Effect of controlled exercise on middle gluteal muscle fibre composition in Thoroughbred foals

REASONS FOR PERFORMING STUDY

Most racehorses are trained regularly from about age 18 months; therefore, little information is available on the effect of training in Thoroughbred foals.

HYPOTHESIS

Well-controlled exercise could improve muscle potential ability for endurance running.

METHODS

Thoroughbred foals at age 2 months were separated into control and training (treadmill exercise) groups and samples obtained from the middle gluteal muscle at 2 and 12 months post partum. Muscle fibre compositions were determined by histochemical and electrophoretical techniques and succinic dehydrogenase (SDH) activity was analysed in each fibre type.

RESULTS

All fibre types were hypertrophied with growth and type I and IIA fibres were significantly larger in the training than the control group at age 12 months. A significant increase of SDH activity was found in type IIX muscle fibres in the training group.

CONCLUSIONS

Training in young Thoroughbred horses can facilitate muscle fibre hypertrophy and increase the oxidative capacity of type IIX fibres, which could potentially enhance stamina at high speeds.

POTENTIAL RELEVANCE

To apply this result to practical training, further studies are needed to determine more effective and safe intensities of controlled exercise.

Effect of high intensity training on anaerobic capacity of middle gluteal muscle in Thoroughbred horses

We hypothesize that high intensity training for Thoroughbred horses that have been subjected to conventional training could further improve the metabolic properties of the middle gluteal muscle. Nine well-trained horses were subjected to high intensity (80-100% Vdot;O(2)max, 5 minx2) training for 12 weeks. Biopsy samples were obtained from the muscle before and after 4 and 12 weeks of training. Three of the 9 horses did not complete the training programme. In the remaining 6 horses, activities of succinic dehydrogenase (SDH), phosphofructokinase (PFK) and 3-hydroxy acyl CoA dehydrogenase (HAD), and the composition of myosin heavy chain isoforms were analyzed by biochemical techniques. After 12 weeks of training, a significant increase was found in PFK activity but not in the SDH and HAD activities. There were no significant changes in the composition of myosin heavy chain isoforms. The high intensity training in this study was effective at increasing glycolytic enzyme activity, indicating the possibility to improve anaerobic capacity, which potentially could contribute greatly to performance in Thoroughbred horses. This study also highlighted a fact that high intensity training should be given with the great care to prevent the skeletal muscle injuries.

Long-term follow-up results of electrogustometry and subjective taste disorder after middle ear surgery

OBJECTIVES

The present study compares the long-term follow-up results of electrogustometry with patient reports of taste dysfunction after middle ear surgery.

STUDY DESIGN

Retrospective review of 371 patients who underwent middle ear surgery.

METHODS

Patients were divided into the following groups depending on the degree of manipulation or surgical damage to the chorda tympani nerves: the no-touch group (group 1 [n = 109]); the touch group (group 2 [n = 149]); and the severed nerve group (group 3 [n = 113]). Electrogustometry was periodically performed over the course of several years.

RESULTS

The incidences of postoperative subjective taste disorder in groups 1, 2, and 3 were 2.8%, 25.5%, and 38.9%, respectively. Although the subjective taste disorder usually recovered within 1 to 2 years after surgery in all groups, it persisted for more than 2 years in 2.7% of the touch group and 5.3% of the severed nerve group. Concerning postoperative electrogustometric results, in the no-touch group, 8.3% of patients showed threshold elevation on electrogustometry, but the elevated thresholds completely recovered in all cases. In the touch group, 45% of patients exhibited elevated electrogustometric thresholds on their first postoperative test, including 32.9% who subsequently had complete electrogustometric recovery, 10.1% who subsequently had incomplete recovery, and 2% who failed to recover during the follow-up period. In the severed nerve group, none of the patients was responsive to the electrical stimulus on the first postoperative test, including 8.8% of patients who subsequently exhibited complete electrogustometric recovery, 32.7% who later had incomplete electrogustometric recovery, and 58.4% who never recovered any electrogustometric responsiveness. Nerve repair in the severed nerve group produced better recovery, as measured electrically.

CONCLUSIONS

The incidence of postoperative subjective taste disorder was low, although inconsistent with the high incidence of threshold elevation on electrogustometry, especially in the severed nerve group. Preservation or repair of the chorda tympani nerve is recommended in order to maintain or recover gustatory function.

Doxorubicin ototoxicity is induced in mice by combination treatment with cyclosporin A

Although doxorubicin [adriamycin (ADM)] ototoxicity has not been detected to date, it has been reported that neurotoxicity in the central nervous system was induced by chemotherapy with ADM in patients receiving chronic cyclosporin A (CsA) treatment. ADM ototoxicity may be induced by combination therapy with CsA because extrusion of ADM from the inner ear by p-glycoprotein (p-gp), which acts as an extrusion pump and is expressed on the surface of endothelial cells of capillary blood vessels, might be inhibited by CsA. resulting in significant accumulation of ADM in the inner ear. ADM (10 mg/kg) was administered to FVB mice either with or without CsA (200 mg/kg). Auditory brainstem responses (ABRs) were recorded before and after treatment. ABR changes were not observed in mice treated with either ADM or CsA alone. Threshold elevation, elongation of wave I-V latencies and interpeak latencies of waves I-II, I-III, I-IV and I-V were detected in mice treated with ADM in combination with CsA. These changes reached their peak values 3 weeks after treatment, and then recovered to pre-treatment levels. In normal mice, ADM is extruded by p-gp from the inner ear and auditory pathway, thus preventing hearing disorder. However, ADM ototoxicity was induced by combination therapy with CsA, indicating that CsA has an inhibitory action on p-gp function in the auditory pathway, including the inner ear. After organ transplantation, therefore, clinical administration of ADM in combination with CsA should be performed with caution.

Expression of p-glycoprotein is associated with that of multidrug resistance protein 1 (MRP1) in the vestibular labyrinth and endolymphatic sac of the guinea pig

Expression of p-glycoprotein (p-gp) and multidrug resistance protein 1 (MRP1) was detected in the vestibular labyrinth and endolymphatic sac (ES) of the guinea pig by immunohistochemical staining using anti-p-gp monoclonal antibody (mAb) C219 and anti-MRP mAb MRPr1. P-gp was detected in capillary endothelial cells of the crista ampullaris, utricle, saccule and ES. MRP1 was detected in the epithelial lining of the crista ampullaris, utricle, saccule, and epithelial cells of the ES. Since p-gp and MRP1 act as extrusion pumps, they may coordinate with each other in vestibular organs and ES and play an important role in the blood-labyrinth barrier.

Cyclosporin A inhibits the extrusion pump function of p-glycoprotein in the inner ear of mice treated with vinblastine and doxorubicin

Cyclosporin A (CsA) inhibits the membrane transport protein p-glycoprotein (p-gp) and can enhance the accumulation of vinblastine (VBL) and doxorubicin (Dx) in the inner ear of mice. In mice pretreated with 200 mg/kg of CsA, there were significantly increased VBL and Dx concentrations detected in the inner ear tissue and other organs, with a small but significant increase in the brain. Furthermore, hearing thresholds measured by auditory brainstem responses were significantly elevated 3 weeks after VBL or Dx treatment in combination with CsA. However, the altered thresholds recovered to pretreatment levels 8 weeks after treatment. Pharmacokinetic and functional alterations observed in this study suggest caution in applying these combinations in clinical practice.

Expression of multidrug resistance protein 1 (MRP1) in the rat cochlea with special reference to the blood-inner ear barrier

Expression of multidrug resistance protein 1 (MRP1) was detected in the rat cochlea by RT-PCR and immunohistochemistry using anti-MRP monoclonal antibody MRPr1. Use of primers specific for rat mrp1 gene resulted in the amplification of an expected 394 bp fragment prepared from brain and cochlear tissues. Immunohistochemically, MRP was found in the choroid plexus, stria vascularis, spiral ligament, spiral prominence and cochlear nerve in the modiolus. From these results, it was suggested that MRP in the rat cochlea might function as an extrusion pump and play an important role in the blood-inner ear barrier.

Recent outcome of tympanoplasty in the elderly

OBJECTIVE

To investigate the outcome of tympanoplasty in the elderly (patients older than 60 years) compared with younger patients.

PATIENTS AND STUDY DESIGN

Retrospective review of 87 (28.3%) older patients among a total of 307 patients with chronic otitis media with or without cholesteatoma who were surgically treated at a university hospital by the senior author. Follow-up was systematically provided at the same institution.

INTERVENTIONS

Surgery included tympanoplasty with mastoidectomy performed as the primary procedure in 358 ears. Tympanoplasty was performed with canal-wall-up or canal-wall-down with canal wall reconstruction, ossiculoplasty with autologous or homologous ossicle interposition or columella. Mean follow-up was 30 months (range, 12-70 months).

MAIN OUTCOME MEASURES

Pre- and postoperative air- and bone-conduction thresholds were calculated as an average of three speech frequencies (0.5, 1, and 2 kHz). Analysis was subsequently carried out on the postoperative air-bone gap, hearing gain, and postoperative problems such as elevation of the bone-conduction threshold, delayed epithelialization, and reperforation of the eardrum. Statistical analysis was performed by chi-square or Student's t-test. A p value less than 0.05 was considered significant.

RESULTS

Compared with results from younger patients, there was no particular disadvantage in postoperative hearing results and complications in the elderly, although preoperative bone-conduction thresholds were gradually worsened with age.

CONCLUSIONS

There is no contraindication for tympanoplasty in older patients if their physical status is the same or better than what is normal for their chronological age.

Spinal projections of cat primary afferent fibers innervating caudal facet joints

The spinal projections of afferent fibers innervating the facet joints between caudal vertebrae were examined by the use of anterograde transport of wheat germ agglutinin-horseradish peroxidase (WGA-HRP). Experiments were performed on 5 adult cats in which spinal dorsal roots below the 2nd sacral segment (S2) on the right side were cut. Injections of WGA-HRP into the caudal facet joints gave rise to extensive cranio-caudal distribution of WGA-HRP positive products along the spinal cord, indicating that many afferent fibers innervating unilateral facet joints terminate bilaterally in laminae I-II, V-VI and X of the thoracic, lumbar, sacral and caudal spinal cord. These afferent fibers may convey a series of sensory information from the caudal facet joints to the spinal cord.

Use of an instrument sandwiched between the hoof and shoe to measure vertical ground reaction forces and three-dimensional acceleration at the walk, trot, and canter in horses

OBJECTIVE

To develop an instrument that could be sandwiched between the hoof and shoe of horses and that would reliably measure vertical ground reaction forces and three-dimensional acceleration at the walk, trot, and canter.

ANIMALS

5 clinically sound Thoroughbreds.

PROCEDURES

The recording instrument (weight, 350 g) consisted of 2 metal plates, 2 bolts, 4 load cells, and 3 accelerometers. It was mounted to the hoof with a glue-on shoe and devised to support as much load exerted by a limb as possible. The load cells and accelerometers were wired to a 16-channel transmitter, and transmitted signals were received and amplified with a telemetry receiver.

RESULTS

The recording instrument could measure in real time the 4 components of the ground reaction force or their resultant force along with acceleration in 3 dimensions as horses walked, trotted, or cantered on a treadmill. Patterns of force-time curves recorded for consecutive strides were similar to each other and to those previously reported, using a force plate.

CONCLUSIONS AND CLINICAL RELEVANCE

The recording instrument developed for use in the present study allowed us to record vertical ground reaction force and acceleration in 3 dimensions in horses at the walk, trot, and canter.

Electromyographic and kinematic studies of tail movements during falling in cats

When falling from an inverted position, EMG activities of tail muscles (the m. extensor caudae lateralis, m. abductor caudae externus, m. flexor caudae longus) and tail movements were recorded in 7 long-tailed adult cats. After being released from an elevated position, cat rotates the tail in a reverse direction to rotation of other parts of the cat's body then lands on four legs. Rotation of the tail was started by EMG activities of the tail muscles on one side. Both synchronized and alternating groups of discharge occur between its left and right side, while extensor and flexor movements and displacements of its tail appear in the air. After transection of ventral roots from the coccygeal spinal segments innervating tail muscles, cats often fail to land on four legs. These facts suggest that that tail movements control body balance in the air when falling from an inverted position.

Neuronal pathways from low-threshold muscle and cutaneous afferents innervating tail to trunk muscle motoneurons in the cat

We studied neuronal pathways from low-threshold muscle (group I, II) and cutaneous afferents (group A(alpha)beta) innervating the tail to motoneurons innervating trunk muscles (m. iliocostalis lumborum and m. obliquus externus abdominus) in 18 spinalized cats. Stimulation of group I muscle afferents produced excitatory postsynaptic potentials or excitatory postsynaptic potentials followed by inhibitory postsynaptic potentials in all motoneurons innervating the m. iliocostalis lumborum which showed effects (32%), and predominantly inhibitory postsynaptic potentials in motoneurons innervating the m. obliquus externus abdominus (47%). Stimulation of group I+II afferents produced significant increases of the incidence of motoneurons showing postsynaptic potentials (the notoneurons innervating the m. iliocostalis lumborum, 87%; the motoneurons innervating the m. obliquus externus abdominus, 82%). The effects of low threshold cutaneous afferents were bilateral, predominantly producing inhibitory postsynaptic potentials in motoneurons innervating both muscles. These results suggest that neuronal pathways from muscle afferents to back muscle motoneurons mainly increase the stiffness of the trunk to maintain its stability, while those to abdominal muscles help to extend the dorsal column by decreasing their activities. The results also indicate that neuronal pathways from cutaneous afferents to trunk motoneurons functionallY disconnect the tail from the trunk.

The effect of pyramidal stimulation upon tail muscle motoneurons in the decerebrate cat

This study aimed to determine the effects of the corticospinal tract (CST) on the motoneurons innervating the tail muscles in cats. The stimulation of the pyramidal tract predominantly evoked excitatory postsynaptic potentials (EPSPs; 48/90 motoneurons: 53%). Single-pulse stimulation produced EPSPs in 18 of 48 motoneurons, but double shocks evoked postsynaptic potentials in most of the remaining cells (26/48). Monosynaptic excitatory connections between pyramidal tract fibers and tail motoneurons were confirmed in 4 motoneurons. Inhibitory postsynaptic potentials (IPSPs) were recorded from motoneurons innervating long tendinous tail muscles (7/90: 8%) and the shortest neuronal pathways of IPSPs were shown to be disynaptic pathways. Interactions between the CST and reflex pathways from low-threshold muscle and cutaneous afferents innervating the tail and hindlimbs were observed.

Effects of a canine Elizabethan collar on ambulatory electrocardiogram recorded by a Holter recording system and spontaneous activities measured continuously by an accelerometer in Beagle dogs

Ambulatory electrocardiogram (ECG) has been recorded in dogs wearing a jacket to protect a Holter recording system, but the jacket was often damaged by dogs. We compared ECG recorded by a Holter recording system and spontaneous activity measured by an accelerometer in Beagle dogs with or without an Elizabethan collar. There were few significant differences in mean values (per hr) of the heart rate and the amount of spontaneous activity between dogs with or without the Elizabethan collar. Mean values (per 23 hr) of them had no significant difference between them. We concluded that the Elizabethan collar did not have any effect on ambulatory ECG and canine movements and was effective to protect the recording apparatus.

An intracellular study of pudendal afferent inputs onto tail motoneurons in the spinalized cat

Postsynaptic potentials, elicited by stimulation of the sensory pudendal (SPud) and superficial perineal nerves (SPeri) on both sides, were recorded from motoneurons innervating tail muscles in the non-anaesthetized and spinalized cat. The stimulation of SPud and SPeri on both sides predominantly produced excitatory postsynaptic potentials (EPSPs) in all kinds of tail motoneurons (70-95%). The inhibitory postsynaptic potentials (IPSPs) were often observed in motoneurons innervating ventral tail muscles (30-33%). The means of averaged central latencies of EPSPs and IPSPs ranged from 4.3 to 7.3 ms, and from 4.6 to 8.4 ms, respectively. The findings suggests that polysynaptic neuronal pathways from pudendal nerve to tail motoneurons produce tonic activities of all tail muscles to raise the tail in micturation, defecation and sexual movements which are induced by stimulation of pudendal nerves.

Spontaneous activities measured continuously by an accelerometer in beagle dogs housed in a cage

Spontaneous activities in 10 beagle dogs housed in an individual cage were recorded continuously for 2 hr by an accelerometer fixed to dogs and by a video camera. The responses of the accelerometer were compared to movements identified from the video tapes. We found that gross differentiation of quantitative spontaneous activities might be possible by using only the accelerometer if the threshold of the accelerometer and the amount of acceleration volume were set adequately: the responses of the accelerometer at the threshold of 0.10 G with the acceleration number of 251 or more revealed only movements of the whole-body, and those at the threshold of 0.02 G all movements including changes of the part(s) of the body.

Muscle adaptation of Thoroughbred racehorses trained on a flat or sloped track

OBJECTIVE

To determine histochemical and biochemical properties of muscle during adaptation to training on a flat or sloped track.

ANIMALS

22 Thoroughbreds.

PROCEDURE

Samples were obtained from the middle gluteus muscle before and after training programs were conducted, using a needle-biopsy technique. Training programs consisted of horses running 1,600 m on a flat or sloped track for 16 weeks. Amplitude of middle gluteus muscle activity per burst was calculated. Muscle fiber composition and area were examined on serial cross sections processed by standard histochemical staining procedures (ATPase stain after prior incubation with an acid or base, followed by succinate dehydrogenase [SDH] stain). Furthermore, SDH and phosphofructokinase activities were determined biochemically, and composition of myosin heavy chain (MHC) isoforms was analyzed electrophoretically.

RESULTS

Training resulted in substantial adaptations. Relative contribution of muscle fiber with high SDH activity (type-I and -IIa fibers) to total cross-sectional area, SDH activity, and composition of MHC-IIa isoforms were increased. Gel electrophoresis revealed a large amount of MHC-IIx isoform and a small amount of MHC-IIb isoform in the muscle. Although root mean square of muscle activity for training on a sloped track was 7.6% higher than the value obtained while training on a flat track, muscle histochemical and biochemical properties did not differ significantly between groups training on flat and sloped tracks.

CONCLUSIONS

Training adaptations for contractile and metabolic properties of the middle gluteus muscle were evident for the 2 types of training. However, training adaptations did not differ significantly between groups trained on flat or sloped tracks.

Neuronal pathways from low-threshold hindlimb cutaneous afferents to motoneurons innervating trunk muscles in low-spinal cats

Postsynaptic potentials (PSPs) evoked in motoneurons innervating the back and abdominal muscles in the lumbar part of the body by stimulating hindlimb cutaneous afferents were investigated in unanesthetized decerebate and spinal cats. Various types of PSP: pure excitatory postsynaptic potential (EPSP), pure inhibitory postsynaptic potential (IPSP), and mixed PSP (i.e., EPSP followed by IPSP, EPSP/IPSP; and IPSP followed by EPSP, IPSP/EPSP) were observed. The weak stimulation at 2 times threshold (2T) produced predominantly the EPSP, while at 5T the incidence of IPSP or EPSP followed by IPSP was increased. In about 20-50% of the various groups of motoneurons, PSPs evoked by ipsi- and contralateral nerves were qualitatively and quantitatively similar. For the other motoneurons, PSPs evoked by ipsi- and contralateral nerves were markedly different with respect to magnitude and/or polarity. These findings suggest that, within each motoneuron pool, some neurons act to increase stiffness of the trunk or to move vertically in response to an increased activity of cutaneous afferents, while the other motoneurons act to produce lateral bending of the trunk.

EMG activity of the muscles of the neck and forelimbs during different forms of locomotion

We recorded the electromyographic (EMG) activity of 7 skeletal muscles in the forequarters and 1 in the hindquarters of 6 Thoroughbred horses during overground walking, swimming in a circular pool, and walking and trotting in a water treadmill. Bipolar fine wire electrodes were inserted into the muscles and the EMG signals were recorded using a telemetric system. The splenius exhibited tonic EMG activity during swimming. The brachiocephalicus showed its highest intensity during swimming followed by the walk and trot in the water treadmill and then walking overground. The triceps brachii caput longum had a similar activity pattern to the brachiocephalicus. The brachialis showed only weak EMG activity in all 3 types of locomotion. The extensor digitorum communis had higher intensity of EMG activity in the walk in the water treadmill than in other kinds of locomotion. The flexor digitorum profundus exhibited the most intense EMG activity during swimming. These results indicated that swimming evoked strong EMG activity in the antigravity muscles in spite of reduced gravitational force. Walking in the water treadmill may require more intensified EMG activity of the forelimb than the trot in the same treadmill.

Histochemical analysis of fiber composition of skeletal muscles in pigeons and chickens

The fiber type composition of 12 skeletal muscles in pigeon and chicken were studied by staining for myofibrillar adenosine triphosphatase (ATPase: pH 10.3) and succinate dehydrogenase (SDH). The muscles contained three types of muscle fibers: FG (fast-twitch glycolytic), FOG (fast-twitch oxidative glycolytic), and SO (slow-twitch oxidative). The numbers and diameters of the different types of fibers were examined. The muscles of chickens and pigeons consisted mainly of FG and FG + FOG fibers, respectively. In m. pectorals superficialis (PS) and m. latissimus dorsi (LD), which produce flapping movements in pigeons, some clusters of FG fibers were observed among FOG fibers and the diameter of FG fibers was more than twice as large as that of FOG fibers.

Age-related changes in the brainstem auditory evoked potentials of the marmoset

Changes in brain-stem auditory evoked potentials (BAEPs) with age were recorded in common marmosets (Callithrix jacchus) at the age of 1-2, 6-8 and 10-12 years. The auditory function was assessed by thresholds, latencies and amplitudes of BAEPs evoked by use of tone burst stimulations with audible frequencies ranging from 1 to 99 kHz. Prolongation of the latencies of later waves was observed in the animals at the age of 6-8 and 10-12 years at high frequencies, suggesting that aging in marmosets, as reported previously in humans and other animals, may cause earlier hearing loss at high frequency than at low frequency within the hearing range. At 10-12 years of age, the elevations of BAEP thresholds and the declines of BAEP amplitudes in older animals were also observed. As the differences in the parameters are small, it was suggested that only a moderate hearing loss occurred with onset late in life in common marmoset similar to that in CBA/Ca mice. Based on the results obtained in this study, BAEP latencies appear to be more sensitive indicators than BAEP thresholds and amplitudes for the early detection of hearing impairment.

Aqueous humor dynamics in beagle dogs with caffeine-induced ocular hypertension

In order to investigate the possible mechanisms for caffeine-induced ocular hypertension, the intraocular pressure (IOP) and the outflow through the trabecular meshwork were measured in beagle dog eyes after dosing with intravenous caffeine (30 mg/kg) alone or in combination with the topical beta-blocker befunolol [applied as 100 microliters of a 1% (w/v) solution] which inhibits aqueous humor formation in the ciliary body. Intravenous injections of caffeine significantly increased the IOP at 0.25 and 1 hr after a single dose. The ocular hypertension recovered within 2 hr following dosing. Over time, there were no differences in the outflow between the caffeine and control groups. The instillation of befunolol lowered outflow and produced ocular hypotension. The levels of the IOP and outflow in dogs treated with caffeine and befunolol in combination were almost the same as those in dogs treated with befunolol alone. Single-dose and combination-dose studies demonstrate that intravenous caffeine increases the IOP in normal beagle dogs possibly by increasing aqueous humor formation and not by the inhibition of aqueous humor drainage through the trabecular meshwork.

Polysynaptic neuronal pathways from group I and group II afferents innervating tail muscles to hindlimb motoneurons in the cat

Postsynaptic potentials evoked in motoneurons innervating m. posterior biceps and semitendinosus (PBSt) and m. triceps surae (GS) by low threshold afferents from various tail muscles located at the level of the second-third caudal vertebrae were investigated in the non-anesthetized and spinalized cat. Afferent inputs from tail muscles on both sides predominantly evoked depolarizing potential in PBSt motoneurons and hyperpolarizing potential in GS motoneurons. The findings suggest that in general, tail muscle afferents facilitate flexor and inhibit extensor hindlimb motoneurons through polysynaptic pathways, so that the pelvic girdle is kept in a low position to maintain the stability of the body irrespective of different movements or posture of the tail.

Effects of the lateral vestibulospinal tract on rhythmic discharges induced by stimulation of the mesencephalic locomotor region (MLR) in the decerebrated cat

The purpose of this experiment is to confirm the effects of the descending pathway from the lateral vestibular nucleus (LVN) on rhythmic discharges induced by stimulation of the mesencephalic locomotor region (MLR) in the decerebrated cat. The experiments were performed on 18 adult cats (2.5-4.0 kg) of either sex. The rhythmic discharges produced by the MLR stimulation were recorded from hindlimb extensor muscle (LGS: lateral gastrocnemius and soleus) and flexor muscle (PBST: posterior biceps and semitendinosus) nerves. The LVN stimulation influenced the amplitude and interval of the rhythmic discharges in both extensor and flexor muscle nerves.

Relationship between caffeine-induced ocular hypertension and ultrastructure changes of non-pigmented ciliary epithelial cells in rats

The purpose of this study was to morphologically assess a possible mechanism for caffeine-induced ocular hypertension. Taking into consideration the relationship between the secretion of aqueous humor and the ultrastructure of the ciliary body, the time course of the morphological features in the ciliary epithelium when caffeine was administered intravenously to male Wistar rats was investigated by electron-microscopy. These morphological findings were also compared with the changes in the intraocular pressure (IOP). A significant increase in IOP was noted 15 min and 1 hr after a single dosing of caffeine alone. This change disappeared in all animals within 2 hr after dosing. The IOP in the animals receiving caffeine and the beta-blocker befunolol, which lowers the IOP by inhibiting aqueous humor secretion, decreased significantly from 15 min after dosing, and this change persisted 2 hr after dosing. In electron-microscopy 15 min and/or 1 hr after dosing with caffeine, a slight dilatation in the lateral intercellular spaces near the basement membrane of the non-pigmented ciliary epithelium was observed and the interdigitations between the non-pigmented epithelial cells were intact. Reversal of these changes was observed 2 hr after dosing. On the other hand, the lateral intercellular spaces between the non-pigmented epithelial cells were markedly dilated and the interdigitations were disorganized following dosing with caffeine alone and in combination with befunolol. These results described here indicate that the intravenous administration of caffeine causes ocular hypertension and also changes in the non-pigmented ciliary epithelium, suggesting an enhancement of aqueous humor transportation. This paradigm in the rat is considered to be useful to further assess caffeine-induced ocular hypertension and for use as an animal model in glaucoma research associated with an aqueous humor secretion.

Frequency selectivity on aspirin-induced hearing loss in rats with auditory stimulus-induced conditioned suppression

The conditioned suppression technique was employed to examine the acute effects of aspirin on auditory function in rats. Lever pressing behavior for water reinforcement was suppressed in the presence of an auditory stimulus that had been previously paired with electric shocks. A single intravenous injection of aspirin at a dose of 225 mg/kg caused an erroneous lever pressing response in the broad sound intensities of 2 kHz tone stimulus during the conditioned stimulus period. A statistically significant increase in the threshold for 2 kHz was found 1 to 72 hr after dosing but not for 4, 8 and 10 kHz. These results suggest that the hearing for low sound frequency in rats is vulnerable to the effects of aspirin. This paradigm in rats may be useful to further assess the different outer hair cells along the cochlear duct and provide an additional evidence for the aspirin ototoxicity research.

Rhythmical discharges recorded from cervical and trunk muscle nerves produced by stimulation of mesencephalic locomotor region (MLR) in the decerebrated cat

This experiment investigated the effects of mesencephalic locomotor region (MLR) stimulation on cervical and trunk motoneurons in decerebrated cats. The experiments were performed on 28 adult cats (2.1-3.9 kg) of either sex. Stimulation of MLR produced the rhythmical discharge of muscle nerves of the splenius (SP), the longissimus lumborum (LL) and the obliquus externus abdominis (OEA). There was a close relationship between rhythmical discharge of SP, LL or OEA muscle nerve and hindlimb muscle nerve. This fact suggests that rhythmical discharges of cervical and trunk muscle nerves relate to locomotion.

Effects of click intensity and frequency on the brain-stem auditory evoked potentials in the common marmoset (Callithrix jacchus)

Brain-stem auditory evoked potentials (BAEPs) were recorded in 20 common marmosets (Callithrix jacchus) to investigate the effects of click frequency up to 99 kHz, in consideration of the higher hearing range of the marmoset, and intensity on wave forms and peak latencies. According to the results of BAEP recordings at frequencies of 4, 32, and 99 kHz, the number of components recorded was affected by the stimulus intensity and the clicks at an intensity of 80 dB peak equivalent sound pressure level (pe SPL) had the maximum number of clear components. Therefore, it was indicated that click stimulations at an intensity of 80 dB pe SPL over a broad range of frequencies appears to be useful for recording the maximum number of components in marmosets and may increase the information obtainable from BAEPs. BAEP latencies were prolonged as the stimulus intensity decreased from 100 to 50 dB pe SPL. The effects of stimulus frequency on the wave latencies and amplitudes in response to 80 dB pe SPL at frequencies between 0.5 and 99 kHz revealed various changes: the amplitude of wave I increased at 16 and 32 kHz, but that of waves III and V increased at 4-8 and 64-99 kHz. These increases in amplitudes of the waves may correlate with higher synchronous activity of the peripheral or central auditory pathways.

Distribution of motoneurons innervating tail muscles in the pigeon

The distribution of motoneurons innervating the tail muscles, M. levator caudae, M. depressor caudae, M. pubocaudalis externus, M. pubocaudalis internus, M. lateralis caudae and M. flexor cruris, in the adult pigeon was examined by retrograde transport of horseradish peroxides. Labeled motoneurons innervating tail muscles were distributed in the longitudinal column of the spinal cord below the sacral spinal segment 5. The average diameter of cell bodies ranged from 23.7 to 62.5 microns. Each motoneuron pool was localized in a characteristic position in the ventral horn.

Discharge of cutaneous afferent fibers innervating tail during passive tail movements in cats

The discharge of cutaneous afferents innervating the tail were recorded from 145 single afferent fibers in 11 spinalized cats (conduction velocity: 32-58 m/s) during sinusoidal tail movements. Cutaneous afferent fibers were roughly classified into two groups, slowly-adapting (SA) and rapidly-adapting fibers (RA). The discharge patterns of afferent fibers during passive tail movements depended on the receptive field on tail skin. The results of the present experiments show that peripheral inputs from cutaneous afferent fibers sent various information regarding tail movement and position to central nervous systems.

Metabolic properties of the sensory neurons in the rat dorsal root ganglion

The dorsal root ganglion (DRG) neurons were classified in the rat on the basis of their metabolic enzyme properties as determined by quantitative analysis in histochemical staining. In particular, nicotinamide adenine dinucleotide-diaphorase (NADH-d) and alpha-glycerophosphate dehydrogenase (alpha-GPD) activities were examined on two serial sections from the same neurons in the lumbar (L4) DRG. The DRG neurons were classified into three groups based on the soma diameter distribution; small, intermediate and large size DRG neurons. The NADH-d activity showed a unimodal distribution in all size groups, while the alpha-GPD activity clearly showed a bimodal distribution in the intermediate and large size neurons, but not in the small size neurons.

Brain-stem auditory evoked potentials in the common marmoset (Callithrix jacchus)

Brain-stem auditory evoked potentials (BAEPs) were recorded in 10 common marmosets (Callithrix jacchus) to investigate the effects of recording electrode configurations, stimulus rate, and stimulus frequency on BAEP wave forms and peak latencies. Tone burst stimulations were used to evaluate the effects of pure tone on BAEP wave forms. Five positive peaks superimposed on positive and negative slow potentials were identified in the BAEP recorded at the linkage between the vertex and the dorsal base of the ear ipsilateral to a monaural stimulus. When the reference electrode was placed at the ipsilateral mastoid or the neck, the amplitudes of positive and negative slow potentials and the incidence of wave I increased. There were no significant changes in peak latencies of BAEP waves with changes in stimulus rate from 5 to 20/s. It was possible to record the BAEPs in response to tone burst stimulations at frequencies extending from 0.5 to 99 kHz. Wave I appeared apparently at high stimulus frequencies; while waves III to V, at low frequencies. Wave II was recorded at frequencies ranging from 0.5 to 99 kHz and comprised a superposition of 2 or 3 potentials.

Location of motoneurons supplying tail muscles in the domestic fowl

The distribution of motoneurons innervating the tail muscles, levator caudae, depressor caudae, pubocaudalis externus, pubocaudalis internus, lateralis caudae and flexor cruris, in the adult domestic fowl was examined by retrograde transport of horseradish peroxidase Labeled motoneurons supplying tail muscles were distributed in longitudinal column in the spinal cord below sacral spinal segment 3 and average diameters of cell bodies ranged from 27 to 59 microns. Each motor pool was localized in a characteristic position in the ventral horn.

Descending pathways from the medial longitudinal fasciculus and lateral vestibular nucleus to tail motoneurons in the decerebrate cat

Responses of motoneurons supplying two tail muscles (m. extensor caudae lateralis [ECL] and m. flexor caudae longus [FCL]) to stimulation of the medial longitudinal fasciculus (MLF) and lateral vestibular nucleus (LVN) were studied using intracellular recording in the decerebrate cat. Stimulation of the MLF and the LVN produced mainly excitatory postsynaptic potentials (EPSPs) or mixed PSPs (EPSP/IPSPs), but inhibitory postsynaptic potentials (IPSPs) were also observed in a few motoneurons. The segmental latencies of early PSPs produced by MLF or LVN stimulation were distributed over a wide range, and PSPs with a segmental latency of mono- or disynaptic origin were observed in ECL and FCL motoneurons. The spatial facilitation technique indicated convergence of the descending pathways from MLF and LVN on a common interneuron.

Polysynaptic pathways from high threshold muscle afferents innervating hindlimb muscles to tail motoneurons in the spinalized cat

The postsynaptic potentials (PSPs) after stimulating hindlimb flexor (PBSt) and extensor muscle nerves (LGS) were recorded from 64 tail motoneurons innervating m. extensor caudae lateralis and m. flexor caudae longus in the spinalized cats. Postsynaptic potentials were produced after stimulating high threshold muscle afferent fibers (group II and group III) and the average central latencies of PSPs were distributed in a wide range between 4.5 and 15.1 ms. Opposite effects on tail motoneurons were observed between stimulation of flexor and extensor muscle nerves, or ipsilateral and contralateral muscle nerves.

Polysynaptic neural pathways from low threshold trunk cutaneous afferents to tail motoneurons in the spinalized cat

Postsynaptic potentials (PSPs) after stimulating the cutaneous nerves of the trunk, dorsal cutaneous nerve (DC) and ventral cutaneous nerve (VC) were recorded from alpha-motoneurons innervating two tail muscles, the m. extensor caudae lateralis (ECL) and m. flexor caudae longus (FCL) in 22 spinalized (T10) cats. Stable recordings were obtained from 33 ECL and 42 FCL motoneurons. Stimulation of cutaneous nerves at 1.5-5 times threshold typically produced three types of synaptic effects in ECL and FCL motoneurons: predominant excitation (EPSP), or predominant inhibition (IPSP), or mixed effects characterized chiefly by early excitation followed by inhibition (EPSP/IPSP). The average central latencies of PSPs were distributed over a wide range (4.5-15.6 ms). Latency measurements indicated that most neural circuits from the trunk cutaneous afferents to the tail muscle motoneurons were oligosynaptic pathways via intraspinal slow-conducting fibers or polysynaptic pathways.

Polysynaptic pathways from hindlimb cutaneous afferent nerves to tail muscle motoneurons in unanesthetized and spinalized cats

Postsynaptic potentials (PSPs) were recorded in 57 extensor caudae lateralis (ECL) motoneurons and 82 flexor caudae longus (FCL) motoneurons of 36 decerebrated and spinalized (L1-2) adult cats, upon electrical stimulation of hindlimb cutaneous nerves, such as the sural nerve, superior peroneus nerve, and plantar section of the tibial nerve. With low threshold stimulation (1.2-5.0 T), excitatory PSPs (EPSP, EPSP/IPSP) predominated in ECL and FCL motoneurons. In a few ECL and FCL motoneurons, however, inhibitory PSPs were observed. Increasing the stimulus intensity from 1.2 T to 5.0 T led to an increase in amplitude of the PSPs. The central latencies of the PSPs were distributed over a wide range and minimal latencies of PSPs corresponded to 3.5 and 3.8 ms in ECL and FCL motoneurons, respectively. The measurement of central latencies reveals the oligo- and polysynaptic neural pathways from hindlimb cutaneous nerves to tail muscle motoneurons.

Effects of hindlimb cutaneous afferent inputs on spinal reflex recording from tail muscle motoneurons in the spinalized cat

In 4 spinalized cats, the effects of afferent inputs from hindlimb cutaneous nerves (sural cutaneous nerve: Sur) on mono-and poly-synaptic reflex recorded from tail muscle motoneurons were studied before and after spinal lesioning at S2-3 level. Monosynaptic reflex was enhanced by ipsilateral Sur stimulation at short conditioning-test stimulus interval and this effect was not observed after spinal lesion of ipsilateral side of spinal cord. Polysynaptic reflex was inhibited by stimulation of Sur in both sides and this inhibitory effect was depressed by contralateral spinal lesioning.

Postnatal development of tail motoneurons and muscles in cat

The postnatal development of motoneurons in two tail muscles, the extensor caudae medialis (ECM) and extensor caudae lateralis (ECL), and that of ECL muscle fibers were studied in cats 1 week to 2 months old. The location of ECL and ECM motoneurons in cats of different ages did not change postnatally. Somal size (average of maximal and minimal diameters) of ECL and ECM motoneurons gradually increased, and the size distribution of ECL was bimodal at 2 months. The activities of succinate dehydrogenase (SDH) and phosphofructokinase (PFK) were studied to determine oxidative and glycolytic activities in ECL growth. SDH activity rapidly decreased between 1 week and 2 weeks of age, while PFK activities increased gradually.

Anatomical structure and action of the tail muscles in the cat

Anatomical structure and movements of tail muscles were studied in 12 adult cats. Tail muscles mainly consisted of the following 6 muscles on both sides, M. sacrocaudalis dorsalis medialis (SDM), M. sacrocaudalis dorsalis lateralis (SDL), M. coccygeus lateralis (CL), M. coccygeus medialis (CM), M. sacrocaudalis ventralis lateralis (SVL) and M. sacrocaudalis ventralis medialis (SVM). Experiments by electrical stimulation of muscles demonstrated that the tail is bent to the dorsal direction by actions of SDM and SDL, curved laterally by those of SDL, CL, CM and SVL, bent to the ventral direction by those of SVL and SVM, and rolled by those of CL and CM on both sides. Contraction of SDL and SVL produced rapid and strong tail movements by actions of their long tendons.

Crossed and uncrossed segmental synaptic effects on rectus abdominis motoneurons from cutaneous and cutaneous-muscle nerve in spinal cats and alpha-chloralose-anesthetized cats

Segmental synaptic responses evoked by stimulation of the dorsal cutaneous and cutaneous-muscle (CD) nerve or the ventral cutaneous and cutaneous-muscle (CV) nerve were investigated with intracellular recording from rectus abdominis (RA) motoneurons in 49 spinal cats and 28 alpha-chloralose-anesthetized cats. No monosynaptic and few disynaptic connections existed in the circuit from the ipsilateral or contralateral CD or CV nerves to RA motoneurons in spinal cats. Polysynaptic EPSP responses equal to or over trisynaptic connections were dominant. In alpha-chloralose-anesthetized cats, RA motoneurons exhibited significantly more polysynaptic EPSP responses at lower stimulus intensities (1.5T and 2T) of ipsilateral CV nerve stimulation than at those of contralateral CV nerve stimulation. The result that there was no monosynaptic or disynaptic PSP in RA motoneurons produced by low-intensity stimulation of the ipsilateral CD or CV nerve containing the cutaneous-muscle nerves indicated that Ia afferents from the cutaneous-muscle did not connect mono- or di-synaptically to the RA motoneuron. RA motoneurons exhibited more polysynaptic IPSP responses in alpha-chloralose-anesthetized cats than in spinal cats. Segmental pathways from the CD or CV nerves to RA motoneurons might receive inhibitory descending inputs from the upper spinal cord or the brain, in contrast to those from the same nerves to obliquus externus abdominis motoneurons previously reported.

Crossed and uncrossed segmental synaptic effects on obliquus externus abdominis motoneurons from cutaneous and cutaneous-muscle nerve in spinal cats and alpha-chloralose-anesthetized cats

Segmental synaptic responses in the obliquus externus abdominis (OEA) for stimulation of the dorsal cutaneous and cutaneous-muscle (CD) nerve and the ventral cutaneous and cutaneous-muscle (CV) nerve were investigated in 49 spinal cats and 28 cats under alpha-chloralose anesthesia (chloralose cats) with an intracellular recording method. The result that there was no monosynaptic PSP in OEA motoneurons for stimulation of the CD or CV nerves (containing the cutaneous-muscle nerve) indicates that the cutaneous muscle of the dorsal or ventral area does not connect monosynaptically to the OEA motoneuron. The OEA motoneurons in chloralose cats received few effects from descending pathways coming from the upper spinal cord and the brain. Almost all OEA neurons had polysynaptic EPSP responses for stimulation of the ipsilateral or contralateral CD or CV nerves at 5-10T stimulus intensity in spinal or chloralose cats, which indicates that the OEA muscle can contract bilaterally when strong impulses of superficial afferents from the left or right skin or cutaneous muscle enter in the spinal cord.

Histochemical fiber composition of cat's tail muscles

A histochemical analysis was performed on the activity of myofibrillar ATPase following preincubation at pH 10.3 with NADH-diaphorase in the cat tail muscles (ECM; extensor caudae medialis, ECL; extensor caudae lateralis, ACE; abductor caudae externus, ACI; abductor caudae internus, FCL; flexor caudae longus, and FCB; flexor caudae brevis). Muscles contained three types of muscle fibers: FG (fast-twitch glycolytic) showed high reaction of myofibrillar ATPase staining and low reaction in NADH-diaphorase staining; FOG (fast-twitch oxidative glycolytic) showed high reaction in myofibrillar ATPase staining and high reaction in NADH-diaphorase staining; and SO (slow-twitch oxidative) showed low reaction in myofibrillar ATPase staining and high reaction in NADH-diaphorase staining. All 6 tail muscles were composed of these three types of fibers, but proportions differed in each tail muscle. Proportions of SO and FG fibers were highest in ECL (SO: 38.6 +/- 2.3, S.D. %) and ACI (FG: 59.2 +/- 5.0%), respectively. The diameters of the fibers were also measured (SO; 50.47 +/- 3.12, FOG; 58.18 +/- 2.78, FG; 70.91 +/- 3.40, S.D. microns).

Effects of afferent inputs from mechanical and nociceptive receptors in the footpads on the monosynaptic reflex in the spinalized cat

We previously reported that the effects of footpad stimulation on the monosynaptic reflexes (MRs) in the cat's lumbar spinal cord depended on stimulated footpads. In this study, the effects of different types of stimulation (tonic pressure, phasic pressure, squeezing and radiant heating at 50 degrees C) on the MRs were studied in 12 adult cats spinalized at T11-12. The effects of tonic pressure were very weak or not detected. The pattern for the effects of phasic pressure was similar to that for squeezing, but the effects of squeezing was stronger than those of phasic pressure. These results indicate that effects of mechanical stimulation were mainly induced from phasic afferent inputs. Radiant heating was effective, and differential effects between mechanical stimulation and radiant heating were observed in some MRs. Our results suggest a difference in neuronal pathways from various types of receptors in the footpads.

Electromyographic and kinematic studies of tail movements in dogs during treadmill locomotion

Electromyographic (EMG) activities of three tail muscles, the extensor caudae lateralis (ECL), abductor caudae externus (ACE), and flexor caudae longus (FCL), were recorded bilaterally in seven adult dogs during walking, trotting, and galloping on a treadmill. Each dog's movements were recorded with a 16 mm high-speed camera system, and angular movements of the tail were analyzed. During walking and trotting, reciprocal EMG bursts were observed between right and left tail muscles and corresponded with lateral movements of the tail. The tonic discharges that were observed in ECL and FCL seemed to maintain the position of the tail. During galloping, synchronized EMG activity of all tail muscles produced reactive torques to counter those generated by cyclic limb movements and kept the tail in a stable position. These results suggest that tail movements are important in maintaining body balance during locomotion in the dog.

Descending projections to coccygeal spinal segments in the cat

The descending projections to coccygeal spinal segments influencing tail movement were studied by retrograde wheat germ agglutinin-horseradish peroxidase (WGA-HRP) tracing methods in 12 cats. WGA-HRP solution was injected into the 3rd and 4th coccygeal segments and hemisection of the right side of the spinal cord was performed at the 3rd sacral-1st coccygeal segmental level. Labelled propriospinal neurons were distributed in laminae III-VIII and X of the spinal cord between the cervical and lumbosacral spinal segments, predominantly on the left. The greatest density of labelled cells as in the lumbar enlargement. In the brainstem a high density of labelled cells was observed mainly in the lateral vestibular, gigantocellular reticular and magnocellular reticular nuclei on the left side, and the nucleus raphe magnus, pallidus and obscurus. These findings indicate significant descending projections to the coccygeal spinal cord in the cat which could be responsible for tail movements in the cat.