Catecholaminergic neurons are affected in several neurological and psychiatric diseases. Tyrosine hydroxylase (TH) is the first, rate-limiting enzyme in catecholamine synthesis. We report a knockin mouse expressing Cre-recombinase from the 3'-untranslated region of the endogenous Th gene by means of an internal ribosomal entry sequence (IRES). The resulting Cre expression matches the normal pattern of TH expression, while the pattern and level of TH are not altered in the knockin mouse. Crossings with two different LacZ reporter mice demonstrated Cre-mediated genomic recombination in TH expressing tissues. In addition, LacZ was found in some unexpected cell populations (including oocytes), indicating recombination due to transient developmental TH expression. Our novel knockin mouse can be used for generation of tissue-specific or general knockouts (depending on scheme of crossing) in mice carrying genes flanked by loxP sites. This knockin mouse can also be used for tracing cell lineages expressing TH during development.

Cerebral gene expressions change in response to traumatic brain injury (TBI), and future trauma treatment may improve with increased knowledge about these regulations. We subjected C57BL/6J mice to injury by controlled cortical impact (CCI). At various time points post-injury, mRNA from neocortex and hippocampus was isolated, and transcriptional alterations studied using quantitative real-time polymerase chain reaction (PCR) and gene array analysis. Spatial distribution of enhanced expression was characterized by in situ hybridization. Products of the upregulated transcripts serve functions in a range of cellular mechanisms, including stress, inflammation and immune responses, and tissue remodeling. We also identified increased transcript levels characterizing reactive astrocytes, oligodendrocytes, and microglia, and furthermore, we demonstrated a novel pattern of scattered cell clusters expressing the chemokine Cxcl10. Notably, a sustained increase in integrin alpha X (Itgax), characterizing antigen-presenting dendritic cells, was found with the transcript located to similar cell clusters. In contrast, T-cell receptor alpha transcript showed only a modest increase. The induced P-selectin (Selp) expression level in endothelial cells, and chemokines from microglia, may guide perivascular accumulation of extravasating inflammatory monocytes differentiating into dendritic cells. In conclusion, our study shows that following TBI, secondary injury chiefly involves inflammatory processes and chemokine signaling, which comprise putative targets for pharmaceutical neuroprotection.

This article briefly summarizes, within the context of a brief review of the relevant literature, the outcome of our recent rat microdialysis studies on (1) the relative importance of serotonin (5-HT)1A versus 5-HT1B autoreceptors in the mechanism of action of 5-HT reuptake blocking agents, including putative regional differences in this regard, and (2) autoreceptor responsiveness following chronic SSRI administration. First, our data are consistent with the primacy of 5-HT1A autoreceptors in restraining the elevation of 5-HT levels induced by SSRIs, whereas nerve terminal 5-HT1B autoreceptors appear to have an accessory role in this regard. Second, there is an important interplay between cell body and nerve terminal 5-HT autoreceptors, and recent findings suggest that this interplay may potentially be exploited to obtain regionally preferential effects on 5-HT neurotransmission in the central nervous system, even upon systemic drug administration. In particular, emerging data suggest that somatodendritic 5-HT1A autoreceptor- and nerve terminal 5-HT1B autoreceptor-mediated feedback may be relatively more important in the control of 5-HT output in dorsal raphe-frontal cortex and median raphe-dorsal hippocampus systems, respectively. Third, 5-HT autoreceptors evidently retain the capability to limit the 5-HT transmission-promoting effect of SSRIs after chronic treatment. Thus, although the responsiveness of these sites is probably somewhat reduced, residual autoreceptor capacity still remains an effective restraint on large increases in extracellular 5-HT, even after prolonged treatment. If a further increase in extracellular 5-HT is crucial to the remission of depression in patients responding only partially to prolonged administration of antidepressants, then sustained adjunctive treatment with autoreceptor-blocking drugs may consequently prove useful in the long term.

Transforming growth factors-beta (TGF-betas), activins, and bone morphogenetic proteins (BMPs) comprise an evolutionarily well-conserved group of proteins controlling a number of cell differentiation, cell growth, and morphogentic processes during development. The superfamily of TGFbeta-related genes include over 25 members in mammals several of which are expressed in the growing nervous system and serve important functions in regionalizing the early CNS. Cultured nerve cells show different responses to these factors. Recent developments have revealed that TGFbetas, activins, and BMPs selectively signal to the responding cells via different hetero-oligomeric complexes of type I and type II serine/threonine kinase receptors. The adult brain exhibits specific expression patterns of some of these receptors suggesting neuronal functions not only during development but also in the mature brain. In particular, the brain is expressing high levels of bone morphogenetic protein receptor type II (BMPR-II), activin receptor type I (ActR-I), and activin receptor type IIA (ActR-II). This indicates that osteogenic protein-1 (OP-1/BMP-7), BMP-2, and BMP-4 as well as activins may serve functions for brain neurons. Expression of the receptors partially overlaps in populations of neurons and has been shown to be regulated by brain lesions. This suggests that brain neurons may use receptors BMPR-II and ActR-I to sense the presence of BMPs. This may form a system parallel to the neurotrophin Trk tyrosine kinase receptors regulating neuroplasticity and brain repair. The presence of BMPs in brain is not well studied, but preliminary in situ data indicate that the BMP relatives growth/differentiation factor (GDF)-1 and GDF-10 are distinctly but differentially expressed at high levels in neurons expressing BMPR-II and ActR-I. The receptors mediating responses to these two GDFs remain, however, to be defined. Finally, recent data show that the signal from the activated type I serine/threonine kinase receptor is directly transduced to the nucleus by Smad proteins that become incorporated into transcriptional complexes. Preliminary in situ hybridization observations demonstrate the existence of different Smad mRNAs. It is concluded that BMPs and their signaling systems may comprise a novel pathway for control of neural activity and offer means for pharmacological interventions rescuing brain neurons.

The expression patterns of serine/threonine kinase receptors in the central nervous system of the developing and adult rat were studied by in situ hybridization. The recently cloned bone morphogenetic factor receptor type II (BMPR-II) was compared with the ActR-II and several type I receptors including ActR-I, ActR-IB, BMPR-IA, BMPR-IB and TbetaR-I. We found that these receptors are spatially and temporally regulated. As early as embryonic day 11 (E11), BMPR-II mRNA was expressed in the neuroepithelium in brain and spinal cord. At E15, the expression of ActR-II mRNA was stronger than that of BMPR-II in the spinal cord, followed in intensity by the expression of ActR-I, ActR-IB, BMPR-IA, BMPR-IB and TbetaR-I mRNA. The BMP type I receptors were expressed only in the ependymal epithelium and in the sympathetic ganglia at E15. Many of the examined receptor mRNAs were expressed at peak levels in the brain around birth. In the adult brain, mRNA for BMPR-II was expressed in different patterns together with ActR-II and ActR-I. Thus, BMPR-II mRNA was found in neurons of the cortex, dentate gyrus, hippocampus, habenula and substantia nigra. ActR-II, ActR-I, ActR-IB and, weakly, TbetaR-I were all expressed in the dentate gyrus. In contrast mRNA for BMPR-IA and BMPR-IB was not found in the adult brain. It is suggested that the expressed receptors may mediate actions of members of the TGFbeta superfamily, e.g. BMPs, controlling the development and plasticity in the nervous system.