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The regional distribution of spinal cord networks producing locomotor-like, as well as non-locomotor-like, activity was studied with the use of an in vitro neonatal rat preparation. Rhythmic activity was induced by bath application of either serotonin (5-HT), acetylcholine (ACh), N-methyl-D,L-aspartate (NMA), or combined 5-HT/NMA, and was monitored via hindlimb flexor (peroneal) and extensor (tibial) electroneurograms (ENGs) or ventral root recordings. In some experiments, synchronous patterns were produced by the addition of inhibitory amino acid (IAA) receptor antagonists. Selective application of 5-HT to cervical and thoracic cord regions induced rhythmic activity in these segments but failed to evoke hindlimb ENG discharge. Exposure of the isolated lumbar region to 5-HT produced tonic activity only. Application of 5-HT to the whole cord produced locomotor-like activity in hindlimb ENGs that persisted after midsagittal section of the spinal cord from the conus to the thoracolumbar junction. In other experiments, transverse hemisection of the rostral lumbar cord during whole cord exposure to 5-HT abolished rhythmic activity in ipsilateral hindlimb ENGs, suggesting that under these conditions rhythmic activity on one side of the lumbar cord was insufficient to maintain rhythmic activity on the contralateral side. Selective application of NMA or ACh to cervical and/or thoracic cord regions evoked rhythmic activity in these supralumbar segments, as well as rhythmic, but non-locomotor-like, activity in the lumbar region. In contrast to the effect of 5-HT, both NMA and ACh evoked rhythmic activity when applied solely to the lumbar region, and the side-to-side alternation produced by whole cord ACh application was uncoupled by midsagittal lesions of the lumbar region. In the presence of IAA antagonists, the side-to-side coupling of bilaterally synchronous rhythms was maintained despite extensive midsagittal lesions leaving all but one or two segments of either cervical, thoracic, or lumbar cord bilaterally intact, and rhythmic activity could be maintained even in single isolated hemisegments. The effects of 5-HT/NMA were similar to those observed with the use of 5-HT alone, although 5-HT/NMA induced rhythmic activity in hindlimb ENGs when applied selectively to supralumbar regions. The results suggest that 1) a 5-HT-sensitive oscillatory network, capable of producing a locomotor-like pattern of activity, is distributed throughout the supralumbar region of the spinal cord and mediates descending rhythmic drive to lumbar motor centers; 2) NMA- and ACh-sensitive rhythmogenic elements are distributed throughout the spinal cord, including the lumbar region; and 3) the spinal cord contains an extensive propriospinal network of reciprocal inhibitory and excitatory connections characterized by redundantly organized side-to-side projections.

1. The role of inhibitory amino acid transmission in the coordination and generation of rhythmic motor activity was examined with the use of an in vitro neonatal rat spinal cord preparation. Before adding gamma-aminobutyric acid (GABA) or glycine receptor agonists and antagonists, rhythmic motor activity was induced by bath application of acetylcholine (ACh), N-methyl-D,L-aspartate (NMA), or serotonin (5-HT) while monitoring bilateral ankle flexor and extensor electroneurograms (ENGs). The timing of rhythmic flexor and extensor discharge was consistent with that seen during overground locomotion in 27% of 84 bath applications of these substances (n = 65 preparations). 2. Subsequent addition of the GABAA receptor agonist muscimol, the GABAB receptor agonist baclofen, or glycine, abolished rhythmic activity in 95% of the tested applications. 3. GABAB receptor blockade did not disrupt alternating patterns of ENG discharge. However, addition of the GABAA receptor antagonist bicuculline, or the glycine receptor antagonist strychnine, transformed alternating flexor-extensor and left-right activity into patterns characterized by bilaterally synchronous rhythmic activation of all hindlimb ENGs. The onset of individual ENG bursts was more abrupt following bicuculline or strychnine. Strychnine also synchronized high-frequency (4-8 Hz) packets of rhythmic discharge within ENG bursts. 4. Some preparations developed synchronous, but unstable, rhythmic activity in the presence of bicuculline or strychnine alone. However, NMA, 5-HT, or ACh was usually required in addition to these antagonists to promote sustained rhythmic activity.(ABSTRACT TRUNCATED AT 250 WORDS)

The neural control system for generation of locomotion is an important system for analysis of neural mechanisms underlying complex motor acts. In these studies, a novel experimental model using neonatal rat brain stem and spinal cord in vitro was developed for investigation of the locomotor system in mammals. The in vitro brain stem and spinal cord system was shown to retain functional circuitry for locomotor command generation, motor pattern generation, and sensorimotor integration. This system was exploited to investigate neurochemical mechanisms involved in neurogenesis of locomotion. Evidence was obtained for peptidergic and gamma-amino-butyric acid-mediated mechanisms in brain-stem circuits generating locomotor commands. Cholinergic, dopaminergic, and excitatory amino acid-mediated mechanisms were shown to activate spinal cord circuits for locomotor pattern generation. Endogenous N-methyl-D-aspartic acid receptors in spinal networks were found to play a central role in the generation of locomotion. The chemically induced patterns of motor activity and rhythmic membrane potential oscillations of spinal motoneurons were characteristic of those during locomotion in other mammals in vivo. The in vitro brain stem and spinal cord model provides a versatile and powerful experimental system with potentially broad application for investigation of diverse aspects of the neurobiology of mammalian motor control systems.

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The authors describe the novel occurrence of homozygosity for the CAG expansion in the androgen receptor gene causing Kennedy disease in two sisters (ages 34 and 42). Symptoms were limited to occasional muscle cramps and twitches. Physical examinations were normal apart from mild hand tremor in both women and rare perioral fasciculations in the older sibling. Electrodiagnostic studies were normal except for evidence of mild motor axonal loss in the sternocleidomastoid muscle of the older sibling.

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Study design: Case report of a patient with subacute delayed myelopathy after an acute low thoracic spine injury. Objectives: To draw awareness to a rarely described complication with potential to add devastating neurological insult to the original spinal cord injury, and to discuss evidence supporting a vascular mechanism. Setting: Health Science Centre, Winnipeg, Manitoba, Canada. Case report: A 35-year-old woman developed clinical and MRI evidence of ascending myelopathy, extending up to C5, 16 days after a T11/12 fracture dislocation. The distribution of MRI signal abnormality, MRI evidence of prominent venous markings, and association with upright mobilization and the wearing of a thoraco-lumbo-sacral orthosis, suggest that elevated spinal venous pressure in conjunction with low arterial pressure may have induced impaired spinal cord vascular perfusion. Conclusion: After recent spinal cord injury, factors exacerbating spinal venous hypertension and/or arterial hypotension may in some patients lead to impaired spinal cord perfusion. These factors should be considered and corrected if symptoms or signs of progressive myelopathy emerge in the first few days or weeks after injury.