Respiratory effects of stimulation of intercostal muscles and saphenous nerve in kittens

Effects of intercostal muscle stimulation were studied in 2- to 7-day-old kittens under ketamine-acepromazine anesthesia. Animals were vagotomized, paralyzed, and artificially ventilated. Stimuli applied during inspiration (TI) inhibited this phase. Stimulus strength necessary for TI inhibition decreased with time. However, an all-or-nothing effect was not always observed. Stimulation during expiration (TE) prolonged this phase. The responsiveness increased with increasing stimulus delay. The effects of intercostal muscle stimulation were compared with those recorded during saphenous nerve stimulation. Stimulation during TI prolonged this phase. Phrenic activity increased after a short-lasting decrease in the on-going activity. Stimulation during the first 50% of TE had variable effects, whereas stimulation with longer delay shortened this phase. Our results indicated that the pattern of breathing in newborns can be affected by both intercostal muscle and other somatic efferents. However, the mechanisms controlling respiratory timing may differ in newborns and in adults. Different effects of respiratory muscle and saphenous nerve stimulation suggest different transmitters involved or different sites of interaction of these inputs with the medullary respiratory rhythm generator.     

Synchronization of respiratory frequency by somatic afferent stimulation.

In cats anesthetized with chloralose-urethan, vagotomized, paralyzed, and artifically ventilated, superficial radial (cutaneous) and hamstring (muscle) nerve afferents were stimulated while phrenic nerve electrical activity was recorded. The results obtained with both types of nerves were similar. Stimulation in mid and late expiration advanced the onset of the next inspiration, shortening its duration. Stimulation in early inspiration advanced, while that in late inspiration delayed, the onset of the next expiration. These effects were often accompanied by changes in phrenic motoneuron firing patterns (earlier recruitment, increased discharge frequency, increased slope of integrated phrenic neurogram). Repetitive somatic afferent stimulation produced sustained increases in respiratory frequency in all cats and in half of them entrainment of respiratory frequency to the frequency of stimulation occurred at ratios such as 4:3, 4:5, 1:2, 1:3, 1:4, and 1:7. The lowest stimulus intensity required for evoking these phase shifts was between 5 and 10T (threshold of most excitable fibers) for muscle afferents and between 1 and 2T for cutaneous afferents. These results demonstrate the existence of a reflex mechanism capable of locking respiratory frequency to that of a periodic somatic afferent input. They also provide an experimental basis for the hypothesis that reflexes are resposible for the observed locking between step or pedal frequency and respiratory rate during exercise in man.     

Retinol enhances differentiation of the gastric parietal cell lineage in developing rabbits.

In the gastric glands, parietal cells are the targets for anti-ulcer drugs because they contain the proton pump or HK-ATPase responsible for acid secretion. Little is known about factors influencing developmental expression and activity of HK-ATPase. In this study, the parietal cell lineage was investigated in rabbits at post-natal days 0 (P0) to P60 by using morphological and biochemical methods. Immunohistochemical and ultrastructural studies show that the HK-ATPase-expressing cells that appear at P0 and P3 are pre-parietal cells. However, terminally differentiated, mature parietal cells make their appearance at P7. These data correlate with the activity of HK-ATPase, measured as K(+)-dependent hydrolysis of p-nitrophenyl phosphate. Three-day-retinol treatment of P3-P30 rabbits induced an increase in the (i) production of parietal cells, (ii) intensity of the HK-ATPase immunostaining per cell, (iii) activity of HK-ATPase and (iv) amount of HK-ATPase protein measured by Western blotting. In conclusion, retinol upregulates the development of HK-ATPase in rabbits, perhaps due to precocious acceleration of the differentiation program of parietal cell lineage.     

Respiratory effects of electric stimulation of pancreatic afferents in lightly anesthetized cats]

Electrical stimulation of the pancreatic anterior part produces a respiratory arrest followed by a short polypnea. In some cases (20%) the same effects are obtained by electrical stimulation of the afferent nerves. The afferent fibres involved in this phenomena are situated in the great splanchnic nerves.     

Frequency modulation of theta bursts of the septal neurons in the removal of ascending afferent effects in rabbits

Medial septal-diagonal band (MS-DB) units were examined extracellularly in chronic rabbits under two experimental conditions: 1) in an intact septum, under anaesthetic doses of pentobarbital (40 mg/kg, i.v.); 2) in a basally undercut septum of unanaesthetized rabbits. The background rhythmic burst activity was undistinguishable in both states. Low-frequency electric stimulation of afferent inputs (MFB, CA1, LS) led to entrainment of the theta-cycles. The upper limit of following was almost normal in the undercut septum, but was strongly reduced under pentobarbital. In units with the driving "by pause", the duration of the initial silent period under pentobarbital was increased almost twofold but in the basally undercut septum it was the same as in the normal state. Some MS-DB units with weak or absent theta-modulation reacted to stimulation by stimulus-locked single spike discharges which followed up to high frequencies in both conditions.