Steven F. Perry

Two regions in the isolated brainstem of the frog that modulate respiratory-related activity.

Using microinjection techniques, we have explored the isolated, complete midline sectioned brainstem of the frog (Rana catesbeiana) to identify regions that influence the endogenous respiratory-related motor activity. Ten-nanoliter injections of lidocaine (1%), GABA (100 mM) and glutamate (10 and 100 mM) into discrete regions of the rostral and the caudal brainstem produced different effects on the phasic neural discharge. In the rostral site lidocaine, GABA and glutamate injections altered neural burst frequency with little or no effect on burst amplitude. In the caudal site, responses to lidocaine and GABA injections consisted primarily of decreases in neural burst amplitude, often, but not always associated with minor decreases in burst frequency. In this same region, the response to glutamate was characterized by a temporary interruption of the rhythmic neural burst activity. The largest responses to substance injection in both regions were obtained at sites ranging between 200 and 500 μm from the ventral surface, in the ventral medullary reticular formation. The results reveal the existence of two areas in the frog brainstem that influence respiratory motor output, one related to the respiratory burst frequency and the other related to the amplitude of the motor output.

Fictive respiratory rhythm in the isolated brainstem of frogs

Spontaneous rhythmically bursting activity was recorded from the trigeminal, vagal and hypoglossal nerve roots of the isolated brainstem from the frogsRana catesbeiana andRana pipiens superfused with a bicarbonate-free HEPES-buffer solution. Burst frequency, burst duration and the activity profile of the spontaneous neural discharges in vitro resembled those of a less radical preparation, the decerebrate, fictively breathing frog. After complete midsagittal section, each half of the isolated brainstem generated its own rhythmic neural activity which resembled that of the intact isolated brainstem. The spontaneous activity generated within each half of the brainstem is probably coordinated by decussating axons or by groups of neurons located along the midline of the brainstem. Our results suggest that these coordinating entities extend the length of the brainstem (in a rostro-caudal dimension) and the degree of contact rather than the location of the contact between the two halves of the brainstem determines the synchronization of the right and left halves. Burst frequency of both the intact and hemisected brainstem preparation was decreased by alkaline challenge and increased by acid challenge. We conclude that this endogeneous rhythmic activity represents the efferent motor output underlying lung ventilation in these animals.

Morphometric Study of the Role of Pulmonary Arterial Flow in Fetal Lung Growth in Sheep

ABSTRACT: Pulmonary hypoplasia has been associated with absent or hypoplastic pulmonary artery in four cases in humans. Despite these reports, the effects of decreased pulmonary arterial flow on fetal lung growth have not been adequately studied. This study defines the effects of left pulmonary artery (LPA) ligation on fetal lung growth in sheep by comparing morphometrically determined pulmonary volumes from LPA-ligated, sham-operated, and unoperated control fetuses. LPA ligation (n = 5) or sham operation (n = 4) was performed at 105- to 114-d gestation. At 140-d gestation these fetuses were delivered and the lungs were intratracheally fixed for light microscopy. At 112 d (n = 4) and at 140 d (n = 4), unoperated control fetuses were similarly delivered. Absolute pulmonary volumes were then measured using standard stereologic methods. Normal growth of the left lung from 112 to 140 d resulted in significant increases in wet and dry wt, displacement volume, and volumes of future airspace and capillary contents. LPA ligation caused significant decreases in left lung wet and dry wt, displacement volume, and in absolute volumes of fine nonparenchyma, future airspace, parenchymal tissue, and capillary contents compared to sham-operated and 140-d controls. Parenchymal tissue volume was also less than in 112-d controls. In addition, lung wt, displacement volume, and future airspace volume were significantly decreased in sham-operated fetuses compared to 140-d controls. The effects of LPA ligation on bronchial collateral circulation and factors known to affect lung growth (i.e. lung fluid volume) remain to be determined. Clearly, during the canalicular and alveolar stage of fetal lung development, pulmonary arterial flow is necessary for normal lung growth.

BRONCHIAL CASTS OF HUMAN LUNGS USING NEGATIVE PRESSURE INJECTION

Negative-pressure casting techniques have been used for obtaining silicone rubber casts of the avian respiratory system, which contains minute air capillaries, noncompressible hollow bones, and highly flexible air sacs. The possibilities of this technique for the study of human airway diseases, which present technical difficulties similar to those of avian lungs, are investigated here. Left lungs from patients with various obstructive lung diseases or with normal lungs were fixed at autopsy under 25 cm H2O airway pressure with 2.5% phosphate-buffered glutaraldehyde. Cannulated, isolated lobes were placed in a vacuum chamber, and Dow Corning 734 RTV silicone elastomer, diluted with 10% low viscosity silicone oil, was introduced into the airways at -10 kPa. Following complete polymerization, the tissue was microdissected to reveal the lung cast in situ, and histological sections were obtained for correlative studies. The tissue was then macerated in 5.25% sodium hypochlorite. The total time from fixation to finished cast was 3-4 days. Linear shrinkage of the elastomer was less than 1% in glutaraldehyde or water and between 1 and 2% in bleach. The negative-pressure injection technique enabled complete and accurate filling of airways to the alveolar duct level at physiological pressures and provided good delineation of blind cavities such as obstructed airways or ectatic mucous gland ducts. The technique proved useful for the study of obstructive lung disease and should also prove useful for modelling aerosol deposition in diseased lungs.

Strychnine eliminates reciprocation and augmentation of respiratory bursts of the in vitro frog brainstem

We have recorded rhythmic bursts of efferent action potentials from nerves of respiratory muscles in the frog (Rana pipiens), using a modified in vitro preparation, in which the brainstem lies in situ in the ventral half of the skull. The burst in the sternohyoid branch of the hypoglossal nerve (Hsh) was augmenting, and alternated with a relatively brief augmenting burst in the main branch of the hypoglossal nerve (Hm). The laryngeal branch of the vagus nerve (XI) displayed a biphasic burst, beginning before peak activity of Hsh and spanning the Hm burst. The spatio-temporal patterns of these bursts closely resemble those recorded from the same nerves in intact and in decerebrate frogs, indicating that the bursting rhythm of this in situ preparation constitutes fictive breathing. The nature of neurotransmission responsible for burst reciprocity and augmentation was investigated by applying the glycine receptor blocker, strychnine. Low levels of strychnine (1 and 5 M) increased the frequency of fictive breathing without changing the shape or timing of Hsh, Hm and XI bursts; at higher doses (10 and 20 M) the bursts in all nerves abruptly changed shape and timing to become synchronous and decrementing. The strychnine-induced changes were associated with the appearance of a prominent peak (10-20 Hz) on the spectral analysis of the nerve discharge, possibly indicating a fundamental change in neurogenesis of the respiratory pattern. We conclude that the burst augmentation and reciprocation discharge characteristics of fictive breathing in the frog require strychnine-sensitive inhibitory networks.

Morphometric diffusing capacity and functional anatomy of the book lungs in the spider Tegenaria spp. (Agelenidae)

The presence of both book lungs and a tracheal system in many spiders raises the question of the functional significance of this double respiratory system. The present physiological and morphometric study of the house spider (Tegenaria spp.) reveals that the diffusing capacity (Dto2) of the lungs alone suffices during rest and following exercise to meet measured rates of oxygen consumption (\documentclass{article}\pagestyle{empty}\begin{document}

Histological Structure of the Lungs of the Loggerhead Turtle, Caretta caretta, before and after Hatching

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Laryngeal Motor Control in Frogs: Role of Vagal and Laryngeal Feedback

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Which came first, the lung or the breath?

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The Airway Longitudinal Elastic Fiber Network and Mucosal Folding in Patients with Asthma

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