Functional acetylcholine receptor (AChR) and sodium channels were expressed in the membrane of Xenopus laevis oocytes following injection with poly(A)+-mRNA extracted from denervated rat leg muscle. Whole-cell currents, activated by acetylcholine or by depolarizing voltage steps had properties comparable to those observed in rat muscle. Oocytes injected with specific mRNA, transcribed from cDNA templates and coding for the AChR of Torpedo electric organ, expressed functional AChR channels at a much higher density. Single-channel currents were recorded from the oocyte plasma membrane following removal of the follicle cell layer and the vitelline membrane from the oocyte. The follicle cell layer was removed enzymatically with collagenase. The vitelline membrane was removed either mechanically after briefly exposing the oocyte to a hypertonic solution, or by enzyme treatment with pronase. Stretch activated (s.a.) currents were observed in most recordings from cell-attached patches obtained with standard patch pipettes. S.a.-currents were evoked by negative or positive pressure (greater than or equal to 5 mbar) applied to the inside of the pipette, and were observed in both normal and mRNA injected oocytes indicating that they are endogenous to the oocyte membrane. The s.a.-channels are cation selective and their conductance is 28 pS in normal frog Ringer's solution (20 +/- 1 degree C). Their gating is voltage dependent, and their open probability increases toward more positive membrane potentials. The density of s.a.-channels is estimated to be 0.5-2 channels per micron 2 of oocyte plasma membrane. In cell-attached patches s.a.-currents are observed much less frequently when current measurement is restricted to smaller patches of 3-5 micron 2 area using thick-walled pipettes with narrow tips. In outside-out patches s.a.-currents occur much less frequently than in cell-attached or inside-out patches. AChR-channel and sodium channel currents were observed only in a minority of patches from oocytes injected with poly(A)+-mRNA from rat muscle. AChR-channel currents were seen in all patches of oocytes injected with specific mRNA coding for Torpedo AChR. In normal frog Ringer's solution (20 +/- 2 degrees C) the conductance of implanted rat muscle AChR-channels was 38 pS and that of sodium channels 20 pS. The conductance of implanted Torpedo AChR channels was 40 pS. The conductance of implanted channels was similar in cell-attached and in cell-free patches.(ABSTRACT TRUNCATED AT 400 WORDS)

The distribution and function of sympathetic innervation in skeletal muscle have largely remained elusive. Here we demonstrate that sympathetic neurons make close contact with neuromuscular junctions and form a network in skeletal muscle that may functionally couple different targets including blood vessels, motor neurons, and muscle fibers. Direct stimulation of sympathetic neurons led to activation of muscle postsynaptic β2-adrenoreceptor (ADRB2), cAMP production, and import of the transcriptional coactivator peroxisome proliferator-activated receptor γ-coactivator 1α (PPARGC1A) into myonuclei. Electrophysiological and morphological deficits of neuromuscular junctions upon sympathectomy and in myasthenic mice were rescued by sympathicomimetic treatment. In conclusion, this study identifies the neuromuscular junction as a target of the sympathetic nervous system and shows that sympathetic input is crucial for synapse maintenance and function

Several studies investigated the effect of physical exercise on emotional behaviors in rodents; resulting findings however remain controversial. Despite the accepted notion that voluntary exercise alters behavior in the same manners as antidepressant drugs, several studies reported opposite or no effects at all. In an attempt to evaluate the effect of physical exercise on emotional behaviors and brain plasticity, we individually housed C57BL/6J male mice in cages equipped with a running wheel. Three weeks after continuous voluntary running we assessed their anxiety- and depression-like behaviors. Tests included openfield, dark-light-box, elevated O-maze, learned helplessness, and forced swim test. We measured corticosterone metabolite levels in feces collected over a 24-h period and brain-derived neurotrophic factor (BDNF) in several brain regions. Furthermore, cell proliferation and adult hippocampal neurogenesis were assessed using Ki67 and Doublecortin. Voluntary wheel running induced increased anxiety in the openfield, elevated O-maze, and dark-light-box and higher levels of excreted corticosterone metabolites. We did not observe any antidepressant effect of running despite a significant increase of hippocampal neurogenesis and BDNF. These data are thus far the first to indicate that the effect of physical exercise in mice may be ambiguous. On one hand, the running-induced increase of neurogenesis and BDNF seems to be irrelevant in tests for depression-like behavior, at least in the present model where running activity exceeded previous reports. On the other hand, exercising mice display a more anxious phenotype and are exposed to higher levels of stress hormones such as corticosterone. Intriguingly, numbers of differentiating neurons correlate significantly with anxiety parameters in the openfield and dark-light-box. We therefore conclude that adult hippocampal neurogenesis is a crucial player in the genesis of anxiety.

. To elucidate the nature of signals that control the level and spatial distribution of mRNAs encoding acetylcholine receptor (AChR), a-, ß-, y-, S-and e-subunits in muscle fibers chronic paralysis was induced in rat leg muscles either by surgical denervation or by different neurotoxins that cause disuse of the muscle or selectively block neuromuscular transmission pre-or postsynaptically and cause an increase of AChRs in muscle membrane. After paralysis, the levels and the spatial distributions of the different subunitspecific mRNAs change discoordinately and seem to follow one of three different patterns depending on the subunit mRNA examined . The level of e-subunit mRNA and its accumulation at the end-plate are largely independent on the presence of the nerve or electrical muscle activity. In contrast, the y-subunit mRNA level is tightly coupled to innervation . It is undetectable or low in innervated normally active muscle and in innervated but disused muscle, whereas it is abundant along T HE nicotinic acetylcholine receptor (AChR)' of mammalian skeletal muscle is a heterooligomeric membrane protein composed of a-, ß-, S-, and either -or y e-subunits Witzemann et al ., 1990) . Functionally, the two AChR subtypes (termed AChRy and AChRe, respectively) differ in their gating and ion conductance properties and their density in the sarcolemmal membrane changes during development . Before innervation, the fetal AChR subtype containing the y-subunit is distributed over the entire surface of the muscle fiber and accumulates at the end-plate as the nerve contacts the muscle fiber. The adult AChR subtype containing the e-subunit appears only postnatally and is predominantly localized at the end-plate. Concomitantly with the switch of the AChR subtypes in the end-plate, the fetal AChRs disappear from the extrajunctional membrane. When the muscle is surgically denervated the fetal AChRs are expressed again along the whole fiber length and disappear upon reinnervation . Thus the abun-1. Abbreviations used in this paper: AChR, acetylcholine receptor ; ci-BuTX, a-bungarotoxin ; BuTX, botulinum toxin; m.e.p.c ., miniature end-plate current; m.e .p.p., miniature end-plate potential; TTX, tetrodotoxin .® The Rockefeller University Press, 0021-9525/91/07/125/17 $2 .00 The Journal of Cell Biology, Volume 114, Number 1, July 1991125-141 the whole fiber length in denervated muscle or in muscle in which the neuromuscular contact is intact but the release of transmitter is blocked . The a-, ß-, and S-subunit mRNA levels show a different pattern . Highest amounts are always found at end-plate nuclei irrespective of whether the muscle is innervated, denervated, active, or inactive, whereas in extrasynaptic regions they are tightly controlled by innervation partially through electrical muscle activity. The changes in the levels and distribution of y-and e-subunit-specific mRNAs in toxin-paralyzed muscle correlate well with the spatial appearance of functional fetal and adult AChR channel subtypes along the muscle fiber. Th...