Avis H. Cohen

Strychnine eliminates alternating motor output during fictive locomotion in the lamprey

The motor program for swimming in the lamprey includes rhythmic bursting of motoneurons with output from the two sides of a spinal segment alternating strictly out of phase. This motor program can be observed in vitro in the isolated spinal cord. Addition of strychnine (5-10 microM) can selectively eliminate the alternation between sides without blocking the temporal pattern of bursting on each side. This result suggests that temporal bursting on the right and left sides of the spinal cord is generated by independent neuronal oscillators, while the alternation between the two sides results from crossed inhibitory coupling between these oscillators.

Behavioral recovery following spinal transection: functional regeneration in the lamprey CNS

Abstract The large larval sea lamprey (4–5 years old) recovers behaviorally from spinal transection. This is accompanied by regeneration of axons across the lesion site. The regenerated portions of these axons form functional synapses and appear to do so selectively with their normal target neurons. By studying ventral root (motor) discharges in the isolated spinal cord, it has been shown that the regenerated connections mediate intersegmental coordination of locomotor circuitry across the healed lesion. The lamprey spinal cord has now met all the criteria for functional regeneration of neurites, and has helped to define the potential of the vertebrate CNS for recovery from traumatic injury. It may also yield insights into the mechanisms of neural development.

Intersegmental coordinating system of the lamprey central pattern generator for locomotion

SummaryIn the lamprey,Ichthyomyzon unicuspis, the wave of activity required for normal swimming movements can be generated by a central pattern generator (CPG) residing in the spinal cord. A constant phase coupling between spinal segments can be organized by intersegmental coordinating neurons intrinsic to the cord. The rostral and caudal segmental oscillators of the CPG have different preferred frequencies when separated from each other. Therefore the system must maintain the segmental oscillators of the locomotor CPG at a single common frequency and with the proper relative timing. Using selective lesions and a split-bath, it is demonstrated that the coordinating system is comprised of at least 3 subsystems, short-axon systems in the lateral and medial tracts and a long axon system in the lateral tracts. Each alone can sustain relatively stable coordinated activity.

Effects of oscillator frequency on phase-locking in the lamprey central pattern generator

The central pattern generator (CPG) for locomotion can be thought of as a chain of segmental oscillators coupled together that produces the basic locomotor pattern. The isolated spinal cord of the lamprey is an excellent preparation in which to formulate general principles for the operation of the CPG. The stability of the preparation and the ease with which surgical lesions can be made in the cord have allowed the study of the coordinating system with a convenience unobtainable in more complex vertebrates. Mathematical models have been developed to help analyze the CPG and other systems of coupled oscillators. The models have pointed to two important parameters for determining the relative timing of a system of coupled oscillators: the nature of the coupling and the difference in frequency among the oscillators. The latter is dealt with here. In lampreys, the frequency differences of the segmental oscillators along the cord can be quite large. This factor is shown to be related to changes in the intersegmental phase lags during serotonin modulation of fictive swimming. An understanding of some effects of the frequency difference is also shown to have been important in helping to formulate a protocol for the demonstration of functional regeneration in the isolated spinal cord preparation.

Evidence for functional regeneration in the adult lamprey spinal cord following transection

We report here that following partial spinal transections in adult lampreys, the fibers of the spinal cords can regenerate and restore some intersegmental coordination to the central pattern generator for locomotion, as tested in the isolated cord preparation. However, the regeneration by this test is not successful in all animals.

Effect of the tail ganglion on swimming activity in the leech

In the medicinal leech, Hirudo medicinalis, isolated segmental nerve cords are capable of generating swimming activity. The role played by the head and tail ganglia in regulating the expression of swimming activity by the segmental nerve cord was evaluated by comparing swimming activity in nerve cord preparations with and without the head and tail ganglia attached. Several swim properties were examined, including length of induced swim episodes, ability to initiate swim episodes, swim cycle period, and phase. We found that, in general, the presence of the tail ganglion attached to isolated nerve cords countered the effects produced by the head ganglion on swimming activity. Moreover, we observed that the tail ganglion itself provides excitatory drive to the swim generating system. Thus, the inputs from the head and tail ganglia influence significantly the expression of swimming activity.

Relationship between forelimb coordination and movement asymmetries during fast gaits, canter and gallop.

The gaits of mammals can be subdivided into two main categories, symmetric and asymmetric. The former, including walk, trot and pace, show a strict alternation of the two limbs of one girdleZ. With the step cycle normalized t o 1, there is a phase difference of 0.5 between the two limbs. The asymmetric gaits form the remaining group, including the different types of gallop in which the phase difference between the limbs of one girdle may range from near 0 to approximately 0.4 (cf. Grillner4). As a consequence of the 0.5 phase shift in symmetric gaits, the limbs of a girdle perform their locomotor movements under the same conditions, landing, supporting, and flexing at the same relative points in the step cycle1, 4. The situation necessarily differs in the asymmetric gaits. Despite the fact that clear asymmetries may be found in some records 2, 7,10, most authors seem to use the simplifying assumption that the limbs are doing the same things (e.g. Miller and van der Mech67). However, little quantification has been made due to the difficulty of recording movements of both limbs simultaneously. The present paper investigates this problem. X-ray cinematography is used, observing the joint angles of both limbs simultaneously. Five male albino rats, 300-500 g, were trained to run in a modified exercise wheel (diameter 35 cm, width 12 cm) as described by Cohen and Gans 2. The wheel was self-driven with the animals permitted to run at their own pace. Once the rats were fully accustomed to the wheel, X-ray movies were taken and the films analyzed frame by frame (see legend, Fig. 1). To simplify the discussion, a new notation based on Philippsons terminology 9 is used. He divided the step cycle into phases of flexion and extension of the limb. The unsupported flexion of the limb is denoted by F. The remainder of the step cycle is subdivided into an unsupported extension, Et and two support phases. Ez denotes the support phase during which the limb flexes under the weight of the body, and Ea, the phase during which the limb extends again. Proximal and distal joints are not necessarily synchronous in the initiation of the phases, thus the notation must specify

Glutamate-like immunoreactivity in the leech central nervous system

SummaryUsing a monoclonal antibody for glutamate the distribution was determined of glutamate-like immunoreactive neurons in the leech central nervous system (CNS). Glutamate-like immunoreactive neurons (GINs) were found to be localized to the anterior portion of the leech CNS: in the first segmental ganglion and in the subesophageal ganglion. Exactly five pairs of GINs consistently reacted with the glutamate antibody. Two medial pairs of GINs were located in the subesophageal ganglion and shared several morphological characteristics with two medial pairs of GINs in the first segmental ganglion. An additional lateral pair of GINs was also located in segmental ganglion 1. A pair of glutamate-like immunoreactive neurons, which are potential homologs of the lateral pair of GINs in segmental ganglion 1, were occasionally observed in more posterior segmental ganglia along with a selective group of neuronal processes. Thus only a small, localized population of neurons in the leech CNS appears to use glutamate as their neurotransmitter.

Neural Regeneration and Transplantation (Frontiers of Clinical Neuroscience Vol. 6)

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