Stimulation of the brainstem reticular formation evokes locomotor activity in embryonic chicken (in ovo)

Investigation of central pattern generators in the spinal cord of chicken embryos

For most quadrupeds, locomotion involves alternating movements of the fore- and hindlimbs. In birds, however, while walking generally involves alternating movements of the legs, to generate lift and thrust, the wings are moved synchronously with each other. Neural circuits in the spinal cord, referred to as central pattern generators (CPGs), are the source of the basic locomotor rhythms and patterns. Given the differences in the patterns of movement of the wings and legs, it is likely that the neuronal components and connectivity of the CPG that coordinates wing movements differ from those that coordinate leg movements. In this study, we used in vitro preparations of embryonic chicken spinal cords (E11-E14) to compare the neural responses of spinal CPGs that control and coordinate wing flapping with those that control alternating leg movements. We found that in response to N-methyl-D-aspartate (NMDA) or a combination of NMDA and serotonin (5-HT), the intact chicken spinal cord produced rhythmic outputs that were synchronous both bilaterally and between the wing and leg segments. Despite this, we found that this rhythmic output was disrupted by an antagonist of glycine receptors in the lumbosacral (legs), but not the brachial (wing) segments. Thus, our results provide evidence of differences between CPGs that control the wings and legs in the spinal cord of birds.

From the eye to the wing: neural circuits for transforming optic flow into motor output in avian flight

Avian flight is guided by optic flow-the movement across the retina of images of surfaces and edges in the environment due to self-motion. In all vertebrates, there is a short pathway for optic flow information to reach pre-motor areas: retinal-recipient regions in the midbrain encode optic flow, which is then sent to the cerebellum. One well-known role for optic flow pathways to the cerebellum is the control of stabilizing eye movements (the optokinetic response). However, the role of this pathway in controlling locomotion is less well understood. Electrophysiological and tract tracing studies are revealing the functional connectivity of a more elaborate circuit through the avian cerebellum, which integrates optic flow with other sensory signals. Here we review the research supporting this framework and identify the cerebellar output centres, the lateral (CbL) and medial (CbM) cerebellar nuclei, as two key nodes with potentially distinct roles in flight control. The CbM receives bilateral optic flow information and projects to sites in the brainstem that suggest a primary role for flight control over time, such as during forward flight. The CbL receives monocular optic flow and other types of visual information. This site provides feedback to sensory areas throughout the brain and has a strong projection the nucleus ruber, which is known to have a dominant role in forelimb muscle control. This arrangement suggests primary roles for the CbL in the control of wing morphing and for rapid maneuvers.

Spinal lumbar dI2 interneurons contribute to stability of bipedal stepping

Peripheral and intraspinal feedback is required to shape and update the output of spinal networks that execute motor behavior. We report that lumbar dI2 spinal interneurons in chicks receive synaptic input from afferents and premotor neurons. These interneurons innervate contralateral premotor networks in the lumbar and brachial spinal cord, and their ascending projections innervate the cerebellum. These findings suggest that dI2 neurons function as interneurons in local lumbar circuits, are involved in lumbo-brachial coupling, and that part of them deliver peripheral and intraspinal feedback to the cerebellum. Silencing of dI2 neurons leads to destabilized stepping in P8 hatchlings, with occasional collapses, variable step profiles and a wide-base walking gait, suggesting that dI2 neurons may contribute to the stabilization of the bipedal gait.

Spinal Cord Injury Significantly Alters the Properties of Reticulospinal Neurons: I. Biophysical Properties, Firing Patterns, Excitability, and Synaptic Inputs

Following spinal cord injury (SCI) for larval lampreys, descending axons of reticulospinal (RS) neurons regenerate, and locomotor function gradually recovers. In the present study, the electrophysiological properties of uninjured (left)-injured (right) pairs of large, identified RS neurons were compared following rostral, right spinal cord hemi-transections (HTs). First, changes in firing patterns of injured RS neurons began in as little as 2-3 days following injury, these changes were maximal at ~2-3 weeks (wks), and by 12-16 wks normal firing patterns were restored for the majority of neurons. Second, at ~2-3 wks following spinal cord HTs, injured RS neurons displayed several significant changes in properties compared to uninjured neurons: (a) more hyperpolarized V_REST; (b) longer membrane time constant and larger membrane capacitance; (c) increased voltage and current thresholds for action potentials (APs); (d) larger amplitudes and durations for APs; (e) higher slope for the repolarizing phase of APs; (f) virtual absence of some afterpotential components, including the slow afterhyperpolarization (sAHP); (g) altered, injury-type firing patterns; and (h) reduced average and peak firing (spiking) frequencies during applied depolarizing currents. These altered properties, referred to as the "injury phenotype", reduced excitability and spiking frequencies of injured RS neurons compared to uninjured neurons. Third, artificially injecting a current to add a sAHP waveform following APs for injured neurons or removing the sAHP following APs for uninjured neurons did not convert these neurons to normal firing patterns or injury-type firing patterns, respectively. Fourth, trigeminal sensory-evoked synaptic responses recorded from uninjured and injured pairs of RS neurons were not significantly different. Following SCI, injured lamprey RS neurons displayed several dramatic changes in their biophysical properties that are expected to reduce calcium influx and provide supportive intracellular conditions for axonal regeneration.

Endometrial stem cells: origin, biological function, and therapeutic applications for reproductive disorders

PURPOSE OF REVIEW

Endometrial stem cells (ESCs) are multipotent cells that are thought to originate locally in the endometrium as well as in the bone marrow (BM). They have remarkable plasticity and hold promise as an autologous source for regenerative medicine. This review focuses on recent studies that have advanced our understanding of the biology and function of ESCs and BM-derived stem cells (BMDSCs) as related to physiological reproductive processes and pathologies. Moreover, it reviews recent data on potential therapeutic applications of stem cells to endometrial disorders that lead to reproductive failure.

RECENT FINDINGS

Growing evidence from basic and preclinical studies suggests that ESCs participate in endometrial tissue regeneration and repair. Recent evidence also suggests that ESCs and BMDSCs play important roles in physiological reproductive functions including decidualization, implantation, pregnancy maintenance, and postpartum uterine remodeling. Initial preclinical and clinical studies with ESCs and BMDSCs suggest they have the potential to provide new therapies for various endometrial disorders associated with reproductive failure.

SUMMARY

Uterine ESCs and BMDSCs appear to play an important biological role in reproductive success and failure, and have the potential to become treatment targets for reproductive diseases including recurrent implantation failure, thin endometrium, Asherman, and recurrent pregnancy loss.

Multidimensional Tuning in Motor Cortical Neurons during Active Behavior

A region within songbird cortex, dorsal intermediate arcopallium (AId), is functionally analogous to motor cortex in mammals and has been implicated in song learning during development. Non-vocal factors such as visual and social cues are known to mediate song learning and performance, yet previous chronic-recording studies of regions important for song behavior have focused exclusively on neural activity in relation to song production. Thus, we have little understanding of the range of non-vocal information that single neurons may encode. We made chronic recordings in AId of freely behaving juvenile zebra finches and evaluated neural activity during diverse motor behaviors throughout entire recording sessions, including song production as well as hopping, pecking, preening, fluff-ups, beak interactions, scratching, and stretching. These movements are part of natural behavioral repertoires and are important components of both song learning and courtship behavior. A large population of AId neurons showed significant modulation of activity during singing. In addition, single neurons demonstrated heterogeneous response patterns during multiple movements (including excitation during one movement type and suppression during another), and some neurons showed differential activity depending on the context in which movements occurred. Moreover, we found evidence of neurons that did not respond during discrete movements but were nonetheless modulated during active behavioral states compared with quiescence. Our results suggest that AId neurons process both vocal and non-vocal information, highlighting the importance of considering the variety of multimodal factors that can contribute to vocal motor learning during development.

Ankle muscle tenotomy does not alter ankle flexor muscle recruitment bias during locomotor-related repetitive limb movement in late-stage chick embryos

In ovo, late-stage chick embryos repetitively step spontaneously, a locomotor-related behavior also identified as repetitive limb movement (RLM). During RLMs, there is a flexor bias in recruitment and drive of leg muscle activity. The flexor biased activity occurs as embryos assume an extremely flexed posture in a spatially restrictive environment 2-3 days before hatching. We hypothesized that muscle afferent feedback under normal mechanical constraint is a significant input to the flexor bias observed during RLMs on embryonic day (E) 20. To test this hypothesis, muscle afference was altered either by performing a tenotomy of ankle muscles or removing the shell wall restricting leg movement at E20. Results indicated that neither ankle muscle tenotomy nor unilateral release of limb constraint by shell removal altered parameters indicative of flexor bias. We conclude that ankle muscle afference is not essential to ankle flexor bias characteristic of RLMs under normal postural conditions at E20.

IGF-1 and BDNF promote chick bulbospinal neurite outgrowth in vitro

Injured neurons in the CNS do not experience significant functional regeneration and so spinal cord insult often results in permanently compromised locomotor ability. The capability of a severed axon to re-grow is thought to depend on numerous factors, one of which is the decreased availability of neurotrophic factors. Application of trophic factors to axotomized neurons has been shown to enhance survival and neurite outgrowth. Although brainstem-spinal connections play a pivotal role in motor dysfunction after spinal cord injury, relatively little is known about the trophic sensitivity of these populations. This study explores the response of bulbospinal populations to various trophic factors. Several growth factors were initially examined for potential trophic effects on the projection neurons of the brainstem. Brain derived neurotrophic factor (BDNF) and insulin-like growth factor (IGF-1) significantly enhance mean process length in both the vestibulospinal neurons and spinal projection neurons from the raphe nuclei. Nerve growth factor (NGF), neurotrophin-4 (NT-4) and glial derived neurotrophic factor (GDNF) did not effect process outgrowth in vestibulospinal neurons. At the developmental stages used in this study, it was determined that receptors for BDNF and IGF-1 were present both on bulbospinal neurons and on surrounding cells with a non-neuronal morphology.

Functional consequences of lumbar spinal cord contusion injuries in the adult rat

Our understanding of the substrates of locomotion, and hence our understanding of the causes of deficits following spinal cord injury, is still incomplete. While severe locomotor deficits can be induced by either contusion or laceration injuries or demyelination of thoracic spinal cord ventral and ventrolateral white matter, loss of mid-thoracic gray matter (intraspinal kainic acid injection) has no impact on locomotion. In contrast, loss of gray matter from the rostral lumbar segments induces severe locomotor deficits. This study examines the histological and locomotor outcomes following contusion injuries involving the rostral segments of the lumbar enlargement in the adult rat. Adult Sprague-Dawley rats received contusion injuries centered on the T13/L1, L2, or L3/4 spinal cord segments. Moderately severe injuries centered on the T13/L1 and L2 spinal cord segments induced more severe locomotor deficits than those centered on the L3/4 segments, despite a significantly smaller total gray matter volume loss (1.7 vs. 2.7 mm3). Moderately-severe injuries at T13/L1, L2, and L3/4 showed 21%, 31%, and 39% white matter sparing, respectively, with 6-week BBB scores of 10, 10, and 15.7, respectively. These data suggest that moderately-severe contusion injuries centered on the rostral segments of the lumbar enlargement induce more severe locomotor deficits than would be predicted by the histological outcome (spared white matter), suggesting that gray matter loss may play a role in functional deficits following some lumbar contusion injuries.

Guineafowl hind limb function. II: Electromyographic analysis and motor pattern evolution

The neuromuscular control of the hind limb of helmeted guineafowl (Numida meleagris) locomoting on a treadmill at 1.0 m/sec was analyzed using simultaneous electromyography (EMG) and cineradiography. Activity from 16 heads representing 14 hip and knee muscles was recorded and correlated with limb movement and myological data to help discern muscle function. The first half of the stance phase is characterized by activity in many hip extensors, which counteract a flexor moment of the ground reaction force to yield hip stability. Simultaneously, medial rotators of the femur mediate pelvic roll and coactive antagonists about the knee control knee flexion of ca. 60°. Later in stance, hip extensors pull the hip through an arc of ca. 25°; knee extension occurs in some strides. N. meleagris hind limb motor patterns were compared to those of their homologs in representative lizards and crocodilians. Using a cladogram of living saurians, motor patterns were reconstructed in hypothetical ancestors. Although data are limited, lizards appear to have very conservative muscle activity similar to that of the ancestral saurian. The extant crocodilian Alligator mississippiensis resembles the reconstructed ancestor of Archosauria in at least 9 of 11 hind limb motor patterns. In contrast, N. meleagris differs from this same ancestor in at least four muscles. Most novelties in extant saurian motor patterns arose on the line to living birds. J. Morphol. 240:127-142, 1999. © 1999 Wiley-Liss, Inc.

Restitution of functional neural connections in chick embryos assessed in vitro after spinal cord transection in Ovo

Functional neural reconnection is not common after spinal cord transection in the CNS of adult higher vertebrates but has been demonstrated in embryonic avian and neonatal mammalian CNS. Chick brainstem spinal cord preparations from nontransected controls and embryos transected at the cervical level on embryonic days (E) 8, 9, or 10 in ovo were assessed in vitro between E12 and E20 for their ability to produce and maintain episodic motor activity (EMA) using electrophysiological, voltage sensitive dye and anatomical tract-tracing techniques. After 3 to 4 days recovery, cycle-by-cycle coupling of EMA between segments separated by a transection was absent or inconsistent, although otherwise normal bouts of locally stimulated and spontaneous EMA were routinely observed restricted to segments of a cord separated by a transection site. After 5-7 days recovery in ovo the cross-transection coordination during bouts of EMA approached that of nontransected controls. The delay between the initiation of EMA in cervical segments to its initiation in lumbosacral segments caudal to a transection was an indicator of reconnection strength. The delay shortened from 0.5 to a few seconds after 3 days of recovery to around 150 ms (i.e., normal) after 5 days of recovery. We conclude that the reconnection of spinal central pattern generators for EMA across the transection was served mainly by axons which established connections with local circuits after extending 1-3 segments through a transection. Propriospinal axons that originated within 1-3 segments rostral to the transection then served to serially initiate EMA in distal caudal segments.

Development of epileptic activity in embryos and newly hatched chicks of the Fayoumi mutant chicken

The homozygous Fayoumi strain of epileptic chickens (Fepi) is affected by generalized convulsions consistently induced by intermittent light stimulation (ILS) and by intense sound. Although interictal EEG recordings show continuous spikes and spike and wave activity, desynchronization and flattening (DF) of the EEG are observed during seizures. We have studied development of the epileptic phenotype in embryonic (E) and posthatching (P) Fepi. As compared with those of chicken embryos of a normal strain, no differences were observed in the EEG before embryonic day (E) 16. Clearly differentiated spikes and spike and waves appeared at E17 in Fepi. Metrazol-induced EEG seizures were observed at E16 in normal embryos and at E17 in Fepi. The Fepi showed some characteristics: Spontaneous EEG seizure-like discharges also appeared at E17 but decreased toward hatching; visual or acoustic hyperexcitability developed at E20 together with evoked responses in normal chickens; desynchronization of the EEG, typical of the epileptic seizure of the adult, could be induced by ILS at B20, but ILS- or sound-induced generalized motor seizures appeared at P1, a few hours after hatching. Results show that Fepi phenotype reaches full expression at P1, but the electric paroxysms are expressed earlier, paralleling synaptic maturation.

Development of calbindin-D28k immunoreactive neurons in the embryonic chick lumbosacral spinal cord

The development of immunoreactivity for the calcium-binding protein calbindin-D28k (CaB) was investigated in the embryonic and hatched chick lumbosacral spinal cord. CaB-immunoreactive neurons were revealed in the dorsal and ventral horns as well as in the intermediate grey matter from early stages of neuronal development. CaB immunoreactivity was first detected in large neurons in the presumptive dorsal horn at embryonic day 5, while small neurons in the lateral dorsal horn were the last to appear, at embryonic day 10. We have identified and traced the morphological maturation of six CaB-immunoreactive cell groups, three in the dorsal horn and three in the ventral horn. In the dorsal horn these groups were (1) large neurons in the lateral dorsal horn (laminae I and IV), (2) small neurons in the lateral dorsal horn (lamina II), and (3) small neurons in the medial dorsal horn (lamina III). All three groups were present throughout the entire length of the lumbosacral spinal cord and showed persistent CaB immunoreactivity. In the ventral horn, CaB-immunoreactive neurons were classified into the following three categories: (1) Neurons dorsal to the lateral motor column (lamina VII). These neurons were present exclusively in the upper lumbosacral segments (LS1-3), and they showed steady CaB immunoreactivity during their maturation. (2) Neurons at the dorsomedial aspect of the lateral motor column (at the border of laminae VII and IX). This population of neurons was characteristic of the lower segments of the lumbosacral cord (LS5-7) and presented transient CaB expression. (3) Neurons within the lateral motor column (lamina IX). These neurons were dispersed throughout the length of the lumbosacral spinal cord. They were three to four times more numerous in the upper than in the lower lumbosacral segments, and their numbers declined throughout LS1-7 as the animal matured. The characteristic features of the development of neurons immunoreactive for CaB are discussed and correlated with previous neuroanatomical and physiological studies concerning sensory and motor functions of the developing chick spinal cord.

Suppression of the onset of myelination extends the permissive period for the functional repair of embryonic spinal cord

In an embryonic chicken, transection of the thoracic spinal cord prior to embryonic day (E) 13 (of the 21-day developmental period) results in complete neuroanatomical repair and functional locomotor recovery. Conversely, repair rapidly diminishes following a transection on E13-E14 and is nonexistent after an E15 transection. The myelination of fiber tracts within the spinal cord also begins on E13, coincident with the transition from permissive to restrictive repair periods. The onset of myelination can be delayed (dysmyelination) until later in development by the direct injection into the thoracic cord on E9-E12 of a monoclonal antibody to galactocerebroside, plus homologous complement. In such a dysmyelinated embryo, a subsequent transection of the thoracic cord as late as E15 resulted in complete neuroanatomical repair and functional recovery (i.e., extended the permissive period for repair).

Development of coordinated movement in chicks: II. Temporal analysis of hindlimb muscle synergies at embryonic day 10 in embryos with spinal gap transections

Spinal neural circuits can recruit muscles to produce organized patterns of activity early in embryonic development. In a previous study, using multichannel electromyographic (EMG) recordings, we characterized burst parameters for these patterns in the legs of chick embryos during spontaneous motility in ovo at embryonic days (E) 9 and E10 (Bradley and Bekoff, 1990). Results of the study suggested both neural and biomechanical factors play an important role in the development of coordinated limb movements. In this study, to explore the contribution of descending neural inputs to the control of leg movements during motility, we applied similar methods to characterize motor patterns produced by the spinal cord in the absence of descending inputs. Thoracic spinal gap transections were performed at E2 and EMG patterns were recorded at E10. Several EMG features for chronic spinal embryos were similar to those for normal embryos and demonstrate that lumbar spinal circuits can be correctly assembled to control limb movements in the absence of connectivity with more rostral neural structures during early differentiation processes. However, certain aspects of the EMG patterns in chronic spinal embryos were different from patterns in normal embryos and provide support for conclusions drawn earlier by Oppenheim (1975). Specifically, our data support the view that propriospinal and/or supraspinal inputs function to regulate the timing of cyclic limb movements controlled by spinal neural circuits. Finally, we consider the possible long-term effects of chronic spinal gap transections as compared to acute spinal transections on the development of motility.