Ia EPSPs Research Articles

The time course of minimal excitory post-synaptic potentials evoked in spinal motoneurones by group Ia afferent fibres.

1. Group Ia EPSPs were recorded from lumbosacral motoneurones in anaesthetized cats after almost complete section of the relevant dorsal roots. The EPSPs were usually of small amplitude (median value of 230 muV) and an averaging device was used to improve the definition of their time course.2. From a total of over 500 averaged EPSPs a smaller number (342) were subjected to analysis. The other EPSPs were rejected either because they showed signs of multiple origin in the rising phase of their time course (see Methods) or because the resting membrane potential of the cell was less than 50 mV. All the selected EPSPs had their rise time (from the 10 to the 90% level) and half-width measured, and a semilogarithmic plot of their decay time course was made.3. 252 of the EPSPs showed an exponential decline in their later time course and the slope of this line was used to give an estimate of the membrane time constant. The range of the time constant for different motoneurones was 2.3-12.9 msec, with a mean value of 5.8 msec.4. In ten cells an EPSP was recorded which was judged to be generated exclusively by synaptic knobs located on the soma. On this assumption measurements of the normalized rise time, half-width and break point time were used to estimate alpha, rho(infinity) and L by the method suggested in Jack & Redman (1971b). The estimated value of alpha ranged from 18 to 65. A positive correlation was found between alpha and tau(m), indicating that for these EPSPs the duration of current injection was independent of the membrane time constant. The peak time of the wave form of current injection was between 0.1 and 0.25 msec. The estimates of rho(infinity) were not thought to be very accurate. A lower limit of 4 was assumed and the highest measured value was 12, but in three cells the time course of the EPSP could not be fitted even with a very high value of rho(infinity). Some possible explanations for this discrepancy are mentioned in the Discussion. The electrotonic length of the dendrites (L) was usually greater than 1.0 lambda and ranged between 0.75 and 1.5 lambda. Evidence for an open-circuit termination of the dendrites was found in some cells.5. The normalized values of the rise time and half-width were used to make an electrotonic distance allocation to the 246 EPSPs which were judged to be non-somatic. The method of allocation was not precise because individual values of rho(infinity) and L were not available for these motoneurones. Instead, a maximum possible range was assumed: for rho(infinity), 4-25; for L, 0.75-1.5. The range of alpha was also assumed, from 12 to 100. With these values the motoneurone model (Jack & Redman, 1971b) was used to set limits within which the normalized rise time and half-width of all EPSPs, generated by current at a single point, should lie. Twenty of the 246 EPSPs lay outside these boundary lines and hence they did not receive a distance allocation. The remaining 226 were assigned values between 0.2 and 1.6 lambda (in 0.2 lambda steps); the majority of the allocations (183) were to the proximal electrotonic part of the dendrites (0.2, 0.4 or 0.6 lambda). The relationship of these distance allocations to the histological results of Conradi (1969) is discussed.6. It is concluded that there is no good evidence against the view that the main time course of minimal Ia EPSPs can be explained by their generation by a brief pulse of synaptic current and subsequent passive spread.

Functional organization of connexions to the ventral spinocerebellar tract

1. The functional organization of synaptic connexions to the ventral spinocerebellar tract (VSCT) has been investigated with intracellular recording from 89 spinal border cells (SBCs). 2. EPSPs from primary afferents. Monosynaptic group I EPSPs were evoked in 62 SBCs, in 50 of them from Ia afferents. Ia EPSPs were from knee extensors in 34 cells and knee flexors in 14 cells. No monosynaptic EPSP was evoked by stimulation of peripheral nerves in 27 SBCs. Dorsal column stimulation was tested in 15 of these cells; the absence of monosynaptic EPSPs in 14 of them proves the existence of VSCT cells without monosynaptic connexions from group I afferents. Polysynaptic EPSPs were woked in some cells from Ib afferents, high threshold muscle and cutaneous afferents. 3. IPSPs from primary afferents. Disynaptic IPSPs were evoked from Ia or Ib afferents in many cells. Ib IPSPs were common in SBCs without monosynaptic group I EPSPs. SBCs with Ia EPSPs received Ia or Ib IPSPs mainly from knee muscles. Convergence of Ia EPSPs and IPSPs from the same nerve was observed in 10 cells. Polysynaptic IPSPs were commonly evoked from Ib afferents and invariably evoked from high threshold muscle and skin afferents. 4. Stimulation of the ipsilateral dorsal and/or ventral quadrant of the spinal cord evoked monosynaptic EPSPs and/or IPSPs in many SBCs. 5. The results show that the synaptic input to the VSCT is much more complex than hitherto believed. It is pointed out that all investigated afferent systems, peripheral or descending, which evoke excitation also give inhibition.

The vestibulospinal tract. Effects on alpha-motoneurones in the lumbosacral spinal cord in the cat.

1. Effects evoked from the vestibulospinal tract in hindlimb motoneurones have been investigated with intracellular recording. Electrical stimulation of Deiters' nucleus was employed and for different effects the effective low threshold area in the brain stem was correlated with the region in which antidromic field potentials were evoked from the vestibulospinal tract. 2. The following effects from the vestibulospinal tract are described: a) Monosynaptic EPSPs are common in knee and ankle extensors, rare in hip and toe extensors and absent in flexor motoneurones. There was no marked difference in size of the monosynaptic EPSPs in motoneurones with short and long afterhyperpolarizations. b) Disynaptic IPSPs are common in flexor but also found in some hip extensor cells. c) Di(poly)synaptic EPSPs are common in extensor and in some pretibial flexor cells. 3. A comparison of the descending monosynaptic EPSP with the Ia EPSP showed that the former has a shorter rise time and duration. With repetitive stimulation the descending EPSPs sum more effectively than the Ia EPSPs. 4. The functional role of the pattern of synaptic action from the vestibulospinal tract is discussed also in relation to effects exerted on γ-motoneurones and interneuronal pathways.

Time course of minimal corticomotoneuronal excitatory postsynaptic potentials in lumbar motoneurons of the monkey.

Time course of minimal corticomotoneuronal excitatory postsynaptic potentials in lumbar motoneurons of the monkey.R Porter, and J HoreR Porter, and J HorePublished Online:01 May 1969https://doi.org/10.1152/jn.1969.32.3.443MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInEmailWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformationCited ByShort-term synchrony in diverse motor nuclei presumed to receive different extents of direct cortical inputDouglas A. Keen, Li-Wei Chou, Michael A. Nordstrom, and Andrew J. Fuglevand15 December 2012 | Journal of Neurophysiology, Vol. 108, No. 12Forelimb Movements and Muscle Responses Evoked by Microstimulation of Cervical Spinal Cord in Sedated MonkeysChet T. Moritz, Timothy H. Lucas, Steve I. Perlmutter, and Eberhard E. Fetz1 January 2007 | Journal of Neurophysiology, Vol. 97, No. 1Synchrony between Neurons with Similar Muscle Fields in Monkey Motor CortexNeuron, Vol. 38, No. 1Comparison of peripheral Ia and corticomotoneuronal composite EPSPs in human motoneuronsElectroencephalography and Clinical Neurophysiology/Electromyography and Motor Control, Vol. 101, No. 5Superposition of antidromic responses in pyramidal tract cell clustersExperimental Neurology, Vol. 89, No. 3The corticomotoneuronal component of the pyramidal tract: Corticomotoneuronal connections and functions in primatesBrain Research Reviews, Vol. 10, No. 1Corticospinal neurons with a special role in precision gripBrain Research, Vol. 261, No. 2On the use and interpretation of cross-correlation measurements in the mammalian central nervous systemJournal of Neuroscience Methods, Vol. 1, No. 2A comparative study of ventrolateral and recurrent excitatory postsynaptic potentials in large pyramidal tract cells in the catBrain Research, Vol. 160, No. 1Corticomotoneuronal connections of precentral cells detected by post-spike averages of EMG activity in behaving monkeysBrain Research, Vol. 114, No. 3Effects of trans-membrane polarization and tea injection on monosynaptic actions from motor cortex, red nucleus and group Ia afferents on lumbar motoneurons in the monkeyBrain Research, Vol. 82, No. 1Functions of the mammalian cerebral cortex in movementProgress in Neurobiology, Vol. 1The meaning for motoneurones of the temporal pattern of natural activity in pyramidal tract neurones of conscious monkeysBrain Research, Vol. 34, No. 1Synaptic actions evoked from the red nucleus on the spinal alpha-motoneurons in the rhesus monkeyBrain Research, Vol. 32, No. 2Time course of pyramidal activation of pontine nuclei cells in the catBrain Research, Vol. 19, No. 2 More from this issue > Volume 32Issue 3May 1969Pages 443-51 https://doi.org/10.1152/jn.1969.32.3.443PubMed4306900History Published online 1 May 1969 Published in print 1 May 1969 Metrics