Adrenocorticoids of the goldfish, Carassius auratus L

Inhibitory neurotransmission drives endocannabinoid degradation to promote memory consolidation

Endocannabinoids retrogradely regulate synaptic transmission and their abundance is controlled by the fine balance between endocannabinoid synthesis and degradation. While the common assumption is that “on-demand” release determines endocannabinoid signaling, their rapid degradation is expected to control the temporal profile of endocannabinoid action and may impact neuronal signaling. Here we show that memory formation through fear conditioning selectively accelerates the degradation of endocannabinoids in the cerebellum. Learning induced a lasting increase in GABA release and this was responsible for driving the change in endocannabinoid degradation. Conversely, Gq-DREADD activation of cerebellar Purkinje cells enhanced endocannabinoid signaling and impaired memory consolidation. Our findings identify a previously unappreciated reciprocal interaction between GABA and the endocannabinoid system in which GABA signaling accelerates endocannabinoid degradation, and triggers a form of learning-induced metaplasticity.

Endocannabinoid levels are controlled by the fine balance between their synthesis and degradation. Here, the authors show that memory formation through fear conditioning selectively accelerates the degradation of endocannabinoids in the cerebellum via a lasting increase in GABA release.

Multiple corticosteroid receptors in a teleost fish: distinct sequences, expression patterns, and transcriptional activities

Corticosteroid hormones, including the mineralocorticoids and the glucocorticoids, regulate diverse physiological functions in vertebrates. These hormones act through two classes of corticosteroid receptors (CR) that are ligand-dependent transcription factors: type I or mineralocorticoid receptor (MR) and type II or glucocorticoid receptor (GR). There is substantial overlap in the binding of these two receptor types to hormones and to DNA. In fish, the overlap in processes controlled by CRs may be different from that in other vertebrates, as fish are thought to synthesize only glucocorticoids, whereas they express both GR and MR. Here we describe the characterization of four CRs in a cichlid fish, Haplochromis burtoni: a previously undescribed GR (HbGR1), another GR expressed in two splice isoforms (HbGR2a and HbGR2b), and an MR (HbMR). Sequence comparison and phylogenetic analysis showed that these CRs sort naturally into GR and MR groups, and that the GR duplication we describe will probably be common to all teleosts. Quantitative PCR revealed differential patterns of CR tissue expression in organs dependent on corticosteroid action. Trans-activation assays demonstrated that the CRs were selective for corticosteroid hormones and showed that the HbMR was similar to mammalian MRs in being more sensitive to both cortisol and aldosterone than the GRs. Additionally, the two HbGR2 isoforms were expressed uniquely in different tissues and were functionally distinct in their actions on classical GR-sensitive promoters. The identification of four CR subtypes in teleosts suggests a more complicated corticosteroid signaling in fish than previously recognized.

Hematological effects of high dose of cortisol on the carp (Cyprinus carpio L.): cortisol effect on the carp blood

The level of circulating cortisol and peripheral blood parameters were determined in carp age 2 years (K(2)) 24, 72, and 216 h after a single intraperitoneal injection of a high dose (200 mg x kg(-1) body wt) of hydrocortisone. The most striking effect of cortisol was manifest as a significant change in the percentage composition of leukocytes, whose number per unit volume of blood remained relatively constant. A profound lymphopenia and eosinopenia were compensated for in the general balance by an increased number of circulating promyelocytes and myelocytes as well as metamyelocytes and mature polymorphonuclear neutrophilic granulocytes. The results and their possible reasons are discussed on the background of literature data.

General overview of mineralocorticoid hormone action

The adrenal cortex elaborates two major groups of steroids that have been arbitrarily classified as glucocorticoids and mineralocorticoids, despite the fact that carbohydrate metabolism is intimately linked to mineral balance in mammals. In fact, glucocorticoids assured both of these functions in all living cells, animal and photosynthetic, prior to the appearance of aldosterone in teleosts at the dawn of terrestrial colonization. The evolutionary drive for a hormone specifically designed for hydromineral regulation led to zonation for the conversion of 18-hydroxycorticosterone into aldosterone through the catalytic action of a synthase in the secluded compartment of the adrenal zona glomerulosa. Corticoid hormones exert their physiological action by binding to receptors that belong to a transcription factor superfamily, which also includes some of the proteins regulating steroid synthesis. Steroids stimulate sodium absorption by the activation and/or de novo synthesis of the ion-gated, amiloride-sensitive sodium channel in the apical membrane and that of the Na+/K+-ATPase in the basolateral membrane. Receptors, channels, and pumps apparently are linked to the cytoskeleton and are further regulated variously by methylation, phosphorylation, ubiquination, and glycosylation, suggesting a complex system of control at multiple checkpoints. Mutations in genes for many of these different proteins have been described and are known to cause clinical disease.

Effects of corticosteroids and protein synthesis inhibitors on activities of oxidative enzymes in a bony fish, Anabas testudineus (Bloch)

The activities of oxidative enzymes of hepatic mitochondria of Anabas testudineus increased following exogenous administration of hydrocortisone and corticosterone. The inhibitors of protein synthesis prevented the hormone-mediated increase of hepatic enzymes, suggesting that corticosteroids regulate the oxidative metabolism of this teleostean species through the protein synthetic machinery of liver.