PubMed · 8457067
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J C Drummond. 1993. Do barbiturates really protect the brain?. https://pubmed.ncbi.nlm.nih.gov/8457067/
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The main functions of the larynx are protection of the airways, respiration, and vocalization. Previous studies have suggested a link between the mechanisms controlling vocalization and afferent feedback from the larynx. We inquired whether stimulation of the laryngeal afferents that run in the internal branch of the superior laryngeal nerve (ISLN) activates neurons of the periaqueductal gray (PAG), a midbrain region implicated in vocalization. We counted the number of neurons expressing Fos, the protein product of the immediate early gene c-fos, in the PAG. The counts were done both in experimental cats after electrical stimulation of the ISLN and nonstimulated controls. We also investigated the possible presence of nitric oxide synthase, an enzyme that synthesizes nitric oxide, in PAG neurons that respond to laryngeal afferent stimulation by double labeling for reduced nicotinamide adenine dinucleotide phosphate (NADPH)-diaphorase and Fos. Fos expression was significantly greater (P < or = 0.00714) in the lateral and dorsolateral regions of the PAG in the experimental group than in the controls. The Fos-immunoreactive neurons did not contain NADPH-diaphorase, a marker for nitric oxide synthase. Our study suggests that laryngeal afferent stimulation activates neurons in discrete longitudinal columns of the PAG including the regions that have previously been shown to be involved in vocalization, and that these neurons do not contain nitric oxide synthase.
UNLABELLED: The hypothesis that the lower midbrain, specifically in and around the retrorubral field (RRF) and/or rubrospinal tract (rs), contains a tonic inhibitory mechanism on non-shivering thermogenesis (NST) was examined in urethane-anesthetized rats. It has been proposed that removal of the tonic inhibitory mechanism in the lower midbrain causes body temperature increase through disinhibition-induced activation of the central sympathetic nervous system. The present experiments were carried out to examine whether and where the proposed midbrain region contains cell bodies that tonically inhibit the NST, and if so, whether they receive any influence from the hypothalamus. Male Wistar rats were anesthetized with urethane (1. 0-1.2 g/kg, i.p.), and various agents were microinjected into the RRF and rs areas of one side before and after knife-cut in the other side of the lower midbrain or isolation of the hypothalamus from the midbrain. Changes in interscapular brown adipose tissue (IBAT), rectum, and tail skin temperatures were monitored. RESULTS: (1) unilateral midbrain procaine increased IBAT and rectal temperatures only after un-injected side of the midbrain had been pre-transected. (2) Effective midbrain sites for procaine to increase IBAT and rectal temperatures was laterally extended. (3) Tetrodotoxin microinjected into the midbrain site where procaine increased IBAT and rectal temperatures also raised both temperatures. (4) l-glutamate decreased IBAT and rectal temperatures when microinjected into one of the most inner midbrain area of procaine-sensitive sites without affecting tail skin temperature. (5) Isolation of the hypothalamus from the lower midbrain did not affect midbrain procaine-induced IBAT and rectal temperature increases. These results suggest that neurons that tonically inhibit the NST are located in the area close to the midline adjacent to the RRF and rs, and that the integrity of the neurons to tonically inhibit the NST is not affected by disconnecting the hypothalamus from the midbrain.
Phenolic compounds are widely used in therapeutic, environmental, and industrial applications. The present work seeks to define the hepatic disposition of 11 phenolic compounds with varying lipophilicities and molecular weights. The hepatic disposition kinetics were studied in a once-through in situ rat liver perfusion preparation in order to avoid extra-hepatic metabolism and recirculation effects. The phenols were administered using the impulse-response technique and the time course of hepatic venous effluent concentration was examined by moments and a two-compartment dispersion model. While the extraction of the phenolic compounds was relatively independent of lipophilicity, the estimated permeability-surface area (PS) product for influx of solutes into the hepatocytes could be related to the compounds' octanol-buffer partition coefficients (log Papp). This log PS-logPapp relationship was consistent with that reported earlier for another series of solutes with a wide range of lipophilicity. The metabolites produced from each of the phenolic compounds used in this study had mean transit times similar to those of their corresponding parent phenols, suggesting that the metabolites were not trapped in the liver as a consequence of their higher polarity. It is concluded that the strong solute lipophilicity-toxicity and lipophilicity-skin penetration relationships often seen for aqueous solutions of phenols are not evident for the hepatic extraction of these compounds. Such a conclusion is consistent with the hepatic extraction of phenolic compounds being mainly determined by a blood flow limitation in delivery of the phenol to the liver, rather than the intrinsic liver metabolic enzyme activities at the doses injected.