A.B. Steffens

A method for frequent sampling of blood and continuous infusion of fluids in the rat without disturbing the animal

Abstract A method is described for the frequent simultaneous sampling of blood and continuous infusion of fluids in the normal wakeful rat.

The course of paraventricular hypothalamic efferents to autonomic structures in medulla and spinal cord

By application of the anterograde transport technique of Phaseolus vulgaris leuco-agglutinin the descending autonomic projection of the paraventricular hypothalamic nucleus was investigated. The Phaseolus lectin technique allowed the detection of the cells of origin in the paraventricular PVN, the precise position of two distinct descending axon pathways and the detailed morphology of terminal structures in midbrain, medulla oblongata and spinal cord.

The Hypothalamus, Intrinsic Connections and Outflow Pathways to the Endocrine System in Relation to the Control of Feeding and Metabolism

Abbreviations

Neuroendocrine states and behavioral and physiological stress responses.

Publisher Summary This chapter presents a novel, behavioral physiological stress concept that originates from the classical view that stress is a response. This new concept is extended to environment, behavior, and physiology, and it incorporates the novel neuroendocrine views including the neuropeptide concept. Stress is viewed as a general biological and usually functional response to environmental and bodily demands. A stress depends on interactions among environment, individual characteristics and the properties of stressors, stress, and the physiological systems, and also among the nervous system, peripheral organ systems, and the neuroendocrine system. To adapt to the altering social and physical environmental demands, man and other animals require a chain of behavioral, neuroendocrine, and autonomic physiological and metabolic responses to maintain bodily and mental homeostasis. The neuroendocrine state of the brain is given a central position in determining the state of health or disease of mind and body.

Behavioral strategy and the physiological stress response in rainbow trout exposed to severe hypoxia.

In higher vertebrates, two opposite behavioral coping strategies can be distinguished that are associated by a typical neuroendocrine pattern. Little is known about the individual variation in the stress response in lower vertebrates such as teleosts. In the present study, rainbow trout were fitted with an indwelling aortic catheter for repeated blood sampling and exposed to severe hypoxia and subsequent recovery and their behavior was characterized semiquantitatively during hypoxia. Blood levels of catecholamines, cortisol, glucose, FFA, lactate, and electrolytes were measured. About 60% of the fish survived the experiment whereas the others died during the recovery period. Behavioral strategy appeared to be highly related to survival since nonsurviving fish displayed strenuous avoidance behavior involving burst type activity whereas surviving fish did not panic and remained quiet. These behavioral differences were associated with marked differences in plasma catecholamine levels, which were 4- to 5-fold higher in nonsurviving fish as compared to survivors whereas the cortisol response tends to be lower in nonsurviving fish. Plasma lactate levels in nonsurvivors were 4- to 5-fold higher as compared to survivors while a severe hyperkalemia developed during recovery indicating the loss of intracellular homeostasis. The individual differences in behavioral concepts and neuroendocrine activation observed in rainbow trout during stress show great similarity with the active and passive coping strategies distinguished in higher vertebrates and may be determinant for survival during hypoxia.

The influence of insulin injections and infusions on eating and blood glucose level in the rat.

Abstract The effect of insulin on blood glucose and food intake in unanesthetized rats was studied under two conditions: (a) after a single intravenous injection of insulin; (b) during continuous insulin infusion over 9 hr. Insulin was given and blood samples were taken without disturbing the animals by means of a double intracardial catheter. After a single injection blood glucose declines steeply to 50 mg% and remains at a plateau until a meal starts, then a sudden rise ensues. Continuous infusion of insulin in normal rats induces hyperphagia: blood glucose decreases slowly to 50 mg%; at which point a meal begins, a sudden rise in glucose ensues, followed by slow return to 50 mg%. This cycle is repeated continually. Identical infusions of insulin into static obese hypothalamic subjects (whose daily food intake is fairly normal) leads to renewed hyperphagia, but the fluctuations in blood glucose that accompany the meal cycle are much reduced in amplitude as compared to normal rats under the same treatment.

Plasma insulin and the time pattern of feeding in the rat

Abstract Blood levels of glucose and insulin during meals and between-meal-intervals were measured in virtually undisturbed rats. After a peak due to glucose absorbed from the meal blood sugar soon reverts to the pre-meal level. Insulin shows a similar peak followed by a continuing decline so that just before the next meal it is lower than at any other time. In terms of the glucostatic theory this might mean that meals are triggered by a critical drop of insulin. However, intravenous infusions of glucose, resulting in continously high insulin, do not affect timing or size of meals. Glucostatic factors probably are of minor importance in meal-to-meal regulation in the rat. However, they may subserve nutritional homeostasis on at least two other points.

Plasma insulin content in relation to blood glucose level and meal pattern in the normal and hypothalamic hyperphagic rat

Abstract Blood samples were withdrawn at short intervals from unanesthetized rats by means of a chronic intracardial cannula. Glucose and insulin levels were determined. Accurate records were kept of the time pattern of feeding in these animals, whose normal behavior was not disturbed at all by the sampling procedure. In the ad libitum situation, the start of a meal entails a rise of the glucose level within two min. This culminates in a peak within 15 min which is followed by a rapid return to pre-meal levels. Insulin is very low (25 μU/ml plasma) before the meal, rises rapidly after its start, and then declines to values markedly above pre-meal levels. (66 μU/ml plasma). In the VMH hyperphagic animal the glucose level is comparable to that in the normal animal but the insulin level is exceedingly elevated. After 24 hr of food deprivation, the glucose level of the intact subject has dropped to about 80 mg % and insulin to 10–20 μU/ml plasma. When food is returned, glucose rises rapidly within one minute after the start of the first meal. Insulin goes up, but attains a much lower peak level than under ad libitum conditions, and declines again to very low values (35.5 μU/ml plasma). In contrast, glucose remains relatively high. In the food deprived VMH hyperphagic animal the glucose level is comparable to that in the deprived intact animal, but the insulin response is also in this case very exaggerated.

Blood glucose levels in portal and peripheral circulation and their relation to food intake in the rat

Rats weighing about 450 g were provided with permanent catheters in the portal vein and the right auricle. This method allows blood sampling from the portal and peripheral circulation at the same moment in the nondisturbed unanesthetized rat. In the ad lib condition the portal glucose level was higher than that in the general circulation before, during, and after the meal. After a fast of 22 hr premeal portal vein levels were equal to those of the general circulation. During the meal the portal glucose levels rose to about 150 mg per 100 ml whereas those of the general circulation did not exceed 130 mg/100 ml. Experiments with glucose infusions systemically and intraportally show that, under conditions of mild deprivation, the level of glucose in the portal vein plays no or only a very minor role in the termination of feeding.

Substrate mobilization and hormonal changes in rainbow trout (Oncorhynchus mykiss, L) and common carp (Cyprinus carpio, L) during deep hypoxia and subsequent recovery

Common carp (at 20°C) and rainbow trout (at 15°C) were fitted with an indwelling cannula in the dorsal aorta. The fish were exposed to a controlled decline of waterpO2 followed by 90 min deep hypoxia at 0.3 kPa (carp) or 4.8 kPa (trout). Thereafter, normoxic recovery was monitored in both species for 48 h. At regular intervals blood samples were analysed for glucose, lactate, free fatty acids, adrenaline, noradrenaline and cortisol. The oxygen restriction was maximal in both species and resulted in a significant increase of plasma lactate levels. In carp, adrenaline, noradrenaline and cortisol levels increased to 2, 50, and 753 ng·ml-1 respectively during anoxia, whereas in trout these hormones increased to 12, 8 and 735 ng·ml-1 respectively during hypoxia. In hypoxic trout, the plasma levels of glucose (3 mol·l-1) were increased modestly whereas levels of free fatty acids (0.25 mmol·l-1) were decreased to 0.15 mmol·l-1. In carp, however, a marked and prolonged hyperglycaemia (from 5 to 10 mmol·l-1) and a significant continuous depression of plasma levels of free fatty acids (from 0.4 to 0.2 mmol·l-1) were observed indicating a difference in metabolic organization. It is suggested that hyperglycaemia is likely to be the result of hepatic glycogenolysis, stimulated by circulating catecholamines and a stimulation of gluconeogenesis by cortisol during recovery. The mechanism for the decline of plasma levels of free fatty acids is most probably a reduction of lipolytic activity, which appears to be an adaptation to hypoxia.