Existing models of the primate photopic electroretinogram (ERG) attribute the light-adapted b–wave to activity of depolarizing bipolar cells (DBCs), mediated through a release of potassium that is monitored by Müller cells. However, possible ERG contributions from OFF-bipolar cells (HBCs) and horizontal cells (HzCs) have not been explored. We examined the contribution of these hyperpolarizing second-order retinal cells to the photopic ERG of monkey by applying glutamate analogs to suppress photoreceptor transmission selectively to HBC/HzCs vs. DBCs.ERGs of Macaca monkeys were recorded at the cornea before and after intravitreal injection of drugs. Photopic responses were elicited by bright 200–220 ms flashes on a steady background of 3.3 log scotopic troland to suppress rod ERG components.2–amino-4–phosphonobutyric acid (APB), which blocks DBC light responses, abolished the photopic b–wave and indicated that DBC activity is requisite for photopic b–wave production.However, applying cis–2,3–piperidine dicarboxylic acid (PDA) and kynurenic acid (KYN), to suppress HBCs/HzCs and third-order neurons, revealed a novel ERG response that was entirely positive and was sustained for the duration of the flash. The normally phasic b–wave was subsumed into this new response. Applying n–methyl-dl-aspartate (NMA) did not replicate the PDA+KYN effect, indicating that third-order retinal cells are not involved. This suggests that HBC/HzC activity is critical for shaping the phasic b–wave.Components attributable to depolarizing vs. hyperpolarizing cells were separated by subtracting waveforms after each drug from responses immediately before. This analysis indicated that DBCs and HBC/HzCs each can produce large but opposing field potentials that nearly cancel and that normally leave only the residual phasic b–wave response in the photopic ERG.Latency of the DBC component was 5–9 ms slower than the HBC/HzC component. However, once activated, the DBC component had a steeper slope. This resembles properties known for the two types of cone synapses in lower species, in which the sign-preserving HBC/HzC synapse has faster kinetics but probably lower gain than the slower sign-inverting G-protein coupled DBC synapse.A human patient with “unilateral cone dystrophy” was found to have a positive and sustained ERG that mimicked the monkey ERG after PDA+KYN, indicating that these novel positive photopic responses can occur naturally even without drug application.These results demonstrate that hyperpolarizing second-order neurons are important for the primate photopic ERG. A “Push-Pull Model” is proposed in which DBC activity is requisite for b–wave production but in which HBC/HzC activity limits the amplitude and controls the shape of the primate photopic b–wave.

The construction of an artificial double helix that mimics natural DNA or RNA has been one of the most challenging endeavors in chemistry. [1][2][3][4][5][6][7][8][9] Recently, Meggers and co-workers showed that even a simple acyclic propylene glycol with two carbon atoms in the main chain (see (S)-GNA in Figure 1) as a nucleobase tether could form a more stable duplex than that of native DNA or RNA. [10][11][12][13] This pioneering work prompted us to synthesize a new foldamer with three carbon atoms in the main chain, acyclic threoninol nucleic acid (aTNA), from d-threoninol. [14] We found that aTNA has the following properties: 1) duplex formation involves complementary pairing in an antiparallel fashion, as for natural DNA or RNA; 2) owing to the flexibility of the backbone, the singlestranded state does not adopt a characteristic preorganized structure; 3) the thermal stability of the duplex is far greater than that of the natural DNA or RNA duplex and even higher than that of the GNA duplex. Studies on aTNA as well as GNA and peptide nucleic acid (PNA) [15,16] have confirmed that scaffold rigidity is not a prerequisite for stable duplex formation as previously thought. However, unlike PNA, with an acyclic scaffold, aTNA can not cross-hybridize with either natural DNA or natural RNA. Although A 15 of (S)-GNA can hybridize with U 15 , the incorporation of several GC pairs severely destabilizes the duplex with RNA.[11] Thus, there are no artificial nucleic acids comprising a fully acyclic backbone with a phosphodiester linkage that can cross-hybridize with DNA or RNA without sequence limitation. We hypothesize that the threoninol scaffold is still not flexible enough to form a duplex with natural DNA or RNA.Herein, we propose a new artificial nucleic acid, serinol nucleic acid (SNA, see Figure 1 a), with a 2-amino-1,3-propanediol (serinol) scaffold, which is even more flexible than threoninol. In comparison with aTNA (Figure 1 a), the only structural difference is the lack of a methyl group next to the amino group. However, this small change affords the SNA oligomer a unique stereochemical property: since this methyl group provides chirality, its absence makes the scaffold achiral as well as flexible. Accordingly, the chirality of the "pure" SNA oligomer synthesized from four SNA monomers (or the helicity of its duplex) depends only on its sequence (see below). This property is specific to the SNA oligomer; DNA, RNA, and previously synthesized aTNA all have chirality (or helicity) that is inherently determined by the chirality of the scaffold. [17] In the present study, we first demonstrated this unique stereochemical property and then cross-hybridized the SNA oligomer, which was found to recognize both DNA and RNA sequence specifically.The chemical structure of the SNA oligomer is shown in Figure 1 a. Serinol (2-amino-1,3-propanediol), which, like DNA, has three carbon atoms in its backbone, is an achiral diol. However, modification of the two hydroxy groups with different functional groups to form an SNA mon...

A new foldamer, acyclic threoninol nucleic acid (aTNA), has been synthesized by tethering each of the genetic nucleobases A, G, C, and T to d-threoninol molecules, which were then incorporated as building blocks into a scaffold bearing phosphodiester linkages. We found that with its fully complementary strand in an antiparallel fashion, the aTNA oligomer forms an exceptionally stable duplex that is far more stable than corresponding DNA or RNA duplexes, even though single-stranded aTNA is rather flexible and thus does not take a preorganized structure.

Photoregulation of RNA remains a challenging task as the introduction of a photoswitch entails changes in the shape and the stability of the duplex that strongly depend on the chosen linker strategy. Herein, the influence of a novel nucleosidic linker moiety on the photoregulation efficiency of azobenzene is investigated. To this purpose, two azobenzene C-nucleosides were stereoselectively synthesized, characterized, and incorporated into RNA oligonucleotides. Spectroscopic characterization revealed a reversible and fast switching process, even at 20 °C, and a high thermal stability of the respective cis isomers. The photoregulation efficiency of RNA duplexes upon trans-to-cis isomerization was investigated by using melting point studies and compared with the known D-threoninol-based azobenzene system, revealing a photoswitching amplitude of the new residues exceeding 90 % even at room temperature. Structural changes in the duplexes upon photoisomerization were investigated by using MM/MD calculations. The excellent photoswitching performance at room temperature and the high thermal stability make these new azobenzene residues promising candidates for in-vivo and nanoarchitecture photoregulation applications of RNA.

Reversible photo-cross-linking of a DNA duplex through the [2+2] photocycloaddition of styrylpyrene is reported. Styrylpyrene moieties on d-threoninol linkers were introduced into complementary positions on DNA strands. Irradiation of the styrylpyrene pair in the duplex with visible light at λ=455 nm induced a [2+2] photocycloaddition between styrylpyrenes that cross-linked the two strands of the duplex. Two diastereomers were formed after [2+2] photocycloaddition as a result of rotation of the styrylpyrene residues. Also, the cycloreversion reaction was induced by UV light at λ=340 nm, which reversibly yielded the uncross-linked strands.