Differential responses of neocortical neurons to glucose and/or O2 deprivation in the human and rat

1. Intracellular recordings were performed in human and rat neocortical neurons with in vitro brain slice techniques. Baseline cellular properties and the effect of O2 and glucose deprivation on these neurons were studied. 2. Intracellular labelings of electrophysiologically identified neurons showed that most neurons recorded from layers 4 and 5 of the neocortex in both rats and humans were pyramidal cells with a regular-spiking or a burst firing pattern. 3. A period of complete anoxia (4-5 min) induced little or no change in membrane potential (Vm) in rat and human neocortical neurons, contrasting with the major depolarization we have previously observed in rat brainstem neurons during a similar period of anoxia. Evident depolarization occurred only when the slices were exposed to a more prolonged period of anoxia (> 7 min in rats and > 10 min in humans). 4. Membrane input resistance (Rm) of neocortical neurons decreased in both species during anoxia. In human neocortical neurons, Rm decreased by a mean of 22% with a marked increase in rheobase and suppression in spontaneous excitatory postsynaptic potentials (EPSPs). Interestingly, the increase in rheobase in human cells occurred even at an early stage (post 2-3 min in anoxia), when Vm and Rm had not yet changed. 5. Perfusing slices with a glucose-free medium for 1-2 h produced a relatively modest change in Vm (mean congruent to 28 mV). However, combined deprivation of both glucose and O2 resulted in a major depolarization (mean congruent to 50 mV) within 5-10 min in both human and rat neocortical neurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Intravesical electrical stimulation--an experimental analysis of the mechanism of action

The working mechanism of intravesical electrical stimulation (IVES) was evaluated in alpha-chloralose anaesthetized cats and rats. IVES involved a direct activation of bladder mechanoreceptor afferents of the A delta type and as a consequence a central reflex activation of the detrusor. The detrusor response was abolished by bilateral transection of the S1-S3 dorsal roots and by intravesical instillation of lidocaine. The optimal stimulation frequency was 20 Hz. The results offer a theoretical rationale for the use of IVES as treatment of weak detrusor contractility in man.

5-Hydroxytryptophan (5-HTP) augments spontaneous and evoked phrenic motoneuron discharge in spinalized rats

Experiments on anesthetized, spinalized rats were conducted to determine the effects of systemic 5-hydroxytryptophan (5-HTP) administration on: (1) spontaneous phrenic nerve activity and (2) evoked phrenic responses to short latency, non-serotonergic synaptic inputs elicited by electrical stimulation of lateral funiculus. 5-HTP augmented spontaneous phrenic activity and allowed expression of a second, longer latency evoked response. Both effects were antagonized by methysergide. Our results suggest that spinal serotonin increases the efficacy of synaptic inputs to phrenic motoneurons.

Synaptic inputs to medullary respiratory neurons from superior laryngeal afferents in the cat

Synaptic inputs from afferents in the superior laryngeal nerve (SLN) to medullary respiratory neurons (n = 154) in the dorsal respiratory group (DRG), ventral respiratory group (VRG) and the region of the Bötzinger complex (BOT) were studied in anesthetized cats. Single pulse stimulation of the SLN-evoked monosynaptic EPSPs in most inspiratory bulbospinal (I-BS) neurons in the DRG, and disynaptic or oligosynaptic chloride-dependent IPSPs in other I-BS neurons in the DRG and VRG. Stimulation of laryngeal afferents also inhibited oligosynaptically expiratory bulbospinal neurons in the VRG, and all types of respiratory neurons recorded in the BOT region. Oligosynaptic potentials (usually EPSPs) were recorded in inspiratory and expiratory laryngeal motoneurons. These results provide evidence of a processing of SLN-evoked synaptic responses by all tested groups of medullary respiratory neurons. The pathways mediating these synaptic responses are discussed.

Effect of 17 beta-oestradiol on contraction, Ca2+ current and intracellular free Ca2+ in guinea-pig isolated cardiac myocytes

1. The effect of 17 beta-oestradiol on cardiac cell contraction, inward Ca2+ current and intracellular free Ca2+ ([free Ca2+]i) was investigated in guinea-pig single, isolated ventricular myocytes. The changes of cell length were measured by use of a photodiode array, the voltage-clamp experiments were performed with a switch clamp system and [free Ca2+]i was measured with the Ca2+ indicator, Fura-2. 2. 17 beta-Oestradiol (10, 30 microM) caused a decrease in cell shortening at both 22 and 35 degrees C. This negative inotropic effect was accompanied by a decrease in action potential duration mainly brought about by a shortening of the plateau region of the action potential. 17 beta-Oestradiol (10, 30 microM) induced a similar decrease in cell shortening in voltage-clamped and current-clamped cells. 3. In Fura-2 loaded cells, 17 beta-oestradiol (10 and 30 microM) decreased systolic Fura-2 fluorescence to 72 +/- 7% and 47 +/- 4% (n = 6, P less than 0.001) of control respectively. 17 beta-Oestradiol (10 microM) had no significant effect on diastolic Fura-2 fluorescence, but at higher concentration (30 microM) induced a slight decrease in resting Fura-2 fluorescence. The effect of 17 beta-oestradiol was reversible after 1-2 min of washout of the steroid. 4. 17 beta-Oestradiol (10 and 30 microM) decreased the peak inward Ca2+ current (ICa), which was sensitive to [Ca2+]o, dihydropyridines and isoprenaline, to 59 +/- 3% and 39 +/- 5% (n = 7 approximately 9, P less than 0.01) respectively, without producing any significant change in the shape of the current-voltage relationship.5. The recovery time of ICa from inactivation was delayed by 17beta-oestradiol (10microM). The inhibitory effect of 17beta-oestradiol on ICa was less at a holding potential of -80 mV than at -40 mV.6. We conclude that 17beta-oestradiol has a negative inotropic effect on guinea-pig single ventricular myocytes by inhibiting ICa and so reducing systolic [Ca2+]i. 17beta-Oestradiol may therefore have a Ca2+ channel blocking property in guinea-pig isolated ventricular myocytes.

Acute effect of 17 beta-estradiol on rabbit coronary artery contractile responses to endothelin-1

We assessed the acute effect of 17 beta-estradiol on coronary artery constrictor responses to endothelin-1. 17 beta-Estradiol significantly shifted endothelin-1, calcium, or BAY K 8644 concentration-dependent contraction curves to the right in endothelium-denuded coronary arteries isolated from nonpregnant female rabbits. The -log 50% effective dose (ED50) of calcium in high KCl medium (100 mM) was 3.8 +/- 0.11 in control and 3.2 +/- 0.1 and 2.8 +/- 0.12 after incubation with 17 beta-estradiol (1 and 10 microM, respectively). The -log ED50 of BAY K 8644 (KCl 15 mM) was 7.8 +/- 0.1 in control and 7.4 +/- 0.08 and 7.2 +/- 0.05 in the presence of 17 beta-estradiol (1 and 10 microM, respectively). The -log ED50 of endothelin-1 was 9.2 +/- 0.08 in control and 8.8 +/- 0.1, 8.4 +/- 0.07, and 8.1 +/- 0.12 after incubation with 17 beta-estradiol (3, 10, and 30 microM, respectively). Similar results were obtained from coronary arteries of male rabbits. These increases of -log ED50 values were significant (P less than 0.05 or 0.01). 17 beta-Estradiol and verapamil induced dose-dependent relaxation in both endothelium-intact or -denuded coronary arteries submaximally precontracted by endothelin-1. NG-monomethyl-L-arginine had no effect on relaxation induced by 17 beta-estradiol, whereas it eliminated relaxation induced by acetylcholine in rings with an intact endothelium. These data suggest that 17 beta-estradiol attenuates the rabbit coronary artery contraction induced by endothelin-1 via an endothelium-independent mechanism, possibly by affecting calcium influx.

Impairment of endothelium dependent responses in a rat model of chronic heart failure: effects of an exercise training protocol

OBJECTIVE

The aim was to document the response of aortic rings from a rat model of heart failure to endothelium dependent and endothelium independent vasodilating agents. The effects of an exercise training schedule upon these responses was studied.

METHODS

Heart failure was produced in one group of female Wistar rats by coronary artery occlusion, and sham operations were performed in a matched group. The rats were allowed to recover for six weeks, following which half the rats with heart failure were started on a treadmill exercise schedule for a further six weeks. After this time the rats were killed, and rings of aorta were studied in an organ bath to measure the response to both endothelium dependent and endothelium independent vasoactive agents.

RESULTS

The presence of heart failure was confirmed in both the non-trained (NT, n = 5) and trained rats (TR, n = 5), but not in the sham operated animals (SH, n = 6). The constrictor response to prostaglandin F2 alpha was similar in aortic rings from all the animals. The relaxation response to the endothelium dependent vasodilator acetylcholine (10(-7) and 10(-6) M) was impaired in the rats with heart failure compared to the sham operated animals (10% v 33% with 10(-7) M acetylcholine, p < 0.005). The dilator response in the trained rats was not significantly greater than in the non-trained rats (TR 35% v NT 24% with 10(-6) M acetylcholine). There was no difference in the response to sodium nitroprusside (10(-7) and 10(-6) M) between the three groups.

CONCLUSIONS

Chronic heart failure impairs the response of aortic rings to the endothelium dependent vasodilator acetylcholine in a rat model of heart failure. The response to sodium nitroprusside, an endothelium independent relaxing agent, is not impaired by heart failure. These findings may help to explain the raised systemic vascular resistance and the failure of vasodilatation in skeletal muscle vasculature which limits exercise capacity in subjects with heart failure.

Comparative responses of brain stem and hippocampal neurons to O2 deprivation: in vitro intracellular studies

Most mammalian neurons are known to be sensitive to oxygen availability, but the nature of the sensitivity is not well understood. Previous results have suggested that brain stem neurons may respond differently than cortical neurons during oxygen deprivation. We pursued this hypothesis by examining the time course of change in membrane potential (Vm) and input resistance (Rn) during periods of reduced oxygen availability in a tissue slice preparation. Since extracellular potassium is an important factor determining resting membrane potential, extracellular K+ activity, (K+o), was also measured. Adult rat neurons from three regions were recorded: hippocampal CA1 region, hypoglossal nucleus (XII), and dorsal vagal motor nucleus (DMNX). At the end of a 5-min hypoxic exposure, all neurons depolarized and this depolarization was greatest in XII (28.8 +/- 3.2 mV) compared with DMNX (17.8 +/- 3.7 mV) and CA1 (6.7 +/- 4.4 mV). K+o increased in all regions and was larger in DMNX (7.1 +/- 2.6 mM) and XII (5.3 +/- 2.1 mM) compared with CA1 (2.2 +/- 1.4 mM). During more severe oxygen deprivation (anoxia), neurons also depolarized at different rates with XII greater than DMNX greater than CA1. K+o increased markedly (28-36 mM) by 5 min into anoxia, and no statistical difference was observed between regions. From these results we conclude that 1) all cells tested were depolarized after 5 min of hypoxia; however, regional variability exists in the sensitivity to hypoxia; brain stem neurons depolarize faster than cortical neurons; 2) during anoxia, all brain stem and cortical neurons show a major depolarization, and 3) these differences in membrane potential cannot be solely attributed to changes in extracellular K+.

Distribution of the microtubule-dependent motors cytoplasmic dynein and kinesin in rat testis

To examine the possible role of microtubule-based transport in testicular function, we used immunofluorescent techniques to study the presence and localization of the microtubule mechanoenzymes cytoplasmic dynein (a slow-growing end-directed motor) and kinesin (a fast-growing end-directed motor) within rat testis. Cytoplasmic dynein immunofluorescence was observed in Sertoli cells during all stages of spermatogenesis, with a peak in apical cytoplasm during stages IX-XIV. Cytoplasmic dynein immunofluorescence was also localized within Sertoli cells to steps 9-14 (stages IX-XIV) germ cell-associated ectoplasmic specializations. In germ cells, cytoplasmic dynein immunofluorescence was observed in manchettes of steps 15-17 (stages I-IV) spermatids, and small, hollow circular structures were seen in the cytoplasm of step 17 and step 18 spermatids during stages V and VI. Kinesin immunofluorescence was observed in manchettes of steps 10-18 spermatids (stages X-VI). The stage-dependent apical Sertoli cell cytoplasmic dynein immunofluorescence, in conjunction with the previously reported orientation of Sertoli cell microtubules (slow-growing ends toward the lumen) and peak secretion of androgen-binding protein and transferrin, is consistent with the hypothesis that cytoplasmic dynein is involved in Sertoli cell protein transport and secretion. Further, the localization of cytoplasmic dynein and kinesin to manchettes is consistent with current hypotheses concerning manchette function.

Detergents inhibit chloramphenicol acetyl transferase

Potent inhibition of chloramphenicol acetyl transferase (CAT) by Triton X-100 and Nonidet P-40 was observed. The CAT activity was also moderately inhibited by sodium deoxycholate and sodium dodecyl sulfate, and least by Tween 20. Detergents should, therefore, not be used for cell lysate preparation when CAT activity is used as the reporter in a transient expression experiment.

Oxidative and glycolytic pathways in rat (newborn and adult) and turtle brain: role during anoxia

Using enzyme histochemistry and in vitro electrophysiological recordings in brain slices, we studied 1) the relative activity of cytochrome c oxidase (Cytox) and hexokinase (HK) and 2) cellular function by examining ionic homeostasis across cell membranes in the turtle and newborn (5 days old) and adult rat central nervous system. We found that Cytox was higher in the rostral than in the caudal brain regions of the adult rat and that the activity in the newborn is at least as high as in the adult rat. In contrast, adult turtles had very low Cytox activity throughout the central nervous system. Compared with that in the adult rat, HK activity in the newborn was generally lower in the rostral brain and cerebellum but similar or higher in the brain stem and spinal cord. In the turtle, HK activity was higher in the cerebellum, brain stem, and ventral horn of the spinal cord than in those in the rat. During anoxia, extracellular K+ increased by approximately 10-fold (from 3.2 to approximately 32 mM) in the adult brain stem but only by 2.6 mM in newborn rats. After glycolysis was blocked with iodoacetic acid (10-20 mM), extracellular K+ increased remarkably in both adult and newborn rats to approximately 35 mM. In contrast, the turtle brain tissue showed a slight and insignificant increase in extracellular K+ during complete anoxia or with iodoacetic acid; there was a modest increase in K+ when anoxia and iodoacetate were administered together. We conclude that 1) the newborn rat brain must rely either on higher glycolytic capacity or on a reduction of metabolic rate during O2 deprivation and 2) the turtle brain can subsist on nonglucose fuels or on fuels not requiring the citric acid cycle and the electron transfer chain.

Role of ATP-sensitive K+ channels during anoxia: major differences between rat (newborn and adult) and turtle neurons

1. It is well known that anoxia induces an increase in extracellular K+. The underlying mechanisms for the increase, however, are not well understood. In the present study, we performed electrophysiological, pharmacological and receptor autoradiographic experiments in an attempt to examine K+ ionic homeostasis during anoxia. Ion-selective microelectrodes were employed to measure intracellular and extracellular K+ activity from hypoglossal neurons in brain slices. 2. During 3-4 min anoxia, adult hypoglossal neurons lose a large amount of their intracellular K+ and this contributes in a major way to the 8-fold increase in extracellular K+. 3. Loss of intracellular K+ from hypoglossal neurons is, to a great extent, due to activation of certain specific K+ channels. Glibenclamide, a potential sulphonylurea ligand and a specific blocker of ATP-sensitive K+ (KATP) channels, has no effect on K+ homeostasis during oxygenated states, but almost halves the anoxia-induced increase in extracellular K+ in the adult rat. 4. [3H]glibenclamide autoradiography shows that the hypoglossal nucleus in the adult rat has high sulphonylurea receptor density, a finding that is consistent with our electrophysiological observation. 5. Since we have previously shown that newborn mammals and reptiles are more resistant to O2 deprivation than adult mammals, we performed comparative studies among adult rat, newborn rat and adult turtle. In sharp contrast to the adult rat, extracellular K+ activity in newborn rat and adult turtle brain increases little (10 to 100 times less than the adult rat) and glibenclamide has a small and insignificant effect on K+ efflux in the newborn rat and none in the turtle. Glibenclamide receptor binding sites are much lower in the newborn rat than in the adult rat central nervous system (CNS) and barely detectable in the turtle brain. 6. These results support the hypothesis that in the adult rat, K+ is lost during anoxia from neurons through sulphonylurea receptor or KATP channels in a major way. Generally, however, KATP channels are poorly expressed in the newborn rat and adult turtle CNS and have little role to play during O2 deprivation.

Cl- and Na+ homeostasis during anoxia in rat hypoglossal neurons: intracellular and extracellular in vitro studies

1. To understand the mechanisms which lead to acute neuronal swelling during anoxia, we studied the ionic movements of Cl- and Na+ during O2 deprivation in the hypoglossal (XII) neurons of rat brain slices using double-barrelled ion-selective microelectrodes. 2. Baseline extracellular Cl- and Na+ activities ([Cl-]o, [Na+]o) were 128.3 +/- 7.4 and 150.0 +/- 3.4 mM respectively (n = 12) in the adult. Similar baseline values were obtained from neonatal brain slices. 3. During a period of anoxia (4 min), [Na+]o decreased by about 40 mM in adult slices while [Na+]o did not show any significant change in the neonate (n = 12). Although anoxia induced a significant decrease of [Cl-]o in both adult and neonate, [Cl-]o dropped 7 times more in the adult than in the neonate (n = 12). 4. Intracellular Cl- activity ([Cl-]i) was studied in twenty-seven adult hypoglossal cells. All showed an increase in [Cl-]i) was studied in twenty-seven adult hypoglossal cells. All showed an increase in [Cl-]i with O2 deprivation. Detailed analysis carried out on ten hypoglossal neurons showed a baseline [Cl-]i of 11.4 +/- 4.5 mM and an increase in [Cl-]i by 20.6 +/- 7.2 mM during O2 limitation. 5. Baseline [Cl-]i in neonatal XII neurons was similar to that of the adult. Anoxia, however, produced an increase in [Cl-]i by only 4.5 +/- 2.4 mM (n = 7). This increase in [Cl-]i was significantly less than that in the adult (P less than 0.001). Prolonged anoxia (6-12 min) in the neonate led to a more substantial increase in [Cl-]i, an observation consistent with the decrease in [Cl-]o after prolonged O2 deprivation. 7. We conclude that during anoxia: (1) intracellular [Cl-] increases in the adult and this most likely occurs because of entry of extracellular Cl- into the cytosol and (2) there is a major maturational difference in mechanisms regulating Cl- and Na+ homeostasis between newborn and adult brain tissue. We speculate that these mechanisms may account, at least partially, for the relative tolerance to anoxia in the newly born.

O2 tension in adult and neonatal brain slices under several experimental conditions

Brain tissue O2 tension (pO2) was measured in brainstem slices of adult and neonatal rats using carbon fiber polarographic microelectrodes. These studies were performed in order to examine the relation between pO2 and a variety of experimental conditions including temperature, distance from slice surface, brain region, animal age, tissue thickness and ambient O2 levels. Baseline brain tissue pO2 was inversely proportional to temperature and depth from slice surface. White matter had a much higher pO2 than gray matter. Tissue thickness and animal age had major effects on tissue pO2. In slices of 800 microns thick at 37 degrees C, for example, brain tissue pO2 in the adult dropped to 0 mm Hg at a depth of 200-300 microns, but remained above 45 mm Hg throughout neonatal (3-10 days) slices, when O2 tension in the perfusate was about 600 mm Hg. In thicker neonatal slices (1500 microns), pO2 decreased also to 0 mm Hg in deep areas. An N2 environment produced a rapid reduction in pO2 to 0 mm Hg within 15 s, and O2 levels of 21, 10 and 5% induced graded pO2 minima and graded latencies to reach each pO2 nadir. We conclude that: (1) tissue thickness has a major effect on tissue pO2 level: pO2 can reach zero if the slice is thicker than 600 microns in the adult and 1500 microns thick in the neonate; (2) pO2 level is higher in neonatal brain tissue at all ambient O2 concentrations than in the adult; and (3) graded hypoxia produces patterned and graded reductions in tissue pO2.

The therapeutic and biological effects of total lymph node irradiation and autologous bone marrow infusion on malignant lymphoma patients

Forty patients with malignant lymphoma were treated by 60Co total lymphoid irradiation (TLI): 21 cases received 6 Gy and 19 received 8 Gy. Ten also received autologous bone marrow infusion (ABMI). Acute radiation damage with digestive tract reaction and hemopoietic and immunological depression was observed. Bone marrow was depressed. WBC and platelets decreased rapidly. Lymphocytes showed quantitative and qualitative changes even at the early stage. All these symptoms subsided within 40 days. TLI accompanied by irradiation of the tumor site could result in effective control. The 1-, 3-, and 5-year survival rates of malignant lymphoma patients were 30/40 (75%), 14/24 (58%) and 4/12 (33%), respectively, while in those with Hodgkin's disease alone, the 1- and 3-year survival rates were 10/13 (76%) and 5/7 (71.4%), respectively. ABMI hastened hemopoietic reconstitution, which recovered relatively quickly after TLI.

[Dynamic variation of saikosaponin contents]

In this paper both the cultivated and wild Bupleurum chinense and B. scorzonerifolium from northeast China of different growing periods and ages were analyzed for the contents of saikosaponins a and d by HPLC and total saikosaponins by spectrophotometry. The results indicated that the saikosaponin content of B. chinense was higher than that of B. scorzonerifolium, and that the saikosaponin contents of the cultivated species were higher than or almost equal to those of the wild ones. It was also found that both the cultivated and wild B. chinense and B. scorzonerifolium featured the highest contents of saikosaponins in the nutrition-growing period.

Effect of anoxia on intracellular and extracellular potassium activity in hypoglossal neurons in vitro

1. A brain slice preparation was used to study the hypoglossal (XII) neuronal response to anoxia. Both intra- and extracellular potassium activities (K+i,K+o) were measured by the use of ion-selective microelectrodes, and K+ flux was assessed by the use of pharmacologic blockers. 2. Extracellular recordings showed that a short period of anoxia (4 min) induced an increase in K+o of 26.4 +/- 7.5 mM (mean +/- SD, n = 20) in the XII nucleus of adult rats. 3. Intracellular recordings (n = 31) in XII neurons showed a substantial decrease in K+i during anoxia. Fourteen neurons were analyzed in detail and these showed that XII neurons depolarized to -25.3 +/- 7.7 mV, whereas K+i dropped from 93.6 +/- 14.9 to 32 +/- 9.0 mM. These results strongly suggested that K+ is lost from XII neurons during anoxia. 4. Although the extracellular space (ECS) shrank by approximately 50% during anoxia, the possibility that the increase in K+o and decrease in K+i were mainly caused by shrinkage of the ECS and swelling of intraneuronal space was excluded to a great degree because the changes in K+i and K+o during anoxia were relatively very large. 5. To study the mechanisms by which K+ is lost from XII neurons, we used several pharmacologic blockers. High concentration of ouabain (10 mM) and strophanthidin (80 microM) increased K+o from baseline (3-4 mM) to 40.9 +/- 2.5 mM (n = 6) but did not abolish an additional anoxia-induced increase in K+o, suggesting that mechanisms other than Na(+)-K(+)-adenosine triphosphatase inhibition were also responsible for the anoxia-induced K+ leakage.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition by barium and glibenclamide of the net loss of 86Rb+ from rabbit myocardium during hypoxia

STUDY OBJECTIVE

The aim was to determine the effects of barium ions and glibenclamide on the hypoxia induced K+ efflux from rabbit myocardium.

DESIGN

Experiments were performed on the isolated interventricular septum of the rabbit perfused with a physiological solution through the septal artery. The stimulation rate was 90 beats.min-1 and the temperature 32 degrees C. The flux of 86Rb+ was used as a surrogate of K+ fluxes.

EXPERIMENTAL MATERIAL

Septa were obtained from adult male New Zealand white rabbits.

MEASUREMENTS AND MAIN RESULTS

The uptake of 86Rb+ by the septum could be fitted to a single exponential curve with a rate constant of 0.024(SEM 0.001) min-1 (n = 14). Washout experiments were performed in which septa were labelled with 86Rb+ and then perfused with unlabelled solution for 60 min. The rate constants for the efflux of 86Rb+ were similar and were 0.022(0.001) min-1 (n = 13) for radioactivity in the tissue and 0.029(0.001) min-1 (n = 13) for radioactivity in the effluent. These rate constants were similar to those reported previously for 42K+. Septa were labelled for 150 to 180 min with 86Rb+ and then perfused with a hypoxic substrate free solution for 15 min followed by reoxygenation. The net loss of 86Rb+ was calculated to be equivalent to 4.00(0.20) mmol.kg-1 wet tissue of K+ (n = 8) and in washout experiments (n = 6) this loss was shown to be due to increased efflux. Ba2+, 0.1 mM and 1.0 mM, added at the onset of hypoxia decreased net tissue loss of 86Rb+ by 64(6)% (n = 5) and 97(1)% (n = 6) respectively (both p less than 0.01). Glibenclamide (0.1 mM) decreased tissue net loss by 52(3)% (n = 6, p less than 0.01).

CONCLUSIONS

Part of hypoxia induced net K+ loss in this preparation can be attributed to activation of ATP sensitive K+ channels but other mechanisms are also involved.

Respiratory neurons in the medulla of the rabbit: distribution, discharge patterns and spinal projections

To determine distribution, discharge patterns and the spinal projections of medullary respiratory neurons (RNs), a systematic mapping of 806 RNs was made in the medulla of anesthetized rabbits. In disagreement with previous reports that there are no discrete medullary respiratory neuronal groups in rabbits, two neuronal groups were identified: (1) dorsal respiratory group (DRG), associated with the nucleus tractus solitarius; and (2) ventral respiratory group (VRG), associated with the nucleus ambiguus compact formation. The density of RNs in the DRG was much lower than that in the VRG. In the VRG, 3 subdivisions of RN populations were found: predominantly expiratory neurons in the caudal and the rostral parts, and mainly inspiratory neurons in the intermediate region. Nine distinct types of RNs were classified on the basis of firing patterns. Nearly all types were found in both the DRG and each VRG subdivision. Antidromic mapping of 64 VRG neurons revealed that 67% projected to the spinal cord. Expiratory bulbospinal neurons in the rostral subdivision of the VRG projected only to the cervical cord (mainly ipsilaterally). Most neurons of the intermediate and caudal subdivisions of the VRG (74%) appeared to project either contralaterally or ipsilaterally below T. The axonal conduction velocity was 40-50 m/s by two-point determinations. We conclude that respiratory neuronal groups in the medulla of the rabbit are generally similar to those of the cat. Nearly equal proportions of bulbospinal RNs projected to the ipsilateral vs contralateral spinal cord.