Transient expression of somatostatin receptors in the brain during development

Gi/o-Protein Coupled Receptors in the Aging Brain

Cells translate extracellular signals to regulate processes such as differentiation, metabolism and proliferation, via transmembranar receptors. G protein-coupled receptors (GPCRs) belong to the largest family of transmembrane receptors, with over 800 members in the human species. Given the variety of key physiological functions regulated by GPCRs, these are main targets of existing drugs. During normal aging, alterations in the expression and activity of GPCRs have been observed. The central nervous system (CNS) is particularly affected by these alterations, which results in decreased brain functions, impaired neuroregeneration, and increased vulnerability to neuropathologies, such as Alzheimer's and Parkinson diseases. GPCRs signal via heterotrimeric G proteins, such as G_o, the most abundant heterotrimeric G protein in CNS. We here review age-induced effects of GPCR signaling via the G_i/o subfamily at the CNS. During the aging process, a reduction in protein density is observed for almost half of the G_i/o-coupled GPCRs, particularly in age-vulnerable regions such as the frontal cortex, hippocampus, substantia nigra and striatum. G_i/o levels also tend to decrease with aging, particularly in regions such as the frontal cortex. Alterations in the expression and activity of GPCRs and coupled G proteins result from altered proteostasis, peroxidation of membranar lipids and age-associated neuronal degeneration and death, and have impact on aging hallmarks and age-related neuropathologies. Further, due to oligomerization of GPCRs at the membrane and their cooperative signaling, down-regulation of a specific G_i/o-coupled GPCR may affect signaling and drug targeting of other types/subtypes of GPCRs with which it dimerizes. G_i/o-coupled GPCRs receptorsomes are thus the focus of more effective therapeutic drugs aiming to prevent or revert the decline in brain functions and increased risk of neuropathologies at advanced ages.

Gene regulation of somatostatin receptors in rats

Using the rat as a model, the present article summarises the spatial, temporal and hormonal regulation of the somatostatin receptor subtypes and their mRNAs in brain and periphery and attempts to provide a molecular basis for somatostatin receptor gene regulation by the structural and functional analyses of their promoters.

des-AA-1,2,5[D-Trp8, IAmp9]somatostatin-14 allows the identification of native rat somatostatin sst1 receptor subtype

Somatostatin exerts multiple activities by interacting with at least five different receptor subtypes (sst[1-5]). The affinity of des-AA(1,2,5)-[D-Trp8, IAmp9]somatostatin-14 (CH-275) was studied by competition experiments using the non-selective radioligand [125I][Leu8, D-Trp22, Tyr25]somatostatin-28 in areas of the rat brain and pituitary known to express identified receptor subtypes. In the cerebellar nuclei and cerebral cortex, which possess the somatostatin sst1 receptor subtype, CH-275 exhibited a moderate affinity (IC50: 10-50 nM). Conversely, in the hippocampus, immature cerebellum and pituitary which contain different subsets of receptors mRNAs (sst[2-5]), the IC50 values were > 1 microM. These data indicate that CH-275 is an appropriate ligand for the identification of native rat somatostatin sst1 receptor subtype.

Influence of the neuropeptide somatostatin on the development of dendritic morphology: a cysteamine-depletion study in the rat auditory brainstem

We investigated the functional role of somatostatin during early ontogeny of the brain, when the neuropeptide as well as its receptors are heavily expressed in the auditory brainstem. Rat pups received a daily injection of cysteamine which, when applied at low concentrations, most selectively depletes somatostatin. Neurons from the lateral superior olive, an auditory brainstem nucleus which transiently receives a dense somatostatinergic input, were intracellularly labeled at postnatal day 14 or 18. The dendritic morphology of these neurons was then analyzed quantitatively and compared with neurons from controls. Cysteamine treatment induced a reduction of the number of dendritic end points by more than 50%. At postnatal day 14, for example, controls and somatostatin-depleted animals had an average of 58 and 28 end points, respectively. The number of primary dendrites was also significantly reduced by cysteamine. In contrast, the size of the somata, the orientation of the dendritic trees within the lateral superior olive, the dendritic areas, and the cross-sectional size of the lateral superior olive were not altered. These results indicate that somatostatin depletion during early development has profound effects on the maturation of dendritic morphology. The selective influence on the dendritic trees suggests that somatostatin acts as an endogenous trophic peptide and promotes the achievement of dendritic complexity.