaicin-treated rats. 4. The chemosensitivity of units was tested in response to acetylcholine (ACh), bradykinin and substance P. Most units tested responded to ACh (78% of MCh units tested) and bradykinin (80% of MCh units), but fewer units responded to substance P (about 50% of MCh units). ACh produced an increased tension which outlasted the increase in afferent activity. Bradykinin gave long-lasting afferent responses which were not always accompanied by increases in tension. The increases in afferent activity produced by substance P were often seen after an increase in tension. 5. The fluorescent dye True Blue injected into the wall of the ileum labelled cell bodies in the spinal and nodose ganglia, predominantly on the left side of an animal. The mean number of labelled cells per animal was eighty-seven, of which the majority was in the T10-T13 spinal ganglia.(ABSTRACT TRUNCATED AT 400 WORDS)

Acetylcholine↗
PubMed1988

Bilateral inputs and supraspinal control of viscerosomatic neurones in the lower thoracic spinal cord of the cat.

1. Single-unit activity has been recorded from eighty-three viscero-somatic neurones in the lower thoracic spinal cord (T9-T11) of chloralose-anaesthetized cats. These neurones were driven by natural and/or electrical stimulation in their somatic receptive fields and gave excitatory responses to electrical stimulation of the ipsilateral splanchnic nerve. Contralateral visceral inputs were tested by electrical stimulation of the contralateral splanchnic nerve. Tonic and phasic descending influences were tested by reversible spinalization with cold block at T7 and by electrical stimulation in nucleus raphe magnus and the immediately adjacent reticular formation. 2. Most viscero-somatic neurones (89%) gave an excitatory response to stimulation of the contralateral splanchnic nerve and were therefore considered to have bilateral visceral inputs. In this group of neurones three categories of cells were identified depending on whether their responses to ipsilateral splanchnic nerve stimulation were decreased (50%), increased (42%) or unchanged (8%) in the spinal state. Only one cell with an exclusively ipsilateral visceral input was tested for the effects of reversible spinalization. Stimulation of contralateral splanchnic nerve failed to evoke activity in this cell in the spinal state. 3. Sixty-four viscero-somatic neurones with bilateral visceral inputs and four neurones with exclusively ipsilateral visceral inputs were tested with electrical stimulation in nucleus raphe magnus and the adjacent reticular formation. Seventy-eight per cent gave an initial excitatory response which was followed by a period of reduced responsiveness to stimulation of visceral and somatic afferents. Three of the four neurones with an exclusively ipsilateral visceral input had no excitatory drive from the brain stem but their responses to stimulation of visceral and somatic afferents were depressed. 4. The majority (77%) of neurones with bilateral inputs were located in laminae VII and VIII with the remainder in the dorsal horn, predominantly laminae I and V, whereas all but one of the neurones with an exclusively ipsilateral visceral input were located in the superficial dorsal horn, predominantly lamina I, and none in laminae VII and VIII. 5. These results show that the majority of viscero-somatic neurones in the cat's lower thoracic spinal cord receive bilateral visceral inputs and that the transfer of this information is subjected to descending control which includes excitation as well as inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1988

Prolonged noxious mechanical stimulation of the rat's tail: responses and encoding properties of dorsal horn neurones.

1. Single-unit electrical activity has been recorded from dorsal horn neurones in the sacral (S1-S2) segments of the spinal cord of barbiturate-anaesthetized rats. Fifty-two neurones responding to a manually applied pinch of their receptive fields in the tail were selected. They were subsequently tested for their responses to four successive 2 min pinches at noxious intensities delivered by a feed-back-controlled mechanical device. 2. Neurones were tested with both innocuous (i.e. brushing and stroking) and noxious (i.e. pinching, pin-prick, and in some cases heating about 45 degrees C) stimulation of their cutaneous receptive fields. Three of the tested cells were driven exclusively by innocuous skin stimulation (mechanoreceptive or class 1), thirty-six were driven by both innocuous and noxious skin stimulation (multireceptive or class 2) and thirteen were driven exclusively by noxious skin stimulation (nocireceptive or class 3). 3. All of the multireceptive and nocireceptive neurones responded to the 2 min noxious pinch with an initial phasic discharge followed by sustained firing that showed little evidence of adaptation throughout the stimulus period. The three mechanoreceptive neurones responded to the 2 min noxious pinch with a short discharge at the stimulus onset, but were silent for the remainder of the stimulus period. 4. Thirty-one cells were tested with successive 2 min pinches of 4, 6 and 8 N (and in some cases, a further 4 N pinch) applied at 10 min intervals. Different encoding properties were observed during the sustained part of the neuronal response according to: (i) the afferent fibre input characteristics of the cell; (ii) whether or not the tail had received a test series of pinches earlier in the same experiment. 5. None of the multireceptive cells with only an A-fibre afferent input encoded the stimulus strength. However, the multireceptive cells with both an A- and a C-fibre afferent input and all nocireceptive cells did encode the stimulus strength, providing that no previous noxious test stimuli had been applied to the tail. The encoding nocireceptive neurones had in general a steeper stimulus-response curve than the encoding multireceptive neurones, though the two groups overlapped to some extent. 6. Three encoding cells (two multireceptive and one nocireceptive) were tested with a second series of pinches (4, 6, 8 and 4 N), 40 min subsequent to the initial test series. These cells did not encode this second test series, but were more excitable, producing a greater response to a given test force.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1987

Distribution of sural nerve afferent fibres within the dorsal horn of adult rats treated at birth with capsaicin.

The distribution of sural nerve afferent fibres within the spinal cord of normal adult rats and of adult rats treated at birth with capsaicin was examined using transganglionic transport of horseradish peroxidase (HRP). Labelled fibres were seen, in normal and in capsaicin-treated rats, in Laminae I-VI of the central third of the dorsal horn, extending rostrocaudally between the L3 and L5 segments. It is concluded that the changes in dorsal horn somatosensory systems induced by neonatal capsaicin are not due to anatomical redistribution of the areas of termination of peripheral nerves within the spinal cord.

Animals↗
PubMed1987

Anorectal temperature sensation: a comparison of normal and incontinent patients.

In the skin, temperature sensation plays an important role in discriminating between gas, liquid and solid. To elucidate the role of temperature sensation in idiopathic faecal incontinence we studied the minimum detectable temperature change in the lower, middle and upper zones of the anal canal and rectum in 33 normal subjects, and 20 patients with idiopathic faecal incontinence. A water perfused thermode was used to vary anorectal temperature from 37 degrees C down to 32.5 degrees C and up to 41.5 degrees C. The temperature change was reported by the patient as the thermode temperature varied from 37 degrees C to each extreme and on return to base line. The anal canal in the control group was highly sensitive to temperature change, the lower rectum was significantly less sensitive (P less than 0.0001). At each level in the anal canal and lower rectum the incontinent group were significantly less sensitive than their controls (P less than 0.005). The mid-rectum had no appreciable sensation in either group. We consider that this sensory deficit may be an important factor in idiopathic faecal incontinence.

Adult↗
PubMed1987

Evidence for a visceral afferent origin of substance P-like immunoreactivity in lamina V of the rat thoracic spinal cord.

A visceral afferent origin of substance P-like immunoreactivity in lamina V of the lower thoracic spinal cord of the rat was investigated. In transverse sections from normal animals there was a moderately dense substance P-immunoreactive innervation of lamina V. In some sections there was a dorsoventrally orientated fibre bundle from the superficial dorsal horn entering lamina V. In parasagittal sections, substance P-immunoreactivity in lamina V was found arranged in clusters, with a periodicity in the rostrocaudal axis of 200-600 microns. In some cases these were seen to be continuous with a dorsoventrally orientated fibre bundle from the superficial dorsal horn. After section of the splanchnic nerve there was a consistent reduction in the density of the substance P-like immunoreactivity in lamina V, with fewer clusters on the operated side. Adult rats treated neonatally with capsaicin showed a substantial reduction of substance P-immunoreactivity in laminae I and II and the virtual abolition of staining in lamina V. These results provide evidence of a visceral origin for some of the substance P-like immunoreactivity in lamina V of the rat thoracic spinal cord. In addition, they confirm that most of the substance P-immunoreactivity in the dorsal horn is of primary afferent origin.

Animals↗
PubMed1987

Somatic and visceral inputs to the thoracic spinal cord of the cat: marginal zone (lamina I) of the dorsal horn.

1. Single-unit electrical activity has been recorded from fifty-five neurones whose recording sites were located in or immediately adjacent to the marginal zone (lamina I) of the lower thoracic spinal cord (T8-T12) of anaesthetized or decerebrate cats. Their responses to stimulation of somatic and visceral afferent fibres and the sizes of their cutaneous receptive fields have been analysed and compared with the responses and receptive fields of neurones recorded throughout the spinal grey matter. 2. Neurones were classified according to their responses to innocuous stimulation of their somatic receptive fields (i.e. brushing and stroking) or to noxious stimulation (i.e. pinching, squeezing and/or heating above 45 degrees C). 52% of all the neurones recorded in lamina I were driven exclusively by noxious stimulation of the skin (nocireceptive); 33% were driven by both noxious and innocuous stimulation of the skin (multireceptive) and 15% were driven exclusively by innocuous stimulation of the skin (mechanoreceptive). 3. Visceral afferent inputs to these neurones were tested by supramaximal electrical stimulation of the ipsilateral splanchnic nerve (15 V, 0.2 ms, 0.3 Hz). Two types of neurone were distinguished according to their responses to visceral stimulation: (i) somatic neurones, driven only by stimulation of somatic afferent fibres and (ii) viscero-somatic neurones, driven by stimulation of somatic and visceral afferent fibres. Of the neurones recorded in lamina I, 33% were somatic and 67% were viscero-somatic. This proportion was very similar to the percentages of somatic and viscero-somatic neurones recorded throughout the grey matter (37 and 63%, respectively). 4. Viscero-somatic neurones in lamina I had somatic receptive field properties similar to those of viscero-somatic neurones of the entire spinal cord. Half of them were multireceptive, 39% were nocireceptive and 11% were mechanoreceptive. However, somatic neurones in lamina I had receptive field properties different from those of somatic neurones from other laminae: no multireceptive somatic neurones were recorded in lamina I; the vast majority (78%) were nocireceptive and 22% were mechanoreceptive. 5. The majority of somatic and viscero-somatic neurones in lamina I had small somatic receptive fields but, even in this group of cells, viscero-somatic neurones had larger receptive fields than somatic cells. 6. Ascending axonal projections in both dorsolateral funiculi and in the contralateral ventrolateral quadrant were tested in eighteen lamina I neurones. Only one neurone was found to project to the cervical cord.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1987

Spinal cord sensory systems after neonatal capsaicin.

Animals with a severe reduction in the number of afferent C-fibres as a consequence of neonatal administration of capsaicin, exhibit a number of neurological and behavioral deficits including increased nociceptive thresholds, altered somato-visceral and viscero-visceral reflexes, depressed cardiovascular and respiratory reflexes and changes in the organisation of spinal cord sensory systems. The reduction in the number of C-fibres produced by neonatal capsaicin does not cause a decrease of similar magnitude in the number of dorsal horn cells driven by the surviving C-fibres. Twenty-two per cent of dorsal horn neurones in capsaicin treated animals respond to electrical stimulation of the surviving afferent C-fibres: a reduction of only 50% from control values. Inhibitory controls on afferent C-fibre evoked responses of dorsal horn neurones are weaker in capsaicin treated rate than in control animals. The cutaneous receptive fields of some dorsal horn neurones can increase in size following stimulation of afferent C-fibres. Tonic descending inhibition on C-fibre evoked responses of dorsal horn neurones is reduced in capsaicin treated rats: fewer neurones show tonic descending inhibition in these animals and those that do are subjected to less powerful inhibitions than similar neurones from control animals. However, some central inhibitory mechanism are unchanged after neonatal capsaicin treatment, specially those that do not involve afferent C-fibres. We suggest that the nervous system develops central inhibition in response to and directed towards the excitations mediated by its afferent drives. Therefore reduced central inhibition in response to a decreased number of afferent C-fibres can compensate for the lost capacity in the signalling of peripheral noxious events.

Afferent Pathways↗
PubMed1986

An in vitro method for recording single unit afferent activity from mesenteric nerves innervating isolated segments of rat ileum.

A technique has been developed for recording single unit afferent activity from mesenteric nerves in isolated segments of rat distal ileum in vitro. The preparation consists of a 3-cm segment of ileum, containing a single neurovascular bundle, held horizontally in an organ bath. One end of the segment is attached to a tension transducer to record changes in longitudinal tension of the gut muscle and the other is connected to a pressure transducer to record changes in intra-luminal pressure. Electromyographic activity of the smooth muscle is recorded using glass-insulated tungsten microelectrodes inserted in the wall of the gut. Afferent nerve activity is recorded with a monopolar platinum wire electrode from filaments of the mesenteric nerves that run between the artery and vein supplying the segment. This preparation permits the detailed analysis of the electrical activity of intestinal afferent nerve fibres correlated with mechanical and chemical events occurring naturally in the gut or imposed experimentally on it.

Animals↗
PubMed1986

Effects of reversible spinalization on the visceral input to viscerosomatic neurons in the lower thoracic spinal cord of the cat.

Single-unit electrical activity has been recorded from 122 viscerosomatic neurons in the T9 and T11 segments of the cat's spinal cord. These neurons were excited by electrical and/or natural stimulation of visceral and somatic afferent fibers. The majority of viscerosomatic neurons (72%) received somatic nociceptive inputs, either exclusively or together with low-threshold somatic inputs. Many of these neurons were excited most strongly by intense mechanical stimulation of subcutaneous tissues, particularly by pinching or squeezing muscle. Twelve viscerosomatic neurons were excited by distensions of the biliary system at levels of biliary pressure greater than 25 mmHg. These intensities of biliary stimulation evoked transient increases in blood pressure, which suggest that the visceral stimuli were of nociceptive nature. The effects of reversible spinalization by cold block were tested on 98 viscerosomatic neurons. Three subgroups of viscerosomatic neurons were distinguished depending on whether their responses to visceral afferent stimulation were increased, decreased, or unchanged in the spinal state. Forty percent of all neurons tested increased the intensity of their responses to visceral stimulation in the spinal state. In addition, many of these neurons developed or increased their background activity and increased their somatic responses in the spinal state. It is concluded that these neurons were subjected to tonic descending inhibition of both somatic and visceral afferent inputs. More than 40% of the neurons in this group were located in or close to lamina V of the dorsal horn. In 44% of all neurons tested the response to visceral stimulation was reduced or abolished by spinalization. The background activity was not affected in the same manner and sometimes even increased during spinalization. The responses to somatic stimuli were fully tested in 11 neurons of this group and were found to be decreased, but not abolished, in nine neurons, unchanged in one cell, and increased in another one. Many of the neurons in this group were located in the ventral horn (laminae VII and VIII). Sixteen percent of all viscerosomatic neurons tested showed no change in their responses to visceral stimulation during spinalization. It is concluded that the visceral input to viscerosomatic neurons in the lower thoracic spinal cord is under considerable descending control, which includes excitation as well as tonic inhibition of visceral afferent information. This may represent part of the widespread effects of visceral nociceptive stimulation.

Animals↗
PubMed1986

Viscerosomatic neurons in the lower thoracic spinal cord of the cat: excitations and inhibitions evoked by splanchnic and somatic nerve volleys and by stimulation of brain stem nuclei.

Single-unit electrical activity has been recorded from 95 viscerosomatic neurons in the T9 and T11 segments of the cat's spinal cord. These neurons were excited by electrical and/or natural stimulation of visceral and somatic afferent fibers. The excitatory and inhibitory effects on these neurons of volleys in somatic and visceral afferent fibers and of electrical and chemical stimulation of the nucleus raphe magnus (NRM) and adjacent areas of the reticular formation (Ret. F.) have been studied. Electrical stimulation of the splanchnic nerve produced, after the initial excitation of the neurons, a period of inhibition lasting for up to 1 s. This inhibition reduced the responsiveness of the neurons to all inputs, somatic and visceral, and was still present after spinalization of the animals with cold block, which indicates a segmental organization of the inhibition. Electrical stimulation of afferent fibers within the somatic receptive field of the neurons produced, after the initial excitation, a period of inhibition similar to that induced by visceral afferent volleys. During this period of inhibition all inputs to the neurons were reduced. Reversible spinalization of the animals with cold block did not abolish this inhibition. On the basis of the effects of reversible spinalization on the visceral input to viscerosomatic neurons, two types of neurons were distinguished: 1) neurons whose visceral responses increased in the spinal state (neurons under tonic descending inhibition) and 2) neurons whose visceral responses were decreased or abolished in the spinal state (neurons subject to descending excitation). Neurons under tonic descending inhibition were inhibited by electrical stimulation of locations within the NRM and Ret. F. This inhibition lasted for less than 100 ms and could be evoked at intensities of stimulation of 100 microA or less. Neurons under descending excitation were also inhibited by electrical stimulation in the NRM and Ret. F. but, in addition, the inhibition was preceded by an excitation in 75% of these neurons. Chemical stimulation with DL-homocysteic acid (DLH) of locations within the NRM and Ret. F. was used to activate cell bodies, but not axons, located in these brain stem sites. The only effect observed following injections of DLH into the NRM and Ret. F. was inhibition of viscerosomatic neurons including those with descending excitation as well as those with descending inhibition.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗
PubMed1985

Cutaneous receptive fields of somatic and viscerosomatic neurones in the thoracic spinal cord of the cat.

Extracellular single-unit recordings were made from 121 neurones in the thoracic spinal cord of the cat. All neurones could be driven by electrical stimulation of dorsal root afferent fibres. The neurones were classified, according to the absence or presence of inputs from the ipsilateral splanchnic nerve, as "somatic" or "viscerosomatic", respectively. Cutaneous receptive fields were identified for 75 of the neurones: 31 were somatic and 44 viscerosomatic. Only two of the somatic cells received cutaneous nociceptive inputs, compared with 33 of the viscerosomatic cells. Sixty-four percent of the whole sample of neurones had receptive fields which included three or more dermatomes. Viscerosomatic cells tended to have larger receptive fields than the somatic neurones, and six of them had fields which did not include the corresponding (T11) dermatome. Neurones with receptive fields in the dorsal one-third of the dermatome tended to be located in the lateral one-third of the dorsal horn, but those with receptive fields in the ventral two-thirds of the dermatome showed no differential distribution within the gray matter. This is discussed with respect to the results of anatomical studies on the dorsal horn projections of cutaneous afferent fibres from different regions of the dermatome. Preliminary results from intracellular staining with horseradish peroxidase reveal extensive branching of primary afferents in the dorsal horn, and large dendritic fields of dorsal horn neurones. Our physiological and morphological results indicate that the somatotopic organisation of the thoracic spinal cord is less well defined than that of the lumbosacral region.

Animals↗
PubMed1985

Supraspinal loops that mediate visceral inputs to thoracic spinal cord neurones in the cat: involvement of descending pathways from raphe and reticular formation.

Single unit electrical activity has been recorded from 29 viscero-somatic neurones in the T11 spinal cord segment of chloralose anaesthetized cats. Twenty-six of these neurones showed changes in their responses to electrical stimulation of the splanchnic nerve after reversible spinalization of the animals by cold block: 14 showed increased responses whereas 12 presented reduced or abolished responses during the spinal block. The majority of neurones in the first group were located in laminae IV, V and VII and were inhibited by electrical stimulation of the nucleus raphe magnus (NRM) and the reticular formation (Ret.F). Most neurones of the second type were located in the ventral horn, and the majority were excited by electrical stimulation of the NRM and the Ret.F. This second type of neurone may play a role in the maintenance of the excitation in the central nervous system which follows visceral noxious stimulation.

Animals↗
PubMed1985

Visceral nociception: peripheral and central aspects of visceral nociceptive systems.

Discomfort and pain are the sensations most commonly evoked from viscera. Most nociceptive signals that originate from visceral organs reach the central nervous system (c.n.s.) via afferent fibres in sympathetic nerves, whereas parasympathetic nerves contain mainly those visceral afferent fibres concerned with the non-sensory aspects of visceral afferent function. Noxious stimulation of viscera activates a variety of specific and non-specific receptors, the vast majority of which are connected to unmyelinated afferent fibres. Studies on the mechanisms of visceral sensation can thus provide information on the more general functions of unmyelinated afferent fibres. Specific visceral nociceptors have been found in the heart, lungs, testes and biliary system, whereas noxious stimulation of the gastro-intestinal tract appears to be detected mainly by non-specific visceral receptors that use an intensity-encoding mechanism. Visceral nociceptive messages are conveyed to the spinal cord by relatively few visceral afferent fibres which activate many central neurons by extensive functional divergence through polysynaptic pathways. Impulses in visceral afferent fibres excite spinal cord neurons also driven by somatic inputs from the corresponding dermatome (viscero-somatic neurons). Noxious intensities of visceral stimulation are needed to activate viscero-somatic neurons, most of which can also be excited by noxious stimulation of their somatic receptive fields. The visceral input to some viscero-somatic neurons in the spinal cord can be mediated via long supraspinal loops. Pathways of projection of viscero-somatic neurons include the spino-reticular and spino-thalamic tracts. All these findings give experimental support to the 'convergence-projection' theory of referred visceral pain. Visceral pain is the consequence of the diffuse activation of somato-sensory nociceptive systems in a manner that prevents accurate spatial discrimination or localization of the stimuli. Noxious stimulation of visceral receptors triggers general reactions of alertness and arousal and evokes unpleasant and poorly localized sensory experiences. This type of response may be a feature of sensory systems dominated by unmyelinated afferent inputs.

Abdomen↗
PubMed1985

C-fibre excitation and tonic descending inhibition of dorsal horn neurones in adult rats treated at birth with capsaicin.

Single unit electrical activity has been recorded from dorsal horn neurones in the lumbar cord of rats anaesthetized with sodium pentobarbitone. Three groups of animals were used: normal adult rats, adult rats that had been treated at birth with capsaicin (50 mg kg-1 s.c.) and adult rats that had been injected at birth with the drug vehicle only. Rats treated at birth with capsaicin showed a substantial reduction in the number of afferent C fibres as indicated by the virtual absence of C waves in the compound action potentials evoked in the sural nerve by antidromic stimulation of the L4-L6 dorsal roots. No significant differences were found in any of the parameters measured between the vehicle treated and the untreated animals. Therefore, rats from these two groups are referred to as control animals. All dorsal horn neurones studied were driven by electrical stimulation of the A fibres in the ipsilateral sural nerve and had cutaneous receptive fields in the ipsilateral hind limb. Two groups of neurone were distinguished: those receiving an input from A fibres only (A only) and those neurones that could also be driven by sural C fibres (A + C). In the control group, 56% of the neurones were A only and 44% were A + C. In capsaicin-treated rats these proportions were significantly different: 78% and 22% respectively. No differences were found in receptive field sizes of A-only neurones between those recorded in control rats and those from capsaicin-treated animals. However, a large and significant increase in receptive field size of A + C neurones was observed in capsaicin-treated rats compared to their counterparts in normal animals. In control rats 80% of the A + C neurones showed tonic descending inhibition of their C-fibre-evoked responses as assessed by reversible spinalization. In capsaicin-treated rats this proportion fell to 47% of the A + C neurones. The magnitude of the tonic descending inhibition was also reduced in the fewer A + C neurones of capsaicin-treated rats that were subjected to it. Only 4% of A + C neurones with tonic descending inhibition in capsaicin-treated rats were powerfully inhibited compared to 26% in control animals. The mean number of spikes evoked by C-fibre stimulation of the sural nerve in A + C neurones of control and of capsaicin-treated rats was not significantly different between these two groups of animals in the intact and in the spinalized states.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMed1984

Distribution of somatic and visceral primary afferent fibres within the thoracic spinal cord of the cat.

Transport of horseradish peroxidase (HRP) through somatic and visceral nerve fibres was used to study the patterns of termination of somatic and visceral primary afferent fibres within the lower thoracic segments of the cat's spinal cord. A concentrated solution of HRP was applied for at least 5 hours to the central end of the righ greater splanchnic nerve and of the left T9 intercostal nerve of adult cats. Some animals remained under chloralose anaesthesia for the duration of the HRP transport times (up to 53 hours) whereas longer HRP application and transport times (4-5 days) were allowed in animals that recovered from barbiturate anaesthesia. Somatic afferent fibres and varicosities (presumed terminals) were found in laminae I, II, III, IV, and V of the ipsilateral dorsal horn and in the ipsilateral Clarke's column. The density of the somatic projection was particularly high in the superficial dorsal horn. In parasagittal sections of the cord, bundles of somatic fibres were seen joining the dorsal horn from the dorsal roots via the dorsal columns and Lissauer's tract. A medio-lateral somatotopic arrangement of somatic afferent terminations was observed, with afferent fibres from the ventral parts of the dermatome ending in the medial dorsal horn and afferent fibres from the dorsal parts of the dermatome ending in the lateral dorsal horn. The total rostro-caudal extent of the somatic projection through a single spinal nerve was found to be of 2 and 2/3 segments, including the segment of entry, the entire segment rostral to it and two-thirds of the segment caudal to it. A lateral to medial shift in the position of the somatic projection was observed in the rostro-caudal axis of the cord. Visceral afferent fibres and varicosities (presumed terminals) were seen in laminae I and V of the ipsilateral dorsal horn. The density of the visceral projection to the dorsal horn was substantially lower than that of the somatic projection. Visceral afferent fibres reached the dorsal horn via Lissauer's tract and joined a lateral bundle of fine fibres that run along the lateral edge of the dorsal horn. The substantia gelatinosa (lamina II) appeared free of visceral afferent fibres. These results are discussed in relation to the mechanisms of viscero-somatic convergence onto sensory pathways in the thoracic spinal cord.

Afferent Pathways↗
PubMed1984

Somatic and visceral primary afferents in the lower thoracic dorsal root ganglia of the cat.

Anterograde transport of horseradish peroxidase (HRP) through somatic and visceral nerves was used to estimate the proportions of somatic and visceral dorsal root ganglion (DRG) cells of the lower thoracic ganglia of the cat. A concentrated solution of HRP was applied for at least 5 hours to the central end of the right greater splanchnic nerve and of the left T9-intercostal nerve of adult cats. Some animals remained under chloralose anaesthesia for the duration of the HRP transport time (up to 53 hours) whereas longer HRP application and transport times (4-5 days) were allowed in animals that recovered from barbiturate anaesthesia. Visceral DRG cells were found in approximately equal numbers in all ganglia examined (T7-T11). Population estimates were obtained for the T8 and T9 ganglia where visceral DRG cells were found to be 6.2% (T8) and 5.2% (T9) of the total cell population. In contrast, somatic DRG cells were found in large numbers in the ganglia examined (T8 and T9) where they amounted to over 90% of the cell population. Measurement of cross-sectional areas and estimates of cell diameters of the DRG cells showed greater proportions of large somatic cells (diameter greater than 40 micron) than of large visceral cells. Similar distributions of cell size were found for both somatic and visceral DRG cells with diameters less than 40 micron. These results show that the proportion of visceral afferent fibres in the dorsal roots that mediate the spinal cord projection of the splanchnic nerve is very small. Since viscerosomatic convergence in the thoracic spinal cord is very extensive, the present results suggest considerable divergence of the visceral afferent input to the central nervous system.

Animals↗