Journal de physiologie最新文献

In co-cultures prepared from the septum and the hippocampus, cholinergic fibers originating in the septal slices grew into the neighboring hippocampal tissue and established functional cholinergic connections with pyramidal cells. To get further insight into the mechanisms governing cholinergic fiber growth, we have added TTX to the growth medium (2 x 10(-7) M) to block propagated electrical activity. Under these conditions, considerably fewer cholinergic cells appeared to survive. A few cholinergic fibers still invaded hippocampal target tissue, but their number was markedly reduced compared with control cultures. Simultaneous application of NGF together with TTX, however, not only increased enzyme levels and enhanced survival of cholinergic neurons, but also led to hippocampal ingrowth in virtually all septo-hippocampal co-cultures. These data, therefore, suggest, that in the absence of spiking activity, cholinergic fibers are capable of growing into a co-cultured target tissue. To test the specificity of growth of septal cholinergic fibers, we have co-cultured septal slices with slices of various brain areas which in situ lack a major cholinergic innervation, in particular the cerebellum. In the vast majority of such co-cultures, cholinergic fibers remained restricted within the septal slices, without innervating cerebellar tissue. This failure might in part be related to the lack of trophic factors released by the target tissue. We have, therefore, grown septo-cerebellar cultures in the presence and absence of NGF. Following application of 100 ng/ml NGF during the entire growth of the cultures, numerous AChE-positive fibers originating in the septal slices invaded the co-cultured cerebellar slices.(ABSTRACT TRUNCATED AT 250 WORDS)

1. Synaptic formations between a rat cerebellar granule cell and a Purkinje cell, and also between an inferior-olivary neuron and a Purkinje cell have been accomplished in culture. 2. The synaptic transmission between an inferior-olivary neuron and a Purkinje cell was far much more potent than that between a granule cell and a Purkinje cell in the culture, and the former always induced in a Purkinje cell an action potential followed by prolonged depolarization, which resembled a climbing fiber response in vivo. 3. Synaptic potentiation was induced by repetitive stimulation (2 Hz, 20 sec) of a granule cell, and the synaptic depression was induced by repetitive conjunctive stimulation of both a granule cell and an inferior-olivary neuron as in a slice preparation. 4. When repetitive stimulation of both neurons were given while the postsynaptic Purkinje cell was voltage-clamped at -80 mV, not the depression but the potentiation took place. When repetitive stimulation of a granule cell was coupled with the postsynaptic strong depolarization induced by direct outward current injection, the depression took place. These two experiments indicate that the postsynaptic depolarization during activation of a presynaptic granule cell is both necessary and sufficient to induce the depression, and that the potentiation is induced without the postsynaptic depolarization. 5. The quantal analysis on the synaptic transmission, where fluctuations of amplitudes of synaptic currents in a Purkinje cell induced by a single granule cell were measured, indicated that the synaptic potentiation involves the enhancement of transmitter release from a presynaptic granule cell and that the depression involves changes of postsynaptic receptors on a Purkinje cell.

We have shown previously that dystrophin is a component of postsynaptic membranes in Torpedo electric organ and is localized at mammalian neuromuscular synapses. In skeletal muscle, dystrophin is also detectable at the non-synaptic membrane of the myofiber, whereas in the electric organ, dystrophin is strictly localized to the postsynaptic membrane, and is not detectable in non-synaptic membranes. Multiple isoforms of dystrophin are present in skeletal muscle, and different isoforms could potentially be targetted to synaptic and non-synaptic membranes. We sought to determine whether the electric organ contains a single, or multiple isoforms of dystrophin, and we show here that the electric organ contains both a and b isoforms of dystrophin. Because dystrophin is found only at the postsynaptic membrane of the electric organ, we conclude that the two isoforms coexist in the postsynaptic membrane.

Experiments were performed using chronically implanted electrodes on the dog smooth muscle wall of the stomach and of the small and large intestines. Electrical activity of the muscle wall was recorded before and after feeding. When reaching the terminal ileum the active part of the migrating myoelectrical complex (MMC) continuously induced bursts of spike potentials superimposed on the slow waves. This electrical activity spread to the ascending colon. We also showed the existence of a spike activity on the terminal ileum independent of the MMC (appearing during the phase 1) and propagating to the colon. A relationship between the spike activities of the small and large intestines was also present after feeding. Beside the well-known gastro-colic reflex, we observed an increase in the spike activity of the terminal ileum and ascending colon between the 4th-5th hours after feeding. This probably corresponds to the arrival of the first portions of contents, evacuated from the arrival of the first portions of contents, evacuated from the stomach, and of the last portions of small intestinal contents. In conclusion, there is a relationship between the spike activities of the small and large intestines in starving animals and after feeding, and the terminal ileum plays a substantial role in this relationship.

The responses to light of retinal ganglion cells with regenerated axons can be recorded from axons teased from peripheral nerve grafts replacing the optic nerve of the adult rat or hamster. These responses resemble those of normal retinal ganglion cells but can no longer be observed several months after grafting, concomitant with ongoing loss of the population of axotomized retinal ganglion cells. Synapses formed with neurons in the superior colliculus by retinal ganglion cell axons regenerated through peripheral nerve grafts mediate both excitatory and inhibitory responses. These experiments demonstrate that when provided with an appropriate milieu for elongation, neurons indigenous to the adult mammalian central nervous system can make functional reconnections with distant targets within the nervous system.

Preganglionic nerve stimulation has been shown to induce delayed or long term changes in the neuron. Different models were used to study the trans-synaptic regulation of the tyrosine hydroxylase (TH): the rat adrenal medulla (AM) and the superior cervical ganglia (SCG). Northern blot analysis, western blot and enzymatic assays demonstrated that the TH mRNA paralleled both an increase in the protein amount and its enzymatic activity. Results of in vitro transcription on nuclei isolated from AM or from SCG after treatment with reserpine suggest that this increase in TH expression is due to an effect on the transcriptional activity of the TH gene. Other gene, cfos, is also induced by reserpine indicating that the TH transcription in these neurons may be mediated by "third messengers". Several putative regulatory elements, in particular an octamer sequence AP1 has been localized in the promoter of TH gene. Gel shift assays with nuclear extracts from untreated and phorbol ester treated cells strongly suggest that a protein complex binds to this AP1 like sequence. Comparative analysis of gel shift assays with AM nuclear extracts exhibit a similar pattern suggesting that this AP1 site could be involved in the trans-synaptic regulation of TH.

The effects of presynaptic impulse activity on the transmitter secretion at developing neuromuscular junctions were examined in Xenopus nerve-muscle cultures. Repetitive suprathreshold stimulation of the presynaptic neuron results in marked potentiation of spontaneous synaptic activity, as shown by whole-cell voltage-clamp recording of synaptic currents in the postsynaptic muscle cell. Our results are consistent with the notion that synaptic efficacy of the developing synapse is potentiated by the presence of electrical activity. Such activity-dependent synaptic modulation enables the early neuronal activity to play a regulatory role during the maturation of synaptic connections.

We are interested in the molecular mechanisms of the regulation of neurotransmitter related gene expression by neurotrophic factors and neuronal activity. Previous work has shown that conditioned medium of muscle cells induces choline acetyltransferase (CAT) activity and represses tyrosine hydroxylase, dopamine-beta-hydroxylase and aromatic L-amino acid decarboxylase (AADC) activities in cultured sympathetic neurons. Here, we show that a new muscle-derived cell line secretes two factors which induce CAT activity in spinal cord cultures; one of those is related to LIF, a CAT inducing factor for sympathetic neurons. Preliminary data are presented on the structure of the human AADC and CAT genes. Putative promoter regions have been coupled to reporter genes; transient transfection experiments will allow us to determine the promoter elements responsible for the regulation by neurotrophic factors. We also summarize the distribution of AADC-immunoreactive cells in rat and cat brain, which will be used as a reference for the study of the specificity of expression of AADC promoter in transgenic mice.

1. The purpose of this investigation was to determine if alterations in extracellular calcium (Ca2+) influx by the dihydropyridine derivatives Bay K 8644 and nifedipine affected skeletal muscle fatigue. 2. Tetanic contractions (80 Hz, 100 msec) of frog sartorius muscles were evoked every sec for 3 min. Muscles were fatigued in normal Ringer's solution (NR), in NR containing 1 microM nifedipine of 10 microM Bay K 8644 or in low Ca2+ Ringer's. 3. In each case, the experimental conditions increased the rate and magnitude of fatigue. Rate constants of fatigue obtained during Bay K 8644, nifedipine and low Ca2+ conditions (-.0122 +/- .0016, -.0397 +/- 0022 and 0.0169 +/- .0064 sec-1, respectively) were significantly greater than NR (-.0104 +/- .0006 sec-1, p less than .05). In addition, tetanic forces developed at the end of the stimulation period under the experimental conditions (3.90 +/- 0.81, 1.21 +/- 1.40 and 2.04 +/- 1.10% of initial) were significantly less than NR (7.18 +/- 1.27%, p less than .05). 4. Caffeine contracture forces (10 mM) evoked immediately after stimulation were not significantly different between conditions. 5. These results suggest that alterations in sarcolemmal Ca2+ exchange has some influence on the fatigue process.

The segmental pattern of peripheral ganglia in higher vertebrates is generated by interactions between neural crest and somite cells. Each mesodermal somite is subdivided into at least two distinct domains represented by its rostral and caudal halves. Most migratory pathways taken by neural crest cells in trunk regions of the axis, as well as the outgrowth of motoneuron fibers are restricted to the rostral domain of each somite. Experimental modification of the somites, achieved by constructing a mesoderm composed of multiple rostral half-somites, results in the formation of continuous and unsegmented nerves, dorsal root ganglia (DRG) and sympathetic ganglia (SG). In contrast, both neurites and crest cells are absent from a mesoderm composed of multiple-caudal half somites. However, the mechanisms responsible for gangliogenesis within the rostral half of the somite, appear to be different for DRG and SG. Vertebral development from the somites is also segmental. In implants of either multiple rostral or caudal somite-halves, the grafted mesoderm dissociates normally into sclerotome and dermomyotome. However, the morphogenetic capabilities of each somitic half differ. The lateral vertebral arch is continuous in the presence of caudal half-somite grafts and is virtually absent in rostral half-somite implants. Therefore, the rostrocaudal subdivision of the sclerotome determines the segmental pattern of neural development and is also important for the proper metameric development of the vertebrae.