Respiratory responses to chemical stimulation of the parabrachial nuclear complex in the rabbit

The respiratory role of the parabrachial nuclear complex (PNC) was investigated in alpha-chloralose-urethane anesthetized, vagotomized, paralysed and artificially ventilated rabbits by means of unilateral microinjections (10-20 nl) of 20 mM dl-homocysteic acid. Chemical stimulation elicited three main types of site-specific respiratory effects: excitatory, apneustic and inhibitory responses. The results suggest that the PNC plays a complex role in the control of breathing.     

Apoptosis in the failing heart

Apoptosis is a tightly regulated, energy-requiring process of programmed cell death. While necrosis is a form of cell death that results from acute cellular injury, apoptosis is controlled autodigestion of the cell that occurs through activation of endogenous proteases. This process results in the cleavage of chromatin into oligonucleosome-length DNA fragments and its multiples. This DNA fragmentation demonstrates a characteristic laddering pattern on DNA agarose gel electrophoresis. The heart undergoes extensive remodeling during embryogenesis wherein apoptosis significantly contributes to the development of the cardiac chambers and correct routing of the great vessels. Pathologic stimuli can also result in apoptosis and include ischemia, hypoxia, inflammation, cytokines, growth factors, and toxic agents. Better understanding of the molecular mechanisms responsible for regulating apoptosis in the failing myocardium may soon lead to strategies aimed at preventing further myocyte loss and enhancing myocyte replacement through regulated cell growth.     

Apoptosis in the failing human heart

BACKGROUND: Loss of myocytes is an important mechanism in the development of cardiac failure of either ischemic or nonischemic origin. However, whether programmed cell death (apoptosis) is implicated in the terminal stages of heart failure is not known. We therefore studied the magnitude of myocyte apoptosis in patients with intractable congestive heart failure. METHODS: Myocardial samples were obtained from the hearts of 36 patients who underwent cardiac transplantation and from the hearts of 3 patients who died soon after myocardial infarction. Samples from 11 normal hearts were used as controls. Apoptosis was evaluated histochemically, biochemically, and by a combination of histochemical analysis and confocal microscopy. The expression of two proto-oncogenes that influence apoptosis, BCL2 and BAX, was also determined. RESULTS: Heart failure was characterized morphologically by a 232-fold increase in myocyte apoptosis and biochemically by DNA laddering (an indicator of apoptosis). The histochemical demonstration of DNA-strand breaks in myocyte nuclei was coupled with the documentation of chromatin condensation and fragmentation by confocal microscopy. All these findings reflect apoptosis of myocytes. The percentage of myocytes labeled with BCL2 (which protects cells against apoptosis) was 1.8 times as high in the hearts of patients with cardiac failure as in the normal hearts, whereas labeling with BAX (which promotes apoptosis) remained constant. The near doubling of the expression of BCL2 in the cardiac tissue of patients with heart failure was confirmed by Western blotting. CONCLUSIONS: Programmed death of myocytes occurs in the decompensated human heart in spite of the enhanced expression of BCL2; this phenomenon may contribute to the progression of cardiac dysfunction.     

Metabolic responses of rabbit corpus cavernosum tissue to various forms of stimulation

The present study was designed to investigate the effect of various forms of stimulation on the levels of high energy phosphates (ATP + CP) in the rabbit corpora cavernosa. Prestimulation with the alpha agonist phenylephrine (200 microM) for five minutes caused a significant decrease in both ATP and Creatine phosphate (CP) when compared with control tissue. Field stimulation (64 Hz) of the precontracted tissue induced an immediate decrease in tension by approximately 50%. The level of ATP + CP after field stimulated-relaxation was not significantly different from that from the initial prestimulation. Field stimulation (FS) from basal tone (2 g) caused a contraction and a significant decrease in both ATP and CP. Phentolamine (10 microM) (alpha-adrenergic antagonist) induced a significant decrease in the 2 g basal tension and a significant increase in the intracellular concentrations of both ATP and CP from that of control levels. In summary, the contractile response to both neuronal and pharmacologic stimulation was similar to that of other smooth muscle, producing a decrease in high energy phosphates. Field stimulated relaxation did not change the level of high energy phosphates from that of prestimulated levels. Finally, our data indicates that in the presence of the alpha blocker phentolamine (10 microM), high energy phosphate levels (ATP + CP) increase significantly. This indicates that in the corpus cavernosum, there is significant basal tone that is linked to significant tonic alpha receptor stimulation and is maintained by a net consumption of ATP.     

The role of cytokines in the failing human heart

Despite repeated attempts to develop a unifying hypothesis that explains the clinical syndrome of heart failure, no single conceptual paradigm has withstood the test of time. In this regard, recent studies have shown that a class of biologically active molecules, generically referred to as cytokines, are overexposed in heart failure. This article will review recent clinical and experimental material that suggest proinflammatory (stress activated) cytokines such as tumor necrosis factor-alpha (TFN-alpha), interleukin-1 (IL-1), and interleukin-6 (IL-6) may play a role in the pathogenesis of congestive heart failure. The scope of this article includes an overview of the biology of cytokines in the heart, as well as review of the clinical studies that have documented elevated levels of cytokines and cytokine receptors in patients with heart failure.     

Mediodorsal thalamic lesions and Pavlovian conditioning of heart rate and eyeblink responses in the rabbit.

Rabbits received ibotenic acid lesions of the mediodorsal nucleus of the thalamus (MD) or sham lesions. These animals were compared on 4 sessions of Pavlovian eyeblink and heart rate conditioning, in which a tone was the conditioned stimulus/stimuli (CS) and a paraorbital electrical shock was the unconditioned stimulus/stimuli (UCS). Lesions of MD retarded acquisition of the eyeblink conditioned response (CR) and abolished the late-occurring tachycardiac component of the heart rate CR. The data are compatible with previous experiments (H. Groenewegen, 1988), suggesting that MD participated in the sympathetic control associated with somatomotor learning. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Troponin I phosphorylation in the normal and failing adult human heart

BACKGROUND: In the failing human heart myofibrillar calcium sensitivity of tension development is greater and maximal myofibrillar ATPase activity is less than in the normal heart. Phosphorylation of the cardiac troponin I (cTnI)-specific NH2-terminus decreases myofilament sensitivity to calcium, while phosphorylation of other cTnI sites decreases maximal myofibrillar ATPase activity. METHODS AND RESULTS: We examined cTnI phosphorylation in left ventricular myocardium collected from failing hearts at the time of transplant (n=20) and normal hearts from trauma victims (n=24). The relative amounts of actin, tropomyosin, and TnI did not differ between failing and normal myocardium. Using Western blot analysis with a monoclonal antibody (MAb) that recognizes the striated muscle TnI isoforms, we confirmed that the adult human heart expresses only cTnI. A cTnI-specific MAb recognized two bands of cTnI, designated cTnI1 and cTnI2, while a MAb whose epitope is located in the cTnI-specific NH2-terminus recognized only cTnI1. Alkaline phosphatase decreased the relative amount of cTnl1, while protein kinase A and protein kinase C increased cTnI1. The percentage of cTnI made up of cTnI1, the phosphorylated form of TnI, is greater in the normal than the failing human heart (P<.00). CONCLUSIONS: This phosphorylation difference could underlie the reported greater myofibrillar calcium sensitivity of failing myocardium. The functional consequence of this difference may be an adaptive or maladaptive response to the lower and longer calcium concentration transient of the failing heart, eg, enhancing force development or producing ventricular diastolic dysfunction.     

Effects of castration on adrenergic, cholinergic and nonadrenergic, noncholinergic responses of isolated corpus cavernosum from rabbit

OBJECTIVE: To investigate the effects of castration and testosterone on the constricting effect of phenylephrine and endothelium-dependent and -independent relaxing effects of different agonists in the corpus cavernosum of male rabbits. MATERIALS AND METHODS: Twenty rabbits were castrated and 10 received testosterone replacement for 1 month after castration; 10 further rabbits underwent a sham operation and acted as controls. One month after operation the rabbits were killed and their penises excised. Strips of corpus cavernosum were used for isometric tension measurements in organ chambers; concentration-response relationships for phenylephrine, carbachol, adenosine and sodium nitroprusside were obtained by adding the reagent cumulatively to the bath. RESULTS: The phenylephrine-induced contractions were markedly lower, with no change in the pD2 values (i.e. the negative logarithm of the concentration for half-maximal response), in cavernosal strips obtained from castrated rabbits than in those from controls. Endothelium-dependent relaxation elicited by carbachol increased in the castrated group but the relaxation induced by sodium nitroprusside did not change and those elicited by adenosine were strongly depressed when compared with controls. There were no significant changes in the pD2 values of agonist-induced relaxation responses in all groups. The relaxation elicited by electrical-field stimulation at lower frequencies increased in strips from castrated rabbits but at higher frequencies were unchanged when compared with controls. Castration-induced changes in the relaxation response of cavernosal strips were significantly restored by in vivo testosterone replacement but those induced by phenylephrine were not. CONCLUSION: The lack of testosterone has an effect on the reactivity of the corpus cavernosum, indicating that testosterone has an important role in erectile function by a pre- or post-synaptic action on the corpus cavernosum.     

Effects of cadmium and lead on adrenergic neuromuscular transmission in the rabbit

The effects of inorganic lead (PbCl2) and cadmium (DdCl2) on the pressor response of rabbit saphenous arteries produced by sympathetic nerve stimulation were examined. A 1- to 3-cm length of artery was removed, placed in a bath containing mammalian Ringer solution, and perfused with the same solution at a constant rate sufficient to maintain a 40-60 mmHg perfusion pressure. Increases in perfusion pressure resulting from electrical stimulation -f periarterial nerve endings were reduced or completely blocked by the addition of 5-20 muM lead or cadmium to the bathing solution for a period of 15-30 min. Responses to norepinephrine or to direct electrical stimulation of the muscle remained relatively unaffected. During lead or cadmium blockade, the response to nerve stimulation could be restored by a fourfold increase in calcium concentration. It is concluded that lead and cadmium reduce the response to sympathetic nerve stimulation primarily through an effect on presynaptic nerve terminals.     

Cerebral evoked responses to gastrointestinal stimulation in humans

Recent advances have permitted recording of evoked potentials (EPs) in response to electrical and mechanical stimulation of the gastrointestinal (GI) organs via methods used primarily in clinical neurophysiology. Current research involving stimulation of the esophagus, rectum, and colon, and recording the corresponding responses on the scalp, is being practiced in only a few laboratories. This review examines the engineering aspects of recording EPs, such as characteristics of the stimuli, placement of stimulus electrodes in the GI tract, and enhancement of evoked potential signals. We also discuss the physiological concepts involved in the generation of EPs, and how these compare with somatosensory evoked responses. Current experimental techniques employed by various investigators and results reported from their laboratories are compared. We believe that cerebral EPs to GI stimulation could be useful in studying a number of pathophysiological conditions such as gastroesophageal reflux disease, diffuse esophageal spasm, chronic inflammatory bowel disorders, chronic abdominal pain, and irritable bowel syndrome, among others. We hope that the present review will generate interest in the use of EPs arising out of GI stimulation, aiding in understanding their physiological implications in healthy subjects and in GI disorders.     

Cardiac responses to stimulation of thoracic afferents in the primate and canine

Excitatory cardiovascular responses to electrically stimulated upper thoracic sympathetic afferent nerves were observed in halothane-anesthetized mongrel dogs and monkeys. The central end of the transected ventral limb of the left ansa subclavia was stimulated before and after several types of denervation. Significant increases in right and left ventricular maximum systolic pressures, systolic and diastolic systemic blood pressures, and aortic flow were observed. The carotid sinuses were denervated bilaterally and stimulation of the ansa was repeated. The cardiovascular responses to stimulation of the ventral ansa after carotid sinus denervation were greater in magnitude than those observed prior to denervation. This carotid sinus modulation of cardiovascular responses was observed in dogs and monkeys. Cardiovascular responses to stimulation of the ventral ansa after bilateral vagotomy were significantly less than the responses observed after carotid sinus denervation prior to vagotomy. However, the responses after vagotomy were statistically identical to responses obtained while stimulating the ventral ansa when the carotid sinuses and vagi remained intact.     

Hemodynamic responses to stellate ganglion stimulation in mongrels and greyhounds

A comparison of the effects of left stellate ganglion stimulation (SGS) on central and aortic hemodynamics has been made in chloralose-anesthetized mongrel (M), and greyhound (GH) dogs. Measurements of aortic pressure and flow, and left ventricular pressure were made during stimulation of the decentralized left SG at different frequencies from 0 to 20 Hz. The increases in aortic pressure and flow with SGS were larger in the GH, especially for low frequencies of stimulation. Stroke volume was increased with SGS in the GH at all stimulation rates, whereas in the M it was unchanged. A greater decrease in left ventricular end-diastolic pressure with SGS was found in the GH. These results suggest that differences exist in both the intrinsic and extrinsic control of cardiac output in the greyhound dog compared to the mongrel. These differences may be in part responsible for the elevated arterial blood pressure in the greyhound compared to the mongrel.     

Coronary hyperreactivity to adrenergic stimulation and increased nocturnal vagal tone trigger coronary vasospasm

The present study was undertaken to analyse the effect of fluoxetine upon murine T-lymphocyte proliferation. We found that fluoxetine exerted a dual effect, which depended on the degree of lymphocyte activation: at mitogenic concentration (2 microg/mL) of concavalin A (Con A), we observed an inhibitory effect on cellular proliferation, whereas, on submitogenic Con A concentration (1 microg/mL), fluoxetine stimulated the cellular response. Given these facts, we studied PKC activation and calcium mobilisation in both stimulatory and inhibitory effects of fluoxetine on T-cell proliferation. We observed that fluoxetine increased PKC translocation obtained with 1 microg/mL Con A concentration, whereas PKC was degraded when 2 microg/mL was used. This mechanism is thought to be mediated by calcium mobilisation. According to our results, fluoxetine seemed to modulate calcium influx, which, in turn, would influence PKC translocation, modulating the immune response.     

Metabolic responses of the neonatal rabbit brain to hydrocephalus and shunting

The metabolic changes that occur in the neonatal brain as a result of hydrocephalus, and the response to ventriculoperitoneal shunting, vary with the maturational stage of the brain. In this study, local glucose utilization (LCMRglu) and oxidative metabolic capacity were estimated using 2-deoxyglucose autoradiography and cytochrome oxidase histochemistry, respectively. Hydrocephalus was induced in rabbit pups via intracisternal kaolin injections at 4-6 days of age. Shunting occurred at 19-26 days of age and the animals were sacrificed at ages ranging from 33 to 331 days. In normal animals there was a high glucose demand early in life which showed a decrease at about 60 days of age. In rabbits sacrificed prior to 60 days of age the controls showed the highest LCMRglu with significant decreases in both the hydrocephalic and shunted animals. After 60 days of age the shunted animals had higher LCMRglu than both the hydrocephalic and control subjects. Oxidative metabolic capacity peaked before 50 days of age in normal animals. At the youngest age, both the hydrocephalic and shunted animals showed higher cytochrome oxidase density rates than the control rabbits. In the older group, the hydrocephalic animals remained high while the shunted animals approximated the control densities. Neither the changes seen in the LCMRglu nor the oxidative metabolic capacity were correlated with changes in cell packing density or increased intracranial pressure. These data suggest that when the brain is compromised by hydrocephalus, there is an initial compensatory increase in oxidative metabolic capacity. The development of the glycolytic pathway appears to be retarded by hydrocephalus, but with shunting and the passage of time, the LCMRglu rebounds to levels above that of controls.     

Ovarial steroids and methionine-enkephalin modulation of adrenergic transmission in rabbit oviduct

1. The effect of methionine-enkephalin on the [3H]-noradrenaline ([3H]-NA) overflow and on contractions evoked by field electrical stimulation (FES) and by exogenous NA were studied in vitro in the isthmic part of oviduct of rabbits (untreated and treated with estradiol or progesterone). 2. The evoked tritium overflow (which reflected [3H]-NA overflow) was determined by liquid scintillation spectrometry. 3. Field electrical stimulation of 4 Hz (trains of 40 pulses, 0.3 msec) evoked guanethidine-sensitive contractions. 4. In all groups of animals methionine-enkephalin dose dependently decreased FES-evoked contractions but not those evoked by exogenous NA. 5. The amount of tritium overflow evoked by 4 Hz stimulation (600 pulses, 1 msec) was significantly lower in tissues from estradiol treated (1.16 +/- 0.19%) compared with those obtained in tissues from untreated (1.82 +/- 0.22%) and progesterone treated (2.07 +/- 0.21%) rabbits. Methionine-enkephalin, 1 microM, decreased the evoked tritium overflow in the isthmus from untreated rabbits by 36.1 +/- 3.6%, in estradiol treated by 22.8 +/- 2.9% and in progesterone treated by 52.3 +/- 4.5%. 6. The results suggest that the methionine-enkephalin effect on FES-evoked contractions could be due to a prejunctional effect on the adrenergic terminals and that there is a hormonal dependence of the opioid effect on [3H]-NA overflow.