Structural Basis of Sirtuin 6-Catalyzed Nucleosome Deacetylation

The reversible acetylation of histone lysine residues is controlled by the action of acetyltransferases and deacetylases (HDACs), which regulate chromatin structure and gene expression. The sirtuins are a family of NAD-dependent HDAC enzymes, and one member, sirtuin 6 (Sirt6), influences DNA repair, transcription, and aging. Here, we demonstrate that Sirt6 is efficient at deacetylating several histone H3 acetylation sites, including its canonical site Lys9, in the context of nucleosomes but not free acetylated histone H3 protein substrates. By installing a chemical warhead at the Lys9 position of histone H3, we trap a catalytically poised Sirt6 in complex with a nucleosome and employ this in cryo-EM structural analysis. The structure of Sirt6 bound to a nucleosome reveals extensive interactions between distinct segments of Sirt6 and the H2A/H2B acidic patch and nucleosomal DNA, which accounts for the rapid deacetylation of nucleosomal H3 sites and the disfavoring of histone H2B acetylation sites. These findings provide a new framework for understanding how HDACs target and regulate chromatin.

Distinct biochemical properties of the class I histone deacetylase complexes

Classical histone deacetylases (HDACs) are enzymes that can hydrolytically cleave acetyl-Lys in histones and other proteins and serve as established drug targets in some forms of cancer. Class I HDACs 1-3 typically exist in a range of multiprotein complexes inside cells and show distinct biological functions in modulating gene expression. In recent years, it has become possible to purify and analyze the structure and enzymatic properties of several of these HDAC complexes, including CoREST, MiDAC, NuRD, Sin3, SMRT, MIER, and RERE. Here, we summarize what is experimentally established and/or computationally predicted about the structure of these complexes to describe their particular catalytic activities and site-specificities with modified nucleosome substrates.

Histone H2B Deacylation Selectivity: Exploring Chromatin's Dark Matter with an Engineered Sortase

We describe a new method to produce histone H2B by semisynthesis with an engineered sortase transpeptidase. N-Terminal tail site-specifically modified acetylated, lactylated, and β-hydroxybutyrylated histone H2Bs were incorporated into nucleosomes and investigated as substrates of histone deacetylase (HDAC) complexes and sirtuins. A wide range of rates and site-specificities were observed by these enzyme forms suggesting distinct biological roles in regulating chromatin structure and epigenetics.

Site-Specific 5-Formyl Cytosine Mediated DNA-Histone Cross-Links: Synthesis and Polymerase Bypass by Human DNA Polymerase η

DNA-protein cross-links (DPCs) between DNA epigenetic mark 5-formylC and lysine residues of histone proteins spontaneously form in human cells. Such conjugates are likely to influence chromatin structure and mediate DNA replication, transcription, and repair, but are challenging to study due to their reversible nature. Here we report the construction of site specific, hydrolytically stable DPCs between 5fdC in DNA and K4 of histone H3 and an investigation of their effects on DNA replication. Our approach employs oxime ligation, allowing for site-specific conjugation of histones to DNA under physiological conditions. Primer extension experiments revealed that histone H3-DNA crosslinks blocked DNA synthesis by hPol η polymerase, but were bypassed following proteolytic processing.

Chemical Screen Identifies Diverse and Novel Histone Deacetylase Inhibitors as Repressors of NUT Function: Implications for NUT Carcinoma Pathogenesis and Treatment

NUT carcinoma (NC), characterized most commonly by the BRD4-NUTM1 fusion, is a rare, aggressive variant of squamous carcinoma with no effective treatment. BRD4-NUT drives growth and maintains the poorly differentiated state of NC by activating pro-growth genes such as MYC, through the formation of massive, hyperacetylated, superenhancer-like domains termed megadomains. BRD4-NUT-mediated hyperacetylation of chromatin is facilitated by the chromatin-targeting tandem bromodomains of BRD4, combined with NUT, which recruits the histone acetyltransferase, p300. Here, we developed a high-throughput small-molecule screen to identify inhibitors of transcriptional activation by NUT. In this dCAS9-based GFP-reporter assay, the strongest hits were diverse histone deacetylase (HDAC) inhibitors. Two structurally unrelated HDAC inhibitors, panobinostat and the novel compound, IRBM6, both repressed growth and induced differentiation of NC cells in proportion to their inhibition of NUT transcriptional activity. These two compounds repressed transcription of megadomain-associated oncogenic genes, such as MYC and SOX2, while upregulating pro-differentiation, non-megadomain-associated genes, including JUN, FOS, and key cell-cycle regulators, such as CDKN1A. The transcriptional changes correlate with depletion of BRD4-NUT from megadomains, and redistribution of the p300/CBP-associated chromatin acetylation mark, H3K27ac, away from megadomains toward regular enhancer regions previously populated by H3K27ac. In NC xenograft models, we demonstrated that suppression of tumor growth by panobinostat was comparable with that of bromodomain inhibition, and when combined they improved both survival and growth suppression. IMPLICATIONS: The findings provide mechanistic and preclinical rationale for the use of HDAC inhibitors, alone or combined with other agents, in the treatment of NUT carcinoma.

[A comparative study of transperitoneal transmesenteric approach versus paracolic sulci approach laparoscopic adrenal tumorectomy for treatment of primary hyperaldosteronism on left side]

Objective: To compare the therapeutic effect of transperitoneal transmesenteric approach versus paracolic sulci approach laparoscopic adrenal tumorectomy for treatment of left-sided primary hyperaldosteronism. Methods: From January 2017 to July 2019, the clinical data of 70 patients with left-sided primary hyperaldosteronism (PHA) who underwent surgery in the First Hospital of Lanzhou University and five other hospitals in Gansu Province were retrospectively analyzed. There are 43 male and 27 female patients. Among them,28 patients were performed transperitoneal transmesenteric approach laparoscopic adrenal tumorectomy and 42 patients were performed transperitoneal paracolic sulci approach laparoscopic adrenal tumorectomy. The general information and perioperative data of the two groups were compared. Results: All 70 cases of surgery were successfully completed. As compared with the paracolic sulci approach group, the operation time was significantly shorter in the transmesenteric approach group[(26.7±8.8)vs (38.9±7.1)min,P<0.001)], and the estimated blood loss was less in the transmesenteric approach group[45(30,50) vs 50(40,60)ml,P=0.042]. There was no statistically significant difference in the postoperative hospitalization days between the two groups[(4.4±1.0)vs(4.5±1.0)d, P=0.669)]. The electrolytes and aldosterone to renin ratio returned to a healthy level in the postoperative one month, and the blood pressure also returned to a healthy level in 53 (75.7%) patients. Conclusion: Transperitoneal transmesenteric approach laparoscopic adrenal tumorectomy is safe and feasible, with a short operation time and relatively less estimated blood loss.

The Chemical Biology of Reversible Lysine Post-translational Modifications

Lysine (Lys) residues in proteins undergo a wide range of reversible post-translational modifications (PTMs), which can regulate enzyme activities, chromatin structure, protein-protein interactions, protein stability, and cellular localization. Here we discuss the "writers," "erasers," and "readers" of some of the common protein Lys PTMs and summarize examples of their major biological impacts. We also review chemical biology approaches, from small-molecule probes to protein chemistry technologies, that have helped to delineate Lys PTM functions and show promise for a diverse set of biomedical applications.

The Recent Progresses in Chemical Synthesis of Proteins with Site-Specific Lysine Post-translational Modifications

In the past two decades, a plethora of lysine (Lys) posttranslational modifications (PTMs) has been discovered on proteins, major groups are acylation, alkylation, and ubiquitination. Although considered biologically important, functional annotation of proteins with Lys PTMs has largely fallen behind the discovery. One grand challenge of characterizing proteins with PTMs is the procurement of homogenously modified proteins. To resolve this obstacle, sophisticated methods have been developed. These include total synthesis, semisynthesis that is based on native chemical ligation, expressed protein ligation, and enzyme-catalyzed peptide ligation, and the amber-suppression based noncanonical amino acid mutagenesis technique that may need to couple with follow-up bioorthogonal chemistry. This review summarizes currently identified significant PTMs and chemical biology methods for their installation in proteins. We hope that the current review will provide helpful insights and critical perspectives to this important research frontier.

Diverse nucleosome Site-Selectivity among histone deacetylase complexes

Histone acetylation regulates chromatin structure and gene expression and is removed by histone deacetylases (HDACs). HDACs are commonly found in various protein complexes to confer distinct cellular functions, but how the multi-subunit complexes influence deacetylase activities and site-selectivities in chromatin is poorly understood. Previously we reported the results of studies on the HDAC1 containing CoREST complex and acetylated nucleosome substrates which revealed a notable preference for deacetylation of histone H3 acetyl-Lys9 vs. acetyl-Lys14 (Wu et al, 2018). Here we analyze the enzymatic properties of five class I HDAC complexes: CoREST, NuRD, Sin3B, MiDAC and SMRT with site-specific acetylated nucleosome substrates. Our results demonstrate that these HDAC complexes show a wide variety of deacetylase rates in a site-selective manner. A Gly13 in the histone H3 tail is responsible for a sharp reduction in deacetylase activity of the CoREST complex for H3K14ac. These studies provide a framework for connecting enzymatic and biological functions of specific HDAC complexes.

Methods and Applications of Expressed Protein Ligation

Expressed protein ligation is a method of protein semisynthesis and typically involves the reaction of recombinant protein C-terminal thioesters with N-cysteine containing synthetic peptides in a chemoselective ligation. The recombinant protein C-terminal thioesters are produced by exploiting the action of nature's inteins which are protein modules that catalyze protein splicing. This chapter discusses the basic principles of expressed protein ligation and recent advances and applications in this protein semisynthesis field. Comparative strengths and weaknesses of the method and future challenges are highlighted.

Proteins with Site-Specific Lysine Methylation

As an important epigenetic mark, lysine methylations play critical roles in the regulation of both chromatin and non-chromatin proteins. There are three levels of lysine methylation, mono-, di-, and trimethylation. Each one has turned out to be biologically distinctive. For the biochemical characterization of proteins with lysine methylation, multiple chemical biology methods have been developed. This concept article will highlight these developments and their applications in epigenetic investigation of protein functions.

A Versatile Approach for Site-Specific Lysine Acylation in Proteins

Using amber suppression in coordination with a mutant pyrrolysyl-tRNA synthetase-tRNAPyl pair, azidonorleucine is genetically encoded in E. coli. Its genetic incorporation followed by traceless Staudinger ligation with a phosphinothioester allows the convenient synthesis of a protein with a site-specifically installed lysine acylation. By simply changing the phosphinothioester identity, any lysine acylation type could be introduced. Using this approach, we demonstrated that both lysine acetylation and lysine succinylation can be installed selectively in ubiquitin and synthesized histone H3 with succinylation at its K4 position (H3K4su). Using an H3K4su-H4 tetramer as a substrate, we further confirmed that Sirt5 is an active histone desuccinylase. Lysine succinylation is a recently identified post-translational modification. The reported technique makes it possible to explicate regulatory functions of this modification in proteins.

The genus Boschniakia in China: An ethnopharmacological and phytochemical review

ETHNOPHARMACOLOGICAL RELEVANCE

As a group of important medicine plants, Boschniakia rossica (Cham. et Schltdl) Fedtsch. and B. himalaica Hook．f．et Thoms, which are the only two species in the genus Boschniakia (Orobanchaceae), have long been used in traditional Chinese medicine for their multiple therapeutic uses related to enhanced renal function, erectile dysfunction, defaecate and hepatoprotective. Additionally, the two species are also used as dietary supplements in wine, cosmetics, and other healthy food.

AIM OF THE REVIEW

By providing comprehensive information and data of genus Boschniakia on botany, traditional medicinal uses, phytochemistry, pharmacological research and toxicology, this review aims to summary the group of natural compounds from Boschniakia discovered so far. The other aims are to reference research findings of their biological activities and functions in medicine, physiology, and cell biology to highlight the compound candidates which can be used for further drug discovery in several pharmaceutical areas including antioxidation, anticancer, anti-inflammation, anti-senile, and immunology.

MATERIALS AND METHODS

All of the available information on B. rossica and B. himalaica was collected from the electronic resources (such as PubMed, SciFinder Scholar, CNKI, TPL (www.theplantlist.org), Google Scholar, Baidu Scholar, and Web of Science).

RESULTS

After a comprehensive analysis of the literatures from available online sources, the results show that both species of genus Boschniakia are valuable and popular herbal medicines with potentials to cure various ailments. The phytochemical studies revealed that the chemical compositions of this genus were mainly iridoid glycosides and phenylpropanoid glycosides. To date, 112 compounds have been isolated from the genus, while their crude extracts and purified compounds have been found to possess a wide range of biological activities including anti-senile, antitumor and anticancer, anti-inflammatory, protecting liver, boost memory, anti-oxidation, anti-lipid peroxidative, and antiviral activities.

CONCLUSIONS

The existing traditional uses of the genus Boschniakia have been evaluated, and the properties of the genus are summarized based on botany, phytochemistry, pharmacological research, and toxicology. This review aims to introduce the utilization and application of the genus Boschniakia to modern drug discovery, traditional medicinal plant utilization, herbal species conservation, and the development of medicinal and health-maintaining products.

A Genetically Encoded Allysine for the Synthesis of Proteins with Site-Specific Lysine Dimethylation

Using the amber suppression approach, N^ϵ -(4-azidobenzoxycarbonyl)-δ,ϵ-dehydrolysine, an allysine precursor is genetically encoded in E. coli. Its genetic incorporation followed by two sequential biocompatible reactions allows convenient synthesis of proteins with site-specific lysine dimethylation. Using this approach, dimethyl-histone H3 and p53 proteins have been synthesized and used to probe functions of epigenetic enzymes including histone demethylase LSD1 and histone acetyltransferase Tip60. We confirmed that LSD1 is catalytically active toward H3K4me2 and H3K9me2 but inert toward H3K36me2, and methylation at p53 K372 directly activates Tip60 for its catalyzed acetylation at p53 K120.

Robust Chemical Synthesis of Membrane Proteins through a General Method of Removable Backbone Modification

Chemical protein synthesis can provide access to proteins with post-translational modifications or site-specific labelings. Although this technology is finding increasing applications in the studies of water-soluble globular proteins, chemical synthesis of membrane proteins remains elusive. In this report, a general and robust removable backbone modification (RBM) method is developed for the chemical synthesis of membrane proteins. This method uses an activated O-to-N acyl transfer auxiliary to install in the Fmoc solid-phase peptide synthesis process a RBM group with switchable reactivity toward trifluoroacetic acid. The method can be applied to versatile membrane proteins because the RBM group can be placed at any primary amino acid. With RBM, the membrane proteins and their segments behave almost as if they were water-soluble peptides and can be easily handled in the process of ligation, purification, and mass characterizations. After the full-length protein is assembled, the RBM group can be readily removed by trifluoroacetic acid. The efficiency and usefulness of the new method has been demonstrated by the successful synthesis of a two-transmembrane-domain protein (HCV p7 ion channel) with site-specific isotopic labeling and a four-transmembrane-domain protein (multidrug resistance transporter EmrE). This method enables practical synthesis of small- to medium-sized membrane proteins or membrane protein domains for biochemical and biophysical studies.

Efficient synthesis of longer Aβ peptides via removable backbone modification

This paper describes a new method for the efficient chemical synthesis of longer Aβ peptides with the combination of the RBM strategy and native chemical ligation.

Protein/peptide secondary structural mimics: design, characterization, and modulation of protein–protein interactions

This review discusses general aspects of novel artificial peptide secondary structure mimics for modulation of PPIs, their therapeutic applications and future prospects.

Revisiting the concept of cancer stem cells in prostate cancer

The cancer stem cell (CSC) model proposes that cells within a tumor are organized in a hierarchical lineage relationship and display different tumorigenic potential, suggesting that effective therapeutics should target rare CSCs that sustain tumor malignancy. Here we review the current status of studies to identify CSCs in human prostate cancer as well as mouse models, with an emphasis on discussing different functional assays and their advantages and limitations. We also describe current controversies regarding the identification of prostate epithelial stem cells and cell types of origin for prostate cancer, and present potential resolutions of these issues. Although definitive evidence for the existence of CSCs in prostate cancer is still lacking, future directions pursuing the identification of tumor-initiating stem cells in the mouse may provide important advances in evaluating the CSC model for prostate cancer.

[Modulatory effects of 17beta-estradiol on the electrical activity of subfornical organ neurons]

The effects of 17beta-estradiol (E(2) ) on electrical activity of neurons in subfornical organ (SFO) slices were examined using extracelluar recording technique. The results are as follows. (1) In 15 SFO units, a low dose of E(2) (0.1 nmol/L) applied into superfusate induced an increase in discharge rate from 3.21+/-0.37 to 6.79+/-0.71 Hz (P<0.001), whereas a high dose of E(2) (100 nmol/L ) caused a decrease in discharge rate from 3.44+/-0.40 to 1.44+/-0.36 Hz (P<0.01); (2) glutamate NMDA receptor antagonist MK-801 (50 pmol/L) blocked the excitatory effects induced by low dose of 17beta-estradiol in 7 units; (3) L-arginine (L-arg, 1 mmol/L), a physiological precursor of NO, abolished the excitatory effects induced by low dose of 17beta-estradiol in 7 units; (4) application of N-omega-nitro-L-arginine methyl ester (L-NAME, 10 mmol/L), an inhibitor of NOS, blocked the inhibitory effects induced by high dose of 17beta-estradiol in 6 units. The above results suggest that the estrogen exerts dual action on SFO neuron. E(2) at low dosage increases the discharge rate of SFO neuron, an effect which may be related to the activation of NMDA receptors, whereas E(2) at high dosage decreases the discharge rate, an effect which may be attributed to the activation of NOS with resultant production of NO.

[Adenosine inhibits spontaneous and glutamate induced discharges of hippocampal CA1 neurons]

Effects of adenosine (Ado) on spontaneous and glutamate induced discharges of neurons in CA1 area of hippocampal slices were examined using extracelluar recording technique. The results are as follows. (1) In response to the application of Ado (0.01 0.1 micromol/L, n=20) into the superfusate, spontaneous discharge rates (SDR) of 20 neurons decreased significantly in a dose dependent manner. (2) Both Ado non selective receptor antagonist 8 phenyltheophylline (8-PT, 0.5 mmol/L) and Ado selective A1 receptor antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX, 50 nmol/L), completely blocked the inhibitory effects of Ado in 22 CA1 units. (3) In 10 units, ATP sensitive K(+) channel blocker glibenclamide (Gli, 15 mmol/L) also abolished the effect of Ado. (4) Application of glutamate (Glu, 0.2 mmol/L) into the superfusate for 2 min led to a marked increase in the discharge rate of 15 neurons in an epileptiform pattern; the epileptiform discharges induced by glutamate (Glu, 0.2 mmol/L) in 15 neurons were suppressed significantly by application of Ado (10 micromol/L) into the superfusate. (5) 8-PT (2 mmol/L), DPCPX (200 nmol/L) and Gli (7 mmol/L) were all capable of abolishing the inhibiting effect of Ado on the action of glutamate. Taken together, it is suggested that Ado can bind with adenosine A1-receptors on CA1 neurons, resulting in an activation of K(ATP) channels and inhibition of neuronal activity. The inhibitory effect of Ado on glutamate induced epileptiform activities in rat hippocampal neurons is also mediated by adenosine A1-receptor with involvement of ATP-sensitive potassium channels.

[Inhibitory effects of nitric oxide on glutamate-induced neuronal activity of CA1 area in rat hippocampal slices]

Using extracellular recording technique, the effects of L-arginine (L-arg), SIN-1 and N-nitro-L-arginine (L-NNA) on glutamate-induced discharge of neurons in CA1 area of hippocampal slices were examined to define the role of L-arg:NO pathway in glutamate-induced discharge of hippocampal neurons and its possible underlying mechanism. The results obtained are as follows. (1) In response to the application of glutamate (0.5 mmol/L) into the superfusate for 1 min, the discharge rate of 12 neurons was increased markedly in an epileptiform pattern. (2) The increased discharge induced by glutamate (0.5 mmol/L) in 10 neurons was suppressed significantly by application of L-arg (10 mmol/L) into the superfusate for 2 min. (3) The glutamate-induced increase of discharge in 12 neurons was decreased markedly by superfusing the brain slice with NO donor SIN-1 (5 mmol/L) for 1 min. (4) As the discharge rate of 12 neurons was increased by pretreatment with glutamate (0.5 mmol/L), application of L-NNA (0.15 mmol/L) into superfusate for 2 min might further augment the discharge intensively and in some case eventually led to abrupt suppression of the discharge. Taken together, it is likely that glutamate binding with NMDA receptors in hippocampal neurons not only induces an increase in discharge, but also activates the L-arg: NO pathway to generate NO responsible for neuroprotection via negative feedback mechanisms.

[Effects of no precursor and donor on neuronal activity of rat hippocampal slices]

Using extracellular recording technique, the effects of L-arginine (L-arg), N-nitro-L-arginine (L-NNA), SIN-1 and methylene blue (MB) on spontaneous discharges of neurons in CA1 area of hippocampal slices were examined to determine the role of L-arg: NO pathway and the possible underlying mechanism. The results were as follows: (1) In response to the application of L-arg (1 mmol/L) into the superfusate for 2 min, spontaneous discharge rate (SDR) of 42/54 (77.8%) neurons was decreased significantly, while that of 12/54 (22.2%) neurons showed no change. Following the application of L-NNA (0.15 mmol/L) into the superfusate for 2 min, SDR of 25/29 (86.2%) neurons was increased markedly and that of 4/29 (13.8%) neurons was not affected. The effect of L-NNA might be reversed by pretreatment with L-arg. (2) With application of NO donor SIN-1 (5 mmol/L), SDR of 25 (100%) neurons was decreased in a dose-dependent manner. (3) After superfusing the brain slice with guanylate cyclase inhibitor, MB (3 mumol/L) for 30 min, SDR of 10 units showed significant increase as compared with control. However, MB failed to abolish the effect of L-arg on hippocampal neurons. Taken together, it is likely that NO is released during the resting state of hippocampal neurons and may inhibit the activity of hippocampus, an effect not mediated by the action of guanylate cyclase.

[Effects of angiotensin II, atrial natriuretic peptide III and arginine vasopressin on activity of paraventricular neurons of rat hypothalamic slices]

The effects of angiotensin II (AG II), atrial natriuretic peptide III (ANP III) and arginine vasopressin on 101 paraventricular nucleus (PVN) neurons from 28 brain slices of rats were observed. After perfusing the brain slices with AG II (10(-7) mol/L, 3 min), spontaneous discharge rate of 28/50 (56.0%) neurons was significantly increased, while that of 5/50 (10.0%) was significantly decreased and 17/50 (34.0%) neurons were non-responsive. Both of excitatory and inhibitory effects of AG II on neurons in PVN were completely blocked by AG II receptor blocker saralasin (10(-6) mol/L). As the brain slices were perfused with ANP III (10(-7) mol/L, 3 min), the firing rate of 16/26 (61.54%) neurons was decreased, while that of 1/26 (3.85%) neurons was increased and 9/26 (34.61%) neurons were non-responsive. During perfusing brain slices with AVP (10(-7) mol/L, 3 min), the firing rate of 19/25 (76.0%) neurons was significantly increased, while that of 1/25 (4.0%) neurons was decreased and 5/25 (20.0%) neurons were non-responsive. Twenty-five PVN neurons were successively perfused with three peptides. Among them, 4 were excited by both AG II and AVP, 2 were excited by AG II and inhibited by ANP III, and 7 were excited by AVP and inhibited by ANP III. The results show that the discharge rate of PVN neurons may be affected by AG II, ANP III and AVP. It is likely that PVN acts as an integrative site for neuroendocrine and autonomic functions.

[Collection, evaluation and utilization of local varieties of Fritillaria thunbergii Miq]

Nine local varieties of Fritillaria thunbergii were collected and their plant morphology, phenology, disease resistance yield characters and breeding rate were studied. A new and better variety (Duozhi) was found and put to use.

[Effects of angiotensin II, atrial natriuretic peptide and arginine vasopressin on activity of subfornical organ neurons in rat brain slices]

The effects of angiotensin II (AG II), atrial natriuretic peptide (ANP) and arginine vasopressin (AVP) on 87 subfornical organ (SFO) neurons from 31 brain slices of rats were observed. After perfusing the brain slices with AG II (10(-7) mol/L, 3 min), spontaneous discharge rate of 40/55 (72.73%) neurons was significantly increased, while that of 3/55 (5.45%) was decreased and 12/55 (21.82%) neurons were non-responsive. The excitatory effects of AG II on neurons in SFO were completely blocked by AG II receptor blocker saralasin (10(-6) mol/L). As the brain slices were perfused with atrial peptide III (AP III) (10(-7) mol/L, 3 min), the firing rate of 7/17 (41.18%) neurons was significantly decreased, while that of 2/17 (11.76%) neurons was increased and 8/17 (47.06%) neurons were non-responsive. By perfusing brain slices with AVP (10(-7) mol/L, 3 min), the firing rate of 8/15 (53.33%) neurons was significantly increased, while that of 3/15 (20.00%) neurons was decreased and 4/15 (26.67%) neurons were non-responsive. Twelve SFO neurons were successively perfused with three peptides. Among them, one was excited by both AG II and AVP, 3 were excited by AG II and inhibited by AP III, and the other one was excited by AVP and inhibited by AP III. The results suggest that the discharge rate of SFO neurons is affected by AG II, ANP and AVP. SFO may be one of the central regions in regulation of water balance and blood pressure.

[Effects of left atrial stretch and carotid occlusion on the single unit activity of anterior and posterior hypothalamus in cat]

The effects of left atrial stretch (AS) and carotid occlusion (CO) on the single unit activity of anterior and posterior hypothalamus (AH and PH) were investigated in 40 urethan-chloralose-anesthetized cats. A total of 185 units with spontaneous discharge were recorded. 46.3% (44/95) of the neurons in AH and 23.3% (21/90) of those in PH were responsive to AS. Majority of the neurons affected by AS exhibited a decrease in firing rate. A few units only showed transient response during the onset and release of AS (on-off response). Out of the 185 units, 85 units were tested by both AS and CO, and 15 units (17.6%) were responsive to both interventions. Among them 11 (73.7%) were inhibited by AS and excited by CO. From the results mentioned above, it is suggested that: (1) AS may exert an inhibitory effect on the activity of neurons in AH. (2) The activity of neurons in PH may be also affected by AS. (3) The inputs from the atrial volume receptor and carotid baroreceptor converge on the same neuron of the hypothalamus.

[Renal responses to left atrial stretch in the cat]

The effects of left atrial stretch (LAS) on urine volume (UV), urinary sodium excretion (UNaV) and potassium excretion (UKV) were studied in 50 anesthetized cats. LAS resulted in a marked increase in UV, UNaV and UKV (all P less than 0.001) in the intact animals. Although LAS still caused an increase in UV and UNaV (P less than 0.01) after vagotomy, the increments were significantly less than those in vagi intact animals (P less than 0.005). LAS also induced an increase in UV, UNaV and UKV (P less than 0.05) in the vagi intact cats with heparin infusion (10U/min/kg), but the increments were significantly less than those in the cats without heparin (P less than 0.05). The responses to LAS were abolished by infusion of heparin after vagotomy (P greater than 0.05). Following left renal denervation, the responses to LAS remained unchanged in the innervated kidney, while those in denervated kidney were attenuated, though still significant. The difference in the response between the innervated and the denervated kidneys was statistically significant (P less than 0.05). These results indicate that LAS can induce a marked increase in UV, UNaV and UKV in anesthetized cats through both neural and humoral mechanisms.