No abstract

Much interest has recently centred on the properties of peptides that modulate the excitability of nerve cells. Such compounds include the undecapeptide substance P, which is particularly well established as an excitatory neurotransmitter, and we examine here its effects on magnocellular cholinergic neurones taken from the medial and ventral aspects of the globus pallidus of newborn rats and grown in dissociated culture. These neurones have previously been shown to respond to substance P3 and are analogous to the nucleus basalis of Meynert in man, which gives a diffuse projection to the cerebral cortex and whose degeneration is the likely cause of Alzheimer's disease. Substance P depolarizes these cultured neurones by reducing an inwardly rectifying potassium conductances; this conductance has been found in several neuronal types and has similar properties to those of certain other cells. As discussed below, modulation of inward (or anomalous) rectification by substance P implies a self-reinforcing element to the depolarization caused by the peptide.

We demonstrate that fiber-based frequency combs with multi-branch configurations can transfer both linewidth and frequency stability to another wavelength at the millihertz level. An intra-cavity electro-optic modulator is employed to obtain a broad servo bandwidth for repetition rate control. We investigate the relative linewidths between two combs using a stable continuous-wave laser as a common reference to stabilize the repetition rate frequencies in both combs. The achieved energy concentration to the carrier of the out-of-loop beat between the two combs was 99% and 30% at a bandwidth of 1 kHz and 7.6 mHz, respectively. The frequency instability of the comb was 3.7x10(-16) for a 1 s averaging time, improving to 5-8x10(-19) for 10000 s. We show that the frequency noise in the out-of-loop beat originates mainly from phase noise in branched optical fibers.

No abstract

We demonstrate a one-dimensional optical lattice clock with ultracold 171 Yb atoms, which is free from the linear Zeeman effect. The absolute frequency of the 1 S 0 ðF ¼ 1=2Þ-3 P 0 ðF ¼ 1=2Þ clock transition in 171 Yb is determined to be 518 295 836 590 864(28) Hz with respect to the SI second.

This study has investigated the fine structure of the Mauthner cell of the goldfish. The animals were divided into three groups of three fish and each group was perfused with one of the following fixatives: osmium tetroxide, glutaraldehyde, or formaldehyde. Large myelinated club endings and smallvesicle boutons (SVBs) are found on the distal part of the lateral dendrite. The club endings have the structure of the mixed synapse and contain large, round synaptic vesicles. The SVBs, appearing as small boutons, show the structural features of the chemical synapse, and contain small synaptic vesicles, which are round when fixed with osmium tetroxide, but become elongated when fixed with aldehyde fixatives. Small myelinated club endings, SVBs, and large-vesicle boutoiis (LVBs) are observed on the proximal part of the lateral dendrite, on the ventral dendrite, and on the cell body (excluding the axon hillock region). The LVBs, mostly appearing as large boutons, show the structure of either the mixed or the chemical synapse. They contain large, round vesicles. On the axon hillock and initial axon segment, there exist unmyelinated club endings containing medium-size elongated vesicles and spiral fiber endings containing round medium-size vesicles. An attempt was made to correlate these different types of endings with physiological functions.

In nucleus basalis neurons, substance P (SP) causes a slow excitation, mediated through a pertussis toxin-insensitive G protein, by suppressing an inward rectifier K+ channel. Here we report that SP applied outside the patch pipette inhibited the single-channel activity, recorded on-cell, of the inward rectifier. The PKC inhibitors staurosporine and PKC(19-36) suppressed this effect in whole-cell mode and in on-cell single-channel mode. A diacylglycerol analog mimicked the SP effect, and PKC(19-36) suppressed this analog effect. SP irreversibly suppressed the inward rectifier in neurons treated with okadaic acid. These results indicate that a diffusible messenger mediates the SP effect, that its signal transduction involves phosphorylation by PKC, and that dephosphorylation by a serine/threonine protein phosphatase mediates its recovery.

The large myelinated club endings (LMCEs) of primary eighth nerve afferents form mixed synapses on the lateral dendrite of the giant Mauthner cell. The double replica freeze-fracture technique was employed to examine the intramembrane fine structure of these LMCE synapses. Morphological correlates of both chemical and electrical transmission were found at the LMCE synapses. Electrical synaptic junctions, or gap junctions, were located over much (10-20%) of the synaptic contact. These were seen in both pre-and postsynaptic membrane as tightly packed P face particle aggregates and corresponding aggregates of E face pits. Specializations characteristic of chemical synaptic junctions were most prominent at the periphery of the synaptic contact. These specializations consisted of postsynaptic E face particle aggregates which were subjacent to presynaptic active zones. The active zones were distinguishable as regions with an increased density of large particles and vesicle attachment sites represented by P face depressions and E face protuberances. Quantitative analysis of gap junction particle (connexon) number at five LMCEs revealed 24,000-106,000 connexons per LMCE. Comparison with data from electrophysiological studies of single LMCEs indicates that only a small fraction of the connexon channels are open at any given time during electrotonic transmission at an LMCE synapse.