Background-Diminished cardiac vagal activity and higher heart rate predict a high mortality rate of chronic heart failure (CHF) after myocardial infarction. We investigated the effects of chronic electrical stimulation of the vagus nerve on cardiac remodeling and long-term survival in an animal model of CHF after large myocardial infarction. Methods and Results-Two weeks after the ligation of the left coronary artery, surviving rats were randomized to vagaland sham-stimulated groups. Using an implantable miniature radio-controlled electrical stimulator, we stimulated the right vagal nerve of CHF rats for 6 weeks. The intensity of electrical stimulation was adjusted for each rat, so that the heart rate was lowered by 20 to 30 beats per minute.

Neuropeptides are an important class of molecules involved in diverse aspects of metazoan development and homeostasis. Insects are ideal model systems to investigate neuropeptide functions, and the major focus of insect neuropeptide research in the last decade has been on the identification of their receptors. Despite these vigorous efforts, receptors for some key neuropeptides in insect development such as prothoracicotropic hormone, eclosion hormone and allatotropin (AT), remain undefined. In this paper, we report the comprehensive cloning of neuropeptide G protein-coupled receptors from the silkworm, Bombyx mori, and systematic analyses of their expression. Based on the expression patterns of orphan receptors, we identified the long-sought receptor for AT, which is thought to stimulate juvenile hormone biosynthesis in the corpora allata (CA). Surprisingly, however, the AT receptor was not highly expressed in the CA, but instead was predominantly transcribed in the corpora cardiaca (CC), an organ adjacent to the CA. Indeed, by using a reverse-physiological approach, we purified and characterized novel allatoregulatory peptides produced in AT receptor-expressing CC cells, which may indirectly mediate AT activity on the CA. All of the above findings confirm the effectiveness of a systematic analysis of the receptor transcriptome, not only in characterizing orphan receptors, but also in identifying novel players and hidden mechanisms in important biological processes. This work illustrates how using a combinatorial approach employing bioinformatic, molecular, biochemical and physiological methods can help solve recalcitrant problems in neuropeptide research.

The baroreflex loop consists of a fast neural arc and a slow mechanical arc. We hypothesized that the neural baroreflex arc compensates the slow mechanical response and thus improves the quality of blood pressure regulation. We estimated the open-loop transfer characteristics of the neural baroreflex arc (HP), i.e., from carotid sinus pressure to sympathetic nerve activity (SNA), and that of the effective peripheral baroreflex arc (Hp), i.e., from SNA to arterial pressure, in anesthetized rabbits. The gain of Hn was constant below 0.12 +/- 0.057 Hz and increased with a slope of 6.1 +/- 0.06 dB/octave above its frequency up to 1 Hz. In contrast, the gain of Hp was constant below 0.071 +/- 0.03 Hz and decreased with a slope of -11.0 +/- 1.48 dB/octave above the frequency. These data indicate that Hn accelerates slow peripheral responses in the frequency range of 0.1-1 Hz. Although too much acceleration in the high-frequency range could result in instability of the system, numerical analysis of the closed-loop baroreflex response indicated that the neural arc optimized arterial pressure regulation in achieving both stability and quickness.

We previously isolated a novel dodecapeptide containing a C-terminal -Arg-Phe-NH(2) sequence, SIKPSAYLPLRF-NH(2) (RFamide peptide), from the quail brain. This quail RFamide peptide was shown to decrease gonadotropin release from the cultured anterior pituitary and to be located at least in the quail hypothalamo-hypophysial system. We therefore designated this RFamide peptide gonadotropin inhibitory hormone (GnIH). In the present study we characterized the GnIH cDNA from the quail brain by a combination of 3' and 5' rapid amplification of cDNA ends ('RACE'). The deduced GnIH precursor consisted of 173 amino acid residues, encoding one GnIH and two putative gene-related peptide (GnIH-RP-1 and GnIH-RP-2) sequences that included -LPXRF (X=L or Q) at their C-termini. All these peptide sequences were flanked by a glycine C-terminal amidation signal and a single basic amino acid on each end as an endoproteolytic site. Southern blotting analysis of reverse-transcriptase-mediated PCR products demonstrated a specific expression of the gene encoding GnIH in the diencephalon including the hypothalamus. Furthermore, mass spectrometric analyses detected the mass numbers for matured GnIH and GnIH-RP-2, revealing that both peptides are produced from the precursor in the diencephalon as an endogenous ligand. Taken together, these results lead to the conclusion that GnIH is a hypothalamic factor responsible for the negative regulation of gonadotropin secretion. Furthermore, the presence of a novel RFamide peptide family containing a C-terminal -LPXRF-NH(2) sequence has been revealed.

The sympathetic baroreflex is an important feedback system in stabilization of arterial pressure. This system can be decomposed into the controlling element (mechanoneural arc) and the controlled element (neuromechanical arc). We hypothesized that the intersection of the two operational curves representing their respective functions on an equilibrium diagram should define the operating point of the arterial baroreflex. Both carotid sinuses were isolated in 16 halothane-anesthetized rats. The vagi and aortic depressor nerves were cut bilaterally. Carotid sinus pressure (CSP) was sequentially altered in 10-mmHg increments from 80 to 160 mmHg while sympathetic efferent nerve activity (SNA) and systemic arterial pressure (SAP) were recorded simultaneously under various hemorrhagic conditions. The mechanoneural arc was characterized by the response of SNA to CSP and the neuromechanical arc by the response of SAP to SNA. We parametrically analyzed the relationship between input and output for each arc using a four-parameter logistic equation model. In baseline states, the two arcs intersected each other at the point at which the instantaneous gain of each arc attained its maximum. Severe hemorrhage lowered the gain and offset of the neuromechanical arc and moved the operating point, whereas the mechanoneural arc remained unchanged. The operating points measured under the closed-loop conditions were indistinguishable from those estimated from the intersections of the two arc curves on the equilibrium diagram. The average root mean square errors of estimate for arterial pressure and SNA were 2 and 3%, respectively. Such an analytic approach could explain a mechanism for the determination of the operating point of the sympathetic baroreflex system and thus helps us integratively understand its function.