Dag Lundberg

Central respiratory stimulant effect by thyrotropin in releasing hormone in the rat

Anaesthetized male rats were injected intracerebroventricularly with the tripeptide, thyrotropin releasing hormone (TRH). Respiratory frequency (f), tidal volume (VT) and minute volume (VE) were measured in a closed whole body plethysmograph by a low pressure transducer connected to a Grass polygraph. TRH induced an approximately 50% increase in f, while VT was not altered. VE increased in the same proportion as f. Our results indicate that TRH neurons or TRH-sensitive receptors may be involved in the regulation of central respiratory activity.

Evidence for a dopamine interaction with the central respiratory control system in the rat

Respiratory activity was studied in adult rats during light halothane anesthesia. Dopamine agonists and antagonists were injected intracerebroventricularly (i.c.v.) or systemically. The respiratory parameters were recorded after exposure to O2 or to CO2 in O2. Apomorphine (i.c.v. 300 microgram) induced a biphasic response with an initial decrease in respiratory frequency (f) followed by pronounced tachypnoea after 5 min. The changes in tidal volume (VT) showed an inverse pattern. When apomorphine was administered into the fourth ventricle, only the later phase of the biphasic response was observed. Haloperidol (2 mg/kg i.p.) antagonized the apomorphine-induced response in contrast to domperidone (2 mg/kg i.v.), a dopamine receptor blocking agent which does not pass the blood brain barrier. Administered i.c.v., haloperidol as well as domperidone induced a decrease in f while VT was increased. The same response was observed after the presynaptic dopamine receptor agonist 3-PPP, 3-(3-hydroxyphenyl)-N-n-propylpiperidine. Hypercapnea was found to decrease the tachypnea in apomorphine-treated animals. Apomorphine also induced a decrease in blood pressure and heart rate, which was not reversed by haloperidol. It is concluded that there is a centrally located, tonically activated dopamine system involved in respiratory regulation. The predominant effect seems to be of a respiratory stimulating nature. The possible role of presynaptic and different postsynaptic dopamine receptor mechanisms is discussed.

GABA-ergic mechanisms in central respiratory control in the anesthetized rat

SummaryRats lightly anesthetized with halothane were injected intracerebroventricularly (i.c.v.) with gamma-aminobutyric acid (GABA) and the GABA-like drugs, muscimol, baclofen and gamma-hydroxybutyric acid (GHBA). Respiratory frequency (f) was reduced after GABA (1 mg) but increased after baclofen (0.5 μg), while muscimol (0.5 μg) or GHBA (1 mg) did not affect f. However, GHBA administered repeatedly caused a dose-dependent increase in f.Tidal volume (VT) decreased in a dose-dependent fashion after i.c.v. administration of all the drugs used. Taken together, these changes in f and VT resulted mainly in a dose-dependent decrease in minute volume

EFFECTS OF BRETYLIUM, RELATED QUATERNARY AMMONIUM COMPOUNDS, AND MITOSIS INHIBITORS ON THE DEGENERATION ACTIVITY IN THE SYMPATHETICALLY INNERVATED PERIORBITAL SMOOTH MUSCLE IN THE CONSCIOUS RAT

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Adrenergic Neuron Blockers and Transmitter Release after Sympathetic Denervation Studied in the Conscious Rat

after GABA and muscimol while after baclofen and GHBA

Effects of Colchicine, Vinblastine and Vincristine on Degeneration Transmitter Release after Sympathetic Denervation Studied in the Conscious Rat

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