No abstract

The expression patterns of 13 GABAA receptor subunit encoding genes (alpha 1-alpha 6, beta 1-beta 3, gamma 1-gamma 3, delta) were determined in adult rat brain by in situ hybridization. Each mRNA displayed a unique distribution, ranging from ubiquitous (alpha 1 mRNA) to narrowly confined (alpha 6 mRNA was present only in cerebellar granule cells). Some neuronal populations coexpressed large numbers of subunit mRNAs, whereas in others only a few GABAA receptor-specific mRNAs were found. Neocortex, hippocampus, and caudate-putamen displayed complex expression patterns, and these areas probably contain a large diversity of GABAA receptors. In many areas, a consistent coexpression was observed for alpha 1 and beta 2 mRNAs, which often colocalized with gamma 2 mRNA. The alpha 1 beta 2 combination was abundant in olfactory bulb, globus pallidus, inferior colliculus, substantia nigra pars reticulata, globus pallidus, zona incerta, subthalamic nucleus, medial septum, and cerebellum. Colocalization was also apparent for the alpha 2 and beta 3 mRNAs, and these predominated in areas such as amygdala and hypothalamus. The alpha 3 mRNA occurred in layers V and VI of neocortex and in the reticular thalamic nucleus. In much of the forebrain, with the exception of hippocampal pyramidal cells, the alpha 4 and delta transcripts appeared to codistribute. In thalamic nuclei, the only abundant GABAA receptor mRNAs were those of alpha 1, alpha 4, beta 2, and delta. In the medial geniculate thalamic nucleus, alpha 1, alpha 4, beta 2, delta, and gamma 3 mRNAs were the principal GABAA receptor transcripts. The alpha 5 and beta 1 mRNAs generally colocalized and may encode predominantly hippocampal forms of the GABAA receptor. These anatomical observations support the hypothesis that alpha 1 beta 2 gamma 2 receptors are responsible for benzodiazepine I (BZ I) binding, whereas receptors containing alpha 2, alpha 3, and alpha 5 contribute to subtypes of the BZ II site. Based on significant mismatches between alpha 4/delta and gamma mRNAs, we suggest that in vivo, the alpha 4 subunit contributes to GABAA receptors that lack BZ modulation.

Earlier and more reliable detection of drug-induced kidney injury would improve clinical care and help to streamline drug-development. As the current standards to monitor renal function, such as blood urea nitrogen (BUN) or serum creatinine (SCr), are late indicators of kidney injury, we conducted ten nonclinical studies to rigorously assess the potential of four previously described nephrotoxicity markers to detect drug-induced kidney and liver injury. Whereas urinary clusterin outperformed BUN and SCr for detecting proximal tubular injury, urinary total protein, cystatin C and beta2-microglobulin showed a better diagnostic performance than BUN and SCr for detecting glomerular injury. Gene and protein expression analysis, in-situ hybridization and immunohistochemistry provide mechanistic evidence to support the use of these four markers for detecting kidney injury to guide regulatory decision making in drug development. The recognition of the qualification of these biomarkers by the EMEA and FDA will significantly enhance renal safety monitoring.

Developmental and regional alternative splicing of the NMDAR1 subunit gene transcript was examined by in situ hybridization in the developing and adult rat brain. NMDAR1 mRNA, barely detectable at embryonic day 14, increased gradually during development until the third postnatal week, after which it declined slightly to adult levels, when it was detected in every examined neuronal type. Each splice form of the primary NMDAR1 gene transcript was found to follow a parallel profile of abundance in the brain, but marked regional differences were observed in splicing at both 5′ and 3′ sequences. The individual regional distributions of splice forms appeared to be established around birth, with little change thereafter, except in the overall abundance. The NMDAR1-a and NMDAR1–2 splice forms occurred extensively and approximately homogeneously throughout brain gray matter. The NMDAR1-b variant was found primarily in the sensorimotor cortex, neonatal lateral caudate, thalamus, hippocampal CA3 field, and cerebellar granule cells, but was absent from adult caudate. The NMDAR1–1 and -4 splice forms were detected in almost complementary patterns; the former was concentrated in more rostral structures such as cortex, caudate, and hippocampus, while the latter was principally in more caudal regions such as thalamus, colliculi, and cerebellum. These two splice forms accounted for a greater proportion of the adult NMDAR1 mRNA than that of the neonate. The NMDAR1–3 mRNA variant was scarce, being detected only at very low levels in postnatal cortex and hippocampus. The different splice forms may generate regional differences in NMDA receptor properties during development and in the adult CNS.

The first formal qualification of safety biomarkers for regulatory decision making marks a milestone in the application of biomarkers to drug development. Following submission of drug toxicity studies and analyses of biomarker performance to the Food and Drug Administration (FDA) and European Medicines Agency (EMEA) by the Predictive Safety Testing Consortium's (PSTC) Nephrotoxicity Working Group, seven renal safety biomarkers have been qualified for limited use in nonclinical and clinical drug development to help guide safety assessments. This was a pilot process, and the experience gained will both facilitate better understanding of how the qualification process will probably evolve and clarify the minimal requirements necessary to evaluate the performance of biomarkers of organ injury within specific contexts.