In anesthetized, spontaneously breathing rats, microinjections of selective agonists of neuropeptide Y (NPY) receptor subtypes were made into the medial region of the caudal nucleus of the solitary tract (NTS) at the level of the area postrema. This region of the rat NTS exhibits very high densities of NPY binding sites. Microinjections of the long C-terminal NPY fragment, NPY(13-36), a selective agonist at Y2 receptors, into the caudal NTS elicited pronounced, dose-related reductions in blood pressure and respiratory minute volume. Moreover, the specific pattern of cardiorespiratory responses elicited by NPY(13-36) was remarkably similar, over approximately the same dosage range, with the cardiorespiratory response pattern elicited by intact NPY. In contrast to the potent NTS-mediated responses evoked by NPY(13-36), similar microinjections conducted with either NPY(26-36), an inactive C-terminal NPY fragment, or [Leu31,Pro34]NPY, a NPY analog with specific agonist properties at Y1 receptors, into the same caudal NTS sites did not appreciably affect cardiorespiratory parameters even at 10-20-fold higher dosages. The present results with selective agonists for NPY receptor subtypes suggest that the depressor responses and reductions in minute volume elicited by microinjections of intact NPY and NPY(13-36) were mediated by Y2 receptors in the caudal NTS, likely distributed at presynaptic sites in the medial region of the subpostremal NTS.

Animals↗

PubMedDate not supplied

Peptides from pigeon cerebrum: two-dimensional fingerprinting and amino acid analysis.

The number and heterogeneity of endogenous peptides from pigeon cerebrum were studied by two-dimensional peptide fingerprinting. A highly consistent pattern of 8-9 peptides in the 1000-5000 molecular weight range was obtained from each cerebral sample. Amino acid analysis of the peptide material indicated that 30% of the identified residues were dicarboxylic amino acids and 30% were alphatic amino acids. There was no evidence for the presence of arginine or half-cystine in the peptide fraction.

Amino Acids↗

PubMedDate not supplied

Analysis of peptides from pigeon cerebrum: a comparison of sacrifice methods.

Peptides were extracted and fractionated from pigeon cerebrum and analyzed by thin-layer chromatography, polyacrylamide disc gel electrophoresis, and amino acid analysis. A highly consistent pattern of peptides in the 700-5000 molecular weight range was obtained from each cerebral sample. A comparison was also made between cerebral peptide patterns obtained from animals sacrificed by decapitation with those from animals sacrificed by microwave irradiation. Amino acid analysis of the peptide fraction from microwaved and decapitated animals revealed slight differences in the amount and incidence of various amino acids. These differences may be due to post-mortem proteolysis in the cerebra of decapitated pigeons prior to homogenization and freezing.

Amino Acids↗

PubMedDate not supplied

A central role for adenosine in the hypotension elicited by hypoxia in anesthetized rats.

Brief inhalation of an oxygen-deficient (5%) gas mixture evoked a rapidly developing, profound hypotension in anesthetized rats. Recovery upon reoxygenation was also rapid. A potential involvement of adenosine in the genesis of this hypotension was evaluated with various peripherally administered adenosine antagonists. Caffeine (10 mg/kg), which readily crosses the blood-brain barrier, significantly attenuated the hypoxia-evoked hypotension. 8-p-Sulphophenyltheophylline and xanthine amine congener, which do not readily penetrate the blood-brain barrier, had little effect on the magnitude of the hypotension. The data suggests that hypoxia-elicited hypotension in anesthetized rats results from the activation of central adenosine receptors.

Adenosine↗

PubMedDate not supplied

Cardiorespiratory responses following electrical stimulation of caudal sites in the rat medulla.

A limited occipital craniotomy was conducted on urethane-anesthetized rats to expose the caudal medulla in the region of the obex. Discrete bipolar electrical stimulation was administered at sites in the dorsal medulla of spontaneously breathing rats in the vicinity of the caudal nucleus tractus solitarius (NTS) and adjacent reticular formation. Cardiorespiratory responses were recorded during microstimulation at three separate stimulating frequencies to examine the functional interaction of cardiovascular and respiratory-related neuronal elements in the NTS. Microstimulation was conducted at sites in the dorsal and medial regions of the NTS beginning at the level of the area postrema and extending posteriorly through the rostrocaudal course of the NTS; microstimulation was also conducted at midline sites in the commissural region of the NTS and the ventral and ventrolateral regions of the caudal NTS. Microstimulation of loci in the reticular formation adjacent to these NTS sites did not elicit any cardiorespiratory responses whereas stimulation of individual NTS regions elicited specific patterns of cardiorespiratory responses. Specifically, microstimulation of the dorsal and medial NTS at the level of the area postrema elicited pressor responses associated with apneic/hypopneic responses whereas stimulation of midline sites in the commissural region, dorsomedial sites caudal to the area postrema and the ventral and ventrolateral areas of the caudal regions of the NTS elicited depressor responses associated with bradycardic and apneic/hypopneic responses. The most profound respiratory effects (i.e., apnea) and heart rate responses (i.e., bradycardia) were seen following stimulation of the ventral and ventrolateral regions of the caudal NTS. These findings support the notion that the caudal NTS is a major site for coordinating cardiorespiratory afferent information in the rat and it is also apparent from this study that specific regions of the caudal NTS demonstrate a functional coexistence of cardiovascular and respiratory-related neurons. Finally, the results from this study showing the regional specificity and frequency-dependent characteristics of cardiorespiratory response patterns elicited by microstimulation suggest that the local microcircuitry and intrinsic neuronal networks in the more caudal regions of the rat NTS are more complex and heterogeneous than hitherto revealed.

Animals↗