Determination of Decoquinate in Animal Feeds by Liquid Chromatography: Collaborative Study

The performance characteristics of a liquid chromatographic (LC) method for the analysis of decoquinate (DEC) in supplements, premixes, and complete animal feeds at medicating and trace levels were collaboratively studied. DEC is extracted from ground feed samples with 1 calcium chloridemethanol solution using mechanical agitation for 90 min. After centrifugation for 5 min and dilution (if necessary), an aliquot of the extract is diluted with water. The diluted extracts are filtered and analyzed by reversed-phase LC with fluorescence detection. Suspect positive trace-level samples are confirmed by using an alternate excitation wavelength. Fourteen test samples of medicated feeds, supplement, and medicated premix, along with 8 test samples for trace-level analysis, were sent to 13 collaborators (one in Canada, 4 in Europe, and 8 in the United States). Test samples were analyzed as blind duplicates. Acceptable results were received from 12 laboratories for the medicated test samples and from 13 laboratories for the trace-level samples. Repeatability relative standard deviation estimates ranged from 1.3 to 5.6. Reproducibility relative standard deviations estimates ranged from 2.8 to 6.1, and HorRat values ranged from 0.22 to 0.74.

The kinematics and kinetics of riding a racehorse: A quantitative comparison of a training simulator and real horses

Movement of a racehorse simulator differs to that of a real horse, but the effects of these differences on jockey technique have not been evaluated. We quantified and compared the kinematics and kinetics of jockeys during gallop riding on a simulator and real horses. Inertial measurement units were attached mid-shaft to the long bones of six jockeys and the sacrum of the horse or simulator. Instrumented stirrups were used to measure force. Data were collected during galloping on a synthetic gallop or while riding a racehorse simulator. Jockey kinematics varied more on a real horse compared to the simulator. Greater than double the peak stirrup force was recorded during gallop on real horses compared to the simulator. On the simulator stirrup forces were symmetrical, whereas on a real horse peak forces were higher on the opposite side to the lead limb. Asymmetric forces and lateral movement of the horse and jockey occurs away from the side of the lead leg, likely a result of horse trunk roll. Jockeys maintained a more upright trunk position on a real horse compared to simulator, with no change in pitch. The feet move in phase with the horse and simulator exhibiting similar magnitude displacements in all directions. In contrast the pelvis was in phase with the horse and simulator in the dorso-ventral and medio-lateral axes while a phase shift of 180° was seen in the cranio-caudal direction indicating an inverted pendulum action of the jockey.

Effects of generalized convulsive seizures on corticotropin-releasing factor neuronal systems

Most stressors generate a set of endocrine and neural adaptations that form a stress response. The corticotropin-releasing factor neurons of the paraventricular nucleus of hypothalamus integrate endocrine and neural inputs, and cause a cascade of events with resultant increased levels of pituitary adrenocorticotropic hormone and adrenal hormones. Although activation of the hypothalamic-pituitary-adrenal axis is associated with a large variety of stressors, the effects of seizures on hypothalamic corticotropin-releasing factor neurons are essentially unknown. The goal of the present study was to elucidate the effects of generalized convulsive seizures on distinct and separate corticotropin-releasing factor cell populations in brain. Seizure-activated neurons were identified immunocytochemically through their expression of the Fos protein. Seizures were induced by intraperitoneal injection of kainic acid. In the paraventricular nucleus, the vast majority of corticotropin-releasing factor-like parvocellular neurons also expressed Fos-like protein following seizure elicitation. This response was specific to corticotropin-releasing factor neurons of the paraventricular nucleus, as corticotropin-releasing factor neurons in central nucleus of the amygdala or bed nucleus of the stria terminalis did not simultaneously localize Fos following seizures.

Differential effects of perinatal hypoxia and anoxia on long term seizure susceptibility in the rat

We have previously demonstrated that hypoxia is acutely epileptogenic in the immature rat but not in the adult. The window during which hypoxia induces seizures in the rat ranges from postnatal day (P) 5-17, with the most severe seizures occurring at P10-12. Perinatal hypoxia resulted in significantly more acute seizure activity than perinatal anoxia. The present study evaluates the long term effects of perinatal hypoxia versus anoxia. Animals were exposed to hypoxia (3%O2) or anoxia (0%O2) at P10 and challenged later in adulthood (P55-60) with administration of pentylenetetrazol (PTZ) (45 mg/kg subcutaneously). Compared to normal littermate controls, the animals which had been exposed to perinatal hypoxia had a significantly higher frequency of generalized convulsions (GC) and a significantly shorter latency to the first myoclonic jerk (MJ) after PTZ. In contrast, perinatal anoxia did not alter long term seizure susceptibility. These results are discussed in context of previous studies which have shown variable long term effects using different models of perinatal hypoxia and/or ischemia.

Paraesthesiae and hypaesthesia following prolonged high-frequency stimulation of cutaneous afferents

The activity of cutaneous afferents was recorded in human subjects using microelectrodes inserted into individual fascicles of the median nerve at the wrist before and after a 10 min train of electrical stimuli at 200 Hz delivered to the appropriate digital nerve (via ring electrodes) or to individual afferent axons (via the microelectrode). Changes in neural activity produced by the stimulation were correlated with the time course of paraesthesiae and with changes in the ability to detect cutaneous stimuli. From approximately 20 s after the end of the stimulus train, there was a progressive increase in neural activity, and individual afferents became spontaneously active and discharged in high-frequency bursts. At this time the subjects began to experience paraesthesiae. Repetitive stimulation proximal to a complete digital nerve block induced paraesthesiae that were felt distal to the block in the insensate digit, indicating that they did not arise from the unmyelinated terminal segment of the axon or from a stimulus-induced disorder of receptor function. Recordings of the compound action potential evoked by submaximal test stimuli were made after the 10 min stimulus train and revealed evidence of an early transient increase in excitability superimposed on a long-lasting decrease in excitability, reaching a nadir approximately 30-40 min after the end of the repetitive stimulation. In parallel recordings, there was no detectable change in the cutaneous afferent volley evoked by mechanical stimulation, paraesthesiae, can be attributed directly to a disturbance in peripheral afferent fibres, while the poststimulation negative symptoms such as hypaesthesia arise from stimulation-induced refractoriness at central synaptic relays.

Changes in excitability of human cutaneous afferents following prolonged high-frequency stimulation

Prolonged high-frequency stimulation of cutaneous nerves can result in paraesthesiae that begin 20 to 30 s after the end of the train and last for 5 to 10 min. In the present experiments the effects of such stimulation on the excitability of human cutaneous afferents and on their refractory and supernormal periods were measured to determine whether these changes could explain the postactivation paraesthesiae. Attention was focused on the axons of lowest threshold (1.0-1.5 T) in the compound sensory action potential evoked by stimulating the digital nerves of the index or middle fingers. Repetitive activation produced two opposing effects on the excitability of low-threshold cutaneous afferents. Following stimulus trains of short duration (1-5 min) the dominant effect was a long-lasting decrease in excitability, such that the amplitude of a test afferent volley was always less than before stimulation. With these trains, no subject experienced paraesthesiae. For 10 min after stimulus trains lasting longer than 7 to 12 min the dominant effect was an increase in excitability such that the amplitude of the test volley was greater than before stimulation. Within this interval, following such trains, subjects experienced paraesthesiae. The extent and duration of supernormality induced by a supramaximal conditioning stimulus were greatly increased by stimulation for 1 min. Following stimulation for 10 min, the degree of supernormality of the enhanced test volley was much the same as before stimulation, but was inappropriately high for the size of the test volley. The sum total of the excitability change and the change in supernormality resulted in a larger potential after stimulation, whether the train lasted 1 min or 10 min. It is concluded that the postactivation changes in axonal excitability could predispose the most excitable axons to generate ectopic impulses and, thereby, to produce paraesthesiae.

Activation of neck muscles from the human motor cortex

Percutaneous stimulation of the motor cortex has been used to assess directly the supranuclear projection to the sternomastoid, trapezius and splenius capitis muscles. The projection to sternomastoid had a mean latency of 6.5 ms for the contralateral electromyographic response. A smaller and more variable response, usually with a longer latency (mean 9.5 ms), occurred in the ipsilateral sternomastoid. Electromyographic responses on both sides were potentiated by voluntary contraction or strong inspiratory efforts. They were evoked at lower stimulus intensities in the contralateral sternomastoid. Short-latency responses were recorded from the contralateral but not the ipsilateral trapezius and splenius capitis muscles. These results indicate that weakness of head rotation towards the hemiplegic limb following a supranuclear lesion may reflect reduced power of dorsal neck muscles rather than of sternomastoid.

Changes in muscle and cutaneous cerebral potentials during standing

The cerebral potentials produced by electrical stimulation of mechanoreceptive afferents from the foot were recorded in the sitting and standing postures to determine whether transmission to cortex was altered by the postural change. The latencies of the early components of the cerebral potentials produced by muscle afferents (posterior tibial nerve) and cutaneous afferents (sural nerve) did not change with posture. Standing was associated with an approximately 25-35% decline in amplitude of the earliest components of the posterior tibial cerebral potential (N38-P40, P40-N50) for a stimulus intensity associated with a submaximal afferent volley. The amplitude of the equivalent N38-P40 and P40-N50 components produced by sural afferents also declined during quiet stance. In most experiments the subcortical component (P32-N38) was not reduced by stance so that the amplitude attenuation probably occurs in part at cortical level. Qualitatively similar changes in the cerebral potentials were documented for a range of stimulus intensities, including those which evoked a maximal initial component in the nerve volley. For a similar reduction in the initial (N38-P40) component of the cerebral potential, voluntary plantar flexion in the sitting position produced less attenuation in subsequent components than did standing. Thus, attenuation of the cerebral potential during standing may involve specific posture-related factors in addition to those related to volition.