Tessa Gordon - Academia.edu (original) (raw)
Papers by Tessa Gordon
Oxford University Press eBooks, Oct 1, 2004
Biochemical Pharmacology, Aug 1, 1987
Journal of Neurophysiology, 1996
1. The aims of this study are to determine 1) whether regenerating motor axons have the capacity ... more 1. The aims of this study are to determine 1) whether regenerating motor axons have the capacity to form enlarged motor units (MUs) in muscles reinnervated by few motoneurons and 2) whether the type of nerve injury, repair, and/or growth environment affects this capacity. 2. MU innervation ratio (IR) was estimated by measuring isometric unit tetanic force in reinnervated cat medial gastrocnemius muscles 3-16 mo after denervation by either 1) crushing its nerve, 2) transecting the nerve and suturing the proximal end to the distal stump (N-N suture), or 3) transecting the nerve and suturing the proximal end directly to the muscle fascia (N-M suture). In addition, the number of regenerating axons was experimentally reduced by cutting one of two contributing ventral roots. 3. Muscles were reinnervated by 2-88% of their normal complement of MUs. Mean unit tetanic force increased as the number of reinnervated MUs decreased in reinnervated muscles after nerve crush or N-N suture, but not after N-M suture, even when few axons made functional connections. When the number of MUs was < 20% of normal, mean unit force was significantly higher in reinnervated muscles after nerve crush compared with muscle reinnervated after N-N suture. 4. The cross-sectional areas (CSAs) of all muscle fiber types were similar to normal in reinnervated muscles after nerve crush, but the CSAs of type IIa and IIb fibers were significantly smaller in muscles reinnervated after complete nerve transections (i.e., N-N or N-M sutures). 5. When MU force was normalized to mean muscle fiber CSA, cut motor axons displayed the same capacity to form enlarged MUs as crushed motor axons. The force of the MUs increased by as much as 5-8 times that of normal, provided the axons grew along the distal nerve stump (N-N suture). 6. Tetanic force increased in the normal order slow < fast-fatigue resistant < fast-fatigue intermediate = fast-fatigable. However, the increase in tetanic force of the slow (S) units was significantly larger than the corresponding increase of the more forceful fast (F) units. The disproportional increase in S and not F unit force, was primarily due to a significant decline in CSA of the type IIa and IIb muscle fibers. 7. The technique of glycogen depletion was used to count MU fibers to estimate the IR of MUs in 5 normal and 11 reinnervated muscles (7 N-N sutures, 4 N-M sutures). Unit tetanic force covaried with IR in both normal and reinnervated muscles. 8. These results show that regenerating axons have the same capacity as intact axons in partially denervated muscles to form enlarged MUs to compensate for a reduced number of functioning MUs. Only when axons regenerate in the absence of the distal nerve sheath is this capacity compromised.
![Research paper thumbnail of Neural regulation of [3H]saxitoxin binding site numbers in rat neonatal muscle](https://attachments.academia-assets.com/120663098/thumbnails/1.jpg)
](The Journal of Physiology, Dec 1, 1988
Plastic and Reconstructive Surgery, 2014
PurPose: Macrophages play a key role in axonal regeneration because they secrete IL-6 that is nec... more PurPose: Macrophages play a key role in axonal regeneration because they secrete IL-6 that is necessary for axonal guidance and remyelination. Pro-inflammatory cytokines stimulate macrophage migration into the lesion sites which is necessary for the removal of cell debris and Schwann cell invasion as guidance for axonal outgrowth followed by remyelination. α1-antitrypsin (AAT) is an acute phase protein and it is shown to express anti-inflammatory characteristics in neutrophil and monocyte/macrophage driven models in vitro and in vivo. We asked a question whether AAT can affect regeneration of injured peripheral nerve fibers by initial macrophage mobilization. We have established several models to study peripheral nerve injuries in small animals. In the rat sciatic nerve crush model we developed a standardized method for investigation of nerve regeneration parameters. We could demonstrate that axonal sprouting, as well as myelin sheaths and functional outcome can be improved by adjunct AAT therapy.
The Journal of Physiology, Dec 1, 1978
Plastic and reconstructive surgery. Global open, Apr 1, 2019
Journal of The American College of Surgeons, Oct 1, 2014
Plastic and reconstructive surgery. Global open, Apr 1, 2020
amputations develop symptomatic neuromas. Many patients rely on daily opioids, neuropathic pain m... more amputations develop symptomatic neuromas. Many patients rely on daily opioids, neuropathic pain meds, and/or antidepressant medications that provide suboptimal pain relief with adverse side effects. Many patients cannot return to work as a result of these neuromas. The Regenerative Peripheral Nerve Interface (RPNI) is a surgical technique that involves implantation of a divided peripheral nerve into a free muscle graft. RPNIs mitigate neuroma formation and treat existing neuroma pain in the setting of major limb amputations. The purpose of this study was to determine if RPNIs effectively treat neuroma pain following partial hand and digital amputations.
The Journal of Physiology, Mar 24, 2016
Biophysical Journal, Nov 1, 1982
Canadian Journal of Physiology and Pharmacology, Jul 1, 1981
Methods are described for analyzing the patterns of sensory activity in peripheral nerves during ... more Methods are described for analyzing the patterns of sensory activity in peripheral nerves during unrestrained behaviour. In locomotion, nerves supplying ankle extensors and flexors typically show two bursts of sensory activity per step cycle. Variations in sensory input may be important in modulating the ongoing oscillation. Altered sensory input may also change the phase of an ongoing oscillation (as in human essential tremor) or may only have a transient reflex effect (as in Parkinsonian tremor). Various types of interactions can be analyzed using a model of the peripheral neuromuscular system and its central connections. In general, the following categories are suggested for sensory actions on neural oscillations: (1) modulation of (a) the amplitude or (b) the frequency; (2) resetting (i.e., a maintained change in the timing of an oscillation without changes in frequency); (3) repatterning an oscillation (a) over several cycles (e.g., gait changes in locomotion) or (b) within a cycle or two (e.g., the stumble corrective reaction); and (4) gating an oscillation on or off.
Canadian Journal of Physiology and Pharmacology, Sep 1, 1986
bioRxiv (Cold Spring Harbor Laboratory), Jan 29, 2021
Experimental Neurology, Aug 1, 1985
The kinetics of isolated extensor digitorum longus and soleus muscles from normal and genetically... more The kinetics of isolated extensor digitorum longus and soleus muscles from normal and genetically dystrophic (129/ReJ dy/dy) mice were studied at temperatures from 8 to 38 degrees C. The rate constants for the exponential rise of tetanic force and for the exponential decay of force during an isometric twitch or short tetanus were similar in normal and dystrophic soleus muscles, but the decay rates were significantly reduced in dystrophic extensor digitorum longus muscles. The temperature dependence for several rate constants for isometric twitches and tetani was similar in all muscles studied, suggesting that the same rate limiting processes apply to fast and slow, normal and dystrophic muscles. Thus, the contractile proteins and those in the sarcoplasmic reticulum of dystrophic muscle are probably normal. The slower relaxation phase in dystrophic extensor digitorum longus muscles is compatible with a reduction in Ca2+-pumping sites in the sarcoplasmic reticulum, perhaps secondary to a change in motor unit composition. Some changes in the temperature dependence for measured times, toward those of soleus muscles, is consistent with the increased proportion of slow twitch motor units in dystrophic extensor digitorum longus muscles.
The Journal of Neuroscience, May 1, 1995
The Journal of Physiology, May 1, 1986
Journal of Neurophysiology, Jul 1, 1988
The Journal of Physiology, May 1, 1986
Peripheral nerves to flexor (common peroneal) and extensor (tibial) nerves in a hind limb of seve... more Peripheral nerves to flexor (common peroneal) and extensor (tibial) nerves in a hind limb of seven 2-6 month old cats were cut and cross-united to study the plasticity in the spinal cord. The extent to which motoneurones from extensor and flexor motor pools were misdirected to their antagonistic muscles was determined by measuring the potentials generated at the spinal roots from the crossed nerves. The axons contributing to the extensor nerves normally leave the cord in the L7 and S1 ventral and dorsal roots while the axons contributing to the flexor nerves normally leave the cord in the L6 and L7 ventral and dorsal roots. Following cross-union, medial gastrocnemius (m.g.) and lateral gastrocnemius-soleus (l.g.s.) nerves were primarily supplied by L6 and L7 ventral and dorsal roots, and common peroneal (c.p.) nerves were primarily supplied by L7 and S1 ventral and dorsal roots. A method for quantifying the completeness of cross-reinnervation was developed. The pattern of e.m.g. activity in cross-reinnervated muscles during locomotion was primarily determined by the innervating nerve with the reinnervated flexor muscles being activated during the extensor phase. However, the cross-reinnervated extensor muscles showed evidence of extensor activity in addition to the double-burst pattern typical of flexor nerves. This extensor activity was more prominent when the nerve cross was less complete. We conclude that during locomotion the activity of spinal motoneurones was not substantially modified by inappropriate peripheral connexions, even when the nerve cross was carried out in young animals. This conclusion is discussed in relation to previous studies which suggested some degree of functional modification.
Oxford University Press eBooks, Oct 1, 2004
Biochemical Pharmacology, Aug 1, 1987
Journal of Neurophysiology, 1996
1. The aims of this study are to determine 1) whether regenerating motor axons have the capacity ... more 1. The aims of this study are to determine 1) whether regenerating motor axons have the capacity to form enlarged motor units (MUs) in muscles reinnervated by few motoneurons and 2) whether the type of nerve injury, repair, and/or growth environment affects this capacity. 2. MU innervation ratio (IR) was estimated by measuring isometric unit tetanic force in reinnervated cat medial gastrocnemius muscles 3-16 mo after denervation by either 1) crushing its nerve, 2) transecting the nerve and suturing the proximal end to the distal stump (N-N suture), or 3) transecting the nerve and suturing the proximal end directly to the muscle fascia (N-M suture). In addition, the number of regenerating axons was experimentally reduced by cutting one of two contributing ventral roots. 3. Muscles were reinnervated by 2-88% of their normal complement of MUs. Mean unit tetanic force increased as the number of reinnervated MUs decreased in reinnervated muscles after nerve crush or N-N suture, but not after N-M suture, even when few axons made functional connections. When the number of MUs was < 20% of normal, mean unit force was significantly higher in reinnervated muscles after nerve crush compared with muscle reinnervated after N-N suture. 4. The cross-sectional areas (CSAs) of all muscle fiber types were similar to normal in reinnervated muscles after nerve crush, but the CSAs of type IIa and IIb fibers were significantly smaller in muscles reinnervated after complete nerve transections (i.e., N-N or N-M sutures). 5. When MU force was normalized to mean muscle fiber CSA, cut motor axons displayed the same capacity to form enlarged MUs as crushed motor axons. The force of the MUs increased by as much as 5-8 times that of normal, provided the axons grew along the distal nerve stump (N-N suture). 6. Tetanic force increased in the normal order slow < fast-fatigue resistant < fast-fatigue intermediate = fast-fatigable. However, the increase in tetanic force of the slow (S) units was significantly larger than the corresponding increase of the more forceful fast (F) units. The disproportional increase in S and not F unit force, was primarily due to a significant decline in CSA of the type IIa and IIb muscle fibers. 7. The technique of glycogen depletion was used to count MU fibers to estimate the IR of MUs in 5 normal and 11 reinnervated muscles (7 N-N sutures, 4 N-M sutures). Unit tetanic force covaried with IR in both normal and reinnervated muscles. 8. These results show that regenerating axons have the same capacity as intact axons in partially denervated muscles to form enlarged MUs to compensate for a reduced number of functioning MUs. Only when axons regenerate in the absence of the distal nerve sheath is this capacity compromised.
The Journal of Physiology, Dec 1, 1988
Plastic and Reconstructive Surgery, 2014
PurPose: Macrophages play a key role in axonal regeneration because they secrete IL-6 that is nec... more PurPose: Macrophages play a key role in axonal regeneration because they secrete IL-6 that is necessary for axonal guidance and remyelination. Pro-inflammatory cytokines stimulate macrophage migration into the lesion sites which is necessary for the removal of cell debris and Schwann cell invasion as guidance for axonal outgrowth followed by remyelination. α1-antitrypsin (AAT) is an acute phase protein and it is shown to express anti-inflammatory characteristics in neutrophil and monocyte/macrophage driven models in vitro and in vivo. We asked a question whether AAT can affect regeneration of injured peripheral nerve fibers by initial macrophage mobilization. We have established several models to study peripheral nerve injuries in small animals. In the rat sciatic nerve crush model we developed a standardized method for investigation of nerve regeneration parameters. We could demonstrate that axonal sprouting, as well as myelin sheaths and functional outcome can be improved by adjunct AAT therapy.
The Journal of Physiology, Dec 1, 1978
Plastic and reconstructive surgery. Global open, Apr 1, 2019
Journal of The American College of Surgeons, Oct 1, 2014
Plastic and reconstructive surgery. Global open, Apr 1, 2020
amputations develop symptomatic neuromas. Many patients rely on daily opioids, neuropathic pain m... more amputations develop symptomatic neuromas. Many patients rely on daily opioids, neuropathic pain meds, and/or antidepressant medications that provide suboptimal pain relief with adverse side effects. Many patients cannot return to work as a result of these neuromas. The Regenerative Peripheral Nerve Interface (RPNI) is a surgical technique that involves implantation of a divided peripheral nerve into a free muscle graft. RPNIs mitigate neuroma formation and treat existing neuroma pain in the setting of major limb amputations. The purpose of this study was to determine if RPNIs effectively treat neuroma pain following partial hand and digital amputations.
The Journal of Physiology, Mar 24, 2016
Biophysical Journal, Nov 1, 1982
Canadian Journal of Physiology and Pharmacology, Jul 1, 1981
Methods are described for analyzing the patterns of sensory activity in peripheral nerves during ... more Methods are described for analyzing the patterns of sensory activity in peripheral nerves during unrestrained behaviour. In locomotion, nerves supplying ankle extensors and flexors typically show two bursts of sensory activity per step cycle. Variations in sensory input may be important in modulating the ongoing oscillation. Altered sensory input may also change the phase of an ongoing oscillation (as in human essential tremor) or may only have a transient reflex effect (as in Parkinsonian tremor). Various types of interactions can be analyzed using a model of the peripheral neuromuscular system and its central connections. In general, the following categories are suggested for sensory actions on neural oscillations: (1) modulation of (a) the amplitude or (b) the frequency; (2) resetting (i.e., a maintained change in the timing of an oscillation without changes in frequency); (3) repatterning an oscillation (a) over several cycles (e.g., gait changes in locomotion) or (b) within a cycle or two (e.g., the stumble corrective reaction); and (4) gating an oscillation on or off.
Canadian Journal of Physiology and Pharmacology, Sep 1, 1986
bioRxiv (Cold Spring Harbor Laboratory), Jan 29, 2021
Experimental Neurology, Aug 1, 1985
The kinetics of isolated extensor digitorum longus and soleus muscles from normal and genetically... more The kinetics of isolated extensor digitorum longus and soleus muscles from normal and genetically dystrophic (129/ReJ dy/dy) mice were studied at temperatures from 8 to 38 degrees C. The rate constants for the exponential rise of tetanic force and for the exponential decay of force during an isometric twitch or short tetanus were similar in normal and dystrophic soleus muscles, but the decay rates were significantly reduced in dystrophic extensor digitorum longus muscles. The temperature dependence for several rate constants for isometric twitches and tetani was similar in all muscles studied, suggesting that the same rate limiting processes apply to fast and slow, normal and dystrophic muscles. Thus, the contractile proteins and those in the sarcoplasmic reticulum of dystrophic muscle are probably normal. The slower relaxation phase in dystrophic extensor digitorum longus muscles is compatible with a reduction in Ca2+-pumping sites in the sarcoplasmic reticulum, perhaps secondary to a change in motor unit composition. Some changes in the temperature dependence for measured times, toward those of soleus muscles, is consistent with the increased proportion of slow twitch motor units in dystrophic extensor digitorum longus muscles.
The Journal of Neuroscience, May 1, 1995
The Journal of Physiology, May 1, 1986
Journal of Neurophysiology, Jul 1, 1988
The Journal of Physiology, May 1, 1986
Peripheral nerves to flexor (common peroneal) and extensor (tibial) nerves in a hind limb of seve... more Peripheral nerves to flexor (common peroneal) and extensor (tibial) nerves in a hind limb of seven 2-6 month old cats were cut and cross-united to study the plasticity in the spinal cord. The extent to which motoneurones from extensor and flexor motor pools were misdirected to their antagonistic muscles was determined by measuring the potentials generated at the spinal roots from the crossed nerves. The axons contributing to the extensor nerves normally leave the cord in the L7 and S1 ventral and dorsal roots while the axons contributing to the flexor nerves normally leave the cord in the L6 and L7 ventral and dorsal roots. Following cross-union, medial gastrocnemius (m.g.) and lateral gastrocnemius-soleus (l.g.s.) nerves were primarily supplied by L6 and L7 ventral and dorsal roots, and common peroneal (c.p.) nerves were primarily supplied by L7 and S1 ventral and dorsal roots. A method for quantifying the completeness of cross-reinnervation was developed. The pattern of e.m.g. activity in cross-reinnervated muscles during locomotion was primarily determined by the innervating nerve with the reinnervated flexor muscles being activated during the extensor phase. However, the cross-reinnervated extensor muscles showed evidence of extensor activity in addition to the double-burst pattern typical of flexor nerves. This extensor activity was more prominent when the nerve cross was less complete. We conclude that during locomotion the activity of spinal motoneurones was not substantially modified by inappropriate peripheral connexions, even when the nerve cross was carried out in young animals. This conclusion is discussed in relation to previous studies which suggested some degree of functional modification.