Terminal electron receptors

Balzani, Vogde et al. demonstrated for dendritic cyclam compounds that signalling units are dendritically amplified by increasing the number of peripheral fluorophores. Opportunities for these PET sensor systems exist in the combination of selective coordination sites with the dendritic architecture. The mechanism resembles that described above, but can be influenced by the introduction of dendritic units of different generations into the sensor system. The distance between the terminal naphthalene groups of the dendron and the receptor (ion as guest in the cyclam core) is of crucial importance for electron transfer (ET) (Fig. 8.15) [53],... 

Fig. 20.8. Neuromuscular junctions analyzed by transmission electron microscopy. (A) In wild-type mice, the motor nerve terminal (MN) is depressed into the muscle fiber surface. The terminal is polarized, with small clear vesicles near the presynaptic membrane and mitochondria in the more proximal portion of the terminal. The postsynaptic membrane has deep convolutions (junctional folds, JF) and the membrane near the tops of these folds is very electron dense because of the high density of acetylcholine receptors (arrowheads). (B) In some myasthenias where the nerve sprouts but remains in contact with the muscle, terminals with mitochondria and vesicles are observed in the absence of any postsynaptic specialization. Presumably these are sprouting terminals that have not established a functional connection. (C) Partial innervation of postsynaptic sites is evident as elaborate junctional folds in the muscle membrane with no overlying nerve terminal. In these examples, the interpretations were aided by light microscopy examination of other samples as described in Fig. 20.8 in parallel with electron microscopy. The mutation shown in (B, C) is an unpublished ENU-induced allele of agrin.

In the single electron microscopic immunocytochemical study thus far carried out with these antibodies (242), 5-HT7 receptors were described as located in neuronal somata and dendrites, fine unmyelinated axons, and axon terminals of the mouse suprachiasmatic nucleus (SCN). After double immunoperoxidase (5-HT7) and immunogold labeling, some of these SCN soma-dendrites and axon terminals could be shown to be GABA, vasoactive intestical polypeptide (VIP), or vasopressin (VP) immunoreactive. Astrocytes in the SCN, characterized by their numerous filaments, were also reported as immunopositive for 5-HT7 receptors. 

Nicotinic acetylcholine receptor Receptor, isolated from electro-phorus electricus, was incorporated into a polymeric film formed in situ on an electronic transductor containing two terminal 1.5 cm x 1.5 cm interdigitated gold electrode. The response of the biosensor reached equilibrium within 5 s for ACh and remained stable up to 20 min. Detection limits 25 ng in a 50 pL sample (i.e., 0.5 pg/mL). [93]... 

Figure 7.2. Stractures of synapses, a Some anatomical variations. Left An intemeural synapse connects two nerve cells. Middle A neuromuscular synapse (also called motor endplate) connects the terminal button of a motoneuron to a skeletal muscle cell. Right An automic nerve cell may form several secretory varicosities that release the transmitter in the target tissue, without forming a circtrmscribed contact zone with an individtral target cell, b Electron microcoscopy of a nemomnsctrlar synapse. The synaptic cleft is very narrow, so that diffusion of secreted transmitter to the receptors on the postsynaptic membrane is fast. Ntrmerous vesicles line up close to the presynaptic membrane. Note the striated myofilament in the postsynaptic cell, c Light microscopy. A single nemon branches out and sends terminal buttorrs to multiple muscle fibers.

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