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Biomedical subjects

F R Calaresu

Publications and source records attributed to F R Calaresu.

At least 91 records · Page 5Linked to original sources
PubMed1981

Altered concentration of catecholamines in the hypothalamus of the rat after renal denervation.

Concentrations of noradrenaline, adrenaline, and dopamine were measured using a sensitive radioenzymatic assay in hypothalamic nuclei of rats 4 days after bilateral renal denervation. After renal denervation, catecholamine levels in several hypothalamic nuclei were found to be different from those of sham-operated animals. Noradrenaline was found to be increased in the supraoptic nucleus, adrenaline was increased in the paraventricular nucleus and lateral hypothalamic area, and dopamine was decreased in the supraoptic nucleus, medial preoptic nucleus and lateral hypothalamic area. These data suggest that afferent renal fibers influence the metabolism of hypothalamic catecholamines and that neural information originating in the kidney and transmitted to the hypothalamus is probably involved in physiological responses related to cardiovascular adjustments and body fluid balance.

Animals↗
PubMed1980

Hypothalamic projections of renal afferent nerves in the cat.

In 10 cats anaesthetized with chloralose the electrical activity of spontaneously active hypothalamic units was recorded for changes in discharge rate during electrical stimulation of renal afferent nerves. The discharge rate of 141 single units was altered by stimulation of either the ipsilateral or contralateral renal nerves. Most of the responsive units were located in the regions of lateral preoptic nucleus, lateral hypothalamus, and paraventricular nucleus. These results demonstrate that renal afferent nerves provide information to hypothalamic structures known to be involved in the regulation of arterial pressure and fluid balance.

Afferent Pathways↗
PubMed1980

Distribution of vagal cardioinhibitory neurons in the medulla of the cat.

Experiments were done in cats anesthetized with chloralose, paralyzed and artificially ventilated cats to obtain electrophysiological evidence on the medullary site of origin of vagal cardioinhibitory fibers. The regions of the nucleus ambiguus (AMB), dorsal motor nucleus of the vagus (DMV), nucleus tractus solitarius (NTS), and external cuneate nucleus (ECN) were systematically explored for units responding both to antidromic stimulation of the cardiac branches of the vagus (CBV) and to orthodromic stimulation of the carotid sinus and aortic depressor nerves. Eighty-six single units conforming to these criteria were found in the medulla: 30 in the AMB, 26 in the DMV, 12 in the NTS, 8 in the NTS-DMV border region, and 10 in the ECN. Antidromically evoked spikes had durations of 0.5--2.5 ms and followed stimulation frequencies of 20--500 Hz. The axons of these units conducted at velocities of 3.3--20.8 m/s. The specificity of activation of medullary units by cardioinhibitory fibers was tested in 11 units, which were found to respond consistently with an antidromic spike to stimulation of CBV but not to stimulation of the thoracic vagus. In eight spinal animals low threshold (less than 15 microA) sites eliciting vagal bradycardia were found in the same medullary nuclei where cardioinhibitory units had been located. These results indicate that vagal cardioinhibitory axons, originate in at least three medullary nuclei, the AMB, DMV, and NTS. Unit activity from the ECN may have been recorded from carioinhibitory fibers because of the short duration of the spike potentials.

Animals↗
PubMed1980

Projections to the hypothalamus from buffer nerves and nucleus tractus solitarius in the cat.

In 18 cats anesthetized with chloralose, electrical activity of spontaneously active hypothalamic units was monitored for changes in firing frequency during electrical stimulation of carotid sinus (CSN) and aortic depressor (ADN) nerves and the nucleus tractus solitarius (NTS). Stimulation of the CSN altered the activity of 55% (381/691) of the tested. These responsive units were widely distributed in the ipsi- and contralateral hypothalamus. Of the units tested during stimulation of the ADN only 6% (17/274) changed their firing frequency. Responsive units were located only on the ipsilateral side and primarily in the paraventricular and supraoptic nuclei, Electrical stimulation of the NTS altered the firing frequency of all 84 hypothalamic units previously identified by stimulation of the CSN. NTS stimulation elicited responses that had a significantly shorter latency and followed significantly higher frequencies of stimulation when compared to stimulation of the CSN. These results demonstrate that the two buffer nerves have distinctly different central projections to the hypothalamus and suggest different functional roles for the ADN and CSN in homeostatic regulatory mechanisms mediated by the hypothalamus.

Animals↗
PubMed1980

Role of paraventricular and supraoptic nuclei in central cardiovascular regulation in the cat.

To investigate the role of the paraventricular (PAH) and supraoptic (SON) nuclei in regulation of the cardiovascular system experiments were done in 26 cats anesthetized with alpha-chloralose, paralyzed, and artificially ventilated. Electrical stimulation of histologically verified sites in the region of the PAH and SON elicited increases in arterial pressure in bilaterally vagotomized animals and increases in heart rate both in spinal (C2) animals and in animals bilaterally vagotomized, In addition, stimulation of either the PAH or SON inhibited the reflex vagal bradycardia elicited by stimulation of the carotid sinus nerve (CSN) and bilateral lesions of these areas increased the magnitude of the response. On the other hand, stimulation and lesions of these hypothalamic regions did not alter the magnitude of the cardiovascular responses to stimulation of the aortic depressor nerve. These results demonstrate that stimulation of the PAH and SON elicit cardiovascular responses due to reciprocal changes in activity of the parasympathetic and sympathetic nervous systems and that these structures maintain a tonic inhibitory influence on the heart rate component of the CSN reflex.

Animals↗
PubMed1979

Separate medullary pathways mediatiating reflex vagal bradycardia to stimulation of buffer nerves in the cat.

In this investigation of medullary pathways mediating reflex vagal bradycardia to stimulation of buffer nerves, four series of experiments were done in 37 cats anesthetized with chloralose, paralyzed and artificially ventilated. In the first series using animals in which the contralateral vagus was sectioned and the spinal cord was transected at C2, simultaneous stimulation of the aortic depressor (ADN) and carotid sinus (CSN) nerves elicited a bradycardia of magnitude not significantly different from the algebraic sum of the responses elicited by stimulation of the two buffer nerves separately, suggesting the existence of two separate central pathways mediating vagal bradycardia. In the second series, in spinal unilaterally vagotomized animals, lesions of the nucleus ambiguus (AMB) selectively attenuated the ADN reflex vagal bradycardia but not the CSN response; on the other hand, lesions of the external cuneate nucleus (ECN) attenuated the reflex vagal bradycardia elicited by stimulation of the CSN, but did not alter the ADN response. In the third series of experiments, 153 spontaneously firing single units in the region of the AMB and 98 in the region of the ECN were tested for responses to ADN and CSN stimulation. In the AMB 42% of the responsive units were excited only by stimulation of the ADN, 25% were activated only by stimulation of the CSN and 33% were activated by stimulation of both buffer nerves. Of the single units in the ECN region 85% were excited only by stimulation of the CSN, 15% during stimulation of both the CSN and ADN and none responded to stimulation of only the ADN. In the final series, electrical stimulation of the ECN evoked antidromic compound action potentials in the CSN but not in the ADN. Electrical stimulation of the AMB did not evoke antidromic activity in either the CSN or ADN. These studies provide evidence for the existence of two separate medullary pathways mediating the vagal reflex bradycardia to stimulation of the ADN and CSN.

Animals↗
PubMed1979

Bradycardia during stimulation of the septum and somatic afferents in the rabbit.

Experiments were done in paralyzed rabbits anesthetized with either pentobarbital sodium or alpha-chloralose to test the possibility that the septum may alter the cardiovascular responses elicited by stimulation of somatic afferent fibers. Electrical stimulation of the lesser saphenous nerve (LSN), a branch of the sciatic nerve, at certain parameters elicited bradycardia, which could be abolished by bilateral vagotomy or intravenous injection of atropine methylbromide. Distinct and characteristic changes in mean arterial pressure and heart rate were elicited by electrical stimulation of histologically localized sites in five septal areas. Septal sites from which stimulation elicited bradycardia were chosen for the study of interaction between the septum and LSN. The cardiac slowing elicited by combined stimulation of the lateral septum and LSN was significantly greater than the sum of the responses elicited by separate stimulation of the two different structures. In contrast, the bradycardia elicited by combined stimulation of medial septal structures and LSN was significantly smaller than the sum of the individual responses. These experiments demonstrate that the magnitude of heart rate responses elicited by stimulation of somatic afferent fibers may be modified by the septum.

Animals↗
PubMed1978

Electrophysiological characteristics of renorenal reflexes in the cat.

1. Experiments were done in anaesthetized, paralysed and artificially ventilated cats to determine the fibre composition of renal nerves and to study the functional characteristics of reflex responses recorded in efferent renal nerves during electrical stimulation of contralateral and ipsilateral afferent renal nerves. 2. Renal nerves were found to contain three afferent fibre groups (Abeta, Adelta and C); the majority of these fibres reach the sympathetic chain through the least splanchnic nerve. Efferent sympathetic nerves to the kidney were found to originate from the greater, lesser and least splanchnic nerves through a synapse in the coeliac ganglion. 3. Two contralateral renorenal reflex responses were demonstrated during selective stimulation of renal afferent A and C fibres. The first (A renorenal reflex) was elicited by stimulation with trains of pulses at low voltage and high frequency (200 Hz), had an onset latency of approximately 100 msec and was followed by post-excitatory depression. The second (C renorenal reflex) was demonstrated by trains of pulses at high voltage and low frequency (20--30 Hz), had an onset latency of approximately 350 msec and was also followed by post-excitatory depression. 4. Ipsilateral renorenal reflexes with characteristics similar to the contralateral reflexes were also demonstrated. 5. Renorenal reflexes were abolished by destruction of the spinal cord and administration of nicotine sulphate (5--20 mg/kg, i.v.), but were not affected by bicuculline (0.4 mg/kg, i.f.). 6. The significance and the physiological role of these renorenal reflexes as well as their pathways within the central nervous system remain to be determined.

Animals↗
PubMed1978

The role of renal nerves in the response to dipsogenic stimuli in the rat.

The effect of bilateral renal denervation on water intake and urine volume during specific thirst challenges was studied in rats. Renal denervation attenuated significantly the drinking response elicited by the administration of 30% polyethylene glycol (PG, extracellular challenge) but had no effect on the drinking response after an intracellular challenge (2.5 M NaCl) or after a 24-h water deprivation period. Furthermore, during a PG challenge total water intake was the same in two groups of rats, one with denervated kidneys and the other with beta-adrenergic neural activity in efferent renal nerves eliminated by blocking agents. Urine volumes were not affected by PG administration or water deprivation in denervated rats but were increased significantly after administration of 2.5 M NaCl. These results indicate that renal nerves play an important role in the physiological processes controlling extracellular thirst, and suggest that this role may be related to the neural control of release of renin.

Adrenergic beta-Antagonists↗
PubMed1978

Vagal bradycardia elicited by stimulation of the external cuneate nucleus in the cat.

The role of the external cuneate nucleus (ECN) in the control of heart rate was systematically investigated in 26 chloralosed and 2 decerebrated, paralyzed, and artifically ventilated cats. Electrical stimulation of histologically verified sites in the ventral ECN and dorsal spinal trigeminal tract elicited a marked decrease in heart rate, with threshold currents of 5-25 muA and an optimal frequency of 20 Hz when using a 0.2 ms pulse; this response was shown to be due to vagal excitation. In seven experiments intravenous pentobarbital sodium decreased the magnitude of the bradycardia elicited by stimulation of the ECN, of the nucleus ambiguus (AMB), and of the cervical vagus significantly less than the response from the nucleus of the tractus solitarius. In eight additional experiments in cats with lesions of the AMB made 11-27 days earlier stimulation of the ECN elicited a bradycardia of the same magnitude as that observed in intact animals, although the bradycardia elicited by stimulation of the ipsilateral cervical vagus was significantly reduced by the lesion. Similarly, lesions of the ECN in four cats significantly attenuated the bradycardia elicited by stimulation of the ipsilateral cervical vagus. These results suggest that the ECN is a site of origin of cardioinhibitory axons in the cat.

Animals↗
PubMed1977

Function of lateral reticular nucleus in central cardiovascular regulation in the cat.

The role of the lateral reticular nucleus (LRN) in central cardiovascular regulation was investigated in cats. In 15 cerebellectomized and nine intact chloralosed cats stimulation of 115 histologically verified sites in the LRN elicited increases in arterial pressure and heart rate; the latter was abolished by propranolol but not by bilateral cervical vagotomy. The pressor response was significantly greater in intact animals. Electrical activity was recorded from the right inferior cardiac nerve (ICN) during stimulation fo the LRN and of a vasomotor region in the posteromedial hypothalamus (PMH). Stimulation of sites in the LRN and in the PMH, on both sides, elicited a response in the right ICN that was consistently abolished during baroreceptor excitation. Medullary transection 3 mm rostral to the LRN did not abolish the ICN response to LRN stimulation. The conclusions are drawn that stimulation of the LRN elicits cardiovascular responses probably due to excitation of groups of neurons in this nucleus located in a descending sympathetic pathway originating in the PMH and that these responses can be inhibited by excitation of baroreceptors. In view of the known functional connections of the LRN with the somatomotor system it is suggested that this nucleus may play a major role in somatosympathetic reflexes.

Animals↗