TRPC Channels Activated by G Protein-Coupled Receptors Drive Ca2+ Dysregulation Leading to Secondary Brain Injury in the Mouse Model.

Canonical transient receptor potential (TRPC) non-selective cation channels, particularly those assembled with TRPC3, TRPC6, and TRPC7 subunits, are coupled to Gαq-type G protein-coupled receptors for the major classes of excitatory neurotransmitters. Sustained activation of this TRPC channel-based pathophysiological signaling hub in neurons and glia likely contributes to prodigious excitotoxicity-driven secondary brain injury expansion. This was investigated in mouse models with selective Trpc gene knockout (KO). In adult cerebellar brain slices, application of glutamate and the class I metabotropic glutamate receptor agonist (S)-3,5-dihydroxyphenylglycine to Purkinje neurons expressing the GCaMP5g Ca2+ reporter demonstrated that the majority of the Ca2+ loading in the molecular layer dendritic arbors was attributable to the TRPC3 effector channels (Trpc3KO compared with wildtype (WT)). This Ca2+ dysregulation was associated with glutamate excitotoxicity causing progressive disruption of the Purkinje cell dendrites (significantly abated in a GAD67-GFP-Trpc3KO reporter brain slice model). Contribution of the Gαq-coupled TRPC channels to secondary brain injury was evaluated in a dual photothrombotic focal ischemic injury model targeting cerebellar and cerebral cortex regions, comparing day 4 post-injury in WT mice, Trpc3KO, and Trpc1/3/6/7 quadruple knockout (TrpcQKO), with immediate 2-h (primary) brain injury. Neuroprotection to secondary brain injury was afforded in both brain regions by Trpc3KO and TrpcQKO models, with the TrpcQKO showing greatest neuroprotection. These findings demonstrate the contribution of the Gαq-coupled TRPC effector mechanism to excitotoxicity-based secondary brain injury expansion, which is a primary driver for mortality and morbidity in stroke, traumatic brain injury, and epilepsy.

Sex-Dependent Effects of Chronic Microdrive Implantation on Acquisition of Trace Eyeblink Conditioning.

Neuroscience techniques, including in vivo recording, have allowed for a great expansion in knowledge; however, this technology may also affect the very phenomena researchers set out to investigate. Including both female and male mice in our associative learning experiments shed light on sex differences on the impact of chronic implantation of tetrodes on learning. While previous research showed intact female mice acquired trace eyeblink conditioning faster than male and ovariectomized females, implantation of chronic microdrive arrays showed sexually dimorphic effects on learning. Microdrive implanted male mice acquired the associative learning paradigm faster than both intact and ovariectomized females. These effects were not due to the weight of the drive alone, as there were no significant sex-differences in learning of animals that received "dummy drive" implants without tetrodes lowered into the brain. Tandem mass tag mass spectrometry and western blot analysis suggest that significant alterations in the MAPK pathway, acute inflammation, and brain derived neurotrophic factor may underlie these observed sex- and surgery-dependent effects on learning.

A Corticothalamic Circuit Trades off Speed for Safety during Decision-Making under Motivational Conflict.

Decisions to act while pursuing goals in the presence of danger must be made quickly but safely. Premature decisions risk injury or death, whereas postponing decisions risk goal loss. Here we show how mice resolve these competing demands. Using microstructural behavioral analyses, we identified the spatiotemporal dynamics of approach-avoidance decisions under motivational conflict in male mice. Then we used cognitive modeling to show that these dynamics reflect the speeded decision-making mechanisms used by humans and nonhuman primates, with mice trading off decision speed for safety of choice when danger loomed. Using calcium imaging in paraventricular thalamus and optogenetic inhibition of the prelimbic cortex to paraventricular thalamus pathway, we show that this speed-safety trade off occurs because increases in paraventricular thalamus activity increase decision caution, thereby increasing approach-avoid decision times in the presence of danger. Our findings demonstrate that a discrete brain circuit involving the paraventricular thalamus and its prefrontal input adjusts decision caution during motivational conflict, trading off decision speed for decision safety when danger is close. We identify the corticothalamic pathway as central to cognitive control during decision-making under conflict.SIGNIFICANCE STATEMENT Foraging animals balance the need to seek food and energy against the conflicting needs to avoid injury and predation. This competition is fundamental to survival but rarely has a stable, correct solution. Here we show that approach-avoid decisions under motivational conflict involve strategic adjustments in decision caution controlled via a top-down corticothalamic pathway from the prelimbic cortex to the paraventricular thalamus. We identify a novel corticothalamic mechanism for cognitive control that is applicable across a range of motivated behaviors and mark paraventricular thalamus and its prefrontal cortical input as targets to remediate the deficits in decision caution characteristic of unsafe and impulsive choices.

The Roles of Basolateral Amygdala Parvalbumin Neurons in Fear Learning.

The basolateral amygdala (BLA) is obligatory for fear learning. This learning is linked to BLA excitatory projection neurons whose activity is regulated by complex networks of inhibitory interneurons, dominated by parvalbumin (PV)-expressing GABAergic neurons. The roles of these GABAergic interneurons in learning to fear and learning not to fear, activity profiles of these interneurons across the course of fear learning, and whether or how these change across the course of learning all remain poorly understood. Here, we used PV cell-type-specific recording and manipulation approaches in male transgenic PV-Cre rats during pavlovian fear conditioning to address these issues. We show that activity of BLA PV neurons during the moments of aversive reinforcement controls fear learning about aversive events, but activity during moments of nonreinforcement does not control fear extinction learning. Furthermore, we show expectation-modulation of BLA PV neurons during fear learning, with greater activity to an unexpected than expected aversive unconditioned stimulus (US). This expectation-modulation was specifically because of BLA PV neuron sensitivity to aversive prediction error. Finally, we show that BLA PV neuron function in fear learning is conserved across these variations in prediction error. We suggest that aversive prediction-error modulation of PV neurons could enable BLA fear-learning circuits to retain selectivity for specific sensory features of aversive USs despite variations in the strength of US inputs, thereby permitting the rapid updating of fear associations when these sensory features change.SIGNIFICANCE STATEMENT The capacity to learn about sources of danger in the environment is essential for survival. This learning depends on complex microcircuitries of inhibitory interneurons in the basolateral amygdala. Here, we show that parvalbumin-positive GABAergic interneurons in the rat basolateral amygdala are important for fear learning during moments of danger, but not for extinction learning during moments of safety, and that the activity of these neurons is modulated by expectation of danger. This may enable fear-learning circuits to retain selectivity for specific aversive events across variations in expectation, permitting the rapid updating of learning when aversive events change.

Phasic inhibition of dopamine neurons is an instrumental punisher.

It is well established that the activity of VTA dopamine neurons is sufficient to serve as a Pavlovian reinforcer but whether this activity can also serve as instrumental reinforcer is less well understood. Here we studied the effects of optogenetic inhibition of VTA dopamine neurons in instrumental conditioning preparations. We show that optogenetic inhibition of VTA dopamine neurons causes a response-specific, contingency-sensitive suppression of instrumental responding. This suppression was due to instrumental response, not Pavlovian stimulus, learning and could not be attributed to deepened instrumental extinction learning. These effects of optogenetic inhibition of VTA dopamine neurons on instrumental responding are formally similar to the effects of aversive events in instrumental preparations and show that optogenetic inhibition of VTA dopamine neurons is sufficient to serve as an instrumental punisher. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Long-term depression of excitatory transmission in the lateral septum.

Neurons in the lateral septum (LS) integrate glutamatergic synaptic inputs, primarily from hippocampus, and send inhibitory projections to brain regions involved in reward and the generation of motivated behavior. Motivated learning and drugs of abuse have been shown to induce long-term changes in the strength of glutamatergic synapses in the LS, but the cellular mechanisms underlying long-term synaptic modification in the LS are poorly understood. Here, we examined synaptic transmission and long-term depression (LTD) in brain slices prepared from male and female C57BL/6 mice. No sex differences were observed in whole cell patch-clamp recordings of α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid receptor (AMPA-R)- and N-methyl-d-aspartate receptor (NMDA-R)-mediated currents. Low-frequency stimulation of the fimbria fiber bundle (1 Hz 15 min) induced LTD of the LS field excitatory postsynaptic potential (fEPSP). Induction of LTD was blocked by the NMDA-R antagonist (d)-2-amino-5-phosphonovaleric acid (APV), but not the selective antagonist of GluN2B-containing NMDA-Rs ifenprodil. These results demonstrate the NMDA-R dependence of LTD in the LS. The LS is a sexually dimorphic structure, and sex differences in glutamatergic transmission have been reported in vivo; our results suggest sex differences observed in vivo result from network activity rather than intrinsic differences in glutamatergic transmission.NEW & NOTEWORTHY The lateral septum (LS) integrates information from hippocampus and other regions to provide context-dependent (top down or higher order) regulation of mood and motivated behavior. Learning and drugs of abuse induce long-term changes in the strength of glutamatergic projections to the LS; however, the cellular mechanisms underlying such changes are poorly understood. Here, we demonstrate there are no apparent sex differences in fast excitatory transmission and that long-term synaptic depression in the LS is NMDA-R dependent.

The Mesolimbic Dopamine Activity Signatures of Relapse to Alcohol-Seeking.

The mesolimbic dopamine system comprises distinct compartments supporting different functions in learning and motivation. Less well understood is how complex addiction-related behaviors emerge from activity patterns across these compartments. Here we show how different forms of relapse to alcohol-seeking in male rats are assembled from activity across the VTA and the nucleus accumbens. First, we used chemogenetic approaches to show a causal role for VTA TH neurons in two forms of relapse to alcohol-seeking: renewal (context-induced reinstatement) and reacquisition. Then, using gCaMP fiber photometry of VTA TH neurons, we identified medial and lateral VTA TH neuron activity profiles during self-administration, renewal, and reacquisition. Next, we used optogenetic inhibition of VTA TH neurons to show distinct causal roles for VTA subregions in distinct forms of relapse. We then used dLight fiber photometry to measure dopamine binding across the ventral striatum (medial accumbens shell, accumbens core, lateral accumbens shell) and showed complex and heterogeneous profiles of dopamine binding during self-administration and relapse. Finally, we used representational similarity analysis to identify mesolimbic dopamine signatures of self-administration, extinction, and relapse. Our results show that signatures of relapse can be identified from heterogeneous activity profiles across the mesolimbic dopamine system and that these signatures are unique for different forms of relapse.SIGNIFICANCE STATEMENT It is axiomatic that the actions of dopamine are critical to drug addiction. Yet how relapse to drug-seeking is assembled from activity across the mesolimbic dopamine system is poorly understood. Here we show how relapse to alcohol-seeking relates to activity in specific VTA and accumbens compartments, how these change for different forms of relapse, and how relapse-associated activity relates to activity during self-administration and extinction. We report the mesolimbic dopamine activity signatures for relapse and show that these signatures are unique for different forms of relapse.

Contingency awareness, aging, and the parietal lobe.

Contingency awareness is thought to rely on an intact medial temporal lobe and also appears to be a function of age, as older subjects tend to be less aware. The current investigation used functional magnetic resonance imaging, transcranial direct current stimulation, and eyeblink classical conditioning to study brain processes related to contingency awareness as a function of age. Older adults were significantly less aware of the relationship between the tone-airpuff pairings than younger adults. Greater right parietal functional magnetic resonance imaging activation was associated with higher levels of contingency awareness for younger and older subjects. Cathodal transcranial direct current stimulation over the right parietal lobe led to lower levels of awareness in younger subjects without disrupting conditioned responses. Older adults exhibited hyperactivations in the parietal and medial temporal lobes, despite showing no conditioning deficits. These findings strongly support the idea that the parietal cortex serves as a substrate for contingency awareness and that age-related disruption of this region is sufficient to impair awareness, which may be a manifestation of some form of naturally occurring age-related neglect.

Awareness and differential eyeblink conditioning: effects of manipulating auditory CS frequencies.

The role of awareness in differential delay eyeblink conditioning (EBC) has been a topic of much debate. We tested the idea that awareness is required for differential delay EBC when two cues are perceptually similar. The present study manipulated frequencies of auditory conditioned stimuli (CS) to vary CS similarity in three groups of participants. Our findings indicate that awareness was not necessary for differential delay EBC when two tones are easily discriminable, awareness was also not needed for relatively similar tones but may facilitate earlier conditioning, and awareness alone was not sufficient for differential delay EBC.

Complementary Roles for Ventral Pallidum Cell Types and Their Projections in Relapse.

The ventral pallidum (VP) is a key node in the neural circuits controlling relapse to drug seeking. How this role relates to different VP cell types and their projections is poorly understood. Using male rats, we show how different forms of relapse to alcohol-seeking are assembled from VP cell types and their projections to lateral hypothalamus (LH) and ventral tegmental area (VTA). Using RNAScope in situ hybridization to characterize activity of different VP cell types during relapse to alcohol-seeking provoked by renewal (context-induced reinstatement), we found that VP Gad1 and parvalbumin (PV), but not vGlut2, neurons show relapse-associated changes in c-Fos expression. Next, we used retrograde tracing, chemogenetic, and electrophysiological approaches to study the roles of VPGad1 and VPPV neurons in relapse. We show that VPGad1 neurons contribute to contextual control over relapse (renewal), but not to relapse during reacquisition, via projections to LH, where they converge with ventral striatal inputs onto LHGad1 neurons. This convergence of striatopallidal inputs at the level of individual LHGad1 neurons may be critical to balancing propensity for relapse versus abstinence. In contrast, VPPV neurons contribute to relapse during both renewal and reacquisition via projections to VTA. These findings identify a double dissociation in the roles for different VP cell types and their projections in relapse. VPGad1 neurons control relapse during renewal via projections to LH. VPPV neurons control relapse during both renewal and reacquisition via projections to VTA. Targeting these different pathways may provide tailored interventions for different forms of relapse.SIGNIFICANCE STATEMENT Relapse to drug or reward seeking after a period of extinction or abstinence remains a key impediment to successful treatment. The ventral pallidum, located in the ventral basal ganglia, has long been recognized as an obligatory node in a 'final common pathway' for relapse. Yet how this role relates to the considerable VP cellular and circuit heterogeneity is not well understood. We studied the cellular and circuit architecture for VP in relapse control. We show that different forms of relapse have complementary VP cellular and circuit architectures, raising the possibility that targeting these different neural architectures may provide tailored interventions for different forms of relapse.

Making light work of fine-tuning channelrhodopsins.

The development of genetically engineered proteins that can control cell excitability with light have revolutionized our understanding of the nervous system. The most widely used of these optogenetic tools is the light-gated ion channel, channelrhodopsin 2 (ChR2). A new study by Cho et al. describes the development of ChR2 variants with improved photocurrents and more selective ion permeability using an automated multifaceted fluorescence-based screening. This methodological framework holds promise not only in refining features of ChR2, but also for other proteins in which fluorescence phenotyping is possible.

Distinct Accumbens Shell Output Pathways Promote versus Prevent Relapse to Alcohol Seeking.

Contexts exert bi-directional control over relapse to drug seeking. Contexts associated with drug self-administration promote relapse, whereas contexts associated with the absence of self-administration protect against relapse. The nucleus accumbens shell (AcbSh) is a key brain region determining these roles of context. However, the specific cell types, and projections, by which AcbSh serves these dual roles are unknown. Here, we show that contextual control over relapse and abstinence is embedded within distinct output circuits of dopamine 1 receptor (Drd1) expressing AcbSh neurons. We report anatomical and functional segregation of Drd1 AcbSh output pathways during context-induced reinstatement and extinction of alcohol seeking. The AcbSh→ventral tegmental area (VTA) pathway promotes relapse via projections to VTA Gad1 neurons. The AcbSh→lateral hypothalamus (LH) pathway promotes extinction via projections to LH Gad1 neurons. Targeting these opposing AcbSh circuit contributions may reduce propensity to relapse to, and promote abstinence from, drug use.

Focal Ischaemic Infarcts Expand Faster in Cerebellar Cortex than Cerebral Cortex in a Mouse Photothrombotic Stroke Model.

It is generally accepted that the cerebellum is particularly vulnerable to ischaemic injury, and this may contribute to the high mortality arising from posterior circulation strokes. However, this has not been systematically examined in an animal model. This study compared the development and resolution of matched photothrombotic microvascular infarcts in the cerebellar and cerebral cortices in adult 129/SvEv mice of both sexes. The photothrombotic lesions were made using tail vein injection of Rose Bengal with a 532 nm laser projected onto a 2 mm diameter aperture over the target region of the brain (with skull thinning). Infarct size was then imaged histologically following 2 h to 30-day survival using serial reconstruction of haematoxylin and eosin stained cryosections. This was complemented with immunohistochemistry for neuron and glial markers. At 2 h post-injury, the cerebellar infarct volume averaged ~ 2.7 times that of the cerebral cortex infarcts. Infarct volume reached maximum in the cerebellum in a quarter of the time (24 h) taken in the cerebral cortex (4 days). Remodelling resolved the infarcts within a month, leaving significantly larger residual injury volume in the cerebellum. The death of neurons in the core lesion at 2 h was confirmed by NeuN and Calbindin immunofluorescence, alongside activation of astrocytes and microglia. The latter persisted in the region within and surrounding the residual infarct at 30 days. This comparison of acute focal ischaemic injuries in cerebellar and cerebral cortices provides direct confirmation of exacerbation of neuropathology and faster kinetics in the cerebellum.

The rabbit as a behavioral model system for magnetic resonance imaging.

BACKGROUND: fMRI requires that subjects not move during image acquisition. This has been achieved by instructing people not to move, or by anesthetizing experimental animal subjects to induce immobility. We have demonstrated that a surgically implanted headbolt onto the skull of a rabbit allows their brain to be imaged comfortably while the animal is awake. This article provides a detailed method for the preparation. NEW METHOD: We took advantage of the rabbit's tolerance for restraint to image the brain while holding the head at the standard stereotaxic angle. Visual stimulation was produced by flashing green LEDs and whisker stimulation was done by powering a small coil of wire attached to a fiber band. Blinking was recorded with an infrared emitter/detector directed at the eye with fiber-optic cabling. RESULTS: Results indicate that a single daily session of habituation is sufficient to produce adequate immobility on subsequent days to avoid movement artifacts. Results include high resolution images in the stereotaxic plane of the rabbit. COMPARISON WITH EXISTING METHOD(S): We see no degradation or distortion of MR signal, and the headbolt provides a means for rapid realignment of the head in the magnet from day to day, and across subjects. The use of rabbits instead of rodents allows much shorter periods of habituation, and the rabbit allows behavior to be observed during the day while the animal is in its normal wake cycle. CONCLUSIONS: The natural tolerance of the rabbit for restraint makes it a valuable subject for MRI studies of the brain.

Basolateral Amygdala Neurons Maintain Aversive Emotional Salience.

BLA neurons serve a well-accepted role in fear conditioning and fear extinction. However, the specific learning processes related to their activity at different times during learning remain poorly understood. We addressed this using behavioral tasks isolating distinct aspects of fear learning in male rats. We show that brief optogenetic inhibition of BLA neurons around moments of aversive reinforcement or nonreinforcement causes reductions in the salience of conditioned stimuli, rendering these stimuli less able to be learned about and less able to control fear or safety behaviors. This salience reduction was stimulus-specific, long-lasting, and specific to learning about, or responding to, the same aversive outcome, precisely the goals of therapeutic interventions in human anxiety disorders. Our findings identify a core learning process disrupted by brief BLA optogenetic inhibition. They show that a primary function of the unconditioned stimulus-evoked activity of BLA neurons is to maintain the salience of conditioned stimuli that precede it. This maintenance of salience is a necessary precursor for these stimuli to gain and maintain control over fear and safety behavior.SIGNIFICANCE STATEMENT The amygdala is essential for learning to fear and learning to reduce fear. However, the specific roles served by activity of different amygdala neurons at different times during learning is poorly understood. We used behavioral tasks isolating distinct aspects of learning in rats to show that brief optogenetic inhibition of BLA neurons around moments of reinforcement or nonreinforcement disrupts maintenance of conditioned stimulus salience. This causes a stimulus-specific and long-lasting deficit in the ability of the conditioned stimulus to be learned about or control fear responses. These consequences are the precisely goals of therapeutic interventions in human anxiety disorders. Our findings identify a core learning process disrupted by brief BLA optogenetic inhibition.

Dendritic Organization of Olfactory Inputs to Medial Amygdala Neurons.

The medial amygdala (MeA) is a central hub in the olfactory neural network. It receives vomeronasal information directly from the accessory olfactory bulb (AOB) and main olfactory information largely via odor-processing regions such as the olfactory cortical amygdala (CoA). How these inputs are processed by MeA neurons is poorly understood. Using the GAD67-GFP mouse, we show that MeA principal neurons receive convergent AOB and CoA inputs. Somatically recorded AOB synaptic inputs had slower kinetics than CoA inputs, suggesting that they are electrotonically more distant. Field potential recording, pharmacological manipulation, and Ca(2+) imaging revealed that AOB synapses are confined to distal dendrites and segregated from the proximally located CoA synapses. Moreover, unsynchronized AOB inputs had significantly broader temporal summation that was dependent on the activation of NMDA receptors. These findings show that MeA principal neurons process main and accessory olfactory inputs differentially in distinct dendritic compartments. Significance statement: In most vertebrates, olfactory cues are processed by two largely segregated neural pathways, the main and accessory olfactory systems, which are specialized to detect odors and nonvolatile chemosignals, respectively. Information from these two pathways ultimately converges at higher brain regions, one of the major hubs being the medial amygdala. Little is known about how olfactory inputs are processed by medial amygdala neurons. This study shows that individual principal neurons in this region receive input from both pathways and that these synapses are spatially segregated on their dendritic tree. We provide evidence suggesting that this dendritic segregation leads to distinct input integration and impact on neuronal output; hence, dendritic mechanisms control olfactory processing in the amygdala.

Septal Glucagon-Like Peptide 1 Receptor Expression Determines Suppression of Cocaine-Induced Behavior.

Glucagon-like peptide 1 (GLP-1) and its receptor GLP-1R are a key component of the satiety signaling system, and long-acting GLP-1 analogs have been approved for the treatment of type-2 diabetes mellitus. Previous reports demonstrate that GLP-1 regulates glucose homeostasis alongside the rewarding effects of food. Both palatable food and illicit drugs activate brain reward circuitries, and pharmacological studies suggest that central nervous system GLP-1 signaling holds potential for the treatment of addiction. However, the role of endogenous GLP-1 in the attenuation of reward-oriented behavior, and the essential domains of the mesolimbic system mediating these beneficial effects, are largely unknown. We hypothesized that the central regions of highest Glp-1r gene activity are essential in mediating responses to drugs of abuse. Here, we show that Glp-1r-deficient (Glp-1r(-/-)) mice have greatly augmented cocaine-induced locomotor responses and enhanced conditional place preference compared with wild-type (Glp-1r(+/+)) controls. Employing mRNA in situ hybridization we located peak Glp-1r mRNA expression in GABAergic neurons of the dorsal lateral septum, an anatomical site with a crucial function in reward perception. Whole-cell patch-clamp recordings of dorsal lateral septum neurons revealed that genetic Glp-1r ablation leads to increased excitability of these cells. Viral vector-mediated Glp-1r gene delivery to the dorsal lateral septum of Glp-1r(-/-) animals reduced cocaine-induced locomotion and conditional place preference to wild-type levels. This site-specific genetic complementation did not affect the anxiogenic phenotype observed in Glp-1r(-/-) controls. These data reveal a novel role of GLP-1R in dorsal lateral septum function driving behavioral responses to cocaine.

Dendritic spine heterogeneity and calcium dynamics in basolateral amygdala principal neurons.

Glutamatergic synapses on pyramidal neurons are formed on dendritic spines where glutamate activates ionotropic receptors, and calcium influx via N-methyl-d-aspartate receptors leads to a localized rise in spine calcium that is critical for the induction of synaptic plasticity. In the basolateral amygdala, activation of metabotropic receptors is also required for synaptic plasticity and amygdala-dependent learning. Here, using acute brain slices from rats, we show that, in basolateral amygdala principal neurons, high-frequency synaptic stimulation activates metabotropic glutamate receptors and raises spine calcium by releasing calcium from inositol trisphosphate-sensitive calcium stores. This spine calcium release is unevenly distributed, being present in proximal spines, but largely absent in more distal spines. Activation of metabotropic receptors also generated calcium waves that differentially invaded spines as they propagated toward the soma. Dendritic wave invasion was dependent on diffusional coupling between the spine and parent dendrite which was determined by spine neck length, with waves preferentially invading spines with short necks. Spine calcium is a critical trigger for the induction of synaptic plasticity, and our findings suggest that calcium release from inositol trisphosphate-sensitive calcium stores may modulate homosynaptic plasticity through store-release in the spine head, and heterosynaptic plasticity of unstimulated inputs via dendritic calcium wave invasion of the spine head.

Functional MRI of cerebellar activity during eyeblink classical conditioning in children and adults.

This study characterized human cerebellar activity during eyeblink classical conditioning (EBC) in children and adults using functional magnetic resonance imaging (fMRI). During fMRI, participants were administered delay conditioning trials, in which the conditioned stimulus (a tone) precedes, overlaps, and coterminates with the unconditioned stimulus (a corneal airpuff). Behavioral eyeblink responses and brain activation were measured concurrently during two phases: pseudoconditioning, involving presentations of tone alone and airpuff alone, and conditioning, during which the tone and airpuff were paired. Although all participants demonstrated significant conditioning, the adults produced more conditioned responses (CRs) than the children. When brain activations during pseudoconditioning were subtracted from those elicited during conditioning, significant activity was distributed throughout the cerebellar cortex (Crus I-II, lateral lobules IV-IX, and vermis IV-VI) in all participants, suggesting multiple sites of associative learning-related plasticity. Despite their less optimal behavioral performance, the children showed greater responding in the pons, lateral lobules VIII, IX, and Crus I, and vermis VI, suggesting that they may require greater activation and/or the recruitment of supplementary structures to achieve successful conditioning. Correlation analyses relating brain activations to behavioral CRs showed a positive association of activity in cerebellar deep nuclei (including dentate, fastigial, and interposed nuclei) and vermis VI with CRs in the children. This is the first study to compare cerebellar cortical and deep nuclei activations in children versus adults during EBC.

Percutaneous re-circulating isolated limb perfusion of gentamicin in a large animal model: targeted delivery of gentamicin to limb.

OBJECTIVE: We have developed a percutaneous recirculation system (V-Vascular, V-V) to enable delivery of high levels of antibiotic to the limb in an isolated and targeted manner for the treatment of limb infection. BACKGROUND: Chronic and acute limb infections are relatively commonplace in a variety of wound types. Infection can become refractory to existing treatment strategies and can cause complications associated with wound healing, lead to amputation and even death. METHODS: Gentamicin was delivered to the ovine hind limb (4 mg/kg) using the V-V system, a 'closed' recirculatory catheter system that draws blood from the venous system and returns it to the artery via an oxygenator, or via intra-venous (IV) infusion. Samples of muscle, bone and synovial fluid of the limb were collected at 30 and 60 min post administration of gentamicin. RESULTS: There was a significantly greater concentration of gentamicin observed in the bone and skeletal muscle of limbs receiving the antibiotic via V-V at 30 min post administration compared to IV delivery, (bone V-V 0.05 ± 0.04, I.V 0.004 ± 0.001 mg/L p<0.05; muscle V-V 0.005 ± 0.001, I.V 0.002 ± 0.0005 mg/L p<0.05) and bone and synovial fluid at 60 min post administration (bone V-V 0.06 ± 0.02, I.V 0.005 ± 0.001 mg/L p<0.05; synovial fluid V-V 34.58 ± 14.9, I.V 3.03 ± 0.59 mg/L p<0.05). CONCLUSIONS: These results suggest that the use of percutaneous recirculation is a safe and effective method for delivering a greater concentration of antibiotic to the limb without systemic implications.