Innervation of the limb accessory flexor muscle in several decapod crustaceans. I. Anatomy

The innervation of the accessory flexor muscle of the limbs of several decapod crustaceans was studied by means of vital staining, with methylene blue and electron microscopy. Three patterns of innervation were found. In the first pattern, the distal (DAFM) and proximal (PAFM) heads of the accessory flexor muscle were supplied by two axons (a thick and a thin) which travel in a private nerve along the length of the merus. This pattern was found in the crab (Cancer) and the lobster (Homarus), and conforms to the classical pattern established in the literature. In the second pattern, the nerve to the DAFM is made up of conjoined branches of the flexor and accessory flexor nerves. Consequently, the DAFM receives at least five axons in the portunid crabs, Carcinus, Callinectes, and Ovalipes, and occasionally six axons in Ovalipes. The PAFM in those portunids receives the usual two axons. In the third pattern, based on preliminary observations on the grapsid crab, Pachygrapsus, “super-innervation” of the accessory flexor muscle appears to include not only five axons to the DAFM but also at least three to the PAFM. In all species, methylene blue staining of the axon terminations revealed a regular pattern of blebs which are thought to correspond to synaptic terminals as revealed by electron microscopy.     

Proliferation and relocation of developing lobster neuromuscular synapses

The development of multiterminal innervation from a single identifiable excitatory motoneuron to the lobster distal accessory flexor muscle (DAFM) was studied by serial section electron microscopy. The number, size, and location of neuromuscular synapses and presynaptic dense bars within the peripheral branching pattern of the axon was determined in cross sections of the DAFM in 1st (24-hr-old)-, 4th (2-week-old)-, and 12th (1-year-old)-stage lobsters. The mean size of synapses remains fairly constant in these three stages but synaptic density, i.e., the number of synapses per unit length of fiber, increased more than 20-fold between the 1st and 4th stages and more than 5-fold between the 4th and 12th stages. Synaptic surface area per fiber length showed a parallel increase. Consequently there is a proliferation of synapses along the length of individual muscle fibers during primary development. Furthermore from the 1st stage where only a few fibers are innervated, synapses proliferate to many more fibers in the 4th and to all fibers in the 12th stage. The neuromuscular synapses are distributed in different proportions within the axonal branching pattern in the three stages. Based on the number and size of synapses and presynaptic dense bars, the main axon and primary branches provide almost equal amounts of innervation in the 1st stage. With further branching in the 4th stage, the main axon accounts for only 20–25% of the innervation; the primary branches for 45% and other finer branches the remainder. By the 12th-stage synapses are found only on branches other than the main axon and its primary offshoots. There is therefore a shift in innervation from the main axon to the primary branches and then to the finer branches during primary development. This shift in innervation involves the formation of new synaptic terminals and the restructuring of existing ones into axonal areas. In this way the multiterminal innervation arising from an identifiable motoneuron is remodeled.     

Isolation and characterization of an autonomously replicating sequence (ARSD) from the marine yeast Debaryomyces hansenii.

The marine yeast Debaryomyces hansenii is known to tolerate salinities ranging from 0 to 24%. As a first step toward the molecular analysis of halotolerance in this organism, we report the isolation of an autonomously replicating sequence (ARS) and its use in the construction of a shuttle vector. The ARS from D. hansenii (ARSD) is 0.4 kbp long, and the function rests in 0.13 kbp of the sequence. Sequence analysis of ARSD shows strong homology to ARS from other organisms, including a 12-bp consensus sequence common to all ARS functional in Saccharomyces cerevisiae.     

Development of fluorescence imaging probes for nicotinic acetylcholine α4β21 receptors

Nicotinic acetylcholine α4β2¹ receptors (nAChRs) are implicated in various neurodegenerative diseases and smoking addiction. Imaging of brain high-affinity α4β2¹ nAChRs at the cellular and subcellular levels would greatly enhance our understanding of their functional role. Since better resolution could be achieved with fluorescent probes, using our previously developed positron emission tomography (PET) imaging agent [¹⁸F]nifrolidine, we report here design, synthesis and evaluation of two fluorescent probes, nifrodansyl and nifrofam for imaging α4β2¹ nAChRs. The nifrodansyl and nifrofam exhibited nanomolar affinities for the α4β2¹ nAChRs in [³H]cytisine-radiolabeled rat brain slices. Nifrofam labeling was observed in α4β2¹ nAChR-expressing HEK cells and was upregulated by nicotine exposure. Nifrofam co-labeled cell-surface α4β2¹ nAChRs, labeled with antibodies specific for a β2 subunit extracellular epitope indicating that nifrofam labels α4β2¹ nAChR high-affinity binding sites. Mouse brain slices exhibited discrete binding of nifrofam in the auditory cortex showing promise for examining cellular distribution of α4β2¹ nAChRs in brain regions.     

Phylogeny of the M superhaplogroup inferred from complete mitochondrial genome sequence of Indian specific lineages

Background  

Phylogenetic analysis of human complete mitochondrial DNA sequences has largely contributed to resolving phylogenies and antiquity of different lineages belonging to the majorhaplogroups L, N and M (East-Asian lineages). In the absence of whole mtDNA sequence information of M lineages reported in India that exhibits highest diversity within the sub-continent, the present study was undertaken to provide a detailed analysis of this haplogroup to precisely characterize the lineages and unravel their intricate phylogeny.