The electrical properties of cat medial gastrocnemius (MG) spinal motoneurons were studied 14-21 d following injection of type A botulinum toxin (BTX) into the MG muscle. Treated MG muscles were atrophic, displayed pronounced fibrillation activity, and were markedly but not completely paralyzed. MG motoneuron electrical properties from animals with the highest MG muscle-twitch forces (greater than 20 gm) appeared normal, while motoneuron properties from animals with the lowest MG muscle-twitch forces (less than 10 gm) exhibited axotomy-like changes, though these changes were less pronounced than after axotomy itself. No changes in the axonal conduction velocity were observed, however. Motoneuron connectivity with MG muscle fibers was determined following intracellular stimulation of MG motoneurons by averaging EMG signals from 3 or 4 pairs of recording electrodes inserted into the BTX-treated MG muscles. Normal electrical properties were observed among motoneurons in which detectable EMG activity linked to the intracellular stimulation pulse was observed. The level of this connectivity, however, indicated that a relatively small number of muscle fibers were activated by individual motoneuron action potentials. Axotomy-like changes of electrical properties were observed in MG motoneurons that could not be associated with detectable EMG activity in the BTX-treated MG muscle following repeated trials of intracellular stimulation. These results indicate that the existence of effective neuromuscular transmission at a small number of motor terminals is sufficient to prevent the appearance of axotomy-like changes in motoneuron electrical properties, and that the absence of such transmission at all motor terminals is associated with the appearance of axotomy-like changes. The results suggest that the effects of axotomy itself on motoneuron properties may be based upon the loss or elimination of a potent interaction between muscle and motoneurons normally mediated by neuromuscular transmission.

We thank Dr. Donald Fahrr lor helpful con~ments on the nnnluscript and Mark Duhrow t'or assistance during scveh~l experiment\. WC gratefully :ICknowlrdfe the supp

SUMMARY1. A novel pathway is described which mediates excitation of hindlimb motoneurones from contralateral afferents. Stimulation of contralateral limb nerves evoked short-latency (less than 5 ms) EPSPs in 55 % of motoneurones tested.2. The EPSPs were evoked by fast-conducting contralateral afferents activated by electrical stimuli of 1-04-2-5 times nerve threshold. Stimulation of contralateral muscle nerves did not evoke short-latency EPSPs, whereas nerves which contain afferents from distal skin territories (sural, superficial peroneal, tibial and saphenous nerves) did.3. Central latencies were determined for the EPSPs from the arrival of the earliest components of the afferent volleys at the spinal cord. The earliest latencies were very brief (1-5 ms). These are comparable to the latencies of disynaptic inhibition in rat motoneurones from ipsilateral group I muscle afferents (1-5-1A7 ms). We conclude that a disynaptic relay is likely to be responsible for the earliest of the crossed EPSPs.4. Short-latency crossed EPSPs were found in all types of motoneurone tested (including both flexor and extensor motoneurones) except in six cells innervating intrinsic foot muscles. In view of the origin and distribution of the crossed EPSPs, their possible functional role is discussed.

No abstract

BackgroundThe thoracic aorta usually gives off the 3rd to 11th pairs of posterior intercostal arteries (PIA) and 1 pair of subcostal arteries. The first two pairs of PIA typically originate via the highest intercostal artery via the costocervical trunk of the subclavian artery. The PIA supply blood to the intercostal spaces, spinal cord and spinal nerve roots.A bilateral branching anomaly in multiple PIA were observed in an 81 year‐old male cadaver during routine dissection. The thoracic aorta gave rise to asymmetrical common PIA trunks at different levels on both sides. Five common PIA trunks were found arising from the thoracic aorta and a descending branch of the right vertebral artery was also observed. Two common PIA trunks were observed on the right side branching from the thoracic aorta. The first common PIA trunk supplied the 4th through 7th intercostal spaces while the second common PIA supplied the 10th and 11th intercostal spaces. The 8th and 9th PIAs were direct branches off the thoracic aorta as normal. Three common PIA trunks were observed on the left side originating from the thoracic aorta. The first common trunk supplied the 3rd through 5th intercostal spaces. The second supplied the 6th and 7th intercostal spaces. The third trunk was observed to supply the 11th intercostal space as well as the subcostal region. Another vascular variation observed included a branch from the right vertebral artery that descended inferiorly and dorsally toward the first four ribs through the right costotransverse foramen. This descending branch of the vertebral artery gave off branches to supply the second, third, and fourth intercostal spaces on the right side. While common trunks of PIA have been reported to be highly prevalent, there are normally 1–2 common trunks found in a typical thorax. Thus, a cadaver that displays up to 5 common trunks of PIA in a singular thorax is a rare occurrence. Also anomalous is the presentation of a direct branch of the vertebral artery that courses dorsal to ribs while supplying several intercostal spaces. Understanding such anomalies has important clinical implications to interventional radiologists during thoracic cavity procedures as well as spine and thoracic surgeries.Support or Funding InformationCenter for Anatomical Science and Education, Department of Surgery, Saint Louis University School of MedicineThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.