Biomedical subjects
P R Lennard
Publications and source records attributed to P R Lennard.
Long-term in vitro turtle preparation for the study of spinal organization.
A method by which muscles, nerves, and a section of spinal cord from a turtle can be stably maintained in vitro for many days has been developed. Tests of the viability of central and neuromuscular synapses, and the histochemical properties of muscle fibers have indicated that the preparation is viable and shows little decrement in function over a period of 3-5 days. The system allows continuous access to the muscles, nerves, and the spinal cord, as well as a controlled external environment.
Morphology and histochemistry of the ambiens muscle of the red-eared turtle (Pseudemys scripta).
Six fiber types have been described in the ambiens muscle of red-eared turtles. These include one slow oxidative type, two fast oxidative types, two fast oxidative and glycolytic types, and one fast glycolytic type. Fiber types are non-randomly distributed throughout cross sections of the muscle. There is a decreasing gradient of oxidative staining and an increasing gradient of glycolytic staining along an axis from the superficial to deep regions of the muscle. The slow oxidative fibers are predominantly located within one or two fascicles of the superficial surface of the muscle. The fast glycolytic fibers are predominant in deep fascicles. In contrast to previous reports of histochemically monotypic intrafusal fibers in turtle muscle, ambiens muscle spindles have been observed containing one to eleven intrafusal fibers, including two fiber types. Fiber diameter and area are consistently smaller than observed in most extrafusal fibers. Spindles are predominantly located in superficial and cranial fascicles of the ambiens muscle and are located in regions characterized by extrafusal fibers with high oxidative activity.
Anatomical organization of long ascending propriospinal neurons in the cat spinal cord.
Retrograde transport of lectin-HRP conjugate (WGA-HRP) was used to examine the anatomical organization of long ascending propriospinal neurons (LAPNs) projecting to the cervical enlargement (C5-T1) and to the upper part of the cervical cord (C3-4) in cats. Small injections (0.05-1.0 microliter) of dilute (1-4%) WGA-HRP were made into the C5-T1 or C3-4 regions. The field potential evoked from stimulation of the superficial radial nerve served to position the micropipette delivering injections. Small and localized populations of labelled LAPNs were found in the dorsal horn (laminae IV-V), the intermediate zone (dorsal and medial lamina VII), and the ventral horn (ventral lamina VII, laminae VIII and IX). Ventral horn LAPNs projecting to the C5-T1 region were preferentially located in rostral lumbar regions. Ventral LAPNs projecting to the C3-4 region were more caudally situated. No regional differences in distribution of dorsal horn and intermediate zone LAPNs were noted in comparing the results of C3-4 with C5-T1 injection protocols. It is concluded that the caudally located ventral LAPNs may exert their influence on cervical motor output through C3-4 propriospinal interneurons. Other LAPNs are considered to exert their effect more directly, either at the C5-T1 or the C3-4 levels.
Afferent perturbations during "monopodal" swimming movements in the turtle: phase-dependent cutaneous modulation and proprioceptive resetting of the locomotor rhythm.
Locomotion consists of a repeating series of movement cycles (locomotor rhythm) with an orderly activation of musculature during each movement cycle (intracycle motor pattern). The effects of sensory stimulation, on both the intracycle motor pattern and the locomotor rhythm, were examined during electrically elicited swimming movements of a single turtle hindlimb. The resulting "monopodal" swimming was not subject to movement-related reflexes from other limbs or postural constraints, and provided a sensitive system for analyzing the effects of transient sensory perturbations. During "monopodal" swimming, cutaneous and extensor muscle-nerve stimulation (single 0.1- to 0.3-msec electrical pulse) had similar phase-dependent effects on the swim cycle in progress. Stimuli delivered during the powerstroke (limb retracting) shortened the period of the cycle. Stimulation during the returnstroke prolonged the cycle. Changes in cycle period were accompanied by in-phase adjustments of the EMG burst duration or interburst interval which was being expressed at the time of stimulus delivery. The in-phase adjustment of each muscle served to maintain the timing relationships between muscles, and resulted in the preservation of the intracycle motor pattern. Cutaneous and muscle-nerve stimulation had dramatically different effects on the locomotor rhythm. Cutaneous nerve stimulation produced period changes in poststimulus cycles which led to a temporary phase shift of the swimming rhythm. This temporary modulation suggests that cutaneous afferents do not have direct access to the timing circuitry of the central nervous system locomotor network. Muscle-nerve stimulation only altered the period of the cycle in progress at the time of stimulus delivery, and thus permanently reset the locomotor rhythm. This permanent phase shift suggests that muscle afferents have direct access to a central timing network which controls the locomotor rhythm.
Interlimb coordination during stepping in the cat: in-phase stepping and gait transitions.
The coordination of step cycles between all 4 limbs during in-phase stepping and during transitions to and from alternate stepping was studied in 12 adult cats during repeated overground stepping trials. The temporal spacing of step cycles of the different limbs was determined from analysis of electromyographic (EMG) activity in a single extensor muscle of each limb. Patterns of coordination of the different limbs were established on the basis of the frequency with which phase values separating step cycles were encountered. Steps in which the phasing of step cycles of the two hindlimbs were closer to true in-phase coordination than true alternation (phase between 270 degrees and 90 degrees) and where similar coupling was found in both the preceding and following steps were defined as steady state conditions. Distinct patterns of coordination of forelimb-forelimb and forelimb-hindlimb step cycles were noted under steady state conditions. During stepping sequences which include transitions either to or from alternate stepping, both gradual and abrupt phase changes were found. The changes in both forelimb-forelimb and forelimb-hindlimb phase relationships were more often gradual than abrupt. Where abrupt changes were encountered in the change in phase relationships between one such limb pair the phase change in the other pair was gradual. Changes in hindlimb-hindlimb phase relationships during transitions were nearly always abrupt. It is concluded that the 4 limbs are coordinated during in-phase stepping according to a few patterns, but that the variability about these patterns makes their association with simple neural circuitry rather speculative. The finding that transitions were most often gradual is interpreted in terms of a state-dependent model of interlimb control, in which the type of transition utilized depends on the strength of neural coupling of step cycles of all 4 limbs at the time that the transition is initiated.
Central pattern generator mediating swimming in Tritonia. I. Identification and synaptic interactions.
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Central pattern generator mediating swimming in Tritonia. II. Initiation, maintenance, and termination.
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Swimming movements elicited by electrical stimulation of turtle spinal cord. I. Low-spinal and intact preparations.
1. Electrical stimulation applied within the dorsolateral funiculus of the spinal cord of an intact, unanesthetized turtle can elicit rhythmic limb movements similar to those observed during swimming. 2. A spontaneous display of hindlimb swimming movements is not observed in adult turtles whose spinal cord is transected at D2. Such swimming movements are observed in these "low-spinal" turtles in response to electrical stimulation applied within the dorsolateral funiculus caudad to the transection. 3. The repetition rate of these swimming movements can be altered by changing stimulus parameters, such as the frequency of electrical pulses. 4. The present results indicate that, in the turtle, a neural pattern generator contributing to the production of hindlimb movements during swimming is located mainly in structures caudad to the cervical enlargement of the spinal cord. These data support the hypothesis that a pattern generator for locomotion is largely resident within the spinal cord.
Retention of tactile discriminations following somatosensory cortical lesions in the rat.
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