Myogenic oscillations in rabbit ocular vasculature are very low frequency.

BACKGROUND/AIMS: In a previously described model of isolated rabbit eye, we detected myogenic intrinsic vascular tone of unknown origin in the ophthalmic artery. In order to better understand the origin of these low frequency oscillations, we analyzed their spectral characteristics using fast Fourier. METHODS: Hybrid New Zealand rabbits of either sex (n = 24) were used; they were divided into 2 groups according to age. The spectral characteristics of the myogenic behaviour of the rabbit external ophthalmic artery were analyzed using the fast Fourier algorithm. RESULTS: The frequency of the oscillations of the myogenic activity seen in the rabbit external ophthalmic artery varied between 0.033 and 0.066 Hz (mean 0.045 ± 0.012 Hz), all in the region of very low frequency (VLF) oscillations (VLF <0.07 Hz for the rabbit). The frequency of spontaneous oscillations was higher in younger animals. CONCLUSION: Fast Fourier analysis proved to be an adequate mathematical tool to analyze the myogenic tone oscillations, which were all in the range of VLF in the model we used. These results indicate that myogenic vascular function of ocular blood flow is composed of VLF oscillations, and they provide a new explanation for the origin of VLF in arterial spectra. They also suggest that the ocular local myogenic vascular function observed is more efficient in younger animals.

L-arginine and L-nitroarginine methylester effects on vasomotion in isolated rabbit eyes.

BACKGROUND/AIMS: Although nitric oxide (NO) has been shown to be essential for maintaining the basal blood flow in the retina and optic nerve head, its exact role in vasomotion is still controversial. This study investigated L-arginine (L-Arg) and N-nitro-L-arginine methylester (L-NAME) effects on vascular reactivity in a model of isolated rabbit eye. METHODS: Rabbit external ophthalmic arteries (n = 12) in a head-mounted preparation were cannulated and perfused with warmed Tyrode solution. The effect of intraluminal pressure as a measure of total vascular resistance was assessed. Response curves to intra-arterial injections of 3 growing concentrations of L-Arg (n = 6) and L-NAME (n = 6) were obtained. RESULTS: Without any drug administration, spontaneous oscillations were observed in all the models. L-Arg (NO precursor) induced vasodilation and decreased both frequency and amplitude of the periodic oscillations. L-NAME (NO synthase inhibitor) produced a strong vasoconstrictor tone and stimulated vasomotion, causing a faster rate of pulsatility. CONCLUSION: L-Arg and L-NAME acted as modulators of ocular vascular tone. L-Arg elicited vasodilation and decreased vasomotion while L-NAME produced a strong vasoconstrictor tone and caused a faster rate of pulsatility. These findings justify the need to investigate NO precursors and antagonists as possible alternative therapeutics in vascular eye diseases.

Two anomalous cardiovascular responses to active standing in essential hypertension.

INTRODUCTION: In a previous work we studied, non-invasively, autonomic nervous system control of circulation in healthy subjects, observing the hemodynamic reaction to active standing. We now propose to extend this analysis to essential hypertension (EH), investigating possible autonomic dysfunction. METHODS: The cardiovascular response to postural change from the supine position to active standing of 48 EH patients, of both sexes, with and without medication, was compared with that obtained for healthy subjects. We evaluated arterial systolic (SBP) and diastolic (DBP) blood pressure, stroke volume (SV), inotropic index (INOI), total vascular resistance (TVR), cardiac work (W), stroke work (SW), arterial compliance (AC) and heart rate (HR), using the entirely non-invasive BoMed NCCOM3 thoracic electrical bioimpedance monitor and sphygmomanometry. RESULTS: We found two patient groups characterized by different linear relationships between values of cardiovascular variables in active standing and in supine positions. Except for HR, in both groups these regression lines differed from normal. Compared to the supine position, in active standing, one group (EH-I) presented increased TVR, diminished SV, INOI, W, SW, and AC, and normal HR; the other group (EH-II) presented diminished TVR and HR and increased SV, INOI, W, SW and AC. The two patient groups could be separated on the basis of their age, but not on the basis of their systolic, diastolic and mean arterial blood pressures, gender or medication. The younger patient group (EH-I) included 28 subjects aged 24 to 69 years (50+/-10), of whom 11 were unmedicated, and the older patient group (EH-II) included 20 subjects aged 35 to 75 years (62+/-11), of whom 7 were unmedicated. DISCUSSION: Our results show a depressed response in postural change for older patients, which in the autonomic control of circulation expresses carotid baroreflex impairment, and conversely an enhanced response for younger patients, which can be caused by a maladjustment of the influence of cardiopulmonary mechanoreflexes in the alance with arterial baroreflexes. CONCLUSIONS: This work suggests the existence of two different levels of dysautonomia in EH, according to age. The deterministic changes in cardiovascular variables after postural change show that, regarding autonomic nervous system control to maintain homeostasis, certain circulatory statuses are favored.

Effect of stimulation of sublobule IX-b of the cerebellar vermis on cardiac function.

Activation of sublobule IX-b of the cerebellar vermis evokes hypotension, bradycardia and decrease of the phrenic nerve activity in the anesthetized animal. Cardiac performance during the isovolumic phases of systole and relaxation can be evaluated by dP/dtmax, Vpm, dP/dt/DP40 and tau, respectively. In the present study, we evaluated the changes on cardiac function evoked by the stimulation of sublobule IX-b. New Zealand white rabbits were anesthetized, paralyzed and artificially ventilated. A posterior craniotomy was made to reveal and stimulate the cerebellar uvula (4 s train; 50 Hz; 1 ms; 20 microA). The femoral artery and veins were cannulated and a Swan-Ganz catheter was advanced in the upper abdominal aorta to control afterload when inflating the balloon. The left ventricle was catheterized with a Millar catheter. Blood pressure, heart rate, left ventricular pressure were monitored. Results showed a significant decrease on sublobule IX-b stimulation of all the indices of systolic function and an increase of tau indicating a decrease in the speed of the relaxation. These data provide the first evidence of the influence of sublobule IX-b on cardiac function. They may contribute to the understanding of the origin the cardiovascular changes that were observed in two patients with vermian and paravermian hemorrhage.

Wavelet analysis of autonomic outflow of normal subjects on head-up tilt, cold pressor test, Valsalva manoeuvre and deep breathing.

Non-invasive autonomic evaluation has used fast Fourier transform (FFT) to assign a range of low (LF) and high frequencies (HF) as markers of sympathetic and parasympathetic influences, respectively. However, FFT cannot be applied to brief transient phenomena, such as those observed on performing autonomic tests where the acute changes of cardiovascular signals (blood pressure and heart rate) that represent the first and most important stage of the autonomic performance towards a new state of equilibrium occur. Wavelet analysis has been proposed as a method to overcome and complement information taken exclusively in the frequency domain. With discrete wavelet transform (DWT), a time-frequency analysis can be done, allowing the visualization in time of the contribution of LF and HF to the observed changes of a particular signal. In this study, we evaluate with wavelets the acute changes in R-R intervals and systolic blood pressure that are observed in normal subjects during four classical autonomic tests: head-up tilt (HUT), cold pressor test (CPT), deep breathing (DB) and Valsalva manoeuvre (VM). Continuous monitoring of ECG and blood presure was performed. Also LF, HF and LF/HF were calculated. Consistent with previous interpretations, data showed an increase of sympathetic activity in HUT, CPT and VM. On DB, results reflected an increase in parasympathetic activity and frequencies. In conclusion, when compared with FFT, wavelet analysis allows the evaluation of autonomic variability during short and non-stationary periods of time and may constitute a useful advance in the assessment of autonomic function in both physiological and pathological conditions.

Intraocular pressure variability in the anesthetized rat: a spectral analysis.

PURPOSE: Intraocular pressure (IOP) is a measure of the balance between the inflow and outflow of the aqueous humor, being in close relationship with the venous ocular blood flow. But the influence of the autonomic nervous system upon this variable is not well understood. One of the most frequently used mathematical tools for the evaluation of the autonomic nervous system in the frequency domain is the fast Fourier algorithm (FFT) applied to the analysis of heart rate (HR) and arterial blood pressure (BP). For these variables, a power spectrum has been built showing the major bands: very low frequency, lower frequency, and higher frequency (HF). The range of these bands depends on the animal species. In this study, the authors used FFT to analyze the variability of IOP in anesthetized rats. METHODS: BP and electrocardiogram were acquired at 2 KHz in all animals before and following muscle blockade and artificial ventilation at the same frequency as the spontaneous ventilation. Also, in this last condition, IOP was recorded before and after the application of atropine in the eye. RESULTS: Results show three bands in the IOP spectrum, a similar profile to those observed in the HR and BP spectra, with HF band modified after atropine application DISCUSSION: The discussion calls attention to the influence of the autonomic nervous system on IOP and suggests the possibility of clinical application of this methodology on diagnosis and therapeutic efficacy.

Inhibition of the carotid baroreflex by urinary bladder distension.

OBJECTIVE: The cardiovascular responses to urinary bladder distension include a rise in arterial blood pressure, an increase in vascular resistance and heart rate, which are abolished by sectioning the pelvic and hypogastric nerves. There are indications in the literature that inputs from the arterial baroreceptors and urinary bladder converge at the same autonomic efferent pathways. Recent data provided evidence of a partial inhibitory action of the carotid baroreflex on the reflex cardiovascular responses evoked by bladder distension. In this study, we investigate the influence of urinary bladder distention upon cardiovascular responses elicited by carotid baroreceptor stimulation. METHODS: Wistar Rats were anaesthetised with alpha-choloralose (80 mg/kg, i.p.) supplemented as necessary. The carotid sinus was stimulated randomly with different volumes of saline (0.5-2.0 ml). The ureters were ligated and the bladder was cannulated. Arterial blood pressure (BP), ECG, heart rate (HR), and bladder pressure (BLP) were monitored. Baroreceptor stimulation was undertaken on two levels of BLP (2 and 20 cmH2O). The cardiovascular response to baroreceptor activation was assessed as the maximal variation of BP, HR and R-R interval for different volumes of saline injected. RESULTS: Our results showed that in all tests baroreceptor stimulation evoked a decrease in BP and HR but the magnitude of these responses was significantly different for each volume of saline and for two levels of BLP. The effectiveness and reproducibility of responses to these stimuli were confirmed by injecting a fixed volume of saline into the carotid sinus of two animals at two levels of BLP. In five animals, the variation in BP increased as the magnitude of the stimulus to the baroreceptor increased. However, the response was reduced with increased BLP. The fitted regression line was calculated for all the tests (n = 82; s = 8.2; Yint = 0.62 for BLP = 2 cmH2O; s = 9.5; Yint = 2.9; r = 0.69 for BLP = 20 cmH2O). Similar effects were observed and similar patterns of regression lines were obtained with regard to HR changes (n = 48; s = 13.3; Yint = 2.7; r = 0.82 for BLP = 2 cmH2O; s = 15.8; Yint = 0.89; r = 0.76 for BLP = 20 cmH2O) and interval changes (n = 48; s = 7.1; Yint = 4.3; r = 0.78 for BLP = 2 cmH2O; s = 8.5; Yint = 0.2; r = 0.76 for BLP = 20 cm H2O). CONCLUSIONS: These data suggest that the cardiovascular responses evoked by carotid baroreceptor stimulation are significantly different when the urinary bladder is empty or full with the response diminishing as the urinary bladder is distended.

Convergence properties of solitary tract neurons responsive to cardiac receptor stimulation in the anesthetized cat.

The convergence pattern of cardiac receptors, pulmonary C-fibers, carotid chemoreceptor, and baroreceptor afferents onto neurons within the nucleus of the solitary tract (NTS) was studied in the anesthetized (pentobarbitone sodium, 40 mg/kg,) paralyzed and artificially ventilated cat. Extra- and intracellular recordings were made from NTS neurons while stimulating both cardiac receptors by aortic root injections of veratridine (1-3 micrograms/kg) and pulmonary C-fibers by a right atrial injection of phenylbiguanide (10-20 micrograms/kg). The ipsilateral carotid body was stimulated by using arterial injection of CO2-saturated bicarbonate solution, whereas inflation of the ipsilateral carotid sinus was used to activate baroreceptors. The ipsilateral cardiac vagal branch, cervical vagus, and carotid sinus nerves were stimulated electrically (1 Hz, 0.2-1 ms, 1-35 V). In 78 NTS neurons recorded either extracellularly (n = 47) or intracellularly (n = 31), electrical stimulation of the cardiac branch of the vagus nerve evoked synaptic potentials (spikes and/or excitatory postsynaptic potentials) with an onset latency between 4 and 220 ms. Some neurons displayed both short and long latency inputs(15.5 +/- 1.8 and 160.0 +/- 8.5 ms; n = 14). Of these 78 neurons, 24 responded to veratridine stimulation of cardiac receptors (i.e., cardioreceptive neurons) by exhibiting an augmenting-decrementing discharge of 37 +/- 4 s in duration with a peak frequency of 30 +/- 5 Hz. Convergence from other cardiorespiratory receptors was noted involving either carotid chemoreceptors (n = 7) or pulmonary C-fibers (n = 4) or from both carotid chemoreceptors and pulmonary C-fibers (n = 6). In contrast, only one cardioreceptive NTS neuron was activated by distension of the carotid sinus. Recording sites recovered were confined to the medial NTS at the level of the area postrema and extended caudally into the commissural subnucleus. Our results indicate a convergence of carotid chemoreceptor and pulmonary C-fiber afferent inputs to cardioreceptive NTS neurons. With the paucity of baroreceptor inputs to these neurons it is suggested that sensory integration within the NTS may reflect regulatory versus defensive or protective reflex control.

Hypothalamic modulation of laryngeal reflexes in the anaesthetized cat: role of the nucleus tractus solitarii.

1. This investigation was initiated because activation of laryngeal afferents, either by electrical stimulation of the superior laryngeal nerve (SLN) or by natural stimulation of receptors in the laryngeal mucosa, results in a cardiorespiratory response comprising bradycardia, hypotension and apnoea (phrenic nerve activity was suppressed). This pattern of response is qualitatively equivalent to the response that is evoked on activation of the arterial baroreceptors. 2. Preliminary studies indicated that the effects of activating the SLN were suppressed during stimulation in the hypothalamic defence area (HDA) at points that also blocked the effects of baroreceptor stimulation. 3. Recordings were taken from seventy-two neurones localized within the ipsilateral nucleus tractus solitarii (NTS) whose activity was modified by SLN stimulation. Sixty neurones responded with an EPSP on SLN stimulation; nine of these had an inspiratory firing pattern. Five neurones were seen to receive an IPSP on SLN stimulation. 4. Five respiratory SLN-activated neurones were unresponsive to stimulation of the other nerve inputs, whilst four received convergent EPSP inputs on sinus nerve (SN) stimulation. One cell of these four also received inputs from the aortic and the vagus nerves. Sixty-one non-respiratory SLN-activated neurones also received convergent inputs from the sinus nerve. Of these, fifty displayed an EPSP, four an IPSP and seven an EPSP-IPSP. Fifteen neurones also received inputs from the aortic nerve and seventeen from the vagus. 5. From the population of neurones affected by SLN stimulation, twenty-four of seventy were also influenced by HDA stimulation (3 were respiratory cells). Sixteen of these responses consisted of an EPSP (2 respiratory cells), five of an IPSP (1 respiratory cell) and three of an EPSP-IPSP. 6. In neurones receiving an IPSP on HDA stimulation, the SLN-evoked excitatory response was reduced throughout the period of HDA-evoked inhibition. These neurones were all shown to receive excitatory inputs from the arterial baroreceptors and laryngeal mechanoreceptors. 7. Additionally, in the thirty-seven neurones that were excited by SLN stimulation but received no direct synaptic input on HDA stimulation, a conditioning stimulus to the HDA evoked a block of SLN-evoked responses without an accompanying change in membrane potential. Several of these neurones were also affected by both baroreceptor and laryngeal mechanoreceptor stimulation. 8. These observations are discussed in the context of the role of the NTS in cardiorespiratory control. The potential importance of these interactions in respiratory distress are highlighted and the implications for the organization of central pathways for the control of autonomic and respiratory function are discussed.

The pattern of excitatory inputs to the nucleus tractus solitarii evoked on stimulation in the hypothalamic defence area in the cat.

1. In anaesthetized, paralysed and artificially ventilated cats, recordings have been made in the nucleus tractus solitarii (NTS) to assess further the role of this nucleus in mediating the cardiorespiratory responses that are elicited on stimulation within the hypothalamic defence area (HDA). 2. The responses of NTS neurones to stimulation in the hypothalamus were assessed, as were their patterns of evoked response to electrical stimulation of the sinus (SN), aortic (AN), superior laryngeal (SLN) and vagus (VN) nerves. 3. Stimulation in the HDA affected the activity of 110 NTS neurones (85 studied in intracellular and 25 studied in extracellular recordings). The present study focused on those sixty-eight neurones that were excited by such stimulation (51 intracellular recordings and 17 extracellular recordings). 4. Of the sixty-eight neurones that were excited by HDA stimulation, seven revealed no changes in membrane potential or evoked discharge (2 neurones) but the stimulus facilitated the excitatory effects of stimulating either (or both) the SN and SLN. An additional group of neurones showed powerful excitatory responses to HDA stimulation (15 studied with extracellular and 35 with intracellular recording). Evoked EPSPs had onset latencies in the range of 1-30 ms. Of those thirty-five neurones displaying EPSPs, twenty-six were shown to receive convergent inputs on nerve stimulation. In nine neurones the early EPSP in response to HDA stimulation was followed by an IPSP. 5. In a further group of neurones HDA stimulation elicited a long-lasting IPSP, but this was not analysed further because its features have been described in detail in earlier studies from this laboratory. 6. The patterns of response of several neurones excited by stimulation in the HDA are consistent with them forming a group of NTS interneurones that mediate the hypothalamically evoked cardiovascular responses, including modulation of reflex function, which is a major feature of cardiorespiratory control. This possibility is discussed in the light of the present physiological observations and descriptions of an intrinsic NTS group of GABA-containing neurones that have been suggested to fulfil such a role.

Hypothalamic modulation of the arterial chemoreceptor reflex in the anaesthetized cat: role of the nucleus tractus solitarii.

1. There is evidence in the literature of a mutual facilitatory interaction between the arterial chemoreceptor reflex and the alerting stage of the defence reaction, particularly in relation to the patterning of cardiorespiratory activity. The present study has been designed to test the hypothesis that a portion of this interaction involves synaptic interactions within the nucleus tractus solitarii (NTS). 2. The study has involved an analysis of the effective interactions between the stimulation of the arterial chemoreceptors and the hypothalamic defence area (HDA) on the activity of NTS neurones recorded in anaesthetized, paralysed and artificially ventilated cats. 3. A group of eighteen NTS neurones was classified as chemosensitive, on the basis of displaying EPSPs on sinus nerve stimulation (SN) and their failure to show an excitatory response to baroreceptor stimulation. Thirteen of these neurones displayed pronounced excitatory responses to chemoreceptor stimulation. In sixteen of these neurones HDA stimulation elicited an EPSP; in four of these sixteen neurones this early EPSP was followed by an IPSP. In the remaining two (of 18) neurones HDA stimulation provoked no obvious synaptic response but facilitated the efficacy of both chemoreceptor inputs and SN stimulation. 4. Neurones shown to receive convergent inputs from the arterial chemoreceptors (and SN stimulation) and HDA, often displayed excitatory responses to stimulation of other peripheral inputs. Vagally evoked EPSPs were observed in nine neurones, SLN-evoked responses in seven neurones and aortic nerve-evoked EPSPs in three neurones. 5. The organization of these synaptic interactions is discussed and these data are used to explain the pattern of interaction between chemoreceptor, baroreceptor and HDA inputs within the NTS. Conclusions are drawn regarding the functional role of different classes of NTS neurone, based on the findings in this and the accompanying two papers.

Action of adenosine receptor antagonists on the cardiovascular response to defence area stimulation in the rat.

1. The action of adenosine in the mediation of the cardiovascular changes associated with the defence reaction has been investigated in the rat using two A1 receptor antagonists. 2. Cumulative doses of 1,3 dipropyl-cyclopentylxanthine (DPCPX) (0.3-3 mg kg-1) and ethanol (0.03-0.25 ml) and bolus doses of DPCPX (3 mg kg-1) and 8-sulphophenyltheophylline (8-SPT) (20 mg kg-1) were given into alpha-chloralose, paralysed and artificially ventilated rats. Recordings were made of arterial blood pressure and heart rate. 3. Ethanol, the vehicle for DPCPX, failed to modify the magnitude of the defence response; however, cumulative doses of DPCPX produced a dose-dependent decrease in the HDA (hypothalamic defence area)-evoked increase in arterial blood pressure, accompanied by a similar fall in the magnitude of the evoked heart rate response. 4. The evoked rise in arterial blood pressure was reduced significantly by intravenous injection of DPCPX (3 mg kg-1) but not 8-SPT (20 mg kg-1), a purely peripherally acting adenosine antagonist. 5. These results suggest that adenosine acting at A1 receptors located in the central nervous system, is involved in the HDA-evoked pressor response. Whilst the site of action of the A1 receptors is not known, possible locations are discussed.

A potential role of central A1 adenosine receptors in the responses to hypothalamic stimulation in the anaesthetized cat.

In pentobarbitone anaesthetized and paralysed cats the effects of the A1 adenosine antagonist 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) have been observed on the pressor response to stimulation of the hypothalamic defence area (HDA) and on the effects of baroreceptor and chemoreceptor reflex activation on arterial blood pressure. The administration of DPCPX decreased the magnitude of the HDA pressor response and the chemoreceptor induced rise in blood pressure. The fall in blood pressure induced by baroreceptor activation was enhanced to a small yet significant extent. No changes were observed in the tachypnoea evoked by hypothalamic defence area (HDA) stimulation. These results suggest a possible role for central adenosine A1 receptors in mediating the cardiovascular changes evoked during HDA stimulation.

Hypothalamic-evoked effects in cat nucleus tractus solitarius facilitating chemoreceptor reflexes.

In anaesthetized cats intracellular recordings in the nucleus tractus solitarius (NTS) have been used to identify neurones receiving inputs from the carotid sinus nerve (SN), the aortic nerve and hypothalamic defence area (HDA). In forty-four neurones activated by SN stimulation HDA activation evoked an IPSP in fourteen (32%) and an EPSP in eight (11%). Those neurones receiving an HDA-evoked IPSP, and tested for reflex inputs, responded only to baroreceptor activation. Neurones receiving HDA-evoked EPSPs responded only to chemoreceptor activation. In three neurones unaffected by SN stimulation, short latency inputs from HDA were observed, suggesting direct monosynaptic inputs.

Hypothermia-induced Haemostatic and Biochemical Phenomena. An Experimental Model.

Hypothermia (24°C) was induced in 7 healthy male dogs. Hematological, hemostatic and biochemical parameters were evaluated before the onset and after 3 h of hypothermia. Following hypothermia, there was a significant increase in red cell count, hematocrit and haemoglobin concentration. The white cell and platelet counts were decreased significantly and the mean platelet volume increased significantly. The activated partial thromboplastin time was significantly prolonged whereas the prothrombin time was unchanged. Associated with these changes there was a significant increase in serum glucose and a small increase in aspartate transaminase activity probably due to muscle leakage. No change occurred in the more liver-specific alanine transaminase. The arterial pH decreased and the changes in gasses observed as a result of hypothermia were compatible with a mixed respiratory-metabolic acidosis. The mean aortic blood pressure also dropped markedly. The hematological and hemostatic changes suggest that widespread tissue 'injury' occurs even in short term hypothermia with platelet activation and accumulation in the liver and spleen. This model of hypothermia may be of use in the study of the thrombotic diathesis observed in this condition and serve as a test bed for drugs of potential use in conditions such as Raynaud's syndrome and hypothermic surgery (e.g. coronary artery bypass).

[Primary effect of carotid body stimulation on left ventricular inotropism in swine]. / Efeito primário da estimulação do corpo carotideo sobre o inotropismo ventricular esquerdo no porco.

The cardiovascular response to carotid body stimulation has been a interesting and simultaneously controversial subject. In fact, several authors described different responses depending on the animal species used (cat, dog, rabbit, monkey), time of stimulation (short-term v. long-term) and experimental conditions and procedures. According to our experience, the response to carotid body stimulation with cyanide, in normal breathing dogs, consists in hyperpnoea, bradycardia with arterial blood pressure fall (by means of longer diastolic periods), followed by a marked rise in arterial blood pressure and heart rate, after curarization. Concerning the inotropic response to carotid chemoreceptors stimulation, there exists some controversial and even antagonic opinions. In fact, some authors describe a positive inotropic effect, others a negative inotropic effect, and others still defend no inotropic response at all. In the present work, the authors try to contribute to the solution of this problem, studying a group of animals (pig) anaesthetised with chloralose, in which the major modulators of the inotropic response to carotid body stimulation (ventilation; heart rate; and ventricular load conditions) were controlled. To the evaluation of cardiac contractile state, indexes derived from the systolic isovolumic phase were used (maximum left ventricular pressure, dP/dtmax; dP/dtmin) in all the animals. In some animals, other indexes were also used (Vmax, Vpm, (dP/dt)/DP40, Tau and PB). The authors concluded that, in the present experimental conditions, the primary response to carotid body stimulation, in the pig, includes a positive inotropic effect.

The effects of electrical stimulation of lobule IXb of the posterior cerebellar vermis on neurones within the rostral ventrolateral medulla in the anaesthetised cat.

This study was designed to investigate the effects of electrical stimulation of sublobule IXb of the posterial cerebellar vermis (the uvula) on the activity of neurones in the rostroventral medulla (RVLM) of anaesthetised cats. The ongoing activity of 38 RVLM neurones was studied in detail. One group consisted of 22 neurones that had axons projecting to the spinal cord (Group A, 22 neurones), the second had only an excitatory synaptic input from the spinal cord (Group B, 14 neurones) and the last were inhibited by equivalent spinal cord stimulation (Group C, 2 neurones). In Group A 16 neurones were excited, 2 inhibited and the other 5 showed a biphasic response involving excitation followed by inhibition, to lobule IXb stimulation. In Group B, lobule IXb stimulation excited 9 cells, inhibited 2 and evoked a biphasic response in 3 neurones. In Group C both cells were inhibited on cerebellar stimulation. Some cells in Group A and B were affected by electrical stimulation of the carotid sinus nerve--the predominant effect being an excitation. Specific baroreceptor stimulation invariably caused inhibition and several neurones had pulse modulated discharge. These data indicate that stimulation of sublobule IXb has marked influences on RVLM neuronal activity including a proportion of those neurones that have axons descending to the spinal cord that has been described as presympathetic 'vasomotor' neurones. A striking finding is the more widespread action of sublobule IXb, baroreceptor and sinus nerve inputs on other neurones of the RVLM, and the implications of this for the integration of cardiovascular control are discussed.

Nucleus tractus solitarius as mediator of evoked parabrachial cardiovascular responses in the decerebrate rabbit.

1. The present study has assessed the importance of neurones within the nucleus tractus solitarius (NTS) in mediating the cardiovascular response evoked from the parabrachial nucleus (PBN) in the decerebrate rabbit. Microinjection techniques were employed so that the magnitude of the circulatory responses elicited from the PBN could be compared before, and after, kainic acid or bicuculline were microinjected into restricted regions of the NTS. 2. Electrical stimulation of the PBN (both medial and lateral regions) evoked variable changes in heart rate, a pressor response, vasoconstriction in the hindlimb and an increase in renal sympathetic nerve activity. Glutamate injected into these regions of the PBN elicited a similar pattern of response except that a tachycardia was observed consistently. 3. Both electrical and chemical stimulation of restricted regions of the NTS evoked bradycardia and a depressor response together with an increase in femoral vascular conductance and an inhibition of activity in the renal nerve. 4. Chemical lesions placed in these regions of the NTS by microinjecting kainic acid were found to attenuate both the heart rate and arterial blood pressure responses elicited from sites in the medial and lateral PBN using either electrical or chemical stimulation. Equivalent effects were produced on microinjecting the GABAa receptor antagonist bicuculline into the NTS. 5. These data indicate that NTS neurones play a part in mediating the cardiovascular responses that are evoked from the PBN and suggest that the action of the PBN at the level of the NTS is mediated via a GABAergic mechanism.

Inhibition of barosensitive neurones evoked by lobule IXb of the posterior cerebellar cortex in the decerebrate rabbit.

1. Electrical stimulation of lobule IXb of the posterior cerebellar vermis evoked an increase in heart rate and arterial pressure in the decerebrate rabbit. This pattern of response was followed by a rebound bradycardia which was maintained until arterial pressure had returned to control levels. Activation of the arterial baroreceptors during IXb stimulation failed to elicit reflex changes in heart rate and arterial blood pressure. 2. Extracellular recordings were made from eighty-one single neurones in the nucleus tractus solitarius (NTS), and adjacent structures, that received inputs from the carotid sinus nerve, aortic nerve and/or vagus. A proportion of these were characterized as baro- or chemosensitive by physiological stimuli. The nature of the input from lobule IXb onto these cells was studied subsequently. 3. In twenty-seven out of thirty-five barosensitive neurones, stimulation of lobule IXb either decreased or abolished on-going activity. The latency to onset of inhibition was 21 ms in fourteen cells. In a further twenty-one neurones the spikes evoked orthodromically by electrical stimulation of either the aortic or sinus nerves were either inhibited or severely reduced in number during short-train conditioning stimulation of lobule IXb. This effect was most potent when the cortical conditioning stimulus was timed to occur 25 ms before the aortic or carotid sinus nerves were stimulated. 4. It is suggested that stimulation of lobule IXb in the decerebrate rabbit expresses its influence on the cardiovascular system in part by an inhibitory action on neurones receiving baroreceptor inputs at the level of the NTS.

[Effects induced hypothermia on hepatic portal circulation]. / Effets de l'hypothermie provoquée sur la circulation portale hépatique.

Studies of the liver circulation in dogs during hypothermia, showed that portal blood flow is reduced with no significant changes of blood pressure and with important vascular resistance. These effects are probably due to the contraction of pre-capillaries sphincters.