Contribution of the vertebral artery to cerebral circulation in the rat snake Elaphe obsoleta

Blood supplying the brain in vertebrates is carried primarily by the carotid vasculature. In most mammals, cerebral blood flow is supplemented by the vertebral arteries, which anastomose with the carotids at the base of the brain. In other tetrapods, cerebral blood is generally believed to be supplied exclusively by the carotid vasculature, and the vertebral arteries are usually described as disappearing into the dorsal musculature between the heart and head. There have been several reports of a vertebral artery connection with the cephalic vasculature in snakes. We measured regional blood flows using fluorescently labeled microspheres and demonstrated that the vertebral artery contributes a small but significant fraction of cerebral blood flow (∼13% of total) in the rat snake Elaphe obsoleta. Vascular casts of the anterior vessels revealed that the vertebral artery connection is indirect, through multiple anastomoses with the inferior spinal artery, which connects with the carotid vasculature near the base of the skull. Using digital subtraction angiography, fluoroscopy, and direct observations of flow in isolated vessels, we confirmed that blood in the inferior spinal artery flows craniad from a point anterior to the vertebral artery connections. Such collateral blood supply could potentially contribute to the maintenance of cerebral circulation during circumstances when craniad blood flow is compromised, e.g., during the gravitational stress of climbing. J. Morphol. 238:39–51, 1998. © 1998 Wiley-Liss, Inc.     

Adrenergic innervation of the large arteries and veins of the semiarboreal rat snake Elaphe obsoleta

Fluorescence histochemistry was used to study the adrenergic innervation of the large arteries and veins at six points along the body of the semiarboreal rat snake Elaphe obsoleta. Apart from the vessels adjacent to the heart, there was a marked contrast in the density of adrenergic innervation of anterior and posterior systemic arteries and veins. The anterior arteries and veins have little adrenergic innervation in contrast to the extremely dense innervation of the arteries and veins posterior to the heart. The innervation pattern is consistent with known physiological adjustments to gravity and suggests a mechanism for regulating dependent blood flow via sympathetic nerves. In comparison to the posterior systemic arteries, parallel segments of pulmonary artery taken from the same body position of Elaphe contained a much sparser innervation by adrenergic nerves. The sparser innervation can be correlated with less gravitational disturbance in the pulmonary artery, which is relatively short in this and in other arboreal snakes.     

Hemodynamic adjustments to head-up posture in the partly arboreal snake, Elaphe obsoleta

Radioactively-labeled microspheres were used to quantify adjustments of regional blood flows in 15 snakes (Elaphe obsoleta) subjected to 45 degrees head-up tilt. Heart rate and peripheral vascular resistance increased during tilt to compensate for the passive drop of pressure at the head. Two snakes failed to regulate blood pressure, but in 13 others arterial pressure increased at midbody (where passive changes in pressure are unexpected due to tilt alone) and arterial pressure at the head averaged 67% of the pretilt value. Tissue blood flow was reduced significantly in visceral organs, posterior skin and posterior skeletal muscle, but was maintained at pretilt levels in brain, heart, lung and anterior tissues. Ventricular systemic output averaged 24 ml/min X kg in horizontal posture and 9.4 ml/min X kg during tilt. Comparable values for pulmonary output were 4 and 6.5 ml/min X kg. Patterns of intraventricular shunting of blood acted to maintain pulmonary flow during tilt. A large right-to-left shunt (mean 76%) was present in horizontal snakes, but the shunted fraction declined during tilt (mean 54%). Left-to-right shunt increased during tilt from 7% to 14%.     

Neural regulation of the pulmonary vasculature in a semi-arboreal snake,Elaphe obsoleta

Summary The innervation of the pulmonary vasculature of the semi-arboreal rat snake,Elaphe obsoleta, was examined with glyoxylic acid-induced catecholamine histochemistry, peptide immunohistochemistry, and in vitro perfusion of the pulmonary vasculature. An adrenergic innervation was present on the pulmonary artery, the smaller pulmonary arteries, the veins draining the lung, and the main pulmonary vein. Vasoactive intestinal polypeptide-like immunoreactive axons were observed on the pulmonary artery and vein, small arteries, and occasionally small veins within the lung parenchyma. A dense plexus of substance P-like immunoreactive (SP-LI) axons was observed on the distal extrinsic pulmonary artery. SP-LI axons were found on the more distal arteries within the lung parenchyma, but not on the veins. The distribution of calcitonin gene-related peptide- and SP-LI axons was similar suggesting that the axons are sensory nerves. In the perfused pulmonary vasculature, vagal stimulation caused a predominant vasoconstriction which was abolished by atropine indicating it was cholinergic in nature. A post-stimulus vasodilatation was abolished by bretylium and propranolol indicating it was adrenergic in nature. The responses to nerve stimulation were located in both the extrinsic and intrinsic pulmonary vasculature. No evidence for non-adrenergic, noncholinergic transmission to the vascular smooth muscle was found. The extensive, functional innervation of the main pulmonary artery, as well as the more distal vasculature within the lung, may reflect adaptation to cardiovascular problems imposed by an elongated body and arboreal habits.Abbreviations VIP vasoactive intestinal polypeptide - VIP-LI vasoactive intestinal polypeptide-like immunoreactive - SP substance P - SP-LI substance P-like immunoreactive - SOM somatostatin - SOM-LI somatostatin-like immunoreactive - CGRP calcitonin gene-related peptide - CGRP-LI calcitonin gene-related peptide-like immunoreactive - NANC non-adrenergic noncholinergic - PI perfusion inflow     

Muscular mechanisms of snake locomotion: an electromyographic study of lateral undulation of the Florida banded water snake (Nerodia fasciata) and the yellow rat snake (Elaphe obsoleta)

Electromyography and cinematography were used to determine the activity of epaxial muscles of colubrid snakes during terrestrial and aquatic lateral undulatory locomotion. In both types of lateral undulation, at a given longitudinal position, segments of three muscles (Mm. semispinalis-spinalis, longissimus dorsi, and iliocostalis) usually show synchronous activity. Muscle activity propagates posteriorly and generally is unilateral. With each muscle, large numbers of adjacent segments (30 to 100) show simultaneous activity. Terrestrial and aquatic undulation differ in two major respects. (1) During terrestrial undulation, muscle activity in a particular region begins when that portion of the body has reached maximal convex flexion and ends when it is maximally concave; this phase relation is uniform along the entire snake. During swimming, however, muscle activity passes posteriorly faster than the wave of vertebral flexion, causing the relation of muscle activity to flexion to change along the length of the snake. (2) In the terrestrial mode, the block of active muscle segments remains approximately constant in size as it passes down the snake, whereas during swimming the number of adjacent active muscle segments increases posteriorly. Despite the fact that Elaphe obsoleta has nearly twice as many body vertebrate as Nerodia fasciata (240 vs. 125), the only difference observed in the swimming of these two species is that a larger number of adjacent muscle segments is simultaneously active in comparable regions of Elaphe obsoleta than in Nerodia fasciata.     

The distribution and colocalization of neuropeptides in perivascular nerves innervating the large arteries and veins of the snake,Elaphe obsoleta

Summary Single- and dual-labelling immunohistochemistry were used to determine the distribution and coexistence of neuropeptides in perivascular nerves of the large arteries and veins of the snake, Elaphe obsoleta, using antibodies for vasoactive intestinal polypeptide, substance P, calcitonin gene-related peptide, neuropeptide Y, galanin, somatostatin, and leu-enkephalin. Blood vessels were sampled from four regions along the body of the snake: region 1, arteries and veins anterior to the heart; region 2, central vasculature 5 cm anterior and 10 cm posterior to the heart; region 3, arteries and veins in a 30-cm region posterior to the liver; and region 4, dorsal aorta and renal arteries, renal and intestinal veins, 5–30 cm cephalad of the vent. A moderate to dense distribution of vasoactive intestinal polypeptide-like immunoreactive fibres was found in most arteries and veins of regions 1–3, but fibres were absent from the vessels of region 4. The majority of vasoactive intestinal polypeptide-like immunoreactive fibres contained colocalized substance P-like immunoreactivity, and these fibres were unaffected by either capsaicin or 6-hydroxydopamine (6-OHDA) pretreatment. In the anterior section of the snake, the vagal trunks contained many cell bodies with colocalized vasoactive intestinal polypeptide and substance P-like immunoreactivity. It is suggested that the vasoactive intestinal polypeptide/substance P-like immunoreactive cell bodies and fibres are parasympathetic postganglionic nerves. Neuropeptide Y-like immunoreactive fibres were observed in all arteries and veins, being most dense in regions 3 and 4. The majority of these fibres also contained colocalized galanin-like immunoreactivity, and were absent in tissues from 6-OHDA pretreated snakes, suggesting that neuropeptide Y and galanin are colocalized in adrenergic nerves. A small number of neuropeptide Y-like immunoreactive fibres contained vasoactive intestinal polypeptide but not galanin, and were unaffected by 6-OHDA treatment. All calcitonin gene-related peptide-like immunoreactive fibres contained colocalized substance P-like immunoreactivity, and these fibres were observed in all vessels, being particularly dense in the carotid artery and jugular veins. All calcitonin gene-related peptide/substance P-like immunoreactive fibres appeared damaged after capsaicin treatment suggesting they represent fibres from afferent sensory neurons. A sparse plexus of somatostatin-like immunoreactive fibres was observed in the vessels only from region 4. No enkephalin-like immunoreactive fibres were found in any blood vessels from any region. This study provides morphological evidence to suggest that there is considerable functional specialization within the components of the rat snake peripheral autonomic system controlling the circulation, in particular the regulation of venous capacitance.     

The cranial development of Elaphe obsoleta (Ophidia,colubridae)

The kinetic skull of snakes is a highly specialized structure that has allowed these limbless organisms to exploit a wide variety of habitats. Here we analyze the development of the cranium in the colubrid snake Elaphe obsoleta quadrivittata based on two sets of embryos raised under controlled conditions and preserved at regular intervals during embryogenesis. Emphasis is on the interactions between dermal and endochondral ossification in the basicranium and in the posterior orbitotemporal region. In Elaphe, the laterosphenoid initially develops as an ascending process of the basal plate and is a combination of membrane and cartilage bone. The maxilla shows a peculiar pattern of differentiation from several centers of ossification.     

Temperature tolerance of the mosquitofish, Gambmia affinis (Baird and Girard)

The capacity of a warm-adapted population of mosquito fish ( Gambusia affinis ) from the Sonoran Desert and a cold-adapted population from northern Utah to adjust to changing environmental temperatures has been described in terms of four criteria: (1) critical thermal maxima, (2) resistance times at high, lethal temperatures, (3) upper incipient lethal temperatures, and (4) lower lethal temperatures. Non-genetic scope for adaptation as related to changes in the thermal history of the individual and expressed in terms of the tolerance domain was identical for both populations. Genetic differences in adaptive capacity were apparent. The cold-adapted population was less tolerant of heat and more tolerant of cold as would be anticipated.     

Inbreeding depression in the convict cichlid, Cichlasoma nigrofasciatum (Baird and Girard)

Convict cichlids, Cichlasoma nigrofasciatum , inbred for four and five generations exhibited moderate and severe morphological deformities. Deformed fishes were characterized by a more vertically sloping forehead, irregular jaw, hyoid, opercula and fin structure, reduced growth and irregular swimming behaviour. Inbred fish (F₄, F₅) did not differ from F₁s in their age of maturation or the average size of their first broods. Brood survival was 18.7% in F₅ inbred fish, compared to 75.5% in F₁s.     

Salinity tolerance of the mosquito fish, Gambusia affinis (Baird and Girard)

Experiments were conducted to determine the adaptability of mosquito fish to various salt concentrations. Mosquito fish, Gambusia affinis , (total length (T.L.) 27–37 mm) were subjected to abrupt and gradual changes from fresh water to various salinities (S). Low mortality (10%) occurred when the fish were transferred from fresh water (S = 0·5‰) to 50% sea water (S = 19·5‰ Through gradual adaptation 65·0% of the fish were able to tolerate 100% sea water for 7 days. After a 7 -day stay in sea water, fish were readapted to fresh water during a 3-h period. The results indicate that they were well able to tolerate the abrupt change. Through a gradual adaptation fish were also able to tolerate salinities ranging from 39·0‰ (100% sea water) to 58·8‰     

Size-biased predation by the gila topminnow poeciliopsis occidentalis (Baird and Girard)

The objective of this study is to document under both field and laboratory conditions the phenomenon of size-biased feeding by the Gila topminnow, Poeciliopsis occidentalis, and to shed light on the mechanisms responsible for this process. Adult female Gila topminnows feed in Monkey Spring, Santa Cruz County, Arizona, on a variety of food items, but Hyalella azteca is an important element of its invertebrate diet. The size of the amphipods ingested by female topminnows is a function of the size of the fish, with larger fish taking larger prey. There is also a strong preference for topminnows to select large amphipods from within the size limits imposed by the width of the mouth.The correlation between fish size and prey size was also seen in the laboratory, utilizing Daphnia similis and food pellets as prey. The tendency to select large prey from a range of available sizes was prominent with both Daphnia and pellets. The feeding period in the laboratory is characterized by two distinct phases. During the first phase, feeding is rapid and nonselective. As the feeding progresses, the rate of feeding drops dramatically and selectivity increases.More complex laboratory feeding experiments gave equivocal results. When fish were presented pellets of two sizes at different densities and at different ratios of small to large, size biased feeding was not clearly evident. Both predator and prey densities, agonistic behavior, and reaction distance should be explored more thoroughly as next steps in attempts to mimic feeding behavior in nature.Extracted from a Ph. D. thesis written by the junior author     

Scanning electron microscopy of the cleft of the rat pituitary

Summary Scanning electron microscopy of the lining of the pituitary cleft was carried out in normal, lactating, castrated, adrenalectomized, and cyproterone-treated adult rats. Four cell types could be differentiated in the posterior wall in control and experimental animals: (1) cells with a smooth surface, (2) cells with microvilli located at the cellular borders, (3) ciliated cells, and (4) cells with evenly distributed microvilli. The anterior wall showed mainly cells with few microvilli located at their margins, and clusters of ciliated cells. In normal, and more frequently in experimental animals, the anterior wall showed shriveled cells, and variously sized cavities. Colloid appeared either as a network of finely granular material or as compact bodies adhering to the epithelial surface. These observations suggest that a compact component of the colloid is derived at least in part from degraded cells.Fellow of the Consejo Nacional de Investigaciones Cientificas y Técnicas (CONICET), Argentina. The author owes many thanks to Professor I. Nouzeillez and Dr. J.C. Cavicchia for their assistance in translating this paper     

Scanning electron microscopy of the zonular fibers in the rat eye

Summary The three-dimensional arrangement of the zonular fibers of Zinn and their ultrastructure was studied with the aid of scanning and transmission electron microscopy.Most of the thicker zonular fibers are arranged in straight bundles between the ciliary body and the lens, while the thinner fibers form a complex three-dimensional network interconnecting all the zonular fibers. These do originate from the limiting membrane covering the ciliary body. The zonular fibers are subdivided close to lens and form a complicated network on the surface of the lens capsule, i. e. the zonular lamella. The latter consists of a dense network of fibers and is from a structural point of view closely related to the zonular fibers and not to the lens capsule.The zonular fibers are continuous with those in the vitreous body close to the ciliary body but never in the lenticular two thirds of the zonular fibers or in the retrolental area.The ground substance is possible to demonstrate in freeze-dried specimens by scanning electron microscopy. It appeared granular or amorphous and coated the zonular fibers. It does not form membranes or fill all available space in contrast to its properties in the vitreous body. The many structural similarities between the zonular fibers and the vitreous body indicate perhaps a common origin.Supported by grants from Magnus Bergwalls Stiftelse and the Swedish Medical Research Council (B70-12 X -2543-02, B71-12 X -2543-03).