Rabbit retinal ganglion cell responses to nicotine can be mediated by beta2-containing nicotinic acetylcholine receptors

Muscarinic Acetylcholine Receptors in the Retina-Therapeutic Implications

Muscarinic acetylcholine receptors (mAChRs) belong to the superfamily of G-protein-coupled receptors (GPCRs). The family of mAChRs is composed of five subtypes, M1, M2, M3, M4 and M5, which have distinct expression patterns and functions. In the eye and its adnexa, mAChRs are widely expressed and exert multiple functions, such as modulation of tear secretion, regulation of pupil size, modulation of intraocular pressure, participation in cell-to-cell signaling and modula-tion of vascular diameter in the retina. Due to this variety of functions, it is reasonable to assume that abnormalities in mAChR signaling may contribute to the development of various ocular diseases. On the other hand, mAChRs may offer an attractive therapeutic target to treat ocular diseases. Thus far, non-subtype-selective mAChR ligands have been used in ophthalmology to treat dry eye disease, myopia and glaucoma. However, these drugs were shown to cause various side-effects. Thus, the use of subtype-selective ligands would be useful to circumvent this problem. In this review, we give an overview on the localization and on the functional role of mAChR subtypes in the eye and its adnexa with a special focus on the retina. Moreover, we describe the pathophysiological role of mAChRs in retinal diseases and discuss potential therapeutic approaches.

Retinal dysfunctions in regular tobacco users: The retina as a window to the reward circuit in addictive disorders

The nicotine contained in tobacco is a neuromodulator which affects neurotransmission within the brain. The retina is an easy way to study central synaptic transmission dysfunctions in neuropsychiatric disorders. The purpose of this study is to assess the impact of regular tobacco use on retinal function using pattern (PERG), flash (fERG) and multifocal (mfERG) electroretinogram (ERG). We recorded PERG, fERG and mfERG for 24 regular tobacco users and 30 healthy non-smoking subjects. The protocol was compliant with International Society for Clinical Electrophysiology of Vision standards. The amplitudes and peak times (PT) of P50, N95 waves (PERG), a-, b- and oscillatory potentials (fERG), and N1, P1, N2 (mfERG) were evaluated. Compared to non-smokers, the results (Mann-Whitney U test, Bonferroni correction) for tobacco users suggested a significant increase of ~ 1 ms in the PT of light-adapted 3.0 fERG b-wave (p = 0.002). Using mfERG, we observed the following increases in tobacco users: in ring 3 for P1 PT of ~1,5 ms and in ring 5 for P1 PT of ~ 1 ms and for N2 PT of ~ 1 ms (p = 0.002, p = 0.002 and p = 0.006). It is our hypothesis that these results reflect the consequences of regular tobacco use on retinal synaptic transmission, and more specifically on dopaminergic and cholinergic transmission. We deduce that the retina may provide a crucial site of investigation for neurotransmission modulation of the reward circuit in regular tobacco users.

Cholinergic excitation complements glutamate in coding visual information in retinal ganglion cells

KEY POINTS

Starburst amacrine cells release GABA and ACh. This study explores the coordinated function of starburst-mediated cholinergic excitation and GABAergic inhibition to bistratified retinal ganglion cells, predominantly direction-selective ganglion cells (DSGCs). In rat retina, under our recording conditions, starbursts were found to provide the major excitatory drive to a sub-population of ganglion cells whose dendrites co-stratify with starburst dendrites (putative DSGCs). In mouse retina, recordings from genetically identified DSGCs at physiological temperatures reveal that ACh inputs dominate the response to small spot-high contrast light stimuli, with preferential addition of bipolar cell input shifting the balance towards glutamate for larger spot stimuli In addition, starbursts also appear to gate glutamatergic excitation to DSGCs by postsynaptic and possibly presynaptic inhibitory processes ABSTRACT: Starburst amacrine cells release both GABA and ACh, allowing them to simultaneously mediate inhibition and excitation. However, the precise pre- and postsynaptic targets for ACh and GABA remain under intense investigation. Most previous studies have focused on starburst-mediated postsynaptic GABAergic inhibition and its role in the formation of directional selectivity in ganglion cells. However, the significance of postsynaptic cholinergic excitation is only beginning to be appreciated. Here, we found that light-evoked responses measured in bi-stratified rat ganglion cells with dendrites that co-fasciculate with ON and OFF starburst dendrites (putative direction-selective ganglion cells, DSGCs) were abolished by the application of nicotinic receptor antagonists, suggesting ACh could act as the primary source of excitation. Recording from genetically labelled DSGCs in mouse retina at physiological temperatures revealed that cholinergic synaptic inputs dominated the excitation for high contrast stimuli only when the size of the stimulus was small. Canonical glutamatergic inputs mediated by bipolar cells were prominent when GABA/glycine receptors were blocked or when larger spot stimuli were utilized. In mouse DSGCs, bipolar cell excitation could also be unmasked through the activation of mGluR2,3 receptors, which we show suppresses starburst output, suggesting that GABA from starbursts serves to inhibit bipolar cell signals in DSGCs. Taken together, these results suggest that starbursts amplify excitatory signals traversing the retina, endowing DSGCs with the ability to encode fine spatial information without compromising their ability to encode direction.

Acetylcholine induces GABA release onto rod bipolar cells through heteromeric nicotinic receptors expressed in A17 amacrine cells

Acetylcholine (ACh) is a major retinal neurotransmitter that modulates visual processing through a large repertoire of cholinergic receptors expressed on different retinal cell types. ACh is released from starburst amacrine cells (SACs) under scotopic conditions, but its effects on cells of the rod pathway have not been investigated. Using whole-cell patch clamp recordings in slices of rat retina, we found that ACh application triggers GABA release onto rod bipolar (RB) cells. GABA was released from A17 amacrine cells and activated postsynaptic GABAA and GABAC receptors in RB cells. The sensitivity of ACh-induced currents to nicotinic ACh receptor (nAChR) antagonists (TMPH ~ mecamylamine > erysodine > DhβE > MLA) together with the differential potency of specific agonists to mimic ACh responses (cytisine >> RJR2403 ~ choline), suggest that A17 cells express heteromeric nAChRs containing the β4 subunit. Activation of nAChRs induced GABA release after Ca(2+) accumulation in A17 cell dendrites and varicosities mediated by L-type voltage-gated calcium channels (VGCCs) and intracellular Ca(2+) stores. Inhibition of acetylcholinesterase depolarized A17 cells and increased spontaneous inhibitory postsynaptic currents in RB cells, indicating that endogenous ACh enhances GABAergic inhibition of RB cells. Moreover, injection of neostigmine or cytisine reduced the b-wave of the scotopic flash electroretinogram (ERG), suggesting that cholinergic modulation of GABA release controls RB cell activity in vivo. These results describe a novel regulatory mechanism of RB cell inhibition and complement our understanding of the neuromodulatory control of retinal signal processing.

Nicotinic and muscarinic acetylcholine receptors shape ganglion cell response properties

The purpose of this study was to evaluate the expression patterns of nicotinic and muscarinic ACh receptors (nAChRs and mAChRs, respectively) in relation to one another and to understand their effects on rabbit retinal ganglion cell response properties. Double-label immunohistochemistry revealed labeled inner-retinal cell bodies and complex patterns of nAChR and mAChR expression in the inner plexiform layer. Specifically, the expression patterns of m1, m4, and m5 muscarinic receptors overlapped with those of non-α7 and α7 nicotinic receptors in presumptive amacrine and ganglion cells. There was no apparent overlap in the expression patterns of m2 muscarinic receptors with α7 nicotinic receptors or of m3 with non-α7 nicotinic receptors. Patch-clamp recordings demonstrated cell type-specific effects of nicotinic and muscarinic receptor blockade. Muscarinic receptor blockade enhanced the center responses of brisk-sustained/G4 On and G4 Off ganglion cells, whereas nicotinic receptor blockade suppressed the center responses of G4 On-cells near the visual streak but enhanced the center responses of nonstreak G4 On-cells. Blockade of muscarinic or nicotinic receptors suppressed the center responses of brisk-sustained Off-cells and the center light responses of subsets of brisk-transient/G11 On- and Off-cells. Only nicotinic blockade affected the center responses of G10 On-cells and G5 Off-cells. These data indicate that physiologically and morphologically identified ganglion cell types have specific patterns of AChR expression. The cholinergic receptor signatures of these cells may have implications for understanding visual defects in disease states that result from decreased ACh availability.

Hyperactivity of ON-type retinal ganglion cells in streptozotocin-induced diabetic mice

Impairment of visual function has been detected in the early stage of diabetes but the underlying neural mechanisms involved are largely unknown. Morphological and functional alterations of retinal ganglion cells, the final output neurons of the vertebrate retina, are thought to be the major cause of visual defects in diabetes but direct evidence to support this notion is limited. In this study we investigated functional changes of retinal ganglion cells in a type 1-like diabetic mouse model. Our results demonstrated that the spontaneous spiking activity of ON-type retinal ganglion cells was increased in streptozotocin-diabetic mice after 3 to 4 months of diabetes. At this stage of diabetes, no apoptotic signals or cell loss were detected in the ganglion cell layer of the retina, suggesting that the functional alterations in ganglion cells occur prior to massive ganglion cell apoptosis. Furthermore, we found that the increased activity of ON-type ganglion cells was mainly a result of reduced inhibitory signaling to the cells in diabetes. This novel mechanism provides insight into how visual function is impaired in diabetic retinopathy.

Human Müller glia with stem cell characteristics differentiate into retinal ganglion cell (RGC) precursors in vitro and partially restore RGC function in vivo following transplantation

Müller glia with stem cell characteristics have been identified in the adult human eye, and although there is no evidence that they regenerate retina in vivo, they can be induced to grow and differentiate into retinal neurons in vitro. We differentiated human Müller stem cells into retinal ganglion cell (RGC) precursors by stimulation with fibroblast growth factor 2 together with NOTCH inhibition using the γ-secretase inhibitor N-[N-(3,5-difluorophenacetyl)-l-alanyl]-S-phenylglycine t-butyl ester (DAPT). Differentiation into RGC precursors was confirmed by gene and protein expression analysis, changes in cytosolic [Ca(2+)] in response to neurotransmitters, and green fluorescent protein (GFP) expression by cells transduced with a transcriptional BRN3b-GFP reporter vector. RGC precursors transplanted onto the inner retinal surface of Lister hooded rats depleted of RGCs by N-methyl-d-aspartate aligned onto the host RGC layer at the site of transplantation but did not extend long processes toward the optic nerve. Cells were observed extending processes into the RGC layer and expressing RGC markers in vivo. This migration was observed only when adjuvant anti-inflammatory and matrix degradation therapy was used for transplantation. RGC precursors induced a significant recovery of RGC function in the transplanted eyes as determined by improvement of the negative scotopic threshold response of the electroretinogram (indicative of RGC function). The results suggest that transplanted RGC precursors may be capable of establishing local interneuron synapses and possibly release neurotrophic factors that facilitate recovery of RGC function. These cells constitute a promising source of cells for cell-based therapies to treat retinal degenerative disease caused by RGC dysfunction.

The effects of nicotine on the human electroretinogram

PURPOSE

To examine the effects of nicotine on responses from the human retina measured electrophysiologically.

METHODS

Electroretinogram (ERG) responses were obtained from ten healthy, visually normal adults who were nonsmokers. Nicotine (2 and 4 mg) and a placebo were administered in the form of gum 30 minutes before testing in two separate experiments. ERG responses were collected and analyzed using a full-field ERG system. Responses were recorded from one eye of each subject using a bipolar contact-lens electrode. Intensity-response curves were obtained under both dark- and light-adapted conditions. In experiment 1, both dark- and light-adapted tests were completed sequentially. In experiment 2, only light-adapted testing was performed. Intensity-response functions were analyzed using the Naka-Rushton equation.

RESULTS

In experiment 1, compared with placebo, dark-adapted b-wave amplitude responses decreased significantly after chewing gum containing both 2 and 4 mg of nicotine. Under light-adapted conditions, the peak b-wave amplitude was significantly decreased after chewing gum containing 4 mg of nicotine. In experiment 2, light-adapted b-wave amplitudes were increased after 4 mg nicotine. Oscillatory potentials were measured but no significant effects under nicotine were observed.

CONCLUSIONS

To the knowledge of the authors, this is the first demonstration that nicotine by itself affects responses in the human retina. These data support reports of the expression of nicotinic acetylcholine receptors in rabbit and nonhuman primate retina.

Muscarinic acetylcholine receptor localization and activation effects on ganglion response properties

PURPOSE

The activation and blockade of muscarinic acetylcholine receptors (mAChRs) affects retinal ganglion cell light responses and firing rates. This study was undertaken to identify the full complement of mAChRs expressed in the rabbit retina and to assess mAChR distribution and the functional effects of mAChR activation and blockade on retinal response properties.

METHODS

RT-PCR, Western blot analysis, and immunohistochemistry were used to identify the complement and distribution of mAChRs in the rabbit retina. Extracellular electrophysiology was used to determine the effects of the activation or blockade of mAChRs on ganglion cell response properties.

RESULTS

RT-PCR of whole neural retina resulted in the amplification of mRNA transcripts for the m1 to m5 mAChR subtypes. Western blot and immunohistochemical analyses confirmed that all five mAChR subtypes were expressed by subpopulations of bipolar, amacrine, and ganglion cells in the rabbit retina, including subsets of cells in cholinergic and glycinergic circuits. Nonspecific muscarinic activation and blockade resulted in the class-specific modulation of maintained ganglion cell firing rates and light responses.

CONCLUSIONS

The expression of mAChR subtypes on subsets of bipolar, amacrine, and ganglion cells provides a substrate for both enhancement and suppression of retinal responses via activation by cholinergic agents. Thus, the muscarinic cholinergic system in the retina may contribute to the modulation of complex stimuli. Understanding the distribution and function of mAChRs in the retina has the potential to provide important insights into the visual changes that are caused by decreased ACh in the retinas of Alzheimer's patients and the potential visual effects of anticholinergic treatments for ocular diseases.

Nicotinic acetylcholine receptor subunits in rhesus monkey retina

PURPOSE

The purpose of this study was to detect and establish the cellular localizations of nicotinic acetylcholine receptor (nAChR) subunits in Rhesus monkey retina.

METHODS

Retinas were dissected from the eyes of monkeys killed after unrelated experiments. RNA was extracted and analyzed by RT-PCR, using primers designed against human sequences of alpha3-alpha7, alpha9, and beta2-beta4 nAChR subunits. The RT-PCR products were separated by gel electrophoresis and sequenced. Frozen sections of postmortem fixed monkey eyes were immunolabeled with well-characterized and specific monoclonal antibodies against the alpha3, alpha4, alpha6, alpha7, beta2, or beta4 nAChR subunits and visualized with fluorescence labeling.

RESULTS

Products of the predicted size for the alpha3-alpha7, alpha9, and beta2-beta4 nAChR subunits were detected by RT-PCR in Rhesus monkey retina. Homology between transcripts from monkey retina and human nucleotide sequences ranged from 93 to 99%. Immunohistochemical studies demonstrated that neurons in various cell layers of monkey retina expressed alpha3, alpha4, alpha7, or beta2 nAChR subunits and cells with the morphology of microglia were immunoreactive for the alpha6 or beta4 nAChR subunits.

CONCLUSIONS

nAChR subunits are expressed in the monkey retina and localize to diverse retinal neurons as well as putative microglia. Besides mediating visual processing, retinal nAChRs may influence refractive development and ocular pathologies such as neovascularization.

Calcium mobilization by activation of M(3)/M(5) muscarinic receptors in the human retinoblastoma

Activation of muscarinic acetylcholine receptors (mAChR) is one of the most important signal transduction pathways in the human body. In this study, we investigated the role of mAChR activation in relation to its subtypes in human retinoblastoma cell-lines (WERI-Rb-1) using Ca(2+) measurement, real-time PCR, and Western Blot techniques. Acetylcholine (ACh) produced prominent [Ca(2+)](i) transients in a repeated manner in WERI-Rb-1 cells. The maximal amplitude of the [Ca(2+)](i) transient was almost completely suppressed by 97.3 +/- 0.8% after atropine (1 microM) pretreatment. Similar suppressions were noted after pretreatments with thapsigargin (1 microM), an ER Ca(2+)-ATPase (SERCA) inhibitor, whereas the ACh-induced [Ca(2+)](i) transient was not affected even in the absence of extracellular calcium. U-73122 (1 microM), a PLC inhibitor, and xestospongin C (2 microM), an IP(3)-receptor antagonist, elicited 11.5 +/- 2.9% and 17.8 +/- 1.9% suppressions, respectively. The 50% inhibitory concentration of (IC(50)) values for blockade of a 100 microM ACh response by pirenzepine and 4-DAMP were 315.8 and 9.1 nM, respectively. Moreover, both M(3) and M(5) mAChRs were prominent in quantitative real-time-PCR. Taken together, the M(3)/M(5) subtypes appear to be the major contributor, leading to intracellular calcium mobilization from the internal store via an IP(3)-dependent pathway in the undifferentiated retinoblastoma cells.

Nicotinic acetylcholine receptor expression by directionally selective ganglion cells

Acetylcholine (ACh) enhances the preferred direction responses of directionally selective ganglion cells (DS GCs; Ariel & Daw, 1982; Ariel & Adolph, 1985) through the activation of nicotinic acetylcholine receptors (nAChRs; Ariel & Daw, 1982; Massey et al., 1997; Kittila & Massey, 1997). DS GCs appear to express at least two types of nAChRs, those that are sensitive to the partially subtype-specific antagonist methyllycaconitine (MLA), and those that are MLA-insensitive (Reed et al., 2002). Our purpose was to confirm the expression of alpha7 nAChRs by DS GCs and to assess the contributions of other nAChR subtypes to DS GC responses. Using choline as a nAChR partially subtype-specific agonist, we found that the majority of DS GCs demonstrated responses to choline while under synaptic blockade. The blockade or reduction of choline-induced responses by bath application of nanomolar (nM) concentrations of MLA provided direct evidence that the choline responses were mediated by alpha7 nAChRs. Because choline is a partial agonist for alpha3beta4 nAChRs (Alkondon et al., 1997), the residual choline responses are consistent with mediation by alpha3beta4 nAChRs. Additionally, a subset of DS GCs responded to nicotine but not to choline, indicating the expression of a third nAChR subtype. The pharmacological results were supported by single cell reverse transcription polymerase chain reaction (RT-PCR) and immunohistochemistry experiments. The expression of alpha7 and specific non-alpha7 nAChR subtypes was correlated with the preferred direction. This indicates the possibility of differential responses to ACh depending on the direction of movement. This is the first description of differential expression of multiple nAChR subtypes by DS GCs.

Acute effects of cigarette smoking on multifocal electroretinogram

BACKGROUND

Cigarette smoking was shown to have stimulant effects on pattern visual-evoked potentials. The aim of this study was to investigate the acute effects of cigarette smoking on multifocal electroretinogram (mfERG).

METHODS

This prospective case-control study was held in a tertiary referral centre in Turkish Armed Forces. mfERGs were investigated in a group of habitual smokers (30 right eyes of 30 subjects) in separate real smoking and sham smoking sessions. mfERG responses of the subjects were recorded after overnight abstinence. The responses were averaged over five retinal regions, the central hexagon (CH; central 6 degrees) and four concentric rings (ring 1 [R1; 7-12 degrees], ring 2 [R2; 13-18 degrees], ring 3 [R3; 19-24 degrees], ring 4 [R4; 25-30 degrees]). On each session mfERGs were recorded before (BS) and after smoking (AS) conditions.

RESULTS

Regarding P1 amplitudes (first positive deflection of the mfERG) in the real smoking sessions, the differences were significant in the CH (BS: 66.2 +/- 16.3 microV, AS: 73.3 +/- 19.6 microV, P < 0.001), in R1 (BS: 44.3 +/- 13.0, AS: 48.3 +/- 16.0, P = 0.004) and in R2 (BS: 30.1 +/- 8.3, AS: 33.7 +/- 9.7, P = 0.002). Similar results were found for N1 amplitudes and P1 and N1 (first negative deflection of the mfERG) latencies in the CH, R1 and R2. The differences in outer retinal areas (R3, R4) in the real smoking sessions and in all rings in the sham smoking sessions were not significant.

CONCLUSION

Cigarette smoking may stimulate the central retinal areas in the acute phase. This effect may be related with the stimulant effect of nicotine on neurotransmission, deleterious effects on retinal and/or choroidal circulation, carbon monoxide toxicity and nicotine withdrawal.

Expression of alpha 7 nicotinic acetylcholine receptors by bipolar, amacrine, and ganglion cells of the rabbit retina

Cholinergic agents affect the light responses of many ganglion cells (GCs) in the mammalian retina by activating nicotinic acetylcholine receptors (nAChRs). Whereas retinal neurons that express beta2 subunit-containing nAChRs have been characterized in the rabbit retina, expression patterns of other nAChR subtypes remain unclear. Therefore, we evaluated the expression of alpha7 nAChRs in retinal neurons by means of single-, double-, and triple-label immunohistochemistry. Our data demonstrate that, in the rabbit retina, several types of bipolar cells, amacrine cells, and cells in the GC layer express alpha7 nAChRs. At least three different populations of cone bipolar cells exhibited alpha7 labeling, whereas glycine-immunoreactive amacrine cells comprised the majority of alpha7-positive amacrine cells. Some GABAergic amacrine cells also displayed alpha7 immunoreactivity; alpha7 labeling was never detected in rod bipolar cells or rod amacrine cells (AII amacrine cells). Our data suggest that activation of alpha7 nAChRs by acetylcholine (ACh) or choline may affect glutamate release from several types of cone bipolar cells, modulating GC responses. ACh-induced excitation of inhibitory amacrine cells might cause either inhibition or disinhibition of other amacrine and GC circuits. Finally, ACh may act on alpha7 nAChRs expressed by GCs themselves.

Stratification of α ganglion cells and ON/OFF directionally selective ganglion cells in the rabbit retina

The correlation between cholinergic sensitivity and the level of stratification for ganglion cells was examined in the rabbit retina. As examples, we have used ON or OFF alpha ganglion cells and ON/OFF directionally selective (DS) ganglion cells. Nicotine, a cholinergic agonist, depolarized ON/OFF DS ganglion cells and greatly enhanced their firing rates but it had modest excitatory effects on ON or OFF alpha ganglion cells. As previously reported, we conclude that DS ganglion cells are the most sensitive to cholinergic drugs. Confocal imaging showed that ON/OFF DS ganglion cells ramify precisely at the level of the cholinergic amacrine cell dendrites, and co-fasciculate with the cholinergic matrix of starburst amacrine cells. However, neither ON or OFF alpha ganglion cells have more than a chance association with the cholinergic matrix. Z -axis reconstruction showed that OFF alpha ganglion cells stratify just below the cholinergic band in sublamina a while ON alpha ganglion cells stratify just below cholinergic b . The latter is at the same level as the terminals of calbindin bipolar cells. Thus, the calbindin bipolar cell appears to be a prime candidate to provide the bipolar cell input to ON alpha ganglion cells in the rabbit retina. We conclude that the precise level of stratification is correlated with the strength of cholinergic input. Alpha ganglion cells receive a weak cholinergic input and they are narrowly stratified just below the cholinergic bands.

Rabbit retinal ganglion cells express functional alpha7 nicotinic acetylcholine receptors

It is well known that cholinergic agents affect ganglion cell (GC) firing rates and light responses in the retinas of many species, but the specific receptor subtypes involved in mediating these effects have been only partially characterized. We sought to determine whether functional alpha(7) nicotinic acetylcholine receptors (nAChRs) contribute to the responses of specific retinal GC classes in rabbit retina. We used electrophysiology, pharmacology, immunohistochemistry, and reverse transcriptase-polymerase chain reaction to determine the pharmacological properties and expression of nAChR subtypes by specific rabbit retinal GC classes. Choline was used as an alpha(7) nAChR agonist. Methyllycaconitine (MLA) was used as a competitive alpha(7) nAChR antagonist. The application of choline before synaptic blockade resulted in changes in retinal GC activity, including increases or decreases in maintained firing and/or enhancement or suppression of light responses. Many physiologically identified GC types, including sustained off, sustained on, transient off, and transient on cells, demonstrated responses to choline application while under synaptic blockade. The choline-induced responses could be blocked with MLA, confirming alpha(7) nAChR activation. Individual choline-responsive GCs displayed mRNA transcripts consistent with the expression of functional alpha(7) nAChRs. Other GCs demonstrated physiological responses and mRNA expression consistent with the expression of both alpha(7) and non-alpha(7) nAChRs. Thus mRNA is present for multiple nAChR subunits in whole retina extracts, and functional alpha(7) nAChRs are capable of modulating the responses of GCs in adult rabbit retina. We also demonstrate through physiological responses that subsets of GCs express more than one nAChR subtype.

MLA-sensitive cholinergic receptors involved in the detection of complex moving stimuli in retina

Acetylcholine, acting through nicotinic acetylcholine receptors, mediates the response properties of many ganglion cells in the rabbit retina, including those that are directionally selective (DS; Ariel & Daw, 1982a,b). For example, Grzywacz et al. (1998) showed that cholinergic input is necessary for DS responses to drifting gratings, a form of textured stimulus. However, the identities and locations of the neuronal acetylcholine receptor (nAChR) subtypes that mediate this input are not clear (Keyser et al., 2000). We investigated the role of methyllycaconitine-sensitive, α7-like nAChRs in mediating DS responses to textured stimuli and apparent motion. We recorded extracellularly from On–Off DS ganglion cells in rabbit retina using everted eyecup preparations. Our data provide evidence that MLA-sensitive nAChRs are involved in mediating directionally selective responses to apparent motion and to a variety of complex, textured stimuli such as drifting square-wave gratings, transparent motion, and second-order motion.