Sedoanalgesia for cardioversion: comparison of alfentanil, remifentanil and fentanyl combined with propofol and midazolam: a prospective, randomized, double-blind study.

OBJECTIVE: Electrical cardioversion (EC) is a short but painful procedure to restore sinus rhythm. The aim of this study is to compare the effect of fentanyl, remifentanil and alfentanil in association with propofol and midazolam for elective EC. PATIENTS AND METHODS: Ninety-nine patients older than 18-years, American Society of Anesthesiologists I/II/III grades undergoing elective EC were randomized into 3 groups. All patients received 2 mg midazolam and propofol (0.5 mg/kg). Group A received alfentanil (5 µg/kg i.v. bolus), Group F received fentanyl (0.5 µg/kg i.v. bolus) and Group R received remifentanil (0.25 µg/kg i.v. bolus). Hemodynamics and respiratory variables [Heart rate (HR), systolic blood pressure (SBP), diastolic blood pressure (DBP), mean arterial pressure (MAP), SpO2, respiratory rate (RR)], and Modified Aldrete recovery score (MARS) were assessed at six different time points (baseline, right after EC, and 3rd min, 5th min, 10th min, 30th min following EC). Also, induction times (time to reach RSS to 5) and recovery times (time to reach MARS to 8) were recorded. The incidence of respiratory depression, bradycardia, hypotension and adverse effects were also recorded. RESULTS: Hemodynamic variables were similar in all groups. SpO2 values in Group R were significantly lower at 3rd min (p = 0.005). Induction and recovery times were longest in Group F. There were significant differences at 3rd, 5th and 10th minute MARS values between groups. The incidence of hypotension and bradycardia were similar in all groups (p > 0.05) but respiratory depression was higher in Group R (p = 0.047). CONCLUSIONS: Propofol alfentanil combination has more beneficial advantages in their rapid onset, early recovery time and less respiratory depression than remifentanil and fentanyl.

Polidocanol (Lauromacrogol 400) has anti-angiogenic effects in vitro and in vivo.

OBJECTIVE: Polidocanol is the most frequently used sclerosant for sclerotherapy all around the world. Our experimental research aims to find out the angiogenic effects of Polidocanol. MATERIALS AND METHODS: Angiogenic activity of polidocanol was examined in vivo in the chick chorioallantoic membrane (CAM) model, cell viability assay (human umbilical vein endothelial cells - HUVECs) and in vitro tube formation assay of HUVECs. RESULTS: In CAM assay, a significant decrease on CAM vessel growth was observed after the application of polidocanol solutions. Vessel growth inhibition was strongly dose-dependent. There was a cytotoxic effect on HUVECs in the presence of polidocanol observed with MTT assay (p < 0.05). In the tube formation assay, statistically significant decrease in tube formation was observed in polidocanol group. It was found that polidocanol had an anti-angiogenic effect (p < 0.05). The results provide evidence that polidocanol decreases angiogenesis and has a cytotoxic effect on ECs. CONCLUSIONS: These results provide evidence that Polidocanol (lauromacrogol 400) have strong anti-angiogenic effects in vitro and in vivo. Further researches needed to reveal early and long-term effects of polidocanol in the human vascular system and new treatment approach as an anti-angiogenic therapy.

New probing and warm-wash-out technique improves early patency rates in arteriovenous fistula surgery.

OBJECTIVE: Arteriovenous fistulas (AVFs) are commonly used during hemodialysis. Early failure of AVFs is quite common with incidence of 43% to 63%. In this study we aimed to describe a novel approach to AVF surgery for improving early patency rates. PATIENTS AND METHODS: Patients were divided into two groups according to use of probing and warm-wash-out technique. Group I consisted of 31 patients with additional probing technique. Group II consisted of 32 patients without additional maneuver. End-to-side anastomosis were used to all patients. Technical success was defined as having palpation of a thrill on fistula. Flow rates of draining vein was measured at 1st hour, 24th hour, 1st week and 3rd week of surgery. SURGICAL TECHNIQUE: Classical maneuvers were performed until end of the anastomosis. At this time, vein lumen was washed by low-dosed heparinized warm fluid, with assistance of a simple catheter. RESULTS: Technical success was similar in both groups at 1st hour and 24th hour, while there were significantly differences between groups at 1st week (p = 0.042) and 3rd week (p = 0.05) assessments. Flow rates were also measured significantly higher in Group I at 1st hour (p = 0.011) and 24th hour (p = 0.016). Flow rates were almost similar in two groups at 1st and 3rd weeks but overall success rate was higher in Group I comparing with Group II (96.8% vs. 81.3%, respectively, p = 0.05). CONCLUSIONS: Probing and warm-wash out technique will simply increase the surgical success and flow rate of draining vein.

In vitro effect of sodium nitrite on platelet aggregation in human platelet rich plasma--preliminary report.

OBJECTIVE: The role of nitrates and nitric oxide on platelet functions has obtained an increasing attention with respect to their potential effects on cardiovascular disorders. In this study we aimed to analyze the effect of sodium nitrite on platelet functions in human platelets. PATIENTS AND METHODS: This in vitro study was designed to show the effect of sodium nitrite on platelet functions in seven healthy volunteers. Blood samples were centrifuged to prepare platelet rich plasma and platelet poor plasma. Platelet rich plasma was diluted with the platelet poor plasma to have a final count of 300,000 ± 25,000 platelets. Platelet rich plasma was incubated with six different increasing doses (from 10 µM to 5 mM) of sodium nitrite for 1 hour at 37°C. Then stimulating agents including collagen (3 µg ml-1), adenosine diphosphate (10 µM), and epinephrine (10 µM) were added to the cuvette. Changes in light transmission were observed for 10 minutes. In addition spontaneous aggregation were performed in control group with all aggregating agents separately. RESULTS: Effect of sodium nitrite on agonist-induced platelet aggregation depends on the concentration of sodium nitrite. Compared with control group, agonist-induced platelet aggregations were significantly suppressed by sodium nitrite at the concentration of 5, 1.0 and 0.5 mM. CONCLUSIONS: Our results suggested that sodium nitrite has inhibitory effects in vitro on platelet aggregation in a dose-dependent manner.

Comparison of angiogenic and proliferative effects of three commonly used agents for pulmonary artery hypertension (sildenafil, iloprost, bosentan): is angiogenesis always beneficial?

OBJECTIVE: Pulmonary artery hypertension (PAH) is devastating disease that has very serious outcomes. Dysregulated angiogenesis is one of the main responsible courses in pathophysiology of disease. Our experimental research intends to find out and compare the angiogenic effects of medications used sildenafil, iloprost, and bosentan in the treatment of PAH. MATERIALS AND METHODS: This study was performed in Department of Biochemistry and Cancer and Stem Cell Research Laboratory of our institutes between August and October 2014. Angiogenic activity of sildenafil, iloprost, and bosentan were examined in vivo in chick chorioallantoic membrane (CAM) model and in vitro tube formation assay of human umbilical vein endothelial cells (HUVECs). Proliferative activity of these three agents was also determined through 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay on HUVECs. RESULTS: In CAM assay, when compared to the control and drug groups, treatment with sildenafil solutions resulted in a significant dose-dependent increase (budding, sprouting, extravasation) on CAM vessel growth. While there was no significant proliferative effect with iloprost and bosentan, presence of sildenafil caused a statistically significant proliferation on HUVECs following 24 and 48 h incubation (p < 0.05) compared to the control group. Comparing the tube length/area ratio values, there was statistically significant increase in sildenafil group with respect to the other 2 groups (p < 0.05). Iloprost and bosentan did not show a significant effect. CONCLUSIONS: The results provide evidence that sildenafil but not iloprost and bosentan induces angiogenesis in vitro and in vivo. Dysregulated angiogenesis, as an important pathophysiological part in the progression of PAH, may be triggered by the chronic ingestion of sildenafil in the long treatment period and may cause negative effects.

Local sympathetic stimulation not only have local effects in patients with Raynaud's phenomenon.

OBJECTIVE: Many other organs and system can be affected in the course of Primary Raynaud's Phenomenon (RP). Simultaneously increased vasospasm in the pulmonary vascular bed may likely affect the pulmonary function. Therefore, we investigated the effect of Raynaud's phenomenon on the respiratory functions in this study. PATIENTS AND METHODS: Between March 2014 and December 2014, 30 patients with the diagnosis of PRP more than two years and 32 age-sex matched healthy controls were enrolled into this study. Cold stimulation test (CST) was performed. Pulmonary function test were performed following 30 minutes after CST and spirometric measurements were calculated. RESULTS: There were no statistically significant differences between two groups regarding their demographic and clinical data. Mean duration of symptoms from onset to present was 3.01 ± 1.05 years. Patients with Primary RP had significantly lower FVC and higher FEV1/FVC values compared to the control groups (p = 0.015 and p=0.045, respectively). CONCLUSIONS: We found that statistically significant decrease of FVC values in patients with Primary RP compared to the healthy controls could be a impaired innervation of pulmonary system and a predictor of pulmonary vasospasm and/or pulmonary Raynaud's phenomenon, which may develop in future periods.

Gastrointestinal ostomies and sexual outcomes: a comparison of colorectal cancer patients by ostomy status.

PURPOSE: Research examining effects of ostomy use on sexual outcomes is limited. Patients with colorectal cancer were compared on sexual outcomes and body image based on ostomy status (never, past, and current ostomy). Differences in depression were also examined. METHODS: Patients were prospectively recruited during clinic visits and by tumor registry mailings. Patients with colorectal cancer (N = 141; 18 past ostomy; 25 current ostomy; and 98 no ostomy history) completed surveys assessing sexual outcomes (medical impact on sexual function, Female Sexual Function Index, International Index of Erectile Function), body image distress (Body Image Scale), and depressive symptoms (Center for Epidemiologic Studies Depression Scale-Short Form). Clinical information was obtained through patient validated self-report measures and medical records. RESULTS: Most participants reported sexual function in the dysfunctional range using established cut-off scores. In analyses adjusting for demographic and medical covariates and depression, significant group differences were found for ostomy status on impact on sexual function (p < .001), female sexual function (p = .01), and body image (p < .001). The current and past ostomy groups reported worse impact on sexual function than those who never had an ostomy (p < .001); similar differences were found for female sexual function. The current ostomy group reported worse body image distress than those who never had an ostomy (p < .001). No differences were found across the groups for depressive symptoms (p = .33) or male sexual or erectile function (p values ≥ .59). CONCLUSIONS: Colorectal cancer treatment puts patients at risk for sexual difficulties and some difficulties may be more pronounced for patients with ostomies as part of their treatment. Clinical information and support should be offered.

Generation and characterization of E1/E2a/E3/E4-deficient adenoviral vectors encoding human factor VIII.

The use of adenoviral vectors for gene therapy has been limited due to host immune responses directed toward the vector and/or transgene and vector toxicity. To decrease adenoviral vector immunogenicity and toxicity, we attenuated viral gene expression by eliminating E1, E2a, E3, and E4 early genes from the adenoviral backbone. Two highly attenuated, fourth-generation (Av4) E1/E2a/E3/E4-deficient adenoviral vectors encoding human factor VIII (FVIII) under the control of a liver-specific albumin promoter were generated. One Av4 vector (Av4DeltaE4FVIII) was deficient in the entire E4 coding region and the second vector contained a deletion of the E4 region, except for open reading frame 3 (orf 3; Av4orf3FVIII). The Av4 vectors were compared to an E1/E2a/E3-deficient third-generation vector (Av3H8101) containing an analogous transgene expression cassette in vitro and in vivo following intravenous administration in hemophiliac mice. In vitro transduction of Hep3B cells revealed at all three vectors expressed functional FVIII. However, the Av4DeltaE4FVIII vector could not be scaled-up for in vivo studies. Both Av3H8101 and Av4orf3FVIII initially expressed similar levels of FVIII in hemophiliac mice. However, at 3 months, animals treated with the Av4orf3FVIII vector no longer expressed FVIII while Av3H8101-treated mice displayed persistent FVIII expression. Liver enzyme analyses of plasma samples revealed that the Av4orf3FVIII vector was significantly less hepatotoxic than the Av3H8101 vector. These data demonstrate that further attenuation of the adenoviral vector backbone by removal of the majority of the E4 coding region significantly diminished vector toxicity; however, the duration of transgene expression was reduced.

A versatile framework for the design of ligand-dependent, transgene-specific transcription factors.

The ability to regulate transgene expression will be essential for the safety and efficacy of many gene therapies. Various ligand-dependent transcription factors, including steroid hormone receptors, have been modified to enable transgene-specific regulation. To minimize effects on cellular gene expression, chimeric steroid receptors have been constructed by replacing their native DNA binding domain (DBD) with a heterologous DBD, like that from the yeast transcription factor GAL4. This approach has limitations for human gene therapy, including the potential immunogenicity of the GAL4 domain and the inability to discriminate between different GAL4-linked transgenes in the same cell. To address this, we have constructed chimeric regulators containing the human estrogen receptor (ER) ligand binding domain (LBD) and a Cys(2)-His(2)-type zinc finger DBD. Cys(2)-His(2) zinc finger domains are common among human DNA binding proteins and can be engineered to selectively bind different DNA sequences. We demonstrate over 500-fold drug-dependent transgene induction with these chimeric regulators in vitro and the ability to regulate an adenovirus-delivered transgene in mice. Two chimeras containing different Cys(2)-His(2) domains displayed highly sequence-specific binding and regulation. Incorporating a point mutation in the ER LBD that ablates estrogen binding enables selective in vivo regulation with the clinically useful anti-estrogen tamoxifen. These Cys(2)-His(2)-ER LBD chimeras represent a versatile framework for creating transgene-specific regulators potentially useful for human gene therapy applications.

Evaluation of adenoviral vectors by flow cytometry.

Biological assays for adenoviral gene therapy vectors have included conventional procedures initially developed to detect wild-type adenoviruses. Standard virological assays to quantitate adenoviruses rely on the virus to infect and replicate in the host cell until a cytopathic effect is observed. The appearance of plaques, colonies of rounded, enlarged cells containing infectious virions, usually takes 2 to 3 weeks to reach an endpoint. We describe a flow cytometric bioassay for adenovirus which shortens the time from when the infection takes place to the time that biological titer is determined. A fluorescent focus-forming assay was one of the first rapid adenoviral bioassays developed. Virus titer was determined using fluorescence immunocytochemistry to detect adenovirus proteins and microscopy to count fluorescent foci in cultures of adenovirus-infected cells. In this study, we describe a flow cytometric assay performed on cells stained for adenovirus hexon capsid protein, where virus titer is determined based on the dose-dependent appearance of hexon-positive cells. Adenovirus hexon detection in infected cells can provide data to determine virus titer, inducible promoter function in vector-complementing cells, and vector replication in complementation-deficient cells.

Generation of an adenovirus vector lacking E1, e2a, E3, and all of E4 except open reading frame 3.

Toxicity and immunity associated with adenovirus backbone gene expression is an important hurdle to overcome for successful gene therapy. Recent efforts to improve adenovirus vectors for in vivo use have focused on the sequential deletion of essential early genes. Adenovirus vectors have been constructed with the E1 gene deleted and with this deletion in combination with an E2a, E2b, or E4 deletion. We report here a novel vector (Av4orf3nBg) lacking E1, E2a, and all of E4 except open reading frame 3 (ORF3) and expressing a beta-galactosidase reporter gene. This vector was generated by transfection of a plasmid carrying the full-length vector sequence into A30.S8 cells that express E1 and E2a but not E4. Production was subsequently performed in an E1-, E2a-, and E4-complementing cell line. We demonstrated with C57BL/6 mice that the Av4orf3nBg vector effected gene transfer with an efficiency comparable to that of the Av3nBg (wild-type E4) vector but that the former exhibited a higher level of beta-galactosidase expression. This observation suggests that E4 ORF3 alone is able to enhance RNA levels from the beta-galactosidase gene when the Rous sarcoma virus promoter is used to drive transgene expression in the mouse liver. In addition, we observed less liver toxicity in mice injected with the Av4orf3nBg vector than those injected with the Av3nBg vector at a comparable DNA copy number per cell. This study suggests that the additional deletion of E4 in an E1 and E2a deletion background may be beneficial in decreasing immunogenicity and improving safety and toxicity profiles, as well as increasing transgene capacity and expression for liver-directed gene therapy.

Sustained phenotypic correction of murine hemophilia A by in vivo gene therapy.

Hemophilia A is caused by a deficiency of blood coagulation factor VIII (FVIII) and has been widely discussed as a candidate for gene therapy. While the natural canine model of hemophilia A has been valuable for the development of FVIII pharmaceutical products, the use of hemophiliac dogs for gene therapy studies has several limitations such as expense and the long canine generation time. The recent creation of two strains of FVIII-deficient mice provides the first small animal model of hemophilia A. Treatment of hemophiliac mice of both genotypes with potent, human FVIII-encoding adenoviral vectors resulted in expression of biologically active human FVIII at levels, which declined, but remained above the human therapeutic range for over 9 months. The duration of expression and FVIII plasma levels achieved were similar in both hemophiliac mouse strains. Treated mice readily survived tail clipping with minimal blood loss, thus showing phenotypic correction of murine hemophilia A by in vivo gene therapy.

Elimination of both E1 and E2 from adenovirus vectors further improves prospects for in vivo human gene therapy.

A novel recombinant adenovirus vector, Av3nBg, was constructed with deletions in adenovirus E1, E2a, and E3 regions and expressing a beta-galactosidase reporter gene. Av3nBg can be propagated at a high titer in a corresponding A549-derived cell line, AE1-2a, which contains the adenovirus E1 and E2a region genes inducibly expressed from separate glucocorticoid-responsive promoters. Av3nBg demonstrated gene transfer and expression comparable to that of Av1nBg, a first-generation adenovirus vector with deletions in E1 and E3. Several lines of evidence suggest that this vector is significantly more attenuated than E1 and E3 deletion vectors. Metabolic DNA labeling studies showed no detectable de novo vector DNA synthesis or accumulation, and metabolic protein labeling demonstrated no detectable de novo hexon protein synthesis for Av3nBg in naive A549 cells even at a multiplicity of infection of up to 3,000 PFU per cell. Additionally, naive A549 cells infected by Av3nBg did not accumulate infectious virions. In contrast, both Av1nBg and Av2Lu vectors showed DNA replication and hexon protein synthesis at multiplicities of infection of 500 PFU per cell. Av2Lu has a deletion in E1 and also carries a temperature-sensitive mutation in E2a. Thus, molecular characterization has demonstrated that the Av3nBg vector is improved with respect to the potential for vector DNA replication and hexon protein expression compared with both first-generation (Av1nBg) and second-generation (Av2Lu) adenoviral vectors. These observations may have important implications for potential use of adenovirus vectors in human gene therapy.

Factors affecting retroviral vector function and structural integrity.

Recombinant retroviruses are widely used for gene transfer into eukaryotic cells and exhibit significant potential for human gene therapy. Despite the utility of retroviral vectors, their design is still essentially empirical. We have constructed a series of reciprocal, double-gene vectors to compare the dual expression of beta-galactosidase (beta-gal) and neomycin phosphotransferase (neor) in a retroviral delivery system. The first gene of the pair was driven by the viral LTR promoter and the internal gene was regulated by either the SV40 virus early promoter or the cytomegalovirus (CMV) major late promoter. Clones of vector producer cells were isolated either by G418 selection for expression of neor, or by fluorescence-activated cell sorting for expression of beta-gal, and the activity of both genes was evaluated. In general, vectors using the SV40 promoter performed better than those with the CMV promoter, regardless of whether the selected gene was regulated by the LTR or the internal promoter. Southern analysis of clones indicated that loss of beta-gal gene function was related to significant rearrangements and deletions in vector structure. We also found that the arrangement of genes within the vector was important. When beta-gal preceded neor, gene expression and vector stability were markedly enhanced relative to vectors containing these genes in the inverse order.

Introduction of human genomic sequences renders CHO-K1 cells susceptible to infection by amphotropic retroviruses.

To learn more about the nature of the block to infection by amphotropic retroviruses exhibited by Chinese hamster cells (CHO-K1), CHO-K1 cells were made susceptible to amphotropic retrovirus infection by introducing genomic DNA from infectable human cells. A clone, designated CHO18, was obtained and shown to be infected as efficiently as NIH 3T3 fibroblasts. Susceptibility of CHO18 cells to infection was specific to retroviruses and vectors bearing an amphotropic envelope. By comparison to CHO-K1 cells, CHO18 cells may provide a useful model for analysis of the molecular events involved in the retrovirus-receptor interaction.

Detection of receptor-specific murine leukemia virus binding to cells by immunofluorescence analysis.

Four classes of murine leukemia virus (MuLV) which display distinct cellular tropisms and bind to different retrovirus receptors to initiate virus infection have been described. In the present study, we describe a rapid, sensitive immunofluorescence assay useful for characterizing the initial binding of MuLV to cells. By using the rat monoclonal antibody 83A25 (L. H. Evans, R. P. Morrison, F. G. Malik, J. Portis, and W. J. Britt, J. Virol. 64:6176-6183, 1990), which recognizes an epitope of the envelope gp70 molecule common to the different classes of MuLV, it is possible to analyse the binding of ecotropic, amphotropic, or xenotropic MuLV by using only a single combination of primary and secondary antibodies. The MuLV binding detected by this assay is envelope receptor specific and matches the susceptibility to infection determined for cells from a variety of species. The binding of amphotropic MuLV to NIH 3T3 cells was shown to be rapid, saturable, and temperature dependent. Chinese hamster ovary (CHO-K1) cells normally lack the ability to bind ecotropic virus and are not infectible by ecotropic vectors. Expression of the cloned ecotropic retrovirus receptor gene (Rec) in CHO-K1 cells confers high levels of ecotropic virus-specific binding and confers susceptibility to infection. Characterization of MuLV binding to primary cells may provide insight into the infectibility of cells by retroviruses and aid in the selection of appropriate vectors for gene transfer experiments.

Correlation of 125I-LSD autoradiographic labeling with serotonin voltage clamp responses in Aplysia neurons.

Autoradiographic receptor binding studies using 125I-LSD (2-[125I]lysergic acid diethyamide) revealed intense labelling on the soma of a symmetrically located pair of cells in the abdominal ganglion of Aplysia californica. This binding was blocked by micromolar concentrations of serotonin and lower concentrations of the serotonergic antagonists, cyproheptadine and mianserin (Kadan and Hartig, 1988). Electrophysiological investigation of responses to serotonin of neurons in the left upper quadrant, where one of the labeled neurons is located, revealed a range of serotonin responses. Cells L3 and L6 have a K+ conductance increase in response to serotonin that is not blocked by cyproheptadine or mianserin. Cells L2 and L4 have a biphasic response to serotonin: a Na+ conductance increase, which can be blocked by cyproheptadine and mianserin, followed by a voltage dependent Ca2+ conductance which is blocked by Co2+ but not the serotonergic antagonists. Cell L1, and its symmetrical pair, R1, have in addition to the Na+ and Ca2+ responses observed in L2 and L4, a Cl- conductance increase blocked by LSD, cyproheptadine and mianserin. LSD had little effect on the other responses. We conclude that the symmetrically located cells L1 and R1 have a Cl- channel linked to a cyproheptadine- and mianserin-sensitive serotonin receptor that is selectively labelled by 125I-LSD. This receptor has many properties in common with the mammalian serotonin 1C receptor.

Infection with murine retrovirus confers resistance to the neurotoxin 1-methyl-4-phenylpyridinium ion in PC 12 cells.

High concentrations of the dopaminergic neurotoxin 1-methyl-4-phenylpyridinium ion (MPP+) are toxic to the catecholaminergic cell line PC12, derived from rat phenochromocytoma. Prolonged exposure of wild-type PC12 cells to 500 microM MPP+ yields toxin-resistant colonies at a frequency of 2 X 10(-4). These spontaneously arising MPP(+)-resistant cells are morphologically quite distinct from wild-type PC12 cells, and are lacking in most of their characteristic catecholaminergic properties. In contrast, among PC12 cells infected with the murine retrovirus ZIPNEOSV(X), 20% are resistant to the toxin MPP+, a resistance frequency approximately 1,000 times higher than for uninfected cells. The morphology and catecholaminergic phenotype of the virus-infected MPP+ resistant cells are quite similar to those of wild-type PC12 cells. The results presented in this study suggest a unique mechanism of MPP+ resistance in the infected PC12 cells which may be conferred by the presence and/or expression of the retrovirus ZIPNEOSV(X).

Autoradiographic localization and characterization of [125I]lysergic acid diethylamide binding to serotonin receptors in Aplysia.

The sensitive serotonergic radioligand 2-[125I]lysergic acid diethylamide was used to study the distribution and pharmacological binding properties of serotonin receptors in Aplysia californica. The high specific activity of this radioligand allowed us to develop a methodology for the investigation of receptor binding properties and receptor distribution in a single ganglion. [125I]Lysergic acid diethylamide labels a population of high-affinity serotonergic sites (Kd = 0.41 nM) in Aplysia ganglia whose regional distribution matches that expected from previous electrophysiological and immunohistochemical studies. The properties of [125I]lysergic acid diethylamide binding sites in Aplysia are in general agreement with previous studies on [3H]lysergic acid diethylamide binding in this system but these sites differ from the serotonergic receptor subtypes described in the mammalian brain. Guanine nucleotides were shown to modulate agonist but not antagonist affinity for the [125I]lysergic acid diethylamide binding site in Aplysia, suggesting that this site is coupled to a G-protein. Images of serotonin receptor distribution in the Aplysia nervous system were obtained from autoradiograms of [125I]lysergic acid diethylamide binding. Serotonin receptors in ganglia tissue sections are located primarily within the neuropil. In addition, a subset of neuronal soma are specifically labeled by [125I]lysergic acid diethylamide. These studies indicate that [125I]lysergic acid diethylamide binds to sites in the Aplysia nervous system which display a regional distribution, pharmacological binding properties and evidence of coupling to a G-protein consistent with labeling of a subset of functional serotonin receptors. In addition, the techniques used in this investigation provide a general approach for rapidly characterizing the pharmacological properties and anatomical distribution of receptor binding sites in single invertebrate ganglia. Individual neurons containing these receptor subtypes can be identified by these methods and correlated with physiological responses in the same cell.