Specialized odorant receptors in social insects that detect cuticular hydrocarbon cues and candidate pheromones

Eusocial insects use cuticular hydrocarbons as components of pheromones that mediate social behaviours, such as caste and nestmate recognition, and regulation of reproduction. In ants such as Harpegnathos saltator, the queen produces a pheromone which suppresses the development of workers' ovaries and if she is removed, workers can transition to a reproductive state known as gamergate. Here we functionally characterize a subfamily of odorant receptors (Ors) with a nine-exon gene structure that have undergone a massive expansion in ants and other eusocial insects. We deorphanize 22 representative members and find they can detect cuticular hydrocarbons from different ant castes, with one (HsOr263) that responds strongly to gamergate extract and a candidate queen pheromone component. After systematic testing with a diverse panel of hydrocarbons, we find that most Harpegnathos saltator Ors are narrowly tuned, suggesting that several receptors must contribute to detection and discrimination of different cuticular hydrocarbons important in mediating eusocial behaviour.Cuticular hydrocarbons (CHC) mediate the interactions between individuals in eusocial insects, but the sensory receptors for CHCs are unclear. Here the authors show that in ants such as H. saltator, the 9-exon subfamily of odorant receptors (HsOrs) responds to CHCs, and ectopic expression of HsOrs in Drosophila neurons imparts responsiveness to CHCs.

North American Species of Cerambycid Beetles in the Genus Neoclytus Share a Common Hydroxyhexanone-Hexanediol Pheromone Structural Motif

Many species of cerambycid beetles in the subfamily Cerambycinae are known to use male-produced pheromones composed of one or a few components such as 3-hydroxyalkan-2-ones and the related 2,3-alkanediols. Here, we show that this pheromone structure is characteristic of the cerambycine genus Neoclytus Thomson, based on laboratory and field studies of 10 species and subspecies. Males of seven taxa produced pheromones composed of (R)-3-hydroxyhexan-2-one as a single component, and the synthetic pheromone attracted adults of both sexes in field bioassays, including the eastern North American taxa Neoclytus caprea (Say), Neoclytus mucronatus mucronatus (F.), and Neoclytus scutellaris (Olivier), and the western taxa Neoclytus conjunctus (LeConte), Neoclytus irroratus (LeConte), and Neoclytus modestus modestus Fall. Males of the eastern Neoclytus acuminatus acuminatus (F.) and the western Neoclytus tenuiscriptus Fall produced (2S,3S)-2,3-hexanediol as their dominant or sole pheromone component. Preliminary data also revealed that males of the western Neoclytus balteatus LeConte produced a blend of (R)-3-hydroxyhexan-2-one and (2S,3S)-2,3-hexanediol but also (2S,3S)-2,3-octanediol as a minor component. The fact that the hydroxyketone-hexanediol structural motif is consistent among these North American species provides further evidence of the high degree of conservation of pheromone structures among species in the subfamily Cerambycinae.

(R)-3-hydroxyhexan-2-one is a major pheromone component of Anelaphus inflaticollis (Coleoptera: Cerambycidae)

We report the identification and field bioassays of a major component of the male-produced aggregation pheromone of Anelaphus inflaticollis Chemsak, an uncommon desert cerambycine beetle. Male A. inflaticollis produced a sex-specific blend of components that included (R)-3-hydroxyhexan-2-one, (S)-2-hydroxyhexan-3-one, 2,3-hexanedione, and (2R,3R)- and (2R,3S)-2,3-hexanediols. Field trials with baited bucket traps determined that the reconstructed synthetic pheromone blend and (R)-3-hydroxyhexan-2-one alone attracted adult A. inflaticollis of both sexes, with significantly more beetles being attracted to the blend. We conclude that (R)-3-hydroxyhexan-2-one is a major pheromone component of A. inflaticollis, and our results suggest that one or more of the minor components may further increase attraction of conspecifics. Scanning electron microscopy showed that male A. inflaticollis have pores on the prothorax that are consistent in structure with sex-specific pheromone gland pores in related species. Males also displayed stereotyped calling behavior similar to that observed in other cerambycine species. This study represents the first report of volatile pheromones for a cerambycine species in the tribe Elaphidiini.

Male-produced aggregation pheromones of the cerambycid beetles Xylotrechus colonus and Sarosesthes fulminans

Adults of both sexes of the cerambycid beetles Xylotrechus colonus (F.) and Sarosesthes fulminans (F.) were attracted to odors produced by male conspecifics in olfactometer bioassays. Analyses of headspace volatiles from adults revealed that male X. colonus produced a blend of (R)- and (S)-3-hydroxyhexan-2-one and (2 S,3 S)- and (2R,3R)-2,3-hexanediol, whereas male S. fulminans produced (R)-3-hydroxyhexan-2-one and (2 S,3R)-2,3-hexanediol. All of these compounds were absent in the headspace of females. Two field bioassays were conducted to confirm the biological activity of the synthesized pheromones: (1) enantiomerically enriched pheromone components were tested singly and in species-specific blends and (2) four-component mixture of racemic 3-hydroxyhexan-2-one plus racemic 2-hydroxyhexan-3-one and the four-component blend of the stereoisomers of 2,3-hexanediols were tested separately and as a combined eight-component blend. In these experiments, adult male and female X. colonus were captured in greatest numbers in traps baited with the reconstructed blend of components produced by males, although significant numbers were also captured in traps baited with (R)-3-hydroxyhexan-2-one alone or in blends with other compounds. Too few adult S. fulminans were captured for a statistical comparison among treatments, but all were caught in traps baited with lures containing (R)-3-hydroxyhexan-2-one. In addition to these two species, adults of two other species of cerambycid beetles, for which pheromones had previously been identified, were caught: Neoclytus a. acuminatus (F.) and its congener Neoclytus m. mucronatus (F.). Cross-attraction of beetles to pheromone blends of other species, and to individual pheromone components that are shared by two or more sympatric species, may facilitate location of larval hosts by species that compete for the same host species.

Novel lepidopteran sex pheromone components from Marmara gulosa (Lepidoptera: Gracillariidae)

Marmara gulosa Guillén & Davis (Lepidoptera: Gracillariidae) is a sporadic pest of citrus and a number of other crops in southern and central California. Coupled gas chromatographic-electroantennogram detection analyses of headspace volatiles collected by solid phase microextraction from virgin female moths revealed at least four related compounds in the extracts that elicited significant antennal responses from antennae of male moths. These compounds were identified as (8E,10E)-tetradecadien-1-ol, and the corresponding aldehyde, acetate, and formate ester, representing the first report of a formate as a lepidopteran pheromone component. The four compounds were consistently found in headspace volatiles collected from virgin female moths from different regions of the state and from M. gulosa collected from different host plants (citrus and squash). Repeated field trials determined that the formate ester alone was as attractive or more attractive than any blend of the formate with one or more of the remaining compounds. Although large numbers of moths were caught in some field trials, trap catches were not consistent. Thus, the pheromone may be useful for detection of the moth and setting an initial biofix, but it remains unclear whether the pheromone can be used as a reliable and accurate tool for monitoring densities of M. gulosa populations.

A new pheromone race of Acrobasis nuxvorella (Lepidoptera: Pyralidae)

The sex pheromone of the monophagous Acrobasis nuxvorella Neunzig (Lepidoptera: Pyralidae) was reported as (9E,11Z)-hexadecadienal (9E,11Z-16:Ald) (Biorg. Med. Chem. 4: 331-339, 1996), and it has since been an effective integrated pest management (IPM) tool for monitoring this pest in the United States, but not in Mexico. Field and laboratory studies were conducted to confirm that the species in Mexico was indeed A. nuxvorella and to investigate the pheromone chemistry of the Mexican populations of this species. Initial field trials testing compounds structurally related to the known pheromone component, and blends thereof, indicated that a 100 microg:100 microg blend of (9E,11Z)-hexadecadien-1-yl acetate (9E,11Z-16:Ac):9E,11Z-16:Ald in rubber septa was effective in attracting male moths in Mexico. Coupled gas chromatography-electroantennogram analyses confirmed the presence of these compounds in extracts of pheromone glands of females, and antennae of male moths also responded to the alcohol analog (9E,11Z)-hexadecadien-1-ol (9E,11Z-16:OH). Subsequent field trials of various blends of these three compounds in Mexico showed that 1) both the acetate and aldehyde components were required for optimal attraction of male moths of the Mexican populations, and 2) addition of the alcohol suppressed attraction of males in a dose-dependent manner. Tests with the 1:1 9E,11Z-16:Ac:9E,11Z-16:Ald blend at various sites in the United States showed that this blend attracted some moths, but that moths attracted to 9E,11Z-16:Ald alone were predominant in the population. Furthermore, in preliminary studies the latter seemed not to respond to the blend. These findings indicate that there are two pheromone types of the pecan nut casebearer, and they have major implications for the direct use of these pheromones in pecan IPM.

Identification, synthesis, and bioassay of a male-specific aggregation pheromone from the harlequin bug, Murgantia histrionica

Sexually mature male harlequin bugs produced a sex-specific compound, identified as one of the stereoisomers of the sesquiterpene epoxyalcohol 4-[3-(3,3-dimethyloxiran-2-yl)-1-methylpropyl]-1-methylcyclohex-2-en-1-ol (henceforth murgantiol), a compound with four chiral centers and 16 possible stereoisomers. Production of the compound was highest during the middle of the day. Individual virgin male bugs in separate containers produced the compound at a higher rate than virgin males in groups. The carbon skeleton was verified by synthesis of several mixtures which, in total, contained all possible isomers, one of which matched the insect-produced compound. The relative and absolute configurations of the insect-produced compound remain to be determined. In laboratory bioassays, insect-produced and synthetic murgantiol attracted harlequin bugs of both sexes, suggesting that murgantiol is a male-produced aggregation pheromone, analogous to those found in a number of other phytophagous bug species.

Using Generic Pheromone Lures to Expedite Identification of Aggregation Pheromones for the Cerambycid Beetles Xylotrechus nauticus, Phymatodes lecontei, and Neoclytus modestus modestus

Males of several species of longhorned beetles in the subfamily Cerambycinae produce sex or aggregation pheromones consisting of 2,3-hexanediols and/or hydroxyhexanones. We tested the hypothesis that this diol/hydroxyketone pheromone motif is highly conserved within the subfamily, and the resulting prediction that multiple cerambycine species will be attracted to compounds of this type. We also tested the concept that live traps baited with generic blends of these compounds could be used as a source of live insects from which pheromones could be collected and identified. Traps placed in a mature oak woodland and baited with generic blends of racemic 2-hydroxyhexan-3-one and 3-hydroxyhexan-2-one captured adults of both sexes of three cerambycine species: Xylotrechus nauticus (Mannerheim), Phymatodes lecontei Linsley, and Phymatodes decussatus decussatus (LeConte). Odors collected from male X. nauticus contained a 9:1 ratio of two male-specific compounds, (R)- and (S)-3-hydroxyhexan-2-one. Field trials with synthetic compounds determined that traps baited with (R)-3-hydroxyhexan-2-one (94% ee), alone or in blends with other isomers, attracted similar numbers of X. nauticus of both sexes, whereas (S)-3-hydroxyhexan-2-one (94% ee) attracted significantly fewer beetles. Phymatodes lecontei and P. d. decussatus also were caught in traps baited with hydroxyhexanones, as well as a few specimens of two other cerambycine species, Neoclytus modestus modestus Fall (both sexes) and Brothylus gemmulatus LeConte (only females). Male N. m. modestus produced (R)-3-hydroxyhexan-2-one, which was not present in extracts from females. Neoclytus m. modestus of both sexes also responded to lures that included (R)-3-hydroxyhexan-2-one as one of the components. The only male-specific compound found in extracts from P. lecontei was (R)-2-methylbutan-1-ol, and adults of both sexes were attracted to racemic 2-methylbutan-1-ol in field bioassays. Surprisingly, P. lecontei of both sexes also were attracted to (R)- and (S)-3-hydroxyhexan-2-ones, although neither compound was detected in extracts from this species. Males of all five beetle species had gland pores on their prothoraces that were similar in structure to those that have been associated with volatile pheromone production in other cerambycine species. The attraction of multiple cerambycine species of two tribes to (R)-3-hydroxyhexan-2-one in this study, and in earlier studies with other cerambycine species, suggests that this compound is a widespread aggregation pheromone component in this large and diverse subfamily. Overall, the attraction of multiple species from different cerambycine tribes to this compound at a single field site supports the hypothesis that the hydroxyketone pheromone structural motif is highly conserved within this subfamily.

Isolation, identification, synthesis, and field evaluation of the sex pheromone of the Brazilian population of Spodoptera frugiperda

Several studies have shown intraspecific geographical variation in the composition of sex pheromones. Pheromone lures from North America and Europe were not effective against the fall armyworm Spodoptera frugiperda (Smith, 1797) (Lepidoptera: Noctuidae) in Brazil, so we examined the composition of the sex pheromone produced by females from Brazilian populations. Virgin female gland extracts contained (Z)-7-dodecenyl acetate (Z7-12:Ac), (E)-7-dodecenyl acetate (E7-12:Ac), dodecyl acetate, (Z)-9-dodecenyl acetate, (Z)-9-tetradecenyl acetate (Z9-14:Ac), (Z)-10-tetradecenyl acetate, tetradecyl acetate/(Z)-11-tetradecenyl acetate (Z11-16:Ac), and (Z)-11-hexadecenyl acetate. The relative proportions of each acetate were 0.8:1.2:0.6:traces:82.8:0.3:1.5:12.9, respectively. This is the first time that E7-12:Ac has been reported from the pheromone gland of S. frugiperda. Only three compounds, Z9-14:Ac, Z7-12:Ac, and E7-12:Ac, elicited antennal responses, and there were no differences in catch between traps baited with either Z7-12:Ac + Z9-14:Ac or Z7-12:Ac + Z9-14:Ac + Z11-16:Ac blends. However, the Z7-12:Ac + Z9-14:Ac + E7-12:Ac blend was significantly better than Z7-12:Ac + Z9-14:Ac, indicating that E7-12:Ac is an active component in the sex pheromone of the Brazilian populations of S. frugiperda.

(Z)-9-nonacosene-major component of the contact sex pheromone of the beetle Megacyllene caryae

Male Megacyllene caryae (Gahan) (Coleoptera: Cerambycidae) respond to females only after touching them with their antennae, indicating that mate recognition is mediated by a contact sex pheromone. Gas chromatography-mass spectrometry analyses of whole-body solvent extracts of male and female M. caryae revealed substantial differences in hydrocarbon profiles, with nearly half of the compounds in the extracts from females being absent from those of males. Biological activities of fractions of crude extracts of females, and reconstructed blends of the most abundant straight-chain (nC(27), nC(28), nC(29)), methyl-branched (2Me-C(26), 9Me-C(29), 11, 13, 15Me-C(29)), and unsaturated (Z9:C(29), Z13:C(29), Z14:C(29), Z13:C(31), Z14:C(31), Z15:C(31)) compounds in extracts of females were tested in arena bioassays, assessing four steps in the mating behavior sequence of males (orientation, arrestment, body alignment, mounting and attempting to couple the genitalia). Males showed limited response to dead females treated with fractions of the crude extract or blends of synthetic straight-chain and methyl-branched alkanes, but responded strongly to the blend of synthetic monoenes. Further trials determined that the complete sequence of mating behaviors, up to and including coupling the genitalia, was elicited by Z9:C(29) alone. Z9:C(29) is a homolog of the contact pheromone (Z9:C(25)) of the congener M. robiniae (Förster). Previous work with M. robiniae suggested that wipe sampling of cuticular hydrocarbons of females by solid phase microextraction yielded a more representative profile of components actually encountered by a male's antennae, and so provided a more readily interpretable profile of potential semiochemicals present in the wax layer than does solvent extraction. We tested this hypothesis by comparing hydrocarbon profiles of female M. caryae by the two sampling methods. Z9:C(29) was the only compound among the dominant hydrocarbons that was present in higher abundance in SPME than in solvent extracts ( approximately 12% vs. approximately 8%, respectively), supporting this hypothesis.

Identification, Synthesis, and Field Testing of the Sex Pheromone of the Citrus Leafminer, Phyllocnistis citrella

The citrus leafminer is an important vector of citrus canker in many of the major citrus production areas of the world. (7Z,11Z)-Hexadecadienal was reported as a sex attractant for this insect in the 1980s, based on trap catches during pheromone screening trials in Japan. However, attempts to reproduce this work in other areas of the world have not been successful. We report here that (7Z,11Z)-hexadecadienal is only one component of the pheromone, with the other critical component being the analogous trienal, (7Z,11Z,13E)-hexadecatrienal. Both compounds were identified in the effluvia from live female moths by coupled gas chromatography (GC)-electroantennography using nonpolar and polar GC columns, and the identifications were confirmed by comparisons of mass spectra with those of authentic standards. Stereoisomers of the two compounds, and a number of analogs, were synthesized to confirm the identifications. In field trials, neither compound alone was attractive to male moths, but blends of the two were highly attractive, with thousands of insects being caught per trial. Addition of the isomeric (7Z,11Z,13Z)-hexadecatrienal inhibited attraction to the two-component blend.

Short and simple syntheses of 4-oxo-(E)-2-hexenal and homologs: pheromone components and defensive compounds of Hemiptera

One-step syntheses of 4-oxo-(E)-2-hexenal and 4-oxo-(E)-2-octenal from commercially available 2-ethyl- and 2-butylfuran are described. A two-step synthesis of the homolog 4-oxo-(E)-2-decenal from furan is also reported. These compounds are common components of true bug defensive secretions, and recently have been identified as pheromone components for several species. The simple syntheses reported here will make these compounds readily available for further research.

(3Z,6Z,9Z, 12Z, 15Z)-Pentacosapentaene, a key pheromone component of the fir coneworm moth, Dioryctria abietivorella

The sex pheromone of the fir coneworm moth consists of a blend of (3Z,6Z,9Z,12Z,15Z)-pentacosapentaene and (9Z, 11E)-tetradecadienyl acetate. Analogous blends of polyunsaturated, long-chain hydrocarbons with much shorter chain aldehydes or alcohols recently have been discovered in three other moth species in the superfamily Pyraloidea. These combinations of components from two distinct structural classes may represent an important and widespread new pheromone blend motif within the Lepidoptera.

Mechanism for basic hydrolysis of N-nitrosoguanidines in aqueous solution

A kinetic study was carried out on the hydrolysis of two N-nitrosoguanidines, 1-nitroso-1-methyl-3-tolylsulfonylguanidine (TSGNO) and 1-nitroso-1-methyl-3-benzoylguanidine (BCGNO). We observed an absence of buffer catalysis using H(2)PO(4)(-)/HPO(4)(2)(-), H(3)BO(3)/H(2)BO(3)(-), and HCO(3)(-)/CO(3)(2)(-) regulators and a complex dependency of the rate constant on the pH. We discovered the existence of three simultaneous reaction paths: spontaneous decomposition of the neutral form of the N-nitrosoguanidine, decomposition of the monoanion, and decomposition through the form of the dianion. The analysis of the kinetic data has allowed us to obtain the acidity constant for the formation of the monoanion of the N-nitrosoguanidine, with values of p = 11.5. The reaction rate for the process through the monoanion, k(2), decreases as the acidity increases. The application of the principle of nonperfect synchronization shows that the basicity and reactivity do not correlate when there exists a possibility of stabilization of the negative charge by resonance. This behavior is consistent with the mechanism E1cB whereby the stabler the negative charge, the slower the elimination reaction. When dealing with the case of the elimination through the neutral form we observe that the reaction rate increases together with the capacity of stabilization of the positive charge on the nitrogen atom adjacent to the imino group. For the reaction through the dianion we used a maximum value of k(3) = 10(10) s(-)(1) to estimate the value of p for the formation of the dianion of the N-nitrosoguanidine, obtaining values of p < 24.

Identification of male-specific chiral compound from the sugarcane weevil Sphenophorus levis

Comparative gas chromatographic analyses of airborne volatiles produced by males and females of the sugarcane weevil Sphenophorus levis, showed one male-specific compound. Gas chromatography-mass spectrometry data indicated an aliphatic alcohol that was identified as 2-methyl-4-octanol. Both optical isomers were synthesized in five steps by employing commercially available (R)- and (S)-2.2-dimethyl-1,3-dioxolane-4-methanol as starting material. Enantiomeric resolution by gas chromatography with a chiral column demonstrated that the natural alcohol possessed the S configuration. Preliminary indoor observations suggested that the alcohol elicited aggregation behavior among adults. The same compound has been previously described as an aggregation pheromone in several other curculionid species.

Development and optimization of methods for using sex pheromone for monitoring the mealybug Planococcus ficus (Homoptera: Pseudococcidae) in California vineyards

The sex pheromone of the vine mealybug Planococcus ficus Signoret has been identified as a single component, lavandulyl senecioate. Racemic lavandulyl senecioate was as attractive to male mealybugs as the insect-produced (S)-enantiomer, indicating that the unnatural enantiomer is not inhibitory. Lavandulol, which also was found in extracts from virgin females, antagonized attraction of males at higher doses. Rubber septum lures loaded with 10- to 1,000-microg doses of the pheromone were equally attractive, and lures loaded with 100 microg of racemic pheromone remained attractive for at least 12 wk under field conditions. Delta traps were more effective than double-sided sticky cards and minimized captures of nontarget insects. Pheromone-baited traps had an effective range of at least 50 m. Comparison of visual sampling methods and sampling of males with pheromone-baited traps revealed that trap catches were significantly correlated with the results from visual sampling methods, and with economic damage.

Nitroso group transfer from substituted N-methyl-N-nitrosobenzenesulfonamides to amines. Intrinsic and apparent reactivity

We have studied the nitroso group transfer from substituted N-methyl-N-nitrosobenzenesulfonamides to primary and secondary amines, observing that the rate of the reaction increases as a consequence of the presence of electron withdrawing groups on the aromatic ring of the nitrosating agents. The rate constants determined for the nitroso group transfer, ktr, give good Bronsted-type relationships between log ktr (rate constant for nitroso group transfer) and pKaR2NH2+ and pKaleaving group. The study of the nitrosation processes of secondary amines catalyzed by ONSCN and denitrosation catalyzed by SCN-, in combination with the formation equilibrium of ONSCN, has enabled us to calculate the value of the equilibrium constant for the loss of the NO+ group from a protonated N-nitrosamine (pKNOR2N+HNO), which can be defined by analogy with pKaR2NH2+. The value of pKNOX-NO for the loss of the NO+ group from an N-methyl-N-nitrosobenzenesulfonamide was obtained in a similar way. By using values of delta pKNO = pKNOR2N+HNO - pKNOX-NO, we were able to calculate the equilibrium constant for the nitroso group transfer and characterize the transition state. On the basis of Bronsted-type correlations, we have obtained values of beta nuclnorm and alpha lgnorm approximately equal to 0.55, showing a perfectly balanced transition state. In terms of the Marcus theory, the calculation of the intrinsic barriers for the nitroso group transfer reaction shows that the presence of electron withdrawing groups on the aromatic ring of the N-methyl-N-nitrosobenzenesulfonamides does not cause these barriers to vary.

Hyperacute stroke: evaluation with combined multisection diffusion-weighted and hemodynamically weighted echo-planar MR imaging

PURPOSE

To evaluate acute stroke with conventional, multisection diffusion-weighted (DW), and hemodynamically weighted (HW) magnetic resonance (MR) imaging.

MATERIALS AND METHODS

The three MR imaging techniques were performed in 11 patients within 10 hours of the onset of acute hemiparesis. The volume of DW and HW abnormalities were compared with infarct volumes depicted at initial and/or follow-up MR or computed tomography (CT).

RESULTS

Findings at DW and HW imaging were abnormal in nine of the 11 patients, despite normal findings at initial CT and/or MR. In all nine patients, infarcts were depicted at follow-up CT or MR. The DW abnormality was generally smaller and the HW abnormality was generally larger than the infarct volume determined at subsequent imaging. In the two patients with normal findings at DW and HW imaging, symptoms resolved completely within 1-48 hours.

CONCLUSION

Different aspects of hyperacute cerebral ischemia are depicted at DW and HW imaging before infarction is depicted at conventional MR or CT. These techniques may improve stroke diagnosis and may contribute to advances in treatment.

Altered GABAergic and glutamatergic transmission in audiogenic seizure-susceptible mice

The C57BL/10 SPS/sps mouse mutant are audiogenic seizure-susceptible. The enzymatic activities of glutamate decarboxylase (GAD), GABA aminotransferase (GABA-T), alanine aminotransferase (ALA-T), aspartate aminotransferase (ASP-T), and glutamate dehydrogenase (GDH) of whole brain supernatant are significantly reduced in these epileptic mice. GABA uptake is decreased in cortex, midbrain, and pons medulla. Previous studies showed the presence of two sodium-dependent GLU uptake systems in normal (SPS/SP) mice. Glutamate Umax by System 1 is significantly decreased in these mice, whereas the Umax value for System 2 is significantly increased in the epileptic mice.

GABAergic neurotransmission in the C57BL/10 sps/sps mouse mutant: a model of absence seizures

The C57BL/10 sps/sps mouse mutant displays generalized absence seizure-like behavior. In these mice, glutamic acid decarboxylase activity is reduced in the cortex and hippocampus. Tritiated flunitrazepam binding (3H-flu) is reduced in these areas, as well as in midbrain, cerebellum, and pons-medulla. Quantitative [3H]-flunitrazepam binding autoradiography confirms these observations. GABA uptake by synaptosomes from sps/sps mice is also reduced in all the areas studied. Potassium-stimulated, Ca(2+)-dependent release of radioactivity from synaptosomes preloaded with [14C]-GABA is reduced in the hippocampus, increased in midbrain and pons-medulla, but remains unaltered in the cortex. These results suggest region-specific alterations in GABAergic neurotransmission that may be responsible for the absence-like seizures in C57BL/10 sps/sps mice.