Gary A. Iwamoto

Effects of capsaicin and bradykinin on afferent fibers with ending in skeletal muscle.

Capsaicin, injected into the arterial supply of the skinned hindlimb of dogs, evokes reflex increases in cardiovascular function. Moreover, the cardiovascular reflexes evoked by capsaicin are very similar to those evoked by static exercise. The afferent fibers initiating these reflex increases have not been identified electrophysiologically, although their endings are believed to be located in skeletal muscle. We have, therefore, attempted to determine which afferent fibers are stimulated by capsaicin. In anesthetized dogs, we recorded impulses from afferent fibers with endings in either the gastrocnemius or gracilis muscles and injected capsaicin (10–30 μg/kg) into the abdominal aorta. Capsaicin stimulated 24 of 34 group IV (C fiber) endings, but only 5 of 19 group III (Aδ fiber) endings. By contrast, bradykinin (0.5–1.5 μg/kg) stimulated 17 of 33 group IV endings and 9 of 19 group III endings. Impulse activity for the 24 group IV afferents stimulated by capsaicin increased from 0.7 ± 0.1 to a peak of 9.3 ± 1.4 imp/sec. Firing started 6 ± 1 seconds after injection and remained above control levels for 24 ± 5 seconds. Capsaicin had no significant effect on the firing rate of 30 group I and II muscle afferents. Our results suggest that group IV muscle afferents are primarily responsible for causing the reflex increases in cardiovascular function evoked by injecting capsaicin into the arterial supply of the skinned hindlimb of dogs. Moreover, capsaicin is likely to be a useful pharmacological tool with which to determine the reflex autonomic effects caused by stimulation of group IV muscle afferents.

Loss of cyclin-dependent kinase inhibitors produces adipocyte hyperplasia and obesity

Adipocyte hyperplasia is characteristic of some forms of human obesity, but the role of adipocyte number in obesity and how normal adipocyte number is established are unclear. Preadipocytes proliferate and then differentiate to become mitotically quiescent adipocytes. This involves exit from the cell cycle, a process regulated by cell cycle inhibitors such as the cyclin‐ dependent kinase inhibitors (CDKIs) p27 and p21. 3T3‐L1 preadipocytes show marked changes in p27 and p21 during differentiation, suggesting CDKIs may regulate establishment of adipocyte number in vivo. To study the role of these CDKIs in adipogenesis, we analyzed adult p27 knockout (p27KO), p21 knockout (p21KO), p27/p21 double knockout (DBKO), and wild‐ type (WT) mice. Adult DBKO mice weighed 100% more and had fourfold increases in body fat percentage compared with WT. Fat pad weights were increased 80, 90, and 500% in p27KO, p21KO, and DBKO mice, respectively, compared with WT. Adipocyte numbers of p27KO, p21KO, and DBKO mice were 1.9‐, 1.7‐, and 6.1‐fold, respectively, that of WT; adipocyte size was not increased. DBKO mice showed glucose intolerance, insulin insensitivity, hepatic steatosis and dyslipidemia; gradations of these effects occurred in p27KO and p21KO mice. In conclusion, p27KO and p21KO mice are obese because of adipocyte hyperplasia, and DBKO mice have further increases in obesity and adipocyte hyperplasia, indicating that their functions in establishing adipocyte number are not redundant. p27 and p21 are major regulators of adipocyte number in vivo, and knockouts lacking one or both of these proteins provide models for producing adipocyte hyperplasia and understanding its metabolic consequences.

Resistance exercise training reduces central blood pressure and improves microvascular function in African American and white men

OBJECTIVE African American men have stiffer large central arteries and impaired dilation of smaller peripheral arteries when compared to their white peers. The purpose of this study was to examine the effect of resistance exercise training (RT) on vascular function and central blood pressure (BP) in young (22 years) African American and white men. METHODS Vascular and hemodynamic measures were made in 19 African American and 18 white men at baseline and following 6-weeks of RT. Carotid BP and carotid/brachial artery beta-stiffness were measured by tonometry and ultrasonography, respectively. Aortic BP was measured by radial artery tonometry and a generalized transfer function. Aortic stiffness was measured by pulse wave velocity (PWV). Forearm blood flow (FBF) was measured by strain-gauge plethysmography before and during reactive hyperemia (RH) induced by 5-min of brachial artery occlusion. RESULTS There were similar reductions in central BP and similar increases in FBF-RH in both African American and white men following RT (p<0.05). There were no changes in brachial systolic BP, carotid stiffness, and aortic PWV in either group (p>0.05). There was an increase in brachial stiffness in African American but not white men following RT (p<0.05). CONCLUSIONS RT led to reductions in central BP and increases in microvascular endothelial function with no effect on central artery stiffness in both groups of young men. RT increased brachial stiffness in African American men. Measurement of conventional brachial BP does not capture the central hemodynamic and vascular response to exercise training due to disparate racial changes in regional vascular properties.

Responses to inflation of vagal afferents with endings in the lung of dogs.

In dogs, inflating the lungs to pressures of 9 cm H2O or less reflexly increases heart rate, whereas inflating the lungs to pressures of 10–30 cm H2O reflexly decreases heart rate. The afferent fibers responsible for the cardioacceleration travel in the vagus nerves and are believed to be pulmonary stretch receptors, whereas the afferents responsible for the deceleration also travel in the vagus nerves, but are believed to be lung C-fibers. To identify the afferents responsible for these effects, we recorded the impulse activity of vagal afferents with endings in the left lung, while we slowly inflated that lung to 30–45 cm H2O. We found that 12 slowly adapting receptors fired at significantly lower inflation pressures than did 10 rapidly adapting receptors (5.8 ± 1.5 vs. 13.5 ± 2.2 cm H2O, respectively). We also found that 13 pulmonary C-fibers fired at significantly lower inflation pressures than did 10 bronchial C-fibers (16.4 ± 1.8 vs. 26.5 ± 2.9 cm H2O, respectively). We conclude that slowly adapting receptors are likely to be responsible for the cardioacceleration evoked by low levels of inflation, and that both pulmonary and bronchial C-fibers are likely to be responsible for the cardiodeceleration evoked by high levels of inflation.

Properties of ventrolateral medullary neurons that respond to muscular contraction.

Previous results from this laboratory have suggested that neurons in the ventrolateral medulla (VLM) modulate the pressor response to muscular contraction. The purpose of the present study was to determine 1) if VLM neurons with a discharge pattern related to sympathetic discharge and/or the cardiac cycle are stimulated during muscular contraction, 2) if the neurons activated by muscular contraction project to the intermediolateral columns of the spinal cord and 3) the location of glutamate immunoreactive neurons in the medulla. Single-unit responses of ventrolateral medullary neurons to hindlimb muscular contraction evoked by ventral root (L7 and S1) stimulation were recorded in one group of anesthetized cats. Computer analyses were performed to determine if the resting discharge of VLM neurons correlated temporally with sympathetic nerve discharge and/or the cardiac cycle. The discharge rate of 21 of 27 neurons which had a discharge related to sympathetic nerve activity increased during muscular contraction. Neurons in some of the experiments were tested for axonal projections to the intermediolateral nucleus (T2 or T5) of the spinal cord with antidromic activation techniques. The discharge pattern of 78% of the VLM neurons which were activated antidromically was related to the cardiac cycle or sympathetic nerve discharge. Most (92%) reticulospinal VLM neurons with cardiovascular related discharge were excited by muscular contraction. In a second set of experiments, glutamate immunoreactivity was demonstrated in neurons within an area overlapping the location of VLM neurons which were excited by muscular contraction. These findings suggest that reticulospinal neurons in the ventrolateral medulla which have a discharge pattern related to cardiovascular activity contribute to the pressor reflex evoked by muscular contraction. These neurons may utilize glutamate as a neurotransmitter.

C-reactive protein and cardiac vagal activity following resistance exercise training in young African-American and white men

African Americans have a greater prevalence of hypertension and diabetes compared with white Americans, and both autonomic dysregulation and inflammation have been implicated in the etiology of these disease states. The purpose of this study was to examine the cardiac autonomic and systemic inflammatory response to resistance training in young African-American and white men. Linear (time and frequency domain) and nonlinear (sample entropy) heart rate variability, baroreflex sensitivity, tonic and reflex vagal activity, and postexercise heart rate recovery were used to assess cardiac vagal modulation. C-reactive protein (CRP) and white blood cell count were used as inflammatory markers. Twenty two white and 19 African-American men completed 6 wk of resistance training followed by 4 wk of exercise detraining (Post 2). Sample entropy, tonic and reflex vagal activity, and heart rate recovery were increased in white and African-American men following resistance training (P < 0.05). Following detraining (Post 2), sample entropy, tonic and reflex vagal activity, and heart rate recovery returned to baseline values in white men but remained above baseline in African-American men. While there were no changes in white blood cell count or CRP in white men, these inflammatory markers decreased in African-American men following resistance training, with reductions being maintained following detraining (P < 0.05). In conclusion, resistance training improves cardiac autonomic function and reduces inflammation in African-American men, and these adaptations remained after the cessation of training. Resistance training may be an important lifestyle modification for improving cardiac autonomic health and reducing inflammation in young African-American men.

Cardiovascular reflexes resulting from capsaicin-stimulated gastric receptors in anesthetized dogs.

To determine whether significant cardiovascular reflexes can be generated from gastric receptor stimulation, we developed an autoperfused canine stomach preparation from a dog anesthetized with a-chloralose so that capsaicin, a C fiber agonist, could be injected into the left gastroepiploic artery (ia) supplying the greater curvature of the stomach. Control injections were made into the inferior vena cava (IVC) to determine capsaicins effects on areas downstream from the stomach. Significant cardiovascular reflexes were obtained in 37 of 42 dogs after ia injection and in 26 of 26 dogs after IVC injection. Capsaicin (25-500 jig) caused significant increases in systolic blood pressure (SBP) (15%), heart rate (HR) (4%), contractility (maximal dP/dt) (19%), and systemic vascular resistance (SVR) (18%), whereas there were no changes in left ventricular end-diastolic pressure (LVEDP) or aortic flow (AF). On the other hand, downstream IVC capsaicin injections caused significant decreases in SBP (28%), HR (34%), dP/dt (33%), and AF (41%), but no change in SVR or LVEDP. The dP/dt response to ia injection continued to occur after overdrive right atrial pacing. However, the responses of pressure, rate, and dP/dt were diminished to a large extent by diaphragmatic celiac nerve section and to a smaller extent by diaphragmatic vagus nerve section. We conclude that these results demonstrate that capsaicin, a potent C-fiber agonist, can stimulate gastric or perigastric receptors to induce a significant activation of the cardiovascular system. Thus, the potential of the stomach to function as a reflexogenic organ which regulates the cardiovascular system has been demonstrated. Circ Res 46: 780-788, 1980

Effects of lateral reticular nucleus lesions on the exercise pressor reflex in cats

Electrical stimulation of ventral roots gives rise to a reflex cardiovascular reponse similar to that observed during static exercise. Although the afferent limb of the reflex is known to be comprised of small diameter afferent fibers from the contracting muscle, little is known of the central nervous system pathway(s) involved. The lateral reticular nucleus of the brainstem is known to be an important site of integration for numerous types of visceral and somatic afferent information, many of which give rise to cardiovascular responses. However, the linkage between the small diameter muscle afferents responsible for the exercise pressor reflex and the lateral reticular nucleus has not been established. In anesthetized cats (n = 7), stimulation of L7 and Si ventral roots increased mean arterial pressure (18.6 ± 2.4 mm Hg) and heart rate (7.4 ± 1.7 beats/min). Following bilateral lesions of the lateral reticular nucleus, the increases in mean arterial pressure and in heart rate were essentially abolished (P < 0.005) (mean arterial pressure increased 1.9 ± 0.8 mm Hg and heart rate increased 0.7 ± 0.5 beats/min). Unilateral lateral reticular nucleus lesions and control lesions in pressor sites outside the lateral reticular nucleus (n = 5) did not affect the exercise pressor reflex. The lateral reticular nucleus lesions also produced decreases (P < 0.01) both in resting mean arterial pressure (—27 ± 5.5 mm Hg) and heart rate (—31.0 ± 8 beats/min). These data suggest that the lateral reticular nucleus is important in the central pathway of the exercise pressor reflex and mediates a tonic pressor influence at rest. (Circ Res 51: 4OO-403, 1982)

Central connections of the ovine olfactory bulb formation identified using wheat germ agglutinin-conjugated horseradish peroxidase.

Pheromonal stimuli elicit rapid behavioral and reproductive endocrine changes in the ewe. The neural pathways responsible for these effects in sheep are unknown, in part, because the olfactory bulb projections have not been examined in this species. Using the anterograde and retrograde neuronal tracer, wheat germ agglutinin-conjugated horseradish peroxidase (WGA-HRP), we describe the afferent and efferent olfactory bulb connections of the Suffolk ewe. Injections of WGA-HRP limited to the main olfactory bulb resulted in retrograde labeling of cells in numerous telencephalic, diencephalic, and metencephalic regions. Terminal labeling was limited to layer la of ipsilateral cortical structures extending rostrally from the anterior olfactory nucleus (AON), piriform cortex, anterior-, and posterolateral-cortical amygdaloid nuclei to lateral entorhinal cortex caudally. Injections involving the accessory olfactory bulb and AON produced additional labeling of cells within the bed nucleus of the stria terminalis (BNST), medial nucleus of the amygdala, and a few cells in the posteromedial cortical nucleus of the amygdala. Terminal labeling included a small dorsomedial quadrant of BNST and also extended to the far lateral portions of the supraoptic nucleus. A clearly defined accessory olfactory tract and nucleus was not evident, perhaps due to limitations in the sensitivity of the method. With this possible exception, the afferent and efferent olfactory connections in the sheep appear similar to those reported for other species.

Changes in the exercise activation of diencephalic and brainstem cardiorespiratory areas after training

The purpose of this study was to determine whether exercise training changes the extent or pattern of activation of areas in the central nervous system (CNS) involved in cardiorespiratory control. Rats that spontaneously trained on running wheels for 80-100 days were compared to rats that were not provided an opportunity to exercise. Selected brain regions including the hypothalamic and mesencephalic locomotor regions, and ventrolateral medulla were studied using c-Fos-like immunocytochemistry. A single test bout of exercise evoked significantly less activation as indicated by Fos labeling in the posterior (caudal) hypothalamic area, periaqueductal gray, nucleus of the tractus solitarius and the rostral ventrolateral medulla of the trained rats when compared to sedentary rats. These results are consistent with the concept that the nervous system changes its responses to a given level of exercise after training. These changes may also be related to perceived exertion.