Collagenase Clostridium histolyticum for the pharmacological management of Peyronie's disease.

Peyronie's disease (PD) is defined as the abnormal accumulation of connective tissue in the tunica albuginea of the penis, and is an ongoing physical and psychological challenge for thousands of Americans. In vitro studies in the 1950s uncovered the potential of collagenase Clostridium histolyticum (CCH) to disrupt the collagen-containing plaques in PD, and opened the door to more in-depth clinical trials. Results indicated that with multiple dosage cycles followed by plaque modeling, penile curvature can be corrected, on average, in up to 35% of cases, with the majority of patients achieving ≥ 25% improvement in penile curvature. Most studies also indicated an improvement in patient-reported symptoms from the Peyronie's Disease Questionnaire. Adverse events from treatment with CCH included penile bruising, pain and edema, but most were mild to moderate in severity and usually resolved without intervention, suggesting that CCH is an effective and safe treatment for PD.

Evidence for two distinct mechanisms of neurogenesis and cellular pattern formation in regenerated goldfish retinas.

After its destruction by intraocular injection of ouabain, the goldfish retina regenerates, but little is known about the histogenesis of the new tissue, including the structure and formation of regenerated cell mosaic patterns. In an effort to determine how retinal cells are generated and spatially organized within retina regenerated after ouabain injection, in situ hybridization and immunocytochemical techniques were combined with computational analyses of two-dimensional spatial patterns of identified neurons. Labeling with specific opsin riboprobes revealed two distinct cone patterns in the ouabain-injected eyes, each of which was different from the relatively orderly cone patterns of native retina. Central, regenerated regions had sparse aggregates of cones, and a relatively lower density of each cone type. Peripheral regions of experimental retina, likely derived from the circumferential germinal zone, had high densities of all cone types, each of which tended to be distributed randomly. The spatial patterns of inner retinal neurons in experimental eyes were also disorganized with respect to native retina. These results indicate that although some aspects of retinal regeneration resemble normal retinal development and growth, ouabain-induced regeneration does not produce well-organized mosaics of neurons, indicating a failure of the developmental interactions needed for proper pattern formation, which in turn could compromise visual recovery. Furthermore, the distinct cone patterns in different regions of experimental retina support the hypothesis that new goldfish retina arises via two spatially and cellularly distinct mechanisms after exposure to ouabain.

Metabolic activity in optic tectum during regeneration of retina in adult goldfish.

Retinal and visual function returns following retinal destruction by ouabain in adult goldfish (Carassius auratus). Although the precise cellular mechanisms are unclear, the ability to regenerate CNS neurons and connections that subsequently sustain visual behavior is remarkable, especially for an adult vertebrate. In this paper, we ask whether visual stimulation via new retinal cells can activate existing cells in the optic tectum, which normally receives the largest retinal projection in this species. The right eyes of adult goldfish were injected with ouabain. After 1-18 weeks the conscious, freely moving fish were exposed to spatially and temporally varying visual stimuli and the resulting tectal metabolic activity was determined with the autoradiographic deoxyglucose method. In normal controls without lesions, visual stimulation produced equally strong metabolic activity in both tectal hemispheres, peaking in the layer where most retinotectal projections terminate (N = 6). One week after ouabain injection, metabolic activity in the contralateral, deprived tectum was dramatically reduced (N = 5), closely resembling the effect of unilateral ocular enucleation (N = 5). However, 9-18 weeks after ouabain injection, metabolic activity in the deprived tectum recovered to a level that was statistically indistinguishable from normal controls (N = 6). These findings suggest that, after a comprehensive cytotoxic lesion of the retina, regenerated ganglion cells not only establish new connections with the preexisting optic tectum, but also effectively transmit visual information they receive from newly generated photoreceptors to the "old" tectum.

Morphology and visual pigment content of photoreceptors from injured goldfish retina.

Adult teleost fish retinas can regenerate neurons following either surgical or pharmacological injury. The cellular milieu of the damaged retina within which regenerated neurons are produced might be different in these two model systems of retinal injury, and thus the phenotypic attributes of regenerated neurons in the two model systems might also differ. To determine if the phenotypic attributes of photoreceptors, and by extension the recovery of vision, are different between these two model systems, we compared the visual pigment content and morphology of photoreceptors derived from goldfish retinas of both models with control retina. Visual pigments-which consist of a protein moiety (opsin) and a chromophore--were analyzed in single, isolated photoreceptors using microspectrophotometric techniques. We report that visual pigments and photoreceptor morphologies in the surgical model closely matched those of native retina. In contrast, neither photoreceptor morphology nor visual pigment content matched closely in the pharmacological model. The results indicate that phenotypic attributes of photoreceptors can differ significantly between the two model systems of retinal regeneration, but that in both systems, rod- and cone-mediated visual functions can potentially be reestablished.

Visual function in regenerating teleost retina following cytotoxic lesioning.

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.

Effects of mean luminance on goldfish temporal contrast sensitivity.

The goldfish is an important animal model for retinal processing and for understanding the relationship between retinal structure and function. The purpose of this study was to examine the temporal processing of the visual system of this species. Goldfish were classically conditioned to suppress respiration upon presentation of a sinusoidally flickering stimulus. Temporal contrast sensitivity functions (T-CSFs) were determined by measuring contrast threshold at a variety of temporal frequencies across different mean luminances. Goldfish T-CSFs were found to be similar in shape to those of humans. In addition, as the mean luminance of the stimulus decreased, temporal resolution decreased. This implies that the animal's ability to detect high flicker frequencies decreases as the level of light adaptation decreases, as does that of humans. The results support the notion that temporal processing is similar across vertebrate species, and therefore that the goldfish is a useful model for studying temporal processing in the vertebrate retina.

Limulus vision in the ocean day and night: effects of image size and contrast.

Male horseshoe crabs, Limulus polyphemus, use their eyes to locate mates day and night. We investigated their ability to detect targets of different size and contrast in a mating area of Buzzards Bay, Cape Cod, MA. We found that males can see large, high-contrast targets better than small, low-contrast ones. For targets of the same size, animals must be about 0.1 m closer to a low-contrast target to see it as well as a high-contrast one. For targets of the same contrast, animals must be approximately 0.2 m closer to a small target to see it as well as one twice as large. A decrease of 0.05 steradians in the size of the retinal image of a target can be compensated by a four-fold increase in contrast. About 60% of the animals detect black targets subtending 0.110 steradians (equivalent to an adult female viewed from about 0.56 m), while only 20% detect targets subtending 0.039 steradians. This study shows that horseshoe crabs maintain about constant contrast sensitivity under diurnal changes in light intensity in their natural environment. As a consequence of circadian and adaptive mechanisms in the retina, male horseshoe crabs can detect female-size objects about equally well day and night.

The contributions of ON- and OFF-pathways to contrast sensitivity and spatial resolution in goldfish.

DL-2-amino-4-phosphonobutyric acid (APB) reduces the sensitivity of ON- and OFF-responses in goldfish retina, although the ON-responses are reduced significantly more than the OFF-responses. This paper describes the effects of APB on behavioral sensitivity of goldfish to spatial sinusoidal gratings. Fish were classically conditioned to suppress respiration upon presentation of gratings drifting at 1 Hz; contrast thresholds were measured by an observer-based two-alternative forced-choice procedure. Thresholds were repeated following intraocular injections of APB or physiological saline. Saline had no effect, but APB dramatically reduced contrast sensitivity and shifted contrast sensitivity functions to lower spatial frequencies. The results suggest that both ON- and OFF-pathways are necessary for normal spatial vision and that the effects of APB are consistent with the disruption of both ON- and OFF-pathways.

APB alters photopic spectral sensitivity of the goldfish retina.

Because the glutamate analog 2-amino-4-phosphonobutyric acid (APB) alters synaptic transmission at the outer plexiform layer in goldfish we asked whether intraocular injection of ABP would alter the spectral sensitivity of the retina. The spectral sensitivity of the ON and OFF components of the optic nerve response (ONR) in goldfish was measured in the presence and absence of APB, under four chromatic adaptation condition. APB decreased absolute sensitivity and altered spectral sensitivity for both ON and OFF responses under each adaptation condition. The spectral sensitivity of the OFF response was altered most at short wavelengths, in a manner consistent with a change in the balance of additive cone inputs. For the ON response, the effects of APB were consistent with a change in spectral antagonism, particularly between M- and L-cones. These results suggest that the activity in the retinal cone pathways in goldfish can be influenced by a mechanism incorporating an APB-sensitive receptor, and that this receptor may be intimately involved with setting the balance of cone inputs to spectrally-opponent neurons.

Visual performance of horseshoe crabs day and night.

A circadian clock modulates the structure and function of the lateral eyes of Limulus polyphemus, greatly increasing their sensitivity at night. During the mating season, male Limulus are visually attracted both day and night to females and objects that resemble females. This paper asks how well Limulus can see day and night, and whether the circadian changes in retinal sensitivity might influence the ability of these animals to find mates. We recorded the visual behavior of male and female horseshoe crabs in the vicinity of an object--a cement hemisphere (29.5 cm diameter) similar in size and shape to a female horseshoe crab--placed in a mating area near Mashnee Dike, Bourne, Massachusetts. Males oriented toward this target from an average distance of 0.94 m during the day and 0.88 m at night; and females appeared to avoid the target. We conclude that males can see potential mates at night almost as well as they can during the day. Apparently the circadian changes in the retina help compensate for the daily changes in illumination in the animal's normal environment. This study provides the first evidence for a role of visual circadian rhythms in an animal's natural behavior.

DL-2-amino-4-phosphonobutyric acid does not eliminate "ON" responses in the visual system of goldfish.

DL-2-Amino-4-phosphonobutyric acid (APB) suppresses activity in retinal ON pathways. It is generally assumed that loss of the ON pathway would result in loss of ON responses in the visual system. We tested this assumption by recording activity from the optic nerves of intact goldfish (Carassius auratus) before and after intraocular injection of APB. Whole-nerve responses to increments and decrements of light were compared to electroretinogram responses and to tectal evoked potentials. APB severely reduced the amplitude of the electroretinogram b-wave but left ON and OFF responses from the optic nerve and tectum intact, although decreased in sensitivity. We conclude that APB does not completely eliminate ON responses in the visual system, at least in goldfish. The selectivity and effectiveness of APB must be evaluated in other species before this agent can be relied upon as a useful tool in understanding the roles of ON and OFF pathways in visual function.

Spectral sensitivity of ON and OFF responses from the optic nerve of goldfish.

The vertebrate retina processes visual information in parallel neural pathways known as the ON and OFF pathways. These pathways encode increments and decrements of light independently as excitatory responses. We examined the photopic spectral response of ON and OFF mechanisms in goldfish by measuring the sensitivity of optic nerve responses to the onset and termination of stimuli of various wavelengths. Using various adapting backgrounds, we found that the ON and OFF responses have different spectral sensitivities. The weighting of the cone inputs to the responses was estimated by an algebraic summation model. This model suggests that for the ON response, input from S-cones is stronger and more independent than for the OFF response, and M- and L-cones show stronger antagonism in the ON response than in the OFF response. The OFF response probably receives input from all cone types, but spectral antagonism is weak and its dominant input is from L-cones.

Spatial contrast sensitivity of goldfish: mean luminance, temporal frequency and a new psychophysical technique.

Behavioral contrast sensitivity in goldfish was examined at various mean luminances and stimulus drift rates. Goldfish were classically conditioned to suppress respiration upon presentation of a drifting sinusoidal grating. Contrast threshold at each spatial frequency was determined by means of a new two-alternative forced-choice procedure in which the observer's decision about the presence of the stimulus was based on the animal's respiration pattern. The results show that: (1) as mean luminance decreases, contrast sensitivity to high spatial frequencies decreases and peak sensitivity shifts to lower spatial frequencies; (2) as drift rate increases, contrast sensitivity to low spatial frequencies increases, but sensitivity to high spatial frequencies is relatively unaffected by stimulus drift rate. Both the mean luminance and temporal frequency of the stimulus clearly influence the behavioral contrast sensitivity of the goldfish in ways that would be predicted from behavioral results from other species. We conclude that the mechanisms that mediate contrast sensitivity in goldfish are similar to those that mediate contrast sensitivity in other vertebrates.

Shedding of rod outer segments is light-driven in goldfish.

Rod outer segment (ROS) shedding in goldfish was quantified by measuring the number of phagosomes in the retinas of goldfish that were maintained under natural or artificial cyclic light, constant light, or constant dark conditions. Fish maintained in cyclic light, whether natural or artificial, had robust daily rhythms of ROS shedding. The ROS tips were shed primarily during the light phase of the cycle, and maximum shedding occurred 2-4 hours into the light period. Fish maintained for 1, 3, or 7 days in constant light or constant dark had no daily rhythms in ROS shedding. In these fish, ROSs lengthened, on average, 2.3 microns/day in constant light and 1.5 microns/day in constant dark. After 3 days in constant light, shedding was induced by placing fish in darkness for 2 hours, then returning them to light. Placing fish in darkness for 0.5 hours did not induce shedding, nor did placing them in darkness for 3 hours without returning them to light. ROS shedding thus appears to be goldfish is completely dependent on changes in ambient illumination; no circadian or endogenous components were found. Previous observations of circadian changes in behavioral visual sensitivity therefore cannot be due to endogenous changes in ROS length.

Rod outer segment length and visual sensitivity.

Detection threshold for the rod system was measured psychophysically in adult goldfish before and after exposure to constant illumination of 340 lux (91 microW/cm2) for 7 days. As shown in the previous paper, rod outer segment (ROS) length increases an average of 60% under these conditions. The present work shows that visual sensitivity also increases, in approximate proportion to the additional optical density predicted by the longer ROSs. These results are the first to show that exposure to constant light can enhance visual sensitivity. They imply further that detection threshold is related to ROS length. Apparently, the photopigment in the ROS tips that is normally shed on a daily basis retains its photon-catching ability.

Sensitivity of ERG components from dark-adapted goldfish retinas treated with APB.

The electroretinogram (ERG) of the dark-adapted goldfish was examined before and after intravitreal injection of DL-2-amino-4-phosphonobutyric acid (APB). APB abolished the b-wave and decreased absolute sensitivity of the remaining waveform, which was composed of a vitreal-negative component followed by a vitreal-positive component. The sensitivity, time course and amplitude of these components differed from ERGs obtained from animals treated with sodium aspartate. Spectral sensitivity of both post-APB components closely resembled that of the normal dark-adapted b-wave. The results suggest that APB does not act selectively on any particular class of photoreceptors or photoreceptor pathways in the dark-adapted goldfish retina.

APB selectively reduces visual responses in goldfish to high spatiotemporal frequencies.

Visual responses of goldfish to rotating square-wave gratings were recorded before and after intraocular injection of 2-amino-4-phosphonobutyric acid (APB). High doses of APB reduced the rate of optokinetic nystagmus (OKN) to a relatively high spatial frequency grating moving at a high temporal frequency. Responses to a low spatial frequency grating were not altered, nor were responses to the higher spatial frequency when it rotated slowly. The effects of APB were transient and lasted no longer than 3 d. We conclude that APB reduces OKN to high spatiotemporal frequencies in goldfish.