In anaesthetized cats the activities of Renshaw cells (RCs) and Ia-inhibitory interneurones (IaINs) were recorded during the accumulation of tetanus toxin in the spinal cord following injection into the gastrocnemius muscle. The early response of the RCs increased during the period of development of local tetanus. With some cells there was a subsequent decrease in the early response in later periods of the observation time (16-44 hrs after intramuscular injection). The effects on the spontaneous activity of the RCs were in good correspondence to those on the early response. The hyperactivity of the RCs is proposed to be mediated mainly via disinhibited cholinergic gamma-motoneurones using muscarinic postsynaptic receptors. The "pause" which follows the early response and the recurrent inhibition of IaINs was not reduced during the development of local tetanus. These results indicate that the central action of tetanus toxin in local tetanus does not consist of a general loss of postsynaptic inhibition. It is suggested that tetanus toxin acts mainly on synaptic elements of the alpha- and gamma-motoneurones or on presynaptic nerve terminals in their vicinity. In later periods of disturbing influence on the cholinergic transmission at Renshaw cells seems to occur.

smaller than those in control animals (15 + 1.0 mV versus 5-6 + 2-7 mV; t test, P < 0-001).3. Heteronymous Ia e.p.s.p.s produced by stimulation ofthe lateral gastrocnemiussoleus nerve 5 days after toxin injection were also significantly smaller than those in control animals (0-6 ± 0-6 mV versus 2-5 + 15 mV; P < 0-001). However, these heteronymous Ia e.p.s.p.s remained normal when the lateral gastrocnemius-soleus nerve was ligated and sectioned at the entry to those muscles just before the toxin injection.4. The ascending volleys, which are supposed to represent mainly the action potentials of the dorsal spinocerebellar tract and to be elicited monosynaptically by collaterals of group I afferents, were essentially the same in the left tetanic and right control sides up to 5 days after toxin injection.5. Ia i.p.s.p.s and the hyperpolarizing component of sural p.s.p.s could not be produced or were very small in motoneurones sampled later than 30 h after toxin injection.6. The duration of the after-hyperpolarization and the input resistance of motoneurones remained normal. Axonal conduction velocity of motoneurones measured 5 days after toxin injection was 89-4+12-7 m/s, and was significantly slower than that of control motoneurones (94-1 + 15-4 m/s) (P < 0-005). Differences in the * The laboratory where the present experiments were carried out. K. KANDA AND K. TAKANO amplitude of group I incoming volleys between tetanic leg and contralateral control leg were not observed.7. These results suggest that tetanus toxin blocks excitatory synapses in the central nervous system as well as inhibitory synapses.

The maximum motor nerve conduction velocity of the right and left ulnar motor nerve was measured in more than 650 healthy medical students of both sexes. There was no side difference in the maximum conduction velocity. The shorter person has a statistically significant higher conduction velocity than the taller person. Comparison of students of both sexes showed a slightly higher conduction velocity in females. However, with regard to its relation to height, the conduction velocity was higher in males.

No abstract

No abstract