Observations on the retina and 'optical fold' of a mesopelagic sabretooth fish, Evermanella balbo.

The 'optical fold' of Evermanella balbo covers the ventro-lateral cornea and is presumed to capture illumination that would otherwise remain undetected by the tubular eye of this mesopelagic teleost. It contains alternating bands of cellular and acellular material, running approximately perpendicular to the lateral surface of the eye. Only parts of this lamellar body lie within the eyelid-like structure. The cellular lamellae are 2-2.5 µm thick centrally and composed of fibroblast-like cells. The extracellular bands (4.5-5 µm thick) contain regular arrays of collagen fibrils, with layers of thin fibrils sandwiching a region of thicker fibrils. The thin fibrils are organised in alternating sheets where fibrils, although all parallel, change their orientation by 90° between each sheet. All thick fibrils are oriented parallel to the lateral surface of the 'optical fold'. In the main retina, small bundles of rod inner/outer segments are separated by the processes of the retinal pigment epithelium (rpe) laterally. Centrally, the length of tightly packed rods increases, but rpe processes no longer divide them into bundles. Medially, rod length increases further, but packing is less dense. The accessory retina is significantly thinner, and less well-developed than the main retina. Ventrally, the rods show no regular arrangement and are not grouped. Dorsally, however, rods are arranged into bundles, separated by melanosome-filled rpe processes. The thickness of the retina increases as it approaches the crystalline lens. It is on this dorsal accessory retina that light traversing the 'optical fold' most likely falls, facilitating the detection of moving objects in the ventro-lateral field of view.

[Image-guided pain therapy. Sympathicolysis]. / Bildgestützte Schmerztherapie. Sympathikolyse.

BACKGROUND: In the autonomic nerve system most sympathetic neurons synapse peripherally in the ganglia of the sympathetic trunk. A reduction in sympathicotonia by partial elimination of these ganglia is a therapeutic approach that has been used for more than 100 years. In the early 1920s the first attempts at percutaneous sympathicolysis (SL) were carried out. Nowadays, minimally invasive image-guided SL has become an integral part of interventional radiology. Established indications for SL are hyperhidrosis, critical limb ischemia and the complex regional pain syndrome. METHODS: The standard imaging guidance modality in SL is computed tomography (CT) which allows the exact placement of the puncture needle in the target area under visualization of the surrounding structures. Ethanol is normally used for chemical lysis, which predominantly eliminates the unmyelinated autonomic axons. In order to visualize the distribution of the ethanol during application, iodine-containing contrast medium is added. RESULTS: The sympathetic nervous system (SNS) controls sweat secretion via the efferent neurons; therefore, effective therapy of idiopathic palmar, axillary and plantar hyperhidrosis can be achieved when SL is performed at the corresponding level of the sympathetic trunk. Furthermore, due to the vasomotor innervation of most blood vessels, by reduction of the sympathicotonus an atony of the smooth muscles and therefore vasodilatation occurs, which is used as a palliative therapeutic option in patients with critical limb ischemia. By elimination of the afferent sensory fibers this also results in pain relief. This principle is also used in the SL therapy of the complex regional pain syndrome. CONCLUSION: After the introduction of CT guidance, major complications have become rare events. In addition to the usual risks of percutaneous interventions there are, however, a number of specific complications, such as syncope caused by irritation of cardiac sympathetic nerves in thoracic SL and ureteral injury in lumbar SL.

Reflecting optics in the diverticular eye of a deep-sea barreleye fish (Rhynchohyalus natalensis).

We describe the bi-directed eyes of a mesopelagic teleost fish, Rhynchohyalus natalensis, that possesses an extensive lateral diverticulum to each tubular eye. Each diverticulum contains a mirror that focuses light from the ventro-lateral visual field. This species can thereby visualize both downwelling sunlight and bioluminescence over a wide field of view. Modelling shows that the mirror is very likely to be capable of producing a bright, well focused image. After Dolichopteryx longipes, this is only the second description of an eye in a vertebrate having both reflective and refractive optics. Although superficially similar, the optics of the diverticular eyes of these two species of fish differ in some important respects. Firstly, the reflective crystals in the D. longipes mirror are derived from a tapetum within the retinal pigment epithelium, whereas in R. natalensis they develop from the choroidal argentea. Secondly, in D. longipes the angle of the reflective crystals varies depending on their position within the mirror, forming a Fresnel-type reflector, but in R. natalensis the crystals are orientated almost parallel to the mirror's surface and image formation is dependent on the gross morphology of the diverticular mirror. Two remarkably different developmental solutions have thus evolved in these two closely related species of opisthoproctid teleosts to extend the restricted visual field of a tubular eye and provide a well-focused image with reflective optics.

Synthetic biology as driver for the biologization of materials sciences.

Materials in nature have fascinating properties that serve as a continuous source of inspiration for materials scientists. Accordingly, bio-mimetic and bio-inspired approaches have yielded remarkable structural and functional materials for a plethora of applications. Despite these advances, many properties of natural materials remain challenging or yet impossible to incorporate into synthetic materials. Natural materials are produced by living cells, which sense and process environmental cues and conditions by means of signaling and genetic programs, thereby controlling the biosynthesis, remodeling, functionalization, or degradation of the natural material. In this context, synthetic biology offers unique opportunities in materials sciences by providing direct access to the rational engineering of how a cell senses and processes environmental information and translates them into the properties and functions of materials. Here, we identify and review two main directions by which synthetic biology can be harnessed to provide new impulses for the biologization of the materials sciences: first, the engineering of cells to produce precursors for the subsequent synthesis of materials. This includes materials that are otherwise produced from petrochemical resources, but also materials where the bio-produced substances contribute unique properties and functions not existing in traditional materials. Second, engineered living materials that are formed or assembled by cells or in which cells contribute specific functions while remaining an integral part of the living composite material. We finally provide a perspective of future scientific directions of this promising area of research and discuss science policy that would be required to support research and development in this field.

Posaconazole salvage treatment in paediatric patients: a multicentre survey.

While a paediatric dosage has not been defined, posaconazole is occasionally being used in children. We conducted a multicentre retrospective survey and identified 15 patients (median age 10 years [range 3.6-17.5]) who received posaconazole salvage therapy for proven (9 patients) or probable (6 patients) invasive fungal infections. Posaconazole was administered for a median of 32 days (range 4-262) at a median dosage of 21 mg/kg (range 4.8-33.3). None of the patients discontinued therapy due to adverse events, which were mostly mild and observed in 11 patients. Complete or partial responses were observed in 4/7 patients with zygomycosis, 3/4 patients with invasive mould infection, 1/2 patients with invasive aspergillosis and 1/2 patients with chronic disseminated candidiasis. We conclude from the data that posaconazole displays favourable safety and tolerance and may be useful for management of individual paediatric patients with invasive infections.

An inflammatory myofibroblastic tumor of the stomach as a rare cause of gastric outlet obstruction in an 8-month-old infant.

Inflammatory myofibroblastic tumors (IMT) are a rare entity. Localization in the stomach is extremely seldom and almost exclusively seen in children. Invasive growth of IMT may lead to irresectability or recurrence. In an 8-month-old girl presented with repetitive vomiting for several days. Complete surgical resection of a gastric IMT was possible.

Goldfish retina: a correlate between cone activity and morphology of the horizontal cell in clone pedicules.

In the cone pedicules, the digitations of horizontal cell process lateral to the synaptic ribbon disappear after dark adaptation. This disappearance is correlated with the loss of color opponency and cone function shown in ganglion cell recordings in isolated retinas. Cone function and color-opponent responses are restored by reapplying background light.

[Periinterventional prophylactic antibiotics in radiological port catheter implantation]. / Periinterventionelle prophylsktische Antobiotikagabe bei der radiologischen Portkatheterimplantation.

PURPOSE: To evaluate whether catheter-related infections after radiologically placed port catheters can be reduced by single-shot periinterventional antibiosis. MATERIALS AND METHOD: Between January and September 2002, 164 consecutive patients with indication for central venous port catheter implantation were included in the present study. During implantation the interventional radiologist was responsible for deciding whether to administer a prophylactic single-shot antibiosis. The prophylactic antibiosis entailed intravenous administration of ampicillin and sulbactam (3 g Unacid, Pfizer) or 100 mg ciprofloxacine (Ciprobay, Bayer) in the case of an allergy history to penicillins. Catheter-related infection was defined as a local or systemic infection necessitating port catheter extraction. RESULTS: Indication for port catheter implantation was a malignant disease requiring chemotherapy in 158 cases. The port catheter (Chemosite [Tyco Healthcare] [n = 123], low-profile [Arrow International] [n = 35], other port system [n = 6]) was implanted via sonographically guided puncture of the right jugular vein in 139 patients, via the left jugular vein in 24 cases and via the right subclavian vein in one patient. 75 patients received periinterventional prophylactic antibiosis (Unacid [n = 63] Ciprobay [n = 12]) and 89 patients did not receive antibiosis. The prophylactic antibiosis caused a minor allergic reaction in one patient that improved with antihistamic and corticoid medication. A total of 7 ports, 6 without prophylactic antibiosis versus one with periinterventional prophylaxis, were extracted due to infectious complications. CONCLUSION: Single-shot periinterventional prophylactic antibiosis can reduce early and late infectious complications after radiological-interventional placement of central venous port catheters.

[Long-term results after balloon angioplasty of the crural artery]. / Langzeitergebnisse nach Ballonangioplastie kruraler Arterien.

PURPOSE: To evaluate the technical success rate, procedure-related complications, and clinical long-term results for patients who underwent infrapopliteal angioplasty. MATERIALS AND METHODS: We retrospectively evaluated all patients who underwent infrapopliteal angioplasty to treat critical chronic limb ischemia or severe claudication from 1/1997 to 12/1999. We excluded patients with acute (< 2 weeks) limb ischemia. Procedure-related data were prospectively documented in a database and analyzed with a focus on the technical success rate and procedure-related complications. In addition all clinical documents were analyzed, and a follow-up examination was performed or telephone interviews were conducted with patients, relatives and referring doctors for follow-up. The primary end points were the limb salvage rate and patient survival rate. The secondary end points included the complication rate, technical success rate, and walking distance. RESULTS: 112 patients with a mean age of 72 years (41 women, 71 men) underwent crural angioplasty on 121 limbs. Four patients suffered from severe claudication (Rutherford category 3) and all others had critical chronic limb ischemia (category 4 to 6). The complication rate was 2.7 %. The technical success rate was 92 %. The ankle brachial index increased from 0.59 to 0.88. The mean walking distance increased significantly from 52 +/- 66 to 284 +/- 346 meters at the time of follow-up. The limb salvage rate was 83.6 % after one year and 81.1 % after three years. The mean survival rate according to Kaplan-Meier was 79.4 %, 69.2 %, and 54.2 % at 1, 2, and 3 years, respectively. Patients with at least one patent run-off vessel after angioplasty had a significantly better limb salvage rate. Diabetes was not a risk factor for limb salvage. CONCLUSION: Infrapopliteal angioplasty shows a high technical success rate with an acceptable complication rate. The clinical long-term success seems favorable if a least one open run-off vessel was able to be achieved. However, the survival rate was limited by the co-morbidity in this patient group.

[Peripheral arterial obstruction and acute lower limb ischemia]. / Periphere arterielle Verschlusskrankheit und akute Extremitätenischämie.

In this article, current evidence-based treatment recommendations for acute and chronic lower limb ischemia will be presented considering the varied possibilities of endovascular techniques and open surgical vascular strategies. Beside presentation of the different therapeutic possibilities, advantages of the combination of both techniques will be described. Despite the BASIL trial, there are no prospective randomised controlled trials comparing endovascular and open surgical interventions. Different therapeutic rules along the different vascular segments will be discussed for both acute and chronic peripheral arterial disease. Generally it can be stated that aortoiliac revascularization for chronic obstructions is increasingly being carried out by endovascular means or hybrid procedures using a minimally invasive femoral approach, whereas acute occlusions in this vascular segment are still treated with open surgical techniques (Fogarty balloon thrombectomy). In the infrainguinal region, endovascular therapeutic strategies are gaining favor. However, multilevel occlusions and long-segment obstructions in the femoral and popliteal segment are still treated by bypass procedures. Acute ischemia in the infrainguinal segment is increasingly treated with endovascular methods (local thrombolysis and percutaneous thrombectomy).

Spinules: a case for retinal synaptic plasticity.

In both vertebrate and invertebrate nervous systems, a population of synapses is characterized by having finger-like indentations of the postsynaptic membrane that project into the presynaptic terminal. These 'spinules' are often transitory structures, and their presence has been associated with increased synaptic activity. We have studied the functional role of spinules in the fish retina, where they are observed in horizontal cells invaginating cone pedicles, and in synaptic terminals of bipolar cells. In the cone-horizontal cell synaptic complex, spinules are present during light adaptation; their formation is triggered by external light stimuli as well as by endogenous factors. Pharmacologically, spinules are degraded following an increase, and formed in response to a decrease of the transmitter glutamate released by the cone cells. Dopamine, released by interplexiform cells and acting via a D1 receptor-mediated increase in cAMP, and a protein-kinase-C-based mechanism are also capable of inducing spinule formation. Functionally, the presence and absence, as well as the timecourse, of spinule formation during light adaptation is closely correlated with the development of biphasic chromatic responses in a class of cone horizontal cells and the manifestation of colour-opponency in ganglion cells. This suggests that in the outer retina of fish, spinules are mediating feedback activity essential for the coding of antagonistic colour information.

Effect of astroglial cell swelling on pH of acidic intracellular compartments.

A variety of pathological conditions lead to swelling of astrocytes, which in turn stimulates ion release by activation of ion channels at the plasma membrane. In the present study, acridine orange and fluorescein isothiocyanate coupled to dextran (FITC-dextran) have been used to examine the effect of cell swelling on pH in acidic compartments of cultured astroglial cells. Both NH4Cl (2 mM) and chloroquine (10 microM), known to alkalinize acidic cellular compartments, led to the expected increase in acridine orange fluorescence intensity. Similar, albeit smaller, effects were elicited by a reduction of extracellular osmolarity (-80 mOsm) and treatment of the cells with glutamate (l mM), manoeuvres which enhanced cell volume. Determination of changes in the FITC-dextran fluorescence ratio (485/440 nm) allowed quantification of the pH changes in lysosomal compartments. Treatment with NH4Cl, reduced extracellular osmolarity and glutamate increased lysosomal pH by 0.65 +/- 0.07, 0.85 +/- 0.14 and 0.25 +/- 0.07, respectively. Measurement of cytosolic pH using 2',7',-bis-(2-carboxyethyl)-5- (and -6) carboxyfluorescein (BCECF) demonstrated a pronounced acidification following cell swelling, observed with both reduced extracellular osmolarity (by 0.23 +/- 0.05 pH units) and 1 mM glutamate (by 0.26 +/- 0.02 pH units). In conclusion, pH within lysosomes and possibly other acidic cellular compartments of astrocytes is increased by cell swelling, which may have important consequences for astrocyte function.

Dose finding with a novel recombinant plasminogen activator (BM 06.022) in patients with acute myocardial infarction: results of the German Recombinant Plasminogen Activator Study. A study of the Arbeitsgemeinschaft Leitender Kardiologischer Krankenhausärzte (ALKK).

OBJECTIVES: The aim of this study was to determine the appropriate dose of a novel recombinant tissue-type plasminogen activator (BM 06.022) for thrombolysis in patients with acute myocardial infarction. BACKGROUND: BM 06.022 is a mutant of tissue-type plasminogen activator expressed in Escherichia coli that can be given as a single bolus because of a prolonged half-life, which might obviate the need for complicated regimens. METHODS: BM 06.022 given as a single bolus was investigated in 142 patients in a multicenter sequential dose-finding study. Efficacy of the drug was assessed from infarct-related artery patency by coronary angiography. RESULTS: With the first dose of 10 MU of BM 06.022, the predefined minimal 90-min patency of 70% was not achieved, as indicated by the sequential probability ratio test after treatment of 42 patients (group A). The second dose of 15 MU of BM 06.022 was given subsequently in the preset maximum of 100 patients (group B). Angiography 30, 60 and 90 min after the bolus injection of BM 06.022 revealed a patent infarct-related artery (Thrombolysis in Myocardial Infarction trial [TIMI] grade 2 or 3) in 65% and 66%, 73% and 74% and 66% and 75% of patients in groups A and B, respectively. Very early reocclusion up to the 90-min angiogram occurred in 17% and 13%, late reocclusion until predischarge angiography occurred in 7% and 5%, and rescue percutaneous transluminal coronary angioplasty after the 90-min angiogram was performed in 6 and 14 patients in groups A and B, respectively. Plasma fibrinogen decreased from 2.79 g/liter (range 0.94 to 4.75) to 1.69 g/liter (range 0.0 to 3.95) in group A and from 2.54 g/liter (range 0.0 to 5.02) to 0.92 g/liter (range 0.0 to 2.68) in group B. Two bleeding complications requiring transfusion or surgical intervention and one nonfatal intracranial hemorrhage were encountered. Eight patients had a reinfarction, and five patients died, all of cardiac causes. CONCLUSIONS: With BM 06.022 given as a single bolus, a high early patency rate of the infarct-related coronary artery can be achieved. The speed of thrombolysis seems to be superior to standard thrombolytic drugs. The compound warrants further evaluation with respect to safety and efficacy by clinical end points.

The eyes of deep-sea fish. II. Functional morphology of the retina.

Three different aspects of the morphological organisation of deep-sea fish retinae are reviewed: First, questions of general cell biological relevance are addressed with respect to the development and proliferation patterns of photoreceptors, and problems associated with the growth of multibank retinae, and with outer segment renewal are discussed in situations where there is no direct contact between the retinal pigment epithelium and the tips of rod outer segments. The second part deals with the neural portion of the deep-sea fish retina. Cell densities are greatly reduced, yet neurohistochemistry demonstrates that all major neurotransmitters and neuropeptides found in other vertebrate retinae are also present in deep-sea fish. Quantitatively, convergence rates in unspecialised parts of the retina are similar to those in nocturnal mammals. The differentiation of horizontal cells makes it unlikely that species with more than a single visual pigment are capable of colour vision. In the third part, the diversity of deep-sea fish retinae is highlighted. Based on the topography of ganglion cells, species are identified with areae or foveae located in various parts of the retina, giving them a greatly improved spatial resolving power in specific parts of their visual fields. The highest degree of specialisation is found in tubular eyes. This is demonstrated in a case study of the scopelarchid retina, where as many as seven regions with different degrees of differentiation can be distinguished, ranging from an area giganto cellularis, regions with grouped rods to retinal diverticulum.

An authentic malignant epithelioid hemangioendothelioma of the thyroid: a case report and review of the literature.

Hemangioendotheliomas of the thyroid are neoplasms that are rarely encountered in the Alpine region in Europe. The endemic goiter in this iodine-deficient region can be considered as a predisposing factor. We report the second case of an epithelioid hemangioendothelioma (EHE) of the thyroid gland and the first clinical case with malignant behavior. A 73-year-old woman with a long history of multinodular goiter presented with a rapidly growing thyroid mass, free of distant metastases. A total thyroidectomy was performed. Histologically the lesion had characteristic epithelioid and spindle cell proliferation in a background of chondromyxoid stroma. Cytoplasmic vacuolization in the epithelioid and spindle cells were present. Tumor cells were positive for factor VIII-related antigen, MNF116, PAN-ceratin, CD 34, and CD 31 and negative for cytokeratin allowing the diagnosis of EHE. Nine months after the primary resection the tumor locally recurred. A palliative resection was performed in a second operation followed by interferon-alpha therapy. The patient rapidly developed a second local relapse and died 13 months after the diagnosis of an EHE had been made. An improvement of the very poor prognosis of this rare tumor may depend on early tumor diagnosis and surgery combined with a multimodal treatment.

[Contrast media pressure injection using a portal catheter system--results of an in vitro study]. / Kontrastmitteldruckinjektion in Portkathetersysteme -- Ergebnisse einer In-vitro-Studie.

PURPOSE: Are implanted central venous port catheters suitable for contrast media pressure (power) injection in computed tomography? MATERIAL AND METHODS: In an in vitro study 100 ml of contrast medium (Ultravist 370, Schering, Berlin, Deutschland) was injected through 20 different port catheter systems using a power injector (Stellant, Medrad, Inianola, USA) with a pressure limit of 325 PSI. The injection rate was increased from 2 ml/s to 10 ml/s in increments of 2 ml/s. The maximum injection pressure and maximum injection rate were assessed. RESULTS: An injection rate of 2 ml/s was possible in all catheter systems. Injection rates of 4 ml/s in 18 systems, 6 ml/s in 13 systems and 8 ml/s in 6 systems were achieved. With a given pressure limit of 325 PSI an injection rate of 10 ml/s was not possible in any of the port catheter systems. There were no catheter ruptures, catheter disconnections or contrast extravasations noted. CONCLUSION: Power injection of contrast media with a pressure limit of 325 PSI seems to be tolerated by port catheter systems. Most of the evaluated port systems allow flow rates suitable for multislice computed tomography requiring rapid contrast injection.

Relation of retinomotor responses and contractile proteins in vertebrate retinas.

Photoreceptors of many nonmammalian vertebrate species display pronounced light-dependent movements which are absent in mammalian species. In order to further analyze the molecular basis of receptor movements and of simultaneous migration of melanin granules in pigment epithelial processes, we investigated the distribution of actin, myosin and the actin-binding muscular proteins alpha-actinin and vinculin in the retina of various vertebrate species. The species investigated can be divided in two groups (i) those possessing retinomotor capacity (fish, frog, turtle, chick) and (ii) those in which retinomotor activities are negligible or absent (gecko, mouse, rat). Prominent bundles of actin filaments extending throughout the long axis of photoreceptor inner segments were only found in species possessing retinomotor capacity, while comparable actin filament bundles were absent or poorly developed in photoreceptors of species lacking significant retinomotor capacity. In all species examined, a well developed circumferential band of actin filaments was associated with the zonula adhaerens-like junctions between photoreceptors and Müller (glial) cells forming the external limiting membrane. This area was also identified as the exclusive site of myosin, alpha-actinin and vinculin (only in the chick, alpha-actinin-like immunoreactivity was also found along the photoreceptor actin filament bundles). Thus, the external limiting membrane may be important for both structural support and for providing a possible site of filament sliding for photoreceptor movements. In pigment epithelium actin, myosin, alpha-actinin and vinculin were concentrated circumferentially in the area of the terminal bar which has been previously shown to be contractile. In all species apical pigment-epithelial processes displayed actin-like fluorescence of varying intensities. Another site of actin-like staining were photoreceptor synaptic complexes which represent a well known site for synaptic plasticity. Immunoblotting studies on the avascular chick retina revealed polypeptide bands at Mr approximately 130 000, approximately 100 000, and 42 000 which were specific for vinculin, alpha-actinin and actin, respectively. A faint polypeptide band comigrating with thymus myosin heavy chain indicates myosin to be only a minor component of the retina (chick and fish).

GABA and tyrosine hydroxylase immunocytochemistry reveal different patterns of colocalization in retinal neurons of various vertebrates.

Colocalization of GABA- and tyrosine hydroxylase-like immunoreactivity was studied in the retinae of various vertebrate species in order to ascertain whether the presumed coexistence of GABA and dopamine, reported earlier for mammals (Kosaka et al.: Exp. Brain Res. 66:191-210, '87: Wässle and Chun: J. Neurosci. 8:3383-3394,'88) is a common phenomenon. GABA-immunopositive cells constituted a separate population from tyrosine hydroxylase-positive cells in fish and amphibians, whilst in higher--i.e., amniote--vertebrates, such as reptiles, birds, and mammals, all dopaminergic cells contained GABA-like immunoreactivity. No clear correlation was found between the type of dopaminergic cell (amacrine/interplexiform) and the presence or absence of colocalization.

Incorporation of 3H-fucose into nerve and glial cells: assessment by electron microscopic autoradiography.

Incorporation of 3H-fucose into hypothalamic tissue of rats was studied between ten minutes and seven days after intraventricular injection. In EM autoradiographs grain densities over perikarya of neurons, astro-, and oligodendroglia, and neuropil were evaluated. Grain densities were consistently higher over both types of glial cells as compared to neurons. The glia/neuron ratio was especially high after short experimental intervals and declined with increasing time intervals. Concomitantly there was an increase of grain density over the neuropil. The discussion concentrates on the methodical aspects which have to be considered in interpreting the autoradiographic data. It is concluded that both astroglia and oligodendroglia exhibit a considerably higher synthesis rate of glycoproteins per unit volume than nerve cells. The implications of the results for the interpretation of biochemical data on glycoprotein metabolism of brain tissue are discussed.

Localization of D2 dopamine receptors in vertebrate retinae with anti-peptide antibodies.

Dopamine plays an important role in modulating various aspects of retinal signal processing. The morphology of dopaminergic neurons and its physiological effects are well characterized. Two classes of receptor molecules (D1 and D2) were shown pharmacologically to mediate specific actions, with differences between individual groups of vertebrates. In an attempt to better understand dopaminergic mechanisms at the cellular level, we used antisera against D2 receptors and investigated the localization of the dopamine D2 receptor in the retinae of rat, rabbit, cow, chick, turtle, frog, and two fish species with immunofluorescence techniques. Antisera were raised in rabbits to two oligopeptides predicted from rat D2 receptor cDNA; one specific for the splice-variant insertion in the third cytoplasmic loop and the other directed towards the extracellular amino terminal region shared by both short and long isoforms. Preadsorption with the synthetic peptide resulted in a significant reduction of label, indicating the presence of specific binding in all species except turtle and goldfish. The pattern of labelling produced by the two antisera was essentially identical; however, the staining obtained with antiserum to the extracellular motif was always more intense. Specific staining was present in photoreceptor inner and outer segments, and in the outer and inner plexiform layers of all species. In mammals and chick, strongly fluorescent perikarya were observed in the ganglion cell layer and at the proximal margin of the inner nuclear layer. Label may be present in the pigment epithelium but could not be established beyond doubt. This pattern of labelling is in accordance with previous observations on D2 receptor localization by means of radioactive ligand binding and in situ hybridization techniques. It suggests that retinal dopamine acts as a neuromodulator as well as a transmitter. In the distal retina, it may reach its targets via diffusion over considerable distances, even crossing the outer limiting membrane; in the inner and outer plexiform layers, conventional synaptic transmission seems to coexist with paracrine addressing of more distant targets, and D2 receptors are expressed by both amacrine and ganglion cells.