Correction to: Patient dose reference levels in surgery: a multicenter study.

The original version of this article, published on 01 August 2018, unfortunately contained two mistakes.

Patient dose reference levels in surgery: a multicenter study.

OBJECTIVE: To assess diagnostic reference levels (DRLs) in surgery for the most frequent procedures as required by the European Directive 2013/59/Euratom. METHODS: A survey was conducted in six centers. Eight orthopedic, urology and gastrointestinal surgical procedures were analyzed. Kerma area product (KAP) and fluoroscopy time (FT) were recorded for 50 patients (except for elbow: 30 patients) per procedure and per center from September 2016 to September 2017. DRLs were calculated as the 3rd quartiles of the distributions. For shoulder surgery, DRLs were defined according to the complexity of the procedure. For hand/wrist and foot/ankle surgery, DRLs were defined according to the technology (conventional C-arm vs. mini-C-arm). RESULTS: Results of 1870 procedures were retrieved. DRLs were calculated for the two dosimetric indicators and the eight procedures. DRLs were 2130 mGy.cm2 and 1.4 min for proximal femoral intramedullary nail, 1185 mGy.cm2 and 0.9 min for laparoscopic cholecystectomy and 2195 mGy.cm2 and 1.0 min for double-J (pigtail) ureteral catheter insertion. For shoulder surgery, KAP and FT were significantly higher (p < 0.05) for intramedullary procedures compared to extramedullary procedures. For hand/wrist and foot/ankle surgery, the KAPs were significantly higher (p < 0.05) with conventional C-arm compared to mini-C-arm, but FTs were not significantly different (p: not significant). CONCLUSION: This study reports DRLs in surgery based on a multicentric survey. KEY POINTS: • Delivered dose in surgery depends on procedure, practice and patient. • Diagnostic reference levels (DRLs) are proposed for eight surgical procedures. • DRLs are useful to benchmark practices and optimize protocols.

[Cutaneous metastasis revealing epithelioid angiosarcoma of the abdominal aorta]. / Métastases cutanées révélatrices d'un angiosarcome épithélioïde de l'aorte abdominale.

BACKGROUND: Epithelioid angiosarcomas (EAS) of the aorta are a rare form of tumour usually diagnosed by histopathological analysis of the aorta. We report a case revealed by skin metastasis. CASE REPORT: An 85-year-old man presented skin tumours associated with deterioration of his general condition and intense pain of the right lower limb. Physical examination showed three nodules of the lumbar area associated with an ipsilateral livedo extending to the right lower limb. The course of the disease involved distal ischaemia. Arterial ultrasound, aortography and CAT showed ectasia of the abdominal aorta with thrombosis and right subpopliteal occlusion. Histological examination of a nodule showed proliferation of malignant cells with expression of vimentin, CD 31, cytokeratins AE1/AE3 and cytokeratin 7. Stain for CD34 was negative. Histological investigation of the livedo showed a vascular embolus with epithelial-type cells positive for cytokeratin 7 and CD 31. The PET scan showed intense F-FDG uptake of the aorta extended to the iliac artery. Moreover, skin and osseous F-FDG uptake was seen. These findings suggested a diagnosis of EAS of the aorta with skin and osseous metastasis and vascular emboli. DISCUSSION: Only 27 previous case reports of EAS based on appropriate immunohistochemical analysis have been published in the literature. These tumours typically arise in the abdominal aorta in association with metastasis in more than 80% of cases. Skin metastasis causes papular eruption, nodules and peripheral vascular disease. Embolic vascular occlusion results in ischaemia and in rare cases vasculitis. Our case report emphasizes four key points: the diagnostic value of an association of localized malignant skin tumours, extensive livedo, ipsilateral distal ischaemia, deterioration of the general condition and intense pain; the diagnostic value of endothelial markers, especially CD31, and potentially misleading co-expression of cytokeratin markers; in selected cases, additional imaging, such as PET scans, performed in our case for the first time prior to surgery of the aorta, may be helpful for the diagnosis of such neoplastic lesions of the aortic wall.

Preoperative assessment of anatomical suitability for thoracic endovascular aortic repair.

Endovascular treatment of descending thoracic aortic pathologies requires a preoperatively determined interventional strategy. Its feasibility depends mainly on anatomic factors: the morphology of the proximal and distal fixation sites, the diameter and disease state of the access vessels. These factors represent important predictors of success and the most important exclusion criteria. Current diagnostic evaluation of aortic aneurysm for endovascular repair relies primarily on CT scan associated with 3D-reconstruction to assess the anatomical suitability for endograft implantation. In patients with an inadequate length of the proximal or distal neck, the left subclavian artery or the coeliac trunk can be overstented to effectively exclude thoracic aortic lesions. Deliberate coverage of aortic side branches should be decided prior to the procedure (guided by a extensive anatomical assessment) or carefully be avoided in order to reduce major morbidity, especially cerebral embolization, spinal cord ischemia and ischemic abdominal complications.

'Pole test' measurements in critical leg ischaemia.

BACKGROUND: For the quantification of critical limb ischaemia (CLI) most vascular surgery units use sphygmo-manometric and transcutaneous oxygen pressure (TcPO2) measurements. However, measurements obtained by cuff-manometry can be overestimated especially in diabetic patients because of medial calcification that makes leg arteries less compressible. TcPO2 measurements present a considerable overlap in the values obtained for patients with different degrees of ischaemia and its reproducibility has been questioned. Arterial wall stiffness has less influence on the pole test, based on hydrostatic pressure derived by leg elevation, and this test seems to provide a reliable index of CLI. OBJECTIVE: The objective of this study was to evaluate the pole pressure test for detection of critical lower limb ischaemia, correlating results with cuff-manometry and transcutaneous oxygen pressure. DESIGN: University hospital-prospective study. MATERIALS AND METHODS: Seventy-four patients (83 legs) with rest pain or gangrene were evaluated by four methods: pole test, cuff-manometry, TcPO2 and arteriography. CLI was present if the following criteria were met: (a) important arteriographic lesions+rest pain with an ankle systolic pressure (ASP) < or = 40 mmHg and/or a TcPO2 < or = 30 mmHg, or (b) important arteriographic lesions+tissue loss with an ASP < or = 60 mmHg and/or a TcPO2 < or = 40 mmHg. Fifty-seven lower limbs met the criteria for CLI. RESULTS: Measurements obtained by cuff-manometry were significantly higher to those obtained by pole test (mean pressure difference: 40 mmHg, p<0.001). The difference between the two methods remained statistically significant for both diabetics (50.73, p<0.001) and non-diabetics (31.46, p<0.001). Mean TcPO2 value was 15.51 mmHg and there was no important difference between patients with and without diabetes. Overall, there was a correlation between sphygmomanometry and pole test (r = 0.481). The correlation persisted for patients without diabetes (r = 0.581), but was not evident in patients with diabetes. Correlation between pole test and TcPO2 was observed only for patients with diabetes (r = 0.444). There was no correlation between cuff-manometry and TcPO2. The pole test offered an accuracy of 88% for the detection of CLI. The sensitivity of this test was 95% and the specificity 73%.

A porcine model of systemic and renal haemodynamic responses to infrarenal aortic cross-clamping.

OBJECTIVES: cross-clamping of the infrarenal aorta is associated with complex haemodynamic disturbances. Several experimental models of aortic cross-clamping (AXC) have been described with heterogeneous results. The main purpose of this study was to establish an animal model in which infrarenal AXC could reproduce similar systemic and renal haemodynamic changes to those observed in humans. METHODS: eleven anaesthetised pigs underwent AXC just below the renal arteries. Renal blood flow was measured using clearance of (131)I hippuran. Systemic and renal parameters were collected at 3 consecutive 30-min periods. RESULTS: AXC did not alter the extraction fraction of (131)I hippuran but was accompanied by significant (13%) decrease in cardiac index (p = 0.005) and a 23% increase in mean arterial pressure (p = 0.005). AXC induced significant 135% increase in renal vascular resistance (p = 0.012) and a 35% decrease in renal blood flow (p = 0.016). This worsened after removal of the aortic clamp, whereas systemic variables returned to baseline levels. CONCLUSIONS: this AXC animal model reproduces the changes observed in humans. It provides a reliable animal model which allows to investigate the underlying mechanisms of renal vasoconstriction and the effect of new drugs.

Surgical exposure of superior sulcus lung tumors with vascular involvement.

Choice of exposure route for surgical excision of superior sulcus lung tumors depends on involvement at the thoracic inlet. From December 1985 to September 1999, we performed surgical treatment of superior sulcus tumors in 42 patients, including 22 with vascular involvement. Various exposure techniques were used, including a novel technique combining transverse supraclavicular cervicotomy and posterolateral thoracotomy in 11 cases, anterior transclavicular cervicothoracotomy in 7 cases, isolated posterolateral thoracotomy in 3 cases, and cervicosternotomy in 1 case. Vascular procedures consisted of subadventitial dissection of the subclavian artery in 5 patients, arterial resection-anastomosis in 7, and prosthetic bypass in 10. Postoperative mortality was 11.9% in the overall series of 42 patients (n = 5) and 9% (n = 2) in the subgroup of patients with vascular involvement. During follow-up, 13 patients died of tumor recurrence and 1 patient died of respiratory insufficiency. Actuarial 5-year survival was 22.7 +/- 17.5% overall and 18 +/- 17.9% in the subgroup of patients with vascular involvement. This study indicates that the combined exposure route with transverse supraclavicular cervicotomy and posterolateral thoracotomy was useful for treatment of superior sulcus lung tumors requiring lobectomy and pneumonectomy.

Serotonergic systems in the spinal cord of the amphibian urodele Pleurodeles waltl.

The role of the monoamine serotonin (5-HT) in modulating the neural networks underlying axial locomotor movements was studied in an adult amphibian urodele, Pleurodeles waltl. 5-HT was applied to an in vitro brainstem-spinal cord preparation of P. waltl, which displayed fictive axial locomotor patterns following bath application of N-methyl-D-aspartate (5 microM) with D-serine (10 microM). Our results showed that 5-HT (1-25 microM) produces a reversible increase in the cycle duration and the duration of rhythmic bursting activity recorded extracellularly from ventral roots innervating the axial musculature. When applied alone, 5-HT does not trigger axial locomotor activity. The distribution pattern of 5-HT immunoreactive (5-HT-ir) cells along the spinal cord was investigated both in intact and in chronic spinal animals. The number of 5-HT-ir cell bodies is higher at brachial levels and decreases through crural levels. Sparse oval or fusiform 5-HT-ir somata are present within the gray matter, just ventrolateral to the central canal. Longitudinal fibers were detected throughout the entire white matter, except in the medial part of the dorsal funiculi. Two columns of intensely labeled and profusely branching thick and thin fibers associated with numerous varicosities run continuously along the ventrolateral surface of the spinal cord. Three weeks following full spinal cord transection at the level of the second spinal root, all longitudinal processes had disappeared, indicating their supraspinal origin, whereas the ventrolateral plexes remained, suggesting that they originated from intraspinal 5-HT-ir cell bodies. Our data showing that spinal 5-HT is organized according to a rostrocaudal gradient suggest that the 5-HT systems of P. waltl are not related to the presence of limb motor pools but more likely are related to axial central pattern generators (CPGs) networks down the length of the spinal cord. The possible involvement of these two sources (descending vs. intraspinal) of 5-HT innervation in the modulation of the axial CPGs is discussed.

Quantitative morphological analysis of embryonic cockroach (Periplaneta americana) brain neurons developing in vitro.

Neurons dissociated from the brain of embryonic cockroaches (Periplaneta americana) can be maintained in culture for several weeks. The survival as well as the progressive organization of the neurons into a complex network was studied during a 5-week period under different culture conditions. About 10% of the dissociated cells adhered to the culture dish. This figure remained constant throughout the culture. The cell diameter ranged from 10 to 20 microns and did not change significantly over time in culture. Whereas only a few cells exhibited neurites at the start of the culture, the number of cells exhibiting neurites increased to reach about 99% after 2 weeks. The different cells were then connected to each other, forming a network, which became more and more complex. The number of cells per cluster as well as the length and the diameter of the "connectives" that linked the different clusters were found to increase with time. The morphology of individual neurons within the network was visualized after intracellular injection of biocytin. Labeling with antibodies raised against serotonin or GABA indicated that neurons were able to differentiate and to acquire specific neurotransmitter fates. The serotonergic phenotype was found to appear progressively throughout the culture, in parallel with the formation of the network. Cell density, addition of fetal calf serum, and ecdysone were shown to influence the development of the network.

Development of lumbar rhythmic networks: from embryonic to neonate locomotor-like patterns in the mouse.

Different aspects of spinal locomotor organization have been studied in the mouse during embryonic and neonatal development using in vitro preparations of isolated lumbosacral cords. The first consideration was the embryonic development of an alternating bilateral pattern. From embryonic day (E) 12, perfusion of serotonin could induce relatively synchronous lumbar bursts across the cord. Bilateral activity became progressively alternate at E15 due to the appearance of glycinergic inhibitory interactions (revealed by strychnine application). Strictly alternating patterns were expressed at E18 and were maintained after birth. In a second step, we investigated cellular properties involved in lumbar rhythmogenesis in postnatal day 0-2 preparations which displayed spontaneous locomotor-like activity. Perfusion of receptor antagonists showed the co-operative involvement of N-methyl-D-aspartate (NMDA)- and non-NMDA-receptors for excitatory amino acids-mediated operation of locomotor networks. In a final step we investigated the localization of locomotor networks within the lumbar cord. Data obtained from preparations exhibiting spontaneous or Mg2+-free induced bursts revealed that the networks are present throughout the lumbar cord and that rhythmogenesis is distributed throughout all segmental levels.

Fictive rhythmic motor patterns induced by NMDA in an in vitro brain stem-spinal cord preparation from an adult urodele.

An in vitro brain stem-spinal cord preparation from an adult urodele (Pleurodeles waltl) was developed in which two fictive rhythmic motor patterns were evoked by bath application of N-methyl-D-aspartate (NMDA; 2.5-10 microM) with D-serine (10 microM). Both motor patterns displayed left-right alternation. The first pattern was characterized by cycle periods ranging between 2.4 and 9. 0 s (4.9 +/- 1.2 s, mean +/- SD) and a rostrocaudal propagation of the activity in consecutive ventral roots. The second pattern displayed longer cycle periods (8.1-28.3 s; 14.2 +/- 3.6 s) with a caudorostral propagation. The two patterns were inducible after a spinal transection at the first segment. Preliminary experiments on small pieces of spinal cord further suggested that the ability for rhythm generation is distributed along the spinal cord of this preparation. This study shows that the in vitro brain stem-spinal cord preparation from Pleurodeles waltl may be a useful model to study the mechanisms underlying the different axial motor patterns and the flexibility of the neural networks involved.

[Paraplegia after surgical treatment of primary aorto-duodenal fistula]. / Paraplégie après traitement chirurgical d'une fistule aorto-duodénale primaire.

A 68-year-old patient with chronic cirrhosis underwent surgical repair of the subrenal abdominal aorta presenting an aorto-duodenal fistula. The fistula was considered to be a primary fistula because it occurred without prior surgery and because the aorta had ruptured without formation of an aneurysm. The postoperative period was complicated by paraplegia further compromising the outcome in this severe condition. In general, there are several problems involved in the management of aorto-duodenal fistulae. Neither computed tomography of the abdomen nor gastroduodenal endoscopy are able to provide the diagnosis in all cases before surgery. Surgical treatment is most often conducted in an emergency setting requiring repair of both the digestive tract and of the vascular lesions. It is also important to recognize the risk of neurological events occurring intra-operatively. Prognosis is usually poor.

Pyramidal neurons in rat prefrontal cortex show a complex synaptic response to single electrical stimulation of the locus coeruleus region: evidence for antidromic activation and GABAergic inhibition using in vivo intracellular recording and electron microscopy.

Cognition and acquisition of novel motor skills and responses to emotional stimuli are thought to involve complex networking between pyramidal and local GABAergic neurons in the prefrontal cortex. There is increasing evidence for the involvement of cortical norepinephrine (NE) deriving from the nucleus locus coeruleus (LC) in these processes, with possible reciprocal influence via descending projections from the prefrontal cortex to the region of the LC. We used in vivo intracellular recording in rat prefrontal cortex to determine the synaptic responses of individual neurons to single electrical stimulation of the mesencephalic region including the nucleus LC. The most common response consisted of a late-IPSP alone or preceded by an EPSP. The presence of an early-IPSP following the EPSP was sometimes detected. Analysis of the voltage dependence revealed that the late-IPSP and early-IPSP were putative K(+)- and Cl- dependent, respectively. Synaptic events occurred following short delays and were inconsistent with the previously reported time for electrical activation of unmyelinated LC fibers. Moreover, systemic injection of the adrenergic antagonists propranolol (beta receptors), or prazosin (alpha 1 receptors), did not block synaptic responses to stimulation of the LC region. Finally, certain neurons were antidromically activated following electrical stimulation of this region of the dorsal pontine tegmentum. Taken together, these results suggest that the complex synaptic events in pyramidal neurons of the prefrontal cortex that are elicited by single electrical stimulation of the LC area are mainly due to antidromic activation of cortical efferents. Further insight into the chemical circuitry underlying these complex synaptic responses was provided by electron microscopic immunocytochemical analysis of the relations between the physiologically characterized neurons and either 1) GABA or 2) dopamine-beta-hydroxylase (DBH), a marker for noradrenergic terminals. GABA-immunoreactive terminals formed numerous direct symmetric synapses on somata and dendrites of pyramidal cells recorded and filled with lucifer yellow (LY). In contrast, in single sections, noradrenergic terminals immunoreactive for DBH rarely contacted LY-filled somata and dendrites. These results support the conclusion that IPSPs observed following single electrical stimulation of the LC region are mediated by GABA, with little involvement of NE. These IPSPs, arising from antidromic invasion of mPFC cells innervating the LC, may improve the signal-to-noise ratio and favor a better responsiveness of neighboring neurons to NE released in the mPFC.

Morphologically heterogeneous met-enkephalin terminals form synapses with tyrosine hydroxylase-containing dendrites in the rat nucleus locus coeruleus.

Physiological and anatomical studies have suggested that the endogenous opioid peptide, methionine-enkephalin (ENK), may directly modulate noradrenergic neurons. Additionally, chronic opiate administration has been shown to increase the levels of a number of G-proteins and phosphoproteins including the catecholamine synthesizing enzyme, tyrosine hydroxylase (TH). We combined immunogold-silver localization of tyrosine hydroxylase and immunoperoxidase labeling for ENK in single sections through the nucleus locus coeruleus (LC) in the rostral pons to determine potential substrates for the divergent actions of this opioid peptide. Light microscopic analysis of ENK immunoreactivity in the LC area indicated that ENK fibers are dense and highly varicose. In coronal sections, ENK-immunoreactive processes were punctate and appeared to envelop LC-cell bodies. More rostrally, in the region of catecholamine-immunoreactive extranuclear dendrites, ENK-immunoreactive varicose processes were interdigitated with TH-labeled processes. Electron microscopy of this rostral region revealed that ENK-immunoreactive axon terminals contained small clear as well as large dense core vesicles. The large dense core vesicles (1-10/terminal) were consistently the most immunoreactive and were identified toward the periphery of the axon terminal distal to the active zone of the synapse. Unlabeled axon terminals and glial processes were the most commonly observed elements located adjacent to the plasmalemma of axons containing the labeled dense core vesicles. Axon terminals containing ENK immunoreactivity varied in size (0.3 micron to 2.0 microns) as well as formation of synaptic specializations (i.e., asymmetric versus symmetric). The ENK-labeled terminals formed synapses with dendrites with and without detectable TH immunoreactivity. These results provide the first direct ultrastructural evidence that morphologically heterogeneous terminals containing ENK immunoreactivity form synapses with catecholamine dendrites within the LC. The formation of asymmetric and symmetric synaptic specializations suggests that the opioid peptide, ENK, may be colocalized with other neurotransmitters. Furthermore, the distribution of ENK immunoreactivity in axon terminals apposed to other unlabeled afferents or astrocytic processes suggests that actions of ENK may also include presynaptic modulation of other transmitters and/or effects on astrocytes.

Ultrastructural characterization of neurons recorded intracellularly in vivo and injected with lucifer yellow: advantages of immunogold-silver vs. immunoperoxidase labeling.

Immunoperoxidase labeling of lucifer yellow provides a sensitive method for morphological characterization of neurons recorded intracellularly in vitro or in vivo. However, the reaction product is often so dense that it obscures ultrastructural details necessary for the analysis of synaptic contacts onto individually filled neurons. In the present study, we describe a silver intensification procedure using 1 nm gold labeling of lucifer yellow as an optimal means for immunocytochemically identifying single physiologically characterized neurons at the ultrastructural level. Single neurons in the frontal cortex of anesthetized rats were impaled in vivo and filled with lucifer yellow. The brains were then perfused with an acrolein fixative. Single vibratome sections through the recording site were reacted with a rabbit antibody directed against lucifer yellow followed by goat anti-rabbit 1 nm gold-labeled IgG and silver intensified. For comparison, additional sections were processed for immunoperoxidase detection of lucifer yellow. Labeled sections were processed for light microscopy or embedded in plastic for electron microscopy. The immunogold-silver label as well as peroxidase reaction product of lucifer yellow was readily detected in cell bodies, proximal and distal dendrites, and spines. However, in contrast to immunoperoxidase, the immunogold-silver reaction did not obscure subcellular organelles. Most importantly, the synaptic junctions formed by afferents to the filled neuron were more easily identifiable following the immunogold-silver procedure. This clear visualization of postsynaptic densities is essential for examining synaptic circuitry between afferents and physiologically characterized neurons.

Analysis of synaptic inputs and targets of physiologically characterized neurons in rat frontal cortex: combined in vivo intracellular recording and immunolabeling.

Ultrastructural immunocytochemical identification of transmitters in afferent terminals and targets of individual physiologically characterized neurons is essential for understanding the complex circuitry within the mammalian neocortex. For this type of analysis, we examined the utility of combining in vivo intracellular recording and biocytin injections with silver intensified 1 nm immunogold labeling of GABA and the catecholamine synthesizing enzyme, tyrosine hydroxylase (TH). These transmitters are found to local neurons and afferents known to prominently modulate the activity of pyramidal neurons in the neocortex. Individual neurons were physiologically characterized and filled with biocytin in the frontal cortex of anesthetized rats. The brains were then preserved by vascular perfusion with aldehydes. Single vibratome sections through the recording site were reacted (1) for immunoperoxidase detection of biocytin and (2) for immunogold labeling of GABA or TH. Dually labeled sections were processed for light microscopy or embedded in plastic for electron microscopy. The dense peroxidase product for biocytin was detected in pyramidal neurons. These were located in superficial as well as deep cortical laminae, and were readily distinguished from immunogold silver labeling. GABA labeled terminals formed symmetric synapses with larger biocytin filled dendrites, whereas the TH labeled terminals contacted distal dendrites and spines. Peroxidase labeling for biocytin also was seen in a few axon terminals forming synapses with unlabeled and with GABA immunoreactive dendrites. These results suggest that single pyramidal neurons of the rat frontal cortex receive dual input from both GABA and catecholamine terminals. Additionally, this study demonstrates the usefulness of silver enhancement of 1 nm colloidal gold prior to plastic embedding for electron microscopic detection of neurotransmitters within afferents and targets of neurons physiologically characterized in vivo.

Cholecystokinin-gated currents in neurons of the rat solitary complex in vitro.

1. Ionic conductances controlled by type A and type B cholecystokinin (CCK) receptors were studied in neurons of the rat nucleus tractus solitarius (NTS) and dorsal motor nucleus of the vagus (DMNV), using intracellular and whole-cell patch clamp recordings in current or voltage clamp configuration during bath application of agonists (CCK8, CCK4, BC 264) and antagonists. 2. CCKA receptor-related inhibition was associated with a membrane hyperpolarization and a decrease in input resistance that developed 2-6 min after the arrival of drug into the extracellular medium. These effects were induced by 5 nM CCK8 but not BC 264 and they were blocked by the CCKA antagonist, L-364,718, but not by the CCKB antagonist, L-365,260. 3. CCKA receptor-related inhibition was generated by a potassium current that reversed at a reversal potential E(rev) of -73 +/- 1 (mean +/- SE) mV with bathing potassium concentration [K+]o = 6 mM and at -88 +/- 1 with [K+]o = 3 mM, in agreement with the Nernst equation for potassium ions. 4. CCKB receptor-related excitation was associated with a membrane depolarization and an increase of the input resistance induced by the following agonists at threshold concentrations: CCK8 (0.2 nM) > or = BC 264 (0.4 nM) > CCK4 (10.9 nM). The increase of input resistance was abolished by L-365,260 and was maintained after blockade of the CCKA current by L-364,718. 5. CCKB receptor-related excitation, in the neurons (30% of cases) in which clear response reversal was observed, appeared to be generated by a decrease of a potassium conductance. Responses showed a reversal potential E(rev) of -68 +/- 4 mV with [K+]o = 6 mM and -89 +/- 1 mV with [K+]o = 3 mM, verifying predictions from the Nernst equation applied to potassium ions. However, in 70% of cases, clear reversal was not observed at membrane potentials negative to the theoretical potassium equilibrium potential EK. 6. In voltage clamp studies, CCK8 induced a 181 +/- 17 pA inward current associated with a 26 +/- 4% decrease in the instantaneous current (I(ins)) generated by hyperpolarizing voltage steps. This effect on I(ins) was demonstrated in the absence of effects on the outward noninactivating potassium current (IM) and on the inward noninactivating cationic current (IQ). 7. CCKB receptor-mediated excitation was not suppressed by cobalt, a blocker of calcium currents, and was not associated with a change of the calcium-dependent potassium current (IK(Ca)).(ABSTRACT TRUNCATED AT 400 WORDS)

Extracellular potassium, glial and neuronal potentials in the solitary complex of rat brainstem slices.

Extracellular K+ activities (aKe) and neuronal and glial membrane potentials were recorded in the nucleus tractus solitarius (NTS) and in the dorsal vagal motor nucleus (DVMN) of rat brainstem slices after orthodromic stimulation of the tractus solitarius (TS). In glial cells, repetitive stimulation of the TS induced depolarizations of up to 30 mV followed by repolarizations which were fitted by exponential curves with a time constant of 1.6-5 s. Similar stimulations induced elevations of aKe of up to 8 mM, the recovery of which was fitted by single exponential curves with a time constant ranging between 1.6 and 4 s. These elevations in aKe were reduced by 75% during blockage of synaptic transmission in low Ca2+, high Mg2+ solution, and by 24% with application of 6-cyano-7-nitro-quinoxaline-2,3-dione (CNQX, 50 microM). Perfusion with a low Mg2+ solution increased the aKe response to stimulation of the TS, an effect that was reduced by the addition of 2-amino-5-phosphono-valeric acid (AP7, 50 microM) to the bath. No significant change in aKe and glial potential was seen when superfusing high concentrations of the C-terminal octapeptide of cholecystokinin (CCK8, 1-5 microM) and C-terminal tetrapeptide (CCK4, 50-100 microM). The effect of TS stimulations on solitary complex neurons suggests that extracellular K+ concentration is increased during synaptic activation of non-NMDA or NMDA ionotropic receptors. Conversely, slow depolarizations elicited by repetitive afferent activity or excitation by CCK agonists develop in neurons in the absence of measurable extracellular K+ fluctuations or glial depolarization.

CCK modulates inhibitory synaptic transmission in the solitary complex through CCKB sites.

The CCKB antagonists L-365, 260 and PD134308 and the CCKA antagonist L-364, 718 were applied to neurones of the rat solitary complex (SC) isolated in brainstem slices, while recording either intracellularly or by whole-cell patch-clamp. The CCKB antagonists increased the amplitude of spontaneous or solitary tract-evoked Cl(-)-dependent inhibitory synaptic events by 25 +/- 5% in 5/7 neurones. These events were identified as (1) reversed spontaneous potentials, (2) reversed multisynaptic potentials and (3) outward currents blocked by the GABAA antagonist bicuculline. The CCKB antagonists had no postsynaptic action and increased excitatory synaptic events by 16 +/- 5% in only 3/9 neurones. The CCKA antagonist depolarized neurones but had no effect on synaptic events. Results suggest that CCK, released from the SC tissue, modulates GABAergic interneurones through CCKB sites. This mechanism could contribute to panic attacks, probably mediated by CCKB receptors.

Rhythmic activities in the rat solitary complex in vitro.

In adult rat brainstem slices, rhythmic discharge of action potentials occurred spontaneously in 10 out of 197 cells of the solitary complex. In 6 neurones, fast rhythms (2-6 per min) were characterized by volleys of synaptic activity presenting abrupt onset denoting synchronized discharge of presynaptic elements. Synchronizing signals may be generated by cells discharging bursts of high-frequency action potentials and presenting extensive axonal arborization, as observed in one cell. Slower rhythms (0.3-0.8 per min) monitored in three cells did not involve synchronizing processes and could be evoked in non-rhythmic cells by 15-30 min bath application of the cholecystokinin octapeptide (100 nM). These results suggest distinct operating mechanisms of fast and slow rhythms in the solitary complex in vitro.