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. 1984 Nov;356:401–431. doi: 10.1113/jphysiol.1984.sp015473

Relations among passive electrical properties of lumbar alpha-motoneurones of the cat.

B Gustafsson, M J Pinter
PMCID: PMC1193172  PMID: 6520792

Abstract

The relations among passive membrane properties have been examined in cat motoneurones utilizing exclusively electrophysiological techniques. A significant relation was found to exist between the input resistance and the membrane time constant. The estimated electrotonic length showed no evident tendency to vary with input resistance but did show a tendency to decrease with increasing time constant. Detailed analysis of this trend suggests, however, that a variation in dendritic geometry is likely to exist among cat motoneurones, such that the dendritic trees of motoneurones projecting to fast-twitch muscle units are relatively more expansive than those of motoneurones projecting to slow-twitch units. Utilizing an expression derived from the Rall neurone model, the total capacitance of the equivalent cylinder corresponding to a motoneurone has been estimated. With the assumption of a constant and uniform specific capacitance of 1 mu F/cm2, the resulting values have been used as estimates of cell surface area. These estimates agree well with morphologically obtained measurements from cat motoneurones reported by others. Both membrane time constant (and thus likely specific membrane resistivity) and electrotonic length showed little tendency to vary with surface area. However, after-hyperpolarization (a.h.p.) duration showed some tendency to vary such that cells with brief a.h.p. duration were, on average, larger than those with longer a.h.p. durations. Apart from motoneurones with the lowest values, axonal conduction velocity was only weakly related to variations in estimated surface area. Input resistance and membrane time constant were found to vary systematically with the a.h.p. duration. Analysis suggested that the major part of the increase in input resistance with a.h.p. duration was related to an increase in membrane resistivity and a variation in dendritic geometry rather than to differences in surface area among the motoneurones. The possible effects of imperfect electrode seals have been considered. According to an analysis of a passive membrane model, soma leaks caused by impalement injury will result in underestimates of input resistance and time constant and over-estimates of electrotonic length and total capacitance. Assuming a non-injured resting potential of -80 mV, a comparison of membrane potentials predicted by various relative leaks (leak conductance/input conductance) with those actually observed suggests that the magnitude of these errors in the present material will not unduly affect the presented results.+4

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Selected References

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  1. BROCK L. G., COOMBS J. S., ECCLES J. C. The recording of potentials from motoneurones with an intracellular electrode. J Physiol. 1952 Aug;117(4):431–460. doi: 10.1113/jphysiol.1952.sp004759. [DOI] [PMC free article] [PubMed] [Google Scholar]
  2. Barrett J. N., Crill W. E. Specific membrane properties of cat motoneurones. J Physiol. 1974 Jun;239(2):301–324. doi: 10.1113/jphysiol.1974.sp010570. [DOI] [PMC free article] [PubMed] [Google Scholar]
  3. Binder M. C., Bawa P., Ruenzel P., Henneman E. Does orderly recruitment of motoneurons depend on the existence of different types of motor units? Neurosci Lett. 1983 Mar 28;36(1):55–58. doi: 10.1016/0304-3940(83)90485-8. [DOI] [PubMed] [Google Scholar]
  4. Burke R. E., Dum R. P., Fleshman J. W., Glenn L. L., Lev-Tov A., O'Donovan M. J., Pinter M. J. A HRP study of the relation between cell size and motor unit type in cat ankle extensor motoneurons. J Comp Neurol. 1982 Jul 20;209(1):17–28. doi: 10.1002/cne.902090103. [DOI] [PubMed] [Google Scholar]
  5. Burke R. E. Group Ia synaptic input to fast and slow twitch motor units of cat triceps surae. J Physiol. 1968 Jun;196(3):605–630. doi: 10.1113/jphysiol.1968.sp008526. [DOI] [PMC free article] [PubMed] [Google Scholar]
  6. Burke R. E., Nelson P. G. Accommodation to current ramps in motoneurons of fast and slow twitch motor units. Int J Neurosci. 1971 Jun;1(6):347–356. doi: 10.3109/00207457109146983. [DOI] [PubMed] [Google Scholar]
  7. Burke R. E., Rymer W. Z. Relative strength of synaptic input from short-latency pathways to motor units of defined type in cat medial gastrocnemius. J Neurophysiol. 1976 May;39(3):447–458. doi: 10.1152/jn.1976.39.3.447. [DOI] [PubMed] [Google Scholar]
  8. COOMBS J. S., CURTIS D. R., ECCLES J. C. The electrical constants of the motoneurone membrane. J Physiol. 1959 Mar 12;145(3):505–528. doi: 10.1113/jphysiol.1959.sp006158. [DOI] [PMC free article] [PubMed] [Google Scholar]
  9. COOMBS J. S., ECCLES J. C., FATT P. The electrical properties of the motoneurone membrane. J Physiol. 1955 Nov 28;130(2):291–325. doi: 10.1113/jphysiol.1955.sp005411. [DOI] [PMC free article] [PubMed] [Google Scholar]
  10. Edwards F. R., Redman S. J., Walmsley B. The effect of polarizing currents on unitary Ia excitatory post-synaptic potentials evoked in spinal motoneurones. J Physiol. 1976 Aug;259(3):705–723. doi: 10.1113/jphysiol.1976.sp011490. [DOI] [PMC free article] [PubMed] [Google Scholar]
  11. Fleshman J. W., Munson J. B., Sypert G. W., Friedman W. A. Rheobase, input resistance, and motor-unit type in medial gastrocnemius motoneurons in the cat. J Neurophysiol. 1981 Dec;46(6):1326–1338. doi: 10.1152/jn.1981.46.6.1326. [DOI] [PubMed] [Google Scholar]
  12. Fleshman J. W., Munson J. B., Sypert G. W. Homonymous projection of individual group Ia-fibers to physiologically characterized medial gastrocnemius motoneurons in the cat. J Neurophysiol. 1981 Dec;46(6):1339–1348. doi: 10.1152/jn.1981.46.6.1339. [DOI] [PubMed] [Google Scholar]
  13. Gustafsson B. Changes in motoneurone electrical properties following axotomy. J Physiol. 1979 Aug;293:197–215. doi: 10.1113/jphysiol.1979.sp012885. [DOI] [PMC free article] [PubMed] [Google Scholar]
  14. Gustafsson B., Katz R., Malmsten J. Effects of chronic partial deafferentiation on the electrical properties of lumbar alpha-motoneurones in the cat. Brain Res. 1982 Aug 19;246(1):23–33. doi: 10.1016/0006-8993(82)90138-x. [DOI] [PubMed] [Google Scholar]
  15. HENNEMAN E., SOMJEN G., CARPENTER D. O. FUNCTIONAL SIGNIFICANCE OF CELL SIZE IN SPINAL MOTONEURONS. J Neurophysiol. 1965 May;28:560–580. doi: 10.1152/jn.1965.28.3.560. [DOI] [PubMed] [Google Scholar]
  16. Harrison P. J., Taylor A. Individual excitatory post-synaptic potentials due to muscle spindle Ia afferents in cat triceps surae motoneurones. J Physiol. 1981 Mar;312:455–470. doi: 10.1113/jphysiol.1981.sp013638. [DOI] [PMC free article] [PubMed] [Google Scholar]
  17. Hotson J. R., Prince D. A., Schwartzkroin P. A. Anomalous inward rectification in hippocampal neurons. J Neurophysiol. 1979 May;42(3):889–895. doi: 10.1152/jn.1979.42.3.889. [DOI] [PubMed] [Google Scholar]
  18. Iansek R., Redman S. J. The amplitude, time course and charge of unitary excitatory post-synaptic potentials evoked in spinal motoneurone dendrites. J Physiol. 1973 Nov;234(3):665–688. doi: 10.1113/jphysiol.1973.sp010366. [DOI] [PMC free article] [PubMed] [Google Scholar]
  19. Ito M., Oshima T. Electrical behaviour of the motoneurone membrane during intracellularly applied current steps. J Physiol. 1965 Oct;180(3):607–635. doi: 10.1113/jphysiol.1965.sp007720. [DOI] [PMC free article] [PubMed] [Google Scholar]
  20. Jack J. J., Miller S., Porter R., Redman S. J. The time course of minimal excitory post-synaptic potentials evoked in spinal motoneurones by group Ia afferent fibres. J Physiol. 1971 Jun;215(2):353–380. doi: 10.1113/jphysiol.1971.sp009474. [DOI] [PMC free article] [PubMed] [Google Scholar]
  21. Kernell D., Zwaagstra B. Input conductance axonal conduction velocity and cell size among hindlimb motoneurones of the cat. Brain Res. 1981 Jan 12;204(2):311–326. doi: 10.1016/0006-8993(81)90591-6. [DOI] [PubMed] [Google Scholar]
  22. Krnjević K., Puil E., Werman R. EGTA and motoneuronal after-potentials. J Physiol. 1978 Feb;275:199–223. doi: 10.1113/jphysiol.1978.sp012186. [DOI] [PMC free article] [PubMed] [Google Scholar]
  23. Lev-Tov A., Miller J. P., Burke R. E., Rall W. Factors that control amplitude of EPSPs in dendritic neurons. J Neurophysiol. 1983 Aug;50(2):399–412. doi: 10.1152/jn.1983.50.2.399. [DOI] [PubMed] [Google Scholar]
  24. Lüscher H. R., Ruenzel P., Henneman E. Composite EPSPs in motoneurons of different sizes before and during PTP: implications for transmission failure and its relief in Ia projections. J Neurophysiol. 1983 Jan;49(1):269–289. doi: 10.1152/jn.1983.49.1.269. [DOI] [PubMed] [Google Scholar]
  25. Mayer M. L., Westbrook G. L. A voltage-clamp analysis of inward (anomalous) rectification in mouse spinal sensory ganglion neurones. J Physiol. 1983 Jul;340:19–45. doi: 10.1113/jphysiol.1983.sp014747. [DOI] [PMC free article] [PubMed] [Google Scholar]
  26. Nelson P. G., Frank K. Anomalous rectification in cat spinal motoneurons and effect of polarizing currents on excitatory postsynaptic potential. J Neurophysiol. 1967 Sep;30(5):1097–1113. doi: 10.1152/jn.1967.30.5.1097. [DOI] [PubMed] [Google Scholar]
  27. Nelson P. G., Lux H. D. Some electrical measurements of motoneuron parameters. Biophys J. 1970 Jan;10(1):55–73. doi: 10.1016/S0006-3495(70)86285-3. [DOI] [PMC free article] [PubMed] [Google Scholar]
  28. Pinter M. J., Curtis R. L., Hosko M. J. Voltage threshold and excitability among variously sized cat hindlimb motoneurons. J Neurophysiol. 1983 Sep;50(3):644–657. doi: 10.1152/jn.1983.50.3.644. [DOI] [PubMed] [Google Scholar]
  29. Rall W. Time constants and electrotonic length of membrane cylinders and neurons. Biophys J. 1969 Dec;9(12):1483–1508. doi: 10.1016/S0006-3495(69)86467-2. [DOI] [PMC free article] [PubMed] [Google Scholar]
  30. Redman S. J. The attenuation of passively propagating dendritic potentials in a motoneurone cable model. J Physiol. 1973 Nov;234(3):637–664. doi: 10.1113/jphysiol.1973.sp010365. [DOI] [PMC free article] [PubMed] [Google Scholar]
  31. Schwindt P. C., Crill W. E. Properties of a persistent inward current in normal and TEA-injected motoneurons. J Neurophysiol. 1980 Jun;43(6):1700–1724. doi: 10.1152/jn.1980.43.6.1700. [DOI] [PubMed] [Google Scholar]
  32. Sypert G. W., Munson J. B. Basis of segmental motor control: motoneuron size or motor unit type? Neurosurgery. 1981 May;8(5):608–621. doi: 10.1227/00006123-198105000-00020. [DOI] [PubMed] [Google Scholar]
  33. Ulfhake B., Kellerth J. O. A quantitative morphological study of HRP-labelled cat alpha-motoneurones supplying different hindlimb muscles. Brain Res. 1983 Mar 28;264(1):1–19. doi: 10.1016/0006-8993(83)91116-2. [DOI] [PubMed] [Google Scholar]
  34. Ulfhake B., Kellerth J. O. Does alpha-motoneurone size correlate with motor unit type in cat triceps surae? Brain Res. 1982 Nov 18;251(2):201–209. doi: 10.1016/0006-8993(82)90738-7. [DOI] [PubMed] [Google Scholar]
  35. Zwaagstra B., Kernell D. The duration of after-hyperpolarization in hindlimb alpha motoneurones of different sizes in the cat. Neurosci Lett. 1980 Oct 2;19(3):303–307. doi: 10.1016/0304-3940(80)90278-5. [DOI] [PubMed] [Google Scholar]

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