PubMed Health⌕ Search

Biomedical subjects

D J Stehouwer

Publications and source records attributed to D J Stehouwer.

30 records · Page 2Linked to original sources
PubMed1987

Compensatory eye movements produced during fictive swimming of a deafferented, reduced preparation in vitro.

Movement of the head during locomotion must be offset by movement of the eyes in the opposite direction in order to maintain a stable gaze. These compensatory eye movements are classically attributed to ocular reflexes elicited by vestibular stimulation and by slip of the retinal image. In the present study, compensatory eye movements accompanied episodes of fictive swimming expressed in vitro by a reduced, deafferented preparation of the bullfrog larva (tadpole). Thus, there are mechanisms for generation of eye movements, and their coordination with locomotion, that are endogenous to the central nervous system.

Abducens Nerve↗
PubMed1987

Effect of tectotomy and decerebration on spontaneous and elicited behavior of tadpoles and juvenile frogs.

The performance of tadpoles and juvenile frogs on a battery of behavioral tests was compared before and after tectotomy, removal of the telencephalon (decerebration), tectotomy in conjunction with decerebration, or before and after a sham operation. Posture, righting, and vestibular responses were not altered by any of the lesions at either stage of development, and gross motor abilities were not impaired. Cutaneous reflex thresholds of tadpoles were lower than those of juveniles prior to surgery, but removal of the tectum or the telencephalon, or of both, reduced the thresholds of juveniles to near-larval levels. All of the lesions abolished characteristic defensive responses of juveniles (freezing) and resulted in hyperreactivity to a wide variety of stimuli. Tectotomy and decerebration of larvae each resulted in a 50% reduction in spontaneous locomotion and, in combination, virtually eliminated spontaneous locomotion. None of the lesions had any effect on the level of spontaneous locomotion of juveniles, but activity elicited by the novelty of the testing environment was eliminated in decerebrate subjects. Visual and vestibular nystagmus consisted of eye movements in tadpoles and of head movements in juveniles. Neither nystagmus nor optokinetic locomotion was affected by any of the lesions at either stage.

Animals↗
PubMed1986

Behavior of larval and juvenile bullfrogs (Rana catesbeiana) following chronic spinal transection.

The behavior of larval and juvenile bullfrogs (Rana catesbeiana) was examined for 32 days following cervical spinal transection. The threshold for cutaneously elicited hindlimb withdrawal was not changed at either stage of development but righting reflexes were abolished. Forelimb postural support of juveniles was abolished by the transection but recovered within 3 days. Hindlimb posture was normal and hopping could be elicited by stimulation of the rump with a blunt wire probe. Undulatory swimming of larvae was abolished by the transection but began to recover approximately 1 week later. The hindlimbs of larvae were very active following the transection and displayed long sequences of coordinated stepping in response to a variety of stimuli. Gross examination of the spinal cord in situ after 32 days suggested that fibers may have grown across the transection site. Retransection at the site of the original transection on Postoperative Day 33 had no discernable effect on the behavior juveniles or on the stepping of larvae, but it abolished recovered swimming of larvae. Deafferentation of lumbar segments of larvae eliminated stepping but had no effect on swimming. Deafferentation of cervical segments eliminated forelimb support in juveniles. These results suggest that recovery of larval swimming depends at least in part upon the growth of fibers across the transection site. Stepping of spinal larvae appears to be mediated by proprioceptive reflexes rather than by central pattern generators, and in the normal animal is probably under the control of descending inhibition. Recovery of posture and hopping in juveniles was much more rapid than that described for adult frogs and does not depend on growth across the transection site.

Animals↗
PubMed1985

Development of locomotor mechanisms in the frog.

Tadpoles swim by undulations of the body and tail, whereas frogs locomote by alternate (stepping) and synchronous (frog-kick) movements of the hindlimbs. The development of interlimb coordination was studied by recording the activity of hindlimb motoneurons from the left and right ninth ventral roots of the isolated central nervous system (CNS). Results showed that mechanisms responsible for interlimb coordination of stepping are functional when the hindlimb is still composed of undifferentiated mesenchyme and before the lateral motor column has stabilized (stage III). The early appearance of coordinated activation of hindlimb motoneurons suggests that innervation of appropriate target muscles is not a prerequisite for normal development of circuits that mediate interlimb coordination of stepping. Synchronous activation of left and right hindlimb motoneurons (fictive frog kicks) appeared later in development (stage XIV). Throughout larval development 1:1 frequency coupling between both alternating and synchronous bursts of hindlimb motoneurons and bursts of primary motoneurons (those innervating axial muscles) was found. Recordings of peripheral nerve activity showed that motoneurons innervating antagonistic muscles of the thigh burst in antiphase. This intralimb coordination was present at stage X, a foot paddle stage that was the earliest stage in which the peripheral nerves were successfully dissected. That the neural activity of the isolated nervous system described above indeed underlies coordinated locomotor movements of the hindlimbs was shown by single-frame videotape analysis of hindlimb movements produced by the otherwise isolated CNS. The stepping movements displayed by those preparations were consistent with patterns of electrophysiological burst activity recorded from the ventral roots and peripheral nerves. The ontogenetic sequence in which the different patterns of electrophysiological activity emerged is the same as that of the corresponding behaviors in the intact tadpole. Although there were developmental changes in the reliability with which coordinated activity in the ventral roots and peripheral nerves was observed, each mode of coordination remained qualitatively unchanged from its earliest appearance through metamorphosis. These results show that mechanisms underlying locomotor coordination of the hindlimbs develop very early in larval ontogeny of the frog and can function when isolated from the periphery.

Afferent Pathways↗
PubMed1984

Development of hindlimb locomotor behavior in the frog.

Hindlimb motor behavior of the larval frog (tadpole) begins during midlarval life and occurs with increasing frequency until the tail degenerates during metamorphosis. The threshold for hindlimb withdrawal in response to tactile stimulation is low during premetamorphic stages and rises dramatically during metamorphosis. Testing tadpoles in different environments altered the stage of development at which different hindlimb behaviors were first observed but did not change the ontogenetic sequence of behavioral development. However, even under conditions most favorable to hindlimb locomotion, behavioral expression lagged behind electrophysiological expression. The rates of tail beating, hindlimb stepping, and frog kicks are similar to the rate of bursting of tail and hindlimb motoneurons of the isolated nervous system, but their coordination is variable, whereas that recorded from the isolated CNS is fixed. Because neural mechanisms of hindlimb locomotion are functional prior to their behavioral use, the basic hindlimb locomotor circuits must develop without benefit of practice or sensory feedback. However, sensory activity modulates coordination and alters the probability that particular behaviors will be expressed. Implications of these results for studies of early behavior in other species, and the problem of inferring neural maturity from behavioral observations, are discussed.

Animals↗
PubMed1983

Development of hindlimb locomotor activity in the bullfrog (Rana catesbeiana) studied in vitro.

The isolated central nervous system of the bullfrog larva (tadpole) is a valuable model system for studying the development of central motor control because the neural activity for locomotion is expressed in vitro. Patterned synaptic activation of immature hindlimb motoneurons is present before the bones and muscles of the hindlimb differentiate, and it develops against the background of the tadpole's functionally mature motor program for tail oscillations. This activation of hindlimb motoneurons later produces patterned bursting that underlies coordinated stepping and frog kicks.

Action Potentials↗
PubMed1981

Sensory interactions with a central motor program in anuran larvae.

Swimming in anuran larvae is directed by a central motor program that is modulated by spinal sensory input. Dorsal root stimulation activates the locomotor program in vitro and can produce either an increase or a decrease in the rate of ongoing fictive swimming. Records obtained from the distal stumps of cut dorsal roots during passive tail bending show that receptors respond to tail movement but not to tail position. During episodes of fictive swimming, primary afferent terminals are depolarized and their sensitivity to antidromic stimulation increased, indicating that the motor program exerts presynaptic inhibitory control over spinal sensory transmission. These results suggest that the central program is very sensitive to dorsal root inputs and modulates these inputs during swimming.

Animals↗
PubMed1980

Central and peripheral controls of swimming in anuran larvae.

The isolated nervous system of the bullfrog tadpole (Rana catesbeiana or clamitans) spontaneously exhibits patterned motoneuronal discharges which are the basis for swimming. In vitro recordings from the ventral roots showed that motoneurons on one side of the cord burst in alternation with those on the other side. On each side of the cord, motoneuron bursts occurred in synchrony the entire length of the cord. Patterned activity was found only in the medial motoneurons which innervate the muscles used for swimming. Lateral motoneurons innervating the limbs exhibited unpatterned bursting. The pattern generating mechanism is distributed along the length of the spinal cord. Proprioceptive information entering via the dorsal roots is not necessary for generation of the basic pattern of alternating activity, but interacts with the centrally generated pattern to produce a rostrocaudal lag of activity. These results are compared to those found using the dogfish and possible ontogenetic complications discussed.

Afferent Pathways↗
PubMed1980

Ontogeny of passive avoidance: role of task demands and development of species-typical behaviors.

Preweaning rats 10 to 15 days of age were given passive avoidance training in a circular chamber in which the floor comprised one shock electrode and the wall the other. All ages showed acquisition of the response, but both rate of learning and asymptotic performance increased with age. Yoked-shock controls, adaption controls, and naive controls did not demonstrate passive avoidance on subsequent test trials, ruling out alternative interpretations based on sensitization to shock, fatique, familiarity with the apparatus, and handling. From 10 to 15 days of age, improved performance was due in part to the transition from stereotyped shock-elicited behavior in the younger pups to discrete withdrawal from shock in the older pups. A paradoxical deterioration of performance with observed from 20 to 25 days of age, attributable to the development of species-typical defense reactions which were incompatible with the avoidance response. Retention of the avoidance response was found to increase from about 6 hr in the 10-day-old to at least 5 days in the 15-day-old. The data suggest that maturation of storage and/or retrieval mechanisms, rather than perceptual or experiential changes induced by development, is responsible for improved retention during ontogeny.

Age Factors↗
PubMed1978

Habituation of the forelimb-withdrawal response in neonatal rats.

The purpose of the present research was to examine the ontogeny of habituation in the neonatal rat, using the forelimb-withdrawal response. Thresholds and latencies of the response, changing patterns of responding to shock stimuli, and habituation of the response were studied in rats 3 to 15 days of age. It was found that although response thresholds do not change during this period of development, response latencies decrease and amplitudes increase. Three- and 6-day old pups remain active much longer following shock than do 10- and 15day-olds. When compared for habituation to different frequencies of stimulation, 3-day-old rat pups were found to be much more susceptible to habituation at low frequencies than 15-day-olds. Insertion of a simple intense shock in the habituation series produced marked dishabituation in the 3-day-olds but little or none in the 15-day-olds. This pattern of results was obtained regardless of the locus of the dishabituating shock. Analysis of response latencies showed that although 15-day-olds responded 2 to 3 times more quickly than 3-day-olds, both age groups responded more rapidly to a strong shock than to a weak one. During habituation, response amplitudes of both 3- and 15-day-old pups declined with no change in latency. Age-related differences in habituation were shown to be independent of differences in reactivity to shock and more likely due to the emergence of response sensitization.

Age Factors↗