The receptive-field positions and orientation preferences of neurons occupying the same tangential location in visual cortex are thought to be similar but to have an associated random scatter. However, previous estimates of this scatter may have been inflated by the use of subjective plotting methods, sequential recording of single units, and residual eye movements. Here we report measurements of receptive-field position and orientation scatter in cat area 17 made with tetrodes, which were able to simultaneously isolate and record up to 11 nearby neurons (ensembles). We studied 355 units at 72 sites with moving light and dark bars. Receptive-field sizes and positions were estimated by least-squares fitting of Gaussians to response profiles. We found that receptive-field position scatter was about half of the ensemble average receptive-field size. We confirmed previous estimates of orientation scatter, but calculations suggested that much of it may be accounted for by anatomical scatter in the positions of recorded neurons relative to the tetrode in a smooth map. Orientation tuning width was positively correlated with the degree of orientation scatter. Scatter was not independent in the two eyes: deviations from the local mean for both preferred orientation and receptive-field position were correlated although a significant amount of residual inter-ocular orientation and receptive-field position scatter was present. We conclude that cortical maps of orientation and receptive-field position are more ordered than was previously thought, and that random scatter in receptive-field positions makes a relatively small contribution to cortical point image size.

Based on previous evidence that acetylcholine (ACh) and noradrenaline (NA) play a permissive role in developmental plasticity in the kitten visual cortex, we reinvestigated this topic in the postnatal visual cortex of rats with normal vision. In rats, the functional properties of visual cortical cells develop gradually between the second and the sixth postnatal week (Fagiolini et al., 1994). Cortical cholinergic depletion, by basal forebrain (BF) lesions at postnatal day (PD) 15 (eye opening), leads to a transient disturbance in the distribution of ocular dominance (Siciliano et al., 1997). In the present study, we investigated the development of visual cortical response properties following cytotoxic lesions of the locus coeruleus (LC) alone or in combination with lesions of cholinergic BF. The main result is that early NA depletion impairs the orientation selectivity of cortical neurons, causes a slight increase of their receptive-field size, and reduces the signal-to-noise ratio of cell responses. Similar effects are obtained following NA depletion in adult animals, although the effects of adult noradrenergic deafferentation are significantly more severe than those obtained after early NA depletion. Additional cholinergic depletion causes an additional transient change in ocular-dominance distribution similarly to that obtained after cholinergic deafferentation alone. Comparisons between depletion of NA on the one hand and depletion of both NA and ACh on the other suggest that the effects of combined deafferentation on the functional properties studied result from simple linear addition of the effects of depleting each afferent system alone.

Neurons of the horizontal cell retinal neural network are subject to modulation by the neurotransmitter nitric oxide (NO). We have examined the effects of NO on glutamate receptor function in isolated horizontal cells from the perch (Perca fluviatilis) using the concentration ramp technique to simultaneously record receptor current and agonist concentration. Dose–response curves for glutamate (0–1 mM) and kainate (0–200 μM) were measured in the presence and absence of 1–2 mM sodium nitroprusside (SNP), 1 mM 8-Br-cGMP, 100 μM cyclothiazide or 200 μM dopamine as modulators. SNP increased the EC50 (i.e. decreased affinity) for glutamate and increased Imax (i.e. increased efficacy), whereas 8-Br-cGMP increased EC50, but not Imax. In the presence of the α-amino-3-hydroxy-5-methyl-4-isoxazole-propionic acid (AMPA) receptor desensitization blocker cyclothiazide, the SNP-induced increase in EC50 persisted, but the increase in Imax was blocked. The increase in EC50, but not the increase in Imax, was also observed when the non-desensitizing agonist kainate (100–200 μM) was applied in the presence of SNP. When 2 mM SNP and 200 μM dopamine were applied together, they increased Imax (740 vs. 2455 pA) and EC50 (422 vs. 682 μM). Our findings indicate that NO modulates horizontal cell glutamate responses by reducing the affinity of receptors for glutamate while simultaneously increasing the maximal current. The shift in affinity is cGMP-mediated and independent of desensitization. The action of NO on horizontal cell glutamate receptors is distinct from, but synergistic with, that of dopamine. Glutamate receptor modulation by NO qualitatively predicts the action of NO on horizontal cell light responses in situ and may alter transmission at visual synapses according to adaptational conditions.

Amacrine cells that respond transiently to maintained illumination are thought to mediate transient inhibitory input to ganglion cells. The excitation of these transient amacrine cells is thought to be limited by inhibitory feedback to bipolar cells. We investigated the possibility that desensitizing AMPA and/or kainate (KA) receptors on amacrine cells might also limit the duration of amacrine cell excitation. To determine how these receptors might affect amacrine cell input and output, we made whole-cell recordings from amacrine and ganglion cells in the salamander retinal slice. The specific AMPA receptor antagonist GYKI-53655 blocked non-NMDA receptor-mediated amacrine cell excitatory postsynaptic currents (EPSCs) and kainate puff-elicited currents, indicating that AMPA, and not KA, receptors mediated the responses. Cyclothiazide, an agent that reduces AMPA receptor desensitization, increased the amplitude and duration of amacrine cell EPSCs. To measure the output of transient amacrine cells, we recorded glycinergic inhibitory postsynaptic currents (IPSCs) from ganglion cells, and found that these were also enhanced by cyclothiazide. Thus, prolongation of amacrine cell AMPA receptor activation enhanced amacrine cell output. Current responses elicited by puffing glycine onto ganglion cell dendrites were not affected by cyclothiazide, indicating that the enhancement of glycinergic IPSCs was not due to a direct effect on glycine receptors. These data suggest that rapid AMPA receptor desensitization and/or deactivation limits glycinergic amacrine cell excitation and the resulting inhibitory synaptic output.

Results from earlier experiments indicate that different species of rodent vary both in the number of cone types found in their retinas and in the spectral sensitivities of the cone pigments. These features have now been examined in two types of hamster commonly used for research purposes: Syrian golden hamsters (Mesocricetus auratus) and Siberian dwarf hamsters (Phodopus sungorus). Electroretinogram (ERG) flicker photometry, behavioral discrimination tasks, and opsin antibody labeling were used to investigate hamster photoreceptors and their visual consequences. Results from the three approaches support the following conclusions: (1) The retinas of both species have an abundant population of rods containing a photopigment with peak sensitivity of about 498–500 nm; (2) Siberian dwarf hamsters have two classes of cone: one with maximum sensitivity in the ultraviolet (c. 360 nm), the other with peak sensitivity closely similar to that of its rod; and (3) Syrian golden hamsters have a class of cone with peak sensitivity at about 506 nm, but they lack a second cone type. Implications of these alternative arrangements are discussed.

Adult Japanese quail have an endogenous circadian clock located in their eyes that has been shown to regulate melatonin biosynthesis. We investigated if a circadian oscillator is present in cultures of dispersed embryonic quail retina. Melatonin release in retinal cell culture is modulated by the light cycle, indicating that there are functional photoreceptors in culture. However, when cultures were placed in constant darkness no rhythm of melatonin was observed, indicating that at this period of development the circadian oscillator does not influence melatonin release. To explore further the question of whether a circadian oscillator is present in embryonic cell culture, we examined expression of iodopsin, the red visual pigment. Iodopsin mRNA is expressed in a circadian rhythm with peak levels occurring late in the afternoon (ZT 9). Analysis indicates that the clock influence is at the level of gene transcription. These results suggest that a clock is not “hooked up” to melatonin release embryonically or that a different oscillator regulates photopigment expression versus melatonin release.

We studied the light-evoked responses of AII amacrine cells in the rabbit retina under dark- and light-adapted conditions. In contrast to the results of previous studies, we found that AII cells display robust responses to light over a 6–7 log unit intensity range, well beyond the operating range of rod photoreceptors. Under dark adaptation, AII cells showed an ON-center/OFF-surround receptive-field organization. The intensity–response profile of the center-mediated response component followed a dual-limbed sigmoidal function indicating a transition from rod to cone mediation as stimulus intensities were increased. Following light adaptation, the receptive-field organization of AII cells changed dramatically. Light-adapted AII cells showed both ON- and OFF-responses to stimulation of the center receptive field, but we found no evidence for an antagonistic surround. Interestingly, the OFF-center response appeared first following rapid light adaptation and was then replaced gradually over a 1–4 min period by the emerging ON-center response component. Application of the metabotropic glutamate receptor agonist APB, the ionotropic glutamate blocker CNQX, 8-bromo-cGMP, and the nitric oxide donor SNAP all showed differential effects on the various center-mediated responses displayed by dark- and light-adapted AII cells. Taken together, these pharmacological results indicated that different synaptic circuits are responsible for the generation of the different AII cell responses. Specifically, the rod-driven ON-center responses are apparently derived from rod bipolar cell synaptic inputs, whereas the cone-driven ON-center responses arise from signals crossing the gap junctions between AII cells and ON-center cone bipolar cells. Additionally, the OFF-center response of light-adapted AII cells reflects direct synaptic inputs from OFF-center cone bipolar cells to AII dendritic processes in the distal inner plexiform layer.

In mammals, gap junctions between retinal bipolar cells are generally small and tracer coupling has not been previously demonstrated. In this study, Neurobiotin was injected into the Ba3-type cone bipolar cell, a medium-field cone bipolar cell that ramifies in sublamina a of the rabbit retina. Tracer spread to many other Ba3 bipolar cells, presumably through gap junctions. It also spread to a smaller field bipolar cell called the Ba1 that ramifies at the same depth of the inner plexiform layer. Injection of Neurobiotin into Ba1 bipolar cells did not produce staining beyond the injected cell. Tracer coupling from the Ba3 was therefore both heterologous, in that different cell types were stained, and asymmetric. The unusual properties of this bipolar cell suggest that its function may differ from that of most cone bipolar cells, which are narrow-field, do not overlap, and are poorly coupled to one another.

The projection specificity of retinal ganglion cells and the morphology of their terminals were studied in the plethodontid salamander Plethodon jordani. In an in vitro approach, ganglion cells were stained with biocytin and reconstructed by means of light microscopy. Single retinal ganglion cells often have multiple terminal structures in the thalamus, pretectum, and tectum. The projection pattern in the diencephalic neuropils is related to the depth of the terminal arbor within the tectal fiber layer. Terminal arbors in the tectum differ in location, size, and branching pattern. The following types could be distinguished: The most superficial of the optic terminals in layer 1 are relatively small with a diameter of about 100 μm. With the exception of a few varicosities (beads) in the pretectal neuropils, their stem axons have no further collaterals or terminal arbors in the diencephalic neuropils. Intermediate terminals in layer 2 fan out to form a dense plexus with a medio-lateral extent of 180 μm on average. Some terminals in this layer show obvious antenna-like fibers reaching toward the surface of the tectum. The axons of layer 2 projecting neurons have additional collaterals and terminal arbors in the thalamus and pretectum. The deep layer 3 terminals spread out over a diameter of 400 μm on average and their degree of branching is moderate. The axons of layer 3 projecting ganglion cells have dense additional terminal arbors in the thalamus and pretectum. The deepest retinal terminals in the tectum are found within the predominantly efferent fiber layers. This type consists of an unbranched, but beaded axon which runs rostro-caudally with several bends and loops. The stem axon has an additional very dense terminal arborization in the neuropil of the nucleus Bellonci pars medialis and additional sparse collaterals in the pretectal area.

Teleost fish retinas can regenerate in vivo in adulthood. Retinal and visual function was assessed in adult goldfish following comprehensive retinal destruction by intraocular injection of ouabain. Electroretinograms (ERGs) and the dorsal light reflex (DLR) were used to evaluate the return of visual function. ERGs were detectable in regenerating eyes 50 to 70 days following ouabain injection. Amplitudes of both a- and b-waves increased steadily through day 210 following ouabain treatment, at which time a-wave amplitude was 90% and b-wave amplitude approached 50% of the contralateral control eye. The progressive gain observed in the a-wave was attributed to photoreceptor regeneration. The increase in b-wave amplitude was attributed to an increase in the number of inner nuclear layer cells and the number and efficacy of neuronal connections to or within the inner retina. The photopic spectral sensitivity of the b-wave in regenerating retina closely matched the intrafish control retina, suggesting that the relative numbers of cone photoreceptors was normal in regeneration. The recovery of the DLR (indicated by improved postural balance during regeneration) paralleled electrophysiological gains during retinal regeneration. Fish displayed a marked longitudinal body imbalance toward the control eye following retinal destruction. Improvement in equilibrium was correlated with increasing b-wave amplitudes. When the b-wave reached 50% of control amplitude (30 weeks), normal posture was restored. The return of the ERG indicates that photoreceptors and their synaptic connections must be functional in regenerating retina. Failure of the retina to regenerate produced an abnormal DLR that persisted through 30 weeks and ERGs were not measurable. The return of normal equilibrium indicates that the regenerating retina can establish central connections to the brain, and that the regenerated connections can mediate functional visual behavior.

The retinas of adult teleost fish can regenerate following injury, but little is known about the neuronal integration of the visual scene that is performed by the regenerated retina. Using goldfish retinal ganglion cells (RGCs) as the experimental system, an evaluation of dendritic arbor structure and passive electrotonic properties was developed, the aim being to quantitatively test the hypothesis that native and regenerated RGC dendritic arbors have similar structural and modeled electrotonic attributes. Fractal dimension was chosen as the descriptor of RGC dendritic arbor complexity, and the arbors' transfer function magnitudes were estimated using an electrically passive, equivalent-circuit analysis. For both native and regenerated RGCs, arbors qualitatively judged to be simple tended to have lower fractal dimension values than arbors judged to be more complex. All cells had similar cut-off frequencies, and for random stimulation of greater than 25% of an RGC's population of dendritic tips, there was a positive correlation between fractal dimension and transfer function magnitude. Some regenerated RGCs had abnormally long primary dendrites, but neither the distributions of fractal dimension values, nor the estimated transfer function magnitudes, were significantly different between native and regenerated RGCs. The results appear to support the hypothesis that structural and modeled electrotonic attributes of regenerated goldfish RGCs are similar to those of native RGCs, suggesting that regenerated RGCs may restore normal visual function.

Simple cells display a specific adaptation aftereffect when tested with drifting gratings. The onset of the response to each cycle of the grating is delayed after adapting, but the offset is unaffected. Testing with stationary bars whose luminance was modulated in time revealed that aftereffects occur only at certain points in both space and time. The aftereffects seen with moving stimuli were predicted from those seen with stationary stimuli. These adaptation experiments suggest a model that consists of mutually inhibitory simple cells that are in spatiotemporal quadrature. The inhibition is appropriately localized in space and time to create the observed aftereffects. In this model, inhibition onto direction-selective simple cells arises from simple cells with the same preferred direction.

The patchy pattern of retrograde labeling produced by injections of anatomical tracers into the lateral suprasylvian (LS) visual area was compared to the cytochrome oxidase (CO) blobs in cat visual cortex. Following large injections of anatomical tracers in LS, retrograde labeling formed an irregular lattice of patches with a spacing of slightly less than 1 mm in area 17, and slightly greater than 1 mm in area 18. By comparing labeling in alternate serial sections, patches of LS-projecting cells in both areas were found to align with CO blobs. The conclusion of alignment between CO blob columns and patches of LS-projecting cells was confirmed by a quantitative analysis which showed a significant correlation between the local density of LS-projecting cells in reconstructions of charted cells and the intensity of CO staining in the CO-reacted sections. As for areas 17 and 18, labeling in other afferent areas of LS was also patchy with a spacing on the order of 1 mm except for area 19 where we found patches of LS-projecting cells with a larger spacing, roughly 2 mm. No matching fluctuations in CO density could be discerned in area 19, however. In conjunction with recent evidence that CO blob columns in cats receive strong input from Y-cells of the lateral geniculate nucleus (Boyd & Matsubara, 1996; Shoham, et al., 1996), these data support the hypothesis (Shipp & Grant, 1991) that the patches of LS-projecting cells correspond to Y-cell input columns. As a relationship between the CO architecture and certain classes of efferent cells has previously been shown in primates, these findings show new similarities between CO blobs in different mammalian species.

In a visual delayed matching-to-sample task, compared to a control condition, we had previously identified different components of the human EEG that could reflect the rehearsal of an object representation in short-term memory (Tallon-Baudry et al., 1998). These components were induced oscillatory activities in the gamma (24–60 Hz) and beta (15–20 Hz) bands, peaking during the delay at occipital and frontal electrodes, and two negativities in the evoked potentials. Sustained activities (lasting until the end of the delay) are more likely to reflect the continuous rehearsing process in memory than transient (ending before the end of the delay) activities. Nevertheless, since the delay duration we used in our previous experiment was fixed and rather short, it was difficult to discriminate between sustained and transient components. Here we used the same delayed matching-to-sample task, but with variable delay durations. The same oscillatory components in the gamma and beta bands were observed again during the delay. The only components that showed a sustained time course compatible with a memory rehearsing process were the occipital gamma and frontal beta induced activities. These two activities slowly decreased with increasing delay duration, while the performance of the subjects decreased in parallel. No sustained response could be found in the evoked potentials. These results support the hypothesis that objects representations in visual short-term memory consist of oscillating synchronized cell assemblies.

The hamster intergeniculate leaflet (IGL), part of the circadian rhythm regulatory system, has very extensive interconnections with subcortical visual nuclei. The present investigation describes IGL connections with the hamster diencephalon and telencephalon and compares them with ventral lateral geniculate nucleus (VLG) connections and retinal projections. Connections of the geniculate nuclei were evaluated using anterograde transport of iontophoretically injected Phaseolus vulgaris leucoagglutinin and by retrograde transport of cholera toxin β fragment. The cholera fragment was also injected intraocularly to trace retinal efferents. The IGL has ipsilateral and contralateral projections to the anterior and posterior hypothalamic nuclei, the ventral preoptic, lateral and dorsal hypothalamic areas, but not to the core ventromedial nucleus and very sparsely to the paraventricular nucleus. There are also IGL projections to the medial and lateral zona incerta, anteroventral, anterodorsal, reuniens, parataenial, paraventricular, centrolateral, central medial, and laterodorsal thalamic nuclei. IGL projections to the telencephalon are found in the horizontal limb of the diagonal band, olfactory tubercle, nucleus of the lateral olfactory tract, posterior bed nucleus of the stria terminalis, ventral pallidum, and in nuclei of the medial amygdala. The only substantial VLG projections are to bed nucleus of the stria terminalis, IGL, medial zona incerta, central medial and laterodorsal thalamic nuclei. Several of the IGL targets, the bed nucleus of the stria terminalis and zona incerta in particular, send projections back to the IGL and VLG. In addition, cells are present in the caudal cingulate cortex that project to both nuclei. Retinal projections are found in many of the regions receiving IGL innervation, including nuclei of the medial basal telencephalon, the posteromedial bed nucleus of the stria terminalis, and nuclei of the hypothalamus. A retinal projection is also visible in the lateral olfactory tract from which it extends rostrally, then medially along the base of the rhinal fissure. Fibers also extend caudally, in a superficial location, to perirhinal cortex. The results further demonstrate the widespread connections of the IGL and support the idea that the IGL modulates olfactory, photic, and circadian rhythm regulation of regulatory physiology and behavior.

The spatiotemporal structure of cortical activity evoked by diffuse light flashes was investigated in an isolated eyecup-brain preparation of the pond turtle, Pseudemys scripta. By combining a photomicroscopic image of the preparation with voltage-sensitive dye signals recorded by a 464-element photodiode array, the spread of depolarization within different cortical areas could be directly visualized with millisecond temporal resolution. Diffuse stimulation of the contralateral eyecup initially depolarized the visual cortex at the junction between its lateral and medial divisions in a small area rostral of the ventricular eminence. From this point, the depolarization spread at different velocities (10–100 μm/ms) depending upon the direction of travel. Since the initial depolarization was always in the rostral pole, the largest spread invariably occurred in a rostral → caudal direction. Within the confines of the medial visual cortex, depolarization spread at a constant velocity but slowed after entering the adjoining medial cortex. Increasing the stimulus illuminance increased the velocity of spread. Rostrocaudal spread of depolarization was also observed in response to electrical stimulation of the geniculocortical pathway and by direct focal stimulation of the cortical sheet. These data suggest that excitatory connections between pyramidal cell clusters play a prominent role in the initial activation of the cortex by diffuse retinal stimulation.

It has been suggested that acetylcholine plays a role in contrast discrimination performance and the regulation of visual contrast gain (Smith, 1996). Since alcohol has been shown to reduce levels of acetylcholine and contrast sensitivity, the present study measured the effects of alcohol on contrast discrimination and explored whether the deficits could be explained as a consequence of reduction in contrast gain. Detection thresholds and contrast increment thresholds under placebo and alcohol (0.06% BAC) conditions were measured in six volunteers. Alcohol was found to impair both detection and discrimination of only high spatial frequencies. However, when the base contrasts used in the increment threshold task were equal multiples of detection threshold, no alcohol-induced changes in increment thresholds were obtained at any spatial frequency. We conclude that alcohol impairs contrast discrimination performance but that no change in contrast gain mechanisms need be postulated to account for the data.

To analyze the elemental composition and topology of the extracellular compartments of the compound eye, the eyes of blowflies Calliphora vicina were rapidly frozen and ultrathin cryosections were freeze dried. Three zones of an ommatidium, peripheral cytosol of visual cells, rhabdomeres, and ommatidial cavities were analyzed by X-ray microprobe analysis. The ommatidial cavity was found to contain sodium and potassium in proportion similar to that in the blowfly hemolymph. Potassium-to-sodium ratio in a cytosol was typical for a cytosol. The rhabdomeres displayed an electrolyte content intermediate between the above compartments. Three topologically connected extracellular compartments were characterized by the experiments with tracers, monastral blue and lanthanum: (1) common intercellular space of ommatidia including peripheral clefts between the visual cells, both tracers entered this compartment; (2) the ommatidial cavity, which is not accessible for monastral blue, however, as revealed by our X-ray microanalysis, it was reachable for lanthanum; (3) rhabdomeric loops, which were accessible for lanthanum entering either via the cavity or from the common intercellular clefts. The above characteristics of the ionic content and topology of ommatidial compartments might suggest higher sodium and lower potassium content in the microvilli as compared with the cytosol. The rhabdomeric and “cavital” plasma membranes are assumed to be permeable for these ions so that a voltage of only 25–30 mV, negative inside, is probably formed across them, much lower than the known resting potential −60 mV across the peripheral plasma membrane of a visual cell.

The position, size, and shape of the receptive field (RF) of some cortical neurons change dynamically, in response to artificial scotoma conditioning (Pettet & Gilbert, 1992) and to retinal lesions (Chino et al., 1992; Darian-Smith & Gilbert, 1995) in adult animals. The RF dynamics are of interest because they show how visual systems may adaptively overcome damage (from lesions, scotomas, or other failures), may enhance processing efficiency by altering RF coverage in response to visual demand, and may perform perceptual learning. This paper presents an afferent excitatory synaptic plasticity rule and a lateral inhibitory synaptic plasticity rule—the EXIN rules (Marshall, 1995)—to model persistent RF changes after artificial scotoma conditioning and retinal lesions. The EXIN model is compared to the LISSOM model (Sirosh et al., 1996) and to a neuronal adaptation model (Xing & Gerstein, 1994). The rules within each model are isolated and are analyzed independently, to elucidate their roles in adult cortical RF dynamics. Based on computer simulations, the EXIN lateral inhibitory synaptic plasticity rule and the LISSOM lateral excitatory synaptic plasticity rule produced the best fit with current neurophysiological data on visual cortical plasticity in adult animals (Chino et al., 1992; Pettet & Gilbert, 1992; Darian-Smith & Gilbert, 1995) including (1) the retinal position and shape of the expanding RFs; (2) the corticotopic direction in which responsiveness returns to the silenced cortex; (3) the direction of RF shifts; (4) the amount of change in response to blank stimuli; and (5) the lack of dynamic RF changes during conditioning with a retinal lesion in one eye and the unlesioned eye kept open, in adult animals. The effects of the LISSOM lateral inhibitory synaptic plasticity rule during artificial scotoma conditioning are in conflict with those of the other two LISSOM synaptic plasticity rules. A novel “complementary scotoma” conditioning experiment, in which stimulation of two complementary regions of visual space alternates repeatedly, is proposed to differentiate the predictions of the EXIN and LISSOM rules.

Population-based methods were used to study labeled retinal ganglion cells from the cane toad Bufo marinus and the treefrog Litoria moorei, two visually competent bufonoid neobatrachians with contrasting habitats. In both, cells with large somata and thick dendrites formed distinct types with independent mosaics. The αa, αab, and αc mosaics of Bufo in all major respects resembled those of ranids, studied previously, and could be provisionally matched to the same functional classes. As in other frogs, some αa cells were displaced and many α-cells of all types were asymmetric, but within each type all variants belonged to one mosaic. Nearest-neighbor analyses and spatial correlograms confirmed that all three mosaics were regular and independent. In Litoria, monostratified αa cells were not found. Instead, two bistratified types were present, distinguished individually by soma size and dendritic caliber and collectively by membership of independent mosaics: the larger (∼0.8% of all ganglion cells) was termed α1ab and the smaller (∼2.2%) α2ab. An αc cell type was also present, although too inconstantly labeled for mosaic analysis. Nearest-neighbor analyses and spatial correlograms confirmed that the two αab mosaics were regular and independent. Densities, proportions, soma sizes, and mosaic statistics are tabulated for each species. The emergence of a consensus pattern of α-cell types in fishes and frogs, from which this treefrog partly diverges, offers new possibilities for studying correlations between function, phylogeny, ecology, and neuronal form.