Anti-melanoma differentiation-associated gene 5 antibody-positive dermatomyositis with possible complication of thrombotic microangiopathy

This case study illustrates a 63-year-old Japanese woman who presented with anti-melanoma differentiation-associated gene 5 antibody-positive dermatomyositis. She was administered a therapeutic regimen consisting of corticosteroids, tacrolimus, and cyclophosphamide. However, after a month of treatment, symptoms of confusion and depressive tendencies emerged, followed by the manifestation of hematuria, thrombocytopenia, and fragmented erythrocytes. A disintegrin-like and metalloprotease with thrombospondin type 1 motifs 13 activity was 45%. Thrombotic microangiopathy was contemplated, yet a definitive diagnosis remained elusive. She died 2 months after admission. Although the occurrence of thrombotic microangiopathy in patients with dermatomyositis is rare, the prognosis is poor, emphasizing the importance of prompt diagnosis and treatment.

Continuous ulnar nerve block at the forearm for early active mobilisation following flexor tendon reconstruction

A 63-year-old woman had sustained a subcutaneous rupture of the flexor digitorum profundus tendon of the little finger due to osteoarthritis of the pisotriquetral joint. She underwent excision of the pisiform bone and reconstruction of the flexor digitorum profundus tendon of the little finger using an autogenous palmaris longus tendon graft. After surgery, a continuous ulnar nerve block was performed at the forearm under ultrasound and nerve stimulator guidance. During rehabilitation, she could not actively extend her little finger independently due to the block; however, she could actively extend it when the dorsum of the metacarpophalangeal joint was pressed by the occupational therapist, resulting in successful early active mobilisation. A continuous ulnar nerve block at the forearm may help to facilitate early active mobilisation after reconstructive surgery for little finger flexor tendon rupture. However, it may restrict the active extension of the little finger because the block does not spare the innervation of the intrinsic muscles responsible for little finger extension.

P14.113 The role of maintenance high-dose methotrexate chemotherapy in elderly primary CNS lymphoma patients with complete response to induction immunochemotherapy

BACKGROUND

The addition of high-dose methotrexate (HD-MTX)-based chemotherapy to whole brain irradiation (WBRT) has improved the prognosis of primary central nervous system lymphoma (PCNSL). However, the high neurotoxicity rates observed, especially in the elderly, raised interest in chemotherapy-only treatments. Withholding radiotherapy substantially decreases the risk of neurotoxicity, however, disease control may be compromised. Therefore, developing a novel treatment for the elderly PCNSL patients (ePCNSL) is crucial. In the elderly who cannot tolerate WBRT as a consolidation, maintenance treatment may serve as a feasible approach after an initial response. We treated ePCNSL with induction immunochemotherapy with rituximab (RIT) and HD-MTX, maintenance chemotherapy with HD-MTX and deferred WBRT. Here, we retrospectively investigated the prognosis for ePCNSL that became CR after the induction chemotherapy.

MATERIAL AND METHODS

Newly diagnosed ePCNSL (median age: 74 years) received biweekly RIT/ HD-MTX (375 mg/m2/dose; 3.5g/m2/dose) for 6 cycles (induction) followed by monthly RIT/MTX for 2 cycles (consolidation) and then were treated differently according to the radiological response. With CR patients, HD-MTX was continued with every 3 months (maintenance) for 2 years. Patients who did not obtain consent for maintenance therapy were followed up.

RESULTS

Of the 42 ePCNSL (median age 74 years), 26 had CR after induction and consolidation, of which 18 cases were carried out maintenance (M +) and 8 cases were followed up (M-). The median age was 74 and 76, respectively. Median progression-free survival (mPFS) was 73 months in the M+ group and 24.6 months in the M- group. Median overall survival (mOS) is 92.5 months versus 27.6 months, respectively. Both mPFS (P= 0.025) and mOS (P =0.0003) were significantly prolonged by maintenance therapy. In addition, ePCNSL with tumors involvement of deep brain structure had a poor prognosis.

CONCLUSION

It was suggested that maintenance treatment with HD-MTX may improve the prognosis for ePCNSL that reached complete response after induction therapy.

Is the Carotid Body a Metabolic Monitor?

The carotid body is a multi-modal sensor and it has been debated if it senses low glucose. We have hypothesized that the carotid body is modified by some metabolic factors other than glucose and contributes to whole body glucose metabolism. This study examined the roles of insulin, leptin and transient receptor potential (TRP) channels on carotid sinus nerve (CSN) chemoreceptor discharge. In agreement with other studies, CSN activity was not modified by low glucose. Insulin did not affect the CSN hypoxic response. Leptin significantly augmented the CSN response to hypoxia and nonspecific Trp channel blockers (SKF96365, 2-APB) reversed the effect of leptin. Gene expression analysis showed high expression of Trpm3, 6, and 7 channels in the carotid body and petrosal ganglion. The results suggest that the adult mouse carotid body does not sense glucose levels directly. The carotid body may contribute to neural control of glucose metabolism via leptin receptor-mediated TRP channel activation.

Benzodiazepines and GABA-GABAA receptor system in the cat carotid body

Benzodiazepines (BZs) suppress ventilation possibly by augmenting the GABA(A) receptor activity in the respiratory control system, but precise sites of action are not well understood. The goals of this study were: (1) to identify GABA(A) receptor subunits in the carotid body (CB) and petrosal ganglion (PG); (2) to test if BZs exert their effects through the GABA(A) receptor in the CB chemosensory unit. Tissues were taken from euthanized adult cats. RNA was extracted from the brain, and cDNA sequences of several GABA(A) receptor subunits were determined. Subsequent RT-PCR analysis demonstrated the gene expression of alpha2, alpha3, beta3, and gamma2 subunits in the CB and the PG. Immunoreactivity for GABA and for GABA(A) receptor beta3 and gamma2 subunits was detected in chemosensory glomus cells (GCs) in the CB and neurons in the PG. The functional aspects of the GABA-GABA(A) receptor system in the CB was studied by measuring CB neural output using in vitro perfusion setup. Two BZs, midazolam and diazepam, decreased the CB neural response to hypoxia. With continuous application of bicuculline, a GABA(A) receptor antagonist, the effects of BZs were abolished. In conclusion, the GABA-GABA(A) receptor system is functioning in the CB chemosensory system. BZs inhibit CB neural response to hypoxia by enhancing GABA(A) receptor activity.

Identification of M1 and M2 muscarinic acetylcholine receptors in the cat carotid body chemosensory system

The carotid body is a major arterial chemoreceptor that senses low O2 tension, high CO2 tension and low pH in the arterial blood. It is generally believed that neurotransmitters, including acetylcholine (ACh), participate in the genesis of afferent neural output from the carotid body and modulate the function of chemoreceptor cells (glomus cells). Previous pharmacological studies suggest that M1 and M2 muscarinic ACh receptors (mAChRs) are involved in these processes. This study was designed to demonstrate the presence and localization of M1 and M2 mAChRs in the carotid body and in the petrosal ganglion of the cat. Since DNA sequences of the cat M1 and M2 mAChRs were not known, we first determined partial DNA sequences. These sequences and deduced amino acid sequences highly resembled those of human and the rat. Subsequent reverse transcription-polymerase chain reaction (RT-PCR)analysis has demonstrated that mRNAs for M1 and M2 mAChRs are present in the carotid body and the petrosal ganglion of the cat. Immunohistochemistry has indicated that the localization of these receptors appears different. Immunoreactivity for M1 mAChR was strong in nerves in the carotid body. Nerve endings positively stained for M1 mAChR appear to innervate glomus cells. Weak staining for M1 mAChRs was seen in glomus cells. On the other hand, M2 receptor protein seems to be present in glomus cells but not on nerve endings. One third of the neurons in the petrosal ganglion showed immunoreactivity for M1 mAChR. Many neurons and nerve fibers in the petrosal ganglion expressed M2 mAChR immunoreactivity. The results were consistent with previous pharmacological studies. Thus, activation of M1 mAChRs on afferent nerve endings may be linked to the increase in neural output during hypoxia. Further, M1 and M2 mAChRs on glomus cells modulate the release of neurotransmitters.

Transient ischemic attack due to dissection of the middle cerebral artery--case report

A 57-year-old man presented with a transient ischemic attack due to dissection of the middle cerebral artery. He suffered total aphasia and clouding of consciousness for several minutes. On admission, he was alert without neurological deficit. Magnetic resonance (MR) angiography and conventional angiography depicted irregularity and double lumen of the left middle cerebral artery. The diagnosis was dissection of the middle cerebral artery. After 1 month, he left our institute with no neurological deficit. Transient ischemic attack associated with dissection of an intracranial artery is unusual. The source images of MR angiography are useful for the essential follow up of dissection.

Acetylcholine sensitivity of cat petrosal ganglion neurons

We investigated if neuronal nicotinic acetylcholine receptors (nAChRs) are localized in chemoreceptor afferent neurons in the cat petrosal ganglion (PG) and if acetylcholine (ACh) excites chemoreceptor afferent neurons. Immunocytochemistry revealed that a majority of PG neurons expressed alpha 4 and/or alpha 7 subunits of neuronal nAChRs, and a part of them were tyrosine hydroxylase positive. Excitability of cultured PG neurons was studied with patch clamp techniques (whole cell configuration). ACh and nicotine evoked both inward and outward currents. The inward current was partially blocked by removal of extracellular calcium and by antagonists for alpha 4 beta 2 (dihydro-beta-erythroidine) or alpha 7 nAChRs (methyllycaconitine). Outward current was blocked by 4-aminopyridine (4-AP) and sometimes by atropine. ACh-induced membrane potential changes were well correlated with ACh-induced currents. Depolarization and hyperpolarization occurred in response to ACh. Occasionally depolarization was followed by a train of action potentials. The results suggest that heterogeneous neuronal nAChRs are widely distributed in both chemoreceptor and other PG neurons. In some neurons nAChRs may be functionally coupled with outward K+ channels. Further studies are required to determine whether chemoreceptor neurons have a distinct distribution pattern of nAChRs and K+ channels.

Acetylcholine is released from in vitro cat carotid bodies during hypoxic stimulation

Previous pharmacological, immunocytochemical, electrophysiological, and microfluorometric studies have suggested that acetylcholine (ACh) is a critically important excitatory transmitter in the chemotransduction of hypoxia by the cat carotid body (CB). With the use of HPLC this study shows that the in vitro cat CB releases ACh under normoxic conditions; this release is increased when the CB is challenged with hypoxia. The preliminary observation that greater amounts of ACh are liberated in the presence of gallamine and AFDX116 suggests the presence of functioning M2 muscarinic receptors on the glomus cells of the CB.

L-DOPA and high oxygen influence release of catecholamines from the cat carotid body

Current modelling of carotid body (CB) chemotransduction postulates an essential role for neurotransmitters, including dopamine (DA). Catecholamines (CA) released from incubated/superfused cat CBs has often been reported to diminish rapidly over the course of the exposure. The purpose of the first set of experiments was to determine the effects of including L-dihydroxyphenylalanine (L-DOPA), the immediate precursor to DA, in the incubation medium. CBs were removed from deeply anesthetized cats, cleaned of connective tissue, and placed in separate incubation tubes containing Krebs Ringer Bicarbonate solution (KRB) at 37 degrees C. One tube contained 40 microM L-DOPA. Both tubes were bubbled for 2 hr with a normoxic gas mixture (21% O2/6% CO2). This was followed immediately by a 30-minute exposure to a hypoxic gas mixture (4% O2/5% CO2). The mean amounts of DA, dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA) and norepinephrine (NE) released during 30 min exposures were always greater when L-DOPA was present. The use of gas mixture like the above normoxic gas mixture in incubation studies has often been considered quasi-hypoxic. Hence, in a second set of experiments we tested the effect of high oxygen mixture (95% O2/5% CO2). All other features of these experiments were the same as the above. The high oxygen environment correlated with lower DA release suggesting a reduced excitation/inhibition. The subsequent exposure to hypoxia, however, provoked a much larger release of DA and NE. The data demonstrate the substantial effect of oxygen on the release of CAs and the apparent need of a DA precursor like L-DOPA to allow detection of the changes in CA release from the CBs upon exposure to a hypoxic stimulus.

Acetylcholine release from cat carotid bodies

Hypoxia, hypercapnia and acidosis stimulate the carotid body (CB) sending increased neural activity via a branch of the glossopharyngeal nerve to nucleus tractus solitarius; this precipitates an impressive array of cardiopulmonary, endocrine and renal reflex responses. However, the cellular mechanisms by which these stimuli generate the increased CB neural output are only poorly understood. Central to the understanding of these mechanisms is the determination of which agents are released within the CB in response to hypoxia, and serve as the stimulating transmitter(s) for chemosensory nerve endings. Acetylcholine (ACh) has been proposed as such an agent from the outset, but this proposal has been, and remains, controversial. The present study tests two hypotheses: (1) The CB releases ACh under normoxic/normocapnic conditions; and (2) The amount released increases during hypoxia and other conditions known to increase neural output from the CB. These hypotheses were tested in 12 experiments in which both CBs were removed from the anesthetized cat and incubated at 37 degrees C in a physiological salt solution while the solution was bubbled with four different concentrations of oxygen and carbon dioxide. The incubation medium was exchanged at 10 min intervals for 30 min (three periods of incubation). The medium was analyzed with high performance liquid chromatography-electrochemical detection for ACh content. Normoxic/normocapnic conditions (21% O2/6% CO2) produced a total of 0.639 +/- 0.106 pmol/150 microl (mean +/- S.E.M.; n = 12). All stimulating conditions produced larger total outputs: 4% O2/2% CO2 produced 1.773 +/- 0.46 pmol/150 microl; 0% O2/5% CO2, 0.868 +/- 0.13 pmol/150 microl; 4% O2/10% CO2, 1.077 +/- 0.21 pmol/150 microl. These three amounts were significantly greater than the normoxic/normocapnic condition, but indistinguishable among themselves. Further, the amount of ACh released did not diminish over the 30 min of stimulation. These data support the concept that during hypoxia ACh functions as a stimulating transmitter in the CB, and are consistent with the earlier reports of cholinergic enzymes and receptors found in the CB.

Roles of ion channels in carotid body chemotransmission of acute hypoxia

In this review, we have highlighted the roles of ion channels in carotid body chemotransmission of acute hypoxia. With the application of new technologies, significant breakthroughs have been made in the last decade. The discovery of oxygen-sensitive K(+) channels in rabbit glomus cells has generated the membrane model of hypoxic chemotransmission: the inhibition of oxygen-sensitive K(+) channels by hypoxia initiates the depolarization of glomus cells and increases the firing frequency of glomus cells. The depolarization of glomus cells activates voltage-gated Ca(2+) channels, elevating intracellular Ca(2+) which triggers the release of neurotransmitters. The correlation of these events in rabbit glomus cells has been shown. However, a large corpus of data indicates that various mechanisms may be involved in different species. In rats, Ca(2+)-activated K(+) channels are inhibited by hypoxia. The role of this inhibition on rat glomus cell function is controversial, and the contribution of leak-type K(+) channels to rat glomus cell depolarization has recently been proposed. On the other hand, in cats, nicotinic ACh receptors (ligand-gated cation channels) may play a key role in initiating the depolarization of glomus cells and increasing the cytosolic Ca(2+) of glomus cells in response to hypoxia. Hypoxic inhibition of oxygen-sensitive K(+) channels would participate to further depolarize cat glomus cells. Additionally, the activity of Cl(-) channels and the modulation of ion channels by neurotransmitters may influence the excitability of glomus cells. For generating action potentials in chemoreceptor afferent nerves, nicotinic ACh receptors appear to be involved in cats and rats.

Presence of nicotinic acetylcholine receptors in cat carotid body afferent system

With immunocytochemical techniques using a monoclonal antibody for alpha7 subunits of neuronal nicotinic acetylcholine receptors, we have found these subunits to be exclusively expressed in nerve fibers in the carotid body. Double-immunostaining showed that alpha7 subunit-positive nerve endings enveloped tyrosine hydroxylase-positive glomus cells. Some carotid sinus nerve fibers and tyrosine hydroxylase-positive petrosal ganglion neurons also expressed alpha7 subunits. These data support a role for acetylcholine in carotid body neurotransmission.

Electrophysiological and immunocytological demonstration of cell-type specific responses to hypoxia in the adult cat carotid body

We have recently shown two types of cat carotid body cells based on the oxygen sensitivity of voltage-gated potassium channels. In the present study, we attempted to determine the correlation between cell types (glomus cells, sheath cells, and subtypes of glomus cells) and oxygen sensitivity of potassium channels. Further, changes in membrane potentials in response to hypoxia were also examined. Carotid body cells harvested from adult cats were cultured, and a whole cell patch clamp method was applied to determine the oxygen sensitivity of outward current. The tested cells were identified by Lucifer Yellow in the patch pipette. Glomus cells and sheath cells were immunocytochemically identified using tyrosine hydroxylase (TH) and glial fibrillary acidic protein (GFAP) as markers. The cells whose outward current was inhibited by hypoxia showed TH-immunoreactivity but not GFAP-immunoreactivity. The cells whose outward current was not sensitive to hypoxia were GFAP-positive or TH-negative. One TH-positive cell had oxygen-insensitive outward current. The resting membrane potentials of the cells having oxygen-sensitive outward current were significantly higher (-55+/-3 mV) than those of the cells having oxygen-insensitive outward current (-35+/-2 mV). The former type of cells was depolarized during hypoxia, but not the latter type of cells. These results suggest that most glomus cells of the adult cat carotid body possess oxygen-sensitive potassium channels and are depolarized in response to hypoxia. On the other hand, sheath cells and possibly a small fraction of glomus cells possess oxygen-insensitive potassium channels and their membrane potential is not affected by hypoxia.

Substance P immunoreactive nerve terminals in the dorsolateral nucleus of the tractus solitarius: roles in the baroreceptor reflex

Physiological and light microscopic evidence suggest that substance P (SP) may be a neurotransmitter contained in first-order sensory baroreceptor afferents; however, ultrastructural support for this hypothesis is lacking. We have traced the central projections of the carotid sinus nerve (CSN) in the cat by utilizing the transganglionic transport of horseradish peroxidase (HRP). The dorsolateral subnucleus of the nucleus tractus solitarius (dlNTS) was processed for the histochemical visualization of transganglionically labeled CSN afferents and for the immunocytochemical visualization of SP by dual labeling light and electron microscopic methods. Either HRP or SP was readily identified in single-labeled unmyelinated axons, myelinated axons, and nerve terminals in the dlNTS. SP immunoreactivity was also identified in unmyelinated axons, myelinated axons, and nerve terminals in the dlNTS, which were simultaneously identified as CSN primary afferents. However, only 15% of CSN terminals in the dlNTS were immunoreactive for SP. Therefore, while the ultrastructural data support the hypothesis that SP immunoreactive first-order neurons are involved in the origination of the baroreceptor reflex, they suggest that only a modest part of the total sensory input conveyed from the carotid sinus baroreceptors to the dlNTS is mediated by SP immunoreactive CSN terminals. Five types of axo-axonic synapses were observed in the dlNTS. SP immunoreactive CSN afferents were very rarely involved in these synapses. Furthermore, SP terminals were never observed to form the presynaptic element in an axo-axonic synapse with a CSN afferent. Therefore, SP does not appear to be involved in the modulation of the baroreceptor reflex in the dlNTS.

Acetylcholine increases intracellular calcium of arterial chemoreceptor cells of adult cats

Acetylcholine increases intracellular calcium of arterial chemoreceptor cells of adult cats. J. Neurophysiol. 78: 2388-2395, 1997. Several neurotransmitters have been reported to play important roles in the chemoreception of the carotid body. Among them acetylcholine (ACh) appears to be involved in excitatory processes in the cat carotid body. As one of the steps to elucidate possible roles of ACh in carotid body chemoreception in the cat, we examined the effect of ACh on intracellular calcium concentration ([Ca2+]i) of cultured carotid body cells. The carotid body from adult cats was dissociated and cultured for up to 2 wk. [Ca2+]i was measured from clusters of cells with a microfluorometric technique using Indo-1 AM. Experiments were performed at 37 degrees C, and cells were continuously superfused with modified Krebs solutions equilibrated with 5% CO2-16% O2-79% N2. ACh (100 mu M) caused a marked increase in [Ca2+]i in approximately 70% of clusters, and the responses to 1-300 mu M of ACh were concentration dependent. The magnitude and kinetics of the ACh response were mimicked by the application of nicotine, whereas muscarinic agonists, pilocarpine, and muscarine failed to evoke a similar response. ACh-induced increase in [Ca2+]i was dependent on extracellular Ca2+: it was greatly reduced or completely abolished by a transient removal of extracellular Ca2+. The response was consistently but only partially reduced by caffeine (5 mM) or nifedipine (10 mu M). The effect of mecamylamine (100 mu M) was inhibitory but small. Moreover, the increase in [Ca2+]i in response to ACh was also observed in some clusters that did not respond to high K (100 mM) Krebs. These results suggest that ACh increases [Ca2+]i of cultured carotid body cells by activating neuronal nicotinic ACh receptors, leading to Ca2+ influx via nicotinic channels. In addition, other pathways such as Ca2+ influx through L-type calcium channels, perhaps secondary to membrane depolarization, and Ca2+ release from intracellular stores may participate in increasing [Ca2+]i in response to ACh. Muscarinic receptors appear to play only a small role, if any.

Further cholinergic aspects of carotid body chemotransduction of hypoxia in cats

From the 1930s into the 1970s, the role of acetylcholine (ACh) in the carotid body's chemotransduction of hypoxia was debated. Since the late 1970s, the issue has been pursued only intermittently or not at all. The purpose of this study was to test again with a new preparation the hypothesis that ACh is an excitatory neurotransmitter in the cat carotid body's chemotransduction of hypoxia. We tested the effect of the specific nicotinic blocker mecamylamine and the muscarinic blocker of all five muscarinic receptors, atropine. We further tested the effects of M1 and M2 muscarinic-receptor blockers. The carotid body region was selectively perfused with hypoxic Krebs-Ringer bicarbonate (KRB) solutions that were blocker free or contained varying doses of the blockers. Both mecamylamine and atropine reduced the response to hypoxic KRB in a dose-related manner. The M2 muscarinic-receptor blockers gallamine and AFDX 116 increased the response to hypoxic KRB, whereas the M1 muscarinic-receptor blocker pirenzepine reduced the response to hypoxic KRB. These data are consistent with an excitatory role for ACh in the carotid body chemotransduction of hypoxia in the cat.

Two types of voltage-gated K channels in carotid body cells of adult cats

The purpose of this study was to investigate if the oxygen-sensitive K channel is present in the carotid body cells of adult cats, and if all carotid body cells express the oxygen-sensitive K channel. A standard patch-clamp technique with a whole-cell configuration was applied to cultured carotid body cells from adult cats. The cells were continuously perfused with Krebs equilibrated with 5% CO2/air or 5% CO2/argon at room temperature. The results showed that electrophysiologically at least two types of cells existed in cultured cat carotid body cells. One type expressed the oxygen-sensitive K channel and the other expressed the oxygen-insensitive K channel. The oxygen-sensitive K channel was voltage-dependent with a threshold potential of -30 mV. No inactivation was observed during 40 ms of stimulation. The slope of the steady-state current-voltage curve was almost linear in the range from -30 mV to +50 mV. Hypoxia (pO2 = 25 mmHg) reversibly depressed the K current by 22%. The current was inhibited by 4-aminopyridine (10 mM) and tetraethylammonium (4-25 mM), but insensitive to charybdotoxin (100 nM). The oxygen-insensitive K channel showed similar characteristics to that of the oxygen-sensitive K channel in the threshold and the speed of activation, and the shape of I-V curve. The cat is the third species in which the oxygen-sensitive K channel was found in the carotid body. The sensitivity of K channels to oxygen may be a unique feature of chemosensory cells, but the properties of the oxygen-sensitive K channels are different among cats, rats, and rabbits.

Reflex stimulation of renal sympathetic nerve activity and blood pressure in response to apnea

The purpose of this study was to examine the role of afferent input in the reflex modulation of renal sympathetic nerve activity (SNA) in response to apnea. Apneas of 20-, 40-, and 60-s duration were induced in the anesthetized, paralyzed cat (n = 7) ventilated with either room air or 100% oxygen. While receiving room air, there were increases (p < 0.005) in renal SNA of 34.5 +/- 4.2%, 53.3 +/- 6.4%, and 59.9 +/- 7.2% of maximum during the 20-, 40-, and 60-s apneas, respectively. There were corresponding increases (p < 0.025) in mean arterial pressure (Pa) of 9 +/- 3, 30 +/- 9, and 45 +/- 12 mm Hg during the 20-, 40-, and 60-s apneas while receiving room air, respectively. The effect of 100% oxygen was to reduce (p < 0.0001) the renal SNA response to apnea, at a matched level of PaCO2, by at least 80%, and to eliminate any increase in Pa. During the first breath of the postapneic period, there was a partial inhibition of renal SNA. During the second and third breaths of the postapneic period, there was a marked fall in renal SNA that was associated with a precipitous decline in directly recorded carotid chemoreceptor activity (n = 2). The magnitude of the fall in renal SNA after apnea was related to the degree of postapneic hypertension. We conclude that hypoxic chemoreceptor stimulation is the predominant factor generating the renal SNA response to apnea, with modulating inputs from thoracic afferents and arterial baroreceptors likely contributing to the marked inhibition of renal SNA immediately after the apnea.

Synaptic interactions of retrogradely labeled hypoglossal motoneurons with substance P-like immunoreactive nerve terminals in the cat: a dual-labeling electron microscopic study

This study has investigated the synaptic interactions between hypoglossal motoneurons and substance P (SP)-immunoreactive terminals. Cholera toxin B conjugated to horseradish peroxidase was injected into the tip of the tongue on the right side of six ketamine-anesthetized cats. Two to five days later, the animals were killed. Cells containing HRP were labeled with a histochemical reaction utilizing tetramethylbenzidine (TMB) as the chromogen. TMB forms crystalline reaction products that are very distinct at the electron microscopic level. The tissues were then processed for immunocytochemistry using an antiserum against SP. The chromogen used in this case, diaminobenzidine, yields amorphous reaction products. At the light microscopic level, labeled cells were observed primarily ipsilaterally in both intermediate and ventrolateral subdivisions of the hypoglossal nucleus. The majority of these labeled cells were seen at the level of obex. At the electron microscopic level, both asymmetric and symmetric synapses were observed. SP-immunoreactive nerve terminals formed asymmetric synapses with labeled dendrites and symmetric synapses with labeled perikarya. SP-labeled terminals also synapsed on unlabeled dendrites and somata. These are the first ultrastructural studies demonstrating synaptic interactions between hypoglossal motoneurons and SP terminals. These studies demonstrate that hypoglossal motoneurons that innervate intrinsic tongue muscles are modulated by SP and that SP may play a role in the control of fine movements of the tongue.

Carotid sinus nerve terminals which are tyrosine hydroxylase immunoreactive are found in the commissural nucleus of the tractus solitarius

Tyrosine hydroxylase immunoreactive sensory neurons in the petrosal ganglion selectively innervate the carotid body via the carotid sinus nerve. Central projections of the carotid sinus nerve were traced with horseradish peroxidase. The commissural nucleus of the tractus solitarius was examined by dual labelling light and electron microscopy. Dense bilateral labelling with horseradish peroxidase was found in the tractus solitarius and commissural nucleus of the tractus solitarius. Horseradish peroxidase was found in unmyelinated axons, myelinated axons, and nerve terminals. About 88% of horseradish peroxidase-labelled carotid sinus nerve axons were unmyelinated. Tyrosine hydroxylase immunoreactivity was identified in unmyelinated axons, myelinated axons, dendrites, perikarya, and nerve terminals. Most tyrosine hydroxylase immunoreactive axons (93%) in the commissural nucleus of the tractus solitarius were unmyelinated. Tyrosine hydroxylase immunoreactivity was simultaneously identified in carotid sinus nerve unmyelinated axons, myelinated axons, and nerve terminals. These double-labelled terminals comprised 28% of the number of tyrosine hydroxylase immunoreactive terminals in the commissural nucleus of the tractus solitarius, and 55% of transganglionically-labelled terminals. Therefore, there are both central and peripheral sources of tyrosine hydroxylase immunoreactive nerve terminals in the commissural nucleus of the tractus solitarius. These data support the hypothesis that peripheral tyrosine hydroxylase immunoreactive neurons are involved in the origination of the chemoreceptor reflex. Axo-axonic synapses between peripheral carotid sinus nerve afferent terminals and central terminals containing tyrosine hydroxylase immunoreactivity were observed in 22% of the axo-axonic synapses observed. Thus, central tyrosine hydroxylase immunoreactivity neurons are involved in the modulation of the chemo-and/or baroreceptor reflexes. Synaptic contacts were not observed between carotid sinus nerve afferents and tyrosine hydroxylase immunoreactive perikarya of dendrites. Catecholaminergic neurons are thus unlikely to be the second order neurons of either the chemo-or baroreceptor reflex in the commissural nucleus of the tractus solitarius.

Synaptic interactions of substance P immunoreactive nerve terminals in the baro- and chemoreceptor reflexes of the cat

The neurochemical anatomy and synaptic interactions of morphologically identified chemoreceptor or baroreceptor afferents in the nucleus of the solitary tract (NTS) are poorly understood. A substantial body of physiological and light microscopic evidence suggests that substance P (SP) may be a neurotransmitter contained in first order sensory chemo- or baroreceptor afferents, however ultrastructural support of this hypothesis is lacking. In the present report we have traced the central projections of the carotid sinus nerve (CSN) in the cat by utilizing the transganglionic transport of horseradish peroxidase. Medullary tissues including the commissural NTS (cNTS) were processed for the histochemical visualization of transganglionically labeled CSN afferents and for the immunocytochemical detection of SP by dual labeling light and electron microscopic methods. At the light microscopic level, dense bilateral labeling with TMB was found in the tractus solitarius (TS) and cNTS, caudal to the obex. Rostral to the obex, significant ipsilateral TMB labeling was detected in the dorsal, dorso-lateral, and medial subnuclei of the NTS, as well as in the TS. Significant staining of SP immunoreactive processes was detected in most subnuclei of the NTS. The cNTS was examined by electron microscopy. Either HRP or SP were readily identified in single labeled unmyelinated axons, myelinated axons, and nerve terminals in the cNTS. SP immunoreactivity was also identified in unmyelinated axons, myelinated axons, and nerve terminals in the cNTS which were simultaneously identified as CSN primary afferents. These ultrastructural data support the hypothesis that SP immunoreactive first order neurons are involved in the origination of the chemo- and baroreceptor reflexes. Axo-axonic synapses were observed between CSN primary afferent terminals and: (a) unlabeled nerve terminals; (b) other CSN primary afferent terminals; and (c) terminals containing SP. Axo-axonic synapses were also observed between CSN primary afferents which contained SP, and other SP terminals. These observations may mediate the morphological bases for multiple forms of presynaptic inhibition in the cNTS, including those involved in cardiorespiratory integration. In conclusion, our results indicate that SP immunoreactive nerve terminals may be important in both the origination and the modulation of the chemo- and/or baroreceptor reflexes.

Effects of a continuous infusion of dopamine on the ventilatory and carotid body responses to hypoxia in cats

1. We investigated how a continuous infusion of dopamine (DA; 5 micrograms/kg per min), which is often used clinically, would affect the ventilation and carotid chemoreceptor neural activity in anaesthetized cats. 2. In anaesthetized, spontaneously breathing cats, tidal volume (VT) and respiratory frequency (f) were continuously monitored at five levels of inspired oxygen (PIO2 = 110, 130, 150, 170, 760 mmHg) during Da or saline infusion. VT and f were sampled for 1 min after 3 min exposure to each level of PIO2. Time control study was also performed. 3. DA infusion significantly lowered VT under both normoxia and hypoxia in seven of eight cats. Respiratory frequency was not affected by DA infusion. Depression of ventilation during post-hypoxic hyperoxia was augmented by DA infusion. Chemodenervation abolished the ventilatory response to hypoxia and DA did not further affect the ventilatory response to hypoxia. 4. In a second group of artificially ventilated cats, carotid chemoreceptor neural activity was recorded at five levels of arterial oxygen tension. DA infusion significantly depressed carotid chemoreceptor neural activity during normoxia and hypoxia in six of seven cats. 5. These findings suggest that changes in ventilation during low dosage of DA infusion closely correlate with carotid body neural output. A predominant effect of this dosage of DA (5 micrograms/kg per min) was depression in the ventilatory response to hypoxia due to an inhibition of carotid body neural output.

The cholinergic hypothesis revisited--an unfinished story

Though exogenously delivered acetylcholine excites the carotid body, past evidence has been considered as unsupportive in assigning acetylcholine an excitatory role during hypoxia or hypercapnia. With ganglionic transmission used as the model, data is presented which aims at blocking the postsynaptic cholinergic receptors, at preventing the presynaptic release of acetylcholine, and at quantitating its release under stimulating conditions. The data support an excitatory role for acetylcholine during hypoxia.

Culture of arterial chemoreceptor cells from adult cats in defined medium

Recently patch clamp techniques and optical fluorometric techniques have been applied to freshly dissociated or cultured carotid body. However, very few studies have shown the effects of the dissociation and/or culture conditions on the health and function of the cells. The purpose of this study was to develop a culture method which support healthy and functioning carotid body cells from adult cats. Carotid bodies were dissociated with 0.1-0.2% collagenase and gentle trituration. The cells were plated on glass wells coated with poly-D-lysin and Matrigel, and cultured in chemically defined medium. Culture was maintained for up to 37 days without overgrowth of fibroblasts. Glomus cells extended their processes within and from clusters. Single glomus cells acquired the shape of neurons. Glomus cells synthesized dopamine and its secretion increased during exposure of the cells to hypoxia. Tyrosine hydroxylase was expressed throughout the culture period. These results indicate that glomus cells cultured under conditions described here are healthy and function in a manner similar to that in vivo.

Acetylcholine and carotid body excitation during hypoxia in the cat

The purpose of this study was to test the hypothesis that acetylcholine (ACh) is an excitatory neurotransmitter during the hypoxic stimulation of the carotid body. Cats were anesthetized, paralyzed, and artificially ventilated. The common carotid artery was fitted with a loop containing a stopcock for selectively perfusing the carotid body. Neural activity was recorded from the whole carotid sinus nerve. After the cats had been ventilated on 10% O2 for 3 min with the carotid body being normally perfused with its own hypoxic arterial blood, the stopcock was turned, and either equally hypoxic Krebs-Ringer bicarbonate solution (KRB) containing alpha-bungarotoxin, mecamylamine, and atropine or hypoxic blocker-free KRB perfused the carotid body for 2 min. The stopcock was returned to its original position, allowing blocker-free hypoxic blood to perfuse the carotid body once again. With this protocol we found 1) the cholinergic blockers reduced the carotid body response to hypoxic KRB in a dose-dependent manner; 2) carotid baroreceptor activity was not reduced by the blockers, suggesting that the action of the blockers was not nonspecific (whereas lidocaine rapidly reduced both chemoreceptor and baroreceptor activity); 3) inclusion of the blockers in perfused hypoxic blood also reduced neural output from the carotid body; and 4) the blockers reduced the carotid body's neural response to hypoxic KRB containing substance P (20 micrograms/100 ml), suggesting that substance P may be linked to ACh in the carotid body. We conclude that these data provide good evidence supportive of an excitatory role for ACh in carotid body hypoxic excitation.

Peripheral chemoreceptor modulation of the pulmonary vasculature in the cat

The present study was undertaken to determine whether stimulation of the carotid and aortic bodies (cb and ab) could affect the pulmonary vasculature. Our hypothesis was that each promoted vasodilation and thus could modulate the pulmonary vasoconstrictor response to hypoxia. The experimental design of the first set of experiments took advantage of the facts that 1) the ab, but not the cb, increases its neural output in response to CO, whereas both respond to a decreased arterial PO2 (hypoxic hypoxia, HH) and 2) the aortic nerves in cats are easily transected. Hence, both cb and ab sent neural activity to the brain stem when the intact cat was exposed to 10% O2 in N2. Only the ab sent information during CO hypoxia (COH intact). Only the cb did so during HH in the cat in which the aortic nerves had been transected, removing the aortic body (HH abr); neither ab nor cb did so during COH abr. Fifteen anesthetized paralyzed artificially ventilated cats were fit with catheters in the femoral artery and vein, right and left atria, left ventricle, and pulmonary artery and with an aortic flow probe. In the HH intact and HH abr conditions, there was a significant rise in cardiac output, whereas pulmonary arterial pressure (Ppa) rose initially but then leveled off while cardiac output continued to rise. During the 15-min exposure to HH, pulmonary vascular resistance [PVR = (Ppa - Pla)/cardiac output, where Pla is left atrial pressure] rose initially and then decreased significantly at 2-3 min. In response to COH, PVR showed only a significant decrease. In the second set of experiments, seven cats were instrumented as above and had loops placed in the common carotid arteries for selectively perfusing the cbs. In response to a brief infusion of venous blood mixed with 0.3-0.5 micrograms NaCN, which selectively stimulated only the cb, aortic flow remained relatively constant while heart rate and Ppa - alveolar pressure difference decreased significantly; so also did PVR. These data are consistent with the hypothesis that stimulation of the ab and cb singly or together can provoke a significant pulmonary vasodilation in the anesthetized paralyzed artificially ventilated cat.

Dependency of hypoxic chemotransduction in cat carotid body on voltage-gated calcium channels

The hypothesis that the entry of extracellular calcium ions into some compartment, quite possibly the type I cells, through voltage-gated calcium channels (VGCC) is essential for hypoxic chemotransduction in the cat carotid body was tested using an in situ perfusion technique. The neural output of the carotid body of anesthetized, paralyzed, and artificially ventilated cats in response to perfusions with Krebs-Ringer bicarbonate solution (KRB), calcium-free KRB, KRB containing calcium channel blockers, or KRB containing BAY K 8644 was recorded. Selective perfusion of the carotid body with hypoxic calcium-free KRB significantly decreased carotid chemoreceptor activity, suggesting that extracellular calcium is essential for hypoxic chemotransduction. Selective perfusion of the carotid body with hypoxic KRB containing verapamil (10-100 microM), diltiazem (10-100 microM), or nifedipine (10-100 microM) dose dependently attenuated the increase in chemoreceptor activity produced by hypoxia, suggesting that VGCC need to be activated for hypoxic chemotransduction. The carotid body response to hyperoxic KRB containing the calcium channel agonist BAY K 8644 (10 microM) was 267 +/- 87% of hyperoxic control KRB, suggesting that an enhanced influx of calcium ions through VGCC stimulates carotid chemoreceptor activity. Selective perfusion of the carotid body with severely hypoxic KRB containing BAY K 8644 did not increase chemoreceptor activity above that produced by severe hypoxia alone. This suggests that severe hypoxia increases intracellular calcium in some compartment of the carotid body to achieve stimulatory maximum response and that further increase in intracellular calcium does not produce further elevation of neural activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Sympathetic influence on carotid chemoreceptor response to substance P in the cat

Previous studies have suggested that substance P (SP) may play a role in the carotid chemoreceptor response to hypoxia. Given the data from these studies we speculated that within the carotid body hypoxia might release SP which then acts on the chemosensitive unit. Concomitantly SP might be released in the superior cervical ganglion (SCG) and increase sympathetic outflow to the carotid body by interacting with acetylcholine in the SCG. The resulting vasoconstriction in the carotid body would further increase neural output from the carotid body. Hence we hypothesized that the exogenous SP on the carotid chemoreceptor neural activity would decrease after eliminating preganglionic inflow into the SCG. The hypothesis was tested using anesthetized, paralyzed and artificially ventilated cats. Neural activity from the carotid body (carotid chemoreceptor activity) or from the SCG (ganglioglomerular efferent nerve activity (GGN)) was measured. Close intra-arterial administration of SP (10 micrograms) caused a sustained stimulation of the carotid chemoreceptor activity which was accompanied by a fall in arterial blood pressure. The magnitude and time-course of the carotid body responses were extremely variable among the cats. The duration of increased chemoreceptor activity was significantly shortened after a transection of the cervical sympathetic nerve (CVSN). As a control, the duration of carotid body stimulation produced by the second injection of SP in a group of sham-operated cats was measured. This was essentially the same as the first injection, suggesting that the tachyphylactic effect of SP was negligible. The effects of the commonly used pharmacological agents (nicotine, cyanide, dopamine) on carotid chemoreceptor activity were not affected by the transection of the CVSN, GGN activity was also increased by exogenous SP. These results suggest that the effect of exogenous SP on carotid chemoreceptor activity consists of two components: (1) an initial direct excitatory effect; (2) a slowly developing excitatory effect mediated by the sympathetic outflow to the carotid body. The effects could be augmented by the accompanying hypotension.