Metabotropic glutamate receptors are involved in the detection of IMP and L-amino acids by mouse taste sensory cells.

G-protein-coupled receptors are thought to be involved in the detection of umami and L-amino acid taste. These include the heterodimer taste receptor type 1 member 1 (T1r1)+taste receptor type 1 member 3 (T1r3), taste and brain variants of mGluR4 and mGluR1, and calcium sensors. While several studies suggest T1r1+T1r3 is a broadly tuned lLamino acid receptor, little is known about the function of metabotropic glutamate receptors (mGluRs) in L-amino acid taste transduction. Calcium imaging of isolated taste sensory cells (TSCs) of T1r3-GFP and T1r3 knock-out (T1r3 KO) mice was performed using the ratiometric dye Fura 2 AM to investigate the role of different mGluRs in detecting various L-amino acids and inosine 5' monophosphate (IMP). Using agonists selective for various mGluRs such as (RS)-3,5-dihydroxyphenylglycine (DHPG) (an mGluR1 agonist) and L-(+)-2-amino-4-phosphonobutyric acid (l-AP4) (an mGluR4 agonist), we evaluated TSCs to determine if they might respond to these agonists, IMP, and three L-amino acids (monopotassium L-glutamate, L-serine and L-arginine). Additionally, we used selective antagonists against different mGluRs such as (RS)-L-aminoindan-1,5-dicarboxylic acid (AIDA) (an mGluR1 antagonist), and (RS)-α-methylserine-O-phosphate (MSOP) (an mGluR4 antagonist) to determine if they can block responses elicited by these L-amino acids and IMP. We found that L-amino acid- and IMP-responsive cells also responded to each agonist. Antagonists for mGluR4 and mGluR1 significantly blocked the responses elicited by IMP and each of the L-amino acids. Collectively, these data provide evidence for the involvement of taste and brain variants of mGluR1 and mGluR4 in L-amino acid and IMP taste responses in mice, and support the concept that multiple receptors contribute to IMP and L-amino acid taste.

Estradiol rapidly modulates odor responses in mouse vomeronasal sensory neurons.

In rodents, many social behaviors are driven by the sense of smell. The vomeronasal organ (VNO), part of the accessory olfactory system mediates many of these chemically driven behaviors. The VNO is heavily vascularized, and is readily accessible to circulating peptide or steroid hormones. Potentially, this allows circulating hormones to alter behavior through modulating the output of the primary sensory neurons in the VNO, the vomeronasal sensory neurons (VSNs). Based on this, we hypothesized that steroid hormones, in particular 17ß-estradiol, would modulate activity of VSNs. In this paper, we show that the estrogen receptors, GPR30 and ERα, were present in VSNs and that estradiol may be synthesized locally in the VNO. Our results also showed that 17ß-estradiol decreased responses of isolated VSNs to dilute urine, a potent natural stimulus, with respect to current amplitudes and depolarization. Further, 17ß-estradiol increased the latency of the first action potential (AP) and the AP amplitude. Additionally, calcium responses to sulfated steroids (present in the low molecular weight fraction of urine) that act as ligands for apical vomeronasal receptors were decreased by 17ß-estradiol. In conclusion, we show that estradiol modulates odorant responses mediated by VSNs and hence paves the way for future studies to better understand the mechanisms by which odorant mediated behavior is altered by endocrine status of the animal.

ATP excites mouse vomeronasal sensory neurons through activation of P2X receptors.

Purinergic signaling through activation of P2X and P2Y receptors is critically important in the chemical senses. In the mouse main olfactory epithelium (MOE), adenosine 5'-triphosphate (ATP) elicits an increase in intracellular calcium ([Ca(2+)](I)) and reduces the responsiveness of olfactory sensory neurons to odorants through activation of P2X and P2Y receptors. We investigated the role of purinergic signaling in vomeronasal sensory neuron (VSN)s from the mouse vomeronasal organ (VNO), an olfactory organ distinct from the MOE that responds to many conspecific chemical cues. Using a combination of calcium imaging and patch-clamp electrophysiology with isolated VSNs, we demonstrated that ATP elicits an increase in [Ca(2+)](I) and an inward current with similar EC(50)s. Neither adenosine nor the P2Y receptor ligands adenosine 5'-diphosphate, uridine 5'-triphosphate, and uridine-5'-disphosphate could mimic either effect of ATP. Moreover, the increase in [Ca(2+)](I) required the presence of extracellular calcium and the inward current elicited by ATP was partially blocked by the P2X receptor antagonists pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate and 2',3'-O-(2,4,6-trinitrophenyl) adenosine 5'-triphosphate. Consistent with the activation of P2X receptors, we detected gene expression of the P2X1 and 3 receptors in the VNO by Reverse transcription polymerase chain reaction (RT-PCR). When co-delivered with dilute urine, a natural stimulus, ATP significantly increased the inward current above that elicited by dilute urine or ATP alone. Mechanical stimulation of the VNO induced the release of ATP, detected by luciferin-luciferase luminometry, and this release of ATP was completely abolished in the presence of the connexin/pannexin hemichannel blocker, carbenoxolone. We conclude that the release of ATP could occur during the activity of the vasomotor pump that facilitates the movement of chemicals into the VNO for detection by VSNs. This mechanism could lead to a global increase in excitability and the chemosensory response in VSNs through activation of P2X receptors.

Role of plasma membrane calcium ATPases in calcium clearance from olfactory sensory neurons.

Odorants cause Ca(2+) to rise in olfactory sensory neurons (OSNs) first within the ciliary compartment, then in the dendritic knob, and finally in the cell body. Ca(2+) not only excites but also produces negative feedback on the transduction pathway. To relieve this Ca(2+)-dependent adaptation, Ca(2+) must be cleared from the cilia and dendritic knob by mechanisms that are not well understood. This work focuses on the roles of plasma membrane calcium pumps (PMCAs) through the use of inhibitors and mice missing 1 of the 4 PMCA isoforms (PMCA2). We demonstrate a significant contribution of PMCAs in addition to contributions of the Na(+)/Ca(2+) exchanger and endoplasmic reticulum (ER) calcium pump to the rate of calcium clearance after OSN stimulation. PMCAs in neurons can shape the Ca(2+) signal. We discuss the contributions of the specific PMCA isoforms to the shape of the Ca(2+) transient that controls signaling and adaptation in OSNs.

Pharmacokinetics of metaflumizone and amitraz in the plasma and hair of dogs following topical application.

Controlled laboratory studies have shown that a metaflumizone plus amitraz combination (ProMeris/ProMeris Duo for Dogs, Fort Dodge Animal Health, Overland Park, KS) applied topically is effective for the treatment and control of fleas and ticks on dogs. Two studies were conducted to determine the distribution of both metaflumizone and amitraz in the plasma and hair of dogs following treatment at the minimum recommended dose of approximately 20mg/kg of each active ingredient. Six purpose-bred, adult Beagle dogs were used in each study. Plasma or hair samples were collected from each dog just prior to dosing and periodically through 56 days after treatment. Samples were analyzed by HPLC methods validated for the simultaneous determination of metaflumizone and amitraz. Amitraz was detectable (>3.2ng/ml) but not quantifiable (<50ng/ml) in only two plasma samples, collected 1 and 2 days post-treatment from different dogs. Metaflumizone concentrations in plasma were generally detectable (>1.0ng/ml) but not quantifiable (<50ng/ml). Measurable levels were found in one dog 7 days post-treatment, increasing to a maximum of four dogs at 42 days after dosing, with a metaflumizone range of 59-138ng/ml. Analysis of hair samples indicated that both metaflumizone and amitraz were widely distributed at basically similar levels in the hair within 1-day after administration, reaching maximum concentrations between 2 and 7 days post-treatment. Low but quantifiable levels of both compounds were still present on hair at the end of the 56-day study. These studies indicate that the ectoparasitic activity is due to exposure of the parasites to metaflumizone and amitraz on the surface of the host (hair and/or skin), not to exposure via the circulatory system of the host.

Evaluation of the efficacy and safety of a novel formulation of metaflumizone in cats naturally infested with fleas in Europe.

The efficacy and safety of a novel spot-on formulation of metaflumizone (ProMeris for Cats, Fort Dodge Animal Health, Overland Park, KS) was assessed in cats naturally infested with fleas in a multiregional, clinical field study. Sixteen veterinary clinics in Germany and eight clinics in France enrolled patients to the study. A total of 173 cats with flea infestation qualified as primary patients and were randomly allocated to one of the two treatments in a ratio of approximately 2:1 for metaflumizone (minimum dosage of 40mg/kg) or fipronil (at the recommended label rate). Clinical examinations and baseline parasite counts were performed on Day 0 prior to treatment. Flea counts and safety evaluations were repeated at approximately 2-week intervals for 8 weeks. Both treatments resulted in consistent reductions (>84%) in flea numbers throughout the study, but metaflumizone resulted in numerically higher reductions on most count days. Within groups the flea reduction was highly significant (p<0.0001) compared to baseline at all observation periods. The efficacy of metaflumizone against fleas compared to baseline was 91.0%, 89.4%, 90.8% and 90.7% at Day 14, 28, 42 and 56, respectively. The corresponding efficacies for fipronil were 91.7%, 86.9%, 84.6% and 87.7%. Metaflumizone was highly effective in controlling existing infestations of fleas on cats and was effective against reinfestation for at least 56 days. Metaflumizone showed a good tolerance profile in cats.

Evaluation of the efficacy and safety of a novel formulation of metaflumizone plus amitraz in dogs naturally infested with fleas and ticks in Europe.

The efficacy and safety of a novel spot-on formulation of metaflumizone plus amitraz (ProMeris/ProMeris Duo for Dogs, Fort Dodge Animal Health, Overland Park, KS) was assessed in dogs naturally infested with ticks and/or fleas in a multiregional, clinical field study. Nineteen veterinary clinics in Germany and 11 clinics in France enrolled patients to the study. One hundred eighty one dogs with tick infestation and 170 dogs with flea infestation (plus three dogs harboring both ticks and fleas) qualified as primary patients and were randomly allocated to one of two treatments in a ratio of approximately 2:1 for metaflumizone plus amitraz (minimum dosage of 20 plus 20mg/kg) or fipronil (at the recommended label rate). Clinical examinations and baseline parasite counts were performed on Day 0 prior to treatment. Tick and/or flea counts and safety evaluations were repeated at intervals of about 2 weeks for 8 weeks. Both products resulted in consistent reductions in tick numbers (>81%) throughout the study, with metaflumizone plus amitraz giving consistently higher reductions in tick numbers. The efficacy against tick count compared with Day 0 was 97.6%, 93.5%, 89% and 94% at Day 14, 28, 42 and 56, respectively, for metaflumizone plus amitraz. The corresponding efficacies for fipronil were 86.3%, 81.1%, 84.8% and 86.1%. Within groups, the tick reduction was highly significant (P<0.0001) compared to baseline at all observation periods. Both treatments resulted in consistent (>89%) and highly significant (P<0.0001) reductions in flea numbers relative to the baseline counts throughout the study, although fipronil resulted in numerically higher reductions on each count day. The efficacy against fleas compared to baseline was 91.8%, 88.7%, 91.5% and 92.0% at Day 14, 28, 42 and 56, respectively, for metaflumizone plus amitraz. The corresponding efficacies for fipronil were 98.2%, 96.3%, 95.9% and 96.7%. Metaflumizone plus amitraz was highly effective in controlling existing infestations of fleas and ticks on dogs and was effective against reinfestation for at least 56 days. Metaflumizone plus amitraz showed a good tolerance profile in dogs.

Pharmacokinetics of metaflumizone in the plasma and hair of cats following topical application.

Controlled laboratory studies have shown that a novel spot-on formulation containing 20% (w/v) metaflumizone (ProMeris for Cats, Fort Dodge Animal Health, Overland Park, KS) is effective for the treatment and control of fleas on cats. Two studies were conducted to determine the distribution of metaflumizone in the plasma and hair of cats following treatment at the minimum recommended dose of 40mg/kg. Six purpose-bred cats, three males and three females, were used in each study. Plasma or hair samples were collected from each cat just prior to dosing and periodically through 56 days after treatment. Samples were analyzed by HPLC methods validated for the determination of metaflumizone. Metaflumizone concentrations in plasma were below the method limit of quantification (<50ng/ml) in all samples but one, and were frequently not detectable (<1.1ng/ml). Plasma collected 3 days post-treatment from one cat had a metaflumizone concentration of 57.8ng/ml. The frequency of measurable levels of metaflumizone in the plasma was too low to allow the calculation of pharmacokinetic parameters. Analysis of hair samples indicated that metaflumizone was widely distributed in the hair coat of the cat within 1 day after administration, reaching maximum concentrations within 1 or 2 days post-treatment. Low but quantifiable levels were still present at the end of the 56-day study. Data from the present studies indicate that the ectoparasitic activity is due to exposure of the parasites to metaflumizone on the surface of the host (skin and hair), not to exposure via the circulatory system of the host.

Dose determination of the persistent activity of moxidectin long-acting injectable formulations against various nematode species in cattle.

The effectiveness, safety and production-enhancing benefit (improved weight gains) of moxidectin long-acting injection given subcutaneously in the ear at the rates of 0.75, 1.0 and 1.5mg/kg bw were evaluated in three studies under common protocol. The only adverse reaction to treatment was a mild (<2 tablespoons in volume), and for the most part transient (<28 days for the treatment rate of 1.0mg/kg bw) injection site swelling as noted in a minority of the animals (12.2% of the animals treated at the rate of 1.0mg/kg bw). Regardless of study site, post-treatment interval or dose rate, average daily gains were improved over control cattle by approximately 33%. Reductions in strongyle EPG counts relative to controls were > or = 90% for all dose rates of moxidectin for a post-treatment period of 42 days (Wisconsin), 84 days (Arkansas) and 140 days (Louisiana). In Arkansas and Louisiana, the majority (>80%) of post-treatment strongyle eggs, as determined by coproculture, were Cooperia spp. As determined by sequential necropsies, periods of continuous, post-treatment protection (> or = 90% efficacy in at least two out of three studies) for moxidectin long-acting injection given at the rate of 1.0 mg/kg bw were 90 days (adult Haemonchus spp.), 120 days (Dictyocaulus viviparus and adult Ostertagia and Oesophagostomum) and 150 days (Ostertagia spp. EL4).

Therapeutic and persistent efficacy of moxidectin 1% nonaqueous injectable formulation against natural and experimentally induced lung and gastrointestinal nematodes in cattle.

Four controlled trials were conducted to evaluate the therapeutic and persistent efficacy of a new moxidectin formulation (moxidectin 1% nonaqueous injectable) against nematode parasites in cattle. This injectable moxidectin formulation, given as a single subcutaneous injection at a dose rate of 0.02 ml/kg BW to provide 0.2 mg moxidectin/kg BW, was highly efficacious (>90-100%) against larval and/or adult stages of many species of nematodes in cattle including, Dictyocaulus viviparus, Ostertagia spp., Trichostrongylus axei, Haemonchus placei, Trichostrongylus colubriformis, Cooperia spp., Nematodirus helvetianus, Strongyloides papillosus, Oesophagostomum radiatum and Trichuris spp. This formulation had persistent efficacy of >90% against D. viviparus for at least 6 weeks post-treatment, H. placei and Oe. radiatum for 5 weeks post-treatment, and Ostertagia spp. and T. axei for 2 weeks post-treatment.

Neuromodulatory effects of gonadotropin releasing hormone on olfactory receptor neurons.

The terminal nerve is an anterior cranial nerve that innervates the lamina propria of the chemosensory epithelia of the nasal cavity. The function of the terminal nerve is ambiguous, but it has been suggested to serve a neuromodulatory role. We tested this hypothesis by exposing olfactory receptor neurons from mudpuppies (Necturus maculosus) to a peptide, gonadotropin releasing hormone (GnRH), that is found in cells and fibers of the terminal nerve. We used voltage-clamped whole-cell recordings to examine the effects of 0. 5-50 micrometer GnRH on voltage-activated currents in olfactory receptor neurons from epithelial slices. We found that GnRH increases the magnitude, but does not alter the kinetics, of a tetrodotoxin-sensitive inward current. This increase in magnitude generally begins 5-10 min after initial exposure to GnRH, is sustained for at least 60 min during GnRH exposure, and recovers to baseline within 5 min after GnRH is washed off. This effect occurred in almost 60% of the total number of olfactory receptor neurons examined and appeared to be seasonal: approximately 67% of neurons responded to GnRH during the courtship and mating season, compared with approximately 33% during the summer, when the sexes separate. GnRH also appears to alter an outward current in the same cells. Taken together, these data suggest that GnRH increases the excitability of olfactory receptor neurons and that the terminal nerve functions to modulate the odorant sensitivity of olfactory receptor neurons.

Depletion of moxidectin tissue residues in sheep.

The pattern of tissue depletion of moxidectin (MXD) subcutaneously administered to sheep was characterized in this study. MXD concentration profiles were determined in muscle, fat, and liver and at the site of injection following administration of a formulation combining MXD (0.5% w/v) with a standard 6 in 1 clostridial vaccine. Thirty-five (35) parasite-free Lincoln sheep were treated with the MXD injectable formulation at a dose rate of 0.2 mg of MXD/kg of live weight, administered subcutaneously on the inner surface of the thigh. Treated animals were sacrificed in randomly selected groups of six sheep weekly from day 21 until day 49 post-treatment. Three nontreated animals were sacrificed to obtain blank tissue samples to validate the analytical methodology. MXD concentration profiles were determined by a validated HPLC analytical method using fluorescence detection. MXD has an adequate pattern of absorption, based on the low residual concentrations found in the injection site area at all sampling intervals. Muscle samples showed the lowest MXD concentrations throughout the study period. The highest MXD concentrations at all sampling times were measured in the adipose tissue, indicating that fat is a target tissue for MXD. MXD concentrations in all of the tissues analyzed were below the accepted maximum limit of residue at 21 days post-treatment.

Falls in older Mexican-American women.

OBJECTIVE: To determine the frequency of falls and identify risk factors for falls among older Mexican-American women. DESIGN: A prospective cohort study with an average follow-up of 2.7 years. SETTING: A clinical center at the Palo Alto Veterans Affairs Medical Center, California. PARTICIPANTS: 152 community-dwelling Mexican-American Caucasian women aged 59 years or older. OUTCOME MEASURES: Falls and injurious falls, as determined by monthly telephone interviews. RESULTS: The rate of falls was 508 per 1000 person-years (95% confidence interval (CI), 440-577). Injurious falls requiring medical attention occurred at a rate of 79 per 1000 person-years (95% CI, 52-107). Factors that were associated independently with an increased risk of falling were older age, a history of arthritis or rheumatism, a history of high thyroid, having fainted at least once in the year before baseline, current use of psychotropic medications, and walking fewer than 5 blocks a day. Those persons with an average time for the chair stand test had a lower risk of falling than those with the slowest times or the fastest times. CONCLUSIONS: The frequency of falls and injurious falls in this cohort of 152 relatively acculturated, healthy, older Mexican-American women was similar or slightly higher than previously reported rates for non-Hispanic Caucasian(s). Many of the factors associated with falls in this study were similar to those reported for non-Hispanic Caucasian women, suggesting that fall prevention measures tested mainly among non-Hispanic Caucasian women would also be appropriate for Mexican-American women.

Uptake and release of neurotransmitter candidates, [3H]serotonin, [3H]glutamate, and [3H]gamma-aminobutyric acid, in taste buds of the mudpuppy, Necturus maculosus.

Neurotransmitters in vertebrate taste buds have not yet been identified with confidence. Serotonin, glutamate, and gamma-aminobutyric acid (GABA) have been postulated, but the evidence is incomplete. We undertook an autoradiographic study of [3H]serotonin, [3H]glutamate, and [3H]GABA uptake in lingual epithelium from the amphibian, Necturus maculosus, to determine whether taste bud cells would accumulate and release these substances. Lingual epithelium containing taste buds was incubated in low concentrations (0.4-6 microM) of these tritiated transmitter candidates and the tissue was processed for light microscopic autoradiography. Merkel-like basal taste cells accumulated [3H]serotonin. When the tissue was treated with 40 mM K+ after incubating the tissue in [3H]serotonin, cells released the radiolabelled transmitter. Furthermore, depolarization (KCl)-induced release of [3H]serotonin was Ca-dependent: if Ca2+ was reduced to 0.4 mM and 20 mM Mg2+ added to the high K+ bathing solution, Merkel-like basal cells did not release [3H]serotonin. In contrast, [3H]glutamate was taken up by several cell types, including non-sensory epithelial cells, Schwann cells, and some taste bud cells. [3H]glutamate was not released by depolarizing the tissue with 40 mM K+. [3H]GABA uptake was also widespread, but did not occur in taste bud cells. [3H]GABA accumulated in non-sensory epithelial cells and Schwann cells. These data support the hypothesis that serotonin is a neurotransmitter or neuromodulator released by Merkel-like basal cells in Necturus taste buds. The data do not support (nor rule out) a neurotransmitter role for glutamate or GABA in taste buds.

A cyclic nucleotide-dependent chloride conductance in olfactory receptor neurons.

Whole-cell membrane currents were recorded from olfactory receptor neurons from the neotenic salamander Necturus maculosus. Cyclic nucleotides, released intracellularly by flash photolysis of NPE-caged cAMP or NPE-caged cGMP, activated a transient chloride current. The chloride current could be elicited at constant voltage in the absence of extracellular Ca2+ as well as in the presence of 3 mM intracellular Ca2+, suggesting that the current did not require either voltage or Ca2+ transients for activation. The current could be elicited in the presence of the protein kinase inhibitors H-7 and H-89, and in the absence of intracellular ATP, indicating that activation was independent of protein kinase A activity. These results suggest that Necturus olfactory receptor neurons contain a novel chloride ion channel that may be directly gated by cyclic nucleotides.

Responses to glutamate in rat taste cells.

We studied taste transduction in sensory receptor cells. Specifically, we examined the actions of glutamate, a significant taste stimulus, on the membrane properties of taste cells by applying whole cell patch-clamp techniques to cells in rat taste buds isolated from foliate and vallate papillae. In 55 of 91 taste cells, bath-applied glutamate, at concentrations that elicit taste responses in the intact animal (10-20 mM), produced one of two different responses when the cell membrane was held near its presumed resting potential, -85 mV. "Sustained" glutamate responses were observed in the majority of taste cells (51 of 55) and consisted of an outward current (reduction of the maintained inward current). Sustained glutamate responses were voltage dependent, were decreased by membrane depolarization, and were accompanied by a reduction in membrane conductance. An analysis of the reversal potential of sustained responses in different ionic conditions and the effect of ion substitutions suggested that the currents were carried by cations. The data suggest that sustained responses are mediated by the closure of nonselective cation channels. Other taste cells (4 of 55) responded to glutamate with a transient inward current--so-called "transient" responses. Transient glutamate responses were voltage dependent and Na+ dependent, and appeared to be generated by nonspecific cation channels activated by glutamate. L(+)-2-amino-4-phosphonobutyric acid (L-AP4), a specific agonist of a metabotropic glutamate receptor (mGluR4) recently identified in rat taste cells and believed to be involved in taste transduction, mimicked the sustained glutamate responses. These findings indicate that glutamate, at concentrations at or slightly above threshold for taste in rats, produces two different membrane currents. The properties of these two responses suggest that there may be two different sets of nonspecific cation channels in taste cells, one closed by glutamate (sustained response) and the other opened (transient response). Our findings on the effect of L-AP4 suggest that the sustained response is the membrane mechanism mediating, at least in part, taste transduction for glutamate.

Serotonin modulates voltage-dependent calcium current in Necturus taste cells.

Necturus taste buds contain two primary cell types: taste receptor cells and basal cells. Merkel-like basal cells are a subset of basal cells that form chemical synapses with taste receptor cells and with innervating nerve fibers. Although Merkel-like basal cells cannot interact directly with taste stimuli, recent studies have shown that Merkel-like basal cells contain serotonin (5-HT), which may be released onto taste receptor cells in response to taste stimulation. With the use of whole cell voltage clamp, we examined whether focal applications of 5-HT to isolated taste receptor cells affected voltage-activated calcium current (I(Ca)). Two different effects were observed. 5-HT at 100 microM increased I(Ca) in 33% of taste receptor cells, whereas it decreased I(Ca) in 67%. Both responses used a 5-HT receptor subtype with a pharmacological profile similar to that of the 5-HT1A receptor, but the potentiation and inhibition of I(Ca) by 5-HT were mediated by two different second-messenger cascades. The results indicate that functional subtypes of taste receptor cells, earlier defined only by their sensitivity to taste stimuli, may also be defined by their response to the neurotransmitter 5-HT and suggest that 5-HT released by Merkel-like basal cells could modulate taste receptor function.

Neuromodulation of transduction and signal processing in the end organs of taste.

Chemical synapses transmit gustatory signals from taste receptor cells to sensory afferent axons. Chemical (and electrical) synapses also provide a lateral pathway for cells within the taste bud to communicate. Lateral synaptic pathways may represent some form of signal processing in the peripheral end organs of taste. Efferent synaptic input may also regulate sensory transduction in taste buds. To date, the synaptic neurotransmitter(s) or neuromodulator(s) released at chemical synapses in taste buds have not been identified unambiguously. This paper summarizes the attempts that have been made over the past 40 years to identify the neuroactive substances acting at taste bud synapses. We review the four traditional criteria for identifying chemical transmitters elsewhere in the nervous system-localization, uptake/degradation, release and physiological actions- and apply these criteria to neuroactive substances in taste buds. The most complete evidence to date implicates serotonin as a neuromodulator of taste transduction in the end organs. However, studies also suggest that adrenergic, cholinergic and peptidergic neurotransmission may be involved in taste buds.

Development of voltage-dependent currents in taste receptor cells.

Taste buds, the specialized end organs of gustation, comprise a renewing sensory epithelium. Undifferentiated basal cells become taste receptor cells by elongating and extending processes apically toward the taste pore. Mature taste cells are electrically excitable and express voltage-dependent Na+ Ca2+, and K+ currents, whereas basal stem cells exhibit only slowly activating K+ currents. The question we have addressed in the present study is whether contact with the taste pore is required for expression of voltage-dependent inward currents in Necturus taste cells. Mature taste cells were distinguished from developing cells by labeling the apical surface of the cells with fluorescein-isothiocyanate-conjugated wheat germ agglutinin (FITC-WGA), while the tissue was still intact. Elongate cells lacking FITC-WGA staining were interpreted as developing taste cells that had not yet reached the taste pore. Giga-seal whole-cell recording revealed that most developing taste cells lacked inward currents. Although some developing cells expressed inward currents, they were much smaller than those of mature cells, and the activation kinetics of the K+ currents were slower than in mature cells. Electron microscopy confirmed the identity of labeled and unlabeled cells. All FITC-WGA-labeled cells exhibited the ultrastructural characteristics of mature taste receptor cells, whereas most unlabeled taste cells had a characteristic morphology that was markedly different from mature taste receptor cells or basal stem cells. These data suggest that contact with the taste pore is required for the development of inward currents in taste cells.

Factors contributing to skeletal health of postmenopausal Mexican-American women.

Incidence rates of hip fracture are lower in Hispanic (HC) than non-Hispanic Caucasians (NHC). To investigate factors that may affect skeletal health of Hispanics, we recruited 152 healthy community-dwelling Mexican-American Caucasian women into a 4-year longitudinal study that evaluates bone mass, nutritional status, muscle strength, mobility, falls, and other factors that may contribute to fracture risk. Results from the baseline component of the study are reported herein. Average bone mineral densities (BMD) evaluated by dual-energy X-ray absorptiometry (DXA) in this study group did not differ from BMDs in healthy, NHC women of similar age. Hip axis length (HAL), however, was significantly shorter than that reported for nonosteoporotic NHC. Factors independently associated with greater BMD and BMC at certain skeletal sites were lean body mass, fat mass, acculturation, years of estrogen use, sun exposure, hip adductor strength, grip strength, erythrocyte folate, and serum glucose concentrations. Factors independently associated with lower BMD and BMC at certain skeletal sites were age, parity, and vertebral deformities (all p < 0.05). Thus, the decreased risk of hip fracture in HC compared with NHC does not appear to be due to high bone mass. However, other factors such as HAL and body composition may play a role in maintenance of skeletal integrity.