Non-linear Curve Fitting Analysis Research Articles

Characterization and modelling of odor-active compounds release behavior from Fu-brick tea during boiling-water extraction by molecular sensory science approach

The odor-active compounds in Fu-brick tea and their release behaviors during boiling-water were studied. Fifty-one odor-active compounds were identified, and their release behaviors were identified by continuously recovering 16 sections of condensed water combined with sensory, instrumental, and nonlinear curve fitting analysis. The odor intensities of condensed water and the concentrations of odor-active compounds could be significantly fitted (p < 0.01) to power-function type curves. Hydrocarbons showed the fastest release rate, while organic acids showed the slowest. The release rates had very little correlation with their concentrations, molecular weights, and boiling points. Most odor-active compounds (≥70 %) released need to evaporate more than 24 % of the added water during boiling-water extraction. Meanwhile, on the basis of odor activity value (OAV) calculation, the aroma recombination experiments were performed to explore the odor-active compounds that made major contributions to the formation of the aroma profile of each condensed water.

Probing the interaction of glutathione with different shape of silver-nanoparticles by optical spectroscopy

To understand the influence of the shape of the particles on assay sensitivity using surface plasmon resonance phenomenon (SPR), three different types of silver nanoparticles spherical (SAgNPs), triangular (TAgNPs), and octahedral (OAgNPs) of around 20 nm in size and similar aspect ratio were analyzed after interaction with glutathione (GSH). FTIR peak of Ag-S peak at 2312 cm−1and 2305 cm−1, 2312 cm−1 in SAgNPs, TAgNPs, and OAgNPs respectively confirming interactions. DLS and TEM studies agglomeration of SAgNPs and TAgNPs but not in OAgNPs due to the interaction. Detailed SPR analysis showed interaction of GSH with nanoparticles resulted in alteration of three characteristic features namely changes a decrease in peak height at (506 nm and 398 nm) an increase in peak height (987 nm and 987 nm) and bathochromic shift of absorption peak in 600−700 nm range in the case of SAgNPs and TAgNPs, but no such changes were observed for OAgNPs. To understand the physical phenomenon Marquardt-Levenberg algorithm based non-linear curve fitting analysis where done. In the fitting analysis, GSH concentration-dependent changes of the AS characteristics were fitted to polynomials of different orders, and from the weighted residuals and 95 % prediction interval of the fits, the best models are suggested that describe the changes in the AS of the triangular AgNPs (TAgNPs). The probable reason for the phenomenon lies in surface protection and accessibility of the interaction surface. Unlike SAgNPs, in TAgNPs and OAgNPs the edges of each side are loosely protected with Polyvinylpyrrolidone (PVP) allowing enhanced interaction with GSH from the edges and linear joining. Further, the majority of the ridge of the surface of OAgNPs are not accessible to the other particles which reduce the stability of interaction and joining. As a cumulative result TAgNPs are the best choice for GSH titration among these 3 types of particles.

Hierarchical Hybrid Nanostructures Constructed by Fullerene and Molecular Tweezer.

For the construction of well-defined hierarchical superstructures of pristine [60]fullerene (C60) arrays, pyrene-based molecular tweezers (PT) were used as host molecules for catching and arranging C60 guest molecules. The formation of host-guest complexes was systematically studied in solution as well as in the solid state. Two-dimensional proton nuclear magnetic resonance spectroscopic studies revealed that PT-host and C60-guest complexes were closely related to the molecular self-assembly of PT. Ultraviolet and fluorescence spectroscopic titrations indicated the formation of stable 1:1 and 2:1 (PT/C60) complexes. From the nonlinear curve-fitting analysis, equilibrium constants for the 1:1 (log K1) and 2:1 (log K2) complexes were estimated to be 4.96 and 5.01, respectively. X-ray diffraction results combined with transmission electron microscopy observations clearly exhibited the construction of well-defined layered superstructures of the PT-host and C60-guest complexes. From electron mobility measurements, it was demonstrated that the well-defined hierarchical hybrid nanostructure incorporating a C60 array exhibited a high electron mobility of 1.7 × 10-2 cm2 V-1 s-1. This study can provide a guideline for the hierarchical hybrid nanostructures of host-guest complex and its applications.

Highly Sensitive Bifunctional Probe for Colorimetric Cyanide and Fluorometric H2S Detection and Bioimaging: Spontaneous Resolution, Aggregation, and Multicolor Fluorescence of Bisulfide Adduct.

A 4-methylbenzothiazole linked maleimide-based single molecular bifunctional probe 1 has been synthesized for the colorimetric and fluorometric detection of highly competitive H2S and cyanide ion in aqueous DMSO media. The probe 1 selectively detected CN- under the UV-vis spectroscopy through the rapid appearance of deep pink color. The bright pink color developed due to ICT in the moderately stable cyano substituted enolate intermediate. The absorbance titration of 1 with CN- revealed a new band at 540 nm and the nonlinear curve fitting analysis showed good fit with 1:1 model. In fluorescence channel, 1 was found to be highly selective to H2S in 50% aqueous buffer (pH 7). It exhibited ∼16-fold fluorescence intensity enhancement at 435 nm after reaction with 1 equiv of H2S due to the inhibition of PET. The 1-SH adduct showed TICT phenomenon and behaved like molecular rotor. It further displayed aggregation behavior at higher concentration and excitation wavelength dependent multicolor emission properties. Most interestingly, the spontaneous resolution of chiral S-isomer of the 1-SH adduct occurred during crystallization. The cell imaging study revealed the staining of the cell and multicolor emission in the presence of H2S.

Sorption studies for Cd(II) sequestration from aqueous solution on chemically modified Albizia lebbeck

ABSTRACTIn the present work, a new sorbent was successfully prepared by chemically modifying pods of Albizia lebbeck (AL) by Fenton’s reagent, followed by sodium silicate. Sorption studies were carried out by batch process. The optimum pH was found to be 6. Equilibrium isotherm data were analysed by non-linear curve fitting analysis, to fit Langmuir, Freundlich and Temkin isotherm models. Based on the Langmuir isotherm model, maximum monolayer sorption capacity (qm) was found to be 21.22 mg.g−1 at 50°C. Breakthrough and exhaustive capacities were found to be 10 and 50 mg.g−1, respectively. Desorption study showed 95% recovery of Cd(II) ions.

Differences on photosynthetic limitations between leaf margins and leaf centers under potassium deficiency for Brassica napus L.

Analyzing the proportions of stomatal (SL), mesophyll conductance (MCL) and biochemical limitations (BL) imposed by potassium (K) deficit, and evaluating their relationships to leaf K status will be helpful to understand the mechanism underlying the inhibition of K deficiency on photosynthesis (A). A quantitative limitation analysis of K deficiency on photosynthesis was performed on leaf margins and centers under K deficiency and sufficient K supply treatments of Brassica napus L. Potassium deficiency decreased A, stomatal (gs) and mesophyll conductance (gm) of margins, SL, MCL and BL accounted for 23.9%, 33.0% and 43.1% of the total limitations. While for leaf centers, relatively low limitations occurred. Nonlinear curve fitting analysis indicated that each limiting factor generated at same leaf K status (1.07%). Although MCL was the main component of limitations when A began to fall, BL replaced it at a leaf K concentration below 0.78%. Up-regulated MCL was related to lower surface area of chloroplasts exposed to intercellular airspaces (Sc/S) and larger cytosol diffusion resistance but not the cell wall thickness. Our results highlighted that photosynthetic limitations appear simultaneously under K deficiency and vary with increasing K deficiency intensity.

Selective Recognition of H3.1K36 Dimethylation/H4K16 Acetylation Facilitates the Regulation of All-trans-retinoic Acid (ATRA)-responsive Genes by Putative Chromatin Reader ZMYND8

ZMYND8 (zinc finger MYND (Myeloid, Nervy and DEAF-1)-type containing 8), a newly identified component of the transcriptional coregulator network, was found to interact with the Nucleosome Remodeling and Deacetylase (NuRD) complex. Previous reports have shown that ZMYND8 is instrumental in recruiting the NuRD complex to damaged chromatin for repressing transcription and promoting double strand break repair by homologous recombination. However, the mode of transcription regulation by ZMYND8 has remained elusive. Here, we report that through its specific key residues present in its conserved chromatin-binding modules, ZMYND8 interacts with the selective epigenetic marks H3.1K36Me2/H4K16Ac. Furthermore, ZMYND8 shows a clear preference for canonical histone H3.1 over variant H3.3. Interestingly, ZMYND8 was found to be recruited to several developmental genes, including the all-trans-retinoic acid (ATRA)-responsive ones, through its modified histone-binding ability. Being itself inducible by ATRA, this zinc finger transcription factor is involved in modulating other ATRA-inducible genes. We found that ZMYND8 interacts with transcription initiation-competent RNA polymerase II phosphorylated at Ser-5 in a DNA template-dependent manner and can alter the global gene transcription. Overall, our study identifies that ZMYND8 has CHD4-independent functions in regulating gene expression through its modified histone-binding ability.

Synthesis and Properties of Fluorescent Probe for Monosaccharides Based on Exocyclic Ring-Fused Boron Dipyrromethene Dye Substituted with Phenylboronic Ester

2-Ethoxycarbonyl-3,4-tetramethylenepyrrole prepared from cyclohexene through an improved twostep procedure was treated with excess lithium aluminum hydride at high temperature to give 2-methyl-3,4-tetramethylenepyrrole. Further condensation with protected 4-formylphenylboronic acid in the presence of trifluoroacetic acid as catalyst,followed by oxidation with 2,3-dichloro-5,6-dicyanobenzoquinone( DDQ) and treatment with triethylamine and boron trifluoride etherate, gives a novel exocyclic ring-fused borondipyrromethene( BDP) dye derivative substituted with phenylboronic ester subunit at the meso-position. The UV-Vis absorption titration and fluorescence titration measurements for BDP dye derivative were carried out to examine its responsibility to D-fructose,D-galactose,and D-glucose at specific p H. The influence of covalent interactions of BDP dye derivative with monosaccharides on its spectroscopic properties can be selectively recognized by both absorption and fluorescence spectra. By the nonlinear curve-fitting analysis of the fluorescence titration data,the association constants Ksof BDP derivative 1 with monosaccharide such as Dfructose,D-galactose,and D-glucose are 1045,445 and 130 L / mol,respectively. Thus BDP derivative 1 can be used as a sensitive and selective fluorescent probe for monosaccharides. Moreover,the sensing mechanism of the fluorescent probe was also preliminarily discussed.

A nonlinear isotherm model for sorption of anionic dyes on cellulose fibers: A case study

The sorption data of an anionic dye on cellulose fiber are often correlated with a log-linear model to determine the internal accessible volume of the fiber to the anionic dye (V, L/kg) and as such the standard affinity of the anionic dye to the fiber (−Δμ°, J/mol), but without taking into account the influence of ionized carboxyl groups due to cellulose oxidation ([COO−]f, mol/kg). In this study, a nonlinear isotherm model was derived by incorporating [COO−]f, V and −Δμ° as three model parameters. A set of classical sorption data of C. I. Direct Blue 1 on bleached cotton was correlated with the nonlinear isotherm model. The nonlinear curve fitting analysis showed that the nonlinear isotherm model was in excellent agreement with the sorption data and robust to determine the values of [COO−]f, V and −Δμ° for describing the sorption behaviors of anionic dyes on cellulose fibers.

Fityk: a general-purpose peak fitting program

Fitykis portable, open-source software for nonlinear curve fitting and data analysis. It specializes in fitting a sum of bell-shaped functions to experimental data. In particular, it enables Pawley refinement of powder diffraction data and size–strain analysis.

Kinetics and equilibrium studies for the removal of cadmium ions from aqueous solutions using Duolite ES 467 resin

Kinetic and equilibrium studies were conducted with cation exchange resin (Duolite ES 467) to investigate the effectiveness of removal of cadmium ions from aqueous solutions in a batch mode. The effect of various parameters was studied, such as contact time, agitation speed, sorbent mass, sorbate concentration, pH, competitive ion and temperature. The kinetic data were analyzed by finding their fitness to the well-known Lagergren and pseudo-second-order models using linear and non-linear curve fitting methods. Equilibrium isotherms generated were tested by applying Langmuir and Freundlich isotherm models using both linear and non-linear methods. The optimum contact time and agitation speed were found to be 60 min and 600 rpm, respectively. The presence of sodium chloride ions in solution drastically reduced the cadmium uptake. On the other hand, higher pH and temperature enhanced sorption. The non-linear curve fitting analysis method was found to fit the data better than the linear method. Similarly the Langmuir isotherm model has an edge over the Freundlich model. The calculated thermodynamic parameters such as ΔG 0, ΔH 0 and ΔS 0 indicate the effectiveness of Duolite ES 467 resin to remove cadmium from solution.

Modeling of ultrasonic degradation of non-volatile organic compounds by Langmuir-type kinetics

Sonochemical degradation of phenol (Ph), 4-isopropylphenol (4-IPP) and Rhodamine B (RhB) in aqueous solutions was investigated for a large range of initial concentrations in order to analyze the reaction kinetics. The initial rates of substrate degradation and H 2O 2 formation as a function of initial concentrations were determined. The obtained results show that the degradation rate increases with increasing initial substrate concentration up to a plateau and that the sonolytic destruction occurs mainly through reactions with hydroxyl radicals in the interfacial region of cavitation bubbles. The rate of H 2O 2 formation decreases with increasing substrate concentration and reaches a minimum, followed by almost constant production rate for higher substrate concentrations. Sonolytic degradation data were analyzed by the models of Okitsu et al. [K. Okitsu, K. Iwasaki, Y. Yobiko, H. Bandow, R. Nishimura, Y. Maeda, Sonochemical degradation of azo dyes in aqueous solution: a new heterogeneous kinetics model taking into account the local concentration OH radicals and azo dyes, Ultrason. Sonochem. 12 (2005) 255–262.] and Seprone et al. [N. Serpone, R. Terzian, H. Hidaka, E. Pelizzetti, Ultrasonic induced dehalogenation and oxidation of 2-, 3-, and 4-chlorophenol in air-equilibrated aqueous media. Similarities with irradiated semiconductor particulates, J. Phys. Chem. 98 (1994) 2634–2640.] developed on the basis of a Langmuir-type mechanism. The five linearized forms of the Okitsu et al.’s equation as well as the non-linear curve fitting analysis method were discussed. Results show that it is not appropriate to use the coefficient of determination of the linear regression method for comparing the best-fitting. Among the five linear expressions of the Okitsu et al.’s kinetic model, form-2 expression very well represent the degradation data for Ph and 4-IPP. Non-linear curve fitting analysis method was found to be the more appropriate method to determine the model parameters. An excellent representation of the experimental results of sonolytic destruction of RhB was obtained using the Serpone et al.’s model. The Serpone et al.’s model gives a worse fit for the sonolytic degradation data of Ph and 4-IPP. These results indicate that Ph and 4-IPP undergo degradation predominantly at the bubble/solution interface, whereas RhB undergoes degradation at both bubble/solution interface and in the bulk solution.

Kinetic and equilibrium study for the sorption of cadmium(II) ions from aqueous phase by eucalyptus bark

The efficiency of eucalyptus bark as a low cost sorbent for removing cadmium ions from aqueous solution has been investigated in batch mode. The equilibrium data could be well described by the Langmuir isotherm but a worse fit was obtained by the Freundlich model. The five linearized forms of the Langmuir equation as well as the non-linear curve fitting analysis method were discussed. Results show that the non-linear method may be a better way to obtain the Langmuir parameters. Maximum cadmium uptake obtained at a temperature of 20 °C was 14.53 mg g −1. The influence of temperature on the sorption isotherms of cadmium has been also studied. The monolayer sorption capacity increased from 14.53 to 16.47 when the temperature was raised from 20 to 50 °C. The Δ G° values were negative, which indicates that the sorption was spontaneous in nature. The effect of experimental parameters such as contact time, cadmium initial concentration, sorbent dose, temperature, solution initial pH, agitation speed, and ionic strength on the sorption kinetics of cadmium was investigated. Pseudo-second-order model was evaluated using the six linear forms as well as the non-linear curve fitting analysis method. Modeling of kinetic results shows that sorption process is best described by the pseudo-second-order model using the non-linear method. The pseudo-second-order model parameters were function of the initial concentration, the sorbent dose, the solution pH, the agitation speed, the temperature, and the ionic strength.

Batch sorption dynamics and equilibrium for the removal of cadmium ions from aqueous phase using wheat bran

Studies on a batch sorption process using wheat bran as a low cost sorbent was investigated to remove cadmium ions from aqueous solution. The influence of operational conditions such as contact time, cadmium initial concentration, sorbent mass, temperature, solution initial pH, agitation speed and ionic strength on the sorption kinetics of cadmium was studied. Pseudo-second-order model was evaluated using the six linear forms as well as the non-linear curve fitting analysis method. Modeling of kinetic results shows that sorption process is best described by the pseudo-second-order model using the non-linear method. The sorption of cadmium was found to be dependent on initial concentration, sorbent mass, solution pH, agitation speed, temperature, ionic strength and contact time. The value of activation energy (12.38 kJ mol −1) indicates that sorption has a low potential barrier corresponding to a physical process. Sorption equilibrium isotherms at different temperatures was determined and correlated with common isotherm equations such as Langmuir and Freundlich models. It was found that the Langmuir model appears to well fit the isotherm data but a worse correlation was obtained by the Freundlich model. The five Langmuir linear equations as well as the non-linear curve fitting analysis method were discussed. Results show that the non-linear method may be a better way to obtain the Langmuir parameters. Thermodynamic parameters such as Δ H°, Δ S° and Δ G° were calculated. These parameters indicate that the sorption of cadmium by wheat bran is a spontaneous process and physical in nature involving weak forces of attraction and is also endothermic.

Targeted Overexpression of Sarcolipin in the Mouse Heart Decreases Sarcoplasmic Reticulum Calcium Transport and Cardiac Contractility

The role of sarcolipin (SLN) in cardiac physiology was critically evaluated by generating a transgenic (TG) mouse model in which the SLN to sarco(endoplasmic)reticulum (SR) Ca(2+) ATPase (SERCA) ratio was increased in the ventricle. Overexpression of SLN decreases SR calcium transport function and results in decreased calcium transient amplitude and rate of relaxation. SLN TG hearts exhibit a significant decrease in rates of contraction and relaxation when assessed by ex vivo work-performing heart preparations. Similar results were also observed with muscle preparations and myocytes from SLN TG ventricles. Interestingly, the inhibitory effect of SLN was partially relieved upon high dose of isoproterenol treatment and stimulation at high frequency. Biochemical analyses show that an increase in SLN level does not affect PLB levels, monomer to pentamer ratio, or its phosphorylation status. No compensatory changes were seen in the expression of other calcium-handling proteins. These studies suggest that the SLN effect on SERCA pump is direct and is not mediated through increased monomerization of PLB or by a change in PLB phosphorylation status. We conclude that SLN is a novel regulator of SERCA pump activity, and its inhibitory effect can be reversed by beta-adrenergic agonists.

Plasma membrane-bound cyclic AMP phosphodiesterase activity in 3T3-L1 adipocytes

Plasma membranes were isolated from 3T3-L1 adipocytes. Plasma membrane phosphodiesterase (PM-PDE) was measured in the presence of 5 μM cilostamide. Time course and cAMP dose response ranging from 0 to 2 μM were measured. PM-PDE remained linear up to 20 min. Non-linear curve fitting analysis showed that the low K m cAMP dose data fit a two component curve significantly better than a one component curve, indicating that there are two iso-forms of PDE in the plasma membrane of 3T3-L1 adipocytes, similar to swine adipocytes. The K m and V max values for this two component curve were K m1=0.12 μM, V max1=3.08 pmol min −1 mg −1 protein, and K m2=3.67 μM, V max2=83.8 pmol min −1 mg −1 protein. Inhibitors of PDE1, PDE2 and PDE5 failed to inhibit PM-PDE, as observed in swine adipocyte plasma membranes. However, PDE4 inhibitors were three-fold more effective at inhibiting PDE in 3T3-L1 PM compared to swine adipocyte PM. One mM 1, 3-dipropyl-8- p-sulfophenylxanthine (DPSPX) inhibited PM-PDE by approximately 75% in both preparations. These data demonstrate that PM-PDE is distinct from microsomal membrane PDE and may be responsible for extracellular cAMP metabolism to AMP in 3T3-L1 adipocytes.

Comparison of some models for nonlinear fitting analysis of TSC measurements

Basic differential equations for thermally stimulated conductivity (TSC) measurement have no analytical solutions even for the simplest cases. Therefore, analysis of the obtained results is very difficult. The same equations are used also for thermoluminescence (TL). Nevertheless, TL analysis is much easier due to a number of approximate models, such as general order kinetics and mixed order kinetics. In this paper we discuss usefulness of the approximations in description of TSC with respect to determination of trap parameters using nonlinear curve fitting analysis. For this purpose appropriate equations were derived. The results are compared to the recently derived method based on the quasi equilibrium approximation.

Evaluation of the growth dynamics of Trichophyton rubrum cultures by morphometry and non-linear curve fitting analysis.

To determine the size of dermatophyte thalli, a point-counting procedure with a square lattice grid is proposed instead of using the one-dimensional diameter as the size parameter. For an analysis of the growth dynamics of such colonies, the area values might be subjected to a non-linear curve-fitting procedure. To demonstrate the method, samples of 15 Trichophyton rubrum strains, isolated from human skin and cultured concomitantly on Sabouraud and Selective agar during a period of 8 weeks, were used. The morphometric assessment of the area of the thalli, subjected to non-linear curve fitting, disclosed only a slight difference in the growth dynamics.

Harmaline competitively inhibits [ [formula omitted]]MK-801 binding to the NMDA receptor in rabbit brain

Harmaline, a β-carboline derivative, is known to produce tremor through a direct activation of cells in the inferior olive. However, the receptor(s) through which harmaline acts remains unknown. It was recently reported that the tremorogenic actions of harmaline could be blocked by the noncompetitive NMDA channel blocker, MK-801. This study examined whether the blockade of harmaline's action, in the rabbit, by MK-801 was due to a pharmacological antagonism at the MK-801 binding site. This was accomplished by measurement of [ 3H ]MK-801 binding in membrane fractions derived from tissue containing the inferior olivary nucleus and from cerebral cortex. Harmaline completely displaced saturable [ 3H ]MK-801 binding in both the inferior olive and cortex with apparent IC 50 values of 60 and 170 μM, respectively. These IC 50 values are consistent with the high doses of harmaline required to produce tremor, e.g., 10–30 mg/kg. Non-linear curve fitting analysis of [ 3H ]MK-801 saturation experiments indicated that [ 3H ]MK-801 bound to a single site and that harmaline's displacement of [ 3H ]MK-801 binding to the NMDA receptor was competitive as indicated by a shift in K d but not in B max. In addition, a Schild plot gave a slope that was not significantly different from 1 indicating that harmaline was producing a displacement of [ 3H ]MK-801 from its binding site within the NMDA cation channel and not through an action at the glutamate or other allosteric sites on the NMDA receptor. These findings provide in vitro evidence that the competitive blockade of harmaline-induced tremor by MK-801 occurs within the calcium channel coupled to the NMDA receptor. Our hypothesis is that harmaline produces tremor by acting as an inverse agonist at the MK-801 binding site and thus opening the cation channel.

Characterization of type A and type B CCK receptor binding sites in rat vagus nerve

We employed quantitative receptor autoradiography to analyze pharmacological properties of 125I-Bolton Hunter cholecystokinin (CCK-8)-labeled binding sites in sections of rat cervical vagus nerve that had been ligated 24 h prior to extraction. Binding densities were detected in segments of nerve proximal and distal to the ligature. Analysis was confined to proximal segments. Saturation and competitive binding studies were carried out using sulphated CCK-8 and two selective CCK receptor antagonists: MK-329, to define type-A (CCK A) binding sites; and, L-365,260, to define type-B (CCK B) binding sites. Sulphated CCK-8 was the most potent inhibitor of vagal 125I-CCK binding (IC 50 = 2nM). Nonlinear curve fitting analysis of the CCK binding data favored the presence of a single class of vagal CCK receptorsKD i = 1nM). However, both MK-329 (IC 50 = 18nM) and L-365,260 (IC 50 = 45nM) completed for vagal 125I-CCK binding indicating the presence of CCK A and CCK B binding sites. Co-analysis of the antagonist binding data suggested that CCK A and CCK B receptors were transported in equal concentration within the vagus. MK-329 bound with high affinity to CCK A sites (K i = 3nM) and low-affinity to CCK B sites (K i = 462nM) while L-365,260 bound with high affinity to CCK B sites (K i = 10nM) and low-affinity to CCK A sites (K i = 775nM). These same ligands were used to characterize the specificity of 125I-CCK binding in the medial and lateral divisions of the nucleus of the solitary tract (NTS), two regions innervated by primary vagal afferents carrying CCK receptors. Sulphated CCK-8 was the most potent inhibitor of 125I-CCK binding in both regions of the NTS (IC 50 = 0.6nM, medial;IC 50 = 0.4nM, lateral). In the medial NTS, MK-329 was a potent inhibitor (IC 50 = 21.8nM) while MK-329 was a weak inhibitor (IC 50 = 341nM) of 125I-CCK binding. In contrast, in the lateral NTS, L-365,260 was a potent inhibitor (IC 50 = 21.8nM) while MK-329 was a weak inhibitor (IC> 1,0000 nM) of 125I-CCK binding. These results are consistent with the existence of two populations of vagal afferent fibers projecting to different regions of the NTS. One, containing CCK A receptors, projects principally to the medial NTS, while the other containing CCK B receptors, projects principally to the lateral NTS.