Analysis of macrolide antibiotics

The following macrolide antibiotics have been covered in this review: erythromycin and its related substances, azithromycin, clarithromycin, dirithromycin, roxithromycin, flurithromycin, josamycin, rokitamycin, kitasamycin, mycinamycin, mirosamycin, oleandomycin, rosaramicin, spiramycin and tylosin. The application of various thin-layer chromatography, paper chromatography, gas chromatography, high-performance liquid chromatography and capillary zone electrophoresis procedures for their analysis are described. These techniques have been applied to the separation and quantitative analysis of the macrolides in fermentation media, purity assessment of raw materials, assay of pharmaceutical dosage forms and the measurement of clinically useful macrolide antibiotics in biological samples such as blood, plasma, serum, urine and tissues. Data relating to the chromatographic behaviour of some macrolide antibiotics as well as the various detection methods used, such as bioautography, UV spectrophotometry, fluorometry, electrochemical detection, chemiluminescence and mass spectrometry techniques are also included.     

Determination of pyridonecarboxylic acids in plasma by reverse-phase high-performance liquid chromatography

A simple qualitative and quantitative determination for pyridonecarboxylic acids including nalidixic acid (NA), oxolinic acid (OA) and pipemidic acid (PPA) in chicken plasma was carried out by microbiological, spectrophotometric, thin-layer chromatographic (TLC) and reverse-phase high-performance liquid chromatographic (HPLC) methods. As a test organism for bacteriological bioassay, Bacillus subtilis ATCC-6633 was the most sensitive of seven organisms investigated. Using the cup and the disc methods, a standard curve was obtained by determining the relationship between various drug concentrations and the diameter of the inhibition zone. The three drugs had two strong UV absorbance wavelengths (257 and 330 nm) on spectrophotometry. TLC analysis using a silica gel 60 F254 plate was investigated, and a solution of methanol:chloroform:acetic acid (3:1:1, v/v/v) was found to be the most suitable solvent for separation. The minimum concentration of drug detectable by this method was 0.5 microgram/ml for NA, 0.075 microgram/ml for OA and 0.39 microgram/ml for PPA. For HPLC analysis, a solution of acetonitrile:0.2 M phosphoric acid (1:1, v/v) was superior, and simultaneous determination of all three drugs was possible under the HPLC conditions used. The lowest measurable amount of drug in chicken plasma was 0.01 microgram/g. Recovery from extracts spiked with each drug at a known concentration was close to 100% for NA and OA, but only about 50% for PPA.     

The Numbing Scale: psychometric properties, a preliminary report

Twenty-one antimicrobial agents were incorporated individually into Frey's agar to evaluate their inhibitory activities against 86 isolates of avian mycoplasmas recently detected in Taiwan. Among them, 45 and 37 isolates were found positive with Mycoplasma gallisepticum and Mycoplasma synoviae fluorescent antibody conjugate, respectively. Twenty-one other isolates were unable to be identified by the above 2 conjugates. All of the field isolates were highly sensitive (with MIC50 < 1 microgram/ml) to enrofloxacin, gentamicin, myplabin, tiamutin and tylosin. However, those field isolates were highly resistant (with MIC50 > 32 micrograms/ml) to apramycin, chlortetracycline (CTC), erythromycin (ER), flumequine (FI), nalidixic acid (NA), oxolinic acid (OA), oxytetracycline (OTC) and spiramycin (SP). The inhibitory activities of the antibiotics which possessed an MIC90 of 50 micrograms/ml or less against local isolates were, in decreasing order, enrofloxacin (< 0.004 microgram/ml), gentamicin (1.53 micrograms/ml), tiamutin (1.81 micrograms/ml), tylosin (3.2 micrograms/ml), streptomycin (SM; 12.0 micrograms/ml), colistin (13.1 micrograms/ml), chloramphenicol (14.0 micrograms/ml), spectinomycin (15.0 micrograms/ml), myplabin (16.0 micrograms/ml), spiramycin (30.0 micrograms/ml), minocycline (32.0 micrograms/ml). The MIC90 of OA, CTC, SM, FI, SP, OTC, ER or NA was greater than 50 micrograms/ml; which work poorly in the control of mycoplasmoses. Since the antibiotic control policy is quite loose in Taiwan, many antimicrobial agents are often freely used in clinics, with a resulting gradual decrease in the inhibitory activity to the avian mycoplasmas.     

Long-term follow-up of the clinical relevance of short outer dynein arms in human nasal cilia

A high-performance liquid chromatographic (HPLC) procedure for quantitating ketoprofen in isopropyl myristate (IPM), a compound widely used as a receptor medium in drug diffusion studies of topical aqueous-based formulations, is developed. Previously reported HPLC assays for ketoprofen in IPM have employed relatively complex and tedious methods for purifying the IPM prior to injection onto the HPLC column. The present assay method utilizes a direct injection of the IPM-based sample onto a new reversed-phase ODS column and employs ultraviolet detection at 265 nm. Propyl paraben is employed as the internal standard. The mobile phase consists of acetonitrile-methanol-water (36:54:10, v/v/v) at a flow rate of 1.2 mL/min. The calibration curves are linear (correlation coefficient r > or = 0.988) over concentration ranges of 0.625-10 micrograms/mL and 6.25-100 micrograms/mL. The within-day and between-day precision exhibit coefficients of variation of 1.3-3.3%, and the accuracy (reported as relative error of the mean) varies from -1.9% to 0.6%. The retention times for ketoprofen and propyl paraben are approximately 2.3 and 3.3 min, respectively. The total run time per sample is approximately 7 min. The minimum quantitatable concentration is approximately 0.625 microgram/mL. The assay is stability-indicating, rapid, reproducible, sensitive, and readily adaptable for assaying other non-steroidal anti-inflammatory drugs.     

Disulfide isomerization within the C-terminus of cobrotoxin decelerates by thiol compounds and trinitrophenylation, but accelerates by modification of carboxyl groups

The survival of Yersinia enterocolitica serotype O:3 was examined in an in vitro model of the porcine ileum in the presence of normal ileal microflora using a medium supplemented with the growth-promoting antimicrobials avoparcin, spiramycin, tylosin, carbadox and olaquindox, or without any antimicrobials, at 39 degrees C for 5 d. Growth of Y. enterocolitica was inhibited in all trials in the following order: avoparcin < carbadox < spiramycin < no feed additives < tylosin < olaquindox. The media supplemented with avoparcin, carbadox and spiramycin supported the survival of Y. enterocolitica up to 5 d. When incubated with the normal ileal microflora without any growth-promoting antimicrobials, Y. enterocolitica could not be isolated after 4 d. With olaquindox and tylosin, Y. enterocolitica was not detected after 3 d.     

A high-performance liquid chromatographic assay for the determination of amphotericin B serum concentrations after the administration of AmBisome, a liposomal amphotericin B formulation

A sensitive and selective high-performance liquid chromatographic (HPLC) method has been developed for the determination of amphotericin B in human serum. After methanol deproteinization, amphotericin B and 3-nitrophenol (internal standard) are separated by reversed-phase chromatography and detected by ultraviolet absorbance. The analysis of human serum after the standard addition of amphotericin B (0.05-200.0 micrograms/mL) demonstrated excellent precision and accuracy over a five-day period. The HPLC assay uses two standard curve ranges. The high sensitivity curve range for low AmBisome dosage (1.0 mg/kg) is 0.05-20.0 micrograms/mL (curve 1), and the second curve range for the higher AmBisome dose regimens (2.5-5.0 mg/kg) is 0.5-200 micrograms/mL (curve 2). The intraday and interday coefficients of variations for standard curve 1 were 0.5-4.6% and 3.0-11.5%, respectively. The limit of quantitation was 0.05 microgram/mL. The intraday and interday coefficients of variation for standard curve 2 were 2.0-3.6 and 6.9-10.1, respectively. No interfering peak at the retention time for Amphotericin B and the internal standard were present in blank serums or serum samples spiked with fifteen potential co-administrated drugs with Amphotericin B treatment. The method was used to quantitate serum concentrations of amphotericin B in patients after the administration of AmBisome, a liposomal formulation of amphotericin B.     

Mitochondrial DNA mutations in multiple symmetric lipomatosis

We describe an analytical technique for measuring residues of imidacloprid, a relatively new and highly active insecticide, in water and soil using high-performance liquid chromatography (HPLC). All analyses were performed on reversed-phase HPLC with UV detection at 270 nm using a mobile phase of acetonitrile-water (20:80, v/v). Fortified water samples were extracted with either solid-phase extraction (SPE) or liquid-liquid extraction methods. A detection limit of 0.5 microgram/l was achieved using the SPE method. The imidacloprid residues in soils were extracted with acetonitrile-water (80:20, v/v), and the extract was then evaporated using a rotary evaporator. The concentrated extract was redissolved in 1 ml of acetonitrile-water (20:80, v/v) prior to analysis by reversed-phase HPLC. A detection limit of 5 micrograms/kg was obtained by this method which is suitable for analysis of environmental samples. Accuracy and precision at 10 and 25 micrograms/kg soil samples were 85 +/- 6% and 82 +/- 4%, respectively.     

Point and distributed current density analysis of interictal epileptic activity recorded by magnetoencephalography

Pyrolysis-gas chromatography is shown to be a rapid straightforward method for the qualitative differentiation of the macrolide antibiotics erythromycin, oleandomycin, troleandomycin, spiramycin and tylosin. Organic salts do not interfere and identification of erythromycin and troleandomycin in commercial products is viable. Spectrophotometric quantitation of these same five antibiotics after reaction with concentrated sulphuric acid is studied at about 470 nm. Reaction conditions such as acid concentration, time and temperature are provided. The sugar moieties of the antibiotics are proposed as the reactive sites. Detection limits are about 0.2-1.0 microg ml-1 [corrected] and analysis of pharmaceutical products should be possible.     

A 13-week subchronic toxicity study of josamycin in F344 rats

A 13-week subchronic toxicity study of josamycin was performed in male and female F344 rats to determine the maximum tolerable dose (MTD) for subsequent investigation of the carcinogenicity. As animals refused to take diet containing 5.0% josamycin in our preliminary study, dose levels in the present study were determined as 0, 0.16, 0.32, 0.63, 125 and 2.5% in diet. Rats were randomly allocated to 6 groups, each consisting of 10 males and 10 females. No animal died during the administration period and no group showed significant changes in body weight gain. Definite toxicity of josamycin was not noted in hematological and serum biochemical examinations. Histopathological examinations revealed no particular findings related to josamycin administration except cecal enlargement in the 1.25 and 2.5% groups. based on the results of the present study, it was concluded that the MTD of josamycin in 2.5% in diet, because the dietary dose level of 2.5% proved to exert no significant toxicological signs.     

Does routine follow up after head injury help? A randomised controlled trial

Excess surfactant present in emulsions can influence the rates of transport of incorporated drugs by micellar solubilization, alteration of the partitioning process and by drug-surfactant complexation. Cetyltrimethylammonium bromide (CTAB), a cationic surfactant was selected to investigate these phenomena as it forms relatively stable mineral oil-water (O-W) emulsions and has the potential for ionic interaction. Phenylazoaniline, benzocaine, benzoic acid and phenol were chosen as model drugs for this study. The emulsion critical micelle concentration (CMC) for CTAB determined using a combination of a membrane equilibrium technique and surface-tension measurement was 1.0% w/v in 10% v/v% O-W emulsion systems. Ionic interaction between model drugs and surfactants and drug hydrophobicity affected their transport rates in the emulsion systems. The transport rates of the lipophilic drugs (benzocaine and phenylazoaniline) and the ionized hydrophillic drug (benzoic acid, pH 7.0) in the emulsion systems increased with increasing CTAB concentration up to 0.5% w/v micellar concentration and then decreased at higher concentrations. The rate of transport of phenol was not affected by the presence of micellar phase. Ionic interaction between surfactant and model drugs affected transport rates of model drugs in emulsion systems. The micellar phase was considered to affect the overall transport rates of model drugs.     

Self-reported satisfaction with life and physical health in long-term cancer survivors and a matched control group

The minimal inhibitory concentration (MIC) of tilmicosin for 90% of 112 Staphylococcus aureus isolates from the bovine udder was 0.78 microgram/mL and 149 of 164 (90.8%) other gram-positive udder pathogens were inhibited by tilmicosin concentrations < 3.12 micrograms/mL. The MIC of the drug for 19 of 22 S. aureus isolates was < 0.78 microgram/mL when the test was conducted using Mueller-Hinton (MH) agar or MH agar containing 7.5% skimmed milk. Acute cardiac toxicity followed intravenous (i.v.) injection of the drug at 10 mg/kg to 3 cows, but animals appeared clinically normal within 30 min after treatment. The pharmacokinetics of i.v.-administered tilmicosin is typical for the macrolide class of antibiotics, i.e. low serum drug concentrations and a large volume of distribution (> 2.0 L/kg). The elimination half-life (t1/2 beta) values for 3 cows were 46.4, 56.0 and 72.8 min. The drug was administered subcutaneously (s.c.) to 5 cows at 10 mg/kg; the elimination half-life (t1/2el) was 4.18 +/- 0.55 h and the mean s.c. bioavailability was 22%. Rapid and extensive penetration of tilmicosin from blood into milk, and slow elimination from the milk were among the characteristic kinetic features of the drug after i.v. and s.c. administration. Tilmicosin was injected s.c. at 10 mg/kg once to 9 cows after the last milking of lactation; dry udder secretion samples were collected daily for 11 consecutive days and assayed microbiologically. Concentrations of drug > 0.78 microgram/mL were found in the secretion for 8-9 days after dosing. Systemic side-effects were not observed after s.c. drug administration.     

Contents of lecithin and choline in crude drugs

The determination of lecithin and choline in crude drugs was established by a combination of high performance liquid chromatography (HPLC) with electrochemical detector (ECD) and enzyme reaction. Lecithin in crude drugs extracted with a mixture of chloroform-methanol (2:1) at room temperature was hydrolyzed by phospholipase D. The hydrolyzate was injected to HPLC, and choline was separated from impurities by reverse phase column. The choline was converted to betaine and hydrogen peroxide by passing through column packed with immobilized choline oxidase. This hydrogen peroxide was detected by ECD. The peak area of hydrogen peroxide derived from lecithin was proportional to the concentration of lecithin from 0.10 to 1.52 microgram/ml. Choline in crude drugs was extracted with ethanol under reflux and determined under the same HPLC conditions as lecithin. The peak area of hydrogen peroxide derived from choline was proportional to the concentration of choline from 0.01 to 0.45 microgram/ml. The contents of lecithin and choline in 31 kinds of crude drugs were determined by these established methods. The results showed that Cervi Parvum Cornu, Kokurozin, Foenigraeci Semen and Psoraleae Semen contained more lecithin than other crude drugs, while Angelicae Radix, Foenigraeci Semen, Psoraleae Semen, and especially Hippocampus were found to contain more choline than other crude drugs.     

Development of a multiple-drug delivery implant for intraocular management of proliferative vitreoretinopathy

A prototype multiple-drug delivery implant has been developed for the intraocular management of proliferative vitreoretinopathy (PVR). Because of the recurrent nature of the disease, PVR causes blindness in approximately 7% of patients who have undergone retinal re-attachment surgery. The poly(dl-lactide-co-glycolide) 50/50 (PLGA) implant consists of three cylindrical segments, each of which contains one of the following drugs: 5-fluorouridine (5FUrd, an antimetabolite), triamcinolone (Triam, a corticosteroid), and human recombinant tissue plasminogen activator (t-PA, a thrombolytic agent). The device can be inserted through a 20-gauge syringe needle into the vitreous body of the eye. The implant also possesses a PLGA coating over the t-PA-containing terminal segment, which creates a lag-time to deliver t-PA when most needed and to decrease the risk of postoperative bleeding. Two methods of cylinder fabrication were investigated: heat and solvent extrusion. The release behavior of several drugs was examined as a function of the processing variables including: extrusion method, drug loading, polymer molecular weight, and drug particle size. The presence of either the organic solvent (acetone) during processing or a highly water-soluble drug (5FUrd) in the formulation increased the polymer porosity, which in turn, increased the drug release-rate. Drug loading effects were consistent with percolation concepts, and a low-molecular-weight PLGA (e.g., Mw=42000 for inherent viscosity=0.58 dl/g) was desirable to produce controlled release close to one month. Based on pharmacological and pharmacokinetic data of these compounds and our clinical experience with this disease, several design criteria for a combined implant were devised. Optimal cylindrical segments from the formulation studies were selected and combined in series to form a contiguous implant. After successful combination and coating procedures were developed, prototype implants were prepared. From the 3-drug prototype, 5FUrd and Triam were released approximately 1 microgram/day for over 4 weeks and 10-190 microgram/day over 2 weeks, respectively. The solvent-extrusion procedure did not significantly alter the stability of the encapsulated t-PA (>94+/-5% serine protease activity after preparation). After a lag-time of approximately 2 days, t-PA was released active at a rate of approximately 0.2-0.5 microgram/day in approximately 2 weeks. The release characteristics from the combined implant largely met our initial design criteria. Hence, controlled-release implants of this kind may have potential use for intraocular treatment of PVR.     

Urinary levels of 1-hydroxypyrene, 1-, 2-, 3-, and 4-hydroxyphenanthrene in females living in an industrial area of Germany

The concentrations of 1-hydroxypyrene (1-HOPYR), and 1-, 2-, 3-, and 4-hydroxyphenanthrene (HOPHE) as metabolites of pyrene and phenanthrene, were measured in urine samples collected from 124 housewives (27 smokers and 97 non-smokers) living in Bottrop, an industrial city located in the Ruhr area in Germany. The urine samples were analyzed by a very sensitive and practical high-performance liquid chromatographic (HPLC) method using a two-column switching technique and a special precolumn packing material followed by fluorescence detection. The polycyclic aromatic hydrocarbon (PAH) metabolites are selectively enrichéd on the precolumn and separated from the matrix. Therefore, laborious clean-up steps were omitted. The above-mentioned PAH metabolites could be detected in all urine samples investigated. Smokers had significantly higher urine concentrations of 1-HOPYR (median 0.48 microgram/g creatinine), 3-HOPHE (median 0.61 microgram/g creatinine), 2-HOPHE (0.41 microgram/g creatinine) and 4-HOPHE (median 0.10 microgram/g creatinine) than non-smokers (median 0.15 microgram/g creatinine, 0.31 microgram/g creatinine, 0.31 microgram/g creatinine and 0.04 microgram/g creatinine, respectively). The study shows that the influence of smoking is of such an order of magnitude that potential environmental exposure to PAH in this highly industrialized area is obscured by smoking habits. Furthermore, it can be concluded that the determination of 1-HOPYR, 1-, 2-, 3-, and 4-HOPHE in urine is a diagnostically useful method for the biological monitoring of persons environmentally exposed to PAH.     

Study of the metabolism of spiramycin in pig liver

A major metabolic pathway of spiramycins in pig liver is described. This biochemical reaction involves L-cysteine--a common amino acid present in most animal tissues--which reacts with the aldehyde function of the antibiotic forming a thiazolidine ring. This transformation of spiramycin derivatives drastically increased their polarity. A preliminary HPLC method enabling the quantitation of each metabolite in the range 0.5 microg/g of liver tissue is proposed. Spiramycin S is used as an internal standard while extraction procedures take into account the physico-chemical properties of the thiazolidine moieties. By comparison, previous HPLC methods underestimated the exact amount of antibiotic residues because these metabolites were not extracted from the studied tissues.     

Comparison of a new triazole antifungal agent, Schering 56592, with itraconazole and amphotericin B for treatment of histoplasmosis in immunocompetent mice

A murine model of intratracheally induced histoplasmosis was used to evaluate a new triazole antifungal agent, Schering (SCH) 56592, for treatment of histoplasmosis. MICs were determined for SCH 56592, amphotericin B, and itraconazole by testing yeast-phase isolates from 20 patients by a macrobroth dilution method. The MICs at which 90% of the isolates are inhibited were for 0.019 microgram/ml for SCH 56592, 0.5 microgram/ml for amphotericin B, and < or = 0.019 microgram/ml for itraconazole. Survival studies were done on groups of 10 B6C3F1 mice with a lethal inoculum of 10(5). All mice receiving 5, 1, or 0.25 mg of SCH 56592 per kg of body weight per day, 2.5 mg of amphotericin B per kg every other day (qod), or 75 mg of itraconazole per kg per day survived to day 29. Only 44% of mice receiving 5 mg of itraconazole/kg/day survived to day 29. Fungal burden studies done in similar groups of mice with a sublethal inoculum of 10(4) showed a reduction in CFUs and Histoplasma antigen levels in lung and spleen tissue in animals treated with 2 mg of amphotericin B/kg qod, 1 mg of SCH 56592/kg/day, and 75 mg of itraconazole/kg/day, but not in those treated with lower doses of the study drugs (0.2 mg of amphotericin B/kg qod, 0.1 mg of SCH 56592/kg/day, or 10 mg of itraconazole/kg/day). Serum drug concentrations were measured 3 and 24 h after the last dose in mice (groups of five to seven mice), each treated for 7 days with SCH 56592 (10 and 1 mg/kg/day) and itraconazole (75 and 10 mg/kg/day). Mean levels measured by bioassay were as follows: SCH 56592, 10 mg/kg/day (2.15 micrograms/ml at 3 h and 0.35 microgram/ml at 24 h); SCH 56592, 1 mg/kg/day (0.54 microgram/ml at 3 h and none detected at 24 h); itraconazole, 75 mg/kg/day (22.53 micrograms/ml at 3 h and none detected at 24 h); itraconazole, 10 mg/kg/day (1.33 micrograms/ml at 3 h and none detected at 24 h). Confirmatory results were obtained by high-pressure liquid chromatography assay. These studies show SCH 56592 to be a promising candidate for studies of treatment of histoplasmosis in humans.     

Postantibiotic effect of amikacin, rifampin, sparfloxacin, clofazimine and clarithromycin against Mycobacterium avium

Antimycobacterial drugs acting efficiently against Mycobacterium avium complex have in common low MICs and MBC/MIC ratios. The recently reported clinical efficacy of some of the newer drugs is also clearly linked to their pharmacokinetic properties such as higher serum level and/or intracellular concentrations and half-life. In the present investigation, comparative postantibiotic effects (PAEs) of amikacin, rifampin, sparfloxacin, clofazimine and clarithromycin were investigated. Bacteria were exposed to MIC, MIC x 4 and MIC x 8 concentrations of each drug for 2 h, the drug was removed by centrifugation and cells were thoroughly washed and resuspended in drug-free medium. Growth was compared to control organisms which underwent a similar treatment (but without drugs) and PAEs were assessed using the equation "T-C", where T equals the time required for colony counts to increase by 1 log10 in test samples after antibiotic exposure and C equals the time for 1 log10 growth in control. Our results underlined two distinct patterns concerning PAE: pattern I included drugs for which PAE (in hours) was dose-dependent and varied (for MIC, MIC x 4 and MIC x 8 concentrations) for amikacin (10.3 +/- 1.7, 14.7 +/- 1.9 and 17.7 +/- 4.1), rifampin (28.0 +/- 7.6, 62.0 +/- 18.5 and 71.0 +/- 3.2) and clarithromycin (2.6 +/- 1.0, 15.0 +/- 4.0 and 22.0 +/- 4.0), whereas pattern II included drugs with a stable PAE, relatively independent of the drug concentrations: sparfloxacin (11.0 +/- 2.5, 12.3 +/- 6.4 and 13.0 +/- 2.1) and clofazimine (26.0 +/- 2.8, 28.8 +/- 2.5 and 27.3 +/- 1.3). These results may be useful for guidance in scheduling of drug administration in M. avium-infected AIDS patients overburdened with too many drugs given for various opportunistic infections.     

Comparison of intraoral donor sites for onlay grafting prior to implant placement

The influence of flecainide (0.1, 0.5, 1.0, and 2.0 micrograms/mL) on atrioventricular (AV) conduction was studied in neonatal and adult perfused rabbit hearts using extracellular bipolar surface electrograms and premature atrial and ventricular pacing. Flecainide produced a concentration and rate-related increase in the steady-state nodal conduction (AHmin) and an increase in slow AH conduction (AHmax) in both age groups. The drug produced significant increases in the refractory periods of the atrium, AV node, His-Purkinje system, and ventricular myocardium. The neonatal refractory periods were significantly greater at lower or the same drug concentrations than those of the adult. The neonatal Wenckebach cycle length was significantly greater with a lower concentration of drug (0.5 microgram/mL) than was the adult Wenckebach cycle length. The His-Purkinje system steady-state conduction time (HVmin) was increased by a lower concentration of drug in the neonate (0.5 microgram/mL) as compared with 2.0 micrograms/mL in the adult. These data show that across a wide range of AV conduction parameters, the neonatal preparations responded to a lower concentration of flecainide than did the adult preparations. These findings may, in part, be the basis for the reported greater efficacy of the drug in children than in adults.     

Effects of corticotropin-releasing factor on brain serotonergic activity

The serotonergic dorsal raphe nucleus is innervated by corticotropin-releasing factor (CRF) and expresses CRF receptors, suggesting that endogenous CRF impacts on this system. The present study characterized interactions between CRF and the dorsal raphe serotonin (5-HT) system. The effects of intracerebroventricularly (i.c.v.) administered CRF on microdialysate concentrations of 5-HT in the lateral striatum of freely moving rats were determined. CRF had biphasic effects, with 0.1 and 0.3 microgram decreasing, and 3.0 micrograms increasing 5-HT dialysate concentrations. i.c.v. administration of CRF inhibited neuronal activity of the majority of dorsal raphe neurons at both low (0.3 microgram) and high (3 micrograms) doses. Likewise, intraraphe administration of CRF (0.3 and 1.0 ng) had predominantly inhibitory effects on discharge rate. Together, these results suggest that CRF is positioned to regulate the function of the dorsal raphe serotonergic system via actions within the cell body region. This regulation may play a role in stress-related psychiatric disorders in which 5-HT has been implicated.