Before phototransduction, spontaneous activity in the developing mammalian retina is required for the appropriate patterning of retinothalamic connections, and there is growing evidence that this activity influences the development of circuits within the retina itself. We demonstrate here that the neural substrate that generates waves in the mouse retina develops through three distinct stages. First, between embryonic day 16 and birth [postnatal day 0 (P0)], we observed both large, propagating waves inhibited by nicotinic acetylcholine receptor (nAChR) antagonists and small clusters of cells displaying nonpropagating, correlated calcium increases that were independent of nAChR activation. Second, between P0 and P11, we observed only larger propagating waves that were abolished by toxins specific to ␣3 and ␤2 subunit-containing nAChRs. Third, between P11 and P14 (eye opening) we observed propagating activity that was abolished by ionotropic glutamate receptor antagonists. The time course of this developmental shift was dramatically altered in retinas from mice lacking the ␤2 nAChR subunit or the ␤2 and ␤4 subunits.These retinas exhibited a novel circuit at P0, no spontaneous correlated activity between P1 and P8, and the premature induction at P8 of an ionotropic glutamate receptor-based circuit. Retinas from postnatal mice lacking the ␣3 nAChR subunit exhibited spontaneous, correlated activity patterns that were similar to those observed in embryonic wild-type mice. In ␣3Ϫ/Ϫ and ␤2Ϫ/Ϫ mice, the development and distribution of cholinergic neurons and processes and the density of retinal ganglion cells (RGCs) and the gross segregation of their dendrites into ON and OFF sublaminae were normal. However, the refinement of individual RGC dendrites is delayed. These results indicate that retinal waves mediated by nAChRs are involved in, but not required for, the development of neural circuits that define the ON and OFF sublamina of the inner plexiform layer.

Transcripts for the beta2 and the beta4 nicotinic acetylcholine receptor (nAChR) subunits are found throughout the CNS and the peripheral nervous system. These two beta subunits can form heteromultimeric channels with any of the alpha2, alpha3, alpha4, or alpha5 subunits in heterologous expression systems. Nonetheless, the subunit composition of native nAChRs and the role of different nAChR subtypes in vivo remain unclear. We prepared null mutations for the beta2 and the beta4 genes and bred beta2-/-beta4-/- mice by mating mice of identical beta2-/-beta4+/- or beta2+/-beta4-/- genotype. The beta2-/- and the beta4-/- single-mutant mice grow to adulthood with no visible phenotypic abnormalities. The beta2-/-beta4-/- double mutants survive to birth but have impaired growth and increased perinatal mortality. They also present enlarged bladders with dribbling urination and develop urinary infection and bladder stones. The ocular pupils are widely dilated and do not constrict in response to light. Histological studies revealed no significant abnormalities of brain or peripheral tissues except for hyperplasia in the bladder mucosa of beta4-/- and beta2-/-beta4-/- mutants. Bladder strips from beta2-/-beta4-/- mice did not respond to nicotine but contracted when stimulated with a muscarinic agonist or electric field stimulation. Bladder strips from beta4 mutants did not respond to nicotine despite the absence of major bladder dysfunction in vivo. Acetylcholine-activated whole-cell currents were absent in superior cervical ganglion neurons from beta2-/-beta4-/- mice and reduced in neurons from beta4-/- mice. Although there is apparent redundancy and a superficially normal phenotype in beta2-/- and beta4-/- mice, physiological studies indicate major deficits in the beta4-/- mice. Our previous description of a similar phenotype in alpha3-/- mice and the current data suggest that the alpha3 and the beta4 subunits are major components in autonomic nAChRs. The phenotype of the beta2-/-beta4-/- and alpha3-/- mice resembles the autosomal recessive megacystis-microcolon-hypoperistalsis syndrome in humans.

The ␣3 subunit of the neuronal nicotinic acetylcholine receptor is widely expressed in autonomic ganglia and in some parts of the brain. The ␣3 subunit can form heteromultimeric ion channels with other ␣ subunits and with ␤2 and ␤4 subunits, but its function in vivo is poorly understood. We prepared a null mutation for the ␣3 gene by deletion of exon 5 and found that homozygous (؊͞؊) mice lacked detectable mRNA on Northern blotting. The ؊͞؊ mice survive to birth but have impaired growth and increased mortality before and after weaning. The ؊͞؊ mice have extreme bladder enlargement, dribbling urination, bladder infection, urinary stones, and widely dilated ocular pupils that do not contract in response to light. Detailed histological studies of ؊͞؊ mice revealed no significant abnormalities in brain or peripheral tissues except urinary bladder, where inf lammation was prominent. Ganglion cells and axons were present in bladder and bowel. Bladder strips from ؊͞؊ mice failed to contract in response to 0.1 mM nicotine, but did contract in response to electrical field stimulation or carbamoylcholine. The number of acetylcholine-activated single-channel currents was severely reduced in the neurons of superior cervical ganglia in ؊͞؊ mice with five physiologically distinguishable nicotinic acetylcholine receptor subtypes with different conductance and kinetic properties in wild-type mice, all of which were reduced in ؊͞؊ mice. The findings in the ␣3-null mice suggest that this subunit is an essential component of the nicotinic receptors mediating normal function of the autonomic nervous system. The phenotype in ؊͞؊ mice may be similar to the rare human genetic disorder of megacystismicrocolon-intestinal hypoperistalsis syndrome.The neuronal nicotinic acetylcholine (ACh) receptor (nAChR) gene family consists of eight ␣ subunits (␣2-␣9) and three ␤ subunits (␤2-␤4), each containing four membranespanning domains (1-4). Expression studies in Xenopus oocytes have shown that any one of the ␣2, ␣3, or ␣4 subunits in combination with either ␤2 or ␤4 can produce functional receptors (2, 4-6). Diverse combinations of subunits occur, and even a single population of neurons can express multiple classes of nAChRs (7-9). The ␣3 subunit is widely expressed in autonomic ganglia and in some parts of the brain in multiple organisms (1, 2, 10-13). Although the role of ␣3-containing nAChRs in synaptic transmission in the central nervous system is not known, presynaptic receptors have been implicated in the modulation of the release of dopamine, norepinephrine, and glutamate (13-16).In the peripheral autonomic nervous system, efferent signals are relayed by both sympathetic and parasympathetic ganglia. The ␣3 subunit is the predominant ␣ gene expressed in these ganglia in the chicken (17). Functional deletion of the ␣3 subunit by antisense oligomers eliminated specific subtypes of channels expressed by chicken sympathetic neurons (8). In rat trigeminal sensory neurons, ␣3␤4 is the principal subtype (18). The ␣3 subunit is expressed...

The alpha3 subunit gene was one of the first neuronal nicotinic acetylcholine receptor (nAChR) subunits to be cloned (Boulter et al., 1986), but direct evidence of alpha3 subunit contributions to mammalian central nAChR populations has not been presented. The studies reported here used mice engineered to contain a null mutation in the alpha3 nAChR subunit gene (Xu et al., 1999) to examine the involvement of the alpha3 subunit in central nAChR populations. Heterologously expressed alpha3beta2 and alpha3beta4 nAChRs are pharmacologically similar to native [125I]alpha-conotoxin MII (alpha-CtxMII)-binding and 3-(2(S)-azetidinylmethoxy)pyridine dihydrochloride (A85380)-resistant [125I]epibatidine-binding nAChR subtypes, respectively. The hypothesis that both native sites are alpha3-subtype nAChRs was tested using quantitative autoradiography in alpha3-null mutant mice. Somewhat surprisingly, deletion of the alpha3 nAChR subunit gene did not affect expression of the great majority of [125I]alpha-CtxMII-binding sites, indicating that they do not correspond to heterologously expressed alpha3beta2 nAChRs. The only exception to this was observed in the habenulointerpeduncular tract, where alpha3-dependent [125I]alpha-CtxMII binding was observed. This finding may suggest the presence of an additional, minor nicotinic population in this pathway. In contrast, most -resistant [125I]epibatidine-binding nAChRs were dependent on alpha3 gene expression, suggesting that they do indeed correspond to an alpha3 nAChR subtype. However, widespread but lower levels of alpha3-independent -resistant [125I]epibatidine binding were also seen. Again, this may indicate the existence of an additional, minor population of non-alpha3 -resistant sites.

Fucoxanthin, an allenic carotenoid, can be isolated from edible brown seaweeds. Recent studies have reported that fucoxanthin has many physiological functions and biological properties, such as antiobesity, antitumor, antidiabetes, antioxidant, anti-inflammatory, and hepatoprotective activities, as well as cardiovascular and cerebrovascular protective effects. Therefore, fucoxanthin can be used as both medicinal and nutritional ingredient to prevent and treat chronic diseases. Although fucoxanthin possesses many medicinal ingredient and nutritional qualities, studies indicated that its structure was unstable. In this paper, we consulted the current documents and reviewed structural properties and factors affecting the stability of fucoxanthin. We also reported the metabolism, safety, pharmacological activities, and the methods of improving the bioavailability of fucoxanthin. Based on these studies providing essential background knowledge, fucoxanthin can be developed into marine drugs and nutritional products.