Receptive field organisation and electrophysiological responses of spinal cord thermoreactive neurones in the rat

Summary Receptive fields and electrophysiological responses of seventy-three thermoreactive neurones were studied. The receptive fields were 1 to 10 mm wide and 1 to 15 mm long, for the warm thermoreactive neurones and 5 to 15 mm wide and 2 to 31 mm long for cold thermoreactive neurones. The receptive fields of 5 units excited by warming and heating were 5 to 11 mm wide and 3 to 16 mm long. Six units excited by warming and light mechanical stimulation had receptive fields about 1 to 7 mm wide and 1 to 10 mm long. Those of 3 units excited by cooling and light mechanical stimulation were 3 to 10 mm wide and 3 to 15 mm long. Seven bimodal units had receptive fields that were 2 to 30 mm wide and long. The receptive fields were on the ipsilateral scrotal and or inguinal and perineal skin. Only 1 unit had a bilateral receptive field. Seven dorsal horn neurones showed convergence of warm sensitive and nociceptive afferents. Also, 2 units had convergent inputs from cold sensitive and nociceptive afferents. The noxious mechanical excitatory receptive fields were separate and located on the ipsilateral and contralateral toes, the penis or ipsilateral testicle. The thermal excitatory receptive fields of these units were 15 to 17 mm wide and 20 to 21 mm long. The warm and cold-reactive neurones discharged more with the rise and fall in skin temperature, respectively. Five warm-reactive neurones showed bursting activity. The locations of the thermoreactive neurones studied were similar to those reported earlier. It is concluded that dorsal horn thermoreactive neurones, have mainly ipsilateral receptive fields. Secondly, convergence of temperature sensitive and nociceptive afferents occur in the dorsal horn of the rat.     

Reflex control of cat extrinsic and intrinsic tongue muscles exerted by intraoral receptors

The effects of mechanical and noxious stimulation of the palatal and lingual surfaces on the activity of the extrinsic and intrinsic tongue muscles have been studied in cats. Stimulation of the hard palate produced mainly activation of extrinsic tongue muscles while inhibition was elicited by stimulating the soft palate. Longlasting pressure on the hard palate caused rhythmic tongue flapping by intermittent genioglossal activity. The intrinsic tongue muscles, m. transversus and m. verticalis, were activated by noxious stimuli applied to the hard palate, the effects apparently being mediated by high-threshold afferents. Mechanical and noxious stimulation applied to the dorsal and ventral lingual surfaces of the tongue either activated or inhibited the extrinsic tongue muscles depending on the reflex area stimulated. The intrinsic tongue muscles were activated by noxious stimuli applied to the tongue surfaces. The anastomoses running between the hypoglossal and lingual nerves were found to mediate mainly nociceptive afferent impulses travelling from the hypoglossal to the lingual nerve. The intrinsic muscles were found to be controlled by anastomosal nociceptive afferents.     

Effects of electrical and natural stimulation of skin afferents on the gamma-spindle system of the triceps surae muscle

The aim of the present study was to investigate the extent to which skin receptors might influence the responses of primary muscle spindle afferents via reflex actions on the fusimotor system. The experiments were performed on 43 cats anaesthetized with alpha-chloralose. The alterations in fusimotor activity were assessed from changes in the responses of the muscle spindle afferents to sinusoidal stretching of their parent muscles (triceps surae and plantaris). The mean rate of firing and the modulation of the afferent response were determined. Control measurements were made in absence of any cutaneous stimulation. Tests were made (a) during physiological stimulation of skin afferents of the ipsilateral pad or of the contralateral hindlimb, or (b) during repetitive electrical stimulation of the sural nerve in the ipsilateral hindlimb, or of sural or superficial peroneal nerve in the contralateral hindlimb. Of the total number of 113 units tested with repetitive electrical stimulation of the ipsilateral sural nerve (at 20 Hz), 24.8% exhibited predominantly dynamic fusimotor reflexes, 5.3% mixed or predominantly static fusimotor reflexes. One unit studied in a preparation with intact spinal cord exhibited static reflexes at low stimulation intensities and dynamic ones at higher stimulation strengths. The remaining units (69%) were uninfluenced. When the receptor-bearing muscle was held at constant length and a train of stimuli (at 20 Hz) was applied to the ipsilateral sural nerve, the action potentials in the primary muscle spindle afferent could be stimulus-locked to the 3rd or 4th pulse in the train (and to the pulses following thereafter), with a latency of about 24 ms from the effective pulse. This 1:1 pattern of driving seemed to be mediated via static and/or dynamic fusimotor neurons. Natural stimulation influenced comparatively few units (3 of 65 units tested from the ipsilateral pad and 10 of 98 tested from the contralateral hindlimb), but when the effects were present they were quite large. The results are discussed in relation to previous studies on reflex control of fusimotor neurones from cutaneous afferents. It is suggested that the wide range of fusimotor effects from cutaneous afferent fibres observed in this study (from complete absence of any effect, via moderate excitatory and inhibitory effects, to the 'driving pattern', i.e. pulse-to-pulse response) may reflect that different gamma-motoneurones have individualized reflex profiles, and it may also indicate that groups of fusimotor neurones and spindle afferents play specific roles in different motor acts.     

Excitatory and inhibitory controls of the masseter and temporal muscles elicited from teeth in the rat.

The periodontal mechanism that controls the jaw reflexes was examined in lightly anesthetized rats. Motor-unit activity in the masseter and temporal muscles was recorded electromyographically and pressure stimulation was applied to either an upper incisor or an upper molar. Reflex effects of dental stimulation varied depending on the level of ongoing activity (background activity, BGA) in each motor unit. Incisal or molar stimulation elicited excitatory reflexes in both the masseter and temporal motor units at a low BGA, but inhibitory reflexes in both types of motor unit at a higher BGA. In contrast to these synergistic reflex actions, the reciprocal reflex actions of the two motor units that belonged to the respective muscles occurred when the BGA was intermediate. The results suggest that different patterns of periodontal jaw reflexes may be elicited, depending on the different levels of BGAs. Furthermore, the present reflexes were modified with the site of a stimulated tooth within the dentition. Incisal stimulation produced greater excitation in the masseter motor unit than in the temporal one, and the opposite type of response occurred during molar stimulation. Moreover, smaller-amplitude motor units with a low reflex threshold and larger-amplitude motor units with a higher reflex threshold tended to exhibit excitatory and inhibitory reflexes, respectively.     

The Linguo-Chorda Tympani Reflex—an Electrophysiologically Undescribed Reflex

The impulse activity in the central part of the chorda tympani nerve of the rat was recorded during mechanical stimulation of the oral region. The results obtained at a stimulation rate of 1 Hz show that a) a reflex discharge could be recorded about 6–10 ms after stimulation of the ipsilateral side of the tongue, b) stimulation of the contralateral side increased the latency by about 1–1.5 ms, c) the reflex could be evoked in animals which showed no spontaneous efferent activity in the chorda tympani nerve, d) recordings from nerve filaments showed that a filament could display spontaneous activity without being involved in the reflex, e) the lingual nerve serves as the main sensory link on the reflex to mechanical stimulation of the anterior part of the tongue, and f) the reflex evoked by stimulation of other parts of the oral region had a longer latency and less intense discharge. The results obtained at higher stimulation rate show that a) individual bursts of reflex discharge could be traced at stimulation frequencies up to 60 Hz, b) except for a moderate decrease the discharge did not disappear when stimulus frequencies of 5, 30 and 50 Hz were used.     

Influences of contralateral nerve and skin stimulation on neurones in the substantia gelatinosa of the rat spinal cord

Stimulation of high threshold A delta and C fibre peripheral afferents inhibits dorsal horn cells on the other side of the spinal cord. The substantia gelatinosa (SG) is an area full of interneurones known to have commissural connections across the spinal cord. The role of SG in this contralateral inhibitory pathway is investigated here. Forty-three SG cells were recorded in the lumbar dorsal horn of decerebrate spinal rats. Their ipsilateral excitatory receptive fields and responses to sciatic nerve stimulation were recorded. Repetitive electrical stimulation was then applied to the contralateral sciatic nerve. Eight (19%) units were excited by such stimulation. A brief tetanus was followed by an increase of ongoing activity lasting 30 s to 10 min. These cells did not, however, have excitatory contralateral fields. A small separate group of 4 cells (9%) were mildly inhibited by heating or pinching the contralateral limb. The significance of contralateral excitation of some SG cells is discussed in the light of the predominantly inhibitory contralateral effect on dorsal horn cells in laminae 4 and 5. It is suggested that some SG cells may be inhibitory interneurones in their effect on deeper cells.     

A descriptive tissue evaluation at maxillary interradicular sites: implications for orthodontic mini-implant placement

Few studies have evaluated interradicular anatomy for hard and soft tissue thickness. Because interradicular sites are common regions for mini-implant placement for orthodontic anchorage, the purpose of this study was to provide a guideline to indicate the best location for mini-implants as it relates to the thickness of cortical bone and soft tissue, and to the height of the attached gingival field. CT images from 15 men and 15 women (mean age 27 years, range 23-35 years) were used to evaluate the buccal interradicular cortical bone thickness from and mesial to the central incisor to the 1st molar. To record soft tissue depth at the site of assessment for cortical bone thickness, the mucosa was pierced with a #15 endodontic K-file until the attached rubber stop rested on the mucosa. The height of attached gingiva was measured at the mid-aspect of each tooth using a caliper. There were no significant differences in cortical bone thickness within interradicular sites except for the 2nd premolar/1st molar site. There were also no significant differences in soft tissue thickness within interradicular sites except for the lateral incisor/canine and 2nd premolar/1st molar sites. The height of attached gingiva was greater in the anterior compared to the posterior region and was shortest in the premolar region. Given the limits of this study, mini-implants for orthodontic anchorage may be well placed with equivalent bone-implant contact anywhere within the zone of attached gingiva up to 6 mm apical to the alveolar crest with adequate interradicular space.     

Receptive field properties of human periodontal afferents responding to loading of premolar and molar teeth

Impulses in 45 single mechanoreceptive afferents were recorded from the human inferior alveolar nerve with permucosally inserted tungsten microelectrodes. All afferents responded to mechanical stimulation of one or more premolar or molar teeth and most likely innervated their periodontal ligaments. For each afferent, isolated "ramp-and-hold" shaped force profiles of similar magnitudes (252 +/- 24 mN; mean +/- SD) were applied to the lower first premolar, the second premolar, and the first molar on the recording side. The tooth loads were applied in six directions: lingual, facial, mesial, and distal in the horizontal plane and up and down in the vertical direction of the tooth. The afferents response during the static phase of the stimulus was analyzed. All afferents were slowly adapting, discharging continuously in response to static forces in at least one stimulation direction. Twenty-nine afferents (64%) were spontaneously active, exhibiting an ongoing discharge in the absence of external stimulation. Stimulation of a single tooth was found to excite each afferent most strongly. The most sensitive tooth (MST) was the first premolar for 23, the second premolar for 13, and the first molar for 9 afferents. About half of the afferent population also responded to loading of one or two more teeth. The response profiles of these afferents indicated that the multiple-teeth receptive fields were due to mechanical coupling between the teeth rather than branching of single afferents to innervate several teeth. The afferent responses to loading the mesial and distal halves of the first molars were very similar. Thus both intensive and directional aspects of the afferent response when loading one side of the tooth was preserved to a great extent when loading the other side. When loading the MST, the afferents typically showed excitatory responses in two to four of the six stimulation directions, i.e., the afferents were broadly tuned to direction of tooth loading. In the horizontal plane, the afferent populations at the premolar teeth expressed no clear directional preferences. The afferents at the molar, however, showed a strong directional bias in the distal-lingual direction. In the vertical plane, there was a preference for downward-directed forces with a gradually decreasing sensitivity distally along the dental arch. The present results demonstrate that human periodontal afferents supplying anterior and posterior teeth differ in their capacity to signal horizontal and vertical forces, respectively.     

Synaptic efficacy of inhibitory synapses in hypoglossal motoneurons after transection of the hypoglossal nerves

In cat hypoglossal motoneurons after axotomy the synaptic efficacy of inhibitory synapses made by the lingual nerve afferent fibers was studied. The amplitude of the short- and the long-lasting inhibitory postsynaptic potential produced in tongue protruder motoneurons 24 days after axotomy by stimulation of the lingual nerve was significantly reduced in size as compared with the control on the unoperated side. In most protruder motoneurons 40 days after axotomy a large excitatory postsynaptic potential and a spike was produced by stimulation of either the ipsilateral or the contralateral lingual nerve. We have demonstrated that the decline of synaptic efficacy of inhibitory synapses for the short-lasting inhibitory postsynaptic potential was more prominent than that for the long-lasting inhibitory potential in the motoneuron 24 days after axotomy. After the cut axons of protruder motoneurons were re-united to tongue muscles, we have demonstrated that the decline of synaptic efficacy of inhibitory synapses for the short-lasting inhibitory postsynaptic potential was less prominent than that in axotomized protruder motoneurons.     

The synaptic basis of a bilateral lingual-hypoglossal reflex in cats

1. Reflex discharge of some hypoglossal neurones innervating the intrinsic musculature of the tongue occurred following single stimuli delivered to low threshold afferents in the ipsilateral or contralateral lingual nerves of decerebrate cats.2. The discharge produced by contralateral lingual nerve stimuli was smaller and had a longer latency than that produced by ipsilateral lingual nerve stimuli. The timing of the ipsilateral response suggested that two synapses were included in the reflex arc.3. Intracellular recordings in hypoglossal motoneurones revealed complex depolarizing and later hyperpolarizing synaptic respones following single nerve stimuli. The direction of the early synaptic action in any cell was the same whether low threshold afferents in the ipsilateral or the contralateral lingual nerve were stimulated. The timing of these synaptic responses and the occurrence of ripples on the rising phase of many of the depolarizing potentials was consistent with the presence of an internuncial neurone in the pathway from the afferent fibres to the motoneurone.4. Recordings were made of the discharges of neurones in or near the sensory nucleus of the spinal trigeminal tract caused by lingual nerve stimuli. The latencies of these discharges and the characters of the bursts of responses which followed single lingual nerve stimuli indicated that these neurones could be the internuncials on the reflex pathway.5. The relationship of these findings to the observations of Miller & Sherrington (1915) on the ;licking' reflex is discussed.     

Reflex responses of motor units in human masseter muscle to mechanical stimulation of a tooth

The reflex responses evoked by controlled mechanical stimulation of an upper central incisor tooth in single motor units in the human masseter muscle were examined. The stimuli were (brisk) taps and (slow) pushes of about 2 N peak force, applied orthogonally to the labial surface of the ipsilateral upper central incisor tooth. The reflex responses of the motor units were characterised by analysis of the changes in the durations of the first and second interspike intervals (ISIs) immediately following the stimulus. A significant increase in the duration of these ISIs in comparison with pre-stimulus ISIs indicated inhibition, and significant shortening indicated excitation. Twenty masseter motor units were tested with both the pushes and the taps. The brisk taps elicited a significant reflex inhibition in 16 of the 20 motor units at a latency of 13 ms and duration of 37 ms. This inhibition was followed by significant excitation in 11 of the 20 units at latencies of 71 ms, lasting for 29 ms. The short-latency response to slow pushes was significant inhibition in four units: significant excitation in one unit and no response in 15 units. The slow pushes evoked a significant long-latency excitatory reflex response in 12 of the 20 units at latencies of 77 ms and lasting for 40 ms. The shapes and amplitudes of the compound post-synaptic potentials underlying the reflex responses in the motoneurones were estimated. It is concluded that stimulation of periodontal mechanoreceptors usually activates an excitatory reflex pathway to the jaw-closing motoneurones. This probably helps to grip the food bolus between the teeth during chewing. However, when the rate of application of the stimulus is large enough, a short-latency inhibitory response is evoked which, if of sufficient duration, may over-ride the subsequent excitatory response. Inhibition of the jaw-closing muscles will tend to protect the teeth and soft tissues when one bites unexpectedly on a hard object while chewing.     

Mechanoafferent neurons innervating tail of Aplysia. I. Response properties and synaptic connections

Mechanical, chemical, or electrical stimulation of the tail elicits a short-latency (less than 1 s) tail-withdrawal reflex that is graded with the intensity of the stimulus. The tail-withdrawal reflex is not elicited by stimulation of parts of the body outside of the tail region. Mechanoafferent neurons innervating the tail are located in a small subcluster within a large, homogeneous group of medium-size (40-80 micron) cells on the ventrocaudal (VC) surface of each pleural ganglion. The tail sensory neurons within this large VC cluster are activated by tactile pressure or by electrical stimulation of discrete regions of the tail. They adapt slowly to maintained stimulation and sometimes respond to stimulus offset as well. Both mechanical and electrical stimuli produce responses that are graded with the intensity of the stimulus. Cells in the VC cluster appear to be primary mechanoreceptors because they have axons in peripheral nerves (including nerves innervating the tail), they exhibit action potentials lacking prepotentials in response to tactile stimulation, and these action potentials are still produced by cutaneous stimulation when peripheral and central chemical synaptic transmission is blocked. Stimulation of fields all over the body surface evokes synaptically mediated hyperpolarizing responses in individual mechanoafferent neurons that may represent afferent inhibition. Hyperpolarizing responses lasting many seconds can be produced by brief cutaneous stimuli. The mechanoafferent neurons innervating the tail region make strong monosynaptic connections to tail motor neurons in the ipsilateral pedal ganglion, and through these connections this subpopulation of the VC neurons appears to make a substantial contribution to the short-latency tail-withdrawal reflex. In addition, the combined excitatory receptive fields of these mechanoafferents match the excitatory receptive field of the tail-withdrawal reflex. Mechanoafferent neurons in the VC cluster that have receptive fields on other parts of the body (outside the excitatory receptive field of the tail-withdrawal reflex) have not been observed to make monosynaptic connections to the tail motor neurons. The neurons innervating the tail are reliably found in a discrete region within the larger VC cluster. In addition to this gross somatotopic organization, there is evidence of a finer level of somatotopic organization between the position of the excitatory receptive field on the tail and the position of the cell soma in the tail subcluster.(ABSTRACT TRUNCATED AT 400 WORDS)     

Evidence for the persistence of axons at the apex of the cat's lower canine tooth after section of the inferior alveolar nerve

The aim of this investigation was to establish the degree of denervation produced by inferior alveolar nerve section and to provide histological evidence for the presence of pulpal nerve fibres supplying the teeth which do not travel with the inferior alveolar nerve. Four adult cats were used. Each stage of the experiment was carried out under general anesthesia. The left inferior alveolar nerve was exposed and sectioned near the mandibular foramen. After 56 hours and 7 days, respectively, the jaw opening reflex to electrical stimulation of each lower canine was tested. Recordings were made from the left canine during electrical stimulation of the ipsilateral inferior alveolar nerve central and peripheral to the site of section as well as from the ipsilateral and contralateral inferior alveolar nerve during electrical stimulation of the left canine. Recordings were also made from the lingual nerve. After the recordings were completed two animals were perfused 56 hours after inferior alveolar nerve section, two more 7 days after section. Ultrathin sections of the apices of the lower canine teeth were examined in the electron microscope and each nerve fibre photographed. Each axon was examined to determine whether it was degenerating or normal. A jaw-opening reflex could not be elicited by stimulation of the left canine either 2 or 7 days after nerve section, whereas a normal response was evoked by stimulation of the right, control canine. At 2 days small responses could be recorded from the left canine teeth during stimulation of the left inferior alveolar nerve peripheral to the point of section. In one 2-day animal, responses could be recorded in the lingual nerve during stimulation. No pulpal fibres could be recorded in the inferior alveolar nerve central to the point of section nor from the contralateral inferior alveolar nerve. No pulpal fibres supplying the left canine could be recorded in any of the nerves examined at 7 days. Extensive degeneration was seen histologically even at 2 days. The canine pulp on the operated side contained only 31%, in one animal, and 26% in the other, of the number of axons of normal appearance that were present on the control side. At 7 days the number of remaining normal axons on the operated side were 5% and 13% of the numbers on the control side. All the axons of normal appearance were nonmyelinated. It is possible that the remaining axons represent fibres carried by the lingual nerve or some other alternative pathway that could not be detected electro-physiologically. Alternatively they may be a collateral innervation from adjacent tissues.     

Single-unit responses in the inferior colliculus: different consequences of contralateral and ipsilateral auditory stimulation

Monaural excitatory responses of 181 single units in the central nucleus of the inferior colliculus of 15 anesthetized gerbils (Meriones unguiculatus) were examined quantitatively. Pure-tone stimuli were presented monaurally through sealed, calibrated sound-delivery systems. Most units were excited only by contralateral stimulation (EO); 23% were bilaterally excitable (EE). The threshold frequency tuning curves for contralateral stimulation of EE units were significantly broader than those produced by ipsilateral stimulation of EE units and those produced by contralateral stimulation of EO units. The frequency at which threshold was lowest (best frequency), or BF) was very similar for ipsilateral and contralateral stimulation of individual EE units; however, ipsilateral BFs were slightly but significantly lower than contralateral BFs. For EE units, ipsilateral BF thresholds (mean: 29.2 dB SPL) were significantly higher than contralateral BF thresholds (mean: 14.9 dB SPL). Monotonic and nonmonotonic relationships between discharge rate and stimulus intensity at BF were observed in responses evoked both by contralateral and ipsilateral stimulation. Interestingly, for individual EE units it was not uncommon for the rate/intensity function for one monaural condition to be monotonic although the relationship for stimulation of the other ear was markedly nonmonotonic. There was no qualitative difference between rate/intensity functions evoked by contralateral stimulation in EO and EE units. Ipsilateral discharge rates were characteristically much lower than contralateral rates for a given stimulus intensity. For 50 BF tones of 100 ms duration, the median peak numbers of discharges for contralateral stimulation of EO and EE units were 361 and 339, respectively; the median for ipsilateral stimulation of EE units was 102. The dynamic range of each rate/intensity function was calculated by measuring the intensity range associated with an increase in spike count from 10 to 90% of the peak rate. No differences were detected between the distributions of dynamic range for contralateral stimulation in EO or EE units, or between contralateral and ipsilateral dynamic ranges within individual EE units. For all response types the distributions of dynamic range were approximately normal, with means near 20 dB. The minimum mean latency to the first spike at BF was generally longer for ipsilateral than for contralateral responses.(ABSTRACT TRUNCATED AT 400 WORDS)     

Responses of Single Motor Units in Human Masseter to Transcranial Magnetic Stimulation of Either Hemisphere

The corticobulbar inputs to single masseter motoneurons from the contra- and ipsilateral motor cortex were examined using focal transcranial magnetic stimulation (TMS) with a figure-of-eight stimulating coil. Fine-wire electrodes were inserted into the masseter muscle of six subjects, and the responses of 30 motor units were examined. All were tested with contralateral TMS, and 87 % showed a short-latency excitation in the peristimulus time histogram at 7.0 ± 0.3 ms. The response was a single peak of 1.5 ± 0.2 ms duration, consistent with monosynaptic excitation via a single D- or I₁-wave volley elicited by the stimulus. Increased TMS intensity produced a higher response probability (   n = 13  , paired t test,   P < 0.05  ) but did not affect response latency. Of the remaining motor units tested with contralateral TMS, 7 % did not respond at intensities tested, and 7 % had reduced firing probability without any preceding excitation. Sixteen of these motor units were also tested with ipsilateral TMS and four (25 %) showed short-latency excitation at 6.7 ± 0.6 ms, with a duration of 1.5 ± 0.3 ms. Latency and duration of excitatory peaks for these four motor units did not differ significantly with ipsilateral vs . contralateral TMS (paired t tests,   P > 0.05  ). Of the motor units tested with ipsilateral TMS, 56 % responded with a reduced firing probability without a preceding excitation, and 19 % did not respond. These data suggest that masseter motoneurons receive monosynaptic input from the motor cortex that is asymmetrical from each hemisphere, with most low threshold motoneurons receiving short-latency excitatory input from the contralateral hemisphere only.     

Premotor interneurones contributing to actions of feline pyramidal tract neurones on ipsilateral hindlimb motoneurones

The aim of the study was to analyse the potential contribution of excitatory and inhibitory premotor interneurones in reflex pathways from muscle afferents to actions of pyramidal tract (PT) neurones on ipsilateral hindlimb motoneurones. Disynaptic EPSPs and IPSPs evoked in motoneurones in deeply anaesthetized cats by group Ia, Ib and II muscle afferents were found to be facilitated by stimulation of the ipsilateral, as well as of contralateral, PT. The ipsilateral actions were evoked by either uncrossed or double-crossed pathways. The results show that interneurones mediating reflex actions of muscle afferents may be activated strongly enough by PT stimulation to contribute to movements initiated by ipsilateral PT neurones and that PT actions relayed by them might be enhanced by muscle stretches and/or contractions. However, in some motoneurones disynaptic IPSPs and EPSPs evoked from group Ib or II afferents were depressed by PT stimulation. In order to analyse the basis of this depression, the transmitter content in terminals of 11 intracellularly labelled interneurones excited by PT stimulation was defined immunohistochemically and their axonal projections were reconstructed. The interneurones included 9 glycinergic and 2 glutamatergic neurones. All but one of these neurones were mono- or disynaptically excited by group I and/or II afferents. Several projected to motor nuclei and formed contacts with motoneurones. However, all had terminal projections to areas outside the motor nuclei. Therefore both inhibitory and excitatory interneurones could modulate responses of other premotor interneurones in parallel with direct actions on motoneurones.     

Biochemical characterization of collagen in alveolar mucosa and attached gingiva of pig

Alveolar mucosa and attached gingiva are two continuous but functionally distinct connective tissues covering alveolar bone of the jaw. In this study, the major matrix component of these tissues, collagen, was biochemically characterized and compared. The tissues were obtained from mature pigs and analyzed for collagen content, amino acid composition, collagen types, collagen cross-linking, and gene expression. We found that alveolar mucosa is primarily composed of fibrillar collagens and the collagen content is higher than attached gingiva. The content of type III relative to type I collagen was higher in alveolar mucosa when compared with attached gingiva. The collagen cross-linking pattern also was distinct between the two tissues demonstrating that alveolar mucosa contained fewer reducible cross-links but more non-reducible cross-links in comparison to attached gingiva. The mRNA expression level of type I collagen in alveolar mucosa was significantly lower than that of attached gingiva. These results indicate that alveolar mucosa is a fibrillar collagen-rich tissue and, in comparison to gingival tissue, re-models slowly.     

Quadriceps excitability is enhanced by a conditioning tap to the Achilles tendon

In an effort to more fully investigate spinal reflex pathways in humans, we measured the isometric force-time characteristics of the patellar tendon-tap reflex in ten college-age subjects. We also conditioned the tendon jerk with a tap to the contralateral Achilles tendon or the ipsilateral Achilles tendon. The results clearly demonstrated that a conditioning tap to the Achilles tendon produced a marked (greater than 200 percent) excitatory effect onto the quadriceps muscle. Also, this effect occurred sooner when the quadriceps was conditioned by an ipsilateral stimulus rather than a contralateral stimulus. It is concluded that in accord with other conditioning studies to date, the quadriceps muscle is characterized by a predominantly excitatory effect caused by a conditioning stimulus, and that this arousal is independent of the origin of the conditioning stimulus.     

Extent of the ipsilateral representation in the ventral posterior medial nucleus of the monkey thalamus

Summary Single and multiunit mapping was used to determine the extent of the representation of ipsilateral structures in the ventral posterior medial (VPM) nucleus of the thalamus in cynomolgus monkeys. The extent of the VPM occupied by terminations of afferent fibers arising in the ipsilateral principal trigeminal nucleus was also determined by anterograde transport of horseradish peroxidase. Both methods indicate that most of the medial half of VPM is occupied by the ipsilateral representation. This is much larger than previously suspected. Units in the medial half of VPM have small, well localized receptive fields on the ipsilateral side of the lower lip, tongue and palate, in the ipsilateral cheek pouch and on the ipsilateral teeth. The representation is largest for the ipsilateral side of the tongue and the cheek pouch. Most units in the lateral half of VPM have small, contralateral receptive fields. Few units in VPM have bilateral receptive fields. VPM is clearly distinguishable by cytochrome oxidase (CO) staining. Anteroposteriorly elongated, CO-positive aggreations correspond to elongated aggregations of units with the same or closely similar receptive fields, especially in the medial, ipsilateral representation.Abbreviations CL Central lateral nucleus - CM Centre médian nucleus - DCN Dorsal cochlear nucleus - DIT Dorsal ipsilateral trigeminal tract - IO Inferior olivary nuclei - ML Medial lemniscus - MV Motor trigeminal nucleus - PRV Principal sensory trigeminal nucleus - SO Superior olivary nuclei - SPV Spinal trigeminal nucleus - Ves Vestibular nuclei - VMb Basal ventral medial nucleus - VPI Ventral posterior inferior nucleus - VPL Ventral posterior lateral nucleus - VPM Ventral posterior medial nucleus - IV Trochlear nucleus - VI Abducens nucleus     

Responses of single units in the inferior olive to stimulation of the limb nerves, peripheral skin receptors, cerebellum, caudate nucleus and motor cortex

1. Extra- and intracellular responses of single units in the inferior olive following stimulation of the cerebellum, limb nerves, skin receptors, the caudate nucleus and cerebral cortex have been described.2. Responses following cerebellar stimulation were assumed to be antidromic spikes when they occurred after a latency of less than 4 msec and followed stimulus frequencies greater than 220/sec. Other responses with longer latencies were thought to be transynaptic. Evidence for recurrent inhibition of the Renshaw type is given.3. Following limb nerve stimulation two types of units have been observed; units responding after a short latency and to stimulation of one limb only and units responding with a long latency following stimulation of one or more of the limbs.4. Units responding to stimulation of the limb nerve after a short latency could often be excited by hair movement and/or light touch on the pads. Other units were excited by pinching and others could not be excited by a physiological stimulus. The receptive field of these units was small and there was no evidence of fringe inhibition.5. Most units observed represented the contralateral forelimb but there was a significant number of units representing the ipsilateral limbs.6. The caudato-olivary pathway has been shown to be excitatory. Short latency limb units do not receive afferents from the caudate nucleus.7. Afferents from the motor cortex excite units in the inferior olive. A remarkable correlation of latencies of responses from both the cerebral cortex and the limbs on to individual units has been described.8. The results suggest a complex organization of neurones within the inferior olive. A possible plan of the organization of neurones is given and discussed.