Modulatory effects of histamine on cat carotid body chemoreception

Histamine has been proposed to be an excitatory transmitter between the carotid body (CB) chemoreceptor (glomus) cells and petrosal ganglion (PG) neurons. The histamine biosynthetic pathway, its storage and release, as well as the presence of histamine H1, H2 and H3 receptors have been found in the CB. However, there is only indirect evidence showing the presence of histamine in glomus cells, or weather its application produces chemosensory excitation. Thus, we studied the histamine immunocytochemical localization in the cat CB, and the effects of histamine, and H1, H2 and H3 receptor blockers on carotid sinus nerve (CSN) discharge, using CB and PG preparations in vitro. We found histamine immunoreactivity in dense-cored vesicles of glomus cells. Histamine induced dose-dependent increases in CSN discharge in the CB, but not in the PG. The H1-antagonist pyrilamine reduced the CB responses induced by histamine, the H2-antagonists cimetidine and ranitidine had no effect, while the H3-antagonist thioperamide enhanced histamine-induced responses. Present data suggests that histamine plays an excitatory modulatory role in the generation of cat CB chemosensory activity.     

Measurements of potassium changes in the cat carotid body under hypoxia and hypercapnia

With the aid of potassium-sensitive microclectrodes reinforced by bitumen (tip diameter, 1.5 m), extracellular potassium activity ([K⁺]_e) and DC potential were measured in the cat's carotid body. Under normoxic and normocapnic conditions, potassium values of 1–16 mM (mean value 7.2 mM, standard deviation 3.8 mM) and DC potential values of –11 mV to +13 mV were recorded. With hypoxia, [K⁺]_e increased by between 1 mM and 9 mM; DC potential was reduced by between 0.5 and 3 mV. With hypercapnia, [K⁺]_e decreased by between 1 mM and 5 mM: changes in DC potential were variable. The results suggest that, during hypoxia, potassium influences the nervous structures in the carotid body whereas this influence is absent during hypercapnia.     

Role of MaxiK-type calcium dependent K+ channels in rat carotid body hypoxia transduction during postnatal development

Carotid body chemoreceptors transduce a decrease in arterial oxygen tension into increased sinus nerve action potential (AP) activity which undergoes a maturational increase in the post-natal period. MaxiK-channels channels are proposed to play a major role in organ function based on their maturation-dependent expression in glomus cells and inhibition by acute hypoxia. To better resolve the role of this channel, single-unit AP activity of rat chemoreceptor neurons was recorded, in vitro, during a progressive decrease in oxygen from normoxia (～150 Torr) to moderate hypoxia (～60 Torr). Blockade of MaxiK channels with charybdotoxin (100 nM) in both older (P16-P18) and younger (P2-P3) animals resulted in no significant change in AP activity, but increased nerve conduction speed in the older animals. In dissociated glomus cells, charybdotoxin slightly enhanced the intracellular calcium response to acute hypoxia at both ages. We conclude that MaxiK channels play little or no role in mediating the response to acute, moderate hypoxia, either in the newborn or older animal.     

Histological changes associated with ageing of the human carotid body

A qualitative and quantitative histological study was made of the carotid bodies obtained at necropsy from 47 subjects ranging in age from 14 to 100 years. With increasing age there is a loss of more than a third of the amount of glomic tissue with a diminution in the size of the lobules. In young people the basic histological pattern of clusters, composed of cores of chief cells with surrounding rims of sustentacular cells, has commonly superimposed on it prominence of the dark variant of chief cells. In middle-aged subjects there is proliferation of sustentacular cells which appear to merge imperceptibly into fibrosis of the lobules and becomes associated with diffuse or focal infiltrates of lymphocytes.     

Distribution of carotid body type I cells and other periadventitial type I cells in the carotid bifurcation regions of the cat

Summary The bilateral distribution of carotid body type I cells was investigated in five non-pedigree cats by serially sectioning the carotid bifurcation regions. Carotid body type I cells occurred bilaterally in close proximity to the wall of the occipital artery or one of its proximal branches, and less frequently the ascending pharyngeal artery within a division of connective tissue with defineable but irregular borders. Caudally, and separate from the principal mass of carotid body type I cells, isolated groups of periadventitial type I cells were found in seven out of ten specimens lying freely in the connective tissues around the occipito-ascending pharyngeal trunk and the origin of the occipital artery immediately rostral to the carotid bifurcation. Periadventitial type I cells were not observed at the level of the carotid bifurcation but on one occasion these cells were noted caudal to the carotid bifurcation lying adjacent to the wall of the rostral end of the common carotid artery. From our data on four specimens, reconstructions were made of the carotid body. The occurrence and significance of the periadventitial type I cells is discussed.     

Monoamines and their catabolites in the rabbit carotid body

Monoamines and their metabolites have been measured by high performance liquid chromatography with electrochemical detection, in control rabbit carotid bodies and under several experimental conditions: 1) at different times (3 h, 6 h, 24 h, 48 h) after intravenous injection of reserpine (5 mg/kg); 2) 14 days after sympathectomy; 3) 14 days after section of the carotid sinus nerve. The results were analyzed with probability plotting methods. Dopamine was the most important monoamine in the carotid body (CB) and its variations were very large. It was almost entirely depleted by reserpinization without simultaneous increase in 3,4-dihydroxyphenylacetic acid. Sympathectomy increased dopamine content but did not change noradrenaline content. However data analysis suggested that noradrenaline might be compartmented in two pools: one with a large variance, located in the type I cells was increased after sympathectomy, the other, more constant, located in the sympathetic nerve endings was entirely depleted after sympathectomy. Section of the carotid sinus nerve increased dopamine and noradrenaline and quadrupled the serotonin content of the CB. It is proposed that carotid sinus and sympathetic innervations regulate the monoamine metabolism of the CB.     

The role of the carotid chemoreceptors in the CO2-hyperpnea under hyperoxia

Summary In anesthetized rabbits rebreathing oxygen or inhaling constant mixtures of CO₂ and O₂, the influence of inactivation of the carotid sinus nerves by section or temporary cold blocking on the respiratory response to increased was investigated. In some of the experiments the vagi were intact, in others they were cut. Even during respiration of pure oxygen, in part of the animals blocking of the sinus nerves caused a slight diminution of ventilation which was significant only in the vagotomized preparation (average decrease by 11.4%). However, the diminishing effect of the blockade did not increase, but rather decreased, with increasing . Similarly, section of the sinus nerves did not cause a significant shift or decrease of slope of the response curve. Evidently in the rabbit carotid chemoreceptors do not contribute essentially to the steady-state hyperpnea caused by hypercapnia under hyperoxic conditions.Supported by grant Wi 165 from the Deutsche Forschungsgemeinschaft.     

Local flow velocities in the cat carotid body tissue

With the aid of a new three-dimensional mathematical model local flow velocities in the specific carotid body tissue of the cat measured by hydrogen clearances were calculated to have a mean value of 0.006 cm/s at a perfusion pressure of 50 mm Hg, 0.014 cm/s at a perfusion pressure of 120 mm Hg, and 0.018 cm/s at a perfusion pressure of 170 mm Hg. These results indicate that the carotid body specific tissue possesses a distinct flow heterogeneity with normal capillary flow velocities and a high shunt flow. During hypoxia, the smallest decrease in tissuePO₂ was significantly correlated with the highest decrease in flow velocity. This suggests that the carotid body capillary network itself exhibits aPO₂ sensor mechanisms amplifying the chemoreceptive process in the specific cell elements.     

The volume of the carotid body and periadventitial type I and type II cells in the carotid bifurcation region of the fetal cat and kitten

Summary The bilateral distribution of carotid body type I cells was investigated in 6 fetuses (gestational age 95%) and 9 newborn kittens (aged 1 day to 4 days) by serially sectioning the carotid bifurcation regions. In most specimens type I cells occurred in close proximity to the wall of the occipital artery or one of its small proximal branches within a division of connective tissue with defineable but irregular borders. This combination of type I cells and connective tissue constituted the principal mass of the carotid body. Using an interacting image analysis system, the area of the carotid body in each serial section was measured by accurately contouring its perimeter. The volume of the carotid body was calculated by multiplying the sum of the areas of the serial sections by the thickness of the section. The volume of the carotid body was 0.052±0.018 mm³ in the fetuses and 0.025–0.117 mm³ in the 1–4 day old kittens. A degree of symmetry in the values for the volume of the right and left carotid body was found. Caudally, and separate from the principal mass of carotid body type I cells, isolated groups of periadventitial type I cells were noted in the connective tissues around the occipito-ascending pharyngeal trunk, origin of the occipital artery and rostral end of the common carotid artery in 7 out of 12 specimens from fetal cats and 11 out of 18 specimens in newborn kittens. The volumes of the periadventitial groups of cells ranged between 25–1,365 m³ in fetuses and 10–1,351 m³ in kittens.     

Rate of dopamine metabolism in the rabbit carotid body in vivo

In the rabbit carotid body (CB) in vivo, the rate of dopamine metabolism was estimated to 44.4±3.9 (SD) pmol/CB/h from the decrease in dihydroxyphenylacetic acid content after pargyline inhibition of monoamine oxidase.     

Sustained hypoxia promotes hyperactive response of carotid body in the cat

Carotid body chemosensory activities were measured before and after 0.2, 5,6 and 7 h of sustained isocapnic (PaCO(2) approximately equal to 30 Torr) hypoxia (PaO(2) approximately equal to 43 Torr) in the cats (n=7). The activity increased from 5.4 impsec(-1) at 0.2 h to about 13 impsec(-1) at 7 h. This increase in chemosensory activities were due to both an augmented sensitivity and to a long-term facilitation and not due to arterial [H(+)] changes.     

Oxygen consumption of the isolated carotid body tissue (cat)

Summary The oxygen consumption of the isolated carotid body tissue measured in microchambers (volumes 12 and 20 μl) was 0.0051 μl O₂/mg wet weight min for an average of 54 measurements at 22±1°C, if the calculation was based on the oxygen pressure decrease of the surrounding medium measured polarographically in the range from 120 to 50 torr. It is bound to the presence of exogenous substrate and almost completely inhibited by antimycin but not significantly altered by addition of EGTA (4–16 mM) or Ca²⁺ (2mM). Measurements performed at higher oxygen pressures (300 to 100 torr) in the medium show that the oxygen consumption of isolated carotid body tissue is independent of oxygen pressure at these high oxygen pressures. The findings obtained under the above conditions argue in favor of a mitochondrial oxygen consumption. The results are discussed with regard to data obtained with needle electrodes in the perfused organ.     

淋巴结切除在颈动脉体瘤手术治疗中的作用

目的 总结手术治疗良恶性颈动脉体瘤的经验,探讨颈动脉体瘤手术中瘤体周围淋巴结切除的临床价值。方法 回顾性分析中国医学科学院肿瘤医院1976年1月—2013年10月手术治疗的106例良、恶性颈动脉体瘤患者的临床资料。其中男37例,女69例;年龄7～67岁;肿瘤发生于左侧62例,右侧42例,双侧2例。术前诊断为颈动脉体瘤86例,另20例术前诊断为颈部肿物待查;无一例术前诊断为恶性颈动脉体瘤。根据术中是否行瘤体周围淋巴结切除活检分为淋巴结切除组(54例)和未切除组(52例),随访其术后生存及复发情况。采用Kaplan-Meier生存分析法计算并比较两组患者术后无复发生存率。结果 106例患者中,98例获随访,8例失访,其中淋巴结切除组失访5例,未切除组失访例3例。随访时间7个月~38年,中位随访时间8年。淋巴结切除组术后无复发生存率为97.0%,高于淋巴结未切除组的73.7%(χ²=9.938, P＜0.01);明确诊断良恶性者术后无复发生存率93.4%,高于未行淋巴结切除从而诊断恶性证据不足者的14.0%(χ²=45.054, P＜0.01)。淋巴结切除组神经损伤发生率为35.2%(19/54),低于淋巴结未切除组的55.8%(29/52),差异有统计学意义(χ²=4.530, P＜0.05)。结论 颈动脉体瘤手术中,瘤体周围淋巴结切除活检有助于明确诊断、指导治疗,从而提高颈动脉体瘤手术治疗后无复发生存率;同时,还有利于暴露术野,降低神经损伤发生率。     

The impact of PCO2 and H+ on the release of acetylcholine from the cat carotid body

The carotid body (CB) is a sensor of oxygen, carbon dioxide, hydrogen ion, and glucose in the arterial blood. Many studies of the CB's responses to low oxygen (hypoxia) have been reported. Recently attention has been increasingly focused on its responses to elevated CO2 (hypercapnia). An increase in ventilation or carotid body neural output (CBNO) can result from stimulating the CB with blood or perfusion fluids having an elevated CO2 or H+. The increase in ventilation seen with a hypoxic stimulus is accompanied with an increase in CBNO and an increased release of both acetylcholine (ACh) and ATP from the CB. The present in vitro study using both CBs harvested from six cats was undertaken to determine if hypercapnia also provoked an increased release of ACh from the incubated CBs. The anesthetizing, handling, and euthanizing of the animals were according to the guidelines of the Johns Hopkins Animal Care and Use Committee which are totally consonant with those of the NIH. CBs, once harvested and prepared for the experimental protocol, were subjected to the following steps each lasting 10 min: (1) control; (2) stress; (3) recovery. The stresses were respiratory acidosis (RAC; acidic hypercapnia), compensated respiratory acidosis (CRAC; isohydric hypercapnia), and metabolic acidosis (MtAC). The first and last forms of acidosis generated small but significant increases in the release of ACh from the CBs; the second generated a very small and insignificant increase in ACh release. Since it is generally accepted that ACh is a key excitatory neurotransmitter in the CB along with ATP, these data are consistent with other studies measuring the increase in ventilation in response to a small increase in CO2 and those studies recording CBNO in response to hypercapnia. In five of the six animals the responses to RAC and MtAC were compared to the responses to hypoxia. The latter were statistically indistinguishable from the former two.     

The carotid body of the harbour seal (Phoca vitulina richardsi)

Summary The bilateral distribution of carotid body type 1 and 11 cells was investigated in five harbour seals (Phoca vitulina richardsi), by serially sectioning the carotid bifurcation regions. The cells occurred bilaterally in the animals and were also present in one specimen from a sixth animal available for study. The type 1 and 11 cells were located in the space between the internal and external carotid arteries and had a varied relationship to the occipital and condyloid arteries. They lay within a division of connective tissue with irregular but defineable borders and this combination of connective tissue and type 1 and 11 cells constituted the principal mass of the carotid body. The carotid body occurred in a variety of forms: wedge-shaped, crescentic or horse-shoe shaped, or as a discrete oval structure. In some specimens the carotid body had a central neurovascular core of small blood vesels and nerves. The artery to the organ originated from either the external carotid, internal carotid or common carotid arteries. Using an interactive image analysis system in eight specimens, which had been perfusion-fixed at a normal arterial pressure, the mean volume of the carotid body was 1.666±0.45 (SD) mm³. Caudally and separate from the principal mass of the carotid body periadyentitial type 1 and 11 cells were noted in 4 out of 11 specimens in the connective tissues adjacent to the external carotid artery, origin of the occipital, and the rostral part of the common carotid artery and its bifurcation.     

The effect of common carotid artery occlusion on blood pressure in the barodenervated cat

A 12% blood pressure elevation was found during common carotid occlusion in the barodenervated, thoracotomised cat under Nembutal anaesthesia. This rise in blood pressure appeared to be the net result of an 18% increase of total peripheral resistance and a concomitant 5% decrease of mean aortic flow.When the occlusions were repeated after ganglionic blockade similar values were found, indicating that the increase in resistance had not resulted from reflex vasoconstriction. To test if this increase of total peripheral resistance was caused by a mechanical exclusion, Ohm's law for parallel resistances was applied to the systemic tree to calculate the rise in resistance due to obstruction of the carotid flow. The results thus obtained matched the observed increase of peripheral resistance.It is concluded that common carotid artery occlusion can be used to test completeness of barodenervation in the cat, if an increase in blood pressure of about 12% is allowed for.     

Structural and neurochemical changes in the maturation of the carotid body

Functional maturation of the carotid body in the postnatal period relies partly on structural and neurochemical changes, which are reviewed here. Structural changes include changes in cytological composition, and increases in glomic tissue volume, dense-cored granules of type I cells, synapses of type I cells with type II cells and afferent nerve fibres. Vascular volume also increases, but in the same proportion as extravascular volume. During maturation, the carotid body also shows higher density and hypoxic sensitivity of K⁺-channels and an increased hypoxic [Ca²⁺]_i response. Modulation of content and release of catecholamine occurs, together with decreased expression of tyrosine hydroxylase and dopamine β-hydroxylase and increased expression of choline acetyltransferase. Expression of dopamine 2 receptor and nicotinic α3 and α7 receptor subunits increases, and muscarinic M1 receptor protein, nicotinic α4 and β2 receptor subunits and adenosine receptor 1 decrease. Maturation of the carotid body may also be explained with reference to the developmentally regulated expression of trophic factors and their receptors.     

Pharmacology of pH effects on carotid body chemoreceptors in vitro

1. The carotid body and the carotid nerve were removed from anaesthetized cats and placed in a small Perspex channel through which Locke solution (at various pH values and usually equilibrated with 50% O(2) in N(2)) was allowed to flow. The glomus was immersed in the flowing solution while the nerve was lifted into oil covering the saline. Sensory discharges were recorded from the nerve and their frequency was used as an index of receptor activity. At times, a small segment of carotid artery, containing pressoreceptor endings, was removed together with the glomus. In this case, pressoreceptor discharges were recorded from the nerve.2. The amplitude of either chemo- or pressoreceptor discharges was not changed by strong acid solutions. Acid decreased the frequency of the baroreceptor discharges only when pH fell to less than 4.0. Solutions at low pH increased the chemosensory discharge, but acid depressed the increased chemoreceptor discharge elicited by KCl. These experiments indicated that H(+) ions probably acted as membrane ;stabilizers' without depolarizing either the nerve fibres or endings.3. Acid solutions increased the action of acetylcholine chloride (AChCl) (100-200 mug) on chemoreceptors. This effect probably was due either to inactivation of tissue cholinesterase or to enhanced sensitivity of the sensory endings to ACh.4. Choline chloride (10(-3)M), which favours ACh synthesis, protected the preparation against decay during prolonged experimentation. Hemicholinium-3 (HC-3), which blocks ACh synthesis in low concentrations (10(-5)M), depressed the chemosensory response to acid and to hypoxia when such stimuli were applied repeatedly. This concentration of HC-3 did not change effects of applied ACh.5. Substances which affect ACh release markedly changed the chemoreceptor discharge increase induced by acidity and other forms of stimulation. In the absence of Ca(2+), acid, anoxia, and interruption of flow provoked receptor depression while receptor excitation induced by ACh and KCl persisted. All stimuli excited and showed increased effectiveness as the Ca(2+) concentration was raised, but their effects declined as Ca(2+) was increased above normal values. Mg(2+) ions depressed the chemoreceptor effects induced by all these stimuli. The action of Mg(2+) was not due entirely to nerve ending block. Morphine sulphate (which decreases ACh release in other structures) also depressed the receptor response to acid and flow interruption.6. Cholinergic blocking agents such as mecamylamine, hexamethonium, atropine, dihydro-beta-erithroidine (DHE), HC-3 (10(-4)M), choline and acetylcholine (in combination with choline) depressed the effects of acid and ACh on the chemoreceptors. The effect induced by interruption of flow was depressed only by mecamylamine and DHE.7. Agents which affect the fate of released ACh, such as acetylcholinesterase and eserine salicylate, did not affect clearly the response of chemoreceptors to acid.8. The results suggest that acid stimulates chemoreceptor fibres through an indirect mechanism, viz. through increased release and/or decreased destruction of a presynaptic transmitter from the glomus cell. This transmitter is probably ACh (see following paper, Eyzaguirre & Zapata, 1968).     

Effects of combined cholinergic-purinergic block upon cat carotid body chemoreceptors in vitro

Since acetylcholine (ACh) and ATP have been proposed as excitatory co-transmitters at synapses between glomus cells and sensory nerve endings of the carotid body (CB), we tested such hypothesis by studying the effects of combined cholinergic-purinergic block on the chemosensory activity recorded from cat's carotid bodies perfused and/or superfused in vitro. The preparations were bathed with Tyrode's solution, either normoxic (PO2=98.5+/-13.5 Torr) or hypoxic (PO2=31.8+/-5.2 Torr), and the frequency of chemosensory impulses (fchi) was recorded from the carotid (sinus) nerve. Dose-response curves for fchi increases evoked by intra-stream boluses of acetylcholine, nicotine and ATP were studied. A combination of mecamylamine 2 microM and suramin 50 microM, applied through the perfusate or superfusate, suppressed nicotine- and ATP-induced increases in fchi, but the basal chemosensory activity in normoxia and the chemosensory excitation elicited by hypoxic superfusion were preserved, although variably reduced in most preparations. Thus, in spite of the excitatory effects provoked by applying ACh and ATP to the perfused/superfused CB in vitro, a co-release of these substances cannot account entirely for the chemosensory excitation induced by hypoxic stimulation of the CB.     

Localization of enkephalin-like immunoreactivity in the cat carotid and aortic body chemoreceptors

The purpose of this study was to determine if enkephalin-like immunoreactivity was present in the glomus cells of the carotid and aortic body peripheral arterial chemoreceptors. Cat carotid and aortic bodies were reacted with antisera to met- and leu-enkephalin using the indirect peroxidase-antiperoxidase immunocytochemical method of Sternberger (1979). Both the carotid and aortic bodies demonstrated clusters of immunoreactive cells for both met- and leu-enkephalin. Additionally, met-enkephalin-like immunoreactivity was observed in many of the dense-core vesicles of the glomus cells of the carotid body. The glomus cells of these chemoreceptors are known to contain catecholamines which may modulate chemoreceptor activity. The presence of opioid peptide-like substances co-existing with the glomus cell catecholamines, perhaps in the same vesicles, may have important implications for a trophic influence of these peptides on glomus cell chemoreceptor modulation.