Evidence that GABAergic neurons in the preoptic area of the rat brain are targets of 2,3,7,8-tetrachlorodibenzo-p-dioxin during development.

Abstract

Developmental exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) interferes with masculinization and defeminization of male sexual behaviors and gonadotropin release patterns. We previously demonstrated that the mRNA encoding the arylhydrocarbon receptor (AhR), a protein that mediates TCDD effects, is found in brain regions that control reproductive functions, most notably in the preoptic area (POA). The pattern of distribution of the AhR gene closely overlaps that of an enzyme necessary for γ-aminobutyric acid (GABA) synthesis, glutamic acid decarboxylase (GAD) 67. To test the hypothesis that GABAergic neurons in the POA are targets of TCDD during development, we used dual-label in situ hybridization histochemistry (ISHH) to colocalize GAD and AhR mRNAs in the region. In addition, we used ISHH to determine the effects of TCDD (1 µg/kg body weight, gestational day 15) on GAD 67 gene expression in POA regions in pups examined on postnatal day 3. We found that virtually all GABAergic neurons in the POA expressed the AhR gene. Furthermore, GAD 67 mRNA levels were higher in females than in males in the rostral POA/anteroventral periventricular nucleus (rPOA/AVPV) and in the rostral portion of the medial preoptic nucleus (MPN). TCDD abolished sex differences in the rPOA/AVPV but had no effect in the rostral MPN. In the caudal MPN, there were no sex differences in GAD 67 gene expression, but TCDD depressed expression specifically in males.

Dual-Phenotype GABA/Glutamate Neurons in Adult Preoptic Area: Sexual Dimorphism and Function

“…To maximize detection of GABAergic cells, we used a mixture of three digoxigenin-labeled cRNA probes for GAD mRNAs as described previously (Hays et al, 2002). The cDNA templates for GAD65 probes corresponded to bases 315-944 and 944 -1769 of the full-length clone (Erlander et al, 1991), and the template for the GAD67 probe to bases 232-767 of the full-length clone (Erlander et al, 1991) (both provided by A. Tobin, University of California-Los Angeles, Los Angeles, CA).…”

“…The cDNA templates for GAD65 probes corresponded to bases 315-944 and 944 -1769 of the full-length clone (Erlander et al, 1991), and the template for the GAD67 probe to bases 232-767 of the full-length clone (Erlander et al, 1991) (both provided by A. Tobin, University of California-Los Angeles, Los Angeles, CA). Digoxigenin-labeled probes for GAD65 and GAD67 mRNA were prepared and used in dual-label ISHH studies as described previously (Hays et al, 2002). Sections were thawed, fixed, and prehybridized before applying a mixture of 35 S-labeled cRNA probes for VGLUT1, VGLUT2, or ER␣ (1 ϫ 10 6 cpm), and 0.5 l each of the digoxigenin-labeled GAD65 (0.5:l each of two probes) and GAD67 (0.5 l) probes in 0.5 l of hybridization buffer.…”

Proteomic pathway analysis of the hippocampus in schizophrenia and bipolar affective disorder implicates 14-3-3 signaling, aryl hydrocarbon receptor signaling, and glucose metabolism: Potential roles in GABAergic interneuron pathology

“…Neuropathologically, rats perinatally exposed to TCDD have decreased numbers of parvalbumin-and calbindin-immunoreactive GABAergic neurons in the hippocampus and other limbic areas (Nguyen et al, 2013b), and a reduction of GAD 67 mRNA expression in the preoptic area (Hays et al, 2002). Again, findings are more prominent in male animals.…”

Molecular interactions of the aryl hydrocarbon receptor and its biological and toxicological relevance for reproduction

“…Interestingly, the GAD 67 gene contains multiple canonical XRE sequences (Erlander et al 1991, Pinal et al 1997. GAD 67 mRNA levels in the rostral POA/anteroventral periventricular nucleus (rPOA/AVPV) and in the rostral portion of the medial preoptic nucleus (MPN) are higher in females than in males (Hays et al 2002). GABAergic neurons in the AVPV play a role in onset of puberty, the E2-dependent gonadotropin surge and in ovulation.…”