Prolactin modifies the prostaglandin synthesis, prolactin binding and fluidity of mouse liver membranes

The objective of these studies was to determine if prolactin, known to induce its own receptors, alters the prostaglandin (PG) synthesis which could, in turn, modify the fluidity of the membrane and thus alter the functionality of prolactin receptors. Adult male C₃H mice were injected subcutaneously with 100 μg of oPRL every 4 h for 0, 24 or 48 h and sacrificed 8 h after receiving the last injection. Liver 100,000 × $\text{g}$ membrane pellets were used in the measurement of these parameters. The amount of binding of prolactin to these membranes increased with the duration of injections, the values being 179 and 244% of control values after 24 and 48 h of injections, respectively. The amounts of PGF_2α and PGE synthesized also increased after these injections, the values being 127 and 270% of control for PGF_2α and 634 and 695% of control values for PGE after 24 and 48 h of injections, respectively. Fluorescence polarization, an index of microviscosity, was decreased by 14 and 20% after 24 and 48 h of PRL administration, respectively. Previous studies have demonstrated simultaneous in vitro effects of prostaglandin on both prolactin receptors and membrane fluidity. The current data are in agreement with those observations and suggest that prolactin may modulate its own receptor by increasing the fluidity of the membrane in which it exists by alterations within the PG cascade. Such biochemical changes may then modify existing restraints and allow the hormone receptor to assume a more functional configuration.     

Sex differences in oxytocin receptor binding in forebrain regions: Correlations with social interest in brain region- and sex- specific ways

Social interest reflects the motivation to approach a conspecific for the assessment of social cues and is measured in rats by the amount of time spent investigating conspecifics. Virgin female rats show lower social interest towards unfamiliar juvenile conspecifics than virgin male rats. We hypothesized that the neuropeptide oxytocin (OT) may modulate sex differences in social interest because of the involvement of OT in pro-social behaviors. We determined whether there are sex differences in OT system parameters in the brain and whether these parameters would correlate with social interest. We also determined whether estrus phase or maternal experience would alter low social interest and whether this would correlate with changes in OT system parameters. Our results show that regardless of estrus phase, females have significantly lower OT receptor (OTR) binding densities than males in the majority of forebrain regions analyzed, including the nucleus accumbens, caudate putamen, lateral septum, bed nucleus of the stria terminalis, medial amygdala, and ventromedial hypothalamus. Interestingly, male social interest correlated positively with OTR binding densities in the medial amygdala, while female social interest correlated negatively with OTR binding densities in the central amygdala. Proestrus/estrus females showed similar social interest to non-estrus females despite increased OTR binding densities in several forebrain areas. Maternal experience had no immediate or long-lasting effects on social interest or OT brain parameters except for higher OTR binding in the medial amygdala in primiparous females. Together, these findings demonstrate that there are robust sex differences in OTR binding densities in multiple forebrain regions of rats and that OTR binding densities correlate with social interest in brain region- and sex-specific ways.     

Evaluation of a new model system for studying the formation of heterocyclic amines

Heterocyclic amines (HAs) are an important class of food mutagens and carcinogens, which can be found in cooked meat and fish. Increasing heating temperatures and times usually increase mutagenic activity in meat and meat extracts during cooking. We developed a model system, which allows to examine the effects of precursor composition and heating conditions (time and temperature) on the formation of HAs in meat. Homogenized and freeze dried meat samples (beef, pork chops, chicken breast and turkey breast) are heated with diethylene glycol in closed vials under stirring in a thermostated heating block. After an appropriate sample preparation (extraction and clean-up) ten different HAs were measured by HPLC analyses with gradient elution and mass selective detection. The time courses of HA-formation in the different kinds of meat at varying heating temperatures were determined up to heating times of 30 min. 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine (PhIP) was the most abundant HA in these experiments and reached the highest concentrations in the beef meat samples, as did the other HAs (MeIQ, AalphaC) at 220 degrees C in the heating block under stirred conditions. Additionally the influence of the antioxidant TBHQ (t-butylhydroquinone) on the formation of HAs in the model system was tested. However TBHQ effected only slight reductions of HA formation in all kinds of meat.     

Formation of 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline in a model system by heating creatinine, glycine and glucose

A mixture of creatinine, glucose and glycine was heated in diethylene glycol containing 14% water for 2 h at 128 degrees C, and the mutagens formed were purified by XAD-2 column chromatography, acid-base partition, Sephadex LH-20 column chromatography, 'blue cotton' treatment and HPLC. Two mutagenic substances were isolated by HPLC. The major mutagen was identified by its UV absorption and mass and NMR spectra as 2-amino-3,8- dimethylimidazo [4,5-f]quinoxaline, which was originally isolated from fried beef. This finding supported the idea that creatinine, amino acids and sugars present in meat are precursors in the formation of the mutagenic imidazoquinoxaline derivative.     

Molecular mechanisms of ammonium transport and accumulation in plants

The integral membrane proteins of the ammonium transporter (AMT/Rh) family provide the major route for shuttling ammonium (NH(4)(+)/NH(3)) across bacterial, archaeal, fungal and plant membranes. These proteins are distantly related to the Rh (rhesus) glycoproteins, which are absent in higher plants, but are present in many species, including bacteria and mammals. It appears that the large nitrogen requirement of plants resulted in unique strategies to acquire, capture and/or release ammonium. The biological function of plant ammonium transporters will be discussed and compared to other AMT/Rh proteins.     

Exposure to female pheromones stimulates a specific type of neuronal population in the male but not female magnocellular division of the medial preoptic nucleus (MPN mag) of the Syrian hamster

The magnocellular division of the medial preoptic area (MPN mag) integrates pheromonal and hormonal signals to play a critical role in the expression of male typical sex behavior. The MPN mag contains two morphologically distinct neuronal populations; the percentage of each type within the nucleus is sex specific. Males have more neurons with a single nucleolus whereas females have more with multiple nucleoli. To determine which neuronal subtype mediates pheromonal induction of copulation, tissue from male and female hamsters exposed to female pheromones was immunolabeled for the immediate early protein (EGR-1). Subsequently the tissue was counterstained and the number of ERG-1 neurons with one or two nuclei was determined. The results indicate that pheromones stimulate neurons with single nucleoli in males but fail to stimulate either neuronal subtype in females suggesting that synaptic input to the MPN mag is sexually differentiated.     

Blue cotton, Blue Rayon and Blue Chitin in the analysis of heterocyclic aromatic amines--a review

Heterocyclic amines (HCAs) are a group of compounds formed when protein-rich foods, such as meat or fish, are prepared under normal cooking conditions, such as frying, grilling, or broiling. To evaluate and estimate the risks associated with HCAs contained in the diet, it is important to determine the levels in cooked foods, and the levels of HCAs and metabolites in the body. HCAs are normally found at low amounts in a complex matrix, which necessitates a good purification method and a sensitive detection system. The objective of this review was to briefly present the current knowledge on the use of Blue Cotton, Blue Rayon and Blue Chitin in the analysis of HCAs.     

Determination of heterocyclic aromatic amines in beef extract, cooked meat and rat urine by liquid chromatography with coulometric electrode array detection

This paper describes a method for the determination of heterocyclic aromatic amines (HAs; DMIP, IQ, MeIQ, MeIQx, 4,8-DiMeIQx, 7,8-DiMeIQx, AalphaC, PhIP) by high-performance liquid chromatography (HPLC) with coulometric electrode array detection. The compounds are separated on reversed phase columns (LiChroCart Superspher 60 RP-select B, 250 mm x 2 mm, 4 microm and LiChrospher 60 RP-select B, 250 mm x 4 mm, 5 microm) using mobile phases consisting of acetonitrile/buffer/distilled water and detected at eight working electrodes at potentials between +190 and +680 mV against modified palladium electrodes. In the context of an EU-interlaboratory exercise, the method was applied to analyse a standardised test solution and--after isolation of the analytes by several clean-up steps--for the analysis of standardised beef extract and grilled meat. Further, the method could be applied for the analysis of HAs in suspensions of bacteria and rat urine without any sample preparation step beyond sample dilution. The data obtained show that HPLC with coulometric electrode array detection gives accurate results.     

Chemosensory and hormone information are relayed directly between the medial amygdala, posterior bed nucleus of the stria terminalis, and medial preoptic area in male Syrian hamsters

In many rodent species, including Syrian hamsters, the expression of appropriate social behavior depends critically on the perception and identification of conspecific odors. The behavioral response to these odors is mediated by a network of steroid-sensitive ventral forebrain nuclei including the medial amygdala (Me), posterior bed nucleus of the stria terminalis (BNST), and medial preoptic area (MPOA). Although it is well-known that Me, BNST, and MPOA are densely interconnected and each uniquely modulates odor-guided social behaviors, the degree to which conspecific odor information and steroid hormone cues are directly relayed between these nuclei is unknown. To answer this question, we injected the retrograde tracer, cholera toxin B (CTB), into the BNST or MPOA of male subjects and identified whether retrogradely-labeled cells in Me and BNST 1) expressed immediate early genes (IEGs) following exposure to male and/or female odors or 2) expressed androgen receptor (AR). Although few retrogradely-labeled cells co-localized with IEGs, a higher percentage of BNST- and MPOA-projecting cells in the posterior Me (MeP) expressed IEGs in response to female odors than to male odors. The percentage of retrogradely-labeled cells that expressed IEGs did not, however, differ between and female and male odor-exposed groups in the anterior Me (MeA), posterointermediate BNST (BNSTpi), or posteromedial BNST (BNSTpm). Many retrogradely-labeled cells co-localized with AR, and a higher percentage of retrogradely-labeled MeP and BNSTpm cells expressed AR than retrogradely-labeled MeA and BNSTpi cells, respectively. Together, these data demonstrate that Me, BNST, and MPOA interact as a functional circuit to process sex-specific odor cues and hormone information in male Syrian hamsters.     

Determination of less polar heterocyclic aromatic amines in standardised beef extracts and cooked meat consumed in Austria by liquid chromatography and fluorescence detection

An analysis method was developed for the determination of trace levels of less polar heterocyclic aromatic amines (HAs) in food samples. The development started from a frequently used sample pre-treatment scheme which was slightly improved to make it applicable with high-performance liquid chromatography (HPLC) with fluorescence detection. The method was applied for the analysis of a standardised beef extract containing 5-15 ng/g of HAs and the results are compared with those of the other participants in the same European project. In addition, the method was used for the analysis of less polar HAs in cooked meat consumed in Austria.