Morphine and Nalorphine impair Neuromuscular Transmission

THE narcotic analgesic morphine and the analgesic-antagonist nalorphine both depress the twitch and tetanus of the coaxially stimulated guinea-pig ileum¹. There is general agreement that morphine impairs the release of acetylcholine at this peripheral muscarinic site^1–4. Less is agreed about the effects of morphine at nicotinic sites^1,5–7. Because there is no evidence that the mechanisms of transmitter release differ fundamentally between muscarinic and nicotinic sites, we have examined the effects of morphine and nalorphine on some isolated skeletal neuromuscular preparations. A preliminary account of a portion of this work has already been reported⁸.     

Morphine impairs Acetylcholine Release but facilitates Acetylcholine Action at a Skeletal Neuromuscular Junction

THERE is considerable evidence that morphine impairs the release of acetylcholine (ACh) at cholinergic synapses in the brain^1–5, although there are considerable problems in determining the exact site and mechanism of this action. A simple synaptic model would be useful for pursuing this problem and the question arises whether this action of morphine is universal for cholinergic synapses or is restricted to particular sites. Morphine impairs the release of ACh at peripheral muscarinic sites^6–8 but there are no reports about the effects of morphine on ACh release at nicotinic neuromuscular sites. We have reported that both morphine and nalorphine block neuromuscular transmission in amphibian and mammalian skeletal neuromuscular preparations^9,10, apparently as a result of impairment of ACh release. We have now determined by direct measurement that morphine impairs ACh release at a skeletal neuromuscular junction.     

Dispersal provided resilience to range collapse in a marine mammal: insights from the past to inform conservation biology

Population loss is often a harbinger of species extinction, but few opportunities exist to follow a species’ demography and genetics through both time and space while this occurs. Previous research has shown that the northern fur seal (Callorhinus ursinus) was extirpated from most of its range over the past 200–800 years and that some of the extirpated populations had unique life history strategies. In this study, widespread availability of subfossils in the eastern Pacific allowed us to examine temporal changes in spatial genetic structure during massive population range contraction and partial recovery. We sequenced the mitochondrial control region from 40 ancient and 365 modern samples and analyzed them through extensive simulations within a serial Approximate Bayesian Computation framework. These analyses suggest that the species maintained a high abundance, probably in subarctic refugia, that dispersal rates are likely 85% per generation into new breeding colonies, and that population structure was not higher in the past. Despite substantial loss of breeding range, this species’ high dispersal rates and refugia appear to have prevented a loss of genetic diversity. High dispersal rates also suggest that previous evidence for divergent life history strategies in ancient populations likely resulted from behavioral plasticity. Our results support the proposal that panmictic, or nearly panmictic, species with large ranges will be more resilient to future disturbance and environmental change. When appropriately verified, evidence of low population structure can be powerful information for conservation decision‐making.     

Role of lipid in the cellulose synthetase enzyme system from oat seedlings

Particulate fractions making cellulose from UDP glucose (glucose-¹⁴C)were obtained by chromatography of oat seedling cell wall-freehomogenates on Sepharose 4B. All particle fractions obtainedformed varying proportions of glucolipid and polysaccharide.The optimal pH for cellulose synthesis was about 8. Activitywas higher in Tris buffer than in phosphate buffer. Dithiothreitolenhanced the cellulose synthetase activity. Glycerol (0.37 M)in the incubation medium had no effect on either glycolipidor polysaccharide synthesis. Treatment of particles with phospholipaseA (EC 3.1.1.4 [EC] ) inhibited the enzyme systems in some fractionsobtained by Sepharose chromatography and increased them in others.Non-ionic and anionic detergents greatly inhibited the enzymes.Addition of lecithin to detergent-treated particles partiallyrestored enzyme activity. Solubilization of the enzyme withretention of activity was not obtained. ¹Permanent address: Bar Ilan University, Ramat Gan, Israel (Received June 17, 1969; )