Distension of pulmonary vein--left atrial junction: heart rate responses in conscious and anesthetized dogs

The cardiac chronotropic effects of distension of pulmonary vein-left atrial junction were investigated in conscious dogs and in dogs anesthetized with intravenous alpha-chloralose (100 mg/kg) or pentobarbital (30 mg/kg). All the experiments were made on trained, chronically instrumented, closed chest animals held in horizontal position. Inflation of a single small balloon in the junction elicited a tachycardic response both in conscious and chloralose-anesthetized dogs, while in pentobarbital anesthesia no change in heart rate was found. Contrary to reports of other investigators, no transient bradycardia was found, nor any correlation between predistension heart rate and the increase in heart rate due to the distension. It is suggested that the choice of anesthetic can be done only after its modifying effect on the parameter studied is known. Only the use of trained, chronically instrumented and conscious dogs will reveal this effect.

Effects of alpha-chloralose on the activity of the nigrostriatal dopaminergic system in the cat

The effects of alpha-chloralose anaesthesia were studied in the cat on the release of 3H-dopamine (#H DA) from the caudate nucleus and the substantia nigra using the push-pull cannula method and continuous labelling of the structures with L-3,5-3H-tyrosine. Results were compared to those obtained under the same experimental conditions in both halothane-anaesthetized animals and 'encéphale isolé' preparations. The alpha-chloralose-anaesthetized preparation showed the lowest level of 3H-DA release, both from dopaminergic nerve terminals in the caudate nucleus and from dendrites of dopaminergic neurons in the substantia nigra. Furthermore, the time required to reach a steady-state release of 3H-DA was longer in alpha-chloralose-anaesthetized cats than in animals under halothane. This indicated that the activity of the dopaminergic neurons is depressed under alpha-chloralose anaesthesia. In the second part of the study, we measured the effects of unilateral somatic stimulation on the release of 3H-DA from the caudate nuclei and substantiae nigrae on both sides of the brain. The results show that under alpha-chloralose anaesthesia, the electric stimulation of the paw of the right forelimb does not significantly affect the release of 3H-DA from any of the above four structures. This contrasts with the changes of 3H-DA release seen in the same experimental conditions under halothane anaesthesia.

Cerebral regional oxygen consumption and supply in anesthetized cat

The study involved quantitative measurement of arterial and venous oxygen saturation, oxygen extraction, blood flow, and oxygen consumption in specific areas of the brain. No regional differences in oxygen consumption were found in anesthetized cat brain, and the amount of oxygen available to all regions studied was more than 2.5 times the consumption throughout the brain.

Observations on chloralose-induced myoclonus in guinea-pigs

1 The physiological, biochemical and pharmacological features of alpha-chloralose-induced myoclonus in the guinea-pig have been studied. 2 EMG bursts in muscles jerking in chloralose-induced myoclonus are long, and are not time-locked to any cortical event recorded in the EEG, although they are evoked by auditory or peripheral nerve stimuli. 3 The efferent conduction velocity down the spinal cord of the signals generating the EMG bursts is fast but the afferent conduction velocity up the cord for stimulus-evoked jerks is slow, in distinction to the reverse characteristics of the spino-bulbo-spinal relfex arc. 4 alpha-Choralose did not cause any consistent change in 5-hydroxytryptamine (5-HT) or 5-hydroxyindoleacetic acid levels in any brain area, nor did it alter 5-HT turnover as judged by the depletion of 5-HT after p-chlorophenylalanine pretreatment. 5 Pretreatment of animals with drugs that increase brain 5-HT action (L-tryptophan with a monoamine oxidase inhibitor, or 5-hydroxytryptophan), or antagonize the action of 5-HT (cyproheptadine) did not abolish or obviously increase chloralose-induced myoclonus. 6 Chloralose-induced myoclonus is not similar to 5-HT-sensitive reticular reflex myoclonus in man.

The effects of pentobarbital and related compounds on frog motoneurons

The effect of pentobarbital (PB) and related compounds on frog motoneurons was examined with sucrose gap recording from the ventral roots. PB was found to: (1) depress the action of glutamate, (2) selectively enhance the action of GABA, (3) reverse the non-competitive picrotoxin antagonism of GABA and the competitive strychnine antagonism of beta-alanine, but not the competitive bicuculline methiodide antagonism of GABA, and (4) elicit a GABAmimetic hyperpolarization. The first three actions had a threshold concentration of 10 microM, while the GABAmimetic action required a 10-fold higher concentration. The reversal of picrotoxin's action by PB suggests that PB might modify GABA mechanisms by combining to the picrotoxin recognition site. Phenobarbital shared all of the properties of PB but was approximately one-fifth as potent. The only property that phenytoin shared with PB was a weak depression of glutamate responses. Chlordiazepoxide selectively enhanced GABA responses but was devoid of the other actions of PB. These results suggest that the GABAmimetic effect of PB may be an important feature in the depressant and anesthetic properties of PB. The anesthetic chloralose, which is structurally unrelated to PB, nevertheless shared all of the actions of PB. This finding suggests that the properties described for PB may also be found in other general anesthetics.

Reflexes from isolated carotid sinuses of intact and vagotomized conscious dogs

Exposure of the vascularly isolated carotid sinuses of 8 conscious dogs to static pressures between 50 and 240 mmHg caused significantly smaller increases [23 +/- 5(SE) mmHg] than decreases (37 +/- 4 mmHg) in arterial pressure frossure and heart rate and shifted the stimulus-response curve upward. Bilateral cervical vagotomy in conscious dogs caused sustained (3 h) increases in arterial pressure (40 +/- 5 mmHg), significantly larger than after atropinization (7 +/- 2 mmHg). In anesthetized, but not in conscious dogs, high sinus pressure reversed the hypertension caused by vagotomy. After vagotomy, low sinus pressure resulted in arterial pressures greater than 200 -mHg. In conscious dogs the carotid baroreflex can widely vary arterial pressure and heart rate despite buffering by extracarotid baroreceptors with vagal afferents, but cannot fully compensate for the acute loss of the latter. Extracarotid baroreceptors actively participate with carotid baroreceptors in the regulation of arterial pressure and better buffer carotid baroreflex-induced increases than decreases in arterial pressure.

Effects of anaesthetics on reflexes elicited in the sudomotor system by stimulation of Pacinian corpuscles and of cutaneous nociceptors

Sudomotor neurones supplying sweat glands in the hairless skin of the cat's paws can be activated by the cutaneous afferent inputs deriving from vibrational receptors (Pacinian corpuscles) in the paws and from cutaneous nociceptors. Both reflexes probably have separate spinal pathways. In the present investigation the effects of the anaesthetics ketamine, methohexital, chloralose, halothane and Althesin on both types of sudomotor reflexes were examined. For this purpose the skin potentials were recorded from the hairless skin of the paws with Ag--AgCl-electrodes. Before application of any anaesthetic the cats were in a state of light ketamine anaesthesia. The following results were obtained: (1) the resting activity in the sudomotor system and the synchronization of the activity between both hindpaws and between hind- and forepaws were depressed by all anaesthetics to a variable degree. After chloralose application large synchronous potentials of low frequency appeared; (2) ketamine (18--25 mg/kg injected intramuscularly) enhanced the reflexes on vibrational stimulation and depressed the reflexes on noxious stimulation of skin; (3) methohexital (3--10 mg/kg injected intramuscularly) mostly depressed the reflexes on vibrational stimulation and enhanced the reflexes on noxious cutaneous stimuli; (4) chloralose (4.5--20 mg/kg injected intraperitoneally) enhanced both types of reflexes; (5) halothane (1--1.5 vol. %) and Althesin (2.5--5 mg/kg injected intramuscularly) depressed both types of reflexes; (6) in chronic spinal cats ketamine, methohexital and chloralose had a slightly depressive effect on the resting activity of the sudomotor system, but practically no influence on the reflexes induced by cutaneous stimuli; and (7) these results argue that the effects of anaesthetics on the sudomotor system depend on the type of reflex tested and the type of anaesthetic used. They indicate furthermore that the anaesthetics affect largely supraspinal structures and influence the spinal reflex pathways via descending spinal pathways.

Relationship between plasma renin activity and hypotensive effect of captopril in dogs

The ability of captopril (SQ-14225), an angiotensin I-converting enzyme inhibitor, to reduce blood pressure in dogs anesthetized with either pentobarbital sodium or a combination of morphine plus chloralose was studied over a sixty minute period. In addition, since both of these anesthetic agents cause an increase in the plasma renin activity of these animals, the drug was used to further investigate whether the hypotensive action of this drug is dependent on the level of plasma renin activity. Captopril produced significant but similar decreases in blood pressure of both the anesthetized groups, even though the blood pressure of the morphine-chloralose dogs was significantly lower than that of the pentobarbital animals. Further, the hypotensive action of captopril was not related to the level of plasma renin activity, since the morphine-chloralose dogs had a significantly higher plasma renin activity. It is concluded that the magnitude of blood pressure reduction following the administration of captopril is not related to the level of blood pressure and the pre-drug plasma renin activity and hitherto unexplained mechanisms in addition to the converting enzyme inhibition may be involved in the hypotensive action of this drug.

Anesthetic effects on hemodynamics of spontaneously hypertensive and Wistar-Kyoto rats

We studied the effects of three anesthetic agents on the central hemodynamics of spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats instrumented with chronic electromagnetic flow probes and arterial pressure catheters. Cardiovascular alterations due to ether, pentobarbital sodium (PBS; 50 mg/kg), and a 2% chloralose-7.5% urethan mixture (CU; 6 ml/kg) were determined. Ether produced significant elevations in heart rate (HR), cardiac index (CI), stroke volume (SV), and peak aortic flow velocity (PAFV) in SHRs (P less than 0.01) and elevations of HR and CI in WKYs (P less than 0.05). Ether reduced total peripheral resistance (TPR) and mean arterial pressure (MAP) in WKYs and SHRs (P less than 0.01). PBS decreased HR, CI, SV, MAP, PAFV, and minute work (MW) in both WKYs and SHRs (P less than 0.05--P less than 0.001). PBS also lowered TPR in WKYs (P less than 0.05). CU produced effects similar to those of PBS, but did not alter HR or TPR. Central hemodynamics are therefore significantly altered by these anesthetics when compared to those of conscious rats. These agents also have differential effects on the hemodynamics of SHRs and WKYs.

Microcirculatory actions of general anesthetics

General anesthesia, either with the inhalation or the nonvolatile anesthetics, results in significant changes in the microvasculature. The anesthetics alter microvascular diameters in the resting animal and they change the responses to stress (i.e., catecholamine stimulation or hemorrhage) also. Alterations in the microvasculature involve primarily changes in the diameters of arterioles and venules and these, combined with the associated changes in arterial pressure and cardiac output, are responsible for the changes in organ blood flow that occur during general anesthesia. General anesthetics alter the in vivo vascular smooth muscle responses to topically applied vasoactive substances such as epinephrine or norepinephrine. The microvascular responses to hemorrhage are altered by the anesthetics and the changes are most pronounced in the smaller (approximately 20 micrometers) arterioles. Anesthetic influences on the microcirculation are unique for each agent and are not the result of the general state of narcosis. Anesthetic influences on the microvasculature are both dose-dependent and tissue-specitic. The peripheral vascular effects of the anesthetics may influence the choice of anesthesia and may alter the results of experimental investigations performed in anesthetized animals.

Potentiation of inhibition by general anaesthetics in neurones of the olfactory cortex in vitro

Pentobarbitone, phenobarbitone, methohexitone, chloralose and alphaxalone produced 10-fold increases in the duration of an inhibitory post-synaptic conductance (i.p.s.c.) as recorded intracellularly from neurones of the guinea-pig olfactory cortex in vitro. Higher concentrations slightly depolarised these neurones and reduced their input resistance (Ri), presumably a spontaneous activation of the inhibitory conductance. The excitatory potentials were also depressed. Ketamine, halothane and urethane doubled the i.p.s.c. duration. Higher concentrations depressed synaptic activity and the action potential, as did lignocaine. Ketamine also increased Ri. These results confirm the idea that these compounds produce anaesthesia by prolonging inhibition (accompanied by a depression of the e.p.s.p. with some anaesthetics).

Multiple-unit activity evoked in dorsal cap of inferior olive of the rabbit by visual stimulation

1. Microelectrode recordings of multiple-unit activity were made from the dorsal cap of the inferior olive of anesthetized and unanesthetized rabbits during vestibular and optokinetic stimulation. 2. A large field potential could be evoked in the dorsal cap by photic stimulation of the contralateral eye when the rabbit was anesthetized with sodium pentobarbital or chloralose-urethan. This field potential could not be evoked in rabbits that were anesthetized with halothane or in unanesthetized rabbits. 3. Dorsal cap neurons were maximally excited by large, contrast-rich stimuli presented to the contralateral eye, moving in the posterior-anterior direction at a velocity of 1--2 degrees/s. The discharge rate of dorsal cap neurons was decreased by stimuli moving in the opposite direction. 4. The activity of dorsal cap neurons was not modulated by vestibular stimulation when visual inputs were excluded. 5. Dorsal cap neurons were sensitive to retinal slip velocity and higher derivatives of optokinetic stimulation. Their activity was related to eye movements only when the eye movements affected movement of optokinetic images on the retina.

Ventilation in dogs on cardiopulmonary bypass with and without lungs

In 13 anesthetized or awake dogs, on cardiopulmonary bypass, we varied PaO2 and PaCO2 while continuously monitoring ventilatory responses and mechanics, to assess the dog's ability to maintain eupneic ventilation for any chemical drive. In a second group of 13 dogs on cardiopulmonary bypass we repeated the tests after removal of both lungs, to assess the importance of pulmonary feedback and mechanics. The VE/PO2 plot formed two hyperbolas, asymptotic to 39 Torr PO2 with lungs, and to 27 without; both intercepted zero ventilation near 200 Torr. Hyperoxic apnea occurred at, or below, PCO2 30 +/- 7 Torr under barbiturate and 20 +/- 4 Torr under morphine. Steady-state low PCO2 (10 Torr) turned off hypoxic drives as low as 20 Torr PO2. Empty-chest dogs had a low respiratory frequency (18 vs. 40), and near zero dynamic elastance; ventilatory work per minute and airway resistance were the same with and without lungs. Chest wall ventilatory responses are grossly independent of the presence of absence of lungs.

Perivascular pH and pial arterial diameter during bicuculline induced seizures in cats

The aim of the present study was to correlate locally at the same pial artery the vascular reaction with the perivascular pH during the initial phase of functional hyperemia. As a model of functional hyperemia, bicuculline (3 mg/kg i.v.) induced seizure was taken. Normally, a strong increase of blood pressure occurs together with the start of seizure. Since a discrimination between metabolically induced and pressure dependent vascular reactions is not possible under such conditions, the cats (anesthetized with 40--50 mg/kg chloralose) received in addition 3 mg/kg phentolamine and 10 mg/kg pentobarbital. Under these conditions a significant increase of blood pressure started only 50 s after the onset of seizure. Perivascular pH was recorded using spear type pH microelectrodes in the subarachnoid space surrounding a pial artery. The diameter of the respective artery was measured continuously. After onset of seizure an immediate, increasing perivascular acidosis developed which was accompanied by an increase in pial arterial diameter. The maximal decrease of pH was 0.29 units and occurred 30 s after the start of seizure. These data show that a decrease in perivascular pH can be one factor mediating functional hyperemia in the brain.

Physiologic effects of deep hypothermia and microwave rewarming: possible application for neonatal cardiac surgery

Deep hypothermia (20 C) without cardiopulmonary bypass is a valuable technique during cardiac surgery in infants but rewarming of the heart following circulatory arrest and cardiac repair has traditionally been a lengthy and difficult process. In experimental animals rewarming the heart with microwave energy, as reported in this work, warms the heart before warming the periphery. In 18 mongrel dogs that were surface cooled to 20 C, we found that during microwave rewarming the core temperature rose 4.7 C per hour. Whole body oxygen consumption, heart rate, and cardiac output returned to normal at rates equal to the rates at which they decreased during surface cooling. Blood pressure and arterial gases remained adequate. Microwave rewarming appears to be a useful method for reestablishment of cardiac function and normothermia following deep hypothermia.

The response of three strains of fowl to alpha-chloralose

A heavy and two light strains of pullets suffered a decline in egg production but an improvement in body weight gains when alpha-chloralose, a tranquilizer, was included in their diets at .1 to .3%. Feed efficiency also experienced a decline while egg size and Haugh unit were not affected.

Discharge patterns of Purkinje cells in cats anaesthetized with alpha-chloralose

1. Micro-electrodes have been used to record from 119 Purkinje (P) cells in the paramedian lobule of the cerebellum in cats anaesthetized with alpha-chloralose. 2. The spontaneous discharge rate and degree of irregularity of the discharge varied very much from one cell to another; the over-all mean rate (about 25/sec) was a little lower than has been reported either for barbiturate anaesthetized or for decerebrate unanaesthetized preparations. 3. Following electrical stimulation of a peripheral nerve, most P cells responded with both simple spikes and a climbing fibre response. This initial response was usually succeeded by a prolonged period of silence (over-all mean duration 350 msec) before resumption of the tonic simple spike discharge. Similar response-silence sequences could also be evoked by mechanical stimulation such as a tap applied to the pads of the forepaw. 4. Electrical stimulation of the inferior olive evoked climbing fibre responses followed by a prolonged pause in the simple spike discharge of the cell. 5. In six individual preparations, recordings were made both from P cells of the paramedian lobule and from neurones of nucleus interpositus (to which the former project). Comparison of the responses of the two types of neurone to peripheral nerve and inferior olivary stimulation showed that the end of the pauses in P cell firing correlated well with the end of a prolonged period of facilitation of the interpositus neurones. 6. These results support the hypothesis advanced in an earlier report (Armstrong, Cogdell & Harvey, 1975) that the prolonged facilitatory responses of interpositus neurones are essentially disinhibitory responses resulting from reduction in the activity of overlying cells, and that responses of P cells and of interpositus neurones consist, in general, of modulations of activity which are mutually out of phase.

The influence of trichloroethylene and related drugs on the vestibular system

A previously described experimental model for studying the effect of industrial solvents on the vestibular system of rabbits has been applied to trichloroethylene. Estimation of trichloroethylene and its metabolites in blood and cerebrospinal fluid was performed by gas chromatography. Vestibular function was studied by recording nystagmus, induced by positional changes or accelerated rotation. At blood levels of trichloroethylene above 30 p.p.m. "positional nystagmus" develops. Two metabolites of trichloroethylene, chloral hydrate and trichloroethanol, which are known as central nervous system (CNS) depressants, did not induce this abnormal nystagmus. However, alpha-chloralose, a derivative of chloral hydrate, induced positional nystagmus and also a markedly exaggerated nystagmus developed during rotatory acceleration. It is suggested that solvents like trichloroethylene elicit vestibular disturbances by stimulation of central subcortical vestibulo-oculomotor connections. The stimulation may be caused by a blockage of inhibitory systems.

Pentobarbitone and skeletal muscle contractions: on the interaction with the effect elicited by the beta-adrenoceptor agonist, terbutaline

The soleus, a slow-contracting muscle, and the extensor digitorum longus (EDL), a fast-contracting muscle from guinea-pig were prepared for isometric recording in vitro. Subtetanic contractions were evoked by transmural field-stimulation. Pentobarbitone increased the force of contraction in both muscles. In the soleus it shifted the stimulation frequency-response curve to the left. Terbutaline caused a decrease in the force of subtetanic contractions of the soleus, an effect which was dependent on the stimulation frequency. In the presence of pentobarbitone, the stimulation frequency had to be lowered by about 2 HZ in order to maintain the optimum response to terbutaline. The EDL responded to terbutaline with an increased force of contraction. In this case the stimulation frequency was less critical and the effects were the same in the presence and in the absence of pentobarbitone. Experiments with alpha-chloralose yielded results similar to those obtained with pentobarbitone.