scholarly journals Slowly-conducting pyramidal tract neurons in macaque and rat

2019 ◽  
Author(s):  
A Kraskov ◽  
D Soteropoulos ◽  
I Glover ◽  
RN Lemon ◽  
SN Baker
Keyword(s):  
Motor Cortex ◽  
Pyramidal Tract ◽  
Recurrent Inhibition ◽  
Anatomical Studies ◽  
Slow Conduction ◽  
Pyramidal Tract Neurons ◽  
Conduction Velocities ◽  
Myelinated Fibres ◽  
Anaesthetised Rats

SummaryAnatomical studies report a large proportion of fine myelinated fibres in the primate pyramidal tract (PT), while very few pyramidal tract neurons (PTNs) with slow conduction velocities (CV) (< ∼10 m/s) are reported electrophysiologically. This discrepancy might reflect recording bias towards fast PTNs or prevention of antidromic invasion by recurrent inhibition of slow PTNs from faster axons. We investigated these factors in recordings made with a polyprobe (32 closely-spaced contacts) from motor cortex of anaesthetised rats (n=2) and macaques (n=3), concentrating our search on PTNs with long antidromic latencies. We identified 21 rat PTNs with antidromic latencies > 2.6 ms and estimated CV 3-8 m/s, and 67 macaque PTNs (> 3.9ms, CV 6-12 m/s). Spikes of most slow PTNs were small and present on only some recording contacts, while spikes from simultaneously recorded fast-conducting PTNs were large and appeared on all contacts. Antidromic thresholds were similar for fast and slow PTNS, while spike duration was considerably longer in slow PTNs. Most slow PTNs showed no signs of failure to respond antidromically. A number of tests, including intracortical microinjection of bicuculline (GABAA antagonist), failed to provide any evidence that recurrent inhibition prevented antidromic invasion of slow PTNs. Our results suggest that recording bias is the main reason why previous studies were dominated by fast PTNs.

scholarly journals Slowly-Conducting Pyramidal Tract Neurons in Macaque and Rat

2019 ◽  
Vol 30 (5) ◽  
pp. 3403-3418
Author(s):  
A Kraskov ◽  
D S Soteropoulos ◽  
I S Glover ◽  
R N Lemon ◽  
S N Baker
Keyword(s):  
Motor Cortex ◽  
Pyramidal Tract ◽  
Recurrent Inhibition ◽  
Anatomical Studies ◽  
Myelinated Fibers ◽  
Slow Conduction ◽  
Anesthetized Rats ◽  
Pyramidal Tract Neurons ◽  
Conduction Velocities ◽  
Gabaa Antagonist

Abstract Anatomical studies report a large proportion of fine myelinated fibers in the primate pyramidal tract (PT), while very few PT neurons (PTNs) with slow conduction velocities (CV) (&lt;~10 m/s) are reported electrophysiologically. This discrepancy might reflect recording bias toward fast PTNs or prevention of antidromic invasion by recurrent inhibition (RI) of slow PTNs from faster axons. We investigated these factors in recordings made with a polyprobe (32 closely-spaced contacts) from motor cortex of anesthetized rats (n = 2) and macaques (n = 3), concentrating our search on PTNs with long antidromic latencies (ADLs). We identified 21 rat PTNs with ADLs &gt;2.6 ms and estimated CV 3–8 m/s, and 67 macaque PTNs (&gt;3.9 ms, CV 6–12 m/s). Spikes of most slow PTNs were small and present on only some recording contacts, while spikes from simultaneously recorded fast-conducting PTNs were large and appeared on all contacts. Antidromic thresholds were similar for fast and slow PTNS, while spike duration was considerably longer in slow PTNs. Most slow PTNs showed no signs of failure to respond antidromically. A number of tests, including intracortical microinjection of bicuculline (GABAA antagonist), failed to provide any evidence that RI prevented antidromic invasion of slow PTNs. Our results suggest that recording bias is the main reason why previous studies were dominated by fast PTNs.

Ionic changes induced by excitatory amino acids in the rat cerebral cortex

1987 ◽  
Vol 65 (5) ◽  
pp. 1067-1077 ◽  
Author(s):  
R. Pumain ◽  
I. Kurcewicz ◽  
J. Louvel
Keyword(s):  
Amino Acids ◽  
Motor Cortex ◽  
Nmda Receptors ◽  
Excitatory Amino Acids ◽  
Pyramidal Tract ◽  
Potassium Ions ◽  
Channel Blockers ◽  
Pyramidal Tract Neurons ◽  
Ionic Mechanisms ◽  
Inward Currents

The ionic mechanisms underlying the action of excitatory amino acids were investigated in the rat motor cortex. Ion-selective microelectrodes were attached to micropipettes such that their tips were very close and local changes in extracellular concentration of sodium, calcium, and potassium ions elicited through ionophoretic applications of glutamate (Glu) and of its agonists N-methyl-D-aspartate (NMDA), quisqualate (Quis), and kainate (Ka) were measured. These agents produced moderate increases in [K+]o (up to 13 mM) but, in contrast, substantial tetrodotoxin-insensitive decreases in [Na+]o (maximally of 60 mM). NMDA-induced sodium responses could be blocked by manganese, while the Quis- and Ka-induced responses were not. Quis and Ka produced increases in [Ca2+]o or biphasic responses while NMDA, even with small doses, induced each time drastic decreases in [Ca2+]o (maximally of 1.15 mM), which could be attenuated or blocked by manganese but not by organic calcium channel blockers. NMDA responses could be abolished by reduced doses of 2-amino-phosphonovaierate. The largest Glu- and NMDA-induced calcium responses were observed in the superficial cortical layers, but such maxima disappeared after selective degeneration of pyramidal tract neurons. All amino acids produced sizeable reductions in the extracellular space volume. The following can be concluded. (i) All the excitatory amino acids tested induce an increased permeability to sodium and potassium ions. (ii) In addition, the NMDA-operated channels have specifically a large permeability for calcium, although calcium ions contribute only by less than 10% to the NMDA-induced inward currents, (iii) Glu-induced calcium responses are due to the activation by Glu of NMDA receptors. (iv) In the motor cortex, the largest density of NMDA receptors is found on apical dendrites of pyramidal tract neurons.

Activity of the Motor Cortex During Scratching

2006 ◽  
Vol 95 (2) ◽  
pp. 753-765 ◽  
Author(s):  
Mikhail G. Sirota ◽  
Galina A. Pavlova ◽  
Irina N. Beloozerova
Keyword(s):  
Motor Cortex ◽  
Hind Limb ◽  
Pyramidal Tract ◽  
Average Depth ◽  
Simple Correlation ◽  
Population Activity ◽  
Ankle Muscles ◽  
Pyramidal Tract Neurons ◽  
Awake Cats ◽  
Stimulation Of

In awake cats sitting with the head restrained, scratching was evoked using stimulation of the ear. Cats scratched the shoulder area, consistently failing to reach the ear. Kinematics of the hind limb movements and the activity of ankle muscles, however, were similar to those reported earlier in unrestrained cats. The activity of single neurons in the hind limb representation of the motor cortex, including pyramidal tract neurons (PTNs), was examined. During the protraction stage of the scratch response, the activity in 35% of the neurons increased and in 50% decreased compared with rest. During the rhythmic stage, the motor cortex population activity was approximately two times higher compared with rest, because the activity of 53% of neurons increased and that of 33% decreased in this stage. The activity of 61% of neurons was modulated in the scratching rhythm. The average depth of frequency modulation was 12.1 ± 5.3%, similar to that reported earlier for locomotion. The phases of activity of different neurons were approximately evenly distributed over the scratch cycle. There was no simple correlation between resting receptive field properties and the activity of neurons during the scratch response. We conclude that the motor cortex participates in both the protraction and the rhythmic stages of the scratch response.

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