Anti-agrin staining is absent at abandoned synaptic sites of frog neuromuscular junctions.

The neuromuscular junction is a plastic structure and is constantly undergoing changes as the nerve terminals that innervate the muscle fiber extend and retract their processes. In vivo observations on developing mouse neuromuscular junctions revealed that prior to the retraction of a nerve terminal the acetylcholine receptors (AChRs) under that nerve terminal disperse. Agrin is a protein released by nerve terminals that binds to synaptic basal lamina and directs the aggregation of AChRs and acetylcholinesterase (AChE) in and on the surface of the myotube. Thus, if the AChRs under a nerve terminal disperse, then the cellular signaling mechanism by which agrin maintains the aggregation of those AChRs, must have been disrupted. Two possibilities that could lead to the disruption of the agrin induced aggregation are that agrin is present at the synaptic basal lamina but is unable to direct the aggregation of AChRs, or that agrin has been removed from the synaptic basal lamina. Thus, if agrin were blocked, one would expect to see anti-agrin staining at abandoned synaptic sites; whereas if agrin were removed, anti-agrin staining would be absent at abandoned synaptic sites. We find that anti-agrin staining and alpha-bungarotoxin staining are absent at abandoned synaptic sites. Further, in vivo observations of retracting nerve terminals confirm that agrin is removed from the synaptic basal lamina within 7 days. Thus, while agrin will remain bound to synaptic basal lamina for months following denervation, it is removed within days following synaptic retraction.

Kinematic and electromyographic characteristics of children with cerebral palsy who exhibit genu recurvatum.

The objective of this article was to determine, using selected computerized gait analysis procedures, whether variation exists in the gait patterns of children with cerebral palsy who exhibit genu recurvatum. This descriptive study compared differences in kinematic, temporal-distance, and electromyographic (EMG) variables between two groups of children with cerebral palsy who exhibited genu recurvatum and age-matched controls. The setting was a motion analysis laboratory. Six children with cerebral palsy who showed genu recurvatum and a control group of four normal children participated in this study. Main outcome measures were hip-knee angle-angle diagrams, knee phase plane plots, knee angle versus time diagrams, stride length, cadence, single-limb support, and EMG data. Through use of hip-knee angle-angle diagrams, knee phase plane plots, and knee angle versus time diagrams, distinctive kinematic patterns emerged, allowing for grouping of subjects. Kinematic measures of knee angle at foot-floor contact and knee angle at greatest extension provided further support for the groups created, as did temporal-distance measures of stride length, cadence, and single-limb support. Analysis of variance procedures for the EMG data showed selected time points in the gait cycle during which differences between the groups were observed. Because differences in kinematic, temporal-distance, and EMG variables existed in this study to warrant grouping into two categories, physical therapists and orthopedic surgeons may need to vary the treatments they introduce dependent on the nature of the child's gait pattern.