Biomaterial Database

Adaptive fusimotor reflex control in the decerebrate cat. 1999

P R Murphy

Department of Neurobiology, Medical School, University of Newcastle, Newcastle upon Tyne NE2 4HH, UK. p.r.murphy@ncl.ac.uk

The effect of electrical stimulation of cutaneous afferents in the superficial peroneal nerve on the locomotor discharges of single medial gastrocnemius gamma-motoneurones has been investigated in a decerebrate cat preparation. Units were classified as static (n=9) or dynamic (n=7) indirectly on the basis of their resting and locomotor discharge characteristics. Brief trains of stimulation, at 2 and 3xthreshold (T), were applied at rest and during locomotion. Responses were assessed by calculating the change in mean rate during the 100 ms after stimulus onset compared with a control period. At rest, static and dynamic gamma-motoneurones showed opposite responses. Static neurones were excited while inhibition was dominant with dynamic neurones. Effects were always present at 2T. During locomotion, inhibitory responses occurred with both types of gamma-motoneurone and excitation was not apparent. The inhibition of static neurones was maximum during (four units) or between (five units) EMG bursts and minimum in the opposite phase of EMG activity. For dynamic neurones, inhibition was not related to locomotor phase. Generally (six of seven units), the inhibition of dynamic gamma-motoneurones was reduced throughout the step cycle, including phases in which background discharge rates were comparable to resting levels. Latencies of response were measured from peristimulus time histograms. Subtraction of peripheral conduction times gave estimated central delays of locomotor inhibition for static (2.4+/-0.2 ms, n=6; mean+/-S.E.M.) and dynamic (2.2+/-0.2 ms, n=7) gamma-motoneurones that were not significantly different (P>0. 1) and are consistent with spinal oligosynaptic pathways. We conclude that low threshold skin afferents from the foot dorsum are capable of influencing both types of gamma-motoneurone during walking through short latency spinal inhibitory pathways. Further, a highly specific (reciprocal) control of the reflex responses of static and dynamic gamma-efferents occurs that is dependent upon behavioural context. The results are discussed in relation to cutaneous effects on gamma-motoneurones which are suggested to form an adaptive control system.

UI	MeSH Term	Description	Entries
D008297	Male		Males
D009047	Motor Neurons, Gamma	Motor neurons which activate the contractile regions of intrafusal SKELETAL MUSCLE FIBERS, thus adjusting the sensitivity of the MUSCLE SPINDLES to stretch. Gamma motor neurons may be "static" or "dynamic" according to which aspect of responsiveness (or which fiber types) they regulate. The alpha and gamma motor neurons are often activated together (alpha gamma coactivation) which allows the spindles to contribute to the control of movement trajectories despite changes in muscle length.	Neurons, Fusimotor,Neurons, Gamma Motor,Gamma Motorneurons,Motor Neurons, Gamma-Efferent,Fusimotor Neuron,Fusimotor Neurons,Gamma Motor Neuron,Gamma Motor Neurons,Gamma Motorneuron,Gamma-Efferent Motor Neuron,Gamma-Efferent Motor Neurons,Motor Neuron, Gamma,Motor Neuron, Gamma-Efferent,Motor Neurons, Gamma Efferent,Motorneuron, Gamma,Motorneurons, Gamma,Neuron, Fusimotor,Neuron, Gamma Motor,Neuron, Gamma-Efferent Motor,Neurons, Gamma-Efferent Motor
D011930	Reaction Time	The time from the onset of a stimulus until a response is observed.	Response Latency,Response Speed,Response Time,Latency, Response,Reaction Times,Response Latencies,Response Times,Speed, Response,Speeds, Response
D012018	Reflex	An involuntary movement or exercise of function in a part, excited in response to a stimulus applied to the periphery and transmitted to the brain or spinal cord.
D002415	Cats	The domestic cat, Felis catus, of the carnivore family FELIDAE, comprising over 30 different breeds. The domestic cat is descended primarily from the wild cat of Africa and extreme southwestern Asia. Though probably present in towns in Palestine as long ago as 7000 years, actual domestication occurred in Egypt about 4000 years ago. (From Walker's Mammals of the World, 6th ed, p801)	Felis catus,Felis domesticus,Domestic Cats,Felis domestica,Felis sylvestris catus,Cat,Cat, Domestic,Cats, Domestic,Domestic Cat
D003655	Decerebrate State	A condition characterized by abnormal posturing of the limbs that is associated with injury to the brainstem. This may occur as a clinical manifestation or induced experimentally in animals. The extensor reflexes are exaggerated leading to rigid extension of the limbs accompanied by hyperreflexia and opisthotonus. This condition is usually caused by lesions which occur in the region of the brainstem that lies between the red nuclei and the vestibular nuclei. In contrast, decorticate rigidity is characterized by flexion of the elbows and wrists with extension of the legs and feet. The causative lesion for this condition is located above the red nuclei and usually consists of diffuse cerebral damage. (From Adams et al., Principles of Neurology, 6th ed, p358)	Decerebrate Posturing,Decorticate Rigidity,Decorticate State,Rigidity, Decerebrate,Rigidity, Decorticate,Decerebrate Posturings,Decerebrate Rigidity,Decerebrate States,Decorticate Rigidities,Decorticate States,Posturing, Decerebrate,Posturings, Decerebrate,Rigidities, Decorticate,State, Decerebrate,States, Decerebrate
D004525	Efferent Pathways	Nerve structures through which impulses are conducted from a nerve center toward a peripheral site. Such impulses are conducted via efferent neurons (NEURONS, EFFERENT), such as MOTOR NEURONS, autonomic neurons, and hypophyseal neurons.	Motor Pathways,Efferent Pathway,Pathway, Efferent,Pathways, Efferent
D004558	Electric Stimulation	Use of electric potential or currents to elicit biological responses.	Stimulation, Electric,Electrical Stimulation,Electric Stimulations,Electrical Stimulations,Stimulation, Electrical,Stimulations, Electric,Stimulations, Electrical
D005260	Female		Females
D000222	Adaptation, Physiological	The non-genetic biological changes of an organism in response to challenges in its ENVIRONMENT.	Adaptation, Physiologic,Adaptations, Physiologic,Adaptations, Physiological,Adaptive Plasticity,Phenotypic Plasticity,Physiological Adaptation,Physiologic Adaptation,Physiologic Adaptations,Physiological Adaptations,Plasticity, Adaptive,Plasticity, Phenotypic