Activated somatostatin type 2 receptors traffic in vivo in central neurons from dendrites to the trans Golgi before recycling.

Understanding the trafficking of G-protein-coupled receptors (GPCRs) is of particular importance, especially when modifications of the neurochemic environment occur as in pathological or therapeutic circumstances. In the central nervous system, although some GPCRs were reported to internalize in vivo, little is known about their trafficking downstream of the endocytic event. To address this issue, distribution and expression pattern of the major somatostatin receptor subtype, the somatostatin type 2 (sst2), was monitored in the hippocampus using immunofluorescence, autoradiographic and immunogold experiments from 10 minutes to 7 days after in vivo injection of the receptor agonist octreotide. We then analyzed whether postendocytic trafficking of the receptor was dependent upon integrity of the microtubule network using colchicine-injected animals. Together, our results suggest that upon agonist stimulation, dendritic receptors are retrogradely transported through a microtubule-dependent mechanism to a trans Golgi domain enriched in the t-SNARE syntaxin 6 and trans Golgi network 38 proteins, before recycling. Because we show that the exit rate from the trans Golgi apparatus back to the plasma membrane (hours) is slower than the entry rate (minutes), the neuronal postendocytic trafficking of sst2 receptor is likely to have functional consequences in several neurological diseases in which an increase in somatostatin release occurs.

Expression of the cystathionine beta synthase (CBS) gene during mouse development and immunolocalization in adult brain.

Hyperhomocysteinemia, caused by a lack of cystathionine beta synthase (CBS), leads to elevated plasma concentrations of homocysteine. This is a common risk factor for atherosclerosis, stroke, and possibly neurodegenerative diseases. However, the mechanisms that link hyperhomocysteinemia due to CBS deficiency to these diseases are still unknown. Early biochemical studies describe developmental and adult patterns of transsulfuration and CBS expression in a variety of species. However, there is incomplete knowledge about the regional and cellular expression pattern of CBS, notably in the brain. To complete the previous data, we used in situ hybridization and Northern blotting to characterize the spatial and temporal patterns of Cbs gene expression during mouse development. In the early stages of development, the Cbs gene was expressed only in the liver and in the skeletal, cardiac, and nervous systems. The expression declined in the nervous system in the late embryonic stages, whereas it increased in the brain after birth, peaking during cerebellar development. In the adult brain, expression was strongest in the Purkinje cell layer and in the hippocampus. Immunohistochemical analyses showed that the CBS protein was localized in most areas of the brain but predominantly in the cell bodies and neuronal processes of Purkinje cells and Ammon's horn neurons.