Hypoexpression of benzodiazepine receptors in the amygdala of neophobic BALB/c mice compared to C57BL/6 mice

The distribution of benzodiazepine receptors in the brain of neophobic BALB/c mice was studied by autoradiographic analysis using [3H]-diazepam and compared to that of the same receptors of the "nonemotional" C57BL/6 mice. This technique revealed no significant interstrain difference except for a lower density of diazepam binding sites in the amygdala of BALB/c mice. Therefore, the expression of benzodiazepine receptors in the amygdala of the two strains of mice were quantified by binding studies on brain membranes. The amygdala of BALB/c mice exhibited a fivefold decrease in the density of benzodiazepine receptors compared to C57BL/6 mice. These results suggest that the trait anxiety (neophobia) that characterizes BALB/c mice could be due, at least in part, to a genetic modulation of benzodiazepine receptor expression in the amygdala, a structure known to be strongly involved in fear behavior.

Sulpiride, but not haloperidol, up-regulates gamma-hydroxybutyrate receptors in vivo and in cultured cells

Five days of gamma-hydroxybutyrate (GHB) administration (3 x 500 mg kg(-1) day(-1) i.p.) to rats resulted in a significant decrease in the density of GHB receptors measured in the whole rat brain without modification of their corresponding affinity. Similar administration of (-)-sulpiride (2 X 100 mg kg(-1) day(-1) i.p. for 5 days) induces an up-regulation of GHB receptors without change in their dissociation constants (Kd). Haloperidol (2 X 2 mg day(-1) i.p. for 5 days) showed no effect. Administered chronically via osmotic minipumps directly into the lateral ventricles, (-)-sulpiride (60 microg day(-1) for 7 days) and GHB (600 microg day(-1) for 7 days) up-regulated and down-regulated rat brain GHB receptors, respectively. Finally, in a mouse hybridoma cell line (NCB-20 cells) expressing GHB receptors, the treatment of these cells with 1 mM GHB, 100 microM (-)-sulpiride or 1 mM GABA decreases, increases and induces no change, respectively, in the density of GHB receptors after 3 days of treatments. These results indicate that chronic GHB treatment modifies the expression of its receptor and that sulpiride also induces plastic changes in GHB receptors perhaps via antagonistic properties.

gamma-Hydroxybutyrate conversion into GABA induces displacement of GABAB binding that is blocked by valproate and ethosuximide

gamma-Hydroxybutyrate (GHB) has been reported to be a ligand for GABAB receptor(s), although with low or very low affinity (IC50 = 150-796 microM). In addition, several reports argue for a role of GHB via GABAB receptors in both in vivo and in vitro electro-physiological experiments. In the present study, we demonstrate that the inhibition of GHB's conversion into GABA by rat brain membranes blocks the ability of GHB to interfere with GABAB binding. In particular, the inhibition of GHB dehydrogenase by valproate or ethosuximide and the blockade of GABA-T by aminooxyacetic acid induce the disappearance of the GABA-like effect of GHB at GABAB, but also at GABAA, receptors. This finding could explain the misinterpretation of in vitro or in vivo experiments where GHB possesses a GABA-like effect. But in addition, it is postulated that the normal metabolism of GHB in brain induces GABAB mechanisms that could be blocked by the administration of valproate or ethosuximide.

gamma-Hydroxybutyrate receptor binding in rat brain is inhibited by guanyl nucleotides and pertussis toxin

gamma-Hydroxybutyrate is an endogenous substance of mammalian brain which is primarily derived from GABA. This compound exhibits neuromodulatory influences on dopamine and serotonin synthesis and release in rat brain. These effects are mediated by specific brain receptors which are mainly distributed in the hippocampus, cortex and striatum. In order to characterize this type of receptor, we have studied the possibility that guanosine triphosphate (GTP) and/or pertussis toxin mediated modification of the affinity for gamma-hydroxybutyrate binding to the receptor. Results presented in this paper favor the presence of guanine nucleotide binding proteins (G0 or Gi family), which are coupled to the gamma-hydroxybutyrate receptor, modifying the high-affinity gamma-hydroxybutyrate binding. We conclude that the gamma-hydroxybutyrate receptor in brain belongs to the G-protein family of receptors.

Displacement of [3H] gamma-hydroxybutyrate binding by benzamide neuroleptics and prochlorperazine but not by other antipsychotics

Since gamma-hydroxybutyrate receptor agonists exhibit dopaminergic regulatory properties and neuroleptic-like effects in neuropharmacological tests, the common neuroleptics were tested for [3H] gamma-hydroxybutyrate binding activity on rat brain membranes. (-)-Sulpiride, sultopride, amisulpride and prochlorperazine possess affinity for the gamma-hydroxybutyrate site(s), consistent with their therapeutic dosage. This study has revealed that gamma-hydroxybutyrate receptors represent an additional target for antipsychotics.

Deletion of the pseudoautosomal region and lack of sex-chromosome pairing at pachytene in two infertile men carrying an X;Y translocation

Two males with a 46,Y,der(X),t(X;Y)(p22.3;q11) complement were referred independently for evaluation of sterility with azoospermia. Both patients exhibited minimal symptomatology, characterized only by psychological disturbances. Study of X-chromosome breakpoints with pseudoautosomal probes 68B (DXYZ2 elements), 113D (locus DXYS15), and 19B (locus MIC2) indicated in both patients that at least 97% of the X pseudoautosomal sequences are lost. Hybridization with Xp22.3-specific probes DXS283, DXS284, and DXS31 shows that these loci are retained on the rearranged chromosome. Thus, the X-chromosome breakpoints are located close to the proximal boundary of the pseudoautosomal region, between MIC2 and DXS284.

Analysis of synaptonemal complexes in two fertile heterozygous boars, both carriers of a reciprocal translocation involving an acrocentric chromosome

An electron microscopic study of synaptonemal complexes in two heterozygous fertile boars, one a carrier of a 4;14 reciprocal translocation and the second a carrier of this translocation associated with a 3;7 reciprocal translocation, is reported. The results showed heterologous pairing in almost all quadrivalents, as well as a lack of XY-quadrivalent association. This seemed to be a common feature of translocations in pigs, even if at least one acrocentric chromosome is involved, and may represent a significant meiotic mechanism that prevents spermatocyte loss, while the production of genetically unbalanced gametes leads to loss of progeny through abortion.

Synaptonemal complex study in some species of Gerbillidae without heterochromatin interposition

Synaptonemal complexes were studied in Gerbillus campestris, Meriones libycus, M. shawi, M. crassus, and in two hybrids M. shawi x M. libycus (Gerbillidae, Rodentia). In both the pure species and hybrids, there was no pairing of X and Y chromosomes, as was previously observed in Psammomys obesus and other Gerbillidae species with gonosome-autosome translocations. A pair of autosomes was also located in proximity to the sex chromosomes in pachytene and showed unusual meiotic behavior with no, incomplete, or much delayed pairing. This chromosome pair, composed of late replicating heterochromatin, exists in most Gerbillidae species and is constant in number, but variable in size across the species. Both meiotic and mitotic characteristics indicate that this pair may correspond to a new type of chromosome which is different from B chromosomes. We do not know if there is a relationship between the presence of this chromosome and the unusual behavior of the sex chromosomes. In Gerbillidae species, the lack of pairing of both sex and heterochromatic chromosomes obviously does not prevent their correct meiotic segregation.

Robertsonian heterozygosity and male sterility

Meiotic and synaptonemal complex studies using electron microscopy were carried out on infertile man with a 13/14 translocation. Synaptonemal complex analysis showed a typical trivalent with incomplete pairing of the acrocentric elements. The sterilizing effect caused by the failure of synapsis is discussed. This pairing failure has a diagnostic value and a poor prognosis.

Heterosynapsis in a heterozygous fertile boar carrier of a 3;7 translocation

Silver-stained synaptonemal complexes (SCs) in surface-spread pachytene nuclei from a boar, heterozygous for a reciprocal translocation, were analysed by electron microscopy. In such heterozygotes, cross-shaped quadrivalent configurations are expected to form in order to maximize homologous pairing. Contrary to the classical, expected cross-shaped configuration, heterosynapsis was often observed, with asymmetrical association in the lateral elements of the non-homologous partners of the quadrivalents. This heterosynapsis is assumed to be a mechanism preventing spermatocyte loss, but inducing a secondary segregational type of impairment of fertility due to foetal wastage leading to reduced prolificacy.

Synaptonemal complexes in a subfertile man with a pericentric inversion in chromosome 21. Heterosynapsis without previous homosynapsis

Analysis of surface-spread synaptonemal complexes of zygotene and pachytene spermatocytes was carried out on a human male carrier of a pericentric inversion of chromosome 21 ascertained after four miscarriages. The synaptic behavior of the bivalent, which could be unambiguously identified by its nonaligned kinetochores, was analyzed. All zygotene and pachytene spermatocytes had 22 linearly paired autosomal bivalents, with apparently normal synaptonemal complexes, and no evidence of a loop configuration in the 50 cells analyzed. According to the XY type (classification of Solari), the cells were distributed across zygotene and pachytene stages, not exclusively in the late pachytene to which adjustment is conventionally thought to be confined. It is suggested that inverted segments heterosynapse at early pachytene, without previous homosynapsis. It is expected that this meiotic process leads to failure of crossing-over, reduces the production of unbalanced gametes, and the risk of recombinant offspring, but can increase the incidence of aneuploidy as a result of nondisjunction during meiosis I (a frequent cause of pregnancy wastage).

Reproductive failure and pericentric inversion in man

Pachytene analysis was carried out on an infertile man heterozygous for a pericentric inversion of chromosome 6. The synaptic behavior of the bivalent 6 inversion was analyzed using electron microscopy in silver stained surface microspread of the inversion-bearing spermatocytes. Possible mechanisms of the sterilizing effect caused by the autosomal inversion are discussed.

Synapsis and synaptic adjustment in an infertile human male heterozygous for a pericentric inversion in chromosome 1

Synapsis and "synaptic adjustment" were analyzed, using electron microscopy in silver stained surface microspreads of inversion-bearing spermatocytes, in an infertile human male with an inherited pericentric inversion in chromosome 1. Possible reasons for his infertility are discussed.

Meiotic association between the XY chromosomes and the autosomal quadrivalent of a reciprocal translocation in two infertile men, 46,XY,t(19;22) and 46,XY,t(17;21)

An electron microscopy study of synaptonemal complexes in two men carrying reciprocal translocations, a t(19;22) and a t(17;21), is reported. It is shown that a delay in synapsis affects the segments corresponding to the short arms of the acrocentrics involved in the formation of quadrivalents. This appears to provoke an interaction with the sex bivalent which could lead to a failure of spermatogenesis. A study of the literature comparing reciprocal translocations that do and do not involve acrocentrics in sterile and fertile men shows the existence of a significant association between the presence of an acrocentric in the rearrangement and sterility. These results on reciprocal translocations involving at least one acrocentric chromosome correspond to those obtained in cases of Robertsonian translocations.

Synaptonemal complexes in Gerbillidae: probable role of intercalated heterochromatin in gonosome-autosome translocations

A study of sex chromosomes and synaptonemal complexes in male specimens of Gerbillus chiesmani, G. nigeriae, G. hoogstrali, and Taterillus pygargus is reported. In each of these Gerbillidae species there are two or three translocations of autosomes with X and Y chromosomes. Analysis of mitotic chromosomes consistently shows the presence of constitutive heterochromatin on the der t(X;autosome) at the X-autosome junction and on the der t(Y;autosome). Analysis of the synaptonemal complexes shows the existence of an unusual structure, lightly stained, at the X-autosome junction and at the Y-autosome junction, which is probably heterochromatic in nature, thus corresponding to the mitotic patterns. This heterochromatin separates the autosomal and gonosomal segments, which behave independently and normally. By analogy with findings from humans and other mammals, a general hypothesis is proposed on the role of intercalated heterochromatin between translocated gonosomes and autosomes. This hypothesis explains why the pathological consequences of these translocations may be very different in males and females. The role of intercalated heterochromatin would be to avoid the pathological consequences of gonosome-autosome translocations resulting from inactivation of the sex chromosomes in female somatic cells and male germinal cells.

Cytogenetic study of complex hybrids in the genus Lemur (Primates Prosimians)

A cytogenetic study was carried out of several Lemur hybrids and their progeny. The effects of Robertsonian translocations in the heterozygous state on fertility and the possibility of a preferential transmission of metacentric trivalents are debated.

Spermatogenesis in several intra- and interspecific hybrids of the lemur (Lemur)

Spermatogenesis of various hybrids of the genus Lemur was studied by testicular biopsy. In hybrids between species whose classification is still much debated, the germinal cells had degenerated after the pachytene stage. This abnormality was variable in intensity depending on the parents mating: L. fulvus (2N = 60) subspecies x L. macaco sometimes resulted in fertile offspring while L. fulvus collaris x L. macaco never did. We believe that the defect in spermatogenesis is mostly caused by differences in meiotic behaviour in the germinal cells. In hybrids between two species for which there is not taxonomic doubt (L. fulvus x L. rubriventer), the gonads were completely devoid of germ cells.