Biomedical subjects

Ning Tian

Publications and source records attributed to Ning Tian.

9 recordsLinked to original sources

PubMed2006

Intrinsic ON responses of the retinal OFF pathway are suppressed by the ON pathway.

Parallel ON and OFF pathways conduct visual signals from bipolar cells in the retina to higher centers in the brain. ON responses are thought to originate by exclusive use of metabotropic glutamate receptor 6 (mGluR6) expressed in retinal ON bipolar cells. Paradoxically, we find ON responses in retinal ganglion cells of mGluR6-null mice, but they occur at long latency. The long-latency ON responses are not blocked by metabotropic glutamate or cholinergic receptor antagonists and are not produced by activation of receptive field surrounds. We show that these longer-latency ON responses are initiated in the OFF pathways. Our results expose a previously unrecognized intrinsic property of OFF retinal pathways that generates responses to light onset. In mGluR6-null mice, long-latency ON responses are observed in the visual cortex, indicating that they can be conducted reliably to higher visual areas. In wild-type (WT) mice, APB (DL-2-amino-4-phosphonobutyric acid), an mGluR6 agonist, blocks normal, short-latency ON responses but unmasks longer-latency ones. We find that these potentially confusing ON responses in the OFF pathway are actively suppressed in WT mice via two pharmacologically separable retinal circuits that are activated by the ON system in the retina. Consequently, we propose that a major function of the signaling of the ON pathway to the OFF pathway is suppression of these mistimed, and therefore inappropriate, light-evoked responses.

Action Potentials↗

PubMed2006

[Regulative effect of electroacupuncture of different frequencies on derangement of gastric electric rhythm in rabbits].

OBJECTIVE: To investigate regulative effect of electroacupuncture (EA) of different frequencies on derangement of gastric electric rhythm in rabbits. METHODS: Derangement of gastric electric rhythm model was made with injection of erythromycin into ear vein in 40 rabbits, and randomly divided into a model group, a 3 Hz-EA group, a 20 Hz-EA group and a 100 Hz-EA group. They were treated with EA at Zusanli (ST 36) with 3 Hz, 20 Hz and 100 Hz, respectively. PDP and PTP at different periods were detected with IEGG spectrum analyzer. RESULTS: Erythromycin could significantly enhance PDP and PTP values in the rabbit (P < 0.001). PDP and PTP values were reduced significantly after EA with 3 Hz, 20 Hz and 100 Hz (P < 0.05), with no significant differences in effect on PDP among them (P > 0.05); therapeutic effect of the EA of 20 Hz on PTP was better than that of 3 Hz (P < 0.05), with no significant difference as compared with the EA of 100 Hz. CONCLUSION: EA of the 3 frequencies shows significantly different regulative effects on derangement of gastric electric rhythm in rabbits.

Animals↗

PubMed2004

Visual experience and maturation of retinal synaptic pathways.

The retinal synaptic network continues its maturational refinement after eye opening in mammals. This synaptic refinement is reflected in changes of retinal neuron synaptic activity and connectivity. In mature retina, the dendrites of retinal ganglion cells (RGCs) in the inner plexiform layer (IPL) of retina are separated into ON or OFF sublamina. At early developmental stage, however, the dendrites of most RGCs are ramified throughout the IPL. Recently we found that the postnatal maturational processes converting bistratified ON-OFF responsive RGCs to monostratified ON and OFF responsive RGCs depend upon visual stimulation after eye opening.

Aging↗

PubMed2004

Pathway-specific maturation, visual deprivation, and development of retinal pathway.

One of the fundamental features of the visual system is the segregation of neural circuits that process increments and decrements of luminance into ON and OFF pathways. In mature retina, the dendrites of retinal ganglion cells (RGCs) in the inner plexiform layer (IPL) of retina are separated into ON or OFF sublamina-specific stratification. At an early developmental stage, however, the dendrites of most RGCs are ramified throughout the IPL. The maturation of RGC ON/OFF dendritic stratification requires neural activities mediated by afferent inputs from bipolar and amacrine cells. The synchronized spontaneous burst activities in early postnatal developing retina regulate RGC dendritic filopodial movements and the maintenance or elimination of dendritic processes. After eye opening, visual experience further remodels and consolidates the retinal neural circuit into mature forms. Several neurotransmitter systems, including glutamatergic, acetylcholinergic, GABAergic, and glycinergic systems, might act together to modulate the RGC dendritic refinement. In addition, both the bipolar cells and cholinergic amacrine cells may provide laminar cues for the maturation of RGC dendritic stratification.

Animals↗

PubMed2003

Visual stimulation is required for refinement of ON and OFF pathways in postnatal retina.

ON and OFF pathways separately relay increment and decrement luminance signals from retinal bipolar cells to cortex. ON-OFF retinal ganglion cells (RGCs) are activated via synaptic inputs onto bistratified dendrites localized in the ON and OFF regions of the inner plexiform layer. Postnatal maturational processes convert bistratifying ON-OFF RGCs to monostratifying ON and OFF RGCs. Although visual deprivation influences refinement of higher visual centers, no previous studies suggest that light regulates either the development of the visual-evoked signaling in retinal ON and OFF pathways, nor pruning of bistratified RGC dendrites. We find that dark rearing blocks both the maturational loss of ON-OFF responsive RGCs and the pruning of dendrites. Thus, in retina, there is a previously unrecognized, pathway-specific maturation that is profoundly affected by visual deprivation.

Action Potentials↗

PubMed2003

Vesicular neurotransmitter transporter expression in developing postnatal rodent retina: GABA and glycine precede glutamate.

Vesicular transporters regulate the amount and type of neurotransmitter sequestered into synaptic vesicles and, hence, the kind of signal transmitted to postsynaptic neurons. Glutamate is the prominent excitatory neurotransmitter in retina; GABA and glycine are the main inhibitory neurotransmitters. Little is known about the ontogeny of vesicular neurotransmission in retina. We investigated expression of glutamatergic [vesicular glutamate transporter 1 (VGLUT1)] and GABA/glycinergic [vesicular GABA/glycine transporter (VGAT)] vesicular transporters in postnatal retina. VGLUT1 labels glutamatergic synapses. VGLUT1 and synaptic vesicle 2 colocalized to photoreceptor terminals. VGLUT1 colocalized with PKC to rod bipolar terminals and to ON bipolar terminals in metabotropic glutamate receptor 6+/- mice. Developmentally, VGAT expression precedes VGLUT1. In rat and mouse retina, VGAT occurred in the inner retina by postnatal day 1 (P1). In rat retina, VGLUT1 was in the outer retina by P5-P7 and the inner retina by P7. In the mouse retina, VGLUT1 expression was in the outer retina by P3 and the inner retina by P5. Both rat and mouse retina had an adult pattern of VGLUT1 expression by P14. VGLUT1 expression precedes ribbon synapses, which are first observed in the inner retina at P11 (Fisher, 1979) in mouse and P13 (Horsburgh and Sefton, 1987) in rat. The ribbon synapse marker RIBEYE was not detected in inner retina of P5 or P7 rat. Spontaneous EPSCs in mouse ganglion cells were recorded as early as P7. Together, these findings indicate that vesicular GABA and glycine transmission precedes vesicular glutamate transmission in developing rodent retina. Furthermore, vesicular glutamate transmission likely occurs before ribbon synapse formation in the inner retina.

Age Factors↗

PubMedDate not supplied

Structure of glutamate analogs that activate the ON bipolar cell metabotropic glutamate receptor in vertebrate retina.

Although there are many glutamate receptors in the retina, 2-amino-4-phosphonobutyrate (L-AP4) is an agonist that acts selectively at metabotropic glutamate receptors (mGluR6) of ON bipolar cells. We explored the properties of agonists that activate this receptor. The effects of various glutamate analogs on the b-wave of the electroretinogram (ERG) were used as a measure of their activity. Conformational comparisons among agonists suggest that ligands in an extended conformation preferentially bind to the ON bipolar synaptic receptor. But this property is insufficient to explain the selectivity of mGluR6 because some inactive glutamate analogs could also match this extended conformation. Comparative molecular field analysis (CoMFA) was used to compare the electrostatic and steric potentials of agonists with their action at the ON bipolar synapse. Steric potentials beneath a plane defined by the three putative binding sites plays a key role in determining agonist activity. The CoMFA model was used to predict the activity of glutamate analogs and correlations between predicted and measured activity support the model.

Ambystoma↗

PubMedDate not supplied

Light deprivation suppresses the light response of inner retina in both young and adult mouse.

The retinal synaptic network continues its development after birth in mammals. Recent studies show that postnatal development of retinal circuitry depends on visual stimulation. We sought to determine whether there is a time period during which the retina shows evidence of increased plasticity. We examined the effects of light deprivation on the retinal light response of mouse retina using electroretinogram (ERG) measurements. Our results showed that dark rearing mice from birth to postnatal day (P) 30, 60, and 90 suppressed the amplitudes of oscillatory potentials (OPs) and the magnitudes of suppression were age independent. In addition, dark-rearing-produced suppression of OP amplitudes can be completely reversed in both young and adult mice by returning them to cyclic light/dark conditions for 1 to 2 weeks. However, the recovery time course was age dependent with younger animals needing a longer time to achieve a full recovery. Furthermore, dark rearing of P60 mice raised under cyclic light/dark conditions for 30 days resulted in a similar magnitude of suppression of OP amplitudes as in age-matched mice dark reared from birth. These findings demonstrate that both the normal developmental changes and the maintenance of mature inner retinal light response in adult animals require visual stimulation. These results indicate a degree of activity-dependent plasticity in mouse retina that has not been previously described.

Aging↗

PubMedDate not supplied

Retinopetal axons in mammals: emphasis on histamine and serotonin.

Since 1892, anatomical studies have demonstrated that the retinas of mammals, including humans, receive input from the brain via axons emerging from the optic nerve. There are only a small number of these retinopetal axons, but their branches in the inner retina are very extensive. More recently, the neurons in the brain stem that give rise to these axons have been localized, and their neurotransmitters have been identified. One set of retinopetal axons arises from perikarya in the posterior hypothalamus and uses histamine, and the other arises from perikarya in the dorsal raphe and uses serotonin. These serotonergic and histaminergic neurons are not specialized to supply the retina; rather, they are a subset of the neurons that project via collaterals to many other targets in the central nervous system, as well. They are components of the ascending arousal system, firing most rapidly when the animal is awake and active. The contributions of these retinopetal axons to vision may be predicted from the known effects of serotonin and histamine on retinal neurons. There is also evidence suggesting that retinopetal axons play a role in the etiology of retinal diseases.

Animals↗