Autosomal dominant retinitis pigmentosa: a new multi-allelic marker (D3S621) genetically linked to the disease locus (RP4)

Summary We report the characterization of a new eightallele microsatellite (D3S621) isolated from a human chromosome 3 library. Two-point and multi-locus genetic linkage analysis have shown D3S621 to co-segregate with the previously mapped RP4 ( _m=0.12, Z _m=4.34) and with other genetic markers on the long arm of the chromosome, including D3S14 (R208) ( _m=0.00, Z _m= 15.10), D3S47 (C17) ( _m=0.11, Z _m=4.95), Rho ( _m= 0.07, Z _m=1.37), D3S21 (L182) ( _m=0.07, Z _m=2.40) and D3S19 (U1) ( _m=0.13, Z _m=2.78). This highly informative marker, with a polymorphic information content of 0.78, should be of considerable value in the extension of linkage data for autosomal dominant retinitis pigmentosa with respect to locii on the long arm of chromosome 3.     

Assignment of the gene for dyskeratosis congenita to Xq28

Summary Dyskeratosis congenita is an X-linked recessive disorder with diagnostic dermatological features, bone marrow hypofunction, and a predisposition to neoplasia in early adult life. Linkage analysis was undertaken in an extensive family with the condition using the Xg blood group and 17 cloned X chromosomal DNA sequences which recognise restriction fragment length polymorphisms (RFLPs). No recombination was observed between the locus for dyskeratosis congenita (DKC) and the RFLPs identified by DXS52 (St 14-1) (Z_max=3.33 at _max=0 with 95% confidence limits of 0 to 14 cM). Similarly no recombination was observed for the disease locus and F8 (Z_max=1.23 at _max=0) nor for DXS15 (Z_max=1.62 at _max=0), but both of these markers were only informative in part of the family whereas DXS52 was fully informative. DXS52, DXS15, and F8 are known to be tightly linked and have previously been assigned to Xq28. Thus the gene for dyskeratosis congenita can be assigned to Xq28. These DNA sequence polymorphisms will be of clinical value for carrier detection and prenatal diagnosis.     

Phytoplankton of shallow lakes: Seasonal succession, standing crop and the chief determinants of primary productivity, 1. Cooking Lake, Alberta, Canada

Cooking Lake (113°02′W, 53°26′N), a well-mixed, shallow (mean depth (1.59 m), eutrophic lake in Alberta, Canada, is characterized by eutrophic chlorococcalean and cyanophycean phytoplankton associations, and little change in standing crop with increasing depth. Standing crop and primary productivity are low during the winter but pronounced spring and summer maxima occur. Mean yearly areal standing crop (ΔB) and primary productivity (ΔA) were 212.4 mg m^?2 chlorophyll a and 301.8 mg C h^?1 m^?2 respectively. Annual productivity was estimated at 1322 g C m^?2. The mean increase in the extinction coefficient (?) per unit increase in standing crop (B) was 0.03 In units m^?1. High non-algal light attenuation (?_q) occurred avenging 41 which prevented the ratio B/? from attaining more than 65% of the theoretical maximum except once when algal self-shading occurred. Close correlations existed between B (mg m^?3 chlorophyll a) and A _max (mg h_?1 m_?3) ΔA and ΔB, ΔA and B, A_max, and A_max/?, and ΔA and I_o′, (W m^?2). The depth of the euphotic zone (Z_eu) varied between 0.5 and 1 25 m; the average relationship between z_eu and E was Z_eu= 3.74/?, and the mean standing Crop found in the euphotic zone represented 55.2% of the theoretical maximum, The high ?_q, values made the model of Tailing (1957) inapplicable to Cooking Lake. The Q₁₀ value for the lake was 2.2. The maximum rate of photosynthesis per unit of population per h. Ø^max, (mg C sag chlorophyll a_?1 h_?1) was more closely related to temperature than irradiance and ma depressed by pH values greater than 9.1. Growth of the phytoplankton was not nutrient limited: instead irradiance and temperature were more important. Indirect evidence that free CO₂ limited photosynthetic rates, is provided by the Ø_max: pH relationship.     

A New Locus for Dominant “Zonular Pulverulent” Cataract, on Chromosome 13

Inherited cataract is a clinically and genetically heterogeneous disease that most often presents as a congenital autosomal dominant trait. Here we report the linkage of a new locus for dominant “zonular pulverulent” cataract (CZP) to chromosome 13. To map the CZPlocus we performed molecular-genetic linkage analysis using microsatellite markers in a five-generation English pedigree. After exclusion of eight known loci and several candidate genes for autosomal dominant cataract, we obtained significantly positive LOD scores (Z) for markers D13S175 (maximum Z [Z_max] å 4.06; maximum recombination frequency [u_max] å 0) and D13S1236 (Z_max å 5.75, u_max å 0). Multipoint analysis gave Z_maxå 6.62 (u_max å 0) at marker D13S175. Haplotype data indicated that CZP probably lies in the centromeric region of chromosome 13, provocatively close to the gene for lens connexin46.     

Three DNA markers for hypophosphataemic rickets

Summary This paper presents three markers, 16D/E, pHMAI (DXS208), and CRI-L1391 (DXS274), that show close linkage for X-linked hypophosphataemic rickets (HYP). DXS274 is closely linked to HYP ( _max= 0.00, Z_max = 4.20), and DXS41 (99.6), ( _max= 0.00, Z_max = 5.20). Marker 16D/E maps distal to the disease locus ( _max= 0.05, Z_max = 3.11). The pHMAI probe recognises the same restriction fragment length polymorphism (RFLP) as 99.6. Multipoint analysis suggests that the most probable order of loci is Xpter-(DXS43, 16D/E)-HYP-DXS274-(DXS208, DXS41)-Xcen. The location of DXS274 distal to HYP cannot be excluded, as no recombinants were observed between DXS274 and HYP, or between DXS274 and DXS41/DXS208. One of the families contains a large number of recombinants, four of which are double recombinants. This most probably means that the disease in this family maps elsewhere on the X chromosome or on an autosome, indicating locus heterogeneity.     

Mapping of the gene for X-chromosomal split-hand/split-foot anomaly to Xq26–q26.1

A large inbred kindred from Pakistan in which an isolated type of split-hand/split-foot anomaly is transmitted as an X-chromosomal trait has previously been described. An X/autosomal translocation and an X-chromosomal rearrangement have been excluded by cytogenetic studies. In order to map the gene responsible for this disorder, linkage analysis has been performed by using 14 highly polymorphic DNA markers distributed over the whole X chromosome. Two-point linkage analysis between the disease locus and X-chromosomal marker loci gives maximal lod scores at = 0.00 with the loci DXS294 (Z _max= 5.13) and HPRT (Z _max= 4.43), respectively, suggesting that the gene for the X-chromosomal split-hand/split-foot anomaly is localized at Xq26–q26.1.     

A Model to Estimate Potential Submersed Aquatic Vegetation Habitat Based on Studies in Lake Pontchartrain, Louisiana

The depth distribution of submersed aquatic vegetation (SAV) was studied in Lake Pontchartrain, Louisiana, to develop a model to predict changes in SAV abundance from changes in environmental quality. We conducted annual line‐intercept surveys from 1997 through 2001 and monitored monthly photosynthetically active radiation at four sites with different shoreface slopes. The following relationships between SAV distribution and environmental factors were used as model parameters: (1) water clarity controls SAV colonization depth; (2) fluctuation in annual mean water level and wave mixing determines SAV minimum colonization depth; and (3) site differences in SAV areal coverage under the comparable water quality conditions are due to shoreface slope differences. These parameters expressed as mathematical components of the model are as follows: mean water clarity determines SAV colonization depth (Z_max= 2.3/K_d); mean water level and wave mixing controls SAV minimum depth (Z_min= 0.3 m); and shoreface slope angle (θ) determines the distance from Z_min to Z_max. The equation developed for the potential SAV habitat (PSAV) model is PSAV = (2.3 ? 0.3 ×K_d)/(sinθ×K_d). The model was validated by comparing empirical values from the dataset to values predicted by the model. Although the model was developed to predict the PSAV in Lake Pontchartrain, it can be applied to other coastal habitats if local SAV light requirements are substituted for Lake Pontchartrain values. This model is a useful tool in selecting potential restoration sites and in predicting the extent of SAV habitat gain after restoration.     

NICOTINE AND α-BUNGAROTOXIN BINDING TO AXONAL AND NON-NEURAL TISSUES1

Abstract— Nicotine binds to homogenates of lobster walking leg nerve (K_d= 1.1 ± 0.3 μm , B_max= 2.4 ± 0.5 nmol/g wet tissue), horseshoe crab leg nerve (K_d= 0.11 ± 0.06 μm , B_max= 1.3 ± 0.6nmol/g), and kidney from 18-month-old rats (K_d= 0.8 ± 0.2 μm , B_max= 23 ± 9 nmol/g). The pharmacological sensitivities of nicotine binding to lobster and horseshoe crab leg nerve homogenates are similar to that of the axonal cholinergic binding macromolecule (ACBM) (Denburg et al., 1972) of lobster leg. nerve membrane, while the binding to rat kidney is sensitive to α-bungarotoxin but not atropine or curare. There was no nicotine binding to rat heart or spleen, or to kidney from younger rats; little or no binding to blue crab nerve or to Torpedo electroplax motor nerve; and little binding (around 0.1 nmol/g) to rat liver. [³H]α-Bungarotoxin bound reversibly (0.17 nmol/g) to lobster leg nerve membrane The implications of these results for the distribution and function of the ACBM, and for the specificity of α-bungarotoxin, are discussed.     

Multipoint linkage analysis in X-linked Alport syndrome

Summary In order to localize the gene for the X-linked form of Alport syndrome (ATS) more precisely, we performed restriction fragment length polymorphism analysis with nine different X-chromosomal DNA markers in 107 members of twelve Danish families segregating for classic ATS or progressive hereditary nephritis without deafness. Two-point linkage analysis confirmed close linkage to the markers DXS17(S21) (Z _max = 4.44 at = 0.04), DXS94(pXG-12) (Z _max=8.07 at =0.04), and DXS101(cX52.5) (Z _max=6.04 at =0.00), and revealed close linkage to two other markers: DXS88(pG3-1) (Z _max =6.36 at =0.00) and DXS11(p22–33) (z _max=3.45 at =0.00). Multipoint linkage analysis has mapped the gene to the region between the markers DXS17 and DXS94, closely linked to DXS101. By taking into account the consensus map and results from other studies, the most probable order of the loci is: DXYS1(pDP34)-DXS3(p19-2)-DXS17-(ATS, DXS101)-DXS94-DXS11-DXS42(p43-15)-DXS51(52A). DXS88 was found to be located between DXS17 and DXS42, but the order in relation to the ATS locus and the other markers used in this study could not be determined.     

Statistical analysis of in situ hybridization data: Derivation and use of the Zmax test

There are many situations in which grain distributions resulting from in situ hybridization of radioactively labeled probes to unique genes should be subjected to a statistical analysis. However, the problems posed by analysis of in situ hybridization data are not straightforward, and no completely satisfying method is currently available. We have developed a procedure in which the major and any number of minor site(s) of hybridization may be specifically located and the significance of each tested. This Z_max procedure first tests the overall distribution for departure from randomness and then identifies significantly overlabeled whole chromosomes (or chromosome arms or other large segments), a process that may be repeated to pinpoint significantly overlabeled regions within these chromosomes. We describe in detail the derivation of the Z_max statistic, present tables of significant Z_max levels, and show with examples how Z_max is used in tests of significance of in situ hybridization data.     

Sex specific chromosome polymorphisms in the common Indian Krait,Bungarus caeruleus Schneider (Ophidia,Elapidae)

Chromosome analyses of common Indian Krait, B. caeuleus from three geographical regions of India have revealed variable diploid numbers of 43, 44 and 45 in different female individuals but a constant diploid number of 44 in the males. C-banding and in situ hybridization studies, using radio labelled W sex chromosome specific satellite DNA as a probe, have shown that C-banding and sex chromosome associated satellite DNA's are exclusively localised in the W chromosome. The W chromosome is involved in reciprocal translocations either with a medium sized macroautosome or with a microchromosome resulting in a multiple sex chromosome constitution of Z₁Z₁Z₂Z₂/Z₁Z₂W type. In some female individuals dissociation of the W has resulted in multiple W chromosomes, W₁ and W₂. These polymorphisms are uniquely confined to the female sex only. A predominance of polymorphic females, involving particularly the translocation of a medium sized macrochromosome, in all three geeographical regions and the restriction of the females having the original chromosome constitution (ZW) to one geographical region suggests that polymorphic individuals have adaptive flexibility and higher fecundity.     

Characterization of the Binding of the GABA Agonist [3H]Piperidine-4-Sulphonic Acid to Bovine Brain Synaptic Membranes

Abstract: The binding of radioactive piperidine-4-sulphonic acid ([³H]P4S) to thoroughly washed, frozen, and thawed membranes isolated from cow and rat brains has been studied. Quantitative computer analysis of the binding curves for four regions of bovine brain revealed the general presence of two binding sites. In these brain regions less satisfactory computer fits were obtained for receptor models showing one or three binding sites or negative cooperativity. With the use of Tris-citrate buffer at 0°C the two affinity classes for P4S in bovine cortex membranes revealed the following binding parameters: K_D= 17 ± 7 nM (B_max= 0.15 ± 0.07 pmol/mg protein) and K_D= 237 ± 100 nM (B_max= 0.80 ± 0.20 pmol/mg protein). Heterogeneity was also observed for association and dissociation rates of [³H]P4S. The slow binding component (k_on= 5.6 × 10⁷ or 8.8 × 10⁷ M^-1 min^-1, k_Off= 0.83 min^-1, and K_D= 14.7 or 9.4 nM, determined by two different methods in phosphate buffer containing potassium chloride) corresponds to the high-affinity component of the equilibrium binding curve (K_D= 11 nM, B_max= 0.12 pmol/mg protein in the same buffer system). The association and dissociation rates for the subpopulation of rapidly dissociating sites, apparently corresponding to the low-affinity sites, were too rapid to be measured accurately. The binding of [³H]P4S appears to involve the same two populations of sites with B_max values similar to those for [³H]GABA binding to the same tissue, although the kinetic parameters for the two ligands are somewhat different. Furthermore, comparative studies on the inhibition of [³H]P4S and [³H]GABA binding by various GABA analogues, strongly suggest that P4S binds to the GABA receptors. The different effects of P4S and GABA on benzodiazepine binding are discussed.     

Genetic Linkage Mapping of the Dehydroepiandrosterone Sulfotransferase (STD) Gene on the Chromosome 19q13.3 Region

In the human liver and adrenal, there is a single hydroxysteroid sulfotransferase, which catalyzes the transformation of dehydroepiandrosterone to dehydroepiandrosterone sulfate, the most abundantly circulating steroid in humans, and also catalyzes the sulfation of a series of other 3β-hydroxysteroids as well as cholesterol. Dehydroepiandrosterone sulfate serves as precursor for the formation of active androgens and estrogens in several peripheral tissues, indicating that hydroxysteroid sulfotransferase plays a pivotal role in controlling the hormonal action of sex steroids by regulating their bioavailability. We recently elucidated the structure of the gene encoding hydroxysteroid sulfotransferase (STD), also designated dehydroepiandrosterone sulfotransferase, which spans 17 kb and contains six exons. The STD gene was preliminarily assigned to chromosome 19 by polymerase chain reaction (PCR) amplification of DNA from a panel of human/rodent somatic cell hybrids. To locate the STD gene, the novel biallelic polymorphism found in intron 2 was genotyped in eight CEPH reference families by direct sequencing of PCR products. Two-point linkage analysis was first performed between the latter polymorphism and chromosome 19 markers from Généthon and NIH/CEPH. The closest linkage was observed with D19S412 (Z_max= 9.23; θ_max0.038) and HRC (Z_max= 5.95; θ_max0.036), located on the 19q13.3 region. A framework map including six Généthon markers flanking the polymorphic STD gene was created by multipoint linkage analysis. Thereafter, a high-resolution genetic map of the region was constructed, yielding to the following order: qter–D19S414–D19S224–D19S420–D19S217–(APOC2–D19S412)–(STD–HRC)– KLK–D19S22–D19S180–PRKCG–D19S418–tel.     

Improved carrier testing for multiple endocrine neoplasia,type 1, using new microsatellite-type DNA markers

Familial multiple endocrine neoplasia, type 1 (FMEN1), is an autosomal dominant trait generated by hyperfunction of various endocrine glands. The gene for MEN1 has been mapped to chromosome 11q13 by genetic linkage and deletion mapping in tumors. Eight Finnish families, including 46 individuals carrying the risk haplotype, have been typed for four polymorphic microsatellite DNA markers spanning the MEN1 chromosomal region. Three of the loci concerned, D11S913, D11S987, and D11S1337, displayed maximum lod scores (Z _max ) 6.70, 9.88, and 2.54, respectively, with no recombinations with the disease gene, whereas a Z _max of 8.43 was obtained for D11S971 at a recombination fraction of 0.03. Our results indicate that the use of this set of markers considerably improves the diagnostic value of genotyping patients at risk of developing MEN1.     

Differential distribution of endothelin peptides and receptors in human adrenal gland

Summary Sub-type selective ligands revealed a differential distribution of endothelin (ET) receptors within human adrenal glands. High densities of ET_A receptors were localized, using [¹²⁵I]-PD151242, to the smooth muscle layer of the arteries, smaller vessels within the capsular plexus and to the secretory cells of zona glomerulosa (K _D=139.8±39.7,B _max=69.7±9.1 fmol mg⁻¹ protein, mean of 3 individuals±sem). ET_B receptors were present in the medulla (K _D=145.2±16.4,B _max=75.5±12.3), zona glomerulosa (K_D=100.6±35.1,B _max=63.1±10.0), fasiculata (K _D 145.1±162.,B _max=67.9±6.9) and reticularis (K_D=118.2±18.6,B _max=71.9±6.5). ET_B receptors were not detected within the smooth muscle of the vasculature. Messenger RNA encoding both sub-types was present in adrenals. ET-like immunoreactivity was localized to the cytoplasm of the endothelial cells from arteries supplying the gland and resistance vessels within the capsular plexus. Staining was also detected in these cells using anti-big ET-1 and less intensely with anti-big ET-2 antisera but not within cells within the cortex or medulla. Big ET-3-like immunoreactivity was localized to secretory cells of the medulla. Staining was not found using antiserum that could detect ET-3, suggesting further processing of big ET-3 may occur within the plasma, and that the cdrenals could be a source of ET-3. The presence of ET-1 was confirmed by high performance liquid chromatography and radioimmunoassay although ET-3 was not detected. The results suggest that ET-1 is the predominant mature isoform, which is localized mainly to adrenal vasculature, particularly the capsular plexus, and may contribute to blood flow regulation in the gland.     

Fissions,fusions, and translocations shaped the karyotype and multiple sex chromosome constitution of the northeast‐Asian wood white butterfly,Leptidea amurensis

Previous studies have shown a dynamic karyotype evolution and the presence of complex sex chromosome systems in three cryptic Leptidea species from the Western Palearctic. To further explore the chromosomal particularities of Leptidea butterflies, we examined the karyotype of an Eastern Palearctic species, Leptidea amurensis. We found a high number of chromosomes that differed between the sexes and slightly varied in females (i.e. 2n = 118–119 in females and 2n = 122 in males). The analysis of female meiotic chromosomes revealed multiple sex chromosomes with three W and six Z chromosomes. The curious sex chromosome constitution [i.e. W_1–3/Z_1–6 (females) and Z_1–6/Z_1–6 (males)] and the observed heterozygotes for a chromosomal fusion are together responsible for the sex‐specific and intraspecific variability in chromosome numbers. However, in contrast to the Western Palearctic Leptidea species, the single chromosomal fusion and static distribution of cytogenetic markers (18S rDNA and H3 histone genes) suggest that the karyotype of L. amurensis is stable. The data obtained for four Leptidea species suggest that the multiple sex chromosome system, although different among species, is a common feature of the genus Leptidea. Furthermore, inter‐ and intraspecific variations in chromosome numbers and the complex meiotic pairing of these multiple sex chromosomes indicate the role of chromosomal fissions, fusions, and translocations in the karyotype evolution of Leptidea butterflies.     

A gene for blepharophimosis-ptosis-epicanthus inversus syndrome maps to chromosome 3q23

Blepharophimosis-ptosis-epicanthus inversus syndrome (BPES) is an autosomal dominant malformation of the eyelids that may severely impair visual function. Chromosomal aberrations involving chromosomes 3q23, 3p25 and 7p34 have been reported in BPES but the disease gene has not been hitherto localized by linkage analysis. We have mapped a gene for BPES to chromosome 3q23 in a large French pedigree (Z _max = 4.62 at =0 for probe AFM 182yc5 at locus D3S1549). The best estimate for the location of the disease gene is at locus D3S1549, between the loci D3S1292 and D3S1555 (maximum lod score of 5.10).     

Growth and phosphate uptake kinetics of the cyanobacterium,Cylindrospermopsis raciborskii (Cyanophyceae) in throughflow cultures

• 1 Cylindrospermopsis raciborskii occupies a rapidly expanding geographical area. Its invasive success challenges eutrophication control in many lakes. To understand better the load‐dependent behaviour of this nitrogen fixing cyanobacterium under in situ conditions, we studied P‐dependent growth of a C. raciborskii strain under continuous and pulsed P supply.
• 2 The Droop model reasonably described P‐dependent growth in the continuously supplied chemostats. Large P pulses, however, caused a delay in growth and cells subject to P pulses grew slower than their counterparts with the same P quota supplied continuously.
• 3 The kinetics of P uptake indicated that C. raciborskii is opportunistic with respect to P. Its high excess P storage capacity after a saturating P pulse (Q_ex=95 µg P [mg C]^‐1) and P‐specific uptake capacity (U_max = V_max/Q_P=150–1200) are indicative of storage adaptation. At the same time, the affinity of the P uptake system (U_max/K = 800–4000) is also high.
• 4 Rate of leakage exceeded that of the steady state net P uptake by one to two orders of magnitude. Growth affinity of C. raciborskii (µ_max/K_µ≈ 20) was relatively low, presumably due to the substantial leakage.
• 5 The dynamics of the particular water body determine which trait contributes most to competitive success of C. raciborskii. In deep lakes with vertical nutrient gradients, the cyanobacterium may rely primarily on its high P storage capacity, which is coupled to a lack of short‐term feedback inhibition and efficient buoyancy regulation. In lakes without such gradients, high P uptake affinity may be vitally important.

     

Analysis of Linkage Between Biochemical and Morphological Markers of Rye Chromosomes 1R, 2R,and 5R and Mutations of Self-Fertility at the Main Incompatibility Loci

In F₂ hybrids between self-sterile plants of the Volkhova cultivar and self-fertile lines with established self-fertility mutations (sf mutations) at the major incompatibility loci S (1R), Z (2R), and T (5R), the effect of sf mutations on the inheritance of secalin-encoding, isozyme, and morphological markers located on the same chromosomes was investigated. Linkage between loci Prx7 and Sand locus Sec3 coding for high-molecular-weight secalins on chromosome 1R was shown for the first time. The frequency of recombination between Prx7andSec3and between S and Sec3was 29.1 ± 4.8% and 30.9 ± 7.0%, respectively. Independent inheritance of locus Z and isozyme markers of chromosome 2R, Est3/5 and -Glu, from locus Sec2 encoding 75-kDa -secalins was shown; in hybrids, the recombination frequency between Est3/5 and locus Z varied from 19.2 ± 8.1 to 50%. Independent inheritance of morphological (Ddw and Hs) and isozyme markers (Est4, Est6/9,and Aco2) of chromosome 5R from locus Tlocated on the same chromosome was demonstrated.     

Differential Effects of the Alkylating Agent N-Ethoxycarbonyl-2-Ethoxy-1,2-Dihydroquinoline on Brain α2-Adrenoceptors and I2-Imidazoline Sites In Vitro and In Vivo

Abstract— The alkylating agent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ) is a peptide-coupling agent that is being used to inactivate irreversibly α₂-adrenoceptors and other receptors. The aim of the present study was to assess the in vitro and in vivo effects of EEDQ on the newly discovered brain l₂-imidazoline sites, located mainly in mitochondria. Preincubation of rat cortical membranes with EEDQ (10^?8-10^?5M) markedly decreased (20–90%) the specific binding of the selective antagonist [³H]R821002 to α₂-adrenoceptors without affecting that of [³H]idazoxan (in the presence of adrenaline) to l₂-imidazoline sites. In EEDQ-pretreated membranes (10^?5M, 30 min at 25°c), the density of l₂-imidazoline sites (B_max= 80 ± 4 fmol/mg of protein) was not different from that determined in untreated membranes in the presence of 10^?6M (-)-adrenaline (B_max= 83 ± 4 fmol/mg of protein), and both densities were lower (24%, p < 0.05) than the total native density of [³H]idazoxan binding sites (B_max= 107 ± 6 fmol/mg of protein) (l₂-imidazoline sites plus a₂-adrenoceptors). Treatment of rats with an optimal dose of EEDQ (1.6 mg/kg, i.p., for 2 h to 30 days) reduced maximally at 6 h (by 95 ± 1%) the specific binding of [³H]-R821002 to α₂-adrenoceptors, but also the binding of [³H]idazoxan to l₂-imidazoline sites (by 44 ± 5%). Pretreatment with yohimbine (10 mg/kg, i.p.) fully protected against EEDQ-induced α₂-adrenoceptor inactivation. In contrast, pretreatment with cirazoline (1 mg/kg, i.p.), did not protect against EEDQ-induced inactivation of l₂-imidazoline sites. Treatment with EEDQ (1.6 mg/kg, i.p., for 6 h) did not alter the density of brain monoamine oxidase-A sites labeled by [³H]Ro 41–1049 or that of monoamine oxidase-B sites labeled by [³H]Ro 19–6327 (lazabemide), two relevant mitochondrial markers. Competition experiments with cirazoline against the specific binding of [³H]idazoxan to l₂-imidazoline sites demonstrated the presence of the expected two affinity states for the drug in EEDQ-pretreated membranes as well as in rats treated with EEDQ. The results indicate that EEDQ in vitro is a useful tool for quantitating l₂-imidazoline sites when using [³H]-imidazoline ligands that also recognize α₂-adrenoceptors. In vivo, however, EEDQ is also able to inactivate partially brain l₂-imidazoline sites probably by an indirect mechanism. Key Words: Brain l₂-imidazoline sites—[³H]-Idazoxan—α₂-Adrenoceptors—[³H] R821002—N -Ethoxycarbonyl-2-ethoxy-li2-dihydroquinoline—Monoamine oxidase-A—[³H]Ro 41–1049—Monoamine oxidase-B—[³H]Ro 19–6327.