SUMMARY1. A study has been made of the formation of synapses in developing striated muscles which receive either a focal (the rat hemidiaphragm) or a distributed (the avian anterior latissimus dorsi) innervation using histological, ultrastructural and electrophysiological techniques.2. In the developing diaphragm only a single synaptic contact was initially established at random along the length of the short (300,um) myotubes by a single axon; in the developing ALD more than one synaptic contact could be established initially along the length of the long (2500 ,im) myotubes by axons, but the distance between these was never less than 170gm. 3. Each synapse established by the initial axonal contact in either the diaphragm or the ALD subsequently received a multiple innervation from further exploring axons in the muscles, and all such additional innervation of muscle cells was constrained to the sites of the initial synaptic contacts; this multiple innervation of synaptic sites was lost in the subsequent 4 weeks.4. It is suggested that the axon forming the initial synaptic contact on myotubes induces a property over an adjacent length of myotube which makes its membrane refractory to synapse formation over this length; this characteristic length is longer for axons forming a focal innervation than it is for those forming distributed innervation.

We assessed the relation between clinical apnea and brain-stem neuronal function in 58 preterm babies. The brain-stem conduction time of the auditory evoked response (Wave V-I interval) was longer in babies with apnea than in those without it at a similar postconceptional age (at 32 to 33 weeks: mean, 6.16 vs. 5.35 msec, P less than 0.001; at 34 to 35 weeks: mean, 5.98 vs. 5.33 msec, P less than 0.002). The number of apneas per day decreased over a period that was similar to the period during which brainstem conduction time decreased. In general, apneas ceased when the conduction time decreased to the levels observed in babies of a similar age who did not have apnea. Short brain-stem conduction times were observed in some infants who had prenatal stress, such as intrauterine growth retardation or maternal hypertension. These results suggest that the occurrence of apnea in preterm infants is correlated with neural function in the brain stem.

SUMMARY1. A study has been made of the effects of changing [Ca]. and [Mg]. on the binomial statistic parameters p and n that control the average quantal content (hi) of the excitatory post-synaptic potential (e.p.s.p.) due to

SUMMARY1. A study has been made of the formation of synapses in developing reinnervated and cross-reinnervated amphibian twitch muscles which receive either a focal (iliofibularis) or a distributed (sartorius) innervation from 'en plaque' nerve terminals using histological, ultrastructural and electrophysiological techniques.2. During the development of the tadpole through metamorphosis to the adult frog, the sartorius myofibres increased in length at about twice the rate of the iliofibularis myofibres, due to a fast rate of growth at their insertions on to the pelvic tendon.3 5. Reinnervation or cross-reinnervation of the sartorius and the iliofibularis muscles in adults or at a late stage of development simply reconstituted the normal focal and distributed innervation patterns of the muscles, as found in the control muscles of the contralateral and unoperated legs.6. These observations on synapse formation in amphibia are consistent M. R. BENNETT AND A. G. PETTIGREW with the hypothesis that during development the axon making the initial synaptic contact on the muscle cells induces a property over a length of muscle membrane adjacent to this site which makes it refractory to synapse formation; thus during reinnervation or cross-reinnervation of adult muscles this refractory property constrains synapse formation to these sites.

SUMMARY1. A study has been made of the formation of synapses in spontaneously reinnervated and cross-reinnervated anterior latissimus dorsi (ALD) and posterior latissimus dorsi (PLD) muscles of adult fowls.2. Denervated ALD and PLD muscle fibres have a uniform and high sensitivity to iontophoretically applied acetylcholine (ACh). During early reinnervation the sensitivity distribution to ACh of the ALD muscle fibres begins to return to normal before synaptic potentials can be evoked. The normal ACh sensitivity distribution of PLD muscle fibres is also restored after reinnervation. After cross-reinnervation of the ALD and PLD muscles the ACh sensitivity distribution of many of the muscle fibres is again restored to normal.3. Reinnervating and cross-reinnervating ALD nerve terminals showed a greater than normal degree of facilitation of transmitter release when a test impulse was applied at various intervals after a conditioning impulse. Cross-reinnervating PLD nerve terminals showed facilitation of transmitter release rather than the normal depression in a conditioningtest impulse sequence.4. The distribution of nerve terminals over the surface of spontaneously reinnervated and cross-reinnervated ALD and PLD muscle fibres has been determined from an examination of the sensitivity distribution to applied ACh, the graded versus all-or-none nature of the evoked potential and the distribution of cholinesterase stained synapses.5. The results suggest that the innervation pattern of individual ALD and PLD muscle fibres is restored both after spontaneous reinnervation and cross-reinnervation.