Salivary Testosterone and Sexual Function and Behavior in Men and Women: Findings from the Third British National Survey of Sexual Attitudes and Lifestyles (Natsal-3).

Using data from the third British National Survey of Sexual Attitudes and Lifestyles (Natsal-3) we examined associations between salivary testosterone (Sal-T) and sexual function and behavior. Single morning saliva samples were self-collected from a subsample of participants aged 18-74 years and analyzed using mass spectrometry. 1,599 men and 2,123 women were included in the analysis (40.6% of those invited to provide a sample). We adjusted for confounders in a stepwise manner: in model 1 we adjusted for age only; model 2 for age, season and relationship status, and model 3 we added BMI and self-reported health. In the fully adjusted models, among men, Sal-T was positively associated with both partnered sex (vaginal sex and concurrent partners) and masturbation. Among women, Sal-T was positively associated with masturbation, the only association with partnered sex was with ever experience of same-sex sex. We found no clear association between Sal-T and sexual function. Our study contributes toward addressing the sparsity of data outside the laboratory on the differences between men and women in the relationship between T and sexual function and behavior. To our knowledge, this is the first population study, among men and women, using a mass spectrometry Sal-T assay to do so.

Prevalence of infertility and help seeking among 15 000 women and men.

STUDY QUESTION: What is the prevalence of infertility and of help seeking among women and men in Britain? SUMMARY ANSWER: One in eight women and one in ten men aged 16-74 years had experienced infertility, defined by unsuccessfully attempting pregnancy for a year or longer, and little more than half of these people sought medical or professional help. WHAT IS KNOWN ALREADY: Estimates of infertility and help seeking in Britain vary widely and are not easily comparable because of different definitions and study populations. STUDY DESIGN, SIZE, DURATION: A cross-sectional population survey was conducted between 2010 and 2012 with a sample of 15 162 women and men aged 16-74 years. PARTICIPANTS/MATERIALS, SETTING, METHODS: Participants completed the Natsal-3 questionnaire, using computer-assisted personal interviewing (CAPI) and computer-assisted self-interview (CASI). MAIN RESULTS AND THE ROLE OF CHANCE: The reported prevalence of infertility was 12.5% (CI 95% 11.7-13.3) among women and 10.1% (CI 95% 9.2-11.1) among men. Increased prevalence was associated with later cohabitation with a partner, higher socio-economic status and, for those who had a child, becoming parents at older ages. The reported prevalence of help seeking was 57.3% (CI 95% 53.6-61.0) among women and 53.2% (CI 95% 48.1-58.1) among men. Help seekers were more likely to be better educated and in higher status occupations and, among those who had a child, to have become parents later in life. LIMITATIONS, REASONS FOR CAUTION: These data are cross-sectional so it is not possible to establish temporality or infer causality. Self-reported data may be subject to recall bias. WIDER IMPLICATIONS OF THE FINDINGS: The study provides estimates of infertility and help seeking in Britain and the results indicate that the prevalence of infertility is higher among those delaying parenthood. Those with higher educational qualifications and occupational status are more likely to consult with medical professionals for fertility problems than others and these inequalities in help seeking should be considered by clinical practice and public health. STUDY FUNDING/COMPETING INTERESTS: Funding was provided by grants from the Medical Research Council and the Wellcome Trust, with support from the Economic and Social Research Council and the Department of Health. AMJ is a Governor of the Wellcome Trust. Other authors have no competing interests.

Examining spatial patterns in polycyclic aromatic compounds measured in stream macroinvertebrates near a small subarctic oil and gas operation.

The Cameron River runs through a small, remote petrochemical development in the Cameron Hills (Northwest Territories, Canada). In order to evaluate the exposure of aquatic biota to contaminants from oil and gas activities, we measured polycyclic aromatic compounds (PACs) in macroinvertebrates collected from sites and tributaries along the Cameron River, including upstream and downstream of the development, and sites located near drilled wells (developed). Macroinvertebrate tissue PAC burdens ranged from 0.2-2.8 µg g(-1) lipid for unsubstituted compounds, and from 4.2-63.2 µg g(-1) lipid for alkylated compounds, relatively low compared to similar studies from more industrialized regions in North America. There was no significant difference in tissue PAC burdens between upstream, downstream, or developed sites (p = 0.12), although alkyl PACs in five out of seven developed sites were higher than the regional average. Petrogenic PACs were dominant in most samples, including alkyl fluorines, alkyl phenanthrene/anthracenes, and alkyl dibenzothiophenes. Minimal changes in PAC composition in macroinvertebrate tissues were detected along the Cameron River, with the exception of the two sites furthest downstream that had high concentrations of C3-C4 naphthalene. Overall, our results suggest that oil and gas development in the Cameron Hills has not resulted in substantial increases in PAC bioaccumulation in stream macroinvertebrates, although the potential that alkyl naphthalenes are being transported downstream from the development warrants further attention.

Caffeine in floral nectar enhances a pollinator's memory of reward.

Plant defense compounds occur in floral nectar, but their ecological role is not well understood. We provide evidence that plant compounds pharmacologically alter pollinator behavior by enhancing their memory of reward. Honeybees rewarded with caffeine, which occurs naturally in nectar of Coffea and Citrus species, were three times as likely to remember a learned floral scent as were honeybees rewarded with sucrose alone. Caffeine potentiated responses of mushroom body neurons involved in olfactory learning and memory by acting as an adenosine receptor antagonist. Caffeine concentrations in nectar did not exceed the bees' bitter taste threshold, implying that pollinators impose selection for nectar that is pharmacologically active but not repellent. By using a drug to enhance memories of reward, plants secure pollinator fidelity and improve reproductive success.

Activation of the tonic GABAC receptor current in retinal bipolar cell terminals by nonvesicular GABA release.

Within the second synaptic layer of the retina, bipolar cell (BC) output to ganglion cells is regulated by inhibitory input to BC axon terminals. GABA(A) receptors (GABA(A)Rs) mediate rapid synaptic currents in BC terminals, whereas GABA(C) receptors (GABA(C)Rs) mediate slow evoked currents and a tonic current, which is strongly regulated by GAT-1 GABA transporters. We have used voltage-clamp recordings from BC terminals in goldfish retinal slices to determine the source of GABA for activation of these currents. Inhibition of vesicular release with concanamycin A or tetanus toxin significantly inhibited GABA(A)R inhibitory postsynaptic currents and glutamate-evoked GABA(A)R and GABA(C)R currents but did not reduce the tonic GABA(C)R current, which was also not dependent on extracellular Ca(2+). The tonic current was strongly potentiated by inhibition of GABA transaminase, under both normal and Ca(2+)-free conditions, and was activated by exogenous taurine; however inhibition of taurine transport had little effect. The tonic current was unaffected by GAT-2/3 inhibition and was potentiated by GAT-1 inhibition even in the absence of vesicular release, indicating that it is unlikely to be evoked by reversal of GABA transporters or by ambient GABA. In addition, GABA release does not appear to occur via hemichannels or P2X(7) receptors. BC terminals therefore exhibit two forms of GABA(C)R-mediated inhibition, activated by vesicular and by nonvesicular GABA release, which are likely to have distinct functions in visual signal processing. The tonic GABA(C)R current in BC terminals exhibits similar properties to tonic GABA(A)R and glutamate receptor currents in the brain.

Intent-to-treat analysis of the placebo-controlled trial of letrozole for extended adjuvant therapy in early breast cancer: NCIC CTG MA.17.

BACKGROUND: MA.17 evaluated letrozole or placebo after 5 years of tamoxifen and showed significant improvement in disease-free survival (DFS) for letrozole [hazard ratio (HR) 0.57, P = 0.00008]. The trial was unblinded and placebo patients were offered letrozole. PATIENTS AND METHODS: An intent-to-treat analysis of all outcomes, before and after unblinding, on the basis of the original randomization was carried out. RESULTS: In all, 5187 patients were randomly allocated to the study at baseline and, at unblinding, 1579 (66%) of 2383 placebo patients accepted letrozole. At median follow-up of 64 months (range 16-95), 399 recurrences or contralateral breast cancers (CLBCs) (164 letrozole and 235 placebo) occurred. Four-year DFS was 94.3% (letrozole) and 91.4% (placebo) [HR 0.68, 95% confidence interval (CI) 0.55-0.83, P = 0.0001] and showed superiority for letrozole in both node-positive and -negative patients. Corresponding 4-year distant DFS was 96.3% and 94.9% (HR 0.80, 95% CI 0.62-1.03, P = 0.082). Four-year overall survival was 95.1% for both groups. The annual rate of CLBC was 0.28% for letrozole and 0.46% for placebo patients (HR 0.61, 95% CI 0.39-0.97, P = 0.033). CONCLUSIONS: Patients originally randomly assigned to receive letrozole within 3 months of stopping tamoxifen did better than placebo patients in DFS and CLBC, despite 66% of placebo patients taking letrozole after unblinding.

A dose escalation trial of adjuvant cyclophosphamide and epirubicin in combination with 5-fluorouracil using G-CSF support for premenopausal women with breast cancer involving four or more positive nodes.

BACKGROUND: Dose-dense and dose-intensive regimens have improved the outcome of breast cancer in high-risk women with operable disease. PATIENTS AND METHODS: Sixty-three premenopausal women with Stage 2, 3 breast cancer and > or =4 positive axillary nodes were treated in three successive cohorts with 70 mg/m(2) of epirubicin, 500 mg/m(2) of 5-fluorouracil and G-CSF every 14 days for 12 cycles. Cyclophosphamide (C) was given at 700 mg/m(2), 900 mg/m(2), and 1100 mg/m(2) doses. Patients were evaluated for dose-limiting toxicities (DLTs) in the first four cycles, the primary endpoint of the trial. RESULTS: No DLTs were seen at C 700 mg/m(2); at C 900 mg/m(2) two of 16 patients experienced febrile neutropenia and poor performance status; at C 1100 mg/m(2), 1 of 31 patients experienced poor performance status. Over 6 months, febrile neutropenia, grade 4 thrombocytopenia, grade 3 anemia and severe fatigue were observed. Clinical congestive heart failure occurred in three patients over 4 years. CONCLUSION: A dose-intense and dose-dense regimen of cyclophosphamide, epirubicin and 5-fluorouracil was delivered with G-CSF without apparent increase in acute toxicity. Cyclophosphamide could be increased to more than twice the standard dose at the cost of more anemia and fatigue.

The influence of letrozole on serum lipid concentrations in postmenopausal women with primary breast cancer who have completed 5 years of adjuvant tamoxifen (NCIC CTG MA.17L).

BACKGROUND: The purpose of this study was to evaluate changes in serum lipid parameters {cholesterol, high-density lipoprotein (HDL) cholesterol, low-density lipoprotein (LDL) cholesterol, triglycerides and lipoprotein(a) [Lp(a)]}, in postmenopausal women receiving letrozole or placebo after adjuvant tamoxifen for early stage breast cancer (NCIC CTG MA.17L). PATIENTS AND METHODS: MA.17L is a substudy of MA.17, a randomized, double-blind, placebo-controlled trial of letrozole 2.5 mg taken daily for 5 years in postmenopausal women with primary breast cancer completing approximately 5 years of prior adjuvant tamoxifen. Patients consenting to participate in this companion study had blood drawn and lipid parameters (total cholesterol, HDL cholesterol, LDL cholesterol, Lp(a), triglycerides) evaluated at baseline, 6 months, 12 months and yearly thereafter until completion of protocol therapy. It was required that women be non-hyperlipidemic and not taking lipid-lowering drugs at time of entry on this trial. RESULTS: Three hundred and forty seven women were enrolled in the study. The letrozole and the placebo groups demonstrated marginally significant differences in the percentage change from baseline in HDL cholesterol at 6 months (P=0.049), in LDL cholesterol at 12 months (P=0.033) and triglycerides at 24 months (P=0.036). All comparisons of lipid parameters at other time points were not significantly different between the two treatment groups. No statistically significant differences in the number of patients exceeding the thresholds defined for the lipid parameters were found between the two treatment groups. CONCLUSIONS: The MA.17 trial demonstrated a significant improvement in disease-free survival with the use of letrozole as extended adjuvant therapy post tamoxifen. Results from this study suggests that letrozole does not significantly alter serum cholesterol, HDL cholesterol, LDL cholesterol, triglycerides or Lp(a) in non-hyperlidiemic postmenopausal women with primary breast cancer treated up to 36 months following at least 5 years of adjuvant tamoxifen therapy. These findings further support the tolerability of extended adjuvant letrozole in postmenopausal women following standard tamoxifen therapy.

Mathematical modelling of non-stationary fluctuation analysis for studying channel properties of synaptic AMPA receptors.

1. The molecular properties of synaptic alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) receptors are an important factor determining excitatory synaptic transmission in the brain. Changes in the number (N) or single-channel conductance (gamma) of functional AMPA receptors may underlie synaptic plasticity, such as long-term potentiation (LTP) and long-term depression (LTD). These parameters have been estimated using non-stationary fluctuation analysis (NSFA). 2. The validity of NSFA for studying the channel properties of synaptic AMPA receptors was assessed using a cable model with dendritic spines and a microscopic kinetic description of AMPA receptors. Electrotonic, geometric and kinetic parameters were altered in order to determine their effects on estimates of the underlying gamma. 3. Estimates of gamma were very sensitive to the access resistance of the recording (R(A)) and the mean open time of AMPA channels. Estimates of gamma were less sensitive to the distance between the electrode and the synaptic site, the electrotonic properties of dendritic structures, recording electrode capacitance and background noise. Estimates of gamma were insensitive to changes in spine morphology, synaptic glutamate concentration and the peak open probability (P(o)) of AMPA receptors. 4. The results obtained using the model agree with biological data, obtained from 91 dendritic recordings from rat CA1 pyramidal cells. A correlation analysis showed that R(A) resulted in a slowing of the decay time constant of excitatory postsynaptic currents (EPSCs) by approximately 150 %, from an estimated value of 3.1 ms. R(A) also greatly attenuated the absolute estimate of gamma by approximately 50-70 %. 5. When other parameters remain constant, the model demonstrates that NSFA of dendritic recordings can readily discriminate between changes in gamma vs. changes in N or P(o). Neither background noise nor asynchronous activation of multiple synapses prevented reliable discrimination between changes in gamma and changes in either N or P(o). 6. The model (available online) can be used to predict how changes in the different properties of AMPA receptors may influence synaptic transmission and plasticity.

A characterisation of long-term depression induced by metabotropic glutamate receptor activation in the rat hippocampus in vitro.

1. In the CA1 region of hippocampal slices prepared from juvenile (12- to 18-day-old) rats, activation of group I metabotropic L-glutamate (mGlu) receptors by the specific agonist (RS)-3,5-dihydroxyphenylglycine (DHPG) induces a form of long-term depression (LTD) of excitatory synaptic transmission. 2. We have used a variety of electrophysiological techniques applied to CA1 neurones in hippocampal slices and from pyramidal cells in dissociated hippocampal cultures to investigate the Ca2+ dependence and locus of expression of DHPG-induced LTD. 3. In patch-clamp experiments from hippocampal slices, bath application of DHPG induced a depression of synaptically evoked responses that persisted for the duration of the recording (up to 2 h after commencing washout of DHPG) in 27 of 29 neurones investigated. 4. DHPG-induced LTD was associated with an increase in both the paired-pulse facilitation ratio and the coefficient of variation of EPSCs. 5. Using dendritic recording, there was a decrease in EPSC success rate (number of trials that elicited a detectable response) but no change in potency (mean EPSC amplitude excluding failures) associated with DHPG-induced LTD. 6. In experiments using dissociated hippocampal cultures, application of DHPG elicited a persistent decrease in the frequency of tetrodotoxin-resistant miniature EPSCs but no change in the amplitude of such events. 7. DHPG-induced LTD was not blocked by intracellular application of the calcium chelator BAPTA. It was also unaffected when intracellular calcium stores were depleted by perfusion with thapsigargin. Furthermore, when synaptic transmission was blocked by perfusing with Ca2+-free medium, DHPG application reliably induced LTD. 8. These data suggest that DHPG-induced LTD is Ca2+ independent and is expressed presynaptically.

Air kerma calibration factors and chamber correction values for PTW soft x-ray, NACP and Roos ionization chambers at very low x-ray energies.

This paper evaluates the characteristics of ionization chambers for the measurement of absorbed dose to water using very low-energy x-rays. The values of the chamber correction factor, k(ch), used in the IPEMB 1996 code of practice for the UK secondary standard ionization chambers (PTW type M23342 and PTW type M23344), the Roos (PTW type 34001) and NACP electron chambers are derived. The responses in air of the small and large soft x-ray chambers (PTW type M23342 and PTW type M23344) and the NACP and Roos electron ionization chambers were compared. Besides the soft x-ray chambers, the NACP and Roos chambers can be used for very low-energy x-ray dosimetry provided that they are used in the restricted energy range for which their response does not change by more than 5%. The chamber correction factor was found by comparing the absorbed dose to water determined using the dosimetry protocol recommended for low-energy x-rays with that for very low-energy x-rays. The overlap energy range was extended using data from Grosswendt and Knight. Chamber correction factors given in this paper are chamber dependent, varying from 1.037 to 1.066 for a PTW type M23344 chamber, which is very different from a value of unity given in the IPEMB code. However, the values of k(ch) determined in this paper agree with those given in the DIN standard within experimental uncertainty. The authors recommend that the very low-energy section of the IPEMB code is amended to include the most up-to-date values of k(ch).

A novel, competitive mGlu(5) receptor antagonist (LY344545) blocks DHPG-induced potentiation of NMDA responses but not the induction of LTP in rat hippocampal slices.

1. We have investigated the pharmacological properties of LY344545, a structurally related epimer of the broad spectrum competitive metabotropic glutamate receptor antagonist, LY341495. We have found that LY344545 also antagonizes competitively nearly all mGlu receptor subtypes, but with a wide spectrum of activity. The order of potency for the human receptor isoforms was mGlu(5a) (IC(50) of 5. 5+/-0.6 microM)>mGlu(2)=mGlu(3)>mGlu(1alpha)=mG lu(7)>mGlu(6)=mGlu(8). No significant mGlu(4) receptor antagonist activity was detected at the highest concentration used (100 microM). 100 microM LY344545 displaced 50+/-5% of [(3)H]-CGP39653 binding, but less than 30% of [(3)H]-kainate or [(3)H]-AMPA in radioligand binding assays. 2. LY344545 antagonized L-glutamate stimulated Ca(2+) release in CHO cells transfected with mGlu receptors in a concentration dependent manner with a 10 fold higher affinity for the rat mGlu(5a) receptor (K:(i)=2.1+/-0.6 microM) compared to the rat mGlu(1alpha) receptor (K:(i)=20.5+/-2.1 microM). 50 microM (1S, 3R)-ACPD-induced Ca(2+) rises in hippocampal CA1 neurones were also antagonized (IC(50)=6. 8+/-0.7 microM). 3. LY344545 antagonized 10 microM (S)-3,5-DHPG-induced potentiation of NMDA depolarizations in CA1 neurones (EC(50)=10. 6+/-1.0 microM). At higher concentrations (> or =100 microM), LY344545 was an NMDA receptor antagonist. 4. LY344545 also blocked the induction, but not the expression, of LTP at CA3 to CA1 synapses with an IC(50)>300 microM. This effect is consistent with its weak activity at NMDA receptors. 5. These results demonstrate that the binding of ligands to mGlu receptor subtypes is critically dependent on the spatial orientation of the same molecular substituents within a given chemical pharmacophore. The identification of LY344545 as the first competitive antagonist to show selectivity towards mGlu(5) receptors supports the potential to design more selective and potent competitive antagonists of this receptor. 6. These results further indicate that mGlu receptor-mediated potentiation of NMDA responses is not essential for the induction of LTP.

Isolation and molecular cloning of a secreted immunosuppressant protein from Dermacentor andersoni salivary gland.

A 36-kDa immunosuppressant protein (Da-p36) was isolated from salivary glands of feeding female ixodid ticks Dermacentor andersoni, using its affinity for UltraLink Biosupport Medium (Pierce, Rockford, Illinois)/protein complexes. Using a nested set of forward degenerate oligonucleotide primers corresponding to Da-p36 N-terminal amino acids, a cDNA encoding the immunosuppressant protein was isolated by 3' rapid amplification of cDNA ends. The resulting 772-base pair cDNA encodes a novel protein with predicted molecular weight of 24.9 kDa. Sequence analysis revealed the presence of 5 potential glycosylation sites and 1 myristylation site. Immunoblot analyses showed native Da-p36 is present in salivary glands and saliva from both male and female D. andersoni but not in salivary glands or saliva from Amblyomma americanum or Ixodes scapularis. Reverse transcription polymerase chain reaction and immunoblot analyses showed that Da-p36 expression is temporally regulated in salivary glands with maximum mRNA levels preceding maximum Da-p36 accumulation that occurred at day 6 of feeding. The levels of Da-p36 mRNA and protein were greatly reduced in salivary glands from near-replete females removed from sheep after 8 days of feeding. These data are consistent with a role of Da-p36 in immunosuppression during feeding.

Dexamethasone for the prophylaxis of radiation-induced emesis: a National Cancer Institute of Canada Clinical Trials Group phase III study.

PURPOSE: To investigate the efficacy of dexamethasone as a prophylactic antiemetic for patients receiving fractionated radiotherapy to the upper abdomen in a randomized controlled trial. PATIENTS AND METHODS: One hundred fifty-four patients planned to receive fractionated radiotherapy to fields involving the upper abdomen (minimum total dose, 20 Gy; minimum number of fractions, five) were randomized to receive prophylactic dexamethasone (2 mg orally three times a day [tid], starting in the morning of first treatment and continuing until after their fifth treatment) or placebo. The primary end point of the study was the proportion of patients free from emesis during the study period. Secondary end points included a quality-of-life assessment using the core questionnaire of the European Organization for Research and Treatment of Cancer and side effects of dexamethasone therapy in this population of patients. RESULTS: Fifty-four (70%) out of 75 patients receiving dexamethasone had complete protection versus 37 (49%) out of 75 patients on placebo (P = .025). Most emetic episodes occurred during the initial phase of treatment. Although there was no difference in global quality of life between the two sets of patients, patients receiving dexamethasone had less nausea and vomiting and less loss of appetite but more insomnia. CONCLUSION: Dexamethasone 2 mg tid seems to be an effective prophylactic antiemetic in this situation. Side effects were acceptable, but there seemed to be no overall effect on global quality of life.

Hippocampal LTD expression involves a pool of AMPARs regulated by the NSF-GluR2 interaction.

We investigated whether the interaction between the N-ethyl-maleimide-sensitive fusion protein (NSF) and the AMPA receptor (AMPAR) subunit GluR2 is involved in synaptic plasticity in the CA1 region of the hippocampus. Blockade of the NSF-GluR2 interaction by a specific peptide (pep2m) introduced into neurons prevented homosynaptic, de novo long-term depression (LTD). Moreover, saturation of LTD prevented the pep2m-induced reduction in AMPAR-mediated excitatory postsynaptic currents (EPSCs). Minimal stimulation experiments indicated that both pep2m action and LTD were due to changes in quantal size and quantal content but were not associated with changes in AMPAR single-channel conductance or EPSC kinetics. These results suggest that there is a pool of AMPARs dependent on the NSF-GluR2 interaction and that LTD expression involves the removal of these receptors from synapses.

A CaMKII inhibitor, KN-62, facilitates DHPG-induced LTD in the CA1 region of the hippocampus.

We have shown previously that activation of mGlu receptors using a group I specific mGlu receptor agonist, (R,S)-3,5-dihydroxyphenylglycine (DHPG), can induce long-term depression (LTD) in the CA1 region of the hippocampus (Palmer et al., 1997). We now report that DHPG-induced LTD is facilitated by treatment with KN-62, an inhibitor of certain Ca2+/calmodulin-dependent protein kinases (CaMKs), including CaMKII.

Molecular cloning of cAMP-dependent protein kinase catalytic subunit isoforms from the lone star tick, Amblyomma americanum (L.).

The salivary glands of ixodid ticks are central to tick feeding and to survival during off-host periods. They produce and secrete a number of molecules critical to maintaining the complex host-vector interface and to maintaining osmotic balance. We have previously shown that a cyclic AMP-dependent protein kinase (cAPK) is involved in the mechanism of salivary gland secretion. We have now cloned cDNAs encoding three isoforms of the catalytic subunit (cAPK-C) of the cAPK from Amblyomma americanum, which are probably produced from alternative RNA processing of a single cAPK-C gene. The cDNAs contain unique N-termini of variable lengths that are linked to a common region containing the alpha A helix, catalytic core, and a C-terminal tail. The common region is highly similar to both insect and vertebrate cAPK-Cs. We have examined mRNA profiles in whole ticks and in isolated salivary glands throughout feeding and find that a single cAPK-C isoform is expressed in the salivary glands of both unfed and feeding females.

An investigation of the expression mechanism of LTP of AMPA receptor-mediated synaptic transmission at hippocampal CA1 synapses using failures analysis and dendritic recordings.

There is considerable controversy surrounding the mechanism of expression of long-term potentiation of AMPA receptor-mediated synaptic transmission in the CA1 region of the hippocampus, a process thought to be important for learning and memory in the mammalian CNS. We have re-examined the expression mechanism of this form of synaptic plasticity using whole-cell dendritic recordings, minimal stimulation to activate one or a few synapses, and failures analysis. Dendritic recordings provide improved resolution of small synaptic events, as compared to previous studies using somatic recordings, because there is less dendritic filtering of signals. We find that long-term potentiation (LTP) is associated with changes in the size of synaptic responses when they occur (potency) in all cells and this is accompanied by significant decreases in failure rate in approximately 60% of the experiments. This suggests that in some cells an increase in quantal amplitude is the sole expression mechanism for LTP and, in the cells where failure rate decreased, there is an additional mechanism causing a change in quantal content.

Isolation of two functional retinoid X receptor subtypes from the Ixodid tick, Amblyomma americanum (L.).

Retinoid X receptors (RXR) play a central role in a variety of nuclear signaling pathways in both vertebrates and invertebrates. Vertebrate RXRs are encoded by a multigene family whereas the insect RXR homologue, ultraspiracle (USP), is encoded by a single gene. To determine if acarines possess an RXR homologue similar to insect USPs, we isolated cDNAs encoding two distinct RXR genes, AamRXR1 and AamRXR2, from the ixodid tick, Amblyomma americanum (L.). The DNA binding domains share 95 and 87% identity, respectively, with DNA binding domains from insect USP and vertebrate RXR proteins. However, the ligand binding domains of the AamRXRs are more similar to vertebrate RXRs than to insect USP ligand binding domains (approximately 71 vs approximately 52%). Northern blot and RT-PCR analysis reveal both unique and overlapping patterns of AamRXR1 and AamRXR2 expression. Transactivation analysis show that both AamRXRs encode proteins which can form functional ecdysteroid receptors but are unlikely to bind retinoic acids.

The potent mGlu receptor antagonist LY341495 identifies roles for both cloned and novel mGlu receptors in hippocampal synaptic plasticity.

Understanding the roles of metabotropic glutamate (mGlu) receptors has been severely hampered by the lack of potent antagonists. LY341495 (2S-2-amino-2-(1S,2S-2-carboxycyclopropyl-1-yl)-3-(xanth-9-y l)propanoic acid) has been shown to block group II mGlu receptors in low nanomolar concentrations (Kingston, A.E., Ornstein, P.L., Wright, R.A., Johnson, B.G., Mayne, N.G., Burnett, J.P., Belagaje, R., Wu, S., Schoepp, D.D., 1998. LY341495 is a nanomolar potent and selective antagonist at group II metabotropic glutamate receptors. Neuropharmacology 37, 1-12) but can be used in higher concentrations to block all hippocampal mGlu receptors, identified so far by molecular cloning (mGlu1-5,7,8). Here we have further characterised the mGlu receptor antagonist activity of LY341495 and have used this compound to investigate roles of mGlu receptors in hippocampal long-term potentiation (LTP) and long-term depression (LTD). LY341495 competitively antagonised DHPG-stimulated PI hydrolysis in AV12-664 cells expressing either human mGlu1 or mGlu5 receptors with Ki-values of 7.0 and 7.6 microM, respectively. When tested against 10 microM L-glutamate-stimulated Ca2+ mobilisation in rat mGlu5 expressing CHO cells, it produced substantial or complete block at a concentration of 100 microM. In rat hippocampal slices, LY341495 eliminated 30 microM DHPG-stimulated PI hydrolysis and 100 microM (1S,3R)-ACPD-inhibition of forskolin-stimulated cAMP formation at concentrations of 100 and 0.03 microM, respectively. In area CA1, it antagonised DHPG-mediated potentiation of NMDA-induced depolarisations and DHPG-induced long-lasting depression of AMPA receptor-mediated synaptic transmission. LY341495 also blocked NMDA receptor-independent depotentiation and setting of a molecular switch involved in the induction of LTP; effects which have previously been shown to be blocked by the mGlu receptor antagonist (S)-MCPG. These effects may therefore be due to activation of cloned mGlu receptors. In contrast, LY341495 did not affect NMDA receptor-dependent homosynaptic LTD; an effect which may therefore be independent of cloned mGlu receptors. Finally, LY341495 failed to antagonise NMDA receptor-dependent LTP and, in area CA3, NMDA receptor-independent, mossy fibre LTP. Since in the same inputs these forms of LTP were blocked by (S)-MCPG, a novel type of mGlu receptor may be involved in their induction.