We studied neuronal pathways from low-threshold muscle (group I, II) and cutaneous afferents (group A(alpha)beta) innervating the tail to motoneurons innervating trunk muscles (m. iliocostalis lumborum and m. obliquus externus abdominus) in 18 spinalized cats. Stimulation of group I muscle afferents produced excitatory postsynaptic potentials or excitatory postsynaptic potentials followed by inhibitory postsynaptic potentials in all motoneurons innervating the m. iliocostalis lumborum which showed effects (32%), and predominantly inhibitory postsynaptic potentials in motoneurons innervating the m. obliquus externus abdominus (47%). Stimulation of group I+II afferents produced significant increases of the incidence of motoneurons showing postsynaptic potentials (the notoneurons innervating the m. iliocostalis lumborum, 87%; the motoneurons innervating the m. obliquus externus abdominus, 82%). The effects of low threshold cutaneous afferents were bilateral, predominantly producing inhibitory postsynaptic potentials in motoneurons innervating both muscles. These results suggest that neuronal pathways from muscle afferents to back muscle motoneurons mainly increase the stiffness of the trunk to maintain its stability, while those to abdominal muscles help to extend the dorsal column by decreasing their activities. The results also indicate that neuronal pathways from cutaneous afferents to trunk motoneurons functionallY disconnect the tail from the trunk.

Action Potentials↗

PubMedDate not supplied

Recent advances in basic aging research on the nervous system in Japan.

Recent studies on aging of the nervous system are reviewed with special reference to neuronal cell death, compensatory reaction, trophic factors, brain cholinergic systems and the autonomic nervous system. Studies on spinal motoneurons labeled with a tracer substance transported retrogradely demonstrated differential age effect on different types. Compensatory reactions were also seen among surviving motoneurons. Motoneuronal survival appears to be correlated with the amount of activity. However, the causal relationship between them is not yet conclusive. The effects of nerve growth factor on sympathetic and dorsal-root ganglion cells seem to be well preserved in the aged, although there are some controversial findings on the ratio of NGF-dependent neurons versus NGF-independent neurons. It has been shown that acidic fibroblast growth factor or other substances may prevent degeneration of the basal forebrain cholinergic neurons and improve memory and learning performance in aged animals. The cholinergic system also regulates the regional cerebral blood flow, and this function seems to be well maintained in aged rats. Microneurography techniques have revealed increased activity of postganglionic sympathetic nerves innervating muscles in aged human subjects. The activity of preganglionic sympathetic nerves innervating the adrenal gland and the section rate of noradrenaline have been shown to increase in the aged rat. These changes might cause high blood pressure in the aged, although some species differences have been noted between humans and rats.

Journal Article↗

PubMedDate not supplied

Recovery of motor-unit function after peripheral nerve injury in aged rats.

The potential capacity of aged motoneurons for the reconstruction of motor-units after nerve crush injury was studied in the medial gastrocnemius (MG) muscle of male Fischer rats. The MG nerve in middle-aged (8 months old) and aged (24 months) rats was aseptically crushed under pentobarbital anesthesia. After a 3-month recovery period, the animal was reanesthetized and physiological properties of individual motor-units were recorded. The three different types (fast twitch, fatigable: FF; fast twitch, fatigue resistant: FR and slow twitch: S) of normal motor-unit organization were restored in both middle-aged and aged reinnervated muscles as measured by their relative distributions, mean twitch contraction times and mean tetanic tensions. Some reinnervated units in both aged and middle-aged rats produced a large tetanic tension which exceeded the range for intact units. These findings indicate that aged motoneurons maintain their ability for axonal regenerating and muscle fiber innervation to reestablish normal function of motor-units.

Aging↗

PubMedDate not supplied

Overloading a muscle does not alter the rate of motoneuronal loss in aged rats.

Effects of increased activity on neuronal cell death was investigated in the motor nuclei innervating normal and overloaded medial gastrocnemius (MG) muscles of Fischer 344 rats. The MG muscle was overloaded by the unilateral surgical ablation of synergists at the age of 17 months (group A) or 24 months (group B). When the rats reached the age of 24 and 28 months (group A) or 30 months (group B), motoneurons innervating the MG muscle were labeled bilaterally with horseradish peroxidase injected into the MG nerve. The wet weight of the muscle on the operated side was consistently heavier than that of the contralateral, intact side. The number of labeled neurons decreased with advancing age, and there was no difference in the magnitude of decline found between motor nuclei innervating intact and hypertrophied muscles. Thus, overloading the MG muscle did not retard or accelerate the age-related loss of motoneurons innervating this muscle. These findings indicate that the causal relationship between motoneuronal activity and death with advancing age needs to be studied further.

Age Factors↗