Biomedical subjects

M H Droge

Publications and source records attributed to M H Droge.

11 recordsLinked to original sources

PubMed1993

Glycine effects on in vitro motor pattern generation in mouse spinal cord.

Bath applications of glycine typically inhibited electromyogram (EMG) activity in the gastrocnemius (G) and tibialis anterior (TA) muscles of neonatal mice, in vitro. Although rhythmic bursting occurred in response to glycine administration, cycle alternation between individual EMG bursts in G and TA muscles was not observed. That strychnine (a glycine 1 receptor antagonist) and cycloleucine (a glycine 2 receptor antagonist) could evoke motor rhythm, when given separately or in combination, confirms that glycine transmission is not required for motor pattern generation in mice. Strychnine application resulted in synchronized EMG bursting in G and TA muscles, suggesting that glycine 1 receptor activation does provide some reciprocal inhibition between the G and TA motor nuclei.

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PubMed1993

Distribution of NMDA receptor binding in developing mouse spinal cord.

The role of NMDA receptors in spinal sensorimotor processes has been studied in neonates and adults, while NMDA binding has previously been described only in mature spinal cord. In autoradiographs of mouse lumbar cord, NMDA-sensitive [3H]glutamate binding peaked transiently around postnatal days 6-10. Differentiation increased progressively from day 10 to adulthood. Mature levels were highest in substantia gelatinosa and moderate in dorsomedial dorsal horn. The results are described in relation to functional and anatomical features of developing spinal cord.

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PubMed1992

Comparison of spontaneous motor pattern generation in non-hemisected and hemisected mouse spinal cord.

Spontaneous electromyogram (EMG) patterns in the gastrocnemius (G) and tibialis anterior (TA) muscles of spinal cord-hindlimb explants from neonatal mice were investigated. Compared to non-hemisected explants, neither longitudinal hemisection of the spinal cord nor hemisection plus transection at L1 significantly altered the incidence of spontaneous motor rhythm. Therefore, not only does each half of the neonatal spinal cord contain sufficient circuitry to generate motor rhythm, but the more reduced preparations were just as likely to produce such activity. Hemisected preparations, however, exhibited slower rhythm, perhaps due to the loss of excitatory commissural connections. No correlation was found between the number of cycles in a rhythmic sequence and cycle period. In hemisected as well as non-hemisected explants, sequences of spontaneous EMG rhythm occurred in either the G or TA muscle, but not in both muscles simultaneously. Consequently, cycle-to-cycle alternation between rhythmic bursting in the G and TA muscles was not observed. The excitability in such preparations was apparently insufficient for maintained activations of both muscles (either for cycle-to-cycle alternation or for co-contraction).

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PubMed1991

Spontaneous and NMDA evoked motor rhythms in the neonatal mouse spinal cord: an in vitro study with comparisons to in situ activity.

The current paper presents our initial efforts to establish an in vitro spinal preparation for investigating locomotor pattern generation in mice. We have characterized the step cycle timing from EMG activity in the gastrocnemius (G) and tibialis anterior (TA) muscles of freely moving intact adult as well as neonatal mice and then compared those data with rhythmic EMG activity in an isolated spinal cord-hindlimb preparation. The motor output during the first four days of life was evaluated in an effort to identify the optimal post-partum period for in vitro locomotor studies. The in vitro pattern generating capabilities of the lumbosacral region were tested in both nonhemisected and hemisected preparations. Spontaneous as well as NMDA evoked in vitro activity in the antagonist set of hindlimb muscles included sequences of: 1) synchronous bursting; 2) mixed synchrony and alternation; and/or 3) irregular alternations. The alternating bursting observed in vitro was more often an alternation of sequences rather than a cycle-to-cycle phasing between G and TA muscles. In summary, while there was evidence of reciprocal inhibition in neonates, the circuitry for cycle-to-cycle alternation between antagonists was found to be labile.

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PubMed1986

Multielectrode analysis of coordinated, multisite, rhythmic bursting in cultured CNS monolayer networks.

Laser-deinsulated, printed-circuit electrodes integrated into the floor of culture chambers have been used to monitor the spontaneous activity of mouse spinal monolayer cell cultures. This technique has allowed a multisite analysis of activity over long periods of time in closed chambers. In 63 cultures investigated 3-5 weeks after seeding, 89% included single- or multiunit bursting. Based on a subset of 40 cultures in which all electrodes were sequentially scanned, bursting was found on 41% of the active electrodes (approximately 38% of all units monitored). A total of 35% of the electrodes monitoring spontaneous bursting activity revealed rhythmic sequences that were usually coupled among multiple electrodes. Although most of this coupling was in-phase, three out of 40 cultures exhibited antiphasic bursting. In all cases where coupling was observed, each electrode monitored different burst compositions, demonstrating that the activity was generated by different units. Some rhythmic patterns persisted for over 12 hr and were observed in 400 mm2 monolayer cultures, as well as in much smaller 3 mm2 adhesion islands. The addition of 10 mM MgCl2 consistently blocked both random and patterned (i.e., bursting) spontaneous activity at all recording sites. Strychnine (10(-6) M) typically increased firing frequencies and either disrupted pretest bursting or generated rhythmic activity from random phasic patterns. In certain cases, strychnine also blocked activity on specific electrodes, indicating that glycine is not the only inhibitory transmitter involved. The spontaneous appearance of rhythmic activity in low-density, monolayer cell cultures established from dissociated and randomly seeded spinal tissue can be explained by one or a combination of two hypotheses: an inherent specificity of some interconnections in developing mammalian cultures and the generation of organized activity by random circuits at certain stages of complexity.

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PubMed1984

Intracellular recording from pectoral fin motoneurons of the stingray Dasyatis sabina, an elasmobranch fish.

Intracellular recordings were made from antidromically identified pectoral fin motoneurons in unanesthetized, decerebrate stingrays (Dasyatis sabina). These recordings had the three all-or-none components seen in other vertebrate motoneuron recordings. About 25% of the impalements had resting membrane potentials that were greater than -80 mV, which is larger than those of motoneurons from other vertebrate species. A novel depolarizing afterpotential (DAP) is associated with the isolated action potential occurring at the first node of Ranvier of the axon (M-spike). Occlusion experiments exclude recurrent events as the source of this potential. A capacitive source for the DAP is postulated. Using morphological and passive electrical data on motoneurons from previous studies, calculations of the passive decay of the nodal spike indicate that the membrane resistance of the initial segment is low and nearly equal to that of nodal membrane. The soma-dendritic (SD) spike is followed by a prominent, humped delayed depolarization (DD). The DD is temporally associated with the onset of the action potential produced by the initial segment (IS spike). Sources of the long-lasting period of repolarization recorded with the IS spike, which may underlie the DD, are postulated. The afterhyperpolarization (AHP) of stingray motoneurons tends to be shorter and smaller in amplitude than that of other vertebrate motoneurons. A negligible conductance change was often found during the period following an SD spike. No significant correlation was found between AHP duration and axonal conduction velocity. The input conductance of stingray motoneurons ranged between 1.5 X 10(-7) and 13.3 X 10(-7) S. The relationship between input conductance and axonal conduction velocity was determined from 42 motoneurons. These data were fitted by a power function with an exponent of 1.7, indicating that, in terms of membrane conductance properties, large stingray motoneurons are simply scaled-up versions of the small motoneurons.

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PubMed1983

Organization of spinal motor nuclei in the stingray, Dasyatis sabina.

The Atlantic stingray, Dasyatis sabina, has enlarged pectoral fins consisting of a series of antagonist dorsal (elevator) and ventral (depressor) muscles. Each muscle is divided into superficial and deep components. The retrograde transport of horseradish peroxidase (HRP) was used to determine the organization of motoneuron pools innervating fin and epaxial muscles. HRP applied to a single peripheral nerve labeled motoneurons within a single spinal segment. Following intramuscular injection of HRP, 3 distinct cell groups were identified in the transverse plane. Motoneurons innervating elevator muscles were lateral in the ventral horn, while motoneurons innervating depressor muscles were dorsomedial. The epaxial muscles were found to be innervated by a distinct cell column along the ventral border of the ventral horn. Separate injections of the superficial and deep bundles of the elevator muscle resulted in considerable overlap in the distribution of labeled motoneurons. Soma areas for both elevator and depressor motoneurons were unimodally distributed. The mean cell diameters were 33.6 and 31.8 micron respectively. Motoneurons innervating the superficial and deep bundles of elevator muscle also had similar size distributions. The location of motoneurons innervating elevator and depressor fin muscles in the stingray supports the hypothesis that motoneurons innervating muscle derived from the dorsal premuscle mass are located laterally in the ventral horn while motoneurons innervating muscle derived from the ventral premuscle mass are located medially.

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PubMed1983

Swimming pattern in intact and decerebrated stingrays.

Stingrays swim with a rostral-to-caudal wave of elevation and depression of the enlarged pectoral fins. The present study compares the timing relations of swimming before and after decerebration in the same animals using electromyograms (EMGs). EMGs were recorded from several freely swimming, intact animals. Most recordings, however, were from stingrays suspended by vertebral clamps. Activity recorded from restrained animals exhibited the same timing relations as freely swimming animals. Therefore, the restrained preparation was used to compare locomotor rhythm in intact and decerebrate stingrays. The delay from the onset of activity recorded at a rostral segment to the onset of activity at successively caudal recording sites (intersegmental delay) was linearly related to the extent of the segmental separation. This relation was not changed by decerebration. Both the intersegmental delay and the EMG burst duration were linearly related to the period of the swim cycle. The intercepts for both relations fell around the origin. Therefore, stingray swimming demonstrates constant phase coupling. Neither the slopes nor the intercepts of the coupling relations were altered by decerebration. Histological examination of the fins indicates that at least two types of muscles exist. Superficial muscle is activated during slow swimming, while the deeper muscle is recruited during faster swimming.

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PubMed1983

Swimming rhythm in decerebrated, paralyzed stingrays: normal and abnormal coupling.

Rhythmic motoneuronal activity was recorded from decerebrated, paralyzed stingrays and compared with electromyograms recorded from the same animals. Before and after paralysis, a rostral-to-caudal sequence of alternation occurred between dorsal (elevator) and ventral (depressor) efferents. The swimming pattern was thus observed in the absence of phasic afferent input, and this constitutes fictive locomotion. After paralysis, both the intersegmental delay (time between activation at progressively caudal recording sites) and the burst duration remained linearly related to the swim cycle period. In many instances, neither the slope nor the intercept was significantly altered by immobilization. The intercepts all fell near the origin, indicating that the fictive rhythm remains constant phase coupled. Although the swimming rhythm was obtained after paralysis, some differences occurred. These included fewer and shorter spontaneous sequences, a greater range of cycle periods, and longer burst durations. During fictive swimming, the burst duration:cycle period ratio usually increased to 0.53 from 0.39 observed before paralysis. Therefore, the silent periods seen between burst discharges in antagonist efferents during movement were often absent after paralysis. Mechanical stimulation of the tail reduced both cycle periods and burst durations; however, the burst:cycle ratio remained greater than or equal to 0.50. The linear relation between burst duration and cycle period found for spontaneous sequences was not changed by stimulation of the tail. During fictive swimming the inter- and intrasegmental coupling that characterizes stingray swimming becomes labile. Abnormal coupling appears more often during sequences with long swim cycles. Intrasegmental coupling is tighter than intersegmental coupling at any cycle period. Rhythmic activity at one segmental level can be independent of activity at other levels. This suggests that multiple oscillator circuits exist that are not dependent on propriospinal circuits interconnecting different segments. Rhythmicity in elevator and depressor motoneurons is not dependent on reciprocal connections between the circuitry driving the motor nuclei. Therefore, separate oscillators for elevators and depressors appear to be present within one spinal segment.

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PubMed1981

Induction of swimming in the high spinal stingray by L-DOPA.

Stingrays with high spinal transections, which do not spontaneously locomote, can be induced to swim by intravenous injection of L-DOPA. The L-DOPA-induced swim of the spinal animal is associated with patterns of EMG activity that appear similar to those of the spontaneous swim of the decerebrate preparation. However, in contrast to the decerebrate condition, the L-DOPA-induced cycles of swimming are slower and less vigorous. Furthermore, secondary periodicites and altered intersegmental timing relationships are also evident.

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PubMed1979

Locomotion in the decerebrate stingray.

Stingrays swim with an active elevation-depression sequence of the pectoral fin resembling an extension-flexion sequence. During forward locomotion this sequence passes caudally along the pectoral fin. Immediately following high decerebration, stingrays are capable of locomotion, and the pattern of muscle activity closely resembles that of intact animals. Spontaneous and midbrain evoked rhythmic motoneuron discharges can be recorded in paralyzed decerebrated animals. In contrast to dogfish sharks, stringrays with high spinal transections do not locomote.

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