Interaction of baroreceptor afferents from carotid sinus and aorta at the nucleus tractus solitarii

Summary In chloralose-urethane anaesthetized cats, low-threshold baroreceptor afferents of the carotid sinus and aortic nerves were stimulated electrically. Evoked responses were recorded within the nucleus tractus solitarii near the obex. At a certain electrode position in this area an evoked potential (E. P.) was elicited by stimulation of the homolateral carotid sinus or aortic nerve as well as the contralateral sinus or aortic nerve.At this site an interaction of these four baroreceptor nerves was demonstrated by testing the E. P. of one nerve after a conditioning stimulation of another nerve. Simultaneous E. P.'s did not show arithmetical summation. A strong reduction of the test-E.P. (mean value of reduction: 50%) occurred with a conditioning-testing interval of 10–20 msec. The test-E. P. came back to the control amplitude at an interval of 100–150 msec.Neither picrotoxin nor strychnine changed the time course or extent of these interactions.It was further observed that the most effective conditioning-testing interval for inhibition of test response corresponded closely to the difference between the arrival times of arotic and sinus nerve activities evoked by the cardiovascular pulse (aortic 16±5 msec before sinus nerve).A summary of these studies was presented at the 35th Meeting of the Deutsche Physiologische Gesellschaft [5].     

Vestibulospinal and reticulospinal interactions in the activation of back muscle EMG in the rat

Summary The effects of electrical stimulation of the lateral vestibular nucleus (LVN) and medullary reticular formation (RF) on electromyographic activity in axial muscles medial longissimus (ML) and lateral longissimus (LL) in the rat were studied. Long trains (150–500 ms) at 200–330 Hz and 20–100 A were sufficient to activate ML and LL at latencies of 20–100 ms from the beginning of the train. Results of stimulation at 200–330 Hz to RF or LVN showed that muscle units were activated at a fixed latency from any effective pulse in the stimulus train. Using high frequency (1 kHz) trains of 3–6 pulses to LVN, EMG activity was detected at minimum latencies of 3.5–6 ms. When conduction times from the medulla to the spinal cord, and the spinal cord to the muscle are subtracted, this latency range is consistent with monosynaptic activation. In many cases, muscle units were recruited in order of size, with both RF and LVN stimulation. Combined stimulation of LVN and RF sites in n. gigantocellularis led to EMG activity in ML and LL at currents which were insufficient to evoke activity when presented singly. When stimulation of one site (300–400 ms train) was just sufficient to evoke a response, a shorter, overlapping train (100–150 ms) to the other site led to a higher rate of muscle activity that continued through the end of the long train, even after the short train had ended. In all cases, the effect of RF facilitating LVN was similar to the effect of LVN facilitating RF. The evidence for convergence between these two systems in the medulla and the spinal cord is discussed.     

Effects of graded pulsatile pressure on the reflex vasomotor responses elicited by changes of mean pressure in the perfused carotid sinus-aortic arch regions of the dog

1. In the anaesthetized dog, the carotid sinuses and aortic arch were isolated from the circulation and separately perfused with blood by a method which enabled the mean pressure, pulse pressure and pulse frequency to be varied independently in each vasosensory area. The systemic circulation was perfused at constant blood flow by means of a pump and the systemic venous blood was oxygenated by an extracorporeal isolated pump-perfused donor lung preparation.2. We have confirmed our previous observations that under steadystate conditions the vasomotor responses elicited reflexly by changes in mean carotid sinus pressure are modified by alterations in carotid sinus pulse pressure, whereas those evoked by changes of mean aortic arch pressure are only weakly affected by modifications of aortic pulse pressure.3. When the carotid sinus and aortic arch regions are perfused in combination at constant pulse frequency (110 c/min), the relationship between mean carotid sinus-aortic arch pressure and systemic arterial perfusion pressure is dependent on the size of the pulse pressure.4. Increasing the pulse pressure alters the curve relating the mean carotid sinus-aortic arch pressure to systemic arterial perfusion pressure in such a way that the perfusion pressure is lower at a given carotid sinus-aortic arch pressure within the range 80-150 mm Hg. The larger the pulse pressure, up to about 60 mm Hg, the greater the fall in systemic arterial perfusion pressure. Above a mean carotid sinus-aortic arch pressure of about 150 mm Hg, alterations of pulse pressure have little effect.5. There is a family of curves representing the relation between mean carotid sinus-aortic arch pressure and systemic vascular resistance, depending on the pulse pressure.     

Comparison of the reflex vasomotor responses to separate and combined stimulation of the carotid sinus and aortic arch baroreceptors by pulsatile and non-pulsatile pressures in the dog

1. In the anaesthetized dog the carotid sinuses and aortic arch were isolated from the circulation and separately perfused with blood by a method which enabled the mean pressure, pulse pressure and pulse frequency to be varied independently in each vasosensory area. The systemic circulation was perfused at constant blood flow by means of a pump and the systemic venous blood was oxygenated by an extracorporeal isolated pump-perfused donor lung preparation.2. When the vasosensory areas were perfused at non-pulsatile pressures within the normal physiological range of mean pressures, the reflex reduction in systemic vascular resistance produced by a given rise in mean carotid sinus pressure was significantly greater than that resulting from the same rise of aortic arch pressure.3. On the other hand, when the vasosensory areas were perfused at normal pulsatile pressures and within the normal physiological range of mean pressures, there was no difference in the size of the reflex vascular responses elicited by the same rise in mean pressure in the carotid sinuses and in the aortic arch.4. Whereas the vasomotor responses elicited reflexly by changes in mean carotid sinus pressure are modified by alterations in pulse pressure, those evoked by the aortic arch baroreceptors through changes of mean pressure are only weakly affected by modifications in pulse pressure. Evidence for this was obtained from single stepwise changes of mean pressure in each vasosensory area during pulsatile and non-pulsatile perfusion, and from curves relating the mean pressure in the carotid sinuses or aortic arch and systemic arterial perfusion pressure.5. The vasomotor response elicited by combined stimulation of the carotid sinus and aortic arch baroreceptors was greater than either response resulting from their separate stimulation.6. When the mean perfusion pressures in the two vasosensory areas are changed together, the curve relating mean pressure to systemic arterial pressure during pulsatile perfusion of the areas is considerably flatter than that for non-pulsatile perfusion.7. Increasing the pulse pressure in the carotid sinuses or aortic arch caused a decrease in systemic vascular resistance, the response elicited from the carotid sinuses being the larger.8. Altering the phase angle between the pulse pressure waves in the carotid sinuses and aortic arch had no effect on systemic vascular resistance.9. In both vasosensory areas, increasing the pulse frequency caused a reduction in systemic vascular resistance.     

The reflex control of vascular tone during hypothermia

Summary The vascular reflexes were studied in dogs, cats, and rabbits during stimulation of the receptors of carotid sinus, lungs, and urinary bladder; the reflexes were also investigated during stimulation of the sensory nerves (vagus, aortic, sciatic). A marked reduction of all vascular reflexes was noted during hypothermia; they disappeared almost completely when the body temperature dropped below 20°C.Depressor reflexes were subjected to more rapid and profound depression than pressor. To investigate the role of the receptor link in the changes mentioned, experiments were carried out with the local application of cold upon the carotid sinus receptors. It was found that when cooled to a temperature of 20–26°C the carotid sinus receptors showed no reduction of their sensitivity either to various chemical stimulants or to changes in the intravascular pressure. On the contrary, within this temperature range the excitability of the receptor formations was even higher than normal.(Presented by Active Member AMN SSSR, N. N. Gorev) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 50, No. 9, pp. 65–69, September, 1960     

An analysis of the inhibition of phrenic motoneurones which occurs on stimulation of some cranial nerve afferents

1. Inhibition and excitation of spontaneous phrenic nerve discharges in response to stimulation of the sinus, glossopharyngeal, aortic and superior laryngeal (SLN) nerves has been investigated in cats.

2. The inhibition, in response to a single shock, had a latency of 5-10 msec and lasted for 20-40 msec; the response to SLN stimulation was the most prolonged.

3. Excitation of phrenic motoneurones also occurred and was seen either before or after the end of the inhibition of the inspiratory burst and sometimes also during expiration.

4. Intravenous strychnine blocked the inhibition.

5. Intracellular recording from phrenic motoneurones showed that hyperpolarization was evoked by each nerve during the central phrenic depolarizing potential (CPDP) but only rarely in the interval between these potentials.

6. When the CPDP was suppressed, hyperpolarization could sometimes be evoked.

7. There were no changes in amplitude or time course of hyperpolarization during the passage of current through the cell membrane. No change in membrane conductance could be shown by passing current pulses.

8. Raising the pressure in the carotid sinus also depressed phrenic activity and evoked a hyperpolarization whilst the CPDP was suppressed.

9. Inspiratory interneurones in the brain stem were suppressed by nerve stimulation and by a rise in carotid sinus pressure.

10. Expiratory interneurones in the brain stem were both excited and suppressed by electrical stimuli and unaffected by a change in carotid sinus pressure.

     

The localization of the first synapse in the carotid sinus baroreceptor reflex pathway and its alteration of the afferent input

Summary In 78 anaesthetized cats the lower brain stem was explored with microelectrodes for localization of the secondary neurones of the carotid sinus primary afferents. By means of recording single unit activities and evoked potentials (E.P.) by stimulation of the carotid sinus nerve (CSN) these neurones were located exclusively in the nucleus tractus solitarius (NTS) at the level of the obex.The E. P. was recorded with both ipsilateral and contralateral CSN stimulation.During repetitive stimulation of the CSN the frequency transmission across the synapse showed a sharp frequency limitation. With 10 Imp/sec the amplitude of the E.P. was only 50% of the maximal amplitude obtained with 1 Imp/sec. This frequency limitation is also manifested in the frequency effectiveness of the whole baroreceptor reflex measured as blood pressure reduction. It showed a maximum with frequencies of 20–30 Imp/sec, while stimulation of the secondary neurones in the NTS showed an increase in blood pressure reduction up to the tested frequencies of 120 Imp/sec.The E.P. was tested in the different phases of the respiratory cycle. No difference in amplitude or latency between the E.P. was noted.The relevance of these findings to the arrangement of the central neural substrates for the cardiovascular control is discussed.This work was supported by the Deutsche Forschungsgemeinschaft.A summary of these studies was presented at the 34. Tagung der Deutschen Physiologischen Gesellschaft [46].     

Evidence for the involvement in the baroreceptor reflex of a descending inhibitory pathway

1. The onset and time course of baroreceptor inhibition of pre- and post-ganglionic sympathetic reflex activity has been examined in the anaesthetized cat.2. The shortest time to the onset of inhibition of an intercostal evoked reflex response in cardiac and renal nerve was less than 90 msec following a rise in pressure in a carotid sinus blind sac, and around 55 msec following stimulation of the ipsilateral sinus nerve. The cardiac nerve response was completely inhibited before the renal nerve response.3. Because of the long delays in the somato-sympathetic reflex pathway it is argued that these minimum times will be much less than the real central delay of baroreceptor inhibition. These were estimated by adding on the central times for the somato-sympathetic reflexes to give latencies of 94-143 msec for the inhibition.4. A spinal sympathetic reflex was inhibited by 30-75% following a rise in pressure in a carotid sinus blind sac or sinus nerve stimulation. The minimum time for this inhibition was around 100 msec.5. The baroreceptor inhibition of the spinal sympathetic reflex was abolished following section of a restricted region in the dorsolateral part of the lateral funiculus of the cervical spinal cord.6. Both pre- and post-ganglionic reflexes could be inhibited when stimulating within three regions of the medulla oblongata. The latency to inhibition elicited from the ventromedial reticular formation was short, some 5-30 msec, whereas that elicited from a ventrolateral region or the mid line raphe nucleus was long, some 90-160 msec.7. The possibility is discussed that the baroreceptor inhibition of both the pre- and post-ganglionic reflexes examined in this study is occurring at the spinal level via a pathway from either the raphe nuclei or ventrolateral medulla.     

Interaction of aortic and carotid sinus baroreceptors: effect of activation times.

Changes in pulse-wave velocity were simulated by changing the relative timing between aortic and carotid sinus barorecptor activity in anesthetized rabbits and dogs. In the rabbit, electrical stimulation was used to vary the timing; in the dog, it was also varied by perfusing the carotid sinuses with externally generated pressure pulses that could be triggered in any portion of the cardiac cycle. Changing the relative delay between aortic and carotid sinsus nerve stimulation did not result in variations of blood pressure or heart rate in the rabbit. Varing the time of electrical stimulation of the carotid sinus nerve caused at most 5 mmHg change of blood pressure in the dog. Delay-related heart-rate changes could be usually observed only when the stimulus consisted of short, high-intensity bursts. When the carotid sinus was externally perfused with pulses of pressure, only one out of five dogs showed delay-related variations in blood pressure (3mmHg) and heart rate (6 beats/min). It is concluded that variations in pulse-wave velocity are unlikely to play a significant role in acute cardiovascular control.     

Responses of cells in the brain stem of the cat to stimulation of the sinus, glossopharyngeal, aortic and superior laryngeal nerves

1. The distribution and properties of 146 brain stem units whose activity was influenced by electrical stimulation of sinus, glossopharyngeal, aortic and superior laryngeal nerves were studied in cats.2. Cells excited by electrical stimulation of one or more of the nerves were distributed throughout the brain stem in an area extending rostrocaudally from Horsley-Clarke co-ordinates P 7.5 to P 16.5 and laterally between 1.5 and 5 mm from the mid line.3. Most of the units excited (n = 129) or inhibited (n = 17) by nerve stimulation were localized in the nucleus reticularis gigantocellularis and nucleus reticularis parvocellularis.4. The latencies of activation varied from as short as 1.5 msec to as long as 35-40 msec. A high degree of convergence was observed.5. Evoked responses varied from single spikes to bursts of impulses, the frequencies of which were sometimes as high as 1000/sec following a single shock to the nerve.6. Spontaneously active cells inhibited (seventeen) by nerve stimulation were located primarily in NRG and NRP. None of the cells was inhibited by stimulation of one nerve and excited by stimulation of the others.7. The responses of cells to a sudden rise in carotid sinus pressure were similar in kind to the responses to electrical stimulation of the nerves.     

Studies of Blood-pressure Regulation IV. The Effects of Impulse Train Stimulation of the Carotid-sinus Nerves

The effect of sinus nerve stimulation on the blood pressure and heart rate was studied in dogs. Electrical stimulation of the sinus nerves of both sides was given both in the form of 2 types of intermittent impulse trains and as impulses of constant frequency. The intermittent impulse bursts, which were synchronized with the ECG, comprised 5–50 imp which coincided with systole (150 ms). Comparisons were made between stimulation with a constant frequency and the intermittent types, with the same number of impulses per cardiac cycle. It was found that the maximal blood pressure reduction was already reached at 5–10 imp per cardiac cycle. The difference between stimulation with a constant frequency and the intermittent types, with the same number of impulses per cardiac cycle, is negligible as regards blood pressure reduction but the intermittent type has a greater effect on the heart rate. Sinus nerve stimulation in massive haemorrhage and the influence of the amplitude of the stimulation signal were also studied.     

Action ofγ-aminobutyric acid and its phenyl derivative on central links of vascular reflexes from aortic-carotid chemo- and mechanoreptors

Experiments on decerebrate cats revealed an inhibitory effect of -aminobutyric acid (GABA; 100–200 g/kg) and its phenyl derivative, phenyl-GABA (20 mg/kg), on depressor responses of the systemic arterial pressure and on inhibition of spontaneous electrical activity in the renal nerve arising in response to excitation of the carotid sinus mechanoreceptors and afferent fibers on the sinus and depressor nerves carrying impulses from mechanoreceptors. Pressor responses of the systemic arterial pressure and electrical activity evoked in the renal nerve by stimulation of the carotid sinus chemoreceptors were intensified after administration of the same doses of GABA and phenyl-GABA. The results are interpreted from the standpoint of the depriming action of GABA and its phenyl derivative on the paramedian reticular nuclei of the medulla.Paper read at the March, 1974 Meeting of the Volgograd Scientific Society of Pharmacologists.Department of Pharmacology, Volgograd Medical Institute. (Presented by Academician of the Academy of Medical Sciences of the USSR V. V. Zakusov.) Translated from Byulleten' Éksperimental'noi Biologii i Meditsiny, Vol. 79, No. 4, pp. 71–75, April, 1975.     

Responses of neurons in the spinal nucleus of the trigeminal nerve to electrical stimulation of the dura mater of the rat brain

The pathogenesis of migraine is based on the aseptic inflammation of dura mater tissues surrounding the large cranial vessels, such as the superior sagittal sinus. This inflammation develops in conditions of antidromic activation of sensory terminals of the trigeminal nerve and is accompanied by changes in the responses of neurons in the spinal nucleus of the trigeminal nerve to electrical stimulation of the superior sagittal sinus. However, the characteristics of the responses of these neurons to this stimulation have received virtually no study. Experiments on anesthetized rats were performed with recording of the responses of 387 neurons in the spinal nucleus of the trigeminal nerve to electrical stimulation of the superior sagittal sinus. The results showed that the responses of neurons to this stimulation was biphasic, consisting of a short initial phase with a latent period of 7–19 (11.4 ± 0.17) msec, followed by a longer-lived discharge with a latent period of 20–50 (34.2 ± 0.8) msec. It is suggested that the first phase reflects orthodromic activation of perivascular A and C fibers of the trigeminal nerve, while the second phase is associated with activation of meningeal C fibers with low conduction velocities and/or secondary activation of the perivascular sensory endings of the trigeminal nerve by algogenic and vasoactive substances released from them during antidromic activation. These changes seen in animal experiments may serve as an indicator of the efficacy of antimigraine agents.Translated from Rossiiskii Fiziologicheskii Zhurnal imeni I. M. Sechenova, Vol. 90, No. 1, pp. 3–10, January, 2004.     

Quantitative studies of intracellular postsynaptic potentials in the lateral geniculate nucleus of the cat with respect to optic tract stimulus response latencies

Summary LGN cells were intracellularly recorded with glass micropipettes. Electrical stimuli of different amplitude and frequency were applied to the optic tract close to the optic chiasm. The cells were classified according to stimulus response latencies of action potentials as belonging to class I (1.0–1.6 msec) or class II (1.7–3.0 msec).Class I EPSPs had shorter latencies (1.0–1.5 msec), durations (4–12 msec), rise times to peak (0.5–1.4 msec), and decay times (3.0–8.5 msec); the synaptic transmission time was on the average 0.41 msec. Class II EPSPs (1.6–2.6 msec latency) had longer durations (10–30 msec), rise times (1.6–3.7 msec), and decay times (9.0–25 msec); the synaptic transmission time was on the average 0.67 msec.With repetitive stimulation the EPSPs of latency class I revealed almost no stimulus frequency dependence between 1 and 120 Hz, while class II EPSPs decreased in amplitude between 30 and 70% with increasing frequency. Comparable temporal summation of excitation occurred in cells of both latency classes. Negative serial correlation coefficients of first order were found for consecutive EPSP amplitudes of all cells recorded for sufficient periods of time.The IPSPs were subdivided into two groups according to their optic tract response latency. Group 1 IPSPs had shorter latencies (2.0–2.6 msec), durations (15–50 msec), and times from the onset to maximal hyperpolarization (2.4–4.2 msec) than group 2 IPSPs (3.0–4.8 msec latency, 40–100 msec duration, 2.7–7.5 msec time from onset to extremum).The group 2 IPSPs decreased in amplitude by about 90% when the stimulus frequency was increased from 1 to 50 Hz, while the group 1 IPSPs displayed a comparable decrease in the frequency range between 50 and 120 Hz. Effective temporal summation was found in group 2 IPSPs in the frequency range below 70 Hz, and in group 1 IPSPs at stimulus frequencies between 70 and 120 Hz.The EPSP peak latencies and the latencies to the minimum of IPSPs proved to be invariant with respect to PSP amplitude and stimulus frequency in individual cells. The latencies to the extrema of EPSPs and IPSPs as well as the amplitude values were symmetrically distributed.     

Modification of the reflex response to stimulation of carotid sinus baroreceptors during and following stimulation of the hypothalamic defence area in the cat

1. The effects of stimulation of the hypothalamic defence area on carotid sinus baroreceptor reflexes have been investigated by examining the cardiovascular responses to a 15 sec period of increased pressure within the vascularly isolated carotid sinus before, during, and immediately following a 25 sec period of hypothalamic stimulation.2. Identification of the hypothalamic defence area was based on the occurence of atropine-sensitive muscle vasodilatation. Electrode positions were confirmed by histological examination.3. During hypothalamic stimulation the reflex fall in blood pressure resulting from a rise in sinus pressure was found to be undiminished whether sinus pressure was raised at the onset or at the 10th sec of hypothalamic stimulation.4. By contrast, in at least half the cats in which a reflex bradycardia could be evoked from the sinus, this bradycardia was largely if not completely suppressed during hypothalamic stimulation. This suppression of reflex bradycardia occurred when sinus pressure was raised at the onset as well as at the 10th sec of stimulation.5. During the first 5 sec after hypothalamic stimulation the hypotensive response to an increase in carotid sinus pressure was much reduced; on the other hand the reduction in heart rate was exaggerated, sometimes to a very marked degree.6. The results suggest that stimulation of the hypothalamic defence area can modify baroreceptor reflexes and that this modification can include selective alterations in the various components of the reflex response.     

Autonomic effector responses to stimulation of nucleus fastigius

1. In anaesthetized cats electrical stimulation of the nucleus fastigius caused cardiovascular responses, electrodermal responses of the paws and pupil dilation with retraction of the nictitating membranes.2. The cardiovascular responses included rise of arterial pressure and peripheral vasoconstriction. Increase of pulse pressure and tachycardia also occurred.3. The effects of sympathetic blocking drugs indicate that fastigial stimulation causes sympathetic discharge to the heart and to the peripheral vessels. There was no evidence of alteration of vagal activity.4. Fastigial stimulation inhibited reflex bradycardia due to carotid sinus distension, vagal afferent stimulation or phenyl diguanide.5. Fastigial and hypothalamic influences on cardiovascular responses could be evoked after severing the nervous pathways connecting the two.6. The pressor response to fastigial stimulation was still present after bilateral division of the carotid sinus and vagus nerves.     

The paramedian reticular nucleus: a site of inhibitory interaction between projections from fastigial nucleus and carotid sinus nerve acting on blood pressure

1. The interaction between the pressor response to electrical stimulation of the fastigial nucleus (FN), the fastigial pressor response (FPR), and the depressor response to electrical stimulation of the carotid sinus nerve (CSN) was examined in paralysed anaesthetized cats.2. Blood pressure responses evoked by electrical stimulation of the FN and the CSN were mutually inhibitory and summed algebraically.3. The FPR was augmented after denervation of buffer nerves. Lesions of the FN did not alter the depressor response to stimulation of the CSN.4. Bilateral electrolytic lesions of the paramedian reticular nucleus abolished both the FPR and the CSN depressor response without altering base line pressure.5. With micro-electrode recording neurones were discovered within the paramedian reticular nucleus which responded to electrical stimulation of the FN or the CSN. These neurones were polysynaptically excited by stimulation of either the FN or the CSN but rarely from both, and could be further subdivided into cells responding with either a single spike or a burst discharge.6. The interaction between the FN and the CSN projections to the paramedian reticular nucleus was examined by conditioning-test studies. Eleven per cent of FN- and CSN-units were inhibited by conditioning stimulation of the heteronymous input. The interaction was exclusively inhibitory and observed only in units with latencies > 4 msec and having burst responses. The latency for inhibition was > 20 msec, peaked around 100 msec and lasted up to 300 msec.7. We conclude that the FRP is buffered by baroreceptors and that there is a mutually inhibitory interaction between projections from the FN and the CSN acting on sympathetic vasomotor neurones. The paramedian reticular nucleus appears to be an important site for the interaction.8. The findings support the view that interneurones mediating pressor and depressor responses are intermixed within the medial reticular formation of the medulla.     

Bulbo-spinal neurons activated by baroreceptor afferents and their possible role in inhibition of preganglionic sympathetic neurons

In paralyzed cats under chloralose-urethane anaesthesia the medulla oblongata was searched with dye-filled microelectrodes for neurons responding to electrical stimulation of the carotid sinus nerve (CSN) and distension of the isolated carotid sinus (CS). 89 cells localized in the solitary tract nucleus and in the reticular formation ventrally and ventrolaterally to the nucleus exhibited mainly an excitatory input from the CSN. 16 could be also antidromically excited from the cervical spinal cord at C4 level. 11 of these were shown to be excited by a pressure rise in the CS. The latencies of the antidromically driven units ranged from 1.2-2.8 msec and the calculated conduction velocity of the descending fibres was 29 plus or minus 5.2 m/sec. The possibility of involvement of these bulbo-spinal neurons in the inhibition of the preganglionic sympathetic neurons at the spinal cord level is discussed.     

Interoceptive control of blood coagulation

Summary Nicotine or acetylcholine stimulation of the carotid sinus in dogs shortens the coagulation time of the blood. The time of clotting is the shortest 20–30 minutes after the start of stimulation. Perfusion of the carotid sinus with the sinus nerve intact and no stimuli applied, as well as the injection into the denervated zone of nicotine or acetylcholine caused no reflex change of the clotting time. Experiments with the celiac nerve indicate that the secretion of adrenalin by the adrenal glands is an important, though not the sole factor in the reflex effect of the carotid sinus chemoreceptors on the blood coagulation time.Presented by Prof. V. N. Chernigovsky, Active Member of the AMS USSR     

The vasomotor component of the carotid sinus baroreceptor reflex in the cat during stimulation of the hypothalamic defence area

1. The effect of moderate intensities of stimulation of the hypothalamic defence area on the baroreceptor reflex has been investigated in the cat by comparing the responses of arterial blood pressure and perfusion pressure of the isolated hind-limb muscle bed perfused at constant volume inflow, when the isolated carotid sinus was subjected to a series of non-pulsatile pressures with and without simultaneous hypothalamic stimulation.2. In the absence of hypothalamic stimulation the characteristic sigmoid curves relating sinus pressure to blood pressure or muscle perfusion pressure were obtained.3. With simultaneous stimulation of the hypothalamus a similar sigmoid relationship was found. There was no evidence of any reduction in the over-all power or maximum sensitivity of the baroreceptor reflex.4. However, in those cats which had been atropinized to abolish the cholinergically mediated muscle vasodilatation, the curves obtained during hypothalamic stimulation were displaced in such a manner as to suggest that, while baroreceptor modulation of vasoconstrictor tone continued during defence area stimulation, the blood pressure regulating mechanism had been ;reset' so that, within the physiological range of sinus pressures, any given level of sinus pressure was associated with a greater vasoconstrictor tone.5. In non-atropinized cats there was little displacement of the curves relating sinus pressure to blood pressure, while the curves relating sinus pressure to muscle perfusion pressure were displaced in the opposite direction so that over-all muscle vascular resistance was less than normal at each level of sinus pressure.