Visualization of a stationary CPG-revealing spinal wave.

Central Pattern Generator (CPG) is still an elusive concept that has a visual manifestation as a rhythmic oscillation commanded from the spine, but that also has another manifestation as a train of bursts in the surface electromyographic (sEMG) signals recorded on the para-spinal muscles. This leads to the challenging problem of correlating the visually observed spinal wave with the sEMG signals recorded during the session. This paper develops a mathematical model of the spinal wave phenomenon, which, when driven by the sEMG data, yields such visually observable features as wave nodes.

The ontogeny of the enzyme systems for the 5'- and 5-deiodination of thyroid hormones in chick embryo liver.

In the chick embryo liver, generation of T3 from T4 by 5'-deiodinating (5'D) systems is reported to be minimal until just before hatching, which occurs on day 21 of incubation. Studies were, therefore, performed to determine whether this is due to the absence of a 5'D system until late in development or to the presence of an active 5-deiodinating (5D) system capable of converting T4 to rT3 and T3 to 3,3'-diiodothyronine. Studies were performed in microsomes of liver from 15 to 21-day-old chick embryos. T3 was formed from T4 in microsomes from embryos at all stages studied provided that the substrate concentration was at least 5 X 10(-8) M. However, T4 could not be employed for studying changes in 5'D activity because the T3 formed underwent further degradation, and the T4 was also metabolized by 5D systems. rT3 was used instead, since its metabolism was less complex than that of T4, and Eadie-Hofstee plots of kinetic data were linear. Development was associated with a more than 2-fold increase in the maximum velocity of 5'D activity; there was no change in Km. 5D activity, which was studied using T3 as substrate, also exhibited linear reaction kinetics. 5D activity was highest on day 15 and decreased by more than 90% during the last 2 days of development due entirely to a decrease in the maximum velocity. Other characteristics of the two enzymes (substrate preference and inhibitor effects) indicate that they are comparable to the type I and III deiodinases found in mammalian systems. It is concluded that the failure to observe T3 generation from T4 in the developing chick until close to hatching, when substrate concentrations are below 5 X 10(-8) M, is due primarily to the presence of an active deiodinase which rapidly converts T4 and T3 to inactive analogs. It is suggested that the amount of T3 required by the developing embryo is extremely critical and the two enzyme systems act in a coordinated way to protect hepatic T3-sensitive mechanisms from overexposure to T3.

The ontogeny of iodothyronine 5'-monodeiodinase activity in Rana catesbeiana tadpoles.

Generation of T3 from T4 in vivo cannot be demonstrated in tadpoles until just before metamorphic climax (MC). Possible explanations include the absence of the necessary 5'-monodeiodinase (5'D) process, and/or the presence of an active T3 and T4 5-deiodinase (5D) system before MC. In the present study, 5'D activity was determined in the 12,000 x g supernatent fraction of tissue homogenates prepared from tadpoles in premetamorphosis (PM) and MC (induced by immersion in 2 x 10(-8) M T4) by measuring the 125I-formed from [125I] rT3 or [125I]T4 in the presence of 20 mM dithiothreitol. Eadie-Hofstee plots of data were used to determine maximum velocity and Km. During PM, 5'D activity was undetectable in liver, tail, heart, and kidney, minimal in brain and gut, and could be quantitated only in skin. During MC, 5'D activity was undetectable in liver, heart, and kidney, but was present in tail tissue and was increased more than 5-fold in skin and gut. The increased activity was due to a change in maximum velocity, with no change in Km. In its properties, the tadpole 5'D system was comparable to the type II system found in some mammalian tissues. Thus, it exhibited Km values for T4 and rT3 in the nanomolar range, the preferred substrate was T4, and activity was unaffected by propylthiouracil in the presence of 10 mM dithiothreitol. Under comparable incubation conditions, T3 5D activity was detected in most tissues during PM; the highest activity was found in liver, gut, and kidney. 5D activity was barely detectable in MC. From these studies it is suggested that accumulation of T3 generated from T4 in the tadpole is minimal before MD due to the predominance of 5D activity. During MC, accumulation of T3 is possible because of the substantial increase in 5'D activity together with a marked drop in 5D activity. The principle T3-generating organs appear to be gut, skin, and tail tissue.

Hepatic iodothyronine 5-deiodinase activity in Rana catesbeiana tadpoles at different stages of the life cycle.

Conversion of T4 to T3 cannot be demonstrated in vivo in Rana catesbeiana tadpoles until just before metamorphic climax, suggesting that 5'-deiodinase (5'D) activity is not present until this time. In the present study the role of 5-deiodinase (5 D) systems in the metabolism of T4 and T3 in the developing tadpole was examined. 5 D activity capable of converting T3 to 3,3'-diiodothyronine, and T4 to rT3 was present in hepatic microsomes from pre- and prometamorphic tadpoles, but it declined to undetectable levels during metamorphic climax. The preferred substrate was T3. The Vmax for T3 in premetamorphic tadpoles was 30.4 +/- (SE) 6.37 fmol/min X mg microsomal protein, and the Michaelis-Menten constant (Km) was 3.6 +/- 0.72 nM, respectively. The characteristics of the system are similar to those of the type III iodothyronine deiodinase present in mammals. The system has its counterpart in vivo; administration of T3 or T4 to tadpoles resulted in the generation of detectable amounts of the corresponding 5-deiodinated product. rT3 was also shown to be a naturally occurring iodothyronine in this species. Although generation of T3 from T4 was readily demonstrable in vivo in tadpoles that had entered metamorphic climax, hepatic 5'D activity determined in vitro was found to be extremely low at all stages of development. On the basis of these findings, the following alternative explanation for the failure to observe T4 to T3 conversion before climax is offered. In pre- and prometamorphic tadpoles, any T3 produced from T4 is rapidly converted to 3,3'-diiodothyronine by the 5 D system and thus accumulation is prevented. Once climax has begun, 5 D activity declines and thus the T3 generated is able to accumulate. Whether the increased T3 accumulation is also facilitated by an increase in T3 production due to increased 5'D activity remains to be determined.

Event-related potential correlates of primed and unprimed words in children co-morbid for disruptive behaviour disorders and academic delay.

Children with disruptive behaviour disorders and academic delay (DD-AD) were compared to children with disruptive behaviour disorders only (DD) and normal control children with no psychiatric disturbance or academic delay (NO) with respect to scalp-recorded event-related electrical potentials (ERPs) elicited by semantically primed and unprimed words. Primed words were preceded by spoken words having a related meaning, while unprimed words were preceded by nonassociated spoken words. For normal controls, the unprimed words elicited greater N400 amplitudes at frontal-central recording sites than primed words. Primed vs. unprimed N400 differences were not evident at frontal sites in DD and the DD-AD group failed to exhibit differences in primed vs. unprimed N400 amplitudes at either frontal, central or parietal sites. These findings suggest that DD-AD children may represent a unique neuroelectric subgroup of learning disabilities.