Trajectory of group Ia afferent fibers stained with horseradish peroxidase in the lumbosacral spinal cord of the cat: Three dimensional reconstructions from serial sections

1979 ◽  
Vol 186 (2) ◽  
pp. 189-211 ◽  
Author(s):  
Norio Ishizuka ◽  
Hajime Mannen ◽  
Toshinori Hongo ◽  
Shigeto Sasaki
Keyword(s):  
Spinal Cord ◽  
Horseradish Peroxidase ◽  
Three Dimensional ◽  
Serial Sections ◽  
Lumbosacral Spinal Cord ◽  
Ia Afferent ◽  
Afferent Fibers

Intraaxonal injection of neurobiotin reveals the long-ranging projections of A beta-hair follicle afferent fibers to the cat dorsal horn

1996 ◽  
Vol 76 (1) ◽  
pp. 242-254 ◽  
Author(s):  
P. Wilson ◽  
P. D. Kitchener ◽  
P. J. Snow
Keyword(s):  
Spinal Cord ◽  
Horseradish Peroxidase ◽  
Hair Follicle ◽  
Dorsal Horn ◽  
Receptive Fields ◽  
Dorsal Horn Neurons ◽  
Somatotopic Organization ◽  
Afferent Fibers ◽  
Synaptic Boutons

1. The morphology and somatotopic organization of the spinal arborizations of identified A beta-hair follicle afferent fibers (HFAs) with receptive fields (RFs) on the digits have been investigated in the cat by the use of intraaxonal injection of the tracer n-(2 aminoethyl) biotinamide. 2. In three cats, the long-ranging projections of six HFAs were examined by selectively injecting afferents with RFs on digit 2, 4, or 5, directly over the digit 3 representation, and examining their collateral morphology in transverse sections of the spinal cord. The rostral and caudal boundaries of the digit 3 representation were determined by mapping the RFs of identified spinocervical tract (SCT) neurons. 3. In two more cats, three HFAs were injected at random rostrocaudal positions and their morphology was examined in parasagittal sections. In one animal (2 HFAs), the somatotopy of the digit representation was again determined by mapping the RFs of SCT neurons. In the remaining cat (1 HFA), the somatotopy of the dorsal horn was mapped from the RFs of unidentified dorsal horn neurons. 4. Hair follicle afferents emitted many more collaterals, over much greater rostrocaudal distances, than indicated by previous horseradish peroxidase studies, and all collaterals gave rise to synaptic boutons. 5. HFAs that have RFs confined to a small part of a digit give rise to bouton-bearing axonal branches throughout the entire rostrocaudal extent of the hindpaw representation.

Ammonium decreases excitatory synaptic transmission in cat spinal cord in vivo

1989 ◽  
Vol 62 (6) ◽  
pp. 1461-1473 ◽  
Author(s):  
W. Raabe
Keyword(s):  
Spinal Cord ◽  
Synaptic Transmission ◽  
Action Potentials ◽  
Conduction Block ◽  
Excitatory Synaptic Transmission ◽  
Excitatory Postsynaptic Potential ◽  
Presynaptic Terminals ◽  
Ia Afferent ◽  
Afferent Fibers ◽  
Low Threshold

1. Glutamine is thought to be a precursor of the pool of glutamate that is used as synaptic transmitter. NH4+ inhibits glutaminase, the enzyme presumed to cleave glutamine into glutamate in synaptic terminals. Therefore a decrease by NH4+ of excitatory synaptic transmission in hippocampus was suggested to be due to the inability to utilize glutamine as a precursor for glutamate and subsequent transmitter depletion. This study reexamines the effects of NH4+ on excitatory synaptic transmission. 2. The effects of NH4+ on excitatory synaptic transmission from low-threshold afferent fibers, presumably Ia-afferent fibers, to motoneurons was investigated in the spinal cord of anesthetized cats in vivo. 3. Action potentials of low-threshold afferent fibers were recorded at the entry of the dorsal roots into the spinal cord. An extracellular electrode within a motoneuron nucleus recorded the action potential of low-threshold afferent fibers and the extracellular monosynaptic excitatory postsynaptic potential, i.e., the focal synaptic potential (FSP). This extracellular electrode also recorded the antidromic field potential (AFP) in response to ventral root stimulation. Electrodes on the ventral roots recorded the monosynaptic reflex (MSR) and the monosynaptic excitatory postsynaptic potential in motoneurons electrotonically conducted into the ventral roots (VR-EPSP). 4. Intravenous infusion of ammonium acetate (AA) reversibly decreased MSR, VR-EPSP, and FSP, i.e., decreased excitatory synaptic transmission. 5. The decrease of VR-EPSP and FSP was accompanied initially by a decrease of conduction and, eventually, a conduction block in presynaptic terminals of low-threshold afferent fibers. 6. The decreases of VR-EPSP and FSP were also accompanied by the transient appearance of a reflex discharge, triggered by VR-EPSPs of decreased amplitude, and changes of the AFP indicating increased invasion of motoneuron somata by antidromic action potentials. 7. It is suggested that NH4+ depolarizes intraspinal Ia-afferent fibers and motoneurons. This depolarization initially decreases and then blocks conduction of action potentials into the presynaptic terminals of Ia-afferent fibers. The conduction block prevents the release of excitatory transmitter and decreases excitatory synaptic transmission. 8. The suggested depolarizing action of NH4+ may be due to K+-like ionic properties of NH4+ and/or an inhibition of K+-uptake into astrocytes. 9. The conduction block in presynaptic terminals of low-threshold afferent fibers can fully explain the decrease of excitatory synaptic transmission by NH4+. Because of the conduction block in presynaptic terminals, this study does not permit a conclusion as to an inhibition by NH4+ fo the utilization of glutamine as a precursor for glutamate used as synaptic transmitter.

Individual EPSPs produced by single triceps surae Ia afferent fibers in homonymous and heteronymous motoneurons

1976 ◽  
Vol 39 (4) ◽  
pp. 679-692 ◽  
Author(s):  
J. G. Scott ◽  
L. M. Mendell
Keyword(s):  
Spinal Cord ◽  
The Other ◽  
Triceps Surae ◽  
Relative Location ◽  
Spatial Effects ◽  
Epsp Amplitude ◽  
Ia Afferent ◽  
Afferent Fibers ◽  
The Mean ◽  
The Individual

1. The individual EPSPs evoked by the action of single Ia fibers from cat triceps surae (MG, LG, SOL) were recorded in homonymous and heteronymous motoneurons innervating these same three muscles. 2. In general, Ia fibers projected to a greater percentage of homonymous than heteronymous motoneurons. One class of Ia afferent evoked EPSPs in virtually all homonymous motoneurons; the other had a substantially lower projection frequency. Possible difficulties introduced by the limited resolution of the averaging technique are discussed. 3. Individual EPSPs were larger on the average if evoked a) in SOL rather than in MG or LG motoneurons, b) by LG rather than by MG or SOL afferent fibers, or c) in homonymous rather than in heteronymous motoneurons. The mean EPSP was larger in homonymous than in heteronymous motoneurons because the largest EPSPs (greater than 150 muV) were found mainly in homonymous motoneurons. 4. Rise times of EPSPs were only slightly shorter in homonymous than in heteronymous motoneurons, suggesting that other factors besides relative location of Ia terminals account for the observed EPSP amplitude differences. Rise times in SOL motoneurons were longer than those in MG or LG. 5. LG afferent fibers tended to produce larger EPSPs in rostral than in caudal LG motoneurons, and MG afferents produced larger EPSPs in caudal than in rostral MG motoneurons. These spatial effects were in accord with the more rostral entry of LG than MG Ia afferents into the spinal cord. The differential projection of SOL afferents to MG and SOL motoneurons which overlap spatially in the spinal cord suggests a species specificity in addition to a location specificity.

Spinal cord potentials evoked by cutaneous afferents in the monkey

1977 ◽  
Vol 40 (2) ◽  
pp. 199-211 ◽  
Author(s):  
J. E. Beall ◽  
A. E. Applebaum ◽  
R. D. Foreman ◽  
W. D. Willis
Keyword(s):  
Spinal Cord ◽  
Field Potential ◽  
Ventral Horn ◽  
Longitudinal Distribution ◽  
Conduction Delay ◽  
Time Of Arrival ◽  
Spinal Neurons ◽  
Spinothalamic Tract ◽  
Lumbosacral Spinal Cord ◽  
Afferent Fibers

1. Negative intermediary cord potentials and the equivalent field potentials were recorded from the surface or within the monkey lumbosacral spinal cord in response to stimulation of myelinated afferent fibers in cutaneous or mixed nerves of the hindlimb. 2. Cord potentials resembling the N1 and N2 potentials described in the cat spinal cord were found but, in addition, activation of small myelinated fibers produced a later potential named here the N3-wave. By use of a subtraction technique, it is estimated that the N3-wave has a latency of 11.4 (+/- 3.5 SD) ms from the time of arrival of the volley in the largest affs at 9 (+/- 3) ms after its onset, and the wave lasts 23 (+/- 5.7) ms. 3. The N3-wave is not lost following spinal cord transection, but may instead be enhanced. It is thus due to neural circuitry intrinsic to the lumbosacral spinal cord. 4. The longitudinal distribution of the N3-wave is similar to that of the N1- and N2-waves. 5. The field potential associated with the N3-wave and recorded from within the spinal cord has two negative foci in some animals: near the dorsalmost part of the dorsal horn and in an area equivalent to Rexed's laminae IV-VI. The field potential reverses in sign in the ventral horn. 6. The N3-wave is evoked by Adelta fibers. This was shown by grading the stimulus strength, by measuring the conduction delay for producing the wave when stimuli are applied either proximally or distally on the sural nerve, and by showing that the N3-wave persists when the Aalphabeta fibers are anodally blocked. 7. There is often a late burst discharge in spinal neurons, including spinothalamic tract neurons, which can be attributed to Adelta fibers and which corresponds in time to the N3-wave. 8. It is proposed that the N3-wave can be used as a monitor of the central effects of Adelta fibers in the spinal cord.

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