Sensing in Sacral Neuromodulation: A Feasibility Study in Subjects With Urinary Incontinence and Retention.

OBJECTIVES: Sacral neuromodulation (SNM) therapy standard of care relies on visual-motor responses and patient-reported sensory responses in deciding optimized lead placement and programming. Automatic detection of stimulation responses could offer a simple, consistent indicator for optimizing SNM. The purpose of this study was to measure and characterize sacral evoked responses (SERs) resulting from sacral nerve stimulation using a commercial, tined SNM lead. MATERIALS AND METHODS: A custom external research system with stimulation and sensing hardware was connected to the percutaneous extension of an implanted lead during a staged (tined lead) evaluation for SNM. The system collected SER recordings across a range of prespecified stimulation settings (electrode configuration combinations for bipolar stimulation and bipolar sensing) during intraoperative and postoperative sessions in 21 subjects with overactive bladder (OAB) and nonobstructive urinary retention (NOUR). Motor and sensory thresholds were collected during the same sessions. RESULTS: SERs were detected in all 21 subjects. SER morphology (number of peaks, magnitude, and timing) varied across electrode configurations within and across subjects. Among subjects and electrode configurations tested, recordings contained SERs at motor threshold and/or sensory threshold in 75% to 80% of subjects. CONCLUSIONS: This study confirmed that implanted SNM leads can be used to directly record SERs elicited by stimulation in subjects with OAB and NOUR. SERs were readily detectable at typical SNM stimulation settings and procedural time points. Using these SERs as possible objective measures of SNM response has the capability to automate patient-specific SNM therapy, potentially providing consistent lead placement, programming, and/or closed-loop therapy.

Rationale and design of an implant procedure and pivotal study to evaluate safety and effectiveness of Medtronic's tibial neuromodulation device.

Percutaneous tibial neuromodulation is a medical guideline recommended therapy for treating symptoms of overactive bladder. Stimulation is delivered to the tibial nerve via a thin needle placed percutaneously for 30 min once a week for 12-weeks, and monthly thereafter. Studies have shown that this therapy can effectively relieve symptoms of overactive bladder; however, the frequent office visits present a barrier to patients and can impact therapy effectiveness. To mitigate the burden of frequent clinic visits, small implantable devices are being developed to deliver tibial neuromodulation. These devices are implanted during a single minimally invasive procedure and deliver stimulation intermittently, similar to percutaneous tibial neuromodulation. Here, we describe the implant procedure and design of a pivotal study evaluating the safety and effectiveness for an implantable tibial neuromodulation device. The Evaluation of Implantable Tibial Neuromodulation (TITAN 2) pivotal study is a prospective, multicenter, investigational device exemption study being conducted at up to 30 sites in the United States and enrolling subjects with symptoms of overactive bladder.

Evaluation of clinical performance and safety for the rechargeable InterStim Micro device in overactive bladder subjects: 6-month results from the global postmarket ELITE study.

AIMS: Sacral neuromodulation (SNM) is an advanced therapy option for the treatment of overactive bladder (OAB), nonobstructive urinary retention, and fecal incontinence. The aim of this ongoing prospective, multicenter, global, postmarket study is to confirm safety and clinical performance of the InterStimTM Micro system for SNM in all indications. Reported here are the results for the OAB cohort through 6-month follow-up. METHODS: Eligible OAB subjects that had a successful therapy evaluation were enrolled after implant of an InterStim Micro implantable pulse generator (IPG). Subjects completed voiding diaries and the Overactive Bladder Quality of Life questionnaire (OAB-q) at baseline and follow-up visits occurring at 3 months and 6 months postimplant. Safety was evaluated as device-, procedure-, or therapy-related adverse events. The primary objective for the OAB cohort was to demonstrate an improvement in OAB-q Health Related Quality of Life (HRQL) total score at 3 months postimplant compared to baseline. RESULTS: Sixty-eight OAB subjects were enrolled and implanted with an InterStim Micro IPG. Of those, 67 and 66 subjects completed the 3- and 6-month follow-up visits, respectively. The OAB-q HRQL demonstrated a statistically significant improvement from baseline to 3-month follow-up with an average increase of 33 ± 24 points (n = 67, p < 0.001). The change was also observed at 6-months with an average increase of 31 ± 23 points (n = 65) compared to baseline. Eighty-two percent of subjects achieved the minimally important difference in HRQL score at 3- and 6-month, respectively, with a change of 10 points or greater. The majority of subjects reported that their bladder condition was better at 3-month (92.5%, 62/67) and 6-month (89%, 59/66) compared to before they were treated with SNM therapy delivered by the InterStim Micro system. For subjects with urgency urinary incontinence (UUI), the average change from baseline to follow-up in UUI episodes/day was -3.6 (95% CI: -4.7, -2.6; n = 62) at 3-month and -3.7 (95% CI: -4.7, -2.7; n = 61) at 6-month. Among subjects with urgency-frequency (UF), the average change from baseline to follow up in voids/day was -4.5 (95% CI: -6.3, -2.7; n = 52) at 3-months and -4.4 (95% CI: -6.0, -2.7; n = 52) at 6-month. The cumulative incidence of device-, procedure-, or therapy- related adverse events was 7.4% (5/68). Out of these five related adverse events, there was one serious adverse event (1.5%, implant site pain) at the time of database snapshot. CONCLUSIONS: These data confirm the safety and clinical performance of the InterStim Micro device for subjects with OAB by demonstrating a significant improvement in OAB-q HRQL score at 3-month. Similar improvements were observed at 6 months in addition to an incidence of adverse events that is comparable to previously reported rates for SNM.

Prospective, multicenter study to evaluate performance and safety of a re-engineered temporary lead for InterStim™ therapy evaluation.

AIMS: The basic evaluation or percutaneous nerve evaluation (PNE) is a method to assess pre-implantation therapeutic response in patients considering sacral neuromodulation for the treatment of refractory overactive bladder. A new PNE lead with a more robust design and greater distensibility designed to reduce the possibility of lead migration has recently been introduced to the market. The aim of this prospective, multicenter, global, postmarket study was to evaluate the clinical performance and safety of the new InterStim PNE lead with the foramen needle. METHODS: Patients with overactive bladder were enrolled in this study. The primary objective of this study was to determine the proportion of subjects who demonstrated motor or sensory response(s) during lead placement using the InterStim PNE lead. Additional measures included the Patient Global Impression of Improvement (PGI-I), patient satisfaction at the end of therapy evaluation, and change in bladder symptoms from baseline to the end of therapy evaluation (1-week follow-up visit). RESULTS: One-hundred and ten subjects met the inclusion and exclusion criteria and underwent a lead implant procedure. Of those, 108 had a successful procedure and 107 completed the 1-week follow-up visit. Ninety-nine percent of subjects (109/110) had a motor or sensory response during needle placement (95% confidence interval [CI]: 95%-100%) and 97% of subjects (107/110) had a motor or sensory response during lead placement (95% CI: 92%-99%). The majority of subjects (88%, 95/108) reported their bladder condition was better at the follow-up visit compared to before the PNE implant procedure, as reported in PGI-I. Subjects reported being satisfied with how the therapy impacted their voiding symptoms (82%, 88/108) and that they would recommend this therapy (87%, 94/108) to other patients. Symptom improvement was demonstrated with urinary urge incontinence subjects having an average of 4.2 ± 3.4 urinary incontinence episodes/day at baseline and 2.2 ± 2.5 at follow-up, and urinary frequency subjects having an average of 12.5 ± 4.4 voids/day at baseline and 10.5 ± 4.3 voids/day at follow-up. Lead removal was deemed to be easy and safe by the implanting physician, with a total of three adverse device effects in 3/110 subjects. No event was categorized as serious and all were resolved without sequelae. CONCLUSIONS: The updated InterStim PNE lead with a more robust design and greater distensibility designed to reduce migration was shown to have a high rate of motor or sensory response during lead placement. Furthermore, subjects reported high rates of global improvements and amelioration of symptoms, and the lead was easy to remove with minimal morbidity.

Closed-loop sacral neuromodulation for bladder function using dorsal root ganglia sensory feedback in an anesthetized feline model.

Overactive bladder patients suffer from a frequent, uncontrollable urge to urinate, which can lead to a poor quality of life. We aim to improve open-loop sacral neuromodulation therapy by developing a conditional stimulation paradigm using neural recordings from dorsal root ganglia (DRG) as sensory feedback. Experiments were performed in 5 anesthetized felines. We implemented a Kalman filter-based algorithm to estimate the bladder pressure in real-time using sacral-level DRG neural recordings and initiated sacral root electrical stimulation when the algorithm detected an increase in bladder pressure. Closed-loop neuromodulation was performed during continuous cystometry and compared to bladder fills with continuous and no stimulation. Overall, closed-loop stimulation increased bladder capacity by 13.8% over no stimulation (p < 0.001) and reduced stimulation time versus continuous stimulation by 57.7%. High-confidence bladder single units had a reduced sensitivity during stimulation, with lower linear trendline fits and higher pressure thresholds for firing observed during stimulation trials. This study demonstrates the utility of decoding bladder pressure from neural activity for closed-loop control of sacral neuromodulation. An underlying mechanism for sacral neuromodulation may be a reduction in bladder sensory neuron activity during stimulation. Real-time validation during behavioral studies is necessary prior to clinical translation of closed-loop sacral neuromodulation.

Bidirectional synaptic plasticity rapidly modifies hippocampal representations.

Learning requires neural adaptations thought to be mediated by activity-dependent synaptic plasticity. A relatively non-standard form of synaptic plasticity driven by dendritic calcium spikes, or plateau potentials, has been reported to underlie place field formation in rodent hippocampal CA1 neurons. Here, we found that this behavioral timescale synaptic plasticity (BTSP) can also reshape existing place fields via bidirectional synaptic weight changes that depend on the temporal proximity of plateau potentials to pre-existing place fields. When evoked near an existing place field, plateau potentials induced less synaptic potentiation and more depression, suggesting BTSP might depend inversely on postsynaptic activation. However, manipulations of place cell membrane potential and computational modeling indicated that this anti-correlation actually results from a dependence on current synaptic weight such that weak inputs potentiate and strong inputs depress. A network model implementing this bidirectional synaptic learning rule suggested that BTSP enables population activity, rather than pairwise neuronal correlations, to drive neural adaptations to experience.

A new housing development in a familiar neighborhood, a wrong turn that ends up lengthening a Sunday stroll: our internal representation of the world requires constant updating, and we need to be able to associate events separated by long intervals of time to finetune future outcome. This often requires neural connections to be altered. A brain region known as the hippocampus is involved in building and maintaining a map of our environment. However, signals from other brain areas can activate silent neurons in the hippocampus when the body is in a specific location by triggering cellular events called dendritic calcium spikes. Milstein et al. explored whether dendritic calcium spikes in the hippocampus could also help the brain to update its map of the world by enabling neurons to stop being active at one location and to start responding at a new position. Experiments in mice showed that calcium spikes could change which features of the environment individual neurons respond to by strengthening or weaking connections between specific cells. Crucially, this mechanism allowed neurons to associate event sequences that unfold over a longer timescale that was more relevant to the ones encountered in day-to-day life. A computational model was then put together, and it demonstrated that dendritic calcium spikes in the hippocampus could enable the brain to make better spatial decisions in future. Indeed, these spikes are driven by inputs from brain regions involved in complex cognitive processes, potentially enabling the delayed outcomes of navigational choices to guide changes in the activity and wiring of neurons. Overall, the work by Milstein et al. advances the understanding of learning and memory in the brain and may inform the design of better systems for artificial learning.

Mild traumatic brain injury induced by primary blast overpressure produces dynamic regional changes in [18F]FDG uptake.

Changes in 18F-fluorodeoxyglucose ([18F]FDG) measured by positron emission tomography (PET) can be used for the noninvasive detection of metabolic dysfunction following mild traumatic brain injury (mTBI). This study examined the time course of metabolic changes induced by primary blast injury by measuring regional [18F]FDG uptake. Adult, male rats were exposed to blast overpressure (15 psi) or sham injury, and [18F]FDG uptake was measured before injury and again at 1-3 h and 7 days post-injury, using both volume-of-interest (VOI) and voxel-based analysis. VOI analysis revealed significantly increased [18F]FDG uptake in corpus callosum and amygdala at both 1-3 h and 7 days following blast, while a transient decrease in uptake was observed in the midbrain at 1-3 h only. Voxel-based analysis revealed similar significant differences in uptake between sham and blast-injured rats at both time points. At 1-3 h post-injury, clusters of increased uptake were found in the amygdala, somatosensory cortex, and corpus callosum, while regions of decreased uptake were observed in midbrain structures (inferior colliculus, ventrolateral tegmental area) and dorsal auditory cortex. At day 7, a region of increased uptake in blast-injured rats was found in a cluster centered on the cortex-amygdala transition zone, while no regions of decreased uptake were observed. These results suggest that a relatively mild primary blast injury results in altered brain metabolism in multiple brain regions and that post-injury time of assessment is an important factor in observing regional changes in [18F]FDG uptake.

Neurocognitive Driving Rehabilitation in Virtual Environments (NeuroDRIVE): A pilot clinical trial for chronic traumatic brain injury.

BACKGROUND: Virtual reality (VR) technology may provide an effective means to integrate cognitive and functional approaches to TBI rehabilitation. However, little is known about the effectiveness of VR rehabilitation for TBI-related cognitive deficits. In response to these clinical and research gaps, we developed Neurocognitive Driving Rehabilitation in Virtual Environments (NeuroDRIVE), an intervention designed to improve cognitive performance, driving safety, and neurobehavioral symptoms. OBJECTIVE: This pilot clinical trial was conducted to examine feasibility and preliminary efficacy of NeuroDRIVE for rehabilitation of chronic TBI. METHODS: Eleven participants who received the intervention were compared to six wait-listed participants on driving abilities, cognitive performance, and neurobehavioral symptoms. RESULTS: The NeuroDRIVE intervention was associated with significant improvements in working memory and visual search/selective attention- two cognitive skills that represented a primary focus of the intervention. By comparison, no significant changes were observed in untrained cognitive areas, neurobehavioral symptoms, or driving skills. CONCLUSIONS: Results suggest that immersive virtual environments can provide a valuable and engaging means to achieve some cognitive rehabilitation goals, particularly when these goals are closely matched to the VR training exercises. However, additional research is needed to augment our understanding of rehabilitation for driving skills, cognitive performance, and neurobehavioral symptoms in chronic TBI.

Discordance between Documented Criteria and Documented Diagnosis of Traumatic Brain Injury in the Emergency Department.

Accurate diagnosis of traumatic brain injury (TBI) is critical to ensure that patients receive appropriate follow-up care, avoid risk of subsequent injury, and are aware of possible long-term consequences. However, diagnosis of TBI, particularly in the emergency department (ED), can be difficult because the symptoms of TBI are vague and nonspecific, and patients with suspected TBI may present with additional injuries that require immediate medical attention. We performed a retrospective chart review to evaluate accuracy of TBI diagnosis in the ED. Records of 1641 patients presenting to the ED with suspected TBI and a head computed tomography (CT) were reviewed. We found only 47% of patients meeting the American Congress of Rehabilitation Medicine criteria for TBI received a documented ED diagnosis of TBI in medical records. After controlling for demographic and clinical factors, patients presenting at a level I trauma center, with cause of injury other than fall, without CT findings of TBI, and without loss of consciousness were more likely to lack documented diagnosis despite meeting diagnostic criteria for TBI. A greater proportion of patients without documented ED diagnosis of TBI were discharged home compared to those with a documented diagnosis of TBI (58% vs. 40%; p < 0.001). Together, these data suggest that many patients who have sustained a TBI are discharged home from the ED without a documented diagnosis of TBI, and that improved awareness and implementation of diagnostic criteria for TBI is important in the ED and for in- and outpatient providers.

Biochemical markers of striatal desensitization in cortical-limbic hyperglutamatergic TS- & OCD-like transgenic mice.

Tics and compulsions in comorbid Tourette's syndrome (TS) and obsessive-compulsive disorder (OCD) are associated with chronic hyperactivity of parallel cortico/amygdalo-striato-thalamo-cortical (CSTC) loop circuits. Comorbid TS- & OCD-like behaviors have likewise been observed in D1CT-7 mice, in which an artificial neuropotentiating transgene encoding the cAMP-elevating intracellular subunit of cholera toxin (CT) is chronically expressed selectively in somatosensory cortical & amygdalar dopamine (DA) D1 receptor-expressing neurons that activate cortico/amygdalo-striatal glutamate (GLU) output. We've now examined in D1CT-7 mice whether the chronic GLU output from their potentiated cortical/limbic CSTC subcircuit afferents associated with TS- & OCD-like behaviors elicits desensitizing neurochemical changes in the striatum (STR). Microdialysis-capillary electrophoresis and in situ hybridization reveal that the mice's chronic GLU-excited STR exhibits pharmacodynamic changes in three independently GLU-regulated measures of output neuron activation, co-excitation, and desensitization, signifying hyperactive striatal CSTC output and compensatory striatal glial and neuronal desensitization: 1) Striatal GABA, an output neurotransmitter induced by afferent GLU, is increased. 2) Striatal d-serine, a glial excitatory co-transmitter inhibited by afferent GLU, is decreased. 3) Striatal Period1 (Per1), which plays a non-circadian role in the STR as a GLU + DA D1- (cAMP-) dependent repressor thought to feedback-inhibit GLU + DA- triggered ultradian urges and motions, is transcriptionally abolished. These data imply that chronic cortical/limbic GLU excitation of the STR desensitizes its co-excitatory d-serine & DA inputs while freezing its GABA output in an active state to mediate chronic tics and compulsions - possibly in part by abolishing striatal Per1-dependent ultradian extinction of urges and motions.

Behavioral time scale synaptic plasticity underlies CA1 place fields.

Learning is primarily mediated by activity-dependent modifications of synaptic strength within neuronal circuits. We discovered that place fields in hippocampal area CA1 are produced by a synaptic potentiation notably different from Hebbian plasticity. Place fields could be produced in vivo in a single trial by potentiation of input that arrived seconds before and after complex spiking. The potentiated synaptic input was not initially coincident with action potentials or depolarization. This rule, named behavioral time scale synaptic plasticity, abruptly modifies inputs that were neither causal nor close in time to postsynaptic activation. In slices, five pairings of subthreshold presynaptic activity and calcium (Ca2+) plateau potentials produced a large potentiation with an asymmetric seconds-long time course. This plasticity efficiently stores entire behavioral sequences within synaptic weights to produce predictive place cell activity.

Inhibitory suppression of heterogeneously tuned excitation enhances spatial coding in CA1 place cells.

Place cells in the CA1 region of the hippocampus express location-specific firing despite receiving a steady barrage of heterogeneously tuned excitatory inputs that should compromise output dynamic range and timing. We examined the role of synaptic inhibition in countering the deleterious effects of off-target excitation. Intracellular recordings in behaving mice demonstrate that bimodal excitation drives place cells, while unimodal excitation drives weaker or no spatial tuning in interneurons. Optogenetic hyperpolarization of interneurons had spatially uniform effects on place cell membrane potential dynamics, substantially reducing spatial selectivity. These data and a computational model suggest that spatially uniform inhibitory conductance enhances rate coding in place cells by suppressing out-of-field excitation and by limiting dendritic amplification. Similarly, we observed that inhibitory suppression of phasic noise generated by out-of-field excitation enhances temporal coding by expanding the range of theta phase precession. Thus, spatially uniform inhibition allows proficient and flexible coding in hippocampal CA1 by suppressing heterogeneously tuned excitation.

Current perspectives on the use of fetal fibronectin testing in preterm labor diagnosis and management.

One in 10 infants in the United States is delivered preterm (ie, before the 37th week of pregnancy), contributing to the significant burden on the national healthcare system. Nevertheless, a lack of agreement continues among obstetric professional societies on guidelines for standardization of the approach to the diagnosis and management of patients with symptoms of preterm labor (PTL). This disparity in consensus has likely resulted in poor identification of women at an increased risk for preterm birth (PTB). This paper presents an overview of several clinical guidelines and recommendations from a variety of studies regarding the use of fetal fibronectin (fFN) testing and transvaginal ultrasound (TVU) cervical length measurement, 2 tools that are used to assess the risk of spontaneous PTB (sPTB) in women with symptoms of PTL. We identify areas of commonality and discord within these publications. Although inconsistencies exist among the published guidelines, algorithms, and studies on how to diagnose and treat women with symptoms of PTL, each of them supports the use of fFN in conjunction with TVU for assessing the risk of sPTB. In addition, we review a case study from a regional hospital system with results demonstrating the benefits to patients and process outcomes when PTL assessment protocols are standardized, incorporating both fFN and TVU test results. In the absence of consensus on this topic, healthcare providers, administrators, and payers must navigate conflicting recommendations and identify areas of agreement for this evaluation within their own local settings.

Axonal Filtering Allows Reliable Output during Dendritic Plateau-Driven Complex Spiking in CA1 Neurons.

In CA1 pyramidal neurons, correlated inputs trigger dendritic plateau potentials that drive neuronal plasticity and firing rate modulation. Given the strong electrotonic coupling between soma and axon, the >25 mV depolarization associated with the plateau could propagate through the axon to influence action potential initiation, propagation, and neurotransmitter release. We examined this issue in brain slices, awake mice, and a computational model. Despite profoundly inactivating somatic and proximal axon Na(+) channels, plateaus evoked action potentials that recovered to full amplitude in the distal axon (>150 µm) and triggered neurotransmitter release similar to regular spiking. This effect was due to strong attenuation of plateau depolarizations by axonal K(+) channels, allowing full axon repolarization and Na(+) channel deinactivation. High-pass filtering of dendritic plateaus by axonal K(+) channels should thus enable accurate transmission of gain-modulated firing rates, allowing neuronal firing to be efficiently read out by downstream regions as a simple rate code.

"Hyperglutamatergic cortico-striato-thalamo-cortical circuit" breaker drugs alleviate tics in a transgenic circuit model of Tourette׳s syndrome.

The brain circuits underlying tics in Tourette׳s syndrome (TS) are unknown but thought to involve cortico/amygdalo-striato-thalamo-cortical (CSTC) loop hyperactivity. We previously engineered a transgenic mouse "circuit model" of TS by expressing an artificial neuropotentiating transgene (encoding the cAMP-elevating, intracellular A1 subunit of cholera toxin) within a small population of dopamine D1 receptor-expressing somatosensory cortical and limbic neurons that hyperactivate cortico/amygdalostriatal glutamatergic output circuits thought to be hyperactive in TS and comorbid obsessive-compulsive (OC) disorders. As in TS, these D1CT-7 ("Ticcy") transgenic mice׳s tics were alleviated by the TS drugs clonidine and dopamine D2 receptor antagonists; and their chronic glutamate-excited striatal motor output was unbalanced toward hyperactivity of the motoric direct pathway and inactivity of the cataleptic indirect pathway. Here we have examined whether these mice׳s tics are countered by drugs that "break" sequential elements of their hyperactive cortical/amygdalar glutamatergic and efferent striatal circuit: anti-serotonoceptive and anti-noradrenoceptive corticostriatal glutamate output blockers (the serotonin 5-HT2a,c receptor antagonist ritanserin and the NE alpha-1 receptor antagonist prazosin); agmatinergic striatothalamic GABA output blockers (the presynaptic agmatine/imidazoline I1 receptor agonist moxonidine); and nigrostriatal dopamine output blockers (the presynaptic D2 receptor agonist bromocriptine). Each drug class alleviates tics in the Ticcy mice, suggesting a hyperglutamatergic CSTC "tic circuit" could exist in TS wherein cortical/amygdalar pyramidal projection neurons׳ glutamatergic overexcitation of both striatal output neurons and nigrostriatal dopaminergic modulatory neurons unbalances their circuit integration to excite striatothalamic output and create tics, and illuminating new TS drug strategies.

Conjunctive input processing drives feature selectivity in hippocampal CA1 neurons.

Feature-selective firing allows networks to produce representations of the external and internal environments. Despite its importance, the mechanisms generating neuronal feature selectivity are incompletely understood. In many cortical microcircuits the integration of two functionally distinct inputs occurs nonlinearly through generation of active dendritic signals that drive burst firing and robust plasticity. To examine the role of this processing in feature selectivity, we recorded CA1 pyramidal neuron membrane potential and local field potential in mice running on a linear treadmill. We found that dendritic plateau potentials were produced by an interaction between properly timed input from entorhinal cortex and hippocampal CA3. These conjunctive signals positively modulated the firing of previously established place fields and rapidly induced new place field formation to produce feature selectivity in CA1 that is a function of both entorhinal cortex and CA3 input. Such selectivity could allow mixed network level representations that support context-dependent spatial maps.

Ion channel gradients in the apical tuft region of CA1 pyramidal neurons.

Dendritic ion channels play a critical role in shaping synaptic input and are fundamentally important for synaptic integration and plasticity. In the hippocampal region CA1, somato-dendritic gradients of AMPA receptors and the hyperpolarization-activated cation conductance (I(h)) counteract the effects of dendritic filtering on the amplitude, time-course, and temporal integration of distal Schaffer collateral (SC) synaptic inputs within stratum radiatum (SR). While ion channel gradients in CA1 distal apical trunk dendrites within SR have been well characterized, little is known about the patterns of ion channel expression in the distal apical tuft dendrites within stratum lacunosum moleculare (SLM) that receive distinct input from the entorhinal cortex via perforant path (PP) axons. Here, we measured local ion channels densities within these distal apical tuft dendrites to determine if the somato-dendritic gradients of I(h) and AMPA receptors extend into distal tuft dendrites. We also determined the densities of voltage-gated sodium channels and NMDA receptors. We found that the densities of AMPA receptors, I(h,) and voltage-gated sodium channels are similar in tuft dendrites in SLM when compared with distal apical dendrites in SR, while the ratio of NMDA receptors to AMPA receptors increases in tuft dendrites relative to distal apical dendrites within SR. These data indicate that the somato-dendritic gradients of I(h) and AMPA receptors in apical dendrites do not extend into the distal tuft, and the relative densities of voltage-gated sodium channels and NMDA receptors are poised to support nonlinear integration of correlated SC and PP input.

The relationship between single-channel and whole-cell conductance in the T-type Ca2+ channel CaV3.1.

In T-type Ca(2+) channels, macroscopic I(Ba) is usually smaller than I(Ca), but at high Ca(2+) and Ba(2+), single-channel conductance (gamma) is equal. We investigated gamma as a function of divalent concentration and compared it to macroscopic currents using Ca(V)3.1 channels studied under similar experimental conditions (TEA(o) and K(i)). Single-channel current-voltage relationships were nonlinear in a way similar to macroscopic open-channel I/Vs, so divalent gamma was underestimated at depolarized voltages. To estimate divalent gamma, concentration dependence, i(Div), was measured at voltages <-50 mV. Data were well described by Langmuir isotherms with gamma(max)(Ca(2+)) of 9.5 +/- 0.4 pS and gamma(max)(Ba(2+)) of 10.3 +/- 0.5 pS. Apparent K(M) was lower for Ca(2+) (2.3 +/- 0.7 mM) than for Ba(2+) (7.9 +/- 1.3 mM). A subconductance state with an amplitude 70% that of the main state was observed, the relative occupancy of which increased with increasing Ca(2+). As predicted by gamma, macroscopic G(maxCa) was larger than G(maxBa) at 5 mM (G(max)Ca(2+)/Ba:(2+)1.43 +/- 0.14) and similar at 60 mM (G(max)Ca(2+)/Ba:(2+)1.10 +/- 0.02). However, over the range of activation, I(Ca) was larger than I(Ba) under both conditions. This was a consequence of the fact that V(rev) was more negative for I(Ba) than for I(Ca), so that the driving force determining I(Ba) was smaller than that determining I(Ca) over the range of potentials in standard current-voltage relationships.