Schizophrenia: do all roads lead to dopamine or is this where they start? Evidence from two epidemiologically informed developmental rodent models

The idea that there is some sort of abnormality in dopamine (DA) signalling is one of the more enduring hypotheses in schizophrenia research. Opinion leaders have published recent perspectives on the aetiology of this disorder with provocative titles such as ‘Risk factors for schizophrenia—all roads lead to dopamine' or ‘The dopamine hypothesis of schizophrenia—the final common pathway'. Perhaps, the other most enduring idea about schizophrenia is that it is a neurodevelopmental disorder. Those of us that model schizophrenia developmental risk-factor epidemiology in animals in an attempt to understand how this may translate to abnormal brain function have consistently shown that as adults these animals display behavioural, cognitive and pharmacological abnormalities consistent with aberrant DA signalling. The burning question remains how can in utero exposure to specific (environmental) insults induce persistent abnormalities in DA signalling in the adult? In this review, we summarize convergent evidence from two well-described developmental animal models, namely maternal immune activation and developmental vitamin D deficiency that begin to address this question. The adult offspring resulting from these two models consistently reveal locomotor abnormalities in response to DA-releasing or -blocking drugs. Additionally, as adults these animals have DA-related attentional and/or sensorimotor gating deficits. These findings are consistent with many other developmental animal models. However, the authors of this perspective have recently refocused their attention on very early aspects of DA ontogeny and describe reductions in genes that induce or specify dopaminergic phenotype in the embryonic brain and early changes in DA turnover suggesting that the origins of these behavioural abnormalities in adults may be traced to early alterations in DA ontogeny. Whether the convergent findings from these two models can be extended to other developmental animal models for this disease is at present unknown as such early brain alterations are rarely examined. Although it is premature to conclude that such mechanisms could be operating in other developmental animal models for schizophrenia, our convergent data have led us to propose that rather than all roads leading to DA, perhaps, this may be where they start

Similarity Between Rat Brain Nicotinic α-Bungarotoxin Receptors And Stably Expressed α-Bungarotoxin Binding Sites

The present results demonstrate stable expression of α-bungarotoxin (α- BGT) binding sites by cells of the GH4C1 rat pituitary clonal line. Wild- type GH4C1 cells do not express α-BGT binding sites, nor do they contain detectable mRNA for nicotinic receptor α2, α3, α4, α5, α7, β2, or β3 subunits. However, GH4C1 cells stably transfected with rat nicotinic receptor α7 cDNA (α7/GH4C1 cells) express the transgene abundantly as mRNA, and northern analysis showed that the message is of the predicted size. The α7/GH4C1 cells also express saturable, high-affinity binding sites for 125I-labeled α-BGT, with a K(D) of 0.4 nM and B(max) of 3.2 fmol/106 intact cells. 125I-α-BGT binding affinities and pharmacological profiles are not significantly different for sites in membranes prepared either from rat brain or α7/GH4C1 cells. Furthermore, K(D) and K(i) values for 125I-α-BGT binding sites on intact α7/GH4C1 cells are essentially similar to those for hippocampal neurons in culture. Sucrose density gradient analysis showed that the size of the α-BGT binding sites expressed in α7/GH4C1 cells was similar to that of the native brain α-BGT receptor. Chronic exposure of α7/GH4C1 cells in culture to nicotine or an elevated extracellular potassium concentration induces changes in the number of α- BGT binding sites comparable to those observed in cultured neurons. Collectively, the present results show that the properties of α-BGT binding sites in transfected α7/GH4C1 cells resemble those for brain nicotinic α- BGT receptors. If the heterologously expressed α-BGT binding sites in the present study are composed solely of α7 subunits, the results could suggest that the rat brain α-BGT receptor has a similar homooligomeric structure. Alternatively, if α-BGT binding sites exist as heterooligomers of α7 plus some other previously identified or novel subunit(s), the data would indicate that the α7 subunits play a major role in determining properties of the α- BGT receptor

A 5€²-Flanking Region Of The Bovine Tyrosine Hydroxylase Gene Is Involved In Cell-Specific Expression Activation Of Gene Transcription By Phorbol Ester And Transactivation By C-Fos And C-Jun

Tyrosine hydroxylase (TH) is expressed specifically in catecholaminergic cells and is transcriptionally activated via a protein kinase C (PKC)-dependent pathway. To identify regulatory regions of the TH gene, transfected neural crest-derived catecholaminergic cells [human neuroblastoma SH-SY5Y and bovine adrenal medullary (BAM) cells] or glia-derived SF-763 cells were used to analyze expression of a chloramphenicol acetyltransferase (CAT) reporter gene under the control of 5′-flanking sequences of the bovine TH gene. Plasmid pTH(-245/+21)CAT was constructed by fusing the -245 to +21 region of the TH gene to CAT sequences in the promoterless pCAT basic plasmid. Cells transfected with pTH(-245/+21)CAT expressed CAT activity at levels 8- to 100-fold higher than those of cells transfected with pCAT basic. In SH-SY5Y or BAM cells, pTH(-245/+21)CAT supported the expression of CAT at levels similar to or higher than that supported by the tissue nonspecific viral SV40 promoter/enhancer. In glia-like cells, CAT expression from pTH(-245/+2 1)CAT was about 13-fold lower than that under the control of the SV40 promoter. Incubation of neuroblastoma cells with the active phorbol ester, phorbol 12-myristate 13-acetate (PMA), increased expression of CAT from pTH(-245/+2 1)CAT over 6-fold and was accompanied by induction of c-fos and c-jun mRNAs and proteins. The regulation of TH promoter function by c-Fos/c-Jun was corroborated by transactivation of the TH promoter in SH-SY5Y cells engineered to overexpress exogenous c-Fos and c-Jun. TH gene sequences essential for c-Fos/c-Jun transactivation were located in the -245 to -52 region, upstream from a CRE-like element. Gel mobility assays demonstrated binding of c-Fos-antigen(s) to the region of the TH promoter that supports activation by PMA and c-Fos/c-Jun. Temporal patterns of nicotinic agonist-stimulated induction of c-fos and TH mRNA are also consistent with a role for c-Fos in TH gene transcription. Our results demonstrate that the 5′-flanking region of the bovine TH gene operates as an authentic promoter capable (i) of directing cell-specific expression of a bacterial CAT gene and (ii) of conferring responsivity to PKC-stimulation. The results also suggest that the nuclear proteins c-Fos and c-Jun contribute to PKC pathway-mediated activation of the TH gene via direct interaction with the TH gene promoter. The activation of TH gene expression by PKC/c-Fos/c-Jun may serve as an additional or alternative mechanism to activation by the cAMP-CRE pathway. © 1992

Chromosomal localization of the human osteocalcin gene

The human osteocalcin gene was assigned to chromosome 1 by Southern blot analysis of DNAs from a panel of mouse-human somatic cell hybrids with limited numbers of human chromosomes and the complete complement of murine chromosomes. By Southern blot analysis of DNAs from mouse-human hybrids that retain specific segments of human chromosome 1, we have determined that the locus of the human osteocalcin gene is on the long arm of chromosome 1, distal (telomeric) to the -spectrin gene. Osteocalcin is a bone specific protein and it is note worthy that another osteoblast product, the bone/liver/placental alkaline phosphatase gene has also been mapped to chromosome 1

Osteocalcin: characterization and regulated expression of the rat gene

An osteocalcin gene was isolated from a rat genomic DNA library, and sequence analysis indicated that the mRNA is represented in 953 nucleotide segment of DNA consisting of 4 exons and 3 introns. Although the introns in the rat gene are larger, its overall organization is similar to the human gene. Analysis of the 5\u27 flanking sequences of the rat gene shows a modular organization of the promotor as reflected by the the presence of at least 3 classes of regulatory elements. These include (1) typical sequences associated with most genes transcribed by RNA polymerase II (e.g. TATA, CAAT, AP1, AP2), (2) a series of consensus sequences for cyclic nucleotide responsive elements and several hormone receptor binding-sites (estrogen, thyroid and clusters of AG-rich putative Vitamin D responsive elements); and (3) a 24 nucleotide highly conserved sequence between the rat and human gene having a CAAT motif as a central element, designated as an osteocalcin box. Two regulatory factors of osteocalcin gene expression have been identified. First, contained within the 600 nucleotides immediately upstream from the transcription initiation site are sequences which support Vitamin D dependent transcription of the rat osteocalcin gene. 1,25(OH)2D3 increases osteocalcin mRNA by 6-20 fold increases. In contrast, up to a 200 fold increase in osteocalcin gene expression occurs with mineralization of the extracellular matrix produced by osteoblasts. We propose osteocalcin is a bone-specific marker protein of the mature osteoblast in a mineralizing matrix