Neurotensin-like immunoreactivity in presumptive baroreceptor neurons innervating the guinea pig carotid sinus

This study was carried out to determine the ultrastructure and origin of previously described neurotensin-like immunoreactive (NT-LI) nerve fibres in the wall of the carotid sinus of the guinea pig. In our degeneration experiments, these NT-LI axons were unaffected by surgical sympathectomy but disappeared in response to transection of the carotid sinus nerve, thus suggesting a sensory origin. This assumption could be supported by combined retrograde tracing and immunohistochemistry. Primary afferent neurons of the sensory glossopharyngeal (petrosal) ganglion projecting to the carotid sinus were identified by injecting the retrograde fluorescent tracer, Fluoro-Gold, into the sinus wall, and some of these neurons displayed NT-LI. Within the carotid sinus, the terminals of these NT-LI sensory neurons exhibited ultrastructural features characteristic of baroreceptor endings, i.e. axonal swellings filled with mitochondria and closely associated to elastin. However, many endings also fulfilling the ultrastructural criteria for baroreceptors were devoid of immunolabelling. Thus, we conclude that the NT-LI terminals constitute a subgroup rather than the entire population of baroreceptor endings within the guinea pig carotid sinus. With respect to the established pharmacological effects of NT in guinea pig, we propose an involvement of NT-LI fibres in the modulation of baroreception at the peripheral level.     

Central connections of aortic depressor and carotid sinus nerves

Medullary vasomotor regions of the cat were explored for units responding with changes in discharge frequency to stimulation of the carotid sinus nerve or aortic depressor nerve. Neurons excited after a short (< 10 msec) latency by stimulation of the aortic depressor nerve or carotid sinus nerve were located in the regions of nucleus tractus solitarius and medial or paramedian reticular formation. Less than half of these neurons were excited by stimulation of the vagus nerves or the dorsolateral columns of the spinal cord. Inhibition, seen either as cessation of spontaneous discharge or as IPSPs, often followed the short latency excitation from the aortic depressor nerve or carotid sinus nerve and was of short (< 40 msec) duration. Long latency (> 10 msec) excitatory responses and complex excitatory-inhibitory patterns were evoked in neurons of the medial, paramedian and lateral ventral reticular areas by stimulation of the carotid sinus nerve and aortic depressor nerve. Most of these neurons also were influenced orthodromically by vagal nerve and dorsolateral column stimulation. A frequently occurring pattern in response to stimulation of all sites was excitation followed by a long period (> 100 msec) of inhibition of spontaneous discharge. Of the neurons in the lateral ventral reticular region, over half were fired antidromically from the ipsilateral dorsolateral columns. The responses of these neurons to stimulation at all sites resembled the responses to the same inputs previously recorded from sympathetic preganglionic and postganglionic nerves. Thus, it was tentatively concluded that this group of lateral ventral reticular neurons is the final common pathway to preganglionic sympathetic neurons in the intermediolateral columns of the spinal cord. Of the few cardio-synchronous neurons encountered, some had discharge patterns similar (in timing) to those seen in the carotid sinus nerve or aortic depressor nerve but others displayed the inverse of this pattern. This observation, together with the protracted postexcitatory inhibition commonly seen in many of the neurons in the vasomotor regions, could account for considerable modification of the primary afferent signal and may help to explain why cardio-synchronous neurons are so rarely found in the medulla.     

Respiratory sinus arrhythmia and the heart rate response to carotid baroreceptor activation after hard dynamic exercise in humans

The aim of this study was to examine the influence of 20 min of hard exercise (HR>160 beats min(-1)) on the efficacy of the cardiac parasympathetic nervous control of heart rate in humans (20-31 years; of either sex). This intensity of exercise was chosen to produce strong activation of the cardiac sympathetic nerves. Using well-controlled stimulus parameters, the efficacy of cardiac parasympathetic control of heart rate was assessed by recording the heart rate response to carotid baroreceptor activation (CBR) and the amplitude of respiratory sinus arrhythmia (RSA). Measurements were made while the subject performed light exercise (100-135 beats min (-1)) before (Control 1) and after very brief (Control 2) and prolonged (20 min; post) periods of hard exercise. There was no difference in the CBR in the three different measurement periods; 0.33 +/- 0.17, 0.38 +/- 0.18 and 0.39 +/- 0.18 beats min(-1) mm Hg(-1) (mean +/- S.D., N=6) for Control 1, Control 2 and post, respectively. At a heart rate of 120 beats min (-1), amplitude of the RSA was 6.1 +/- 2.4, 5.6 +/- 2.4 and 3.3 +/- 2.1 beats min(-1) for Control 1, Control 2 and post, respectively (P<0.001 post vs. Control 1 and Control 2, N=8). The decrease in RSA amplitude following hard exercise may be attributable to an exercise-induced reduction in airway resistance and work of breathing. Overall, these results do not support the hypothesis that sustained hard exercise that produces strong activation of cardiac sympathetic nerves reduces cardiac parasympathetic efficacy.     

Cardiovascular responses to time delays of electrocardiogram-coupled electrical stimulation of carotid sinus nerves in dogs

In search of improved patterns for electrical stimulation of the carotid sinus nerves (CSNs), which is applied therapeutically in patients with previous therapy refractory hypertension or angina pectoris, the timing of stimulation trains within the cardiac cycle was investigated in anesthetized dogs. Blood pressure responses and prolongations of heart beat intervals upon CSNs were analyzed. Electrocardiogram (ECG)-coupled trains of electrical stimuli were applied to bilateral intact CSNs. Pulses of 1 ms duration and the maximal (5-10 V) and 50% maximal stimulus amplitude were applied. The onset of stimulation trains (150 ms long, 15 impulses/train) was delayed from ECG-R-wave synchronous periods in units of 30 ms to maximally 150 ms. The timing of stimulus trains within the cardiac cycle did not influence the responses. Heart rate and blood pressure reductions upon CSNs were entirely dependent on the amplitudes of stimuli. In conclusion, a phase-dependency of such responses to CSNs, supposedly due to coincidence of electrically induced carotid sinus nerve activity with endogenous signals centrally converging from other cardiovascular afferents, could not be supported, using such stimulation trains. The observed responses did not show the known phase-dependency of sensitivity of the sino-atrial node to changes in effernt vagal activity. In experimental and therapeutic electrical CSNs (baropacing) for obtaining stronger cardiovascular responses with similar parameters, a preferential timing of stimuli relative to the cardiac cycle cannot be recommended.     

H_1 and H_2 receptors in the locus ceruleus are involved in the intracere-broventricular histamine-induced carotid sinus baroreceptor reflex reset-ting in rats

1 Introduction Central histamine (HA) has been regarded as one of the important neurotransmitters or neuromodulators[1]. Brain HA keeps in close touch with the changes of cardio- vascular activities[1-3]. Carotid sinus baroreceptor reflex (CSR) with negative feedback regulation is a predominant approach to maintaining the spontaneous and simultaneous blood pressure homeostasis in mammal. It has been evi- denced that intracerebroventricular (i.c.v.) administration of HA can bring CSR reset…     

Observations on the abdominal stretch receptor and the fine structure of associated axo-dendritic synapses and neuromuscular junctions in homarus

The abdominal stretch receptor of lobster has been examined. Fine structural details of the receptor nerves are presented and neurophysiological correlations are suggested. Both axo-dendritic synapses and neuromuscular junctions were examined. Axo-dendritic synapses are of one type only, possessing elongated, or flattened, presynaptic vesicles approximately 200 Å in diameter and 400–600 Å long. In contrast two distinct types of neuromuscular junctions were observed. The first possesses spherical synaptic vesicles 500–900 Å in diameter. The second possesses synaptic vesicles of dimensions similar to those of axo-dendritic synapses. It is suggested that synapses, both axo-dendritic and neuromuscular, with elongated or flattened vesicles, are inhibitory, and that neuromuscular junctions with spherical vesicles are excitatory.     

The distribution of the cat''s carotid sinus nerve afferent and efferent cell bodies using the horseradish peroxidase technique

The location of both afferent and efferent carotid sinus nerve (CSN) cell bodies in the cat has been determined using the horseradish peroxidase (HRP) technique. Following a limited exposure of the central cut end of the CSN to HRP, labeled sensory ganglion cells were found in both the petrosal and superior ganglia of the IXth cranial nerve. An average of 387 in the former and 16 cells in the latter ganglion were labeled.

Retrogradely labeled neurons were found only within the ipsilateral medulla. These cells were both round and spindle shaped and had an average somal diameter of 19 μm. The number of these CSN efferent cell bodies ranged from 1 to a maximum of 20 in a given animal. They were found in both the nucleus parvocellularis and the retrofacial nucleus. In 8 cases axonal labeling was observed. Axons generally projected dorsomedially from the ventrolateral medulla.     

Injury of the peripheral cranial nerves during carotid endarterectomy

The incidence of local nerve injury among 192 consecutive carotid endarterectomies in 162 patients between 1977-1983 was determined from review of the medical records. Two facial nerve, 5 hypoglossal nerve, and 2 vagus nerve injuries were discovered for a total incidence of 4.7%. Only the 2 facial nerve injuries failed to improve over 2 years. Followup ranged from 1 to 60 months in this group of patients. Careful attention to details of tissue dissection at surgery should lower the incidence of nerve injury during carotid endarterectomy.     

Modulation of the carotid baroreceptor reflex by substance P in the nucleus tractus solitarius

Previous studies have shown that administration of substance P (SP) into the nucleus tractus solitarius (NTS) can evoke a depressor response similar to that produced by activation of the arterial baroreceptors. In addition, some studies have suggested that SP increases the reflex responses to activation of baroreceptor input. The present study was performed to determine the effects of SP on the carotid sinus baroreceptor reflex at the level of the NTS by examining the effects of both exogenous SP microinjected into different rostrocaudal locations in the NTS and blockade of the effects of endogenous SP, through the microinjection of a substance P antagonist (SPa; [D-Pro, D-Trp]-substance P). Changes in pressure in an isolated carotid sinus in anesthetized dogs were used to evoke baroreflex changes in arterial blood pressure (BP) before and after microinjection of SP (0.5 microM) or SPa (10 microM) into barosensitive regions of the NTS. Microinjection of SP or its antagonist did not alter baseline, resting BP but did produce significant changes in baroreflex sensitivity. Microinjection of SP into different rostrocaudal regions of the NTS produced different responses, with rostral and caudal NTS microinjections producing significant increases in sensitivity. No effects on baroreflex sensitivity were obtained in response to SP microinjections into the intermediate NTS. Unlike SP, microinjection of the SPa significantly decreased baroreflex sensitivity at all rostrocaudal levels of the NTS. These data demonstrated that SP has the capability to modulate the carotid baroreflex at the level of the NTS and support a physiological role for endogenously released SP.     

H(1) and H(2) receptors in the locus ceruleus are involved in the intracerebroventricular histamine-induced carotid sinus baroreceptor reflex resetting in rats

Objective To investigate the role of H1 and H2 receptors in the locus ceruleus （LC） in carotid sinus baroreceptor reflex （CSR） resetting induced by intracerebroventricular （i.c.v.） injection of histamine （HA）. Methods The left and right carotid sinus regions were isolated from the systemic circulation in 18 male Sprague-Dawley rats anesthetized with pentobarbital sodium. The intracarotid sinus pressure （ISP） was altered in a stepwise manner in vivo. ISP-mean arterial pressure （MAP） relationship curve and its characteristic parameters were constructed by fitting to the logistic function with five parameters. The changes in CSR performance induced by i.c.v. HA and the effects of pretreatment with H1 or H2 receptors selective antagonist, chlorpheniramine （CHL） or cimetidine （CIM） into the LC, on the responses of CSR to HA were examined. Results I.c.v. HA （100 ng in 5 μl） significantly shifted the ISP-MAP relationship curve upwards （P 〈 0.05） and obviously decreased the value of the reflex parameters such as MAP range and maximum gain （P 〈 0.05）, but increased the threshold pressure, saturation pressure and ISP at maximum gain （P 〈 0.05）. The pretreatment with CHL （0.5 μg in 1 μl） or CIM （1.5 μg in 1 μl） into the LC could obviously attenuate the changes mentioned above in CSR performance induced by HA, but the alleviative effect of CIM was less remarkable than that of CHL （P 〈 0.05）. Respective microinjection of CHL or CIM alone into the LC with the corresponding dose and volume did not change CSR performance significantly （P 〉 0.05）. Conclusion Intracerebroventricular administration of HA results in a rapid resetting of CSR and a decrease in reflex sensitivity, and the responses of CSR to HA may be mediated, at least in part, by H1 and H2 receptors activities in the LC, especially by H1 receptors. Moreover, the effects of the central HA on CSR might be related to a histaminergic descending pathway from the hypothalamus to LC.     

On the fine structure of the distribution of primary nervous system neoplasms in Western Poland

The incidence rates of primary nervous system neoplasms in 5 districts (large administrative units) of Western Poland with a relatively homogeneous health care system but some contrasts in economic activity, as well as in 224 communes (smallest administrative units) located within these 5 districts, with a total population of 3,097,000 were estimated on the appointed day (31.12.79). Testing the hypothesis, assuming a homogeneous distribution of nervous system neoplasms over the region under investigation, that the incidence rates were distributed as a Poisson variable has revealed a focal distribution of these tumours; in 15 communes the frequency was higher than 9.0 and deviated from the remainder in the 5% right tail of the distribution. The main conclusion from the presented results was that tumours of the nervous system, of which 90% were intracranially located, may occur in clusters or foci, and this could prove to be of clinical as well as statistical import.     

Localization of substance P immunoreactive nerves in the carotid body

Immunofluorescent histochemical observation of the rat carotid body revealed the presence of substance P immunoreactive fibers. This supports the hypothesis that substance P is a neurotransmitter of chemoreceptor afferent nerves.