Sensitivity of the olfactory sense declines with the aging in senescence-accelerated mouse (SAM-P1)

The decline in olfaction with age is well documented in histological, psychological, and electroencephalographical studies. However, there are few electrophysiological studies on changes in the sensitivity of the peripheral olfactory cells with age. We evaluated the behavior, the amplitude of electro-olfactogram (EOG), and the thickness of the olfactory epithelium in the Senescence-Accelerated Mouse (SAM-P1). This strain of mouse exhibits accelerated senescence and age-related pathologies, and it is commonly used as a model for research on aging. Its median survival time is 55 weeks. To ensure our results would be restricted to the olfactory system, we chose vanillin as a stimulus, because this stimulus has no definitive chorda tympani (VII) response, and we verified that it is tasteless. The data demonstrate that olfactory sensitivity to vanillin decreases dramatically with age in these mice, and that this is due to loss in the number of olfactory receptor cells.

Zinc modulates the electro-olfactogram of the frog

OBJECTIVE

Zinc is considered an important element in olfaction, however, its exact role is still unclear. A large amount of zinc is contained in the olfactory mucosa, so Zn(2+) may behave as a neuromodulator, as in the hippocampus. To reveal the acute effects of Zn(2+) on olfactory mucosa, electro-olfactograms (EOG) were recorded with or without Zn(2+).

METHODS

The isolated olfactory mucosa of a bullfrog (Rana catesbiana) was set in an EOG recording chamber and bathed in Ringer's solution. Effects of ZnSO(4) (25 microM) on EOGs were examined. Four types of stimulants, n-amyl acetate (200 microM), menthone (10 microM), forskolin (2 microM), and 3-isobutil-methylxisanthine (IBMX, 100 microM) were tested.

RESULTS

Zn(2+) (25 microM) charged with the ciliated surface of the olfactory mucosa attenuates EOGs which were produced not only by odorants but also by forskolin and IBMX. The attenuating ratios of EOGs for stimulants were as follows; n-amyl acetate (0.51+/-0.18, n=4), menthone (0.48+/-0.28, n=4), forskolin (0.61+/-0.16, n=4), and IBMX (0.68+/-0.19, n=4); (mean+/-S.D.). These attenuations were reversible. The results indicate that Zn(2+) may block the c-AMP dependent transduction channels of the olfactory cells.

CONCLUSION

Micro molar Zn(2+) attenuates EOG of the frog. Zn(2+) may be thought to behave as one of the modulators in olfactory reception.

Alcohol up-regulates UDP-glucuronosyltransferase mRNA expression in rat liver and in primary rat hepatocyte culture

The interactions between alcohol and cytochrome P-450 enzymes have been well investigated. However, the data regarding the effect of alcohol on the regulation of UDP-glucuronosyltranferase (UGT) activity are less clear. The aim of the present study was to determine the role of alcohol in the regulation of UGT mRNA expression by using whole animal and primary cultured hepatocytes. Chronic ethanol feeding of rats significantly increased the expression of liver UGT1A1 mRNA to 177% of control. The mRNA levels for UGT1A5, UGT2B1 and UGT2B3 were also enhanced, but did not reach statistical significance. In cultured hepatocytes, treatment with either ethanol or isopentanol significantly increased the expression of UGT1A1, UGT1A5, UGT2B1, and UGT2B3 mRNAs, but to different degrees. The induction of UGT1A1 and UGT2B1 mRNAs by ethanol or isopentanol was time-dependent and maximal changes occurred at 48 h. The expression of UGT1A6 mRNA was not significantly modified by either ethanol or isopentanol. In conclusion, ethanol and isopentanol have direct roles in the regulation of UGT.

Odorants suppress voltage-gated currents in retinal horizontal cells in goldfish

Odorants are known to suppress non-selectively voltage-gated currents in olfactory receptor cells. We found that odorants also suppress voltage-gated currents in neurons of outside of the olfactory system. Under voltage clamp, odorants such as amyl acetate, limonene, and acetophenone suppressed non-selectively voltage-gated currents (a Ca(2+) current, a delayed rectifier K(+) current, a fast transient K(+) current, and an anomalous rectifier K(+) current) in horizontal cells from the goldfish retina. An amyl acetate puff completely and immediately suppressed the Ca(2+) current (I(Ca)) and the delayed rectifier K(+) current induced by repetitive depolarizations, suggesting that amyl acetate is a closed-channel blocker. Odorants did not change significantly the activation curve of I(Ca), but made the slope of inactivation curve of I(Ca) gentler and shifted its half-inactivation voltage toward a negative voltage. These results are similar to the effects of odorants on voltage-gated currents in olfactory receptor cells. This suggests that odorants may suppress the voltage-gated currents in retinal horizontal cells by the same mechanism described in olfactory receptor cells.

Electroencephalographic registration of low concentrations of isoamyl acetate

Previous research has demonstrated electroencephalogram (EEG) changes in response to low-odor concentrations, resulting in near-chance detection. Such findings have been taken as evidence for olfaction without awareness. We replicated and extended previous work by examining EEG responses to water-water control, 0.0001, 0. 001, 0.01, and 1 ppm isoamyl acetate (IAA) in water paired with water only. Detection was above chance (>50%) for.001 and above, and alpha decreased only to those concentrations, suggesting that EEG changes corresponded to IAA awareness. However, when correct trial EEGs were compared to incorrect trial EEGs during.001 ppm, right posterior/central alpha decreased during incorrect trials and alpha decreased more globally (including frontal sites) during correct trials. These data may not reflect awareness or unawareness per se. Instead, results are discussed regarding activation of perceptual systems in the posterior region during incorrect trials and the activation of frontal action systems during a subset of correct trials.

Acetaminophen hepatotoxicity precipitated by short-term treatment of rats with ethanol and isopentanol: protection by triacetyloleandomycin

Ethanol and isopentanol are the predominant alcohols in alcoholic beverages. We have reported previously that pretreatment of rats with a liquid diet containing 6.3% ethanol plus 0.5% isopentanol for 7 days results in a synergistic increase in acetaminophen hepatotoxicity, compared with rats treated with either alcohol alone. Here, we investigated the role of CYP3A in acetaminophen hepatotoxicity associated with the combined alcohol treatment. Triacetyloleandomycin, a specific inhibitor of CYP3A, protected rats pretreated with ethanol along with isopentanol from acetaminophen hepatotoxicity. At both 0.25 and 0.5 g acetaminophen/kg, triacetyloleandomycin partially prevented elevations in serum levels of alanine aminotransferase. At 0.25 g acetaminophen/kg, triacetyloleandomycin completely protected 6 of 8 rats from histologically observed liver damage, and partially protected the remaining 2 rats. At 0.5 g acetaminophen/kg, triacetyloleandomycin decreased histologically observed liver damage in 7 of 15 rats. In rats pretreated with ethanol plus isopentanol, CYP3A, measured immunohistochemically, was decreased by acetaminophen treatment. This effect was prevented by triacetyloleandomycin. These results suggest that CYP3A has a major role in acetaminophen hepatotoxicity in animals administered the combined alcohol treatment. We also found that exposure to ethanol along with 0.1% isopentanol for only 3 days resulted in maximal increases in acetaminophen hepatotoxicity by the combined alcohol treatment, suggesting that short-term consumption of alcoholic beverages rich in isopentanol may be a risk for developing liver damage from acetaminophen.

Odorants suppress T- and L-type Ca2+ currents in olfactory receptor cells by shifting their inactivation curves to a negative voltage

Mechanisms underlying suppression of T- and L-type Ca2+ currents (I(Ca,T) and I(Ca,L)) by odorants were investigated in newt olfactory receptor cells (ORCs) using the whole-cell version of the patch-clamp technique. Under voltage clamp, odorants (amyl acetate, limonene and acetophenone) reversibly suppressed I(Ca,T) and I(Ca, L). These currents disappeared completely within 150 ms following amyl acetate puffs, and recovered in approximately 1 s after the washout. Hyperpolarization of the membrane greatly relieved the odorant block of I(Ca,T) and I(Ca,L). The activation curves of both currents were not changed significantly by odorants, while their inactivation curves were shifted to negative voltages. Half-inactivation voltages of I(Ca,T) were - 66 mV (control), - 102 mV (amyl acetate), - 101 mV (limonene) and - 105 mV (acetophenone) (all 0.3 mM); those of I(Ca,L) were -33 mV (control), - 61 mV (amyl acetate), - 59 mV (limonene), and - 63 mV (acetophenone) (all 0.3 mM). These phenomena are similar to the effects of local anesthetics on I(Ca) in various preparations and also similar to the effects of odorants on I(Na) in ORCs, suggesting that these types of suppression are caused by the same mechanism.

Lipid-dependent activation of protein kinase C-alpha by normal alcohols

Significant stimulation of protein kinase C-alpha (PKCalpha) by n-alcohols was observed in characterized lipid systems composed of phosphatidylcholine/phosphatidylserine/dioleoylglycerol (PC/PS/DO). The logarithm of the alcohol concentrations to achieve half-maximal PKC stimulation (ED(50)) and of the maximal PKC stimulation by alcohols were both linear functions of alcohol chain length, consistent with the Meyer-Overton effect. Binding of phorbol esters to PKC was not significantly affected by octanol. Octanol increased, up to 4-fold, the affinity of PKC binding to the lipid bilayers in both the absence and presence of DO. However, octanol increased PKC activity much more significantly than it enhanced binding of the enzyme to the lipid bilayers, suggesting that the stimulation of PKC is not merely a reflection of the increase in PKC bilayer binding affinity. (31)P NMR experiments did not reveal formation of non-lamellar phases with octanol. Differential scanning calorimetry suggested that alcohols, like diacylglycerol, induce formation of compositionally distinct domains and the maximal enzyme activity with alcohol resided roughly in the putative domain-coexistence region. These results suggest that alcohols are mimicking diacylglycerol in activating PKC, not by binding to the high affinity phorbol ester binding site, but by altering lipid structure and by enhancing PKC-bilayer binding.

Sex steroids and odorants modulate gonadotropin-releasing hormone secretion in primary cultures of human olfactory cells

Olfactory neurons and GnRH neurons share a common origin during development. In the nasal epithelia, GnRH neurons persist throughout fetal life and adulthood. The fate and function of these neurons in vivo have remained unknown. In a previous in vitro study, we isolated, cloned, and propagated primary long term cell cultures from the olfactory neuroepithelium of 8- to 12-week-old human fetuses. These cells expressed both neural proteins as well as olfactory genes and were responsive to odorant stimuli. We now report that these human olfactory cells also express the GnRH gene and protein. Combined HPLC and RIA studies have indicated that these cells release authentic GnRH in spent media. The release of GnRH was time dependent and was positively affected by sex steroids and odorants. Immunohistochemical data demonstrated the presence of sex steroid receptors in these cells. The presence of the alpha- and beta-subtypes of the estrogen receptor was also demonstrated by RT-PCR and Western blot analysis. When the cells were stimulated with increasing concentrations of 17beta-estradiol in the presence of a fixed concentration of progesterone (10(-7) mol/L), the combination of the two steroids induced a 3- to 4-fold increase in GnRH secretion. This stimulatory effect was completely blunted by tamoxifen. Neither 17beta-estradiol nor progesterone was effective when tested separately. Treatment with increasing concentrations of the odorant, l-carvone, induced a time- and dose-dependent dramatic increase in GnRH protein release (1000-fold increase) and gene expression. Repeated application of the stimulus resulted in a progressive lower responsiveness of the cells. To our knowledge, this is the first time that primary cell cultures from human fetal olfactory neuroepithelium have been shown to express and release GnRH. Our results also demonstrate that these cultures, which are sensitive to sex steroids and odorants, can be useful models in the study of the complex array of regulatory factors that finely tune GnRH secretion in humans.

Methionine enhances alcohol-induced narcosis in mice

Methionine is an essential amino acid that has been used as a therapeutic drug in some disorders. In this study we questioned whether methionine affects ethanol-induced loss of righting reflex (narcosis). One hour after IP methionine administration (60, 120, 240, 480, 720, 960, and 1280 mg/kg), mice were injected with ethanol (4.0 g/kg), and the duration of loss of righting reflex was recorded. Methionine, at the higher doses (960 and 1280 mg/ kg), significantly increased this effect on ethanol-treated animals. A time-course study revealed that methionine increased the duration of the loss of righting reflex induced by ethanol until 4 h after being injected. Because methionine did not affect blood ethanol levels, no change in peripheral alcohol can explain the observed effects. This potentiation was not specific for ethanol because methionine increased 3-methyl-1-butanol (0.6 g/kg) and 1-propanol (2.4 g/kg)-induced loss of righting reflex as well. Therefore, the results obtained in this study suggest the need for further investigation into methionine-ethanol interactions prior to the use of methionine as an agent that can be used as an antidepressant and to prevent damage to organic tissue in alcoholism.

Inhibition of the aminopeptidase from Aeromonas proteolytica by aliphatic alcohols. Characterization of the hydrophobic substrate recognition site

Seven aliphatic and two aromatic alcohols were tested as reporters of the substrate selectivity of the aminopeptidase from Aeromonas proteolytica (AAP). This series of alcohols was chosen to systematically probe the effect of carbon chain length, steric bulk, and inhibitor shape on the inhibition of AAP. Initially, however, the question of whether AAP is denatured in the presence of aliphatic alcohols was addressed. On the basis of circular dichroism (CD), electronic absorption, and fluorescence spectra, the secondary structure of AAP, with and without added aliphatic alcohols, was unchanged. These data clearly indicate that AAP is not denatured in aliphatic alcohols, even up to concentrations of 20% (v/v). All of the alcohols studied were competitive inhibitors of AAP with K(i) values between 860 and 0.98 mM. The clear trend in the data was that as the carbon chain length increases from one to four, the K(i) values increase. Branching of the carbon chains also increases the K(i) values, but large bulky groups, such as that found in tert-butyl alcohol, do not inhibit AAP as well as leucine analogues, such as 3-methyl-1-butanol. The competitive nature of the inhibition indicates that the substrate and each alcohol studied are mutually exclusive due to binding at the same site on the enzyme. On the basis of EPR and electronic absorption data for Co(II)-substituted AAP, none of the alcohols studied binds to the dinuclear metallo-active site of AAP. Thus, reaction of the inhibitory alcohols with the catalytic metal ions cannot constitute the mechanism of inhibition. Combination of these data suggests that each of these inhibitors bind only to the hydrophobic pocket of AAP and, consequently, block the binding of substrate. Thus, the first step in peptide hydrolysis is the recognition of the N-terminal amino acid side chain by the hydrophobic pocket adjacent to the dinuclear active site of AAP.

A physiological model for ligand-induced accumulation of alpha 2u globulin in male rat kidney: roles of protein synthesis and lysosomal degradation in the renal dosimetry of 2,4,4-trimethyl-2-pentanol

A physiologically based pharmacokinetic (PBPK) model was constructed for the disposition of 2,4,4-trimethyl-2-pentanol (TMP-2-OH) in male rats and its induction of accumulation of renal alpha2u-globulin (alpha2u). The model included diffusion-restricted delivery of TMP-2-OH to compartments representing liver, lung, fat, kidney, GI tract, aggregated rapidly perfused tissues, and aggregated slowly perfused tissues. Metabolism by oxidation and glucuronidation was included for liver and kidneys. Rates of hepatic alpha2u production and resorption by renal proximal tubules were taken from the literature. Degradation of liganded alpha2u by renal lysosomal cathepsins was modeled with a Km value corresponding to the measured 30% reduction in proteolytic efficiency and with free and bound forms of alpha2u competing for access to the enzymes. Increased pinocytotic uptake of alpha2u into the kidney induces cathepsin activity. A model that ascribed renal alpha2u accumulation solely to reduced lysosomal proteolysis failed to reproduce the observed accumulation. The model could reproduce experimental observations if a transient increase in hepatic synthesis of alpha2u, stimulated by the presence of liganded alpha2u in the blood, and accelerated secretion of the protein from the liver were assumed. This model reproduces time course data of blood and kidney TMP-2-OH and renal alpha2u concentrations, suggesting that renal accumulation of alpha2u is not simply a consequence of reduced proteolytic degradation but may also involve a transient increase in hepatic alpha2u production. The model predicts increased delivery of TMP-2-OH to the kidney and consequent increased renal production of potentially toxic TMP-2-OH metabolites than would be the case if no alpha2u were present. Induced lysosomal activity and increased production of toxic metabolites may both contribute to the nephrotoxicity observed in male rats exposed to an alpha2u ligand or its precursor.

Odorant suppression of delayed rectifier potassium current in newt olfactory receptor cells

Effects of odorants on a delayed rectifier potassium current (IK) in newt olfactory receptor cells (ORCs) were investigated using the whole-cell version of the patch-clamp technique. Under voltage clamp, odorants (amyl acetate, limonene and acetophenone) reversibly suppressed I(K) without shifting its I-V curve. An amyl acetate puff completely suppressed I(K) induced by the first step pulse of repetitive depolarizations, suggesting that binding of an odorant molecule to the open channel is not required to block the channel. Although it is known that odorants suppress Na+ and Ca2+ currents (I(Na), I(Ca)) by shifting their inactivation curves to a negative voltage, odorants did not shift the inactivation curve of I(K) significantly. This suggests that odorants suppress I(K) without changing its voltage dependence. Therefore, the blocking mechanisms by odorants of I(K) in ORCs are different from those of I(Na) and I(Ca).

Vasodilator agents and supracollicular transection fail to inhibit cortical spreading depression in the cat

It remains an open question as to whether cortical spreading depression (CSD) is the pathophysiological correlate of the neurological symptoms in migraine with aura. In the experimental animal, CSD is an electrophysiological phenomenon mainly mediated via NMDA receptors. However, according to case reports in humans, visual aura in migraine can be alleviated by vasodilator substances, such as amyl nitrite and isoprenaline. There is also circumstantial evidence that brainstem nuclei (dorsal raphe nucleus and locus coeruleus) may play a pivotal role in the initiation of aura. In this study, CSD was elicited in alpha-chloralose anesthetized cats by cortical needle stab injury and monitored by means of laser Doppler flowmetry. Topical application of isoprenaline (0.1-1%) and amyl nitrite (0.05%) onto the exposed cortex had no effect on the elicitation or propagation of CSD. Also, after supracollicular transection, subsequent CSDs showed no differences in the speed of propagation and associated flow changes. We conclude from these data that--given CSD probably exists in humans during migraine--spreading neurological deficits during migraine aura are independent of brainstem influence and have a primarily neuronal rather than vascular mechanism of generation.

[Expression of c-fos prooncogene in rat brain induced by an olfactory stimulus]

OBJECTIVE

In order to investigate how widespread the activated regions induced by an olfactory stimulus throughout the central nervous system (CNS), c-fos expressions in CNS of the rat observed, which is known as a combined morphologically and functionally probe.

METHODS

Rats were stimulated by iso-amyl acetate for about 10 times, then one hour later sacrificed with perfusion of fixatives. After ABC immunocytochemi cal staining with anti-c-fos polyclonal antiserum, the c-Fos protein labelling areas on sections of the brain were observed.

RESULTS

The results showed that the labelling areas were estremely widespread throughout the brain and cervical segments of the spinal cord in the rat, expecially much more in the areas above the level of the pons. Nearly all neuronal structures in the limbic system were labeled in addition to structures of the olfactory pathways, suggesting there were neuronal activities in multiple neural circuits, which may be associated with emotional, somatic and visceral responses to the olfactory stimulus. Next, many brain areas which were associated with mechanisms of attention and central state regulation were widely labeled. Unexpected heavy labellings in deep layers of the superior colliculus, inferior colliculus and pontine nuclei were presumably relevant to integrating activity between sensations and motions.

CONCLUSIONS

The present study indicated that a specific olfactory stimulus did induce widespread activities of so-called pan-brain networks within the central nervous system.

Selective and reversible blockage of a fatty acid odour response in the olfactory bulb of the frog (Rana temporaria)

The lectin concanavalin A (ConA) when applied to the olfactory mucosa (OM) of frog and rat, is reported to partially inhibit electro-olfactogram (EOG) responses to fatty acid odours. Control odours like isoamyl acetate were not affected. We have now studied in the frog whether this treatment affects the corresponding olfactory bulb (OB) response. The OB surface was impregnated with a voltage-sensitive dye (RH 414). Spatial and temporal patterns of odour response were measured by changes in dye fluorescence that occur when OB neurons fire. The apparatus, consisted of an epi-fluorescent microscope coupled to a 64 x 64 pixel CCD photodetection camera. This allowed imaging over an 0.9 mm2 area of the OB glomerular layer to high resolution. When the frog OM was bathed with 5 mg ml(-1) ConA in Ringer's solution, the n-butyric acid odour response in the OB largely disappeared while the isoamyl acetate response did not change. When this experiment was repeated in the presence of 20 mM methyl alpha-D mannopyranoside (a ConA inhibitor), ConA failed to inhibit the n-butyric acid response. Moreover the ConA effect was partially reversible. A Ringer's wash of the OM after ConA treatment, partially restored the OB response to n-butyric acid. Thus the olfactory bulb results seem compatible with the EOG results and reinforce the notion that ConA selectively prevents n-butyric acid sensitive olfactory receptor neurons from firing. Chemical modification of the OM and their effect on OB response patterns may provide a useful approach to investigate olfactory quality coding.

Cell extensions in PKC1 mutants of Saccharomyces cerevisiae

To obtain information on cell wall synthesis and its relationship to morphology, we examined the induction of cell extensions of yeast upon the addition of isoamyl alcohol in osmotically fragile mutants that had mutations in genes related to the cell integrity pathway through activation of the mitogen-activated protein kinase cascade. We found that isoamyl alcohol induces cell extensions in pkc1 deletion mutants but not in mutants with mutations in genes positioned downstream or upstream of the PKC1 gene. These results suggest that Pkc1p functions not only in the integrity pathway but also in the induction. We characterized the elongated cells; many had two or more nuclei. We found no difference in cell surface structure between round and elongated cells from the results of chitin staining and cell wall extraction. Actin cytoskeleton was organized in elongated cells, as well as round cells. Cytochalasin D (0.08 mg/mL) inhibited the formation of actin cable but did not affect the induction of cell extensions.

Mechanism of the synergistic induction of CYP2H by isopentanol plus ethanol: comparison to glutethimide and relation to induction of 5-aminolevulinate synthase

We had previously found that combined treatment with isopentanol and ethanol synergistically induced CYP2H protein and activity in cultured chick nepatoytes. Here we investigated the mechanism of induction of CYP2H by the alcohols and whether they caused a coordinate induction of 5-aminolevulinate synthase (ALAS) mRNA. Treatment with isopentanol alone or in combination with ethanol resulted in coordinate increases in CYP2H1 and ALAS mRNAs. With isopentanol alone, the amounts of CYP2H1 and ALAS mRNAs at 4 to 6 h were similar to those observed after treatment with the alcohol combination, but declined by 11 h. Readdition of isopentanol at 11 h again increased the expression of both mRNAs, indicating that the decreases at 11 h were due to limiting amounts of inducer. Similar results were observed in cells exposed to low concentrations of glutethimide. In the combined alcohol treatment, increases in CYP2H1 and ALAS mRNAs were sustained from 4 h to 11 h after addition of the alcohols, but decreased to control levels by 24 h. Using pulse labeling to measure de novo synthesis of CYP2H1/2 protein, we found that the increases in CYP2H1/2 protein reflected the increases in CYP2H1 mRNA. The half-life of CYP2H1/2 protein, measured from pulse-chase experiments, was approximately twofold greater than the half-life of CYP2H1 mRNA. Our results indicate that the alcohols and glutethimide coordinately increase ALAS and CYP2H1 mRNA, and that increases in CYP2H1/2 protein arise from increases in its mRNA.

Odor detection in rats with 3-methylindole-induced reduction of sensory input

Rats were tested on odor-detection tasks after treatment with 400 mg/kg of 3-methyl-indole. As revealed by anterograde transport of horseradish peroxidase from the olfactory epithelium to the olfactory bulb glomeruli, treatment produced a severe (>97%) loss in sensory input relative to untreated controls. In almost all cases, only glomeruli in a restricted ventromedial segment of the bulb contained control levels of reaction product. In Experiment 1, five of nine experimental rats were anosmic or severely hyposmic, but the remaining four rats were able to detect amyl acetate vapor. In Experiment 2, four of seven experimental rats were anosmic, but the remaining three were able to detect each of four different odors. Among all experimental rats, those that were anosmic had significantly fewer glomeruli with dense anterograde transport than did those that could smell. Among rats that could smell, performance accuracy was related to the number of glomeruli with reaction product.

Odour coding is bilaterally symmetrical in the antennal lobes of honeybees (Apis mellifera)

The primary olfactory neuropil, the antennal lobe (AL) in insects, is organized in glomeruli. Glomerular activity patterns are believed to represent the across-fibre pattern of the olfactory code. These patterns depend on an organized innervation from the afferent receptor cells, and interconnections of local interneurons. It is unclear how the complex organization of the AL is achieved ontogenetically. In this study, we measured the functional activity patterns elicited by stimulation with odours in the right and the left AL of the same honeybee (Apis mellifera) using optical imaging of the calcium-sensitive dye calcium green. We show here that these patterns are bilaterally symmetrical (n=25 bees). This symmetry holds true for all odours tested, irrespective of their role as pheromones or as environmental odours, or whether they were pure substances or complex blends (n=13 odours). Therefore, we exclude that activity dependent mechanisms local to one AL determine the functional glomerular activity. This identity is genetically predetermined. Alternatively, if activity dependent processes are involved, bilateral connections would have to shape symmetry, or, temporal constraints could lead to identical patterns on both sides due to their common history of odour exposure.

5-hydroxytryptamine3 (5-HT3) receptor-mediated depolarisation of the rat isolated vagus nerve: modulation by trichloroethanol and related alcohols

The ability of 2,2,2-trichloroethanol (TCE) and related alcohols to modify the 5-hydroxytryptamine3 (5-HT3) receptor-mediated depolarisation of the rat isolated cervical vagus nerve were investigated by extracellular electrophysiological recording using the 'grease gap' technique. TCE at millimolar concentrations increased the magnitude of the 5-HT3 receptor-mediated depolarisations of the rat vagus nerve by a number of agonists (5-HT, phenylbiguanide (PBG), quipazine). Concentration response curves generated for the 5-HT3 receptor agonists. 5-HT and PBG, in the absence and presence of TCE (5 mM) indicated that the potentiation in agonist-induced depolarisation was due to an increase in both agonist potency and apparent efficacy. Following apparent complete 5-HT3 receptor desensitisation (induced by either 5-HT or PBG; 100 microM for 90 min), application of TCE (5 mM) in the continued presence of either agonist induced a depolarisation of the vagus nerve. In addition to TCE, a number of related alcohols (tribromoethanol, isopentanol and 5-chloropentanol but not ethanol) at millimolar concentrations also potentiated depolarisation of the vagus nerve induced by 5-HT. Combined application of both TCE (0.1-20 mM) and isopentanol (20 mM) indicated that the potentiation of the 5-HT3 receptor-mediated depolarisation by these alcohols was not additive. The present studies indicate that the 5-HT3 receptor expressed on the cervical vagus nerve is susceptible to allosteric modulation by a number of alcohols including the anaesthetic agent TCE. Such an interaction may have relevance to the nausea and vomiting experienced by some patients following recovery from general anaesthesia.

Relationship of anesthetic activity of alkyl acetates to hydrophobicity and in vivo effect on membrane fluidity in mice

In vivo anesthetic activity of alkyl acetates in mice was studied in relation to hydrophobicity and the in vivo effect on membrane fluidity. The anesthetic potency (AD50) of alkyl acetates was determined; AD50 shows the i.p. dose required to anesthetize 50% of mice from the treated group. We used log P (n-octanol/water partition coefficient) as an operational definition of hydrophobicity. Membrane fluidity was determined using 1,6-diphenyl-1,3,5-hexatriene (DPH) as fluorescence probe. Log (1/AD50) was a parabolic function of log P, and the value of log P that corresponds to the minimum AD50 was estimated to be 2.08. Brain synaptosomal membranes were prepared from mice 30 min after dosing with each of the three alkyl acetates applied at 1.5-fold AD50: n-butyl, n-amyl, and n-hexyl acetate. In each alkyl acetate group, most of the animals were anesthetized (> 68%). Decreased membrane fluidity was observed for the animals that were anesthetized while no change in the fluidity was seen for the animals that were not anesthetized. The results suggest an involvement of decreased DPH fluidity in alkyl acetate-induced anesthesia.

Olfactory discrimination ability for aliphatic esters in squirrel monkeys and humans

Using a behavioral paradigm designed to simulate olfactory-guided foraging, the ability of five squirrel monkeys to distinguish iso-amyl acetate from n- and iso-forms of other acetic esters (ethyl acetate to decyl acetate) and from other esters carrying the iso-amyl group (iso-amyl propionate to iso-amyl capronate) was investigated. We found (i) that all five animals were clearly able to discriminate between all odor pairs tested; (ii) a significant negative correlation between discrimination performance and structural similarity of odorants in terms of differences in carbon chain length of both the aliphatic alcohol group and the aliphatic acid group of the esters; and (iii) that iso- and n-amyl acetate were perceived as qualitatively similar despite different steric conformation. Using a triple-forced choice procedure, 20 human subjects were tested on the same tasks in parallel and showed a very similar pattern of discrimination performance compared with the squirrel monkeys. Thus, the results of this study provide evidence of well-developed olfactory discrimination ability in squirrel monkeys for aliphatic esters and support the assumption that human and non-human primates may share common principles of odor quality perception.

Environmental signals modulate olfactory acuity, discrimination, and memory in Caenorhabditis elegans

Caenorhabditis elegans uses a variety of attractive olfactory cues to detect food. We show here that the responses to olfactory cues are regulated in a dynamic way by behavioral context and the animal's previous experience. Prolonged exposure to an odorant leads to a decreased response to that odorant, a form of behavioral plasticity called olfactory adaptation. We show that starvation can increase the extent of olfactory adaptation to the odorant benzaldehyde; this effect of starvation persists for several hours after the animals have been returned to food. The effect of starvation is antagonized by exogenous serotonin, which induces many of the same behavioral responses in C. elegans as are induced by food. Starvation also inhibits recovery from adaptation to a different odorant, 2-methylpyrazine, thus enhancing olfactory memory. In addition to its effects on adaptation, starvation modulates olfactory discrimination in C. elegans; starved animals discriminate more classes of odorants than fed animals. Increased olfactory discrimination is also seen in the adaptation-defective mutant adp-1 (ky20). These various forms of behavioral plasticity enhance the ability of starved animals to respond to novel, potentially informative odorants.

Olfactory event-related potentials to amyl acetate in congenital anosmia

Olfactory function was evaluated by olfactory event-related potentials and standardized psychophysical measures including the Smell Identification Test and odor detection threshold tests for 3 chemosensory stimulants in 9 subjects with isolated congenital anosmia and 9 age- and gender-matched normosmic controls. There was a significant difference in Smell Identification Test scores (P < 0.001) and odor detection thresholds for phenylethyl alcohol (P < 0.001) and isoamyl acetate (P < 0.001) between the anosmic and normosmic subjects. Detection thresholds for chloracetyl phenone, a trigeminal stimulant, did not differ between the 2 groups. Olfactory evoked potentials were recorded in response to amyl acetate and air control stimuli presented at volume flow rate of 5 l/min, stimulus duration of 40 ms, and randomized interstimulus intervals of 6-30 s. In the control subjects, evoked potentials to amyl acetate were characterized by 4 reproducible components (P1, N1, P2, and N2). In the subjects with congenital anosmia, no reproducible evoked potential components were identified in response to amyl acetate. No reproducible evoked potential components were seen in response to the air control stimulus in either the anosmic or normosmic groups. These data suggest that olfactory evoked potentials provide a specific measure of olfactory function.