Increased adipose tissue in male and female estrogen receptor-alpha knockout mice

Estrogen regulates the amount of white adipose tissue (WAT) in females, but its role in males and whether WAT effects involve estrogen receptor-alpha (ERalpha) or ERbeta were unclear. We analyzed the role of ERalpha in WAT and brown adipose tissue by comparing these tissues in wild-type (WT) and ERalpha-knockout (alphaERKO) male and female mice. Brown adipose tissue weight was similar in alphaERKO and WT males at all ages. Progressive increases in WAT were seen in alphaERKO males with advancing age. Epididymal, perirenal, and inguinal WAT weighed 139-185% more in alphaERKO than in WT males by 270-360 days of age. Epididymal and perirenal adipocyte size was increased 20% in alphaERKO males. Adipocyte number was 82-168% greater in fat pads of alphaERKO vs. WT males. Compared with WT, 90-day-old alphaERKO females had increases in fat pad weights (54-103%), adipocyte size, and number. Both alphaERKO males and females had insulin resistance and impaired glucose tolerance, similar to humans lacking ERalpha or aromatase. Energy intake was equal in WT and alphaERKO males, indicating that obesity was not induced by hyperphagia. In contrast, energy expenditure was reduced by 11% in alphaERKO compared with WT males, indicating that altered energy expenditure may be important for the observed obesity. In summary, ERalpha absence causes adipocyte hyperplasia and hypertrophy, insulin resistance, and glucose intolerance in both sexes. These results are evidence that estrogen/ERalpha signaling is critical in female and male WAT; obesity in alphaERKO males involves a mechanism of reduced energy expenditure rather than increased energy intake.

Differential effects from parapyramidal region and rostral ventrolateral medulla mediated by substance P

Rostral ventrolateral medulla (rVLM) and parapyramidal region (PPr) serve as important medullary control sites for sympathoexcitation. rVLM and PPr have direct projections to the intermediolateral cell column (IML) that are thought to be important in maintaining mean arterial blood pressure (MAP). Substance P (SP) is found in PPr neurons and in and near the subretrofacial area of the rVLM. At least some of these cells project to the IML. We investigated the involvement of SP at the IML in mediating rVLM- and PPr-evoked pressor responses in the chloralose-anesthetized cat. Pressor responses to electrical and chemical PPr and rVLM stimulation were altered after intrathecal injection, at the level of the T1-T3 spinal cord, of either SP antagonist [D-Pro(2), D-Phe(7), D-Trp(9)]-SP, SP antagonist CP 96,345, or SP antiserum. Although MAP and heart rate responses to PPr stimulation were attenuated by intrathecal SP antagonists or antiserum, MAP responses to rVLM stimulation were augmented. Previous studies have revealed differences in transmitters associated with these two areas, even though the general response of both areas is sympathoexcitatory. The present study implies that the identical substance may increase or decrease the MAP response depending on the pathway activated.

Apparent water diffusion measurements in electrically stimulated neural tissue

The effect of stimulation on diffusion characteristics of electrically stimulated neural tissue was examined. Bullfrog nerves and spinal cords were excised and stimulated electrically during magnetic resonance imaging, and the apparent diffusion coefficients (ADCs) of water parallel and perpendicular to the long axes of the specimens were mapped with and without stimulation of the tissue. Electrophysiological recordings were used to determine the viability of the tissue after each experiment. No stimulus-related ADC changes were observed in either the peripheral nervous system or the central nervous system tissue. These experiments may help to define further the nature of previously reported ADC changes in stimulated neural tissue in situ.

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.

A multiple echo pulse sequence for diffusion tensor imaging and its application in excised rat spinal cords

A new imaging sequence for rapid determination of the apparent self-diffusion tensor of water was developed and tested on fixed excised rat spinal cords. To reduce the time required to determine the tensor, the sequence utilized a new single-shot approach with multiple spin echoes. An assumption of cylindrical symmetry in the sample was made, thus requiring the measurement of only four of the six unique elements of the tensor. This assumption was found experimentally to be valid, and the results obtained using the new sequence were found to be quantitatively the same as results obtained using a standard spin-echo sequence.

Identification of diencephalic and brainstem cardiorespiratory areas activated during exercise

The purpose of this study was to identify diencephalic and brainstem sites active during exercise (EX) in conscious rats running on a treadmill. Brain areas active during exercise, compared to rest conditions (non-EX), were identified using immunocytochemical labelling of the protein product of the proto-oncogene c-fos. Increased labelling was observed in the 'defence area' or 'hypothalamic/subthalamic locomotor regions' including the posterior and lateral hypothalamic areas. Increased labelling with EX was found in both colliculi, the periaqueductal gray matter, the parabrachial complex and the cuneiform nucleus ('mesencephalic locomotor region'). Increased labelling with EX was also found in the medial portion of n. tractus solitarius, and both the rostral and caudal ventrolateral medulla. Conspicuous by an absence of labelling during EX were cells in thalamic areas associated with somatosensory function, although the dorsal column nuclei were also labelled above control. Thus, areas in which labelling was increased during exercise closely correlate with the brain areas which have been implicated in both autonomic and somatomotor control. These results from awake, exercising rats support those obtained previously in anesthetized animal preparations.

Lateral tegmental field neurons sensitive to muscular contraction: a role in pressor reflexes?

The medullary lateral tegmental field (LTF) has a major role in sympathetic nerve discharge (SND) rhythmicity, but its role in pressor reflexes generated by hindlimb muscular contraction (MC) is unknown. Therefore, two sets of experiments were performed in 17 chloralose-urethane anesthetized cats. First, responses of single LTF neurons to MC induced by L7-S1 ventral root stimulation were examined. The majority (30 of 47) of LTF neurons increased firing during MC. Most LTF neurons had a basal discharge correlated with the 2-10 Hz rhythm of SND or the cardiac cycle and responded to increases in blood pressure. Only seven neurons were inhibited by MC, most having a respiratory rhythm. Second, pressor responses to MC and to caudal hypothalamic stimulation were examined before and after bilateral LTF microinjections of a synaptic blocker (CoCl2) as well as with lidocaine. Microinjection of CoCl2 or lidocaine significantly attenuating the dominant 2-10 Hz power coefficient of SND had no effect on the pressor responses to MC or caudal hypothalamic stimulation. Therefore, LTF may be important for basal rhythms in SND and may help synchronize SND during MC, but its contribution to basal rhythms is apparently not required for pressor reflexes evoked by hindlimb MC or hypothalamic stimulation.

Reflex control of glucoregulatory exercise responses by group III and IV muscle afferents

Group III and IV muscle afferents are active during exercise and relay information from mechano- and metaboreceptors in muscle. We hypothesized that these afferents participate in the regulation of endocrine and metabolic adjustments to exercise. Muscle branches of the femoral nerves were electrically stimulated in 10 anesthetized and paralyzed cats at 3, 20, and 140 times motor threshold, for 10 min at each intensity, recruiting group III afferents at 20 times motor threshold and group III and IV afferents at 140 times motor threshold. Six cats were not stimulated but were otherwise treated as stimulated cats. [3-3H]glucose was infused intravenously, and arterial blood was sampled for analysis of substrates and hormones. Three times motor threshold stimulation induced no changes in measured metabolic parameters. Twenty times motor threshold stimulation elicited increases (P < 0.05 vs. control) in glucose production (8.2 +/- 1.8 mumol.min-1.kg-1) and plasma glucose (0.29 +/- 0.07 mmol/l) and adrenocorticotropic hormone (ACTH; 35 +/- 12 pg/ml). Stimulation at 140 times motor threshold elicited increases (P < 0.05 vs. control) in glucose production (10.2 +/- 5.4 mumol.min-1.kg-1), plasma glucose (0.53 +/- 0.10 mmol/l), ACTH (94 +/- 28 pg/ml), beta-endorphin (17 +/- 6 pg/ml), and Met-enkephalin (15 +/- 2 pg/ml) and decreases (P < 0.05 vs. control) in insulin (0.65 +/- 0.14 microU/ml). Glycerol and glucagon did not change with stimulations. The findings provide evidence for a reflex control from muscle of hormone secretion and mobilization of glucose during exercise.

A re-evaluation of the effects of gonadal steroids on neuronal activity in the male rat

Single unit activity (SUA) was recorded from 77 cells located in the arcuate nucleus (ARC) and medial preoptic area (MPA) of anesthetized, intact male rats. Animals were administered vehicle, testosterone (T; 5 or 50 micrograms) or 17 beta-estradiol (E; 0.5 microgram) intravenously and SUA was monitored for 8-12 min. T (50 micrograms) reduced SUA in 50% of ARC units and 44% of MPA units within 2.1 +/- 0.46 and 3.3 +/- 0.92 min, respectively. Inhibition of ARC SUA was more pronounced than MPA SUA. A small percentage (9%) of ARC units were excited by T. E reduced SUA in 29% of ARC units and 27% of MPA units. Single doses of 5 micrograms T did not affect ARC activity. However, when followed within 10 min by an additional dose of 5 or 50 micrograms T, 30% and 43% of ARC units were inhibited, respectively. Doses (10 micrograms) of T produced plasma T concentrations within physiological limits, although 50 micrograms doses produced supraphysiological T levels. Neither dose affected circulating LH concentrations. We conclude that physiological and supraphysiological concentrations of T can rapidly affect SUA within the ARC.

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.

Effects of muscular contraction on discharge patterns of neurons in the medullary raphe nuclei

Cells of the medullary raphe nuclei were characterized as sympathoinhibitory (SI), sympathoexcitatory (SE) or serotonergic (5-HT). When muscular contraction (MC) was evoked by stimulation of the L7 and S1 ventral roots, putative SI cells were inhibited while putative SE cells were excited. 5-HT cells were unaffected by MC. These data are discussed in relation to integration of somatosensory and cardiovascular reflexes.

Cardiorespiratory responses to chemical stimulation of the caudal most ventrolateral medulla in the cat

Chemical stimulation of caudal ventrolateral medulla evoked both pressor and depressor responses. The pressor sites were generally located caudal to depressor sites. Effects on heart rate were variable. Significant increases in minute ventilation were also observed, which were primarily due to changes in respiratory frequency.

Cardiovascular responses to chemical stimulation of the inferior olive in the cat

Previous studies have suggested that electrical stimulation of the inferior olivary nucleus of anesthetized cats does not alter arterial pressure but does inhibit the depressor response to baroreceptor stimulation. However, it was not determined if the observed alteration of the baroreceptor reflex was due to an effect on cell bodies or on fibers of passage. The purpose of the present study was to determine the responses to selective activation of cell bodies in the inferior olive in anesthetized cats. Unilateral microinjections of kainic acid, D,L-homocysteic acid and glutamate were made into the inferior olive at the level of or just rostral to the obex. In addition, the baroreceptor reflex was examined before and after microinjection of kainic acid. The microinjections produced an increase in arterial pressure accompanied by variable effects on heart rate. However, the cardiovascular responses to activation of arterial baroreceptors were not altered by kainic acid microinjections. These results indicate that neurons in the inferior olivary nucleus can exert effects which increase arterial pressure but the inferior olive at this level does not modulate the baroreceptor reflex in anesthetized cats.

Discharge patterns of ventrolateral medullary neurons during muscular contraction

Static muscular contraction is known to elicit reflex increases in arterial pressure. However, the areas of the central nervous system that mediate this reflex remain elusive. A recent study from this laboratory suggested that neurons in the ventrolateral medulla (VLM) participate in the pressor reflex to muscular contraction. In the present study, we sought to ascertain whether extracellular single-unit activity of VLM neurons is altered by static contraction of hindlimb muscles. In anesthetized cats, muscular contraction elicited by stimulation of L7 and S1 ventral roots evoked increases in arterial pressure, heart rate, and minute ventilation. The firing frequency in 33 of 50 VLM units increased greater than 70% during muscular contraction. VLM units displayed two types of discharge patterns in response to contraction: 1) a rapid onset response (0.5-3 s) and 2) a delayed onset response (10-20 s). Computer averaging analysis showed that 14 of 28 VLM units tested had a cardiac-related rhythm and 10 of those 14 also responded to muscular contraction. Muscular contraction had no effect on the discharge patterns of most neurons located outside the VLM. These findings suggest that neurons in the ventrolateral medulla respond to muscular contraction and may have a role in the pressor reflex to muscular contraction.

Pathophysiologic effects of anatoxin-a(s) in anaesthetized rats: the influence of atropine and artificial respiration

The pathophysiologic effects of anatoxin-a(s) from the cyanobacterium Anabaena flos-aquae NRC-525-17 were investigated in anaesthetized adult male Sprague Dawley rats given the toxin by continuous intravenous infusion until death. Rats (n = 6) pretreated with atropine sulfate (50 mg/kg) intraperitoneally survived significantly longer (P less than 0.05) than non-atropinized rats (n = 6), suggesting that the muscarinic effects of anatoxin-a(s) were important in the lethal syndrome. In contrast to rats only given toxin, rats that were pretreated with atropine had a decrease in heart rate and mean blood pressure that followed profound reductions in respiratory tidal and minute volume, suggesting that neuromuscular blockade of the muscles of respiration was the cause of death. Even when survival time of rats was increased by pretreatment with atropine, phrenic nerve amplitude increased, indicating a lack of a depressive effect of anatoxin-a(s) on central mediation of respiration. Rats (n = 3) continuously ventilated during toxin infusion survived a dose more than 4 fold greater than a consistently lethal dose of the toxin. Thus, the cardiovascular effects of anatoxin-a(s) alone could not account for the death of rats. Electromyographic activity recorded from the diaphragms of rats (n = 5) during continuous toxin administration revealed an increase in muscular electrical activity that became more random and finally decreased prior to death, suggesting a toxin-induced neuromuscular blockade in vivo which ultimately was the cause of death of the anatoxin-a(s) dosed rats.

Cardiorespiratory responses to stimulation of the nucleus reticularis gigantocellularis

The nucleus reticularis gigantocellularis (NGC) has been shown to be involved in somatosensory and somatomotor functions. The purpose of the present study was to determine, in anesthetized cats, the modulatory influence of the portion of the NGC at the ponto-medullary border on respiratory and cardiovascular control. Electrical stimulation (25-100 microA 70 Hz, and 1.0-msec pulse duration) significantly depressed mean arterial pressure, heart rate, breathing frequency, tidal volume and phrenic amplitude. Chemical stimulation of NGC cell bodies (1.0 M L-glutamate or 10(-3) M kainic acid) elicited similar decreases in ventilation, arterial pressure and heart rate. These results show that selective activation of cell bodies in the ponto-medullary NGC can depress, in parallel, respiratory and cardiovascular activity and suggests that the influence of diverse sensory information within this region of the reticular formation must be inhibitory to respiratory and cardiovascular output.

Localization of tyrosine hydroxylase and phenylethanolamine N-methyltransferase immunoreactive cells in the medulla of the dog

The tyrosine hydroxylase (TH)- and phenylethanolamine N-methyltransferase (PNMT)-immunoreactive cells of the medulla are closely associated with cardiovascular control in both the cat and rat. Although it is often the species of choice for cardiovascular studies, no previous study had characterized these cell groups in the dog. The TH- and PNMT-immunoreactive cells of the dog were distributed much as they are in both cat and rat but with some species variations, which may be indicative of their functional role.

Effect of anatoxin-a(s) from Anabaena flos-aquae NRC-525-17 on blood pressure, heart rate, respiratory rate, tidal volume, minute volume, and phrenic nerve activity in rats

The effects of anatoxin-a(s) [antx-a(s)] from the cyanobacterium Anabaena flos-aquae NRC-525-17 on mean arterial blood pressure, heart rate, respiratory rate, tidal volume, minute volume, and phrenic nerve activity were evaluated in anesthetized Sprague-Dawley rats. Anatoxin-a(s) was administered by continuous intravenous infusion. The initial effect of the toxin was to slow the heart rate and reduce arterial blood pressure, followed by much more pronounced reductions in these parameters. The marked decline in heart rate and blood pressure frequently occurred before there was a large decrease in respiratory minute volume [reduced by only 15.4 +/- 3% (mean +/- S.E.) compared to the predose period], suggesting that antx-a(s) has an important muscarinic action on the cardiovascular system in vivo. Phrenic nerve amplitude increased, but, nevertheless, tidal and minute volumes decreased progressively, indicating that antx-a(s), unlike most low-molecular-weight organophosphorus cholinesterase inhibitors, does not have any remarkable inhibitory action on central mediation of respiration.

Distribution of cell bodies for primary afferent fibers from the stomach of the cat

The distribution of primary afferent cell bodies supplying the stomach of the cat was localized using lectin-conjugated horseradish peroxidase. Labelled cells were found in the nodose ganglia and dorsal root ganglia T4-L2 or T4-L1. The spinal entry levels of the stomach afferents do not overlap extensively with those of the cardiac afferents.

Mobilization of glucoregulatory hormones and glucose by hypothalamic locomotor centers

Recent studies suggest that, in addition to classical humoral metabolic feedback mechanisms, the mobilization of glucoregulatory hormones and glucose in exercise may be regulated by motor centers in the brain. We, therefore, studied the effect of electrically stimulating the posterior hypothalamic locomotor region (PHLR) for 10 min in decorticated (n = 6) and alpha-chloralose-anesthetized (n = 8) cats. Blood pressure and heart rate were measured, and blood samples were drawn for analysis of hormones and metabolites before, during, and after 10 min of PHLR stimulation. Feedback from contracting muscles was prevented by neuromuscular blockade in decorticated cats and by the anesthesia in anesthetized cats. In decorticated cats, PHLR stimulation elicited increases (2 P less than 0.05) in glucose production (delta 54 +/- 16 mumol.min-1.kg-1), plasma glucose (delta 2.2 +/- 0.7 mmol/l), epinephrine (delta 4.9 +/- 1.8 pmol/l), norepinephrine (delta 2.2 +/- 0.9 pmol/l), glucagon (delta 16 +/- 5 pmol/l), decreases (2 P less than 0.05) in plasma insulin (delta 27 +/- 7 pmol/l), and increases (2 P less than 0.05) in blood pressure (delta 48 +/- 9 mmHg) and heart rate (delta 26 +/- 7 beats/min). In anesthetized cats, PHLR stimulation elicited increases (2 P less than 0.05) in glucose production (delta 12 +/- 4 mumol.min-1.kg-1), plasma glucose (delta 0.4 +/- 0.1 mmol/l), blood pressure (delta 39 +/- 7 mmHg), and heart rate (delta 28 +/- 7 beats/min), whereas changes in catecholamine and insulin concentrations did not reach statistical significance.(ABSTRACT TRUNCATED AT 250 WORDS)

Ventrolateral medullary neurons modulate pressor reflex to muscular contraction

Cardiorespiratory alterations during exercise are mediated through feedback from contracting muscles and descending drive from rostral brain sites such as the posterior hypothalamus. The role of medullary sites, which process this information, was examined in this study. In anesthetized cats, muscular contraction elicited by stimulation of L7 and S1 ventral roots and electrical stimulation of sites in the posterior hypothalamus both evoked increases in arterial pressure, heart rate, and minute ventilation. The reflex increase in arterial pressure produced by muscular contraction was attenuated significantly 15-20 min after bilateral microinjections of an excitatory amino acid (EAA) receptor antagonist, kynurenic acid (KYN), into the ventrolateral medulla (VLM). The reflex increase in arterial pressure evoked by muscular contraction returned to control levels 90 min after VLM microinjections of KYN. Microinjection of KYN into the VLM had no effect on the cardiorespiratory responses to posterior hypothalamic stimulation. These findings suggest that neurons in the VLM modulate the reflex pressor response evoked by muscular contraction. This reflex may be mediated through an interaction with EAA receptors on neurons in the VLM.

Hypothalamic influences on cardiovascular response of beagles to dynamic exercise

We studied nine young adult beagles at rest and during four levels of dynamic exercise before and after electrolytic lesions were made in the hypothalamus in the region of the fields of Forel. The beagles were habituated to run freely on a motor-driven treadmill and were instrumented chronically to allow repeated measurement of cardiovascular variables. Variables measured or calculated included O2 consumption, cardiac output, arteriovenous O2 difference, systemic arterial pressure, systemic vascular resistance, heart rate, and mixed venous blood lactate concentration. In addition, regional blood flow was measured with radioactive microspheres in two beagles at rest and during peak exercise (6.4 km/h, 20% grade). After prelesion treadmill studies, the beagles were anesthetized and the tips of stainless steel electrodes were placed bilaterally in the hypothalamus in locations that when stimulated (100-300 microA) evoked increases in cardiovascular and muscle motor function. Lesioning (5 mA; 15 s) abolished the responses evoked by stimulation. By contrast, the cardiovascular variables measured in the beagles at rest and during dynamic exercise were similar pre- and postlesion. Therefore, loss of hypothalamic sites that produce increases in cardiovascular and muscle motor function when stimulated electrically does not appear to comprise the cardiovascular response of awake beagles to dynamic exercise.

Stimulating somatic afferent fibers alters coronary arterial resistance

We used a constant flow preparation to study the changes in left circumflex coronary arterial (LCCA) pressure and resistance evoked by electrical stimulation of branches of muscle, cutaneous, and mixed nerves in the hindlimb of anesthetized dogs. Stimulation (20 Hz) of all three nerve types at 20, 70, 100, and 200 times the voltage threshold that evoked compound action potentials significantly (P less than 0.05) increased LCCA resistance. Stimulation at three and five times threshold had no effect on this same variable. Cooling the nerve to 2-4 degrees C, temperatures that block myelinated nerve fibers, attenuated but did not abolish the increase in LCCA resistance. Combinations of beta- and alpha-adrenergic and cholinergic blockade established that the biphasic change evoked by nerve stimulation was due to an initial alpha-adrenergic vasoconstriction followed by a metabolite-induced vasodilation. These data demonstrate that stimulation of muscle, cutaneous, or mixed nerve afferent C-fibers increases coronary arterial resistance by alpha-adrenergic vasoconstriction.

Occlusion of pressor responses to posterior diencephalic stimulation and muscular contraction

Although neural occlusion has been suggested to occur between the central and reflex mechanisms increasing arterial pressure, evidence consistent with this phenomenon is lacking. To assess the possibility of neural occlusion we recorded, in chloralose-anesthetized cats, the pressor responses to statically contracting the hindlimb muscles and to electrically stimulating histologically confirmed sites in the posterior hypothalamus and subthalamus. We also recorded the pressor responses to topical application of capsaicin onto the intestine and to stimulation of these diencephalic sites. The pressor responses to simultaneous static contraction and diencephalic stimulation were significantly smaller than the algebraic sum of the pressor responses to contraction and diencephalic stimulation evoked separately. Likewise, the pressor responses to simultaneous capsaicin application and diencephalic stimulation were significantly smaller than the algebraic sum of the responses evoked separately. High intensity stimulation of the L7 dorsal root or the diencephalic sites evoked pressor responses similar in magnitude to the algebraic sum of the two responses evoked separately; thus, the inability of the simultaneous maneuvers to evoke pressor responses that summed algebraically was not due to the fact that they caused a maximal effect. Our findings are consistent with the hypothesis that neural occlusion occurs during stimulation of the posterior diencephalon and static muscular contraction.

Microinjection of GABA antagonists into the posterior hypothalamus elicits locomotor activity and a cardiorespiratory activation

It is well known that electrical stimulation of an area (subthalamic locomotor region, STLR) of the posterior hypothalamus evokes locomotion as well as increases in cardiorespiratory activity. Uncertainty exists over whether these responses are due to stimulation of STLR neurons or to activation of fibers of passage originating outside this area. The purpose of the present study was to determine if stimulation of STLR neurons alone would elicit the cardiorespiratory and locomotor responses. Neurons were stimulated by microinjections of gamma-aminobutyric acid (GABA) antagonists (picrotoxin and bicuculline) into the posterior hypothalamus of anesthetized cats. Both picrotoxin and bicuculline produced increases in arterial pressure, heart rate and minute ventilation which were accompanied by locomotor movements of the limbs. Increases in arterial pressure, heart rate and phrenic nerve activity were also caused by picrotoxin microinjections in paralyzed, ventilated cats. Microinjections of GABA or a GABA agonist (muscimol) reversed all of these responses. In contrast, microinjection of GABA or muscimol into the STLR without a prior antagonist injection had only small, transient effects upon cardiorespiratory activity. However, microinjection of muscimol prevented the responses to a subsequent injection of bicuculline. These results indicate that: (1) stimulation of cell bodies alone in the subthalamic locomotor region of the hypothalamus produces all the cardiorespiratory and locomotor responses evoked by electrical stimulation; (2) the responses evoked by picrotoxin and bicuculline are due to an interaction with GABA receptors and (3) a GABAergic mechanism exerts a tonic depressive influence over the cardiorespiratory and locomotor systems by an action in the posterior hypothalamus.

Cardiovascular responses at the onset of exercise with partial neuromuscular blockade in cat and man

1. In decerebrated cats the cardiovascular, heart rate and blood pressure responses to static muscle contractions were followed from the onset of stimulation of the cut L7-S1 ventral roots. Heart rate and blood pressure were also followed during maximal voluntary and electrically induced static muscle contractions in man using one leg. In both cat and man contractions were performed under control conditions and tubocurarine-induced neuromuscular blockade. 2. In the cat, heart rate and blood pressure increased 1.7 s after the onset of the contraction. No cardiovascular responses were seen when the muscle contraction was blocked by tubocurarine. 3. In man, both heart rate and blood pressure increased at the onset of voluntary contractions. Partial curarization reduced strength to 39% of control. The heart rate response was unaffected by tubocurarine while the blood pressure response was reduced from 61 to 32 mmHg. 4. Electrical stimulation of the muscles resulted in 75% of voluntary strength in man. The heart rate response was delayed one R-R interval in the electrocardiogram but was as large as during voluntary contractions. During partial curarization the heart rate response was significantly smaller and the blood pressure response was reduced from 11 to 8 mmHg. 5. In conclusion, processes in active muscles elicit an increase in heart rate and blood pressure which depends on the intensity of the muscle contraction developed. However, the immediate cardiovascular responses at the onset of voluntary muscle contractions cannot be accounted for by reflexes generated in the working muscles alone.

Caudal ventrolateral medullary cells responsive to muscular contraction

The pressor reflex evoked by muscular contraction (exercise pressor reflex) is held to be an important mechanism in producing the cardiovascular adjustments to static exercise. Recent experiments using lesioning and metabolic labeling methods have indicated that the caudal ventrolateral medulla may be a key integrative site for the reflex evoked by muscular contraction induced by ventral root stimulation. Therefore, we sought to determine whether cells in this region could be associated with the cardiovascular reflex accompanying muscular contraction through analysis of their discharge characteristics. Eighty cells were characterized as to their response to ventral root stimulus-induced static muscular contraction, intra-arterial capsaicin (selective groups III and IV stimulus), and mechanical probing. The cells' receptive fields were also determined by mechanical probing. The receptive fields were usually large, often including all four limbs and the trunk. Four response patterns were observed to static contractions: a brisk initial discharge followed by a gradual return toward control levels (slowly adapting), a brief onset and cessation response, a brief inhibition followed by a slowly adapting discharge, and inhibition alone. Virtually all cells tested were responsive to capsaicin. Histological analysis verified the position of the recorded cells. It is suggested that the cells most likely to participate in the pressor response to muscular contraction were those cells in the general region of the lateral reticular nucleus which responded with an initial and sustained discharge and the cells that were inhibited in the region of the nucleus ambiguus (possible inhibition of vagal outflow).

Gradation of isometric tension by different activation rates in motor units of cat flexor carpi radialis muscle

Single motor units of the flexor carpi radialis (FCR) muscle were activated with a series of constant-rate stimulus trains to study the relation between the frequency of activation and isometric tension development (F-T relation). The tension produced by each stimulus train was expressed as a percentage of the maximum tension-time area (Amax) found for a given unit. Between 25 and 75% Amax a clear separation was seen in the rates needed to produce the same relative tension for the F-T curves of slow-twitch (type S) and fast-twitch (type F) units. Over the steepest portion of the F-T curve (25-50% Amax), where tension output was most sensitive to changes in activation rate, type F units required substantially higher stimulation rates (30 pps) to achieve the same relative tension output as type S units. Furthermore, the frequency range that corresponded to the steep portion of the curve was 2.3 times greater for type F units. For both type S and F units, twitch duration was deemed to be an important determinant of the F-T curve, as has been shown previously. A direct continuous relation was seen between the integrated twitch time (ITT) and the stimulus interval needed to produce 50% Amax (r = 0.94, P less than 0.001). Thus, units that had relatively brief twitches required higher activation rates to achieve the same relative percentage of Amax. Comparison of F-T curves from FCR with those derived by other investigators for cat hindlimb units (medial gastrocnemius and peroneus longus) revealed that significant differences in activation rates were needed to produce the same percentage of Amax throughout the midrange of the F-T curve. At 50% Amax, type F units in FCR required activation rates approximately 20 pps higher than type F units in the hindlimb. Type S units in FCR required only slightly higher rates (approximately equal to 5 pps). Based on a number of well-founded assumptions, F-T curves derived from FCR units were used to estimate the potential contribution of rate coding to total muscle tension by type S and F units. This analysis leads to the conclusion that rate modulation is a potentially important factor in the gradation of tension for the FCR muscle.

Immunoneutralization of substance P attenuates the reflex pressor response to muscular contraction

We previously reported that subarachnoid injection of a peptide antagonist to substance P attenuated by half the reflex pressor response to static muscular contraction. Subsequently, some of the peptide antagonists to substance P have been found to possess local anesthetic effects. Therefore, we have repeated our experiments using a substance P antiserum, which was shown to be without local anesthetic effect. We found that intrathecal injection of the antiserum attenuated by more than half the reflex pressor response to static contraction of the triceps surae muscles of cats.

Regional blood flow responses to stimulation of the subthalamic locomotor region

Recent studies have suggested that descending central command from an area in the diencephalon (subthalamic locomotor region - STLR) is involved in the control of ventilation, arterial pressure and heart rate during exercise. The purpose of this study was to determine if electrical activation of the STLR in anesthetized cats elicits changes in regional blood flow and vascular resistances similar to those evoked by exercise. Therefore, organ blood flows (radioactive microsphere technique), arterial pressure (AP), heart rate (HR), and respiratory output (quantified from phrenic nerve activity) were recorded during resting conditions and during STLR stimulation. Stimulation of the subthalamic locomotor region produced increases in AP, HR and respiratory output similar to those reported previously. These changes were accompanied by increased blood flow to the heart, diaphragm and limb skeletal muscles. A concomitant decrease occurred in blood flow to the kidneys. In addition, the vascular resistances of the intestines, gallbladder and stomach increased. These vascular and respiratory responses are similar to those occurring during static exercise in conscious cats.

Phosphorylation of rabbit skeletal muscle myosin in situ

Myosin light chain (P light chain) is phosphorylated by Ca2+ X calmodulin-dependent myosin light chain kinase. Based on studies with rat skeletal muscles, it has been shown that P light chain phosphorylation correlated to the extent of potentiation of isometric twitch tension. It is not clear whether this correlation exists in rabbit skeletal muscle, which has been the primary source of contractile proteins for biochemical studies. Therefore, phosphorylation of myosin P light chain in rabbit slow-twitch soleus and fast-twitch plantaris muscles in situ was examined. Electrical stimulation (5 Hz, 20 seconds) of plantaris muscle produced an increase in the phosphate content of P light chain from 0.17 to 0.45 mol phosphate/mol P light chain. This increase in phosphate content was accompanied by a 58% increase in maximal isometric twitch tension. Tetanic stimulation (100 Hz, 15 seconds) of rabbit soleus muscle resulted in only a small increase in P light chain phosphate content from 0.02 to 0.10 mol phosphate/mol P light chain, and posttetanic twitch tension did not increase significantly. The correlation between potentiated isometric twitch tension and P light chain phosphorylation in rabbit fast-twitch muscle is similar to that observed in rat skeletal muscle. These results were consistent with the hypothesis that phosphorylation of rabbit skeletal muscle myosin, which results in an increase in actin-activated ATPase activity, may be related to isometric twitch potentiation.

Classification of motor units in flexor carpi radialis muscle of the cat

Motor units in the cat flexor carpi radialis (FCR) muscle, one of two primary wrist flexors, were classified into three groups: slow twitch, fatigue resistant (S); fast twitch, fatigue resistant (FR); and fast twitch, fatigue sensitive (FF). Classification was based on 1) the ratio of the tension-time area produced by a train of stimuli delivered at 40 pps and the maximum tension-time area (A40/Amax), and 2) the cumulative force index (CFI), calculated from a series of trains (40 pps) delivered intermittently for a period of 4 min. The CFI is defined as the ratio between the force accumulated in the last 2 min of stimulation to the first 2 min of stimulation. Motor units with values for A40/Amax greater than 0.50 were classified as type S units, and less than 0.50 as type F. A40/Amax is essentially equivalent to the "sag" profile of an unfused tetanus in its ability to separate units into "slow" and "fast" contracting units. In general, units with area ratios less than 0.50 had twitch contraction times less than 25 ms, whereas units with area ratios greater than 0.50 had contraction times greater than 25 ms. Separation of type F units into two groups was based on the CFI, with ratios less than or equal to 0.75 corresponding to type FF units and greater than 0.75 as type FR units. Type S units also had CFIs greater than 0.75. Based on this classification scheme, 40.4% of FCR motor units were type S, 37.5% type FR, and 22.1% type FF. The a priori assumption of three motor-unit types based on the distributions of A40/Amax and CFI was evaluated by cluster analysis. The analysis supported the assumption of three primary groups of motor units. Furthermore, when cluster formation proceeded to the point where only three clusters remained in the analysis, each of these clusters consisted exclusively of one type of unit (i.e., S, FR, or FF). The validity of the classification scheme was further tested by stepwise discriminant analysis. Units classified as types S, FR, and FF were predicted to be classified with 100% accuracy. All units had a high probability (a posteriori) of having group membership in their originally classified group (P greater than 0.99 for 129 units; P greater than 0.90 for 7 units). The duration of potentiated twitch contractions for type FR and FF units was found to be less than reported for most populations of hindlimb units.(ABSTRACT TRUNCATED AT 400 WORDS)

Pressor reflex evoked by muscular contraction: contributions by neuraxis levels

The pressor reflex evoked by muscular contraction (exercise pressor reflex) is one important model of cardiovascular adjustments during static exercise. The central nervous system (CNS) structures mediating this reflex have remained largely obscure. Therefore, we examined the contribution of selected levels of the neuraxis in mediating the pressor reflex evoked by muscular contraction from stimulation of ventral roots. Decerebrate cats exhibited larger pressor reflexes than those found in intact alpha-chloralose-anesthetized cats, a difference more apparent at low (5 Hz or repeated twitch) rather than at high (50 Hz or tetanic) stimulus frequencies. Although a depressor response to 5-Hz stimulation was observed in the intact anesthetized cats, it appeared to be primarily due to anesthetic level, since a depressor response was not observed in decerebrate animals (nonanesthetized). Cerebellectomy produced no changes in the reflexes of the decerebrate animal. Further transection of the neuraxis (caudal to the midcollicular level) attenuated the exercise pressor reflex. The spinal cat demonstrated slight evidence of exercise pressor reflex activity. These results provide clarification as to representation of this pressor reflex within the CNS and establish the reflex's characteristics at several levels of neuraxis integration.

Peripheral factors influencing expression of pressor reflex evoked by muscular contraction

The effect of evoked muscle tension, active muscle mass, and fiber-type composition on the pressor reflex evoked by muscular contraction was examined in decerebrate and anesthetized cats. Muscular contraction was induced by stimulating the L7 and S1 ventral roots with 0.1-ms duration pulses three times motor threshold at various frequencies. The experiments were designed to isolate the variable under study as much as possible and included the use of selectively denervated preparations to limit contractions to specific muscles. It was found that altering the evoked tension by varying the resting muscle length had commensurate effects on the pressor reflex (greater evoked tension caused a larger reflex). In addition it was found that changing the amount of active muscle mass caused similar changes in the reflex (the smaller the muscle mass, the smaller the reflex). Finally, it was found that contrary to other accounts, pressor reflexes could be evoked by activation of the slow-twitch muscle soleus, composed exclusively of red (type I) fibers.

Effects of naloxone on the cardiovascular responses to muscular contraction in decerebrate cats

The cardiovascular responses to muscular contraction induced by ventral root (L7 and S1) stimulation were studied in unanesthetized decerebrate cats before and after the administration of the opiate antagonist naloxone. Intravenous naloxone (1.0-2.0 mg/kg) did not alter the heart rate or arterial pressure responses to either tetanic or repeated twitch contractions. However, naloxone did increase resting arterial pressure.

Activation of caudal brainstem cell groups during the exercise pressor reflex in the cat as elucidated by 2-[14C]deoxyglucose

Cell groups of the caudal brainstem were labeled with 2-[14C]deoxyglucose during the pressor response evoked by contraction of hindlimb muscles (exercise pressor reflex). The nuclear groups which were labeled in excess of control levels included: the lateral reticular nucleus, the inferior olive (medial accessory olive), and the lateral tegmental field (adjacent to the lateral reticular nucleus).

Localization of the cells of origin for primary afferent fibers supplying the gallbladder of the cat

Horseradish peroxidase was utilized to study the distribution of afferent fibers from the gallbladder in cats. The afferent cell bodies were found in the nodose ganglion and T4 to L1 dorsal root ganglia.

Cardiovascular reflexes arising from the gallbladder and pancreas in spinal and in decerebrate cats

Cardiovascular responses to chemical stimulation of thin-fiber afferents from the gallbladder and pancreas were determined before and after C1 transection of the spinal cord in cats. Additional cats were studied before and after decerebration. Stimulation of gallbladder and pancreatic afferents caused significant increases in arterial pressure and heart rate in all groups; however, smaller responses often occurred in spinal cats. These results demonstrate that spinal circuitry alone can generate cardiovascular responses to visceral stimulation and that supraspinal, though not necessarily suprapontine areas, are involved in producing the full response.

The exercise pressor reflex: evidence for an afferent pressor pathway outside the dorsolateral sulcus region

Pressor reflexes evoked by muscle contraction following stimulation of the cut distal portions of the L7 and S1 ventral roots were studied in decerebrate unanesthetized cats. Reflex responses evoked by this simulated exercise persisted after lesions were made in the dorsolateral sulcus region of the T13-L1 spinal cord, indicating that this area is not essential for mediation of these reflexes. Additional evidence suggested that the pathway responsible for the exercise pressor reflex located in the surviving spinal cord is most likely bilateral.

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 afferent 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.

Reflex cardiovascular depression induced by capsaicin injection into canine liver

Capsaicin was injected into the portal circulation of 29 dogs after a blood delay pathway was constructed between the liver and right heart, through which capsaicin-contaminated blood could be replaced while systemic hemodynamics were maintained constant. Capsaicin (500 micrograms) rapidly decreased left ventricular systolic pressure (-10%), mean arterial pressure (-12%), heart rate (-4%), renal vascular resistance (-7%), maximal rate of left ventricular pressure rise (dP/dtmax) (-12%), and dP/dt at 25 mmHg developed left ventricular pressure (-15%) in animals with paced hearts. Left ventricular end-diastolic pressure did not change. Vagus nerve interruption at the level of the diaphragm did not alter hemodynamic changes occurring during capsaicin injections, but anterior hepatic nerve interruption eliminated the changes, suggesting that the cardiovascular responses were reflex in origin and that the principal afferent pathway traverses the hepatic nerve. This study demonstrates that activation of afferent fiber receptors within the liver tissue can contribute to neural regulation of the cardiovascular system, but the natural stimulus for these receptors is not known.

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 microgram/kg) into the abdominal aorta. Capsaicin stimulated 24 of 34 group IV (C fiber) endings, but only 5 of 19 group III (A delta fiber) endings. By contrast, bradykinin (0.5-1.5 microgram/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.

Anatomical distribution of flexor carpi radialis and flexor carpi ulnaris motor nuclei in the cat spinal cord

The distribution of motoneurons innervating the flexor carpi radialis (FCR) and flexor carpi ulnaris (FCU) muscles was studied utilizing retrograde labeling with horseradish peroxidase (HRP). The motor nuclei showed considerable differences in their longitudinal extents. The FCR nucleus occupied spinal segments C6-T1 while FCU ranged from the C7-C8 junction to T1. Results with localized i.m. injection of HRP suggested a somatotopic distribution of these motoneurons.