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The use of norepinephrine and the restriction of intraoperative hydration have gained increasing acceptance over the last few decades. Recently, there have been concerns regarding the impact of this approach on renal function. The objective of this study was to examine the influence of norepinephrine, intraoperative fluid administration and their interaction on acute kidney injury (AKI) after cystectomy. In our cohort of 1488 consecutive patients scheduled for cystectomies and urinary diversions, the overall incidence of AKI was 21.6% (95%—CI: 19.6% to 23.8%) and increased by an average of 0.6% (95%—CI: 0.1% to 1.1%, p = 0.025) per year since 2000. The fluid and vasopressor regimes were characterized by an annual decrease in fluid balance (−0.24 mL·kg−1·h−1, 95%—CI: −0.26 to −0.22, p < 0.001) and an annual increase in the amount of norepinephrine of 0.002 µg·kg−1·min−1 (95%—CI: 0.0016 to 0.0024, p < 0.001). The interaction between the fluid balance and norepinephrine levels resulted in a U-shaped association with the risk of AKI; however, the magnitude and shape depended on the reference categories of confounders (age and BMI). We conclude that decreased intraoperative fluid balance combined with increased norepinephrine administration was associated with an increased risk of AKI. However, other potential drivers of the observed increase in AKI incidence need to be further investigated in the future.

The aim of this study was to evaluate the feasibility of opioid-free anesthesia (OFA) in open radical cystectomy (ORC) with urinary diversion and to assess the impact on recovery of gastrointestinal function. We hypothesized that OFA would lead to earlier recovery of bowel function. A total of 44 patients who underwent standardized ORC were divided into two groups (OFA group vs. control group). In both groups, patients received epidural analgesia (OFA group: bupivacaine 0.25%, control group: bupivacaine 0.1%, fentanyl 2 mcg/mL, and epinephrine 2 mcg/mL). The primary endpoint was time to first defecation. Secondary endpoints were incidence of postoperative ileus (POI) and incidence of postoperative nausea and vomiting (PONV). The median time to first defecation was 62.5 h [45.8–80.8] in the OFA group and 118.5 h [82.6–142.3] (p < 0.001) in the control group. With regard to POI (OFA group: 1/22 patients (4.5%); control group: 2/22 (9.1%)) and PONV (OFA group: 5/22 patients (22.7%); control group: 10/22 (45.5%)), trends but no significant results were found (p = 0.99 and p = 0.203, respectively). OFA appears to be feasible in ORC and to improve postoperative functional gastrointestinal recovery by halving the time to first defecation compared with standard fentanyl-based intraoperative anesthesia.

Cancer and surgery represent a major stress on the human body. Any condition that prevents patients from tolerating the physiological stress is a risk factor for poor outcome. There is a need to identify these impairments early in the process with a simple screening, followed by assessments that provide a holistic picture of the patient. The proposed path of multimodal prehabilitation acts synergistically with enhanced recovery after surgery care to achieve optimal patient outcomes.

To determine whether early acute kidney injury affects mid-term renal function, to identify risk factors for impaired mid-term renal function, and to highlight the evolution of plasma creatinine and estimated glomerular filtration rate in the first 12 months after cystectomy and urinary diversion.We conducted a single-center retrospective observational cohort study from 2000 to 2019. We included 900 consecutive patients undergoing cystectomy and urinary diversion. Patients with incomplete data and preoperative hemodialysis were excluded. Early acute kidney injury was defined as an increase in plasma creatinine of50% or26.5 μmol/L within 24 h after surgery. Multiple linear regression analysis was performed to model the association between risk factors and change in plasma creatinine and estimated glomerular filtration rate at 12 months.Early acute kidney injury was diagnosed in 183/900 patients (20.3%) and was associated with significant mid-term plasma creatinine increase compared to preoperative value (+10.0 μmol/L [95% confidence interval -1.5, 25.0] vs +4.0 μmol/L [-7.0, 13.0]; P 0.001). Similarly, a significant estimated glomerular filtration rate change was found (-11.2 mL/min [95% confidence interval -19.8, 0.6] vs -4.9 mL/min [-15.6, 5.3]; P 0.001). In the linear regression model, early acute kidney injury increased creatinine at 12 months by 9.8% (estimated glomerular filtration rate: decrease by 6.2 mL/min), male sex by 12.0%. Limitations include retrospective analysis from prospectively assessed data.Early acute kidney injury resulted in elevated plasma creatinine and decreased estimated glomerular filtration rate values 12 months postoperatively, albeit the clinical relevance remains questionable.

Prostatectomy is associated with relevant acute postoperative pain. Optimal analgesic techniques to minimize pain and enhance recovery are still under investigation. We aimed to compare the effect of three different analgesic techniques on quality of recovery.This investigator-initiated, prospective, randomized, three-arm, parallel-group, active-controlled, interventional superiority trial was performed in a Swiss teaching hospital from 2018 to 2021. Consecutive patients undergoing open or robotic-assisted radical prostatectomy were randomized to spinal anaesthesia (SSS, bupivacaine 0.5% + fentanyl), bilateral transversus abdominis plane block (TAP, ropivacaine 0.375% + clonidine) or systemic administration of lidocaine (SA, lidocaine 1%) in addition to general anaesthesia. Primary outcome was quality of recovery 15 (QoR-15) score on postoperative day one compared to baseline. Secondary outcomes were QoR-15 at discharge, postoperative nausea and vomiting, pain scores, return of gastrointestinal function and use of rescue analgesia.From 133 patients, 40 received spinal anaesthesia, 45 TAP block and 48 systemic analgesia. QoR-15 scores did not differ on day 1 (p = 0.301) or at discharge (p = 0.309) when compared to baseline. QoR-15 changes were similar in all groups. At discharge, median QoR-15 scores were considered as good (122) in all groups: SSS 134 [IQR 128-138]; TAP 129 [IQR 122-136] and SA 128 [IQR 123-136]. There were no significant differences in the other secondary outcomes.Quality of recovery on postoperative day one compared to baseline did not differ if spinal anaesthesia, TAP block or systemic administration of lidocaine was added to general anaesthesia.Optimal analgesic techniques to enhance recovery after prostatectomy are still under investigation. In this 3-arm randomized controlled trial, addition of spinal anaesthesia or transversus abdominis plane block to general anaesthesia did not improve quality of recovery after radical prostatectomy compared to less invasive intravenous lidocaine infusion (standard of care/control group). Quality of recovery at the time of discharge was considered as good in all three groups.

Background The intraoperative effect of 20% albumin on plasma volume during surgery involving major blood loss has not been explored extensively due to methodological difficulties. Crystalloids poorly expand the plasma volume, and using a colloid might then be a way to avoid fluid overload. As doubts have been raised about synthetic colloids, albumin solutions are currently used more extensively. This study presents a methodological development showing how plasma volume expansion can be studied in surgical settings with the coinfusion of 20% albumin and lactated Ringer's solution. Methods In this single-arm, single-center feasibility study, an intravenous (i.v.) infusion of 3 mL·kg·BW of 20% albumin was administered over 30 minutes to 23 cystectomy patients during the bleeding phase in addition to lactated Ringer's solution to correct blood loss. Blood samples were measured at regular intervals over a period of 300 minutes to estimate the blood volume expansion resulting from simultaneous infusions of lactated Ringer's and 20% albumin solutions, using a regression equation and the area under the volume-time curve method. Results Mean hemorrhage was 974 mL (standard deviation [SD] ± 381). The regression method showed strong correlation (r = 0.58) between blood loss minus blood volume expansion and the independent effects of the infused volume of lactated Ringer's and 20% albumin solutions. The mean plasma volume expansion attributable to the infusion of lactated Ringer's solution amounted to 0.38 (95% confidence interval [CI], 0 .31-0.49) of the infused volume; for the 20% albumin, it was 1.94 mL/mL (95% CI, 1.41-2.46 mL/mL) over 5 hours on average (regression method). The mean within-patient change was 0.20 mL/mL (± 0.06 mL/mL) for the lactated Ringer's solution and 2.20 mL/mL (±1.31 mL/mL) for the 20% albumin using the area under the volume-time curve method. Conclusions Blood volume expansion averaged 1.9-2.2 times the infused volume of 20% albumin during surgery associated with hemorrhage of around 1000 mL. This effect was long standing and approximately 5 times stronger than for the lactated Ringer's solution. Twenty percent albumin boosts the plasma volume expansion of lactated Ringer's solution to as high as 40% of the infused volume on the average, which is an effect that lasts at least 5 hours.

OBJECTIVE The goal of this article is to provide a pragmatic approach to implementing a prehabilitation pathway and service guide. DATA SOURCES The article presents data from peer-reviewed scientific articles (ie, reviews and original studies) and narrative reviews, as well as professional insights and experiences of the author in setting up a prehabilitation clinic. CONCLUSION Successful setup of a prehabilitation unit is highly feasible and rewarding, if led by enthusiastic idealists who work in cooperation with a passionate multidisciplinary team (MDT) with clear vision to collectively improve patient outcomes and experiences. It requires a well-integrated MDT to deliver a successful prehabilitation service. IMPLICATIONS FOR NURSING PRACTICE Nurses are the supporting pillar in many areas of the health care system. The field of prehabilitation is no exception to this with the mainstay contribution nursing provides. A combination of patient care, medical knowledge, and administrative capabilities are required to modify the perioperative pathway and introduce the concept of prehabilitation. Nursing staff are ideally positioned to be strong advocates to developing and delivering an effective MDT prehabilitation clinical pathway.

Objectives The aim of this study was to determine the influence of perioperative fluid management and administration of vasopressors on early surgical revision and flap-related complications in free tissue transfer. Materials and methods Intraoperative amount of fluid and of vasopressors, relevant perioperative parameters, and comorbidities were recorded in 131 patients undergoing head and neck microvascular reconstruction and compared with early surgical complications, defined as interventions requiring surgery after a flap-related complication, and/or other surgical problems in the operating room within 30 days after initial surgery. The relationship between perioperative variables for each revision category was determined using an optimized multiple logistic regression. Results The administration of diuretics (p=0.001) as a treatment for perioperative fluid overload and the type of flap (p=0.019) was associated with a higher risk of early surgical revisions. Perioperative fluid overload (p=0.039) is significantly related to flap-related complications. We found no effect of intraoperative administration of vasopressors on early surgical revisions (p=0.8) or on flap-related complications (norepinephrine p=0.6, dobutamine p=0.5). Conclusion Perioperative fluid overload is associated with higher risks of early surgical revision and flap-related complications. In contrast, the administration of vasopressors seemed to have no effect on either surgical revision rate or flap-related complications. Clinical relevance In patients receiving microvascular reconstructions, a balanced fluid administration perioperatively and a targeted use of vasopressors should be the necessary strategy to reduce the complication rates in head and neck surgery.

OBJECTIVE To assess if uninterrupted anticoagulant agents' administration affects blood loss and blood transfusion during open radical cystectomy (RC) and urinary diversion. PATIENTS AND METHODS We conducted an observational single-centre cohort study of a consecutive series of 1430 RC patients, between 2000 and 2020. Blood loss was depicted according to body weight and duration of surgery (mL/kg/h), and blood transfusion. The group 'with anticoagulant agents' was considered if surgery was performed with uninterrupted low-dose aspirin (ASS), oral anticoagulants (OAC) with an international normalised ratio (INR) goal of 2-2.5 or bridging with therapeutic low-molecular-weight heparin (LMWH). Outcomes were intraoperative blood loss, blood transfusion rate (separately analysed if administered within 24 h perioperatively or >24 h after surgery) and the 90-day major adverse cardiac events (MACE) rate. We used propensity score (PS)-matching analysis to adjust for imbalances between groups with or without anticoagulant agents. RESULTS The PS-matched median (interquartile range [IQR]) blood loss was 2.10 (1.50-2.94) mL/kg/h in patients with anticoagulant agents vs 2.11 (1.47-2.94) mL/kg/h without anticoagulant agents (Padj > 0.99). The PS-matched blood transfusion rates were 26.2% vs 35.1% (Padj = 0.875) within 24 h perioperatively and 57.0% vs 55.0% (Padj = 0.680) if administered >24 h postoperatively. A sub-analysis of the three different anticoagulant agents could not detect any significance between ASS, OAC, or LMWH. The PS-matched incidence of MACE was 9.1% in the group with anticoagulant agents and 8.1% in those without anticoagulant agents (Padj > 0.99). Limitations include selection bias and retrospective analysis from prospectively assessed data. CONCLUSIONS Perioperative continuation of ASS, uninterrupted OAC with low INR goal or bridging with LMWH had no impact on blood loss and transfusion rate in RC patients. Therefore, there might be no compulsory need for discontinuation of anticoagulant agents.

The activation of N-methyl-D-aspartate receptors (NMDARs) in substantia nigra pars compacta (SNc) dopamine (DA) cells is central to generate the bursting activity, a phasic signal linked to DA-related behaviours via the change in postsynaptic DA release. NMDARs are recruited during excitatory synaptic transmission by glutamate release, but the glycine site level of occupancy of these receptors during basal action potential-dependent activity is not known for SNc DA neurons. We explored NMDAR-dependent signals during exogenous applications of co-agonists in midbrain slices from juvenile rats. We found that both glycine and D-serine strengthened the NMDAR-dependent component of excitatory postsynaptic currents (EPSCs) in a concentration-dependent manner. EPSCs were also increased by endogenous glycine via the blockade of the glycine transport. The glycine site of NMDARs contributing to synaptic transmission is therefore subsaturated. The behaviourally relevant burst firing was more sensitive to exogenous D-serine and endogenous glycine than to exogenous glycine. The mechanisms regulating the availability of the co-agonists exert consequently a critical influence on the excitability of DA neurons via NMDARs. The modulation of the phasic firing in DA neurons by ambient NMDAR co-agonists may be important for nigral information processing and downstream motor-related behaviour.

Although several ionic mechanisms are known to control rate and regularity of the slow pacemaker in dopamine (DA) neurons, the core mechanism of pacing is controversial. Here we tested the hypothesis that pacemaking of SNc DA neurons is enabled by an unconventional conductance. We found that 1-(2,4-xylyl)guanidinium (XG), an established blocker of gating pore currents, selectively inhibits pacemaking of DA neurons. The compound inhibited all slow pacemaking DA neurons that were tested, both in the substantia nigra pars compacta, and in the ventral tegmental area. Interestingly, bursting behavior was not affected by XG. Furthermore, the drug did not affect fast pacemaking of GABAergic neurons from substantia nigra pars reticulata neurons or slow pacemaking of noradrenergic neurons. In DA neurons, current-clamp analysis revealed that XG did not appear to affect ion channels involved in the action potential. Its inhibitory effect persisted during blockade of all ion channels previously suggested to contribute to pacemaking. RNA sequencing and voltage-clamp recordings yielded no evidence for a gating pore current to underlie the conductance. However, we could isolate a small subthreshold XG-sensitive current, which was carried by both Na+ and Cl− ions. Although the molecular target of XG remains to be defined, these observations represent a step towards understanding pacemaking in DA neurons.

The aim of this study was to determine the influence of perioperative fluid management and administration of vasopressors on early surgical revision and flap-related complications in free tissue transfer.Intraoperative amount of fluid and of vasopressors, relevant perioperative parameters, and comorbidities were recorded in 131 patients undergoing head and neck microvascular reconstruction and compared with early surgical complications, defined as interventions requiring surgery after a flap-related complication, and/or other surgical problems in the operating room within 30 days after initial surgery. The relationship between perioperative variables for each revision category was determined using an optimized multiple logistic regression.The administration of diuretics (p=0.001) as a treatment for perioperative fluid overload and the type of flap (p=0.019) was associated with a higher risk of early surgical revisions. Perioperative fluid overload (p=0.039) is significantly related to flap-related complications. We found no effect of intraoperative administration of vasopressors on early surgical revisions (p=0.8) or on flap-related complications (norepinephrine p=0.6, dobutamine p=0.5).Perioperative fluid overload is associated with higher risks of early surgical revision and flap-related complications. In contrast, the administration of vasopressors seemed to have no effect on either surgical revision rate or flap-related complications.In patients receiving microvascular reconstructions, a balanced fluid administration perioperatively and a targeted use of vasopressors should be the necessary strategy to reduce the complication rates in head and neck surgery.

Although several ionic mechanisms are known to control rate and regularity of the pacemaker in dopamine (DA) neurons from the substantia nigra pars compacta (SNc), a conductance essential for pacing has yet to be defined. Here we provide pharmacological evidence that pacemaking of SNc DA neurons is enabled by an unconventional conductance. We found that 1-(2,4-xylyl)guanidine (XG), an established blocker of gating pore currents in mutant voltage gated sodium channels, selectively stops pacemaking of DA SNc neurons and is without effect on the main pore of their voltage-gated channels. We isolated a voltage-dependent, non-inactivating XG-sensitive current of 20-25 pA which operates in the relevant subthreshold range and is carried by both Na+ and Cl- ions. While the molecular identity of this conductance remains to be determined, we show that this XG-sensitive current is crucial to sustain pacemaking in these neurons.

BACKGROUND The impact of anaesthetic techniques on recurrence of cancers is controversial. Elevated plasma catecholamine levels have been implicated in angiogenesis and metastasis in various cancers. OBJECTIVES To assess the potential association between continuous intra-operative norepinephrine administration and tumour-related outcome in muscle-invasive bladder cancer patients undergoing radical cystectomy with urinary diversion. DESIGN Retrospective observational cohort study. SETTING Single tertiary centre, from 2000 to 2017. PATIENTS We included a consecutive series of 1120 urothelial carcinoma patients undergoing radical cystectomy and urinary diversion, including 411/1120 patients (37%) who received a continuous intra-operative administration of more than 2 μg kg BW h norepinephrine. MAIN OUTCOME MEASURES The primary outcome was time to tumour recurrence within 5 years after surgery, with death as competing outcome. We used inverse probability of treatment weighting to adjust for imbalances between treatment groups, one having received more than 2 μg kg BW h norepinephrine and the other having received less. We furthermore adjusted for intra-operative variables or years of surgery as sensitivity analyses. RESULTS The continuous administration of more than 2 μg kg BW h norepinephrine slightly increased tumour recurrence (hazard ratio: 1.47, 95% CI 0.98 to 2.21; P = 0.061). After adjustment for intra-operative variables, and year of surgery hazard ratios were 1.82 (95% CI 1.13 to 2.91, P = 0.013) and 1.85 (95% CI 1.12 to 3.07, P = 0.017), respectively. Overall mortality (with or without tumour recurrence) was not affected by norepinephrine (hazard ratio: 0.84, 95% CI 0.65 to 1.08, P = 0.170). CONCLUSION Continuous administration of more than 2 μg kg BW h norepinephrine was associated with a slightly increased hazard ratio for tumour recurrence if adjusted for intra-operative variables and year of surgery. This observation could reflect a low potential pro-oncogenic effect of norepinephrine during the intra-operative period. TRIAL REGISTRATION Not applicable.

In many neuronal types, axon initial segment (AIS) geometry critically influences neuronal excitability. Interestingly, the axon of rat SNc dopaminergic (DA) neurons displays a highly variable location and most often arises from an axon-bearing dendrite (ABD). We combined current-clamp somatic and dendritic recordings, outside-out recordings of dendritic sodium and potassium currents, morphological reconstructions and multicompartment modeling on male and female rat SNc DA neurons to determine cell-to-cell variations in AIS and ABD geometry, and their influence on neuronal output (spontaneous pacemaking frequency, action potential [AP] shape). Both AIS and ABD geometries were found to be highly variable from neuron to neuron. Surprisingly, we found that AP shape and pacemaking frequency were independent of AIS geometry. Modeling realistic morphological and biophysical variations helped us clarify this result: in SNc DA neurons, the complexity of the ABD combined with its excitability predominantly define pacemaking frequency and AP shape, such that large variations in AIS geometry negligibly affect neuronal output and are tolerated. SIGNIFICANCE STATEMENT In many neuronal types, axon initial segment (AIS) geometry critically influences neuronal excitability. In the current study, we describe large cell-to-cell variations in AIS length or distance from the soma in rat substantia nigra pars compacta dopaminergic neurons. Using neuronal reconstruction and electrophysiological recordings, we show that this morphological variability does not seem to affect their electrophysiological output, as neither action potential properties nor pacemaking frequency is correlated with AIS morphology. Realistic multicompartment modeling suggests that this robustness to AIS variation is mainly explained by the complexity and excitability of the somatodendritic compartment.

The aim of this review is to present an anesthesiological overview on surgical safety for radical cystectomy implementing the cornerstones of today's rapidly evolving field of perioperative medicine.This is a narrative review of current perioperative medicine and surgical safety concepts for major surgery in general with special focus on radical cystectomy.The tendency for perioperative care and surgical safety is to consider it a continuous proactive pathway rather than a single surgical intervention. It starts at indication for surgery and lasts until full functional recovery. Preoperative optimization leads to superior outcome by mobilizing and/or increasing physiological reserve. Multidisciplinary teamwork involving all the relevant parties from the beginning of the pathway is crucial for outcome rather than an isolated specialist approach. This fact has gained importance in times of an ageing frail population and rising health care cost. We also present our 2019 Cystectomy Enhanced Recovery Approach for optimization of perioperative care for open radical cystectomy in a high caseload center.With the implementation of in itself simple but crucial steps in perioperative medicine such as multimodal prehabilitation, safety checks, better perioperative monitoring and enhanced recovery concepts, even complex surgical procedures such as radical cystectomy can be performed safer. Emphasis has to be laid on a more global view of the patients' path through the perioperative process than on the surgical procedure alone.

Although small-conductance Ca(2+)-activated K(+) (SK) channels and various types of voltage-gated Ca(2+) (Cav) channels have been described in midbrain dopaminergic neurons, the nature of their interactions is unclear. More particularly, the role of various Cav channel types in either promoting irregularity of firing (by generating an inward current during SK channel blockade) or promoting regularity of firing (by providing the source of Ca(2+) for the activation of SK channels) has not been systematically explored. We addressed this question using intracellular and extracellular recordings from substantia nigra, pars compacta (SNc), dopaminergic neurons in rat midbrain slices. Neurons were pharmacologically isolated from their differences. When examining the ability of various Cav channel blockers to inhibit the SK-mediated afterhyperpolarization (AHP), we found that only the N-type Cav channel blocker ω-conotoxin-GVIA was able to reduce the apamin-sensitive AHP, but only partially (~40%). Specific blockers of L, P/Q, T or R channels had no effect on this AHP. Combining ω-conotoxin-GVIA and other specific blockers did not yield greater block and even the broad Cav blocker Cd(2+) induced a submaximal (~75%) effect. Extracellular recordings examining firing regularity yielded congruent results: none of the specific blockers was able to increase firing irregularity to the extent that the specific SK blocker apamin did. The irregularity of firing observed with apamin could only be reversed by blocking L-type Ca(2+) channels. Thus various sources of Ca(2+) appear to be required for SK channel activation in SNc neurons (some of them still unidentified), ensuring robustness of pacemaking regularity.

Dopaminergic (DA) neurons located in the ventral midbrain continuously generate a slow endogenous pacemaker activity, the mechanism of which is still debated. It has been suggested that, in the substantia nigra pars compacta (SNc), the pacemaking relies more on Ca(2+) channels and that the density of L-type Ca(2+) channels is higher in these DA neurons than in those located in the ventral tegmental area (VTA). This might lead to a higher Ca(2+) load in SNc DA neurons and explain their higher susceptibility to degeneration. However, direct evidence for this hypothesis is lacking. We found that the L-type current and channel density are indeed higher in the somata of rat SNc DA neurons and that this current undergoes less inactivation in this region. Nonstationary fluctuation analysis measurements showed a much higher number of L-type channels in the soma of SNc DA neurons, as well as a smaller single-channel conductance, pointing to a possible different molecular identity of L-type channels in DA neurons from the two areas. A major consequence of this is that pacemaking and, even more so, bursting are associated with a larger Ca(2+) entry through L-type channels in SNc DA neurons than in their VTA counterparts. Our results establish a molecular and functional difference between two populations of midbrain DA neurons that may contribute to their differential sensitivity to neurodegeneration. SIGNIFICANCE STATEMENT Dopamine neurons from the substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) are involved in various brain functions, such as movement initiation and goal directed behavior, respectively. This work shows that, although both neurons fire in a similar regular and slow pacemaker mode, this firing activity is supported by different calcium channel landscapes. Indeed, the L-type calcium current is larger in the soma of dopamine neurons of the SNc, leading to a higher charge transfer through L-type channels during pacemaking and bursting. Therefore, these neurons may be physiologically exposed to a larger stress than their neighbors from the VTA.

Key points The hyperpolarization-activated cation current Ih is expressed in dopamine neurons of the substantia nigra, but the subcellular distribution of the current and its role in synaptic integration remain unknown. We used cell-attached patch recordings to determine the localization profile of Ih along the somatodendritic axis of nigral dopamine neurons in slices from young rats. Ih density is higher in axon-bearing dendrites, in a membrane area close to the axon origin, than in the soma and axon-lacking dendrites. Dual current-clamp recordings revealed a similar contribution of Ih to the waveform of single excitatory postsynaptic potentials throughout the somatodendritic domain. The Ih blocker ZD 7288 increased the temporal summation in all dendrites with a comparable effect in axon- and non-axon dendrites. The strategic position of Ih in the proximity of the axon may influence importantly transitions between pacemaker and bursting activities and consequently the downstream release of dopamine. Abstract Dendrites of most neurons express voltage-gated ion channels in their membrane. In combination with passive properties, active currents confer to dendrites a high computational potential. The hyperpolarization-activated cation current Ih present in the dendrites of some pyramidal neurons affects their membrane and integration properties, synaptic plasticity and higher functions such as memory. A gradient of increasing h-channel density towards distal dendrites has been found to be responsible for the location independence of excitatory postsynaptic potential (EPSP) waveform and temporal summation in cortical and hippocampal pyramidal cells. However, reports on other cell types revealed that smoother gradients or even linear distributions of Ih can achieve homogeneous temporal summation. Although the existence of a robust, slowly activating Ih current has been repeatedly demonstrated in nigral dopamine neurons, its subcellular distribution and precise role in synaptic integration are unknown. Using cell-attached patch-clamp recordings, we find a higher Ih current density in the axon-bearing dendrite than in the soma or in dendrites without axon in nigral dopamine neurons. Ih is mainly concentrated in the dendritic membrane area surrounding the axon origin and decreases with increasing distances from this site. Single EPSPs and temporal summation are similarly affected by blockade of Ih in axon- and non-axon-bearing dendrites. The presence of Ih close to the axon is pivotal to control the integrative functions and the output signal of dopamine neurons and may consequently influence the downstream coding of movement.

Dendrites of dopaminergic neurons receive and convey synaptic input, support action potential back-propagation and neurotransmitter release. Understanding these fundamental functions will shed light on the information transfer in these neurons. Dendritic patch-clamp recordings provide the possibility to directly examine the electrical properties of dendrites and underlying voltage-gated ion channels. However, these fine structures are not easily accessible to patch pipettes because of their small diameter. This report describes a step-by-step procedure to collect stable and reliable recordings from the dendrites of dopaminergic neurons in acute slices. Electrophysiological measurements are combined with post hoc recovery of cell morphology. Successful experiments rely on improved preparation of slices, solutions and pipettes, adequate adjustment of the optics and stability of the pipette in contact with the recorded structure. Standard principles of somatic patch-clamp recording are applied to dendrites but with a gentler approach of the pipette. These versatile techniques can be implemented to address various questions concerning the excitable properties of dendrites.

Dopamine (DA) neurons and GABA neurons of the substantia nigra (SN) promote distinct functions in the control of movement and have different firing properties and action potential (AP) waveforms. APs recorded from DA and GABA neurons differed in amplitude, maximal rate of rise, and duration. In addition, the threshold potential for APs was higher in DA neurons than in GABA neurons. The activation of voltage-gated Na+channels accounts largely for these differences as the application of a low concentration of the voltage-gated Na+channel blocker TTX had an effect on all of these parameters. We have examined functional properties of somatic Na+channels in nucleated patches isolated from DA and GABA neurons. Peak amplitudes of macroscopic Na+currents were smaller in DA neurons in comparison to those in GABA neurons. The mean peak Na+conductance density was 24.5 pS μm−2in DA neurons and almost twice as large, 41.6 pS μm−2, in GABA neurons. The voltage dependence of Na+channel activation was not different between the two types of SN neurons. Na+channels in DA and GABA neurons, however, differed in the voltage dependence of inactivation, the mean mid-point potential of steady-state inactivation curve being more positive in DA neurons than in GABA neurons. The results suggest that specific Na+channel gating properties and Na+conductance densities in the somatic membrane of SN neurons may have consequences on synaptic signal integration in the soma of both types of neurons and on somatodendritic release of dopamine by DA neurons.

The hyperpolarization-activated cation current Ih is expressed in dopamine neurons of the substantia nigra, but the subcellular distribution of the current and its role in synaptic integration remain unknown. We used cell-attached patch recordings to determine the localization profile of Ih along the somatodendritic axis of nigral dopamine neurons in slices from young rats. Ih density is higher in axon-bearing dendrites, in a membrane area close to the axon origin, than in the soma and axon-lacking dendrites. Dual current-clamp recordings revealed a similar contribution of Ih to the waveform of single excitatory postsynaptic potentials throughout the somatodendritic domain. The Ih blocker ZD 7288 increased the temporal summation in all dendrites with a comparable effect in axon- and non-axon dendrites. The strategic position of Ih in the proximity of the axon may influence importantly transitions between pacemaker and bursting activities and consequently the downstream release of dopamine.Dendrites of most neurons express voltage-gated ion channels in their membrane. In combination with passive properties, active currents confer to dendrites a high computational potential. The hyperpolarization-activated cation current Ih present in the dendrites of some pyramidal neurons affects their membrane and integration properties, synaptic plasticity and higher functions such as memory. A gradient of increasing h-channel density towards distal dendrites has been found to be responsible for the location independence of excitatory postsynaptic potential (EPSP) waveform and temporal summation in cortical and hippocampal pyramidal cells. However, reports on other cell types revealed that smoother gradients or even linear distributions of Ih can achieve homogeneous temporal summation. Although the existence of a robust, slowly activating Ih current has been repeatedly demonstrated in nigral dopamine neurons, its subcellular distribution and precise role in synaptic integration are unknown. Using cell-attached patch-clamp recordings, we find a higher Ih current density in the axon-bearing dendrite than in the soma or in dendrites without axon in nigral dopamine neurons. Ih is mainly concentrated in the dendritic membrane area surrounding the axon origin and decreases with increasing distances from this site. Single EPSPs and temporal summation are similarly affected by blockade of Ih in axon- and non-axon-bearing dendrites. The presence of Ih close to the axon is pivotal to control the integrative functions and the output signal of dopamine neurons and may consequently influence the downstream coding of movement.

It is widely accepted that the hippocampus plays a major role in learning and memory. The mossy fiber synapse between granule cells in the dentate gyrus and pyramidal neurons in the CA3 region is a key component of the hippocampal trisynaptic circuit. Recent work, partially based on direct presynaptic patch-clamp recordings from hippocampal mossy fiber boutons, sheds light on the mechanisms of synaptic transmission and plasticity at mossy fiber synapses. A high Na(+) channel density in mossy fiber boutons leads to a large amplitude of the presynaptic action potential. Together with the fast gating of presynaptic Ca(2+) channels, this generates a large and brief presynaptic Ca(2+) influx, which can trigger transmitter release with high efficiency and temporal precision. The large number of release sites, the large size of the releasable pool of vesicles, and the huge extent of presynaptic plasticity confer unique strength to this synapse, suggesting a large impact onto the CA3 pyramidal cell network under specific behavioral conditions. The characteristic properties of the hippocampal mossy fiber synapse may be important for pattern separation and information storage in the dentate gyrus-CA3 cell network.

The nervous system adapts to experience by changes in synaptic strength. The mechanisms of synaptic plasticity include changes in the probability of transmitter release and in postsynaptic responsiveness. Experimental and neuropharmacological evidence points toward a third variable in synaptic efficacy: changes in presynaptic transmitter concentration. Several groups, including our own, have reported changes in the amplitude and frequency of postsynaptic (miniature) events indicating that alterations in transmitter content cause alterations in vesicular transmitter content and vesicle dynamics. It is, however, not a priori clear how transmitter metabolism will affect vesicular transmitter content and how this in turn will affect pre- and postsynaptic functions. We therefore have constructed a model of the presynaptic terminal incorporating vesicular transmitter loading and the presynaptic vesicle cycle. We hypothesize that the experimentally observed synaptic plasticity after changes in transmitter metabolism puts predictable restrictions on vesicle loading, cytoplasmic–vesicular transmitter concentration gradient, and on vesicular cycling or release. The results of our model depend on the specific mechanism linking presynaptic transmitter concentration to vesicular dynamics, that is, alteration of vesicle maturation or alteration of release. It also makes a difference whether differentially filled vesicles are detected and differentially processed within the terminal or whether vesicle filling acts back onto the terminal by presynaptic autoreceptors. Therefore, the model allows one to decide, at a given synapse, how transmitter metabolism is linked to presynaptic function and efficacy.

Hemmende Synapsen der hoheren Hirnareale sind uberwiegend GABAerg, d.h. sie verwenden den Transmitter γ-Aminobuttersaure. Diese Synapsen sind das Ziel verschiedener klassischer Antikonvulsiva, die durch Modulation des postsynaptischen GABAA-Rezeptors die Effizienz der Hemmung steigern. Daneben sind GABAerge Synapsen aber durch weitere Funktionselemente gekennzeichnet, insbesondere durch spezialisierte GABA-Transporter sowie durch die Schlusselenzyme des GABA-Metabolismus. Neuere Antikonvulsiva beeinflussen speziell diese Zielmolekule durch Hemmung der Transmitteraufnahme (GABA-Aufnahmehemmer, z.B. Tiagabin) sowie durch Blockade des Transmitterabbaus (GABA-Transaminase- Inhibitoren, z.B. Vigabatrin). Beide Wirkprinzipien fuhren mittels unterschiedlicher zellularer Mechanismen zu einer verstarkten Hemmung. Neuere Untersuchungen in vitro geben Hinweise darauf, dass die Wirkungsspektren dieser nichtkonventionellen GABAergen Pharmaka uber den Anwendungsbereich der langer etablierten Rezeptormodulatoren (Benzodiazepine und Barbiturate) hinausgehen. Diese alternativen pharmakologischen Konzepte zur Verstarkung der Inhibition bieten daher die Chance zur Entwicklung alternativer antikonvulsiver Strategien.

Formylation of morpholine with “supercritical” CO2 using the bidentate ruthenium catalyst RuCl2(dppe)2 affords high N-formylmorpholine production rate at almost 100% selectivity. The solventless reaction could be an interesting alternative to the present N-formylmorpholine synthesis routes, which are based on environmentally harmful formylation agents. Video monitoring of the reaction mixture during reaction revealed a complex phase behavior, including the formation of solid carbamate, which was most prominent at low conversion and gradually disappeared with higher conversion, i.e., with the formation of N-formylmorpholine and water as a by-product. Addition of water as an additive suppressed solid carbamate formation and enhanced the reaction rate. Infrared spectroscopy was applied to follow the changes in the liquid and dense gas phase. The ruthenium catalyst was confined to the liquid phase, containing morpholine, N-formylmorpholine, water, dissolved carbon dioxide and hydrogen. Although the solubility of the ruthenium catalyst in the liquid phase decreased with increasing conversion, good performance in the synthesis of N-formylmorpholine could be achieved.

1. The production of the central inhibitory transmitter GABA (gamma-aminobutyric acid) varies in response to different patterns of activity. It therefore seems possible that GABA metabolism can determine inhibitory synaptic strength and that presynaptic GABA content is a regulated parameter for synaptic plasticity. 2. We altered presynaptic GABA metabolism in cultured rat hippocampal slices using pharmacological tools. Degradation of GABA by GABA-transaminase (GABA-T) was blocked by gamma-vinyl-GABA (GVG) and synthesis of GABA through glutamate decarboxylase (GAD) was suppressed with 3-mercaptopropionic acid (MPA). We measured miniature GABAergic postsynaptic currents (mIPSCs) in CA3 pyramidal cells using the whole-cell patch clamp technique. 3. Elevated intra-synaptic GABA levels after block of GABA-T resulted in increased mIPSC amplitude and frequency. In addition, tonic GABAergic background noise was enhanced by GVG. Electron micrographs from inhibitory synapses identified by immunogold staining for GABA confirmed the enhanced GABA content but revealed no further morphological alterations. 4. The suppression of GABA synthesis by MPA had opposite functional consequences: mIPSC amplitude and frequency decreased and current noise was reduced compared with control. However, we were unable to demonstrate the decreased GABA content in biochemical analyses of whole slices or in electron micrographs. 5. We conclude that the transmitter content of GABAergic vesicles is variable and that postsynaptic receptors are usually not saturated, leaving room for up-regulation of inhibitory synaptic strength. Our data reveal a new mechanism of plasticity at central inhibitory synapses and provide a rationale for the activity-dependent regulation of GABA synthesis in mammals.

First we found that applying substances that change intracellular presynaptic GABA concentration alter the synaptic efficacy of hippocampal GABAergic neurons. The amplitude as well as the frequency of occurrence of spontaneous postsynaptic currents (mIPSCs) are affected. Then, we developed a model of presynaptic vesicle dynamics to better understand the causal relationship between cytosolic GABA concentration and mIPSC amplitude and frequency. One way to explain our experimental findings is to postulate that the filling of vesicles as well as their transition into the readily releasable pool depends on vesicular GABA content.

GABA uptake is crucial for the termination of inhibitory synaptic events. In addition, GABA transporters may also control the level of diffusely distributed GABA in the extracellular space. We analysed this function by superfusing rat hippocampal slices with different concentrations of GABA. Whole-cell patch clamp recordings of CA1 pyramidal cells revealed small increases in chloride conductance at 5-10 microM GABA which increased dramatically upon addition of the GABA uptake blocker tiagabine. Tiagabine alone induced a significant chloride conductance indicating that spontaneous release of GABA in hippocampal slices is neutralized by GAT-1, the main hippocampal GABA transporter. Thus, GAT-1 clears the extracellular space in the hippocampus from diffusely distributed GABA with high efficacy.

Vigabatrin (gamma-vinyl-GABA, VGB) is a gamma-aminobutyric acid (GABA) derivative designed to boost synaptic inhibition by inhibiting the degradation of GABA in brain tissue. Indeed, VGB shows potent anti-convulsant activity in animal models of epilepsy and in humans with complex partial seizures. However, details of the mechanism of action of VGB are not well understood and the systemic effects include possible pro-convulsant actions. We therefore analysed the effects of VGB in rat brain slices in the low-Mg(2+) model in vitro. VGB at 100 microM-5 mM showed a concentration- and time-dependent reduction of interictal-like events in the hippocampal CA1 region. Likewise, VGB suppressed epileptiform discharges in the medial entorhinal cortex (mEC), which are known to resist conventional anti-convulsants. In contrast, evoked population spikes in CA1 (which became repetitive after washout Mg(2+)) were not altered by VGB. Our data show that VGB is efficient against epileptiform discharges in temporal structures including pharmacoresistant patterns of activity. The waveform of evoked population spikes in this in vitro model is no indicator for the anti-convulsant properties of drugs.

Rigorous analysis of synaptic transmission in the central nervous system requires access to presynaptic terminals. However, cortical terminals have been largely inaccessible to presynaptic patch-clamp recording, due to their small size. Using improved patch-clamp techniques in brain slices, we recorded from mossy fiber terminals in the CA3 region of the hippocampus, which have a diameter of 2-5 microm. The major steps of improvement were the enhanced visibility provided by high-numerical aperture objectives and infrared illumination, the development of vibratomes with minimal vertical blade vibrations and the use of sucrose-based solutions for storage and cutting. Based on these improvements, we describe a protocol that allows us to routinely record from hippocampal mossy fiber boutons. Presynaptic recordings can be obtained in slices from both rats and mice. Presynaptic recordings can be also obtained in slices from transgenic mice in which terminals are labeled with enhanced green fluorescent protein.

Action potentials in central neurons are initiated near the axon initial segment, propagate into the axon, and finally invade the presynaptic terminals, where they trigger transmitter release. Voltage-gated Na(+) channels are key determinants of excitability, but Na(+) channel density and properties in axons and presynaptic terminals of cortical neurons have not been examined yet. In hippocampal mossy fiber boutons, which emerge from parent axons en passant, Na(+) channels are very abundant, with an estimated number of approximately 2000 channels per bouton. Presynaptic Na(+) channels show faster inactivation kinetics than somatic channels, suggesting differences between subcellular compartments of the same cell. Computational analysis of action potential propagation in axon-multibouton structures reveals that Na(+) channels in boutons preferentially amplify the presynaptic action potential and enhance Ca(2+) inflow, whereas Na(+) channels in axons control the reliability and speed of propagation. Thus, presynaptic and axonal Na(+) channels contribute differentially to mossy fiber synaptic transmission.

After release, neurotransmitters are removed from the extracellular space by high-affinity uptake. Specific sodium-dependent transporters serve this function for the inhibitory transmitter gamma-aminobutyric acid (GABA). However, it is largely unknown to which proportion GABA is taken up by GABAergic interneurons, glia cells or principal neurons. We analyzed the distribution of mRNA for the main GABA-transporter subtype in the hippocampus, GAT-1, in adult rats. Most interneurons were strongly stained for GAT-1 mRNA, indicating re-uptake by the GABA-releasing cells. Surprisingly, prominent signals for GAT-1 were also found throughout the principal cell layers (granule and pyramidal cells). These data indicate that GABA transporters may be present in non-GABAergic projection cells of the rat hippocampus which contribute to the clearance of GABA from the extracellular space.