Some physiological characteristics of motor cortex neurons of aged rabbits.
Neurophysiological alterations occurring in the motor cortex of aged rabbits have been examined. Experiments were performed on rabbits of three age groups: one year old (young), four to five years old (middle-aged) and six to seven years old (aged). Extracellular unit activity was recorded in the motor projection of a forelimb. Several sessions of rhythmic (2 Hz) electrocutaneous stimulation were delivered to contralateral forelimb. The neuronal activity was recorded before and after rhythmic stimulation. We also measured the firing rate during spontaneous electromyogram activity of the extensor carpi radialis. Neurons having slow spontaneous firing activity were predominant in aged rabbits as compared with young animals. In young animals the highest values of spontaneous firing rate (15-20 impulses/s) were observed in neurons related to movement. In aged rabbits spontaneous firing rate of movement-related neurons did not exceed 16 impulses/s. During spontaneous movements of extensor carpi radialis, the level of neuronal activity in young rabbits was twice as high as that in aged ones. In young rabbits after rhythmic electrocutaneous stimulation of a forelimb, 20% of recorded neurons exhibited periodic fluctuations in firing rate with the period of preceding stimulation. The repeated stimulation sessions increased the number of rhythmic firing neurons to 40-50%. In aged rabbits, patterns of firing activity of motor cortex neurons did not change significantly after several sessions of rhythmic electrocutaneous stimulation. Decreased neuronal excitability may be the cause of functional alterations in motor cortex neurons of aged rabbits.
Mednikova YuS
Institute of Higher Nervous Activity and Neurophysiology, Russian Academy of Science, Moscow.
Kopytova
F V
FV
D000375:Aging / Q000502:physiology*; D000818:Animals; D004558:Electric Stimulation / Q000379:methods; D004576:Electromyography; D004594:Electrophysiology; D005552:Forelimb; D008297:Male; D009043:Motor Activity / Q000502:physiology; D009044:Motor Cortex / Q000166:cytology / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D010507:Periodicity; D011817:Rabbits; D012879:Skin Physiological Phenomena