Dorsal Root Terminals Research Articles

The effect of picrotoxin on the dorsal root potential of bullfrog spinal cords.

Effects of picrotoxin on the DRPs and GABA-depolarization of dorsal root terminals of isolated bullfrog spinal cords were studied. The early phase of DR-DRP was depressed but its late phase was enhanced and prolonged by picrotoxin. On the other hand, the entire course of GABA-depolarization was evenly depressed by this drug. These results suggested that the DR-DRP composed two different components. The early component (phase) might be generated by GABA and the late component (phase) by some unknown neurotransmitters. It was suggested that the release ofthese unknown neurotransmitters from internuncial neurones in the spinal cord was increased in the presence of picrotoxin and the DR-VRP as well as the late component of DR-DRPs were consequently augmented.

The effects of Lioresal on synaptic activity in the isolated spinal cord.

The perfused in vitro frog: spinal cord preparation was used as an experimental model to investigate thie effects of Lioresal and GABA on the spinal cord. Both compounds reduceid depolarizing synaptic potentials and depressed propagated reflex activity recorded from the ventral roots. However, in contrast to GABA, which produced potent effects on rnotoneurons, Lioresal produced only minor alterations of motoneuron excitability and membrane potential and the resporise of motoneurons to glutamate and aspartate, putative excitatory transmitters. Lioresal had effects on presynaptic structures, decreasing the excitability of and hyperpolarizing dorsal root terminals; GABA depolarizedl the same terminals. These data suggest that Lioresal produces most of its actions presynaptically, possibly by blocking impulse conduction in preterminal axons. This mechanism may contribute to the clinical effects OX Lioiresal in patients with spasticity.

Synaptic organization of the nucleus gracilis of the cat. Experimental identification of dorsal root fibers and cortical afferents.

AbstractThe synaptic organization throughout the nucleus gracilis has been investigated in unoperated cats. Axon terminals of variable size can establish synaptic contacts with neuronal somata, dendritic processes, initial segment of axons or with other axon terminals at “complex synaptic arrangements.” Large boutons with rounded vesicles are regularly associated with smaller boutons containing flattened vesicles; the latter type of bouton forms frequently a double synapse being presynaptic to the large bouton and to the element postsynaptic to this (“complex synaptic arrangements”). Medium‐sized to small axon terminals of the “isolated” type contain primarily either rounded or flattened vesicles. These boutons are surrounded by a thin glial process which also wraps the postsynaptic element, mostly represented by a small dendritic profile. The “isolated” type of bouton seems to be more abundant in the rostral than in the caudal part of the nucleus. In all unoperated control animals altered axons and axon terminals are present. They are enlarged and display hyperplasia and dilatation of tubular profiles of smooth endoplasmic reticulum as well as proliferation of microtubules and various aspects of mitochondrial degeneration.In cats sacrificed 48 hours after section of lumbo‐sacral dorsal roots a high number of “dark” boutons are observed in various stages of degeneration. These terminals are identifiable with the large boutons containing rounded vesicles and postsynaptic to the smaller boutons with flattened vesicles. The morphology of dorsal root terminals in the nucleus gracilis is discussed in relation to that of primary afferent terminals in other central structures and to the functional aspects of axo‐axonic contacts.The sensori‐motor cortex was removed in another series of animals which were sacrificed after one to four days. As a consequence of such lesions cortical fiber terminals in the nucleus gracilis may undergo either the “dark” or the “light” type of degeneration. These terminals are of smaller size than those of primary afferents, they usually synapse on dendritic profiles of small diameter, are not involved in axo‐axonic contacts and seem to contain rounded vesicles. Therefore they can be identified with at least some of the small and medium‐sized boutons of the “isolated” type.

The effects of bicuculline on the isolated spinal cord of the frog

An investigation has been made of the effects of topically applied bicuculline, a reported gamma-aminobutyric acid (GABA) antagonist, on the isolated, hemisected frog spinal cord by recording ventral and dorsal root potentials and reflexes evoked by volleys to various spinal cord inputs. Bicuculline had potent excitatory effects causing depolarization, spontaneous potentials in ventral and dorsal roots, and an increased polysynaptic ventral root reflex. More importantly, the alkaloid blocked presynaptic inhibition of orthodromic reflex activity produced by preceding ventral root stimulation and primary afferent depolarization. These effects were attributed to a demonstrated antagonism of the direct depolarizing effects of GABA on dorsal root terminals by the alkaloid. These actions of bicuculline suggest that GABA may be the transmitter responsible for primary afferent depolarization and presynaptic inhibition in the amphibian.

Dorsal root projections to the motor nuclei in the cat spinal cord.

AbstractThe dorsal root projections to the motor nuclei of the L7 spinal cord segment were examined with light and electron microscopy in cats surviving dorsal rhizotomies of L6–S2 for periods of 2–15 days. Light microscopy demonstrated maximal Nauta‐Gygax and Fink‐Heimer degeneration around large neurons and their dendrites of the motor nuclei within the four to eight day period. Electron microscopy revealed axonal degeneration without any accompanying synaptic knob degeneration. Counts of the synaptic populations in the 12 and 15 day animals revealed that one particular synaptic type, the M knob, occurred less frequently and was smaller in size. In the normal animals the M knob, which was present up to 8 days postoperatively, was a large terminal containing rounded vesicles and making multiple synaptic contacts which had specialized subsynaptic densities. It was found primarily on proximal dendrites of large neurons and was often accompanied by a smaller flattened vesicle knob. All other synaptic knobs described in the normal animal were intact throughout all postoperative periods.The possibility that dorsal root afferents synapse farther out on the motoneuronal dendritic tree, as well as the possibility that few dorsal root terminals synapse on the motoneuronal surface, is discussed. The lack of any morphological evidence for presynaptic inhibition of dorsal root afferents in lamina IX is also discussed and possible alternative mechanisms are considered.

Gamma-aminobutyric acid antagonism and presynaptic inhibition in the frog spinal cord.

The convulsant alkaloid bicuculline blocked presynaptic inhibition, dorsal root potentials, primary afferent depolarization, and depolarizing effects of gamma-aminobutyric acid on dorsal root terminals of the amphibian spinal cord, but did not block effects of other putative amino acid transmitters. These actions of bicuculline suggest that gamma-aminobutyric acid may be the transmitter involved in spinal presynaptic inhibition.

Reflex response changes of the toad spinal cord to variations in temperature and pH

1. 1. Effects of temperature and pH were assessed on the isolated spinal cord of Bufo marinus. 2. 2. Decreased temperatures caused a synchronization and augmentation of the early phase of the ventral root reflex (VRR) and a reduction in its duration. This was accompanied by motoneurone hyperpolarization. 3. 3. Increased temperatures caused a prolongation of the VRR accompanied by motoneurone depolarization. 4. 4. Temperature increases depolarized and decreases hyperpolarized dorsal root terminals. The dorsal root reflex was augmented on cooling. 5. 5. Increases in the H + concentration caused a depolarization with a simultaneous decrease in amplitude and increase in duration of the VRR, dorsal and ventral root potentials.

Afferent nerves to Clarke's and the lateral cuneate nuclei in the cat.

It is generally stated that Clarke's nucleus extends from the upper thoracic to the upper lumbar portion of the spinal cord and that it is a relay nucleus between the hindlimb and lower trunk and the cerebellum. The lateral cuneate nucleus is likewise believed to be a relay nucleus between the forelimb and the cerebellum. In an earlier study (Liu,131954) on transneuronal degeneration, it was found that Clarke's nucleus receives an extensive supply from the dorsal roots of all body parts except the neck, and that the dorsal root terminals show an extensive overlap within the nucleus. These observations indicated that Clarke's nucleus is supplied by dorsal root afferents from the forelimb, as well as from the trunk and the hindlimb. The aims of the present study were (1) to determine the distribution and termination of representative dorsal roots from various body parts (neck, trunk, tail, and limbs)