Selective dopamine D2 receptor deletion from Nkx6.2 expressing cells causes impaired cognitive, motivation and anxiety phenotypes in mice.

Abnormal dopamine neurotransmission is a common trait of some psychiatric diseases, like schizophrenia or bipolar disorder. Excessive dopaminergic tone in subcortical brain regions is associated with psychotic episodes, while reduced prefrontal dopaminergic activity is associated with impaired cognitive performance and reduced motivation, among other symptoms. Inhibitory interneurons expressing the calcium binding protein parvalbumin are particularly affected in both schizophrenia and bipolar disorder, as they set a fine-tuned physiological inhibitory/excitatory balance. Parvalbumin and somatostatin interneuron subtypes, are born from the medial ganglionic eminence and require the sequential expression of specific transcription factors for their specification, such as Nkx6.2. Here, we aimed at characterizing in detail interneuron subtypes derived from Nkx6.2 expressing progenitors by the generation of an Nkx6.2 Cre transgenic mouse line. We show that Nkx6.2 specifies over a third part of the total population of cortical somatostatin interneurons, preferentially at early developmental time points, whereas at late developmental stages, Nkx6.2 expressing progenitors shift to parvalbumin interneuron specification. Dopamine D2 receptor deletion from Nkx6.2 expressing progenitors causes abnormal phenotypes restricted to cognitive, motivation and anxiety domains. Our results show that Nkx6.2 have the potential to specify both somatostatin and parvalbumin interneurons in an opposite timed program and that DRD2 expression is required in Nkx6.2 expressing progenitors to avoid impaired phenotypes commonly associated to the pathophysiology of psychiatric diseases.

MicroRNA in Acromegaly: Involvement in the Pathogenesis and in the Response to First-Generation Somatostatin Receptor Ligands.

Acromegaly is a chronic and systemic disease due to excessive growth hormone and insulin-like growth factor type I caused, in the vast majority of cases, by a GH-secreting pituitary adenoma. About 40% of these tumors have somatic mutations in the stimulatory G protein alpha-subunit 1 gene. The pathogenesis of the remaining tumors, however, is still not fully comprehended. Surgery is the first-line therapy for these tumors, and first-generation somatostatin receptor ligands (fg-SRL) are the most prescribed medications in patients who are not cured by surgery. MicroRNAs are small, non-coding RNAs that control the translation of many mRNAs, and are involved in the post-transcriptional regulation of gene expression. Differentially expressed miRNAs can explain differences in the pathogenesis of acromegaly and tumor resistance. In this review, we focus on the most validated miRNAs, which are mainly involved in acromegaly's tumorigenesis and fg-SRL resistance, as well as in circulating miRNAs in acromegaly.

Basal forebrain somatostatin cells differentially regulate local gamma oscillations and functionally segregate motor and cognitive circuits.

The basal forebrain delivers extensive axonal projections to the cortical mantle regulating brain states and cognitive processing. Recent evidence has established the basal forebrain as a subcortical node of the default mode network that directionally influences cortical dynamics trough gamma oscillations, yet their synaptic origin has not been established. Here, we used optogenetic stimulation and in vivo recordings of transgenic mice to show that somatostatin neurons exert an anatomically specialized role in the coordination of subcortical gamma oscillations of the rostral basal forebrain. Indeed, the spike timing of somatostatin cells was tightly correlated with gamma oscillations in the ventral pallidum, but not in the medial septum. Consequently, optogenetic inactivation of somatostatin neurons selectively disrupted the amplitude and coupling of gamma oscillations only in the ventral pallidum. Moreover, photosupression of somatostatin cells produced specific behavioral interferences, with the ventral pallidum regulating locomotor speed and the medial septum modulating spatial working memory. Altogether, these data suggest that basal forebrain somatostatin cells can selectively synchronize local neuronal networks in the gamma band directly impinging on cortical dynamics and behavioral performance. This further supports the role of the basal forebrain as a subcortical switch commanding transitions between internally and externally oriented brain states.

Characterization and distribution of GHRH, PACAP, TRH, SST and IGF1 mRNAs in the green iguana.

The somatotropic axis (SA) regulates numerous aspects of vertebrate physiology such as development, growth, and metabolism and has influence on several tissues including neural, immune, reproductive and gastric tract. Growth hormone (GH) is a key component of SA, it is synthesized and released mainly by pituitary somatotrophs, although now it is known that virtually all tissues can express GH, which, in addition to its well-described endocrine roles, also has autocrine/paracrine/intracrine actions. In the pituitary, GH expression is regulated by several hypothalamic neuropeptides including GHRH, PACAP, TRH and SST. GH, in turn, regulates IGF1 synthesis in several target tissues, adding complexity to the system since GH effects can be exerted either directly or mediated by IGF1. In reptiles, little is known about the SA components and their functional interactions. The aim of this work was to characterize the mRNAs of the principal SA components in the green iguana and to develop the tools that allow the study of the structural and functional evolution of this system in reptiles. By employing RT-PCR and RACE, the cDNAs encoding for GHRH, PACAP, TRH, SST and IGF1 were amplified and sequenced. Results showed that these cDNAs coded for the corresponding protein precursors of 154, 170, 243, 113, and 131 amino acids, respectively. Of these, GHRH, PACAP, SST and IGF1 precursors exhibited a high structural conservation with respect to its counterparts in other vertebrates. On the other hand, iguana's TRH precursor showed 7 functional copies of mature TRH (pyr-QHP-NH2), as compared to 4 and 6 copies of TRH in avian and mammalian proTRH sequences, respectively. It was found that in addition to its primary production site (brain for GHRH, PACAP, TRH and SST, and liver for IGF1), they were also expressed in other peripheral tissues, i.e. testes and ovaries expressed all the studied mRNAs, whereas TRH and IGF1 mRNAs were observed ubiquitously in all tissues considered. These results show that the main SA components in reptiles of the Squamata Order maintain a good structural conservation among vertebrate phylogeny, and suggest important physiological interactions (endocrine, autocrine and/or paracrine) between them due to their wide peripheral tissue expression.

Somatostatin signaling system as an ancestral mechanism: Myoregulatory activity of an Allatostatin-C peptide in Hydra.

The coordination of physiological processes requires precise communication between cells. Cellular interactions allow cells to be functionally related, facilitating the maintaining of homeostasis. Neuropeptides functioning as intercellular signals are widely distributed in Metazoa. It is assumed that neuropeptides were the first intercellular transmitters, appearing early during the evolution. In Cnidarians, neuropeptides are mainly involved in neurotransmission, acting directly or indirectly on epithelial muscle cells, and thereby controlling coordinated movements. Allatostatins are a group of chemically unrelated neuropeptides that were originally characterized based on their ability to inhibit juvenil hormone synthesis in insects. Allatostatin-C has pleiotropic functions, acting as myoregulator in several insects. In these studies, we analyzed the myoregulatory effect of Aedes aegypti Allatostatin-C in Hydra sp., a member of the phylum Cnidaria. Allatostatin-C peptide conjugated with Qdots revealed specifically distributed cell populations that respond to the peptide in different regions of hydroids. In vivo physiological assays using Allatostatin-C showed that the peptide induced changes in shape and length in tentacles, peduncle and gastrovascular cavity. The observed changes were dose and time dependent suggesting the physiological nature of the response. Furthermore, at highest doses, Allatostatin-C induced peristaltic movements of the gastrovascular cavity resembling those that occur during feeding. In silico search of putative Allatostatin-C receptors in Cnidaria showed that genomes predict the existence of proteins of the somatostatin/Allatostatin-C receptors family. Altogether, these results suggest that Allatostatin-C has myoregulatory activity in Hydra sp, playing a role in the control of coordinated movements during feeding, indicating that Allatostatin-C/Somatostatin based signaling might be an ancestral mechanism.

Differential responses of the somatotropic and thyroid axes to environmental temperature changes in the green iguana.

Growth hormone (GH), together with thyroid hormones (TH), regulates growth and development, and has critical effects on vertebrate metabolism. In ectotherms, these physiological processes are strongly influenced by environmental temperature. In reptiles, however, little is known about the direct influences of this factor on the somatotropic and thyroid axes. Therefore, the aim of this study was to describe the effects of both acute (48h) and chronic (2weeks) exposure to sub-optimal temperatures (25 and 18°C) upon somatotropic and thyroid axis function of the green iguana, in comparison to the control temperature (30-35°C). We found a significant increase in GH release (2.0-fold at 25°C and 1.9-fold at 18°C) and GH mRNA expression (up to 3.7-fold), mainly under chronic exposure conditions. The serum concentration of insulin-like growth factor-I (IGF-I) was significantly greater after chronic exposure (18.5±2.3 at 25°C; 15.92±3.4 at 18°C; vs. 9.3±1.21ng/ml at 35°C), while hepatic IGF-I mRNA expression increased up to 6.8-fold. Somatotropic axis may be regulated, under acute conditions, by thyrotropin-releasing hormone (TRH) that significantly increased its hypothalamic concentration (1.45 times) and mRNA expression (0.9-fold above control), respectively; and somatostatin (mRNA expression increased 1.0-1.2 times above control); and under chronic treatment, by pituitary adenylate cyclase-activating peptide (PACAP mRNA expression was increased from 0.4 to 0.6 times). Also, it was shown that, under control conditions, injection of TRH stimulated a significant increase in circulating GH. On the other hand, while there was a significant rise in the hypothalamic content of TRH and its mRNA expression, this hormone did not appear to influence the thyroid axis activity, which showed a severe diminution in all conditions of cold exposure, as indicated by the decreases in thyrotropin (TSH) mRNA expression (up to one-eight of the control), serum T4 (from 11.6±1.09 to 5.3±0.58ng/ml, after 2weeks at 18°C) and T3 (from 0.87±0.09 to 0.05±0.01ng/ml, under chronic conditions at 25°C), and Type-2 deiodinase (D2) activity (from 992.5±224 to 213.6±26.4fmolI(125)T4/mgh). The reduction in thyroid activity correlates with the down-regulation of metabolism as suggested by the decrease in the serum glucose and free fatty acid levels. These changes apparently were independent of a possible stress response, at least under acute exposure to both temperatures and in chronic treatment to 25°C, since serum corticosterone had no significant changes in these conditions, while at chronic 18°C exposure, a slight increase (0.38 times above control) was found. Thus, these data suggest that the reptilian somatotropic and thyroid axes have differential responses to cold exposure, and that GH and TRH may play important roles associated to adaptation mechanisms that support temperature acclimation in the green iguana.

Comparative analysis of the river buffalo somatostatin gene.

The somatostatin protein plays a crucial role in the regulation of multiple biological functions, such as growth, fat deposition, and nutrient absorption in vertebrates. Polymorphisms in the somatostatin gene have been associated with growth traits in livestock species, including cattle and goat. In this study, we conducted complete molecular characterization of the somatostatin gene in Bubalus bubalis (Murrah breed) by sequencing a Murrah BAC clone spanning 72,489 base pairs (bp) in length. The buffalo somatostatin gene contains 1481 bp organized into a 5'-untranslated region (135 bp), exon 1 (139 bp), intron 1 (839 bp), exon 2 (212 bp), and 3'UTR (156 bp). Comparative analysis between the buffalo somatostatin DNA coding sequence and the amino acid sequence with other bovids (cattle, goat, and sheep), horse, pig, human, rodents (mouse and rat), and chicken. Identity varied from 83-99% on the DNA sequence level and 88-100% on the protein level. In addition, a comparison of gene sequences between Murrah and Mediterranean breeds revealed 6 potential single-nucleotide polymorphisms (1 in exon 1 and 5 in intron 1), which were validated in different buffalo populations. This comparative analysis provides basic information for future studies of different buffalo herds using the position candidate gene approach, quantitative trait loci analysis, and polymorphisms associated with growth traits.

Polymorphism of somatostatin gene and its association with growth traits in Chinese cattle.

Somatostatins play a crucial role in the regulation of growth and development in vertebrates, especially muscle growth. We assessed the association of somatostatin gene polymorphisms with growth traits by PCR-SSCP (polymerase chain reaction-single strand conformation polymorphism) and DNA sequencing methods in 694 individuals from six Chinese cattle breeds. A novel single nucleotide polymorphism, G126A, was detected, and significant associations were found with body length, body height, hip width, heart girth, and hucklebone width index. Polymorphism of the somatostatin gene was found to be highly associated with growth traits in the Qinchuan breed at various ages. Gene frequency analysis showed significant differences among the breeds. Individuals with genotype AA had significantly lower body height, body length, hip width, and hucklebone width values compared to AG at 1.5 years old, and had significantly lower hip width, body length and hucklebone width compared to AG at 2 years old. At 2.5 years old, populations with genotype AA had significantly lower body length, hip width and hucklebone width than AG individuals, with the exception of the Luxi breed, in which two genotypes were found. The Luxi and Ximentaer crossbreed had the lowest frequency of the G allele, while the highest G allele frequencies were found in the Luxi breed.

Time-dependent effect of melatonin on actin mRNA levels and incorporation of 35S-methionine into actin and proteins by the rat hypothalamus.

The synthesis of the cytoskeletal protein actin exhibits, in the rat hypothalamus, a diurnal variation with maxima during morning hours. The objective of the present study was to assess whether melatonin injection could affect the in vitro incorporation of 35S-methionine into actin, as well as the levels of actin mRNA, in the hypothalamus of adult male rats treated either acutely or chronically with the hormone at 10:00 or 18:00. Injection of 100 micrograms/kg of melatonin for ten days at either time induced a significant depression in the incorporation of 35S-methionine into a 43 kDa protein with the electrophoretic mobility of actin. The specific activity of total soluble proteins after labeled methionine incubations decreased only after evening melatonin administration (100 micrograms/kg, ten days). Hypothalamic actin mRNA levels, quantitated by dot-blot analysis, decreased only after the injection of 100 micrograms/kg melatonin for ten days at 10:00. Neither a 10-micrograms/kg dose of melatonin, nor a single injection of 100 micrograms/kg melatonin, caused any significant change in the parameters examined. Melatonin (100 micrograms/kg for ten days) did not modify hypothalamic somatostatin or H-Ras mRNA concentration. These results suggest the existence of an inhibitory effect of melatonin on hypothalamic actin synthesis.