Anaesthetic-related occurrence of early ventricular arrhythmias during acute myocardial ischaemia in rats

The cardiovascular responses of rats anaesthetised with different anaesthetic agents to acute coronary artery ligation were studied. Before thoracotomy, urethane-anaesthetised animals exhibited significantly lower blood pressures. Ligation of the left coronary artery induced a high incidence of ventricular tachycardia or fibrillation in rats anaesthetised with pentobarbitone, urethane, or ether inhalation followed by chloralose. Ketamine-anaesthetised animals had a significantly lower incidence of ventricular arrhythmias. The mortality rate was also lower, though not statistically significant. However, all groups of rats showed essentially similar blood pressure and heart rate changes following coronary artery ligation as well as the time of onset of ventricular tachycardia or fibrillation. The findings demonstrate the influence of anaesthetics on the occurrence of early ventricular arrhythmias following acute coronary artery ligation in rats.

Alpha-chloralose opens the chloride channel of frog isolated sensory neurons

The effect of alpha-chloralose on the sensory neurons isolated enzymatically and mechanically from frog dorsal root ganglia was studied using a suction-pipette technique. The threshold concentration of alpha-chloralose was around 3 x 10(-5) M and the current produced by alpha-chloralose saturated at the concentration of 3 x 10(-3) M or more. The dose-response curve for alpha-chloralose provided a Ka value of 6 x 10(-4) M and a Hill coefficient of 1.8. The reversal potential of the response elicited by alpha-chloralose was close to the equilibrium potential for Cl- (ECl), indicating that the current was carried through Cl- channels. The current-voltage relationship indicated that there was little voltage dependence in the alpha-chloralose-induced response. The analysis of the variance of the alpha-chloralose-induced Cl- current fluctuations showed two types of the receptor-ionophore complexes with different channel conductances.

Regional hemodynamic responses to nicotine in conscious and anesthetized dogs: comparative effects of pentobarbital and chloralose

This study was conducted in 12 dogs to evaluate regional hemodynamic responses during intravenous infusion of nicotine (36 micrograms/kg/min) in the conscious state and compare them with those in the same dogs following either pentobarbital (n = 6) or chloralose anesthesia (n = 6). Values for regional blood flow were obtained with 15-microns radioactive microspheres and used to calculate regional vascular conductance. In the conscious state, nicotine increased aortic pressure (+70%) and caused hyperventilation that reduced arterial PCO2 (-44%). These systemic effects were associated with decreases in vascular conductance in the renal cortex (-48%), pancreas (-81%), duodenum (-58%), and cerebral cortex (-55%), whereas no significant change in vascular conductance was evident in spleen, liver, or myocardium. Pentobarbital anesthesia blunted the increases in aortic pressure and respiratory activity and the reductions in vascular conductance in the renal cortex, pancreas, duodenum, and cerebral cortex during nicotine infusion. In contrast, chloralose anesthesia accentuated the increase in aortic pressure and the decrease in vascular conductance in the renal cortex during nicotine infusion, while it converted no change in vascular conductance in the spleen into a decrease and no change in vascular conductance in the myocardium into an increase. Chloralose anesthesia blunted nicotine-induced hyperventilation. These findings demonstrate that general anesthetic agents may have markedly different effects on cardiovascular reflex pathways. They emphasize the importance of considering the particular characteristics of the anesthetic agent used in interpreting results from studies of cardiovascular pharmacology and physiology in anesthetized animals.

Chloralose alters both basal hemodynamics and cardiovascular responses to alveolar hypoxia in chronically instrumented, spontaneously breathing lambs

We studied the effects of chloralose anesthesia on the basal hemodynamic state and on the cardiovascular response to alveolar hypoxia in chronically instrumented, spontaneously breathing lambs, compared with responses to the saline vehicle. Chloralose significantly increased heart rate (23%), mean systemic arterial pressure (11%), systemic vascular resistance (21%), mean pulmonary arterial pressure (23%), and pulmonary vascular resistance (46%) (n = 30, p less than 0.05, ANOVA). These changes were unrelated to baseline tone of the circulation, cardiac output, mean left atrial pressure, or physiologically important changes in arterial blood gas tensions. In addition, chloralose-treated lambs had increased heart rate, systemic vascular resistance, and pulmonary vascular resistance compared to controls during alveolar hypoxia (13-15% FiO2). Importantly, chloralose-treated lambs did not increase their cardiac output during alveolar hypoxia as did control lambs. During hypoxia, systemic vascular resistance remained elevated in chloralose-treated lambs, but declined in control lambs. Chloralose has been recommended as an ideal anesthetic agent for cardiovascular experimentation. Our data suggest that chloralose-induced alterations in basal hemodynamics and in cardiovascular responses to alveolar hypoxia represent an uncontrolled variable in acute experimental studies. Complex cardiovascular alterations caused by anesthesia should be considered in experimental design.

An effective combination of anaesthetics for 6-h experimentation in the golden Syrian hamster

The anaesthetics described for use in hamsters to date are suitable for the performance of short-term experimentation. However, an anaesthetic regimen was required which would provide a stable preparation for 6 h and hence, a suitable combination was developed. In the first set of experiments, the effect of anaesthetics (chloralose, urethane, and pentobarbital) were examined alone and in combination on arterial blood measurements. In the second set of experiments the effect of the combination of anaesthetics on arterial blood measurements and minute ventilation was examined for up to 6 h. Chloralose, urethane and pentobarbital when used alone in the hamster were considered inadequate for our needs. Chloralose did not produce adequate surgical anaesthesia whereas urethane and pentobarbital resulted in marked respiratory depression. Urethane also produced a trend towards metabolic acidosis. In contrast, the combination of agents resulted in surgical anaesthesia and the arterial blood measurements were adequate. Further, the use of the combination of anaesthetics in hamsters resulted in a stable preparation where arterial blood measurements and minute ventilation were maintained in a good range for up to 6 h. The combination of chloralose, urethane and sodium pentobarbital in hamsters should prove useful in long-term non-recovery experimentation which requires early surgical intervention, minimal respiratory depression and an even depth of anaesthesia.

Effects of althesin and urethan-chloralose on neurohumoral cardiovascular regulation

The cardiovascular effects of althesin (ALT) and urethan-chloralose (UC) anesthesia were compared in conscious, chronically instrumented rats. Althesin had no effect on arterial pressure or base-line resistance in the renal, superior mesenteric, and hindquarters vasculatures but increased heart rate. In contrast, UC decreased arterial pressure, heart rate, and mesenteric resistance. Although UC attenuated depressor responses to nitroglycerin, neither anesthetic significantly altered regional vascular reactivity to intravenous phenylephrine and nitroglycerin. The cardiac chronotropic baroreflex was examined by comparing the slope of the curves relating maximal changes (delta) in heart rate (pulse interval) that occurred at the point coinciding in time with the maximal changes in mean arterial pressure produced by phenylephrine and nitroglycerin. Neither anesthetic significantly altered the baroreflex slope (delta pulse interval/delta mean arterial pressure) for pressor and depressor stimuli. Both anesthetics attenuated the sympathoexcitatory response to cerebroventricular angiotensin II, although ALT had less of a depressive effect (pressor response during ALT and UC = 65 and 30%, respectively, of conscious). Plasma renin activity (PRA) and the hemodynamic response to peripheral angiotensin-receptor antagonism were significantly increased (PRA by almost 6-fold) during UC, whereas ALT was without effect. Similarly, UC but not ALT induced vasopressin-dependent vascular tone. Ganglionic blockade indicated that peripheral neurogenic tone was not altered by ALT anesthesia. These data suggest that althesin produces fewer hemodynamic disturbances than urethan-chloralose and largely maintains cardiovascular regulation intact.

Noradrenaline-induced constriction of large and small coronary arteries in the anaesthetized dog

1. In the anaesthetized dog external diameter of the left circumflex coronary artery and blood flow through that artery were measured to allow the effect of noradrenaline to be compared in large arteries and resistance vessels. 2. The injection of noradrenaline (0.5 micrograms kg-1) into the coronary artery, after bilateral vagotomy and antagonism of beta-adrenoreceptors, decreased large coronary artery diameter and coronary blood flow. Calculation of resistance in the large coronary artery and in the total left circumflex coronary vascular bed revealed that noradrenaline induced increases of 66% and 89% respectively. 3. Intra-coronary (i.c.) injection of the alpha 1-adrenoreceptor agonist phenylephrine (0.5-2 micrograms kg-1) decreased large coronary artery diameter and coronary blood flow. The alpha 2-adrenoreceptor agonist B-HT 920 (0.5-2 micrograms kg-1 i.c.) decreased coronary blood flow but did not significantly affect large coronary artery diameter. 4. Antagonism of alpha 1-adrenoreceptors with prazosin (10 micrograms kg-1 i.c.) abolished the noradrenaline-induced constriction of the large coronary artery but only partially attenuated the decrease in blood flow. The alpha 2-adrenoreceptor antagonist idazoxan (50 micrograms kg-1 i.c.) partially attenuated the noradrenaline-induced decrease in coronary blood flow but did not affect the large artery constriction. 5. It is concluded that noradrenaline constricts both large and small coronary arteries. Noradrenaline-induced constriction of the resistance vessels is more powerful than in the large artery. The constriction of large arteries in response to noradrenaline is mediated by alpha 1-adrenoreceptors. Postjunctional alpha 1- and alpha 2-adrenoreceptors are both involved in the constriction of the resistance vessels.

The electrophysiological effects of alpha-chloralose anesthesia in the intact dog: (1) alone and (2) in combination with verapamil

The electrophysiological effects of alpha-chloralose anesthesia were determined in 13 chronically instrumented dogs and compared to baseline electrophysiological parameters in the conscious state. Alpha-chloralose anesthesia (75 mg/kg of a 4% solution in polyethylene glycol (PEG) delayed conduction and prolonged refractoriness of the AV node: (1) the P-R interval increased from 108 +/- 14 msec (mean +/- SD) in the conscious state to 125 +/- 23 msec (P less than 0.02); (2) the A-H from 98 +/- 12 msec to 108 +/- 16 msec (P less than 0.04); (3) the AV nodal effective refractory period from 136 +/- 16 to 153 +/- 29 msec (P = .05) and the AV nodal functional refractory period from 232 +/- 58 to 247 +/- 46 msec (P = 0.07); and (4) the AV block cycle length from 228 +/- 54 msec to 248 +/- 43 msec (P less than 0.04). Chloralose anesthesia also increased the ventricular refractory period from 139 +/- 13 msec to 161 +/- 22 msec (P less than .03) and the QTc interval from 273 +/- 22 to 306 +/- 32 msec (P less than 0.0002). To determine whether these effects on AV nodal conduction would influence experimental results, responses to verapamil were studied in the conscious state and during chloralose anesthesia. During chloralose anesthesia, (1) no relationship was detected between the sinus cycle length and verapamil concentrations; (2) a greater increment in AV conduction time was seen for a given verapamil concentration; and (3) AV block occurred at verapamil concentrations associated with 1:1 conduction in the conscious state. We conclude that chloralose anesthesia has significant electrophysiological effects and that these effects must be taken into consideration during the interpretation of experiments performed in animals during chloralose anesthesia.

Anesthetic effects on tonic and reflex renal sympathetic nerve activity in awake cats

Renal sympathetic nerve activity (RNA), arterial blood pressure (AP), and heart rate (HR) were simultaneously measured before and after administration of pentobarbital sodium (PB), chloralose (CHL), or urethan (URE) in conscious cats. We examined the time courses and magnitudes of the changes in RNA, AP, and HR over a period of 5 h under anesthesia with spontaneous or artificial respiration. In both respiratory conditions, PB initially decreased and then increased RNA, AP, and HR; CHL sustainedly increased RNA but had almost no effect on AP and HR. Under artificial respiration, URE transiently decreased RNA but had no effect on AP and HR. To examine the baroreflex response of RNA, AP was increased to 150 mmHg by norepinephrine and decreased to 65 mmHg by nitroprusside. RNA responded inversely to the alterations of AP in both awake and anesthetized states. Compared with the awake state, the inverse AP-RNA relationship curve initially shifted downward and then upward under PB, and the slope of the relation curve was initially decreased. On the other hand, under CHL the relationship curve shifted only upward, and the slope increased. Thus the anesthetic drugs affected differently and time dependently tonic and reflex renal sympathetic nerve activity in the conscious cat.

Responses of the three-toed sloth, Bradypus tridactylus, to some commonly used pharmacologic agents. II. Chloralose and reserpine

1. Chloralose, 50 mg/kg i.v., is a safe effective anesthetic for sloths and reduces incidence of cardiac arrhythmias. 2. However, chloralose blocks baroreflexes and may reduce the sensitivity of beta 1 cardiac receptors. 3. Reserpine, 0.70 mg/kg given i.v. in divided doses, blocks the hypertensive effect of 100 micrograms/kg of tyramine in sloths. 4. Reserpine in this dosage materially reduces arterial pressure and heart rate; these effects last at least 7 days. 5. Reserpine potentiates the hypertensive effects of epinephrine and norepinephrine materially. 6. In sloths reserpine increases cardiac irritability but does not block baroreflexes. 7. As is true with most other drugs sloths are more sensitive to chloralose and reserpine than most common laboratory animals.

Thermal salivation in rats, anesthetized with barbiturates, chloralose, urethane and ketamine

1. The relationship between thermal salivation (TS) and thermoregulation was studied in anesthetized rats. 2. Of the 6 anesthetics used, ketamine-anesthetized rats secreted the largest amount of saliva. Salivation, however, was thermal and not induced by ketamine itself. 3. Ketamine-anesthetized rats readily secreted saliva at core temperatures less than 40 degrees C but TS was remarkably enhanced by hyperthermia of 40-42.5 degrees C. 4. The equilibrium phase in the triphasic heat response of core temperature was a consequence of equilibrium between heat gain and heat loss by salivation.

Alpha-chloralose as a capture and restraint agent of birds: therapeutic index determination in the chicken

The median effective dose for capture (ED50) and the median lethal dose (LD50) of alpha-chloralose given orally to domestic chickens (Gallus domesticus) were determined by probit analysis to be 45 mg/kg and 300 mg/kg, respectively. The therapeutic index (TI = LD50/ED50) was 6.7. This indicates that alpha-chloralose is only a marginally safe capture agent in domestic species and particularly in field applications involving other wild avian species in which the amount of the drug ingested by an individual bird is not controlled.

Chloralose alters circulatory response to alpha-receptor stimulation and blockade

Chloralose anesthesia is commonly used in animals for cardiovascular research despite limited data on possible receptor-drug interactions. To investigate potential interactions with alpha-adrenergic receptors, we studied the response of chronically instrumented, spontaneously breathing young lambs to alpha-receptor stimulation (by methoxamine) and blockade (by phentolamine) after infusion of 30 mg/kg of chloralose or an equal volume of vehicle. Both experiments were performed in each animal on different days and in alternate order. Chloralose altered the systemic arterial pressure and heart rate response to both alpha-agonist challenge and to alpha-blockade when compared with control. Despite potentiating the systemic arterial pressor response to methoxamine, chloralose attenuated the reflex decrease in heart rate after alpha-agonist-induced hypertension. This observation suggests that the baroreceptor reflex was blunted. Chloralose, commonly considered an ideal anesthetic for cardiovascular studies, may have important effects on the cardiovascular response to alpha-adrenergic test agents. The potential for interactive effects should be considered in experimental designs that couple the use of chloralose and alpha-adrenergic agents.

Recording of visual-evoked potentials in dogs with scalp electrodes

Following unsuccessful attempts to record visual-evoked potentials (VEPs) in dogs with scalp electrodes, adoption of a new stimulation technique seems to be beneficial. Previously, flashes of white light administered after dark adaptation induced relatively high amplitude electroretinograms (ERGs) covering any VEP activity over the surface of the skull. ERG amplitude, however, can be significantly reduced using flashes of red light after light adaptation (mostly cone stimulation). Simultaneous ERG and VEP recording allows identification of VEPs composed of three significantly different negative peaks (N1, N2, and N3) measured in dogs anesthetized with chloralose and halothane. No more than two of the three peaks were seen in one recording. Only the N1 and N3 waves were consistently recorded in dogs anesthetized with thiopental and thiopental combined with halothane. In 50% of all recordings, N1 was seen alone. The other VEPs consisted of N1 and N2, or N1 and N3 occurring concurrently. The simultaneous occurrence of N2 and N3 waves, however, was never seen. Among all recordings, N1 was most frequently recorded (85% of measurements), followed by N3 and N2 (38% and 31% of measurements, respectively). Peaks of less than 90 ms are highly reproducible. Anesthesia is necessary to eliminate frequent artifacts obtained in conscious and sedated dogs. Thiopental and/or halothane had no effect on measured latencies compared with chloralose.

Effects of anesthetics on cardiovascular responses of the marmot Marmota flaviventris

The effects of pentobarbital (30 mg/kg), urethan (2 g/kg), chloralose/urethan (50 mg/kg, 500 mg/kg), and thiobutabarbital (Inactin, 100 mg/kg) on the mean arterial pressure (BP) and heart period (HP) of Marmota flaviventris were examined. Anesthesia significantly decreased BP by 22-27 mm Hg and HP by 123-151 msec. In a series of paired studies with eight marmots it was found that pentobarbital increased the BP response to phenylephrine and almost abolished the baroreflex HP responses to phenylephrine and nitroglycerin. In another series of animals right carotid occlusion in unanesthetized animals produced greater changes in BP and HP than occlusion of the left carotid. Chloralose/urethan, urethan, or Inactin reduced the reflex BP response to unilateral carotid occlusion by 50% and the HP response by 96%. It was concluded that the anesthetic agents investigated depress baroreflex responses significantly by influencing efferent sympathetic and parasympathetic reflex responses. They, therefore, are not appropriate for cardiovascular studies in acute, anesthetized preparations of the marmot and, perhaps, other hibernating species.

Hypotensive effects of lesions of the rostral ventrolateral medulla in rats are anesthetic-dependent

These studies were designed to determine if the hypotensive effects of bilateral electrolytic lesions of the rostral ventrolateral medulla are dependent on the type of anesthetic agent used. The lesions caused an immediate fall in mean arterial pressure (MAP) in rats anesthetized with urethane, alpha-chloralose or sodium pentobarbital. At 30 min after placement of the lesions, severe hypotension (MAP = 54 +/- 5 mm Hg) persisted in the rats anesthetized with urethane. However, 30 min after placement of the lesions, the MAP of rats anesthetized with alpha-chloralose or sodium pentobarbital was 87 +/- 9 mm Hg and 99 +/- 10 mm Hg, respectively. Subsequent transection of the cervical spinal cord produced a much greater decrease in MAP in rats anesthetized with alpha-chloralose and sodium pentobarbital as compared to rats anesthetized with urethane. Heart rate was significantly lower after placement of the lesions in all 3 groups. We conclude that the magnitude of the hypotensive effect caused by placement of lesions in the rostral ventrolateral medulla is anesthetic-dependent and that the rostral ventrolateral medulla is not the only area of the central nervous system capable of maintaining vasomotor tone.

Effects of the volatile anesthetic agents on sinus node function and atrioventricular conduction in dogs: A comparison with chloralose anesthesia

The effects of equipotent concentrations (1.5 times minimum alveolar concentration) of the inhalational agents halothane, enflurane, and isoflurane on sinus node function, and atrioventricular (A-V) conduction and refractoriness were compared with chloralose anesthesia in 49 mongrel dogs. Sinus node function was assessed using corrected sinus node recovery time. Atrial-His and His-ventricular conduction times were measured at paced heart rates of 150, 180, and 200 beats/min, and A-V refractoriness was assessed by Wenckebach periodicity. There was no evidence that sinus node function was impaired by any of the inhalational agents. Enflurane anesthesia was associated with a significant prolongation of atrial-His conduction at paced heart rates of 180 and 200 beats/min when compared to chloralose anesthesia and the other two inhalational agents (P < .001). Atrioventricular refractoriness was impaired by enflurane (P < .001) and halothane (P < .05), but not isoflurane, when compared with chloralose anesthesia. Ventricular-His conduction was not altered by any of the agents. The authors conclude that enflurane is associated with a greater impairment of A-V conduction and refractoriness than halothane or isoflurane, and that these changes are related to the anesthetic agent and not the anesthetic state.

Effects of hemorrhage and hepatic nerve stimulation on venous compliance and unstressed volume in cat liver

Intrahepatic blood volume-pressure relationships were studied using plethysmography to measure hepatic blood volume and a hepatic venous long-circuit to control intrahepatic pressure. In cats anesthetized with pentobarbital or with ketamine-chloralose, hemorrhage (to reduce hepatic blood flow to 60% of control) caused marked reductions in hepatic blood volume and intrahepatic pressure but did not significantly change hepatic blood volume-pressure relationships. We were unable to demonstrate an active reflex venous response to hemorrhage in these preparations, although a large passive response occurred. The volume-pressure relationships in innervated livers were different from those in denervated livers: apparent venous compliance was much greater and apparent unstressed volume was zero or negative. Hepatic nerve stimulation in denervated livers caused a marked decrease in hepatic blood volume at low intrahepatic pressures but failed to alter hepatic blood volumes at high intrahepatic pressures (15 mmHg) (1 mmHg = 133.3 Pa). This resulted in large apparent compliances and apparently negative unstressed volumes, as seen in the innervated livers. Thus blood volume-pressure relationships in innervated livers may not give valid measurements of compliance and unstressed volume. A remarkable feature in all these experiments was the linearity of the relationship between hepatic blood volume and intrahepatic pressure. Exudation of fluid begins at higher intrahepatic pressures in innervated compared with denervated livers.

Ventilatory effects of stimulation of phrenic afferents

The diaphragm, a ventilatory muscle, has abundant sensory innervation. The effects of phrenic afferent activation on ventilation have been varied. In this study the proximal end of the phrenic nerve was electrically stimulated, and the effects on ventilation were measured in supine dogs anesthetized with either alpha-chloralose or pentobarbital sodium. We found a maximum increase in ventilation of 45 +/- 4% in the alpha-chloralose group and an increase in mean arterial blood pressure of 18 +/- 4%. This response was obtained at high stimulus intensities (60 times twitch threshold). Stimulation of the proximal end of the gastrocnemius nerve produced a similar ventilatory response (61 +/- 10%) but at lower stimulus intensities. During pentobarbital sodium anesthesia both the hyperventilation and the pressor response were produced; however, ventilation was increased by an increase in respiratory frequency. The reflex was abolished by sectioning of the cervical dorsal roots (C4-C7). Proximal cold blockade of the nerve abolished the response at a perineural temperature of 1.35 +/- 0.64 degrees C. The main effect of activation of phrenic afferents was an increase in ventilation and blood pressure that was mediated by unmyelinated fibers and possibly thin myelinated fibers. This response is similar to skeletal muscle afferent activation and may play a role in ventilatory drive during such conditions as exercise and respiratory muscle fatigue.

Effects of barbiturates on the inhibitory action of GABA on excitatory response of the stomach to stimulation of vagal afferent fibers in cat

Effects of barbiturates on the inhibitory action of GABA to the hexamethonium-resistant excitatory response of the stomach to stimulation of the vagal afferent fibers were studied in cats. Inhibition of the hexamethonium-resistant excitatory response by GABA were compared under alpha-chloralose, alpha-chloralose-phenobarbital (PhB), and alpha-chloralose-pentobarbital (PB)-anesthesia in cats. The ID50 of GABA on the hexamethonium-resistant excitatory response was not significantly affected by PhB, but reduced by PB. Both picrotoxin and bicuculline antagonized the effects of GABA. The present experiments demonstrated that PB potentiated the inhibitory effect of GABA on the hexamethonium-resistant excitatory response of the stomach, and suggested that the potentiation by PB may be due to activation of GABA-receptor-ionophore complex.

The measurement of single motor-axon recurrent inhibitory post-synaptic potentials in the cat

1. Signal averaging was used in forty experiments on low-spinal cats to measure and characterize the oligosynaptic responses of seventy-six motoneurons supplying the medial gastrocnemius muscle to the single impulses of antidromically stimulated single motor axons supplying the same muscle. 2. In thirteen experiments on chloralose-urethane anaesthetized preparations, twelve (43%) of the tested twenty-eight motoneurones exhibited a single-axon recurrent inhibitory post-synaptic potential (recurrent i.p.s.p.), as compared to sixty-four (62%) of the 103 motoneurones tested in twenty-seven animals in the absence of anaesthetic after ischaemic decapitation. 3. Single-axon recurrent i.p.s.p.s most often consisted of a single, long-lasting hyperpolarization. Ten of the recurrent i.p.s.p.s contained a second late peak of hyperpolarization. In another eight of the i.p.s.p.s, a small late depolarization was evident. 4. The distinct profiles of the recurrent i.p.s.p.s were readily distinguished from the relatively flat profiles with low noise levels in the averages of the fifty-five 'no-response' cells. The transmembrane and post-synaptic nature of the i.p.s.p.s was confirmed by extracellular control recordings taken immediately outside seven of the cells with positive responses. In addition, ten cells with positive responses were subjected to current passage during the averaging procedure. In all cases, depolarization increased and hyperpolarization reduced the amplitude of their single-axon recurrent i.p.s.p.s. 5. The mean amplitude of the responses was 12.0 microV in chloralose-urethane preparations as compared to a peak-to-peak noise level less than 6.0 microV in the no-response averages. Corresponding values in ischaemic-decapitate preparations were 46.2 microV and less than 7.5 microV, respectively. 6. Latency, rise-time and half-width (i.e. duration at half-amplitude) values of the i.p.s.p.s were similar for chloralose-urethane and ischaemic-decapitate preparations. The average values in both preparations were 2.5, 5.6 and 19.3 ms, respectively. The latency values indicated both disynaptic and, perhaps, longer components in the recurrent i.p.s.p.s. The rise-time and half-width values were relatively similar to those reported or measured from published records for analogous composite recurrent i.p.s.p.s (i.e. responses to antidromic stimulation of the whole muscle nerve rather than single motor axons). A weak, but significant, correlation between rise-time and half-width was observed for the sixty-six single-axon recurrent i.p.s.p.s with a single negative-going peak.(ABSTRACT TRUNCATED AT 400 WORDS)

Stimulatory effect of pentobarbital and some anesthetics on gastric secretion in the continuously perfused stomach in rats under urethane anesthesia

Effects of some anesthetics (pentobarbital, thiopental, alpha-chloralose and urethane) on gastric acid secretion were studied in the continuously perfused stomach in rats. Under urethane anesthesia, pentobarbital, thiopental and alpha-chloralose showed a definite stimulation on gastric acid secretion. Pretreatment with atropine or hexamethonium abolished the pentobarbital-induced acid secretion. Pentobarbital and thiopental did not elicit acid secretion in bilateral truncal vagotomized rats. In spinal rats, pentobarbital also stimulated acid secretion, but urethane, which was subcutaneously administered, reduced spontaneous acid output. The present results indicated that some anesthetics could stimulate gastric secretion in the anesthetized rat in contrast to the previously described inhibitory effect in the Shay rat.

Forebrain contribution to sympathetic nerve discharge in anesthetized cats

We tested the hypothesis that the forebrain is responsible for a component of basal sympathetic nerve discharge (SND) in the anesthetized cat. For this purpose integrated postganglionic inferior cardiac SND and blood pressure were measured before and after serial transections of the midbrain at stereotaxic planes A3 and AP0. In the first series of experiments on baroreceptor-denervated cats anesthetized with alpha-chloralose, A3 transection significantly reduced SND to 62 +/- 7% of control. Blood pressure was reduced 33 +/- 4 mmHg. SND and frontal-parietal cortical activity were temporally related prior to A3 transection in many of these animals. Recovery of SND and blood pressure to control levels occurred within 30 min after A3 transection. A second midbrain transection at AP0 failed to affect SND and blood pressure at this time. This observation suggests that the effects of A3 transection were due to the loss of a component of SND of forebrain origin rather than to generalized trauma. The effects of A3 transection were not attributable to cataleptic anesthesia with alpha-chloralose, since SND and blood pressure were significantly reduced by midbrain transection in baroreceptor-denervated cats anesthetized with diallylbarbiturate-urethan. A3 transection also reduced SND and blood pressure in some baroreceptor-innervated cats. Finally, medial diencephalic ablation prevented the effects of A3 transection. We conclude that the forebrain is responsible for a significant component of sympathetic tone in anesthetized cats. Recovery from the loss of this component, however, occurs rapidly even in animals deprived of their compensatory baroreceptor reflex mechanisms.

Reflex responses to baroreceptor, chemoreceptor and nociceptor inputs in single renal sympathetic neurones in the rabbit and the effects of anaesthesia on them

Reflex responses of renal postganglionic neurones to stimulation of arterial baroreceptors, arterial and central chemoreceptors and cutaneous nociceptors, and the rhythmicity of their resting activity were studied in paralyzed, artificially ventilated rabbits, anaesthetized with either alfathesin or chloralose-urethane. A 'vasoconstrictor' response pattern was seen in all units. Perivascular balloon-induced falls in blood pressure increased firing while pressure rises silenced 90% of units and reduced firing in the rest. Resting activity was linked to pressure changes within the cardiac cycle and to the artificial respiratory cycle. The largest excitation occurred during hypoxia and injections of CO2 saturated solutions into the carotid artery while hypercapnia and stimulation of cutaneous nociceptors only slightly increased firing. Parameters characterizing rhythmicities and reflex responses were unimodally distributed with no apparent subgrouping of units on quantitative grounds. Unit response patterns were similar to those recorded in the whole renal nerve. With one exception, no silent units were found which responded to the afferent inputs studied. Nor was there a small-spike fibre group which was excited by angiotensin. However, reflex responses were significantly influenced by the anaesthetic regime selected for use. Under alfathesin, baroreceptor and chemoreceptor reflexes were double those found with chloralose-urethane. Under chloralose-urethane, hypoxia increased both rhythmicities, while under alfathesin, cardiac rhythmicity was decreased and respiratory rhythmicity was variably affected. We concluded that renal sympathetic neurones are a functionally uniform population which behave like vasoconstrictors.

Genesis of anal canal pressures in the opossum

The purpose of the present investigation was to examine the role of the internal and external anal sphincters in the maintenance of resting pressures in the anal canal. The studies were performed in opossums anesthetized with alpha-chloralose. The radial and axial pressures in the anal canal were monitored using a continuously perfused catheter assembly. Electromyography of the external anal sphincter was monitored using bipolar tungsten hook electrodes. To examine the contribution of the external anal sphincter and surrounding skeletal muscle to the resting tone in the anal canal, pancuronium bromide was administered in a dose that abolished the electromyographic activity of the external anal sphincter muscle. The abolition of external anal sphincter activity did not modify the peak anal canal pressures, suggesting that these pressures are due to the internal anal sphincter. The alpha-adrenergic antagonist, phentolamine, did not modify the anal canal pressure, suggesting that basal internal anal sphincter pressure is not due to tonic adrenergic activity. Tetrodotoxin in a dose that produced obliteration of the anorectal reflex causing anal sphincter relaxation did not produce any change in the peak anal canal pressures. These studies show that the resting pressures in the anal canal of opossums are due to myogenic properties of the internal anal sphincter.

Micturition in rats: a chronic model for study of bladder function and effect of anesthetics

The volume-evoked micturition reflex (VEMR) and the effects of anesthetics on the VEMR were studied in a chronic unanesthetized rat model. The bladder catheter was implanted chronically through a laparotomy and externalized percutaneously. An intrathecal (IT) catheter was implanted chronically in animals scheduled for an IT injection. By 2 days after implantation, infusion of saline (200 microliter/min) in the bladder reliably resulted in a low base-line pressure (BP) followed by a transient increase in bladder pressure, an opening of the sphincter (bladder opening pressure, BOP) corresponding to expression of urine (volume of urination, V), then a further rise in pressure (peak pressure, PP) and a subsequent return to base line. Seven days after implantation, values (means +/- SE) for BP, BOP, PP, and V were 10 +/- 0.3, 30 +/- 2, 67 +/- 6 cmH2O, and 1.0 +/- 0.1 ml, respectively. Residual volumes were reliably less than 2-4% of the expressed volume. The VEMR was reliably evoked up to 28 days after implantation. V values in unimplanted and implanted animals were not different. In implanted animals, VEMR parameters were not different during infusion or during spontaneous urination after oral fluid load. Administration of pentobarbital sodium (50 mg/kg ip), alpha-chloralose (130 mg/kg ip), ketamine (100 mg/kg im), halothane (in air 2%), and local anesthetics (2-chloroprocaine 3% or bupivacaine 0.75%, 10 microliter IT) produced a complete blockade of the VEMR and overflow incontinence at pressures significantly higher than BOP values. To compare overflow pressures and passive compliance of the bladder, unanesthetized animals were decapitated.(ABSTRACT TRUNCATED AT 250 WORDS)

Influence of anaesthetics on rat striatal dopamine metabolism in vivo

The effects of 4 anaesthetics, halothane, alpha-chloralose, chloral hydrate and pentobarbitone, on rat striatal extracellular dihydroxyphenylacetic acid (DOPAC) levels were determined using in vivo voltammetry. Stable baseline levels of DOPAC were maintained under halothane/N2O and alpha-chloralose while the extracellular levels of DOPAC gradually declined under chloral hydrate or pentobarbitone anaesthesia. Administration of haloperidol (0.3 mg/kg i.p.) significantly increased DOPAC using halothane/N2O, alpha-chloralose or chloral hydrate but not under pentobarbitone anaesthesia. The greatest increase in DOPAC was seen in rats anaesthetized with alpha-chloralose greater than halothane/N2O greater than chloral hydrate greater than pentobarbitone. Apomorphine (0.5 mg/kg s.c.) given 2 h after haloperidol partially reversed the increase in DOPAC produced by haloperidol. The results suggest care needs to be exercised in the choice of anaesthetic used for voltammetric studies with pentobarbitone being the least recommended.

Periaqueductal gray and cerebral cortex modulate responses of medial thalamic neurons to noxious stimulation

The response of medial thalamic neurons to noxious peripheral stimulation were studied with intracellular recording methods in the cat. Electrical stimulation of the contralateral forepaw produced an EPSP-IPSP sequence followed by rebound excitation in these medial thalamic neurons. Action potentials appeared with the initial EPSP or with the rebound excitation. The mean latency to onset was 15 ms for the EPSP and 33 ms for IPSP. In contrast, electrical stimulation of the PAG or of the pericruciate cerebral cortex produced large IPSPs in the medial thalamic neurons. When PAG or cortex stimulation were paired with noxious stimulation, both the PAG and cortex responses predominated over the noxious response. This shows that the PAG and the cerebral cortex have the capabilities of influencing the responses of the medial thalamus to noxious stimulation. The medial thalamus is part of the relay system which sends information about noxious stimulation to the cerebral cortex where the noxious information reaches conscious awareness, so influencing the message at the level of the medial thalamus would probably alter the conscious perception of pain. The data suggest the existence of an ascending pain modulation system from the midbrain to the thalamus and also suggests a mechanism of cortical control over pain perception.

The effects of barbiturates upon the hemodynamic responses to intravenous methionine-enkephalin in dogs: modulation by the GABA complex

In conscious animals, the intravenous administration of enkephalins increases heart rate (HR) and mean systemic arterial blood pressure (MAP); however, when given during barbiturate anesthesia, enkephalins reduce HR and MAP. We have investigated the potential role of the gamma-aminobutyric acid (GABA) complex (consisting of chloride-ion channel and binding sites for GABA, benzodiazepine, and barbiturate/picrotoxin) as the site of modulation of enkephalin responses by certain anesthetic agents in our chronically instrumented dog model. In our model, methionine-enkephalin (Met5-ENK) (35 micrograms/kg intravenously) increased HR and MAP, but following induction of general anesthesia with barbiturate (pentobarbital) or of sedation with benzodiazepine (diazepam), Met5-ENK produced vasodepressor responses despite differing levels of consciousness in the treated animals. Subsequent administration of picrotoxin restored pressor responses to Met5-ENK in the barbiturate-treated dogs, but not in those treated with benzodiazepine; picrotoxin did not alter the level of consciousness. Picrotoxin had no effect upon Met5-ENK responses in the conscious state. In contrast, alpha-chloralose, a convulsive anesthetic agent which does not appear to alter GABA complex activity, blunted but did not reverse pressor responses to Met5-ENK, despite causing a level of anesthesia similar to that produced by barbiturate. The observed pressor response to Met5-ENK during alpha-chloralose anesthesia was totally inhibited by naloxone, indicating that this response was still mediated by opiate receptors. Our data are compatible with modulation of enkephalin responses by GABA complex activity. Systemic enkephalins may generate afferent signals which may subsequently undergo GABA complex processing; the state of activation of the GABA complex may then determine whether systemic enkephalin signals are translated as vasopressor or vasodepressor responses.

The effect of naloxone on pressor responses to angiotensin II in anaesthetized greyhounds

In greyhounds anaesthetized with morphine and chloralose, vertebral artery infusions of angiotensin II resulted in a similar pressor response but smaller tachycardia than in greyhounds anaesthetized with chloralose alone. The pressor responses to intravenous infusions of angiotensin II were significantly larger in the morphine premedicated greyhounds. In greyhounds anaesthetized with morphine and chloralose, pressor responses to vertebral artery angiotensin II were potentiated following the administration of naloxone via either a vertebral artery or intravenously although the effect was more consistent with the former route. No such effect was seen in greyhounds anaesthetized with chloralose alone. Naloxone had no effect on the pressor responses to intravenous angiotensin II or carotid artery occlusion. The heart rate responses to vertebral artery angiotensin II in greyhounds anaesthetized with morphine and chloralose were potentiated by naloxone such that they were not significantly different from the responses obtained in greyhounds anaesthetized with chloralose alone before naloxone. As was observed with the pressor responses, the potentiation was more apparent with the vertebral artery route of administration of naloxone. There was no potentiation of the heart rate responses in the chloralose group of greyhounds. It is suggested that morphine premedication may repress the vagal withdrawal mechanism while potentiating the sympathetic vasomotor mechanism mediating the central cardiovascular actions of angiotensin II.

[Hypothalamic modulation of baroreceptor inhibition of the electrical activity in the renal nerve]

Changes in the renal nerve sympathetic activity in response to electrical stimulation of posterior hypothalamus and vago-aortic nerve were studied in acute experiments on cats. It was shown that stimulation of certain points in hypothalamus defence area led to the suppression of baroreceptor reflex-mediated inhibition of the renal nerve sympathetic activity. Chloralosa depressed hypothalamic modulation of baroreceptor reflexes.

Morphine selectively facilitates the inspiratory-inhibitory vagal reflex in adult rabbits

In rabbits naive to opiates or pretreated with morphine a selective morphine-induced facilitation of the Breuer-Hering inflation reflex is described.

Influence of different anesthetic agents on the release of cholecystokinin in dogs

The purpose of this study was to investigate the effect of pentobarbital, halothane, and chloralose anesthesia on the endogenous release of cholecystokinin-33 (CCK-33) in dogs prepared with duodenal fistulas. Release of CCK-33 was induced by intraduodenal infusion of a medium-chain triglyceride (corn oil, 1 gm/kg/hr). Plasma CCK-33 concentrations were measured by means of a specific radioimmunoassay. Pentobarbital and chloralose were administered intravenously, and halothane was administered by a vaporizer (semiclosed technique), with O2 and N2O used as carriers. No incidence of hypotension was found with the use of these anesthetic agents. Basal concentrations of plasma CCK-33 were elevated, although not significantly, during pentobarbital or chloralose anesthesia. In conscious dogs (control study), peak plasma CCK-33 concentrations of 529 +/- 53 pg/ml were measured 30 minutes after intraduodenal infusion of fat. Under pentobarbital anesthesia, peak plasma CCK-33 concentrations of 452 +/- 264 pg/ml were found 80 minutes after infusion of fat. Under halothane anesthesia, fat-induced release of CCK-33 was abolished, whereas chloralose anesthesia did not influence fat-induced release of CCK-33. These findings may have implications for the design of future studies of gastrointestinal physiology. In CCK-33 studies that require anesthesia, chloralose appears to be an appropriate anesthetic agent.

An increase in metabolic acidosis induced by chloralose anaesthesia in dogs after sino-vagal denervation

Chloralose anaesthesia in dogs increased the H+ ion concentration significantly from its reference values. The findings favoured that it was most probably engendered through anaesthetic depression of neural centre regulating H+ ion concentration of blood. Such increase was largely contributed by a significant increase in its metabolic fraction. A further increase of metabolic fraction after separate and joint section of carotid sinus nerves and vagi indicated their holding effect. The section of carotid sinus nerve induced greater increase in this fraction than that of vagi. It indicated differences between the two nerves in their metabolic fraction controlling influence. Hyperpnoea after vagi section decreased the carbonic acid fraction, whereas marginally reduced ventilation after carotid sinus nerve section increased the carbonic acid fraction. Moreover, the overall changes in H+ ion concentration followed the changes in carbonic acid fraction. The present study suggested that the depressive effect of chloralose anaesthesia on H+ ion controlling neural mechanism could be largely determined by degree of increase in its metabolic fraction.

A comparison of electromyographic and mechanical fatigue properties in motor units of the cat hindlimb

Single motor units were isolated in medial gastrocnemius (MG) or soleus (Sol) muscles of the cat. Single shocks delivered to the motor axon elicited EMG waveforms which were recorded in the muscle. The amplitude of each individual EMG waveform as well as the area under the full-wave rectified waveform were measured. Mechanical properties of the motor units were then measured so that each unit could be classified as FF, FR or S according to the criteria of Burke. Finally, each unit was stimulated continuously at 80 pulses per second (pps), and changes in electrical and mechanical responses were recorded and compared. IEMG was positively correlated with maximum tetanic tension of motor units in MG. The relationship could be fitted with a parabola showing that 'large' motor units produce relatively more electrical activity than do 'small' motor units. Two types of electrical changes were seen during continuous stimulation of motor units at 80 pps: a smooth continuous decline in IEMG was attributed to electrical changes occurring at a site or sites distal to the neuromuscular junction; and random, abrupt changes in unit-EMG waveform and hence IEMG amplitude, were attributed to failure of the action potential to propagate past axonal branch points, resulting in the intermittent failure of groups of muscle fibers to respond to stimuli. The rates of decline of electrical and mechanical activity were compared for motor units. It was found that in fast fatiguing motor units, tetanic tension declined more rapidly than did IEMG, while in slowly fatiguing motor units, IEMG declined more rapidly than did force. We conclude that fatigue of motor units induced by continuous 80 pps stimulation can occur at different sites in the motor unit, and that the site of fatigue depends on motor unit properties or motor unit type.

Studies on the in vivo release of vasoactive intestinal polypeptide (VIP) from the cerebral cortex: effects of cortical, brainstem and somatic stimuli

The release of vasoactive intestinal polypeptide (VIP) from the surface of the sensorimotor (parietal) cortex of anesthetized cats was measured by radioimmunoassay (RIA) procedures. Two types of anesthetics were examined (chloralose-urethane and halothane). Increasing the dose or concentration of anesthetics produced a suppression of electrocortical activity and resulted in a reduction in the resting release of VIP from cerebral cortex. The mean rate of resting release of endogenous VIP in cats anesthetized with chloralose-urethane was 16.8 +/- 4.6 fmol/30 min/cm2 cortex. Although there were differences in the basal levels of VIP-like immunoreactivity (VIP-LI) among different animals, the baseline levels of VIP-LI varied little during the initial period of 6-7 h period of anesthesia with chloralose-urethane (40 and 300 mg/kg). Examination of representative electrocorticography which corresponded with the superfusion period revealed an association between stable levels and a relatively invariant pattern of electrical activity. All experimental manipulations were carried out during the period of stable release. The rate of release was increased by focal, unilateral stimulation of the cerebral cortex both ipsilateral and contralateral to the side of stimulation (3.2 +/- 1.1 and 1.4 +/- 0.5 times the resting release, respectively). Bilateral stimulation of the mesencephalic reticular formation (MRF) produced a frequency-dependent increase in cortical VIP release over the range of 60-100 Hz. Bilateral electrical stimulation of sciatic nerves at intensities that recruit A delta and C fibers failed to consistently increase the release of VIP-LI from the cortex in chloralose-urethane anesthetized cats but did evoke a significant increase of cortical VIP output in cats anesthetized with 1.5 and 1% halothane. Removal of calcium ions from the superfusing fluid and substitution of cobalt (a calcium channel blocker) or EDTA (a calcium chelating agent) for calcium ions did not affect the resting release of endogenous VIP, but attenuated the increase in VIP release normally evoked by electrical stimulation of the cortical surface or MRF. Tetrodotoxin (TTX), which blocks sodium channels and thus blocks the propagation of nerve impulses, did not influence the resting release of VIP. TTX, at concentrations that prevent the increase in VIP release evoked by veratridine, greatly enhanced the surface-stimulated release but abolished the increase in VIP release evoked by MRF stimulation.(ABSTRACT TRUNCATED AT 400 WORDS)

Gastric acid secretion during halothane, chloralose, pentobarbital and etomidate anaesthesia in the pig

The gastric acid secretion in the awake state of the pig was compared to that during halothane, chloralose, pentobarbital and etomidate anaesthesia. After collection of basal juice, acid secretion was stimulated with pentagastrin in the dosages of 0.25, 1.00 and 4.00 micrograms/kg/h. Halothane strongly inhibited acid secretion, whereas acid secretion during chloralose anaesthesia was enlarged by a factor 6 as compared to that of the awake animal. The mean acid output after receiving pentobarbital was close to that of the awake condition, but the interindividual variation was large. Nearly identical values for acid secretion were found during etomidate anaesthesia, but with much higher consistency in the results. Etomidate anaesthesia seems to be the most suitable method for measurements of gastric acid secretion during anaesthesia in the pig.

The action of intravenous anaesthetic and central depressant drugs on the contractures elicited by tetraethylammonium in the chick biventer cervicis muscle

A group of intravenous anaesthetic drugs was compared with methohexitone sodium for their ability to potentiate tetraethylammonium induced contractures of the chick biventer cervicis muscle (TEA test). The equipotent concentrations in the TEA test were: methohexitone 8.8 X 10(-5) M, propanidid 1.78 X 10(-4) M, althesin 3.58 X 10(-5) M (in terms of alphaxalone), etomidate 1.6 X 10(-4) M, thiopentone 2.13 X 10(-5) M and valium 4.95 X 10(-5) M. There was no relation between activity in the TEA test and excitatory muscular activity reported clinically. The central depressant drugs ethyl alcohol and urethane also potentiated TEA but they were only active in high concentrations (10(-1) - 10(-2) M). alpha-Chloralose was inactive but paraldehyde (3.8 X 10(-3) M) actually reduced TEA induced contractures. Lipophilicity is only one factor in determining activity in the TEA test, the ability to block Ca2+ reuptake may also be important.

[Alterations in local cerebral glucose utilization during various anesthesia--the effect of urethane and a review]

Anesthetic is thought to depress the energy metabolism or oxygen consumption of the brain as a whole. It has been clear, however, that anesthetic agent may either decrease or increase local metabolic rate of the brain since [14C] 2-deoxyglucose method made one possible to measure local cerebral glucose utilization. In this paper, the authors report the effect of urethane anesthesia on the local cerebral glucose utilization. We measured local cerebral glucose utilization by means of [14C] 2-deoxyglucose method in 87 brain structures of albino rats (about 300 g) under urethane anesthesia, 1 g/kg (n = 5), and conscious state (n = 6). When the whole brain metabolism was computed as a weighted average with the acid of the computerized image-processing system, there was 33% reduction in glucose utilization of the brain as a whole in the rats under urethane anesthesia. Urethane decreased the local rate of glucose metabolism, but the metabolic effect was not homogeneous throughout the brain. The neural structures in which no metabolic depression was observed were entorhinal cortex, many nuclei in hypothalamus, medial habenula-interpeduncular nucleus, nucleus tractus solitarius, and some white matters. The selective metabolic sparing in the habenula-interpeduncular system was also reported to be observed during chloral hydrate and enflurane anesthesia. However, the mechanism involved in the phenomenon remains unclear. In the discussion, we discussed the differential effects of various anesthetics of the local cerebral glucose utilization. We reviewed the literatures on the effects of various anesthetics; barbiturate, chloralose, chloral hydrate, enflurane, ketamine, nitrous oxide and halothane on the local rate of metabolism of the brain.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of capillary transport reserve by sodium pentobarbital anesthesia in isometrically contracting dog heart

We tested the hypothesis that different anesthetic may produce different effects on the ability of the myocardium to recruit capillaries. The experiments were performed on the isolated hearts of five dogs anesthetized with sodium pentobarbital (Nembutal), and six dogs anesthetized with chloralose. The isolated hearts were perfused with heparinized blood at controlled flows from a support dog anesthetized with the same agent. The adaptive capacity of the heart to recruit capillaries in response to rising left ventricular pressure (LVP) was determined by measuring the permeability-surface area product. (PS) of 22Na and 51Cr-ethylenediamine tetraacetic acid (EDTA). The myocardial ability to recruit functional capillary perfusion and transport was estimated by the ratio of the PS-Na (and EDTA) obtained at a given LVP to the PS-Na (and EDTA) at LVP = 0. In chloralose-anesthetized dogs there was a gradual increase in PS as a function of LVP. At systolic LVP ranges of 60-120 mm Hg and 130-200 mm Hg, mean PS-Na ratios were 1.15 and 1.60, while mean PS-EDTA ratios were 1.10 and 1.50, respectively. In Nembutal-anesthetized dogs there was no increase in PS associated with the increases in LVP. For the same range of LVP, the mean PS ratios for both Na and EDTA varied between 1.05 and 1.18. The results show the inhibition of capillary recruitment in Nembutal anesthetized dogs for LVP of 130-200 mm Hg. They also support the concept that Nembutal inhibits the ability of the myocardium to increase blood tissue transport of nutrients in response to increased metabolic demands.

Factors influencing the cholinesterases of cerebrospinal fluid in the anaesthetized cat

Both acetylcholinesterase and non-specific cholinesterase are found in cerebrospinal fluid and blood plasma of the cat; the ratio of activities acetylcholinesterase/non-specific cholinesterase is about 1.5 in cerebrospinal fluid and 0.15 in plasma. A search was made for factors capable of influencing the concentration of the two cholinesterases in cerebrospinal fluid. Either the ventricular system was perfused with artificial cerebrospinal fluid from a lateral ventricle to the aqueduct, or the atlanto-occipital membrane was punctured and cerebrospinal fluid was collected continuously from the cisterna magna. Factors studied included: (a) procedures affecting the composition or formation of cerebrospinal fluid, such as changes in the ionic constituents of the perfusate, the inhibition of cerebrospinal fluid formation by acetazolamide or ouabain, or the rapid intra-carotid infusion of hypertonic urea; (b) arousal (noise or stimulation of the central ends of the sciatic nerves), or deepening of anaesthesia; (c) changes in blood pressure; (d) central stimulants and depressants, pyrogens, prostaglandins, antagonists of acetylcholine. Whereas most procedures or drugs tested increased the concentration of acetylcholinesterase, some central depressants (e.g. chlorpromazine) reduced, while another (ether) increased the appearance of acetylcholinesterase in the cerebrospinal fluid. The effect of ether was, in all probability, due to damage to the blood-brain barrier. A rise in acetylcholinesterase concentration was obtained upon stimulation of the central ends of the sciatic nerves; this was inhibited by atropine but not by N-methylatropine, indicating that the rise was due to increased nervous activity and not to the circulatory effects of the stimulation, since the changes in blood pressure caused by the stimulation remained the same after atropine administration. Amphetamine or leptazol raised the levels of acetylcholinesterase but it was not possible to determine whether this was due only to increased central nervous activity, since there was invariably leakage through the blood-brain barrier which by itself would be sufficient to produce the effect. A rise in the level of acetylcholinesterase was seen after administration of pyrogen; this was apparently not a simple effect of warming the body, but due to the action of the pyrogen on centers concerned with temperature control, since warming the animal by external heat failed to produce a similar change.(ABSTRACT TRUNCATED AT 400 WORDS)

Comparison of the effects of Althesin, chloralose-urethane, urethane, and pentobarbital on mammalian physiologic responses

Physiological responses to anesthetic doses of four chemically dissimilar agents, namely, Althesin, urethane, chloralose-urethane, and pentobarbital sodium were compared in rats. The tail-flick test revealed Althesin had greater antinociceptive potency than urethane, chloralose-urethane, and pentobarbital, but its duration of action was shorter than that of chloralose-urethane. Althesin produced minimal or no suppression of core body temperature and mean arterial pressure, and only moderate reduction of mean pulse pressure. The heart rate and respiratory rate of Althesin-treated rats were slower than those of chloralose-urethane and urethane-treated counterparts, respectively, but were not significantly decreased from normal controls. It is concluded that Althesin is a suitable anesthetic for short-term surgery and for studies of body temperature, heart rate, and mean arterial pressure. Because release of gonadotropin-releasing hormone into hypophysial portal blood can be observed under Althesin but is suppressed or blocked by chloralose-urethane, urethane, and pentobarbital, Althesin is the anesthetic of choice in studies concerned with the neural control of ovulatory hormone release.

Ventricular fibrillation following canine coronary artery reperfusion: different outcomes with pentobarbital and alpha-chloralose

We compared the incidence of ventricular fibrillation after release of a 20 min-proximal left anterior descending coronary artery ligation in dogs anesthetized with either pentobarbital (N = 26) or morphine sulfate plus alpha-chloralose (N = 26). Results were analyzed using the logistic risk regression model. In each group, outcome correlated with the amount of myocardium perfused by the ligated vessel (myocardium "at risk") as measured by postmortem coronary injection of monastral dyes. At any given myocardium at risk, animals anesthetized with alpha-chloralose were less likely to fibrillate after release than those anesthetized with pentobarbital (p less than 0.01). This difference in outcome can be described by the myocardium at risk at which half the animals are expected to fibrillate (MAR50). MAR50 was 20.9 g for the pentobarbital group and 30.7 g for the alpha-chloralose group. Myocardium at risk should be taken into account in intervention studies using this coronary reperfusion arrhythmia model. We chose the logistic risk regression model to correct for this variable because it allowed a good fit of the data and offered a concise standard format for expressing the results. Outcome in reperfusion studies may be influenced by the choice of anesthetic agent.

Effect of hypnorm, chloralosane and pentobarbital on the ultrastructure of the inner membrane of rat heart mitochondria

Rat heart mitochondria were isolated from four groups of animals treated in a different way. The animals of the first group were killed after decapitation (D-group) without previous anaesthesia. The three other groups of animals were anaesthetised with different anaesthetics. The second group (N-group) was anaesthetised with nembutal (sodium pentobarbital), the third group with chloralosane (C-group) and the fourth group with hypnorm (H-group). From these three anaesthetics only nembutal is known to interact with mitochondria. After retrograde perfusion and excision of the heart, mitochondria were prepared from the ventricles by standard methods. After freeze-fracturing the mitochondrial suspension, the intramembrane particle dimension and density on both fracture faces of the inner mitochondrial membrane were measured. The intramembrane particle diameter on the P-face of the inner membrane of the N-group mitochondria was significantly different from D-, C- and H-group mitochondria. Also the density and diameter of the intramembrane particles on the mitochondrial inner membrane of D-group mitochondria compared to C- and H-group mitochondria were significantly different at the 95% level of confidence. Between C- and H-group mitochondria no differences of these parameters were observed. From these results it is clear that, depending on the pretreatment of the animals, a different substructure of the inner membrane of heart mitochondria is obtained.

Analgesic potencies of non-narcotic, narcotic and anesthetic drugs as determined by the bradykinin-induced biting-like responses in rats

Aversive (nociceptive) biting-like responses induced by micro-application of bradykinin solution onto rat tooth pulp were dose-dependently suppressed by non-narcotic drugs such as baclofen and lidocaine as well as carbamazepine and phenytoin, which are employed for clinical treatment of trigeminal neuralgia. The potency order of these drugs on a molar basis is baclofen (4.20) greater than carbamazepine (1.00) greater than lidocaine (0.94) greater than phenytoin (0.19). Such responses were also inhibited by morphine, pentazocine and cyclazocine (potency ratio of the three general analgesics, 1.00:0.46:8.11), indomethacin (a non-narcotic and anti-inflammatory analgesic) and alpha-chloralose (an anesthetic). The latter drug produced an analgesic effect at doses much lower than those used for anesthesia. These findings suggest that our method is feasible for evaluating the activities of general and particular analgesic drugs in the trigeminal regions.

Motor pool organization in monosynaptic reflexes: responses in three different muscles

Recruitment order of motoneurons was measured as a function of their conduction velocities in the presence of monosynaptic reflexes evoked by dorsal root stimulation. Motoneurons were studied in three cat hindlimb muscles: medial gastrocnemius (MG), plantaris (Pl), and tibialis anterior (TA). A relationship between recruitment order and unit conduction velocity (CV) was clearly seen in all three muscles. The correlation between these two variables was lower than that found in previous studies. A CV-dependent recruitment order was most clearly sen in tibialis anterior motoneuron pool; the relationship was poorest in plantaris. Recruitment order of MG motoneurons was measured and related to their conduction velocities in response to monosynaptic reflexes evoked by L7 + S1 dorsal root stimulation. Recruitment order was then retested in the presence of rostral root stimulation (largely heteronymous) alone and again in the presence of caudal root stimulation (largely homonymous) alone. Changing the composition of the afferent input changed the critical firing levels (rank order) of some motoneurons by as much as 40% and that of others, not at all. Some motoneurons became harder to recruit and others easier; changes in recruitment order were not related to conduction velocities of the units. 1a-afferent inputs are not uniformly distributed to all the motoneurons of a pool. It appears that this nonuniformity is a determining factor in establishing a recruitment order. TA, which receives the most uniformly distributed monosynaptic input, also has the most nearly size-dependent recruitment order. Fractionation of input ca induce additional nonuniformity, and results in recruitment-order changes in some motor units that are independent of their conduction velocity. It is concluded that nonuniformity of afferent inputs, whether present or induced by experiment, can produce large recruitment-order changes among individual motoneurons in a pool and that these individual motoneurons need not share a common property such as conduction velocity or recruitment threshold in response to a control input. Therefore, arguments based on reversals in recruitment order of pairs of motor units or even changes in rank order of individual motor units do not present sufficient evidence for the presence of input specifically directed to motor units sharing a particular property.

Alpha-chloralose suppression of neuronal activity

Alpha-chloralose, an anesthetic agent widely used in neurophysiologic studies, caused a significant and long-lasting suppression of single neuron activity recorded from two areas of the central nervous system in decerebrate cats. A 50 mg/kg dose (an average anesthetic dose used in many neurophysiologic studies) caused suppression of spontaneous and evoked activity of neurons in the dorsal horn of the spinal cord and greater suppression of neurons in the nucleus reticularis gigantocellularis (NRGC) of the medial medullary reticular formation. Many researchers are of the opinion that alpha-chloralose causes less suppression of the central nervous system (CNS) than other commonly used anesthetic agents. The neuronal suppression recorded in this study appears similar in many ways to suppression caused by other anesthetic agents in the same two areas of the CNS. The results of the present study suggest that alpha-chloralose may be capable of producing significant suppression of neurons in the dorsal horn of the spinal cord and NRGC. Its ability to influence other areas of the CNS should not be inferred from these results, but the data do indicate the importance of evaluating the effects of anesthetics upon neurophysiologic systems under study.