Reflectionless grating couplers for Silicon-on-Insulator photonic integrated circuits.

We propose a novel grating coupler design which is inherently reflectionless by focusing the reflected light away from the entrance waveguide. The design rules for this reflectionless grating coupler are explained and the grating coupler design is investigated by means of 3D FDTD simulations for the case of a Silicon-on-Insulator based platform.

Quantitative myelin imaging with coherent anti-Stokes Raman scattering microscopy: alleviating the excitation polarization dependence with circularly polarized laser beams.

The use of coherent anti-Stokes Raman scattering microscopy tuned to the lipid vibration for quantitative myelin imaging suffers from the excitation polarization dependence of this third-order nonlinear optical effect. The contrast obtained depends on the orientation of the myelin membrane, which in turn affects the morphometric parameters that can be extracted with image analysis. We show how circularly polarized laser beams can be used to avoid this complication, leading to images free of excitation polarization dependence. The technique promises to be optimal for in vivo imaging and the resulting images can be used for coherent anti-Stokes Raman scattering optical histology on native state tissue.

A Wireless Optoelectronic Neuroscience Platform for Chronic Fluorescence Sensing in Freely Behaving Rodents.

We present a new head mountable wireless fiber biophotometry microsystem conceived to detect fluorescent signal fluctuations correlated with neuronal activity. The proposed system incorporates all aspects of a conventional tethered fiber-based biophotometry system encompassed into a wireless microsystem. The interface includes an LED as excitation light source, a custom designed CMOS biosensor, a multimode fiber, a microcontroller (MCU), and a wireless data transceiver enclosed within a 3D-printed, small and light weight, plastic housing. Precisely, the system incorporates a new optoelectronic biosensor merging two individual building blocks, namely a low-noise sensing front-end and $\mathrm {a}2 ^{nd}$ order continuous-time $\Sigma \Delta $ modulator (CTSDM), into a single module for enabling high-sensitivity and high energy-efficiency photo-sensing. The proposed CMOS biosensor is implemented in $\mathrm {a}0 .18- \mu m$ CMOS technology, consuming $41 \mu W$ from $\mathrm {a}1 .8- V$ supply voltage, while achieving a peak dynamic range of $86 dB$ over a $50- Hz$ input bandwidth at a 20-kS/s sampling rate. This new interface opens new avenues for conducting in-vivo experiments with live animals.

Striatal Neurons Expressing D1 and D2 Receptors are Morphologically Distinct and Differently Affected by Dopamine Denervation in Mice.

The loss of nigrostriatal dopamine neurons in Parkinson's disease induces a reduction in the number of dendritic spines on medium spiny neurons (MSNs) of the striatum expressing D1 or D2 dopamine receptor. Consequences on MSNs expressing both receptors (D1/D2 MSNs) are currently unknown. We looked for changes induced by dopamine denervation in the density, regional distribution and morphological features of D1/D2 MSNs, by comparing 6-OHDA-lesioned double BAC transgenic mice (Drd1a-tdTomato/Drd2-EGFP) to sham-lesioned animals. D1/D2 MSNs are uniformly distributed throughout the dorsal striatum (1.9% of MSNs). In contrast, they are heterogeneously distributed and more numerous in the ventral striatum (14.6% in the shell and 7.3% in the core). Compared to D1 and D2 MSNs, D1/D2 MSNs are endowed with a smaller cell body and a less profusely arborized dendritic tree with less dendritic spines. The dendritic spine density of D1/D2 MSNs, but also of D1 and D2 MSNs, is significantly reduced in 6-OHDA-lesioned mice. In contrast to D1 and D2 MSNs, the extent of dendritic arborization of D1/D2 MSNs appears unaltered in 6-OHDA-lesioned mice. Our data indicate that D1/D2 MSNs in the mouse striatum form a distinct neuronal population that is affected differently by dopamine deafferentation that characterizes Parkinson's disease.

Development and Implementation of a Registry of Patients Attending Multidisciplinary Pain Treatment Clinics: The Quebec Pain Registry.

The Quebec Pain Registry (QPR) is a large research database of patients suffering from various chronic pain (CP) syndromes who were referred to one of five tertiary care centres in the province of Quebec (Canada). Patients were monitored using common demographics, identical clinical descriptors, and uniform validated outcomes. This paper describes the development, implementation, and research potential of the QPR. Between 2008 and 2013, 6902 patients were enrolled in the QPR, and data were collected prior to their first visit at the pain clinic and six months later. More than 90% of them (mean age ± SD: 52.76 ± 4.60, females: 59.1%) consented that their QPR data be used for research purposes. The results suggest that, compared to patients with serious chronic medical disorders, CP patients referred to tertiary care clinics are more severely impaired in multiple domains including emotional and physical functioning. The QPR is also a powerful and comprehensive tool for conducting research in a "real-world" context with 27 observational studies and satellite research projects which have been completed or are underway. It contains data on the clinical evolution of thousands of patients and provides the opportunity of answering important research questions on various aspects of CP (or specific pain syndromes) and its management.

Bridging the cleft at GABA synapses in the brain.

A fragile balance between excitation and inhibition maintains the normal functioning of the CNS. The dominant inhibitory neurotransmitter of the mammalian brain is GABA, which acts mainly through GABAA and GABAB receptors. Small changes in GABA-mediated inhibition can alter neuronal excitability profoundly and, therefore, a wide range of compounds that clearly modify GABAA-receptor function are used clinically as anesthetics or for the treatment of various nervous system disorders. Recent findings have started to unravel the operation of central GABA synapses where inhibitory events appear to result from the synchronous opening of only tens of GABAA receptors activated by a saturating concentration of GABA. Such properties of GABA synapses impose certain constraints on the physiological and pharmacological modulation of inhibition in the brain.

Junctional versus extrajunctional glycine and GABA(A) receptor-mediated IPSCs in identified lamina I neurons of the adult rat spinal cord.

Colocalization of GABA and glycine in synaptic terminals of the superficial dorsal horn raises the question of their relative contribution to inhibition of different classes of neurons in this area. To address this issue, miniature IPSCs (mIPSCs) mediated via GABA(A) receptors (GABA(A)Rs) and glycine receptors (GlyRs) were recorded from identified laminae I-II neurons in adult rat spinal cord slices. GABA(A)R-mediated mIPSCs had similar amplitude and rise times, but significantly slower decay kinetics than GlyR-mediated mIPSCs. Lamina I neurons appeared to receive almost exclusively GlyR-mediated mIPSCs, even after application of hypertonic solutions. Yet, all neurons responded to exogenous applications of both GABA and glycine, indicating that they expressed both GABA(A)Rs and GlyRs. Given that virtually all glycinergic interneurons also contain GABA, the possibility was examined that GABA(A)Rs may be located extrasynaptically in lamina I neurons. A slow GABA(A)R-mediated component was revealed in large, but not minimally evoked monosynaptic IPSCs. Administration of the benzodiazepine flunitrazepam unmasked a GABA(A)R component to most mIPSCs, suggesting that both transmitters were released from the same vesicle. The isolated GABA(A)R component of these mIPSCs had rising kinetics 10 times slower than that of the GlyR component (or of GABA(A)R mIPSCs in lamina II). The slow GABA(A)R components were prolonged by GABA uptake blockers. It is concluded that, whereas GABA and glycine are likely released from the same vesicle of transmitter in lamina I, GABA(A)Rs appear to be located extrasynaptically. Thus, glycine mediates most of the tonic inhibition at these synapses. This differential distribution of GABA(A)Rs and GlyRs confers distinct functional properties to inhibition mediated by these two transmitters in lamina I.

Region-specific developmental specialization of GABA-glycine cosynapses in laminas I-II of the rat spinal dorsal horn.

The spinal dorsal horn is the first level of the CNS in which nociceptive input from sensory afferents is integrated and transmitted. Although inhibitory control in this region has a crucial impact on pain transmission, the respective contribution of GABA and glycine to this inhibition remains elusive. We have previously documented co-release of GABA and glycine at the same inhibitory synapse in spinal laminas I-II of adult rats [older than postnatal day 30 (P30)]. However, despite this co-release, individual miniature inhibitory postsynaptic currents (mIPSCs) were mediated by either glycine receptors (GlyR) or GABA(A) receptors (GABA(A)R), yet never by the two together. In contrast, recent studies of ventral horn immature inhibitory synapses (

Loss of presynaptic and postsynaptic structures is accompanied by compensatory increase in action potential-dependent synaptic input to layer V neocortical pyramidal neurons in aged rats.

Reduction in both presynaptic and postsynaptic structures in the aging neocortex may significantly affect functional synaptic properties in this area. To directly address this issue, we combined whole-cell patch-clamp recording of spontaneously occurring postsynaptic currents (PSCs) with morphological analysis of layer V pyramidal neurons in the parietal cortex of young adult (1- to 2-month-old) and aged (28- to 37-month-old) BN x F344 F(1) hybrid rats. Analysis of spontaneous PSCs was used to contrast functional properties of basal synaptic input with structural alterations in the dendritic tree of pyramidal neurons and density of terminals in contact with these cells. We observed significant changes in a number of morphological parameters of pyramidal neurons in aged rats. These include smaller cell body size and fewer basal dendritic branches (but not of oblique dendrites and dendritic tufts) and spines. Ultrastructural analysis also revealed a lower density of presynaptic terminals per unit length of postsynaptic membrane of labeled pyramidal neurons in the aged brain. This reduction in both presynaptic and postsynaptic elements was paralleled by a significant decrease in frequency of tetrodotoxin-insensitive miniature (action potential-independent) PSCs (mPSCs). The frequency of excitatory and inhibitory mPSCs was reduced to the same extent. In contrast, no significant change was observed in the frequency of spontaneous PSCs recorded in absence of tetrodotoxin (sPSCs), indicating an increase in action potential-dependent (frequency(sPSCs) - frequency(mPSCs)) input to pyramidal neurons in the aged group. This functional compensation may explain the lack of drastic loss of spontaneous neuronal activity in normal aging.

Quantitative analysis of substance P-immunoreactive boutons on physiologically characterized dorsal horn neurons in the cat lumbar spinal cord.

A quantitative analysis of substance P (SP)-immunoreactive (IR) terminals contacting physiologically characterized dorsal horn neurons was performed. Three types of neuron were studied: nociceptive specific (NS) from lamina I (n = 3), wide dynamic range (WDR) from laminae II-IV (n = 3), and nonnociceptive (NN) from lamina IV (n = 3). The nociceptive response of focus was a slow, prolonged depolarization to noxious stimuli, because this response was previously shown to be blocked by selective neurokinin-1 (NK-1) receptor antagonists. Ultrastructural immunocytochemistry was used to quantify the relative number of SP-IR boutons apposed to the intracellularly labeled cell per unit of length (density). Densities of the total population (SP immunoreactive+nonimmunoreactive) of apposed boutons were similar in all three regions (cell body, proximal and distal dendrites) for the three functional types of neuron. NS neurons received a significantly higher density of appositions from SP-IR boutons than NN cells in all three regions. However, compared to WDR cells, NS cells possessed a significantly higher density of appositions from SP-IR boutons only in the cell body and proximal dendrites. WDR cells had a higher density of appositions from SP-IR boutons than NN cells, but only in the proximal and distal dendrites. On average, 33.5% of the SP-IR boutons apposed to the cells displayed a synaptic contact. Finally, 30-45% of the SP-IR boutons apposed to the cells colocalized calcitonin gene-related protein (CGRP) immunoreactivity, indicating their primary sensory origin. The data indicate a direct correlation between the amount of SP-IR input and the nociceptive nature of the cells and suggest that SP acts on NK-1 receptors at a short distance from its release site.

The effects of raising intracellular calcium on synaptic GABAA receptor-channels.

The effects of various calcium (Ca2+) loads imposed through whole-cell patch electrodes on dentate gyrus granule cells were investigated on synaptic GABAA receptor-channels. The kinetics of spontaneous inhibitory postsynaptic currents (sIPSCs) were similar when recorded without any exogenous Ca2+ buffers in the patch electrode or with up to 30 mM BAPTA in the pipette. Unbuffered Ca2+ concentrations of 20-100 microM in the patch pipettes induced a gradual prolongation of miniature IPSC (mIPSC) decays over the course of the recording (10-40 min) with no apparent change in their rise times, peak amplitudes, or frequency of occurrence. This effect was not mimicked by other divalent cations such as strontium. Infusion into the cells of free ionic Ca2+ concentrations buffered with various affinity chelators in the pipette had more pronounced effects on synaptic GABAA currents. Free ionic Ca2+ buffered in the range of 200-400 nM with BAPTA prolonged the decay time constant of mIPSCs. Introducing buffered Ca2+ into the neurons in excess of 1 microM, with a relatively low affinity buffer such as Br2BAPTA, resulted in a marked inhibition of mIPSCs. A similar effect was observed following release of Ca2+ from intracellular stores induced by caffeine (10 mM). We conclude that Ca2+ has a biphasic effect on synaptic GABAA receptor-channels. A high affinity potentiation, consistent with a prolongation of channel burst duration, and a low affinity depression of channel activity both contribute to a complex regulation of synaptic GABAA receptors by [Ca2+]i that has a profound bearing on cellular mechanisms of plasticity and pathological alterations in neuronal excitability.

Peripheral vibration causes an adenosine-mediated postsynaptic inhibitory potential in dorsal horn neurons of the cat spinal cord.

We have previously reported a vibration-induced, adenosine-mediated inhibition of nociceptive dorsal horn neurons in the cat spinal cord. The present study was conducted to investigate the mechanisms of this inhibition. In vivo intracellular recording was obtained from dorsal horn neurons in the lower lumbar segments of the anaesthetized cat. Vibration (80-250 Hz for 2-3 s every 15-20 s) was applied to the glabrous skin of the toes of the hind foot using a feedback-controlled mechanical stimulator. In 32 of 43 neurons tested, vibration produced a pronounced hyperpolarization of the membrane potential. This hyperpolarization peaked at -10 mV and decayed throughout the period of the application of vibration. It was associated with a decrease in membrane resistance, had a reversal potential negative to the resting membrane potential and was Cl(-)-independent, suggesting that it was due to an increase in a K+ conductance, properties typical of the response to adenosine. This inhibitory postsynaptic potential was unaffected by intravenous administration of bicuculline, strychnine and naloxone but was blocked by iontophoretic administration of 8-sulphophenyltheophylline, a P1-purinergic receptor antagonist. These results confirm our previous finding that vibration-induced inhibition of nociceptive dorsal horn neurons is mediated via the release of an endogenous purine compound and further suggests that this inhibition involves a postsynaptic inhibitory mechanism.

Differential progression of Dark Neuron and Fluoro-Jade labelling in the rat hippocampus following pilocarpine-induced status epilepticus.

To investigate the progression of cellular injury in a model of hippocampal epileptogenesis, we used two histochemical methods reported to specifically label injured neurons, the Dark Neuron stain and Fluoro-Jade. Pilocarpine was administered systemically (380mg/kg i.p.) to induce status epilepticus. The duration of status epilepticus was controlled to last 1h by stopping it with diazepam (4mg/kg i.p.). The progression of cellular damage was quantified at six specific time points following the initial pilocarpine-induced insult: 3h, 6h, 12h, 24h, one week, and three weeks. To assess, in parallel, neuronal loss in specific hippocampal regions throughout epileptogenesis, the neuronal nuclear protein NeuN was used as a specific marker of neurons. Results revealed a different time-dependent progression of Dark Neuron and Fluoro-Jade labelling following status epilepticus. A significantly greater proportion of silver-impregnated cells labelled by the Dark Neuron stain was quantified in the stratum radiatum and stratum pyramidale of CA1 at the early time point of 3h compared with the proportion of Fluoro-Jade labelling in adjacent sections. In contrast, the maximal staining with Fluoro-Jade appeared at a later stage during epileptogenesis (between 24h and one week), with a significantly greater proportion of neurons labelled compared to the Dark Neuron stain in the stratum radiatum of CA1, stratum pyramidale of CA1, stratum radiatum of CA3 and the polymorphic layer of the dentate gyrus. Neurons from control animals were not significantly labelled by either of the two staining methods. Interestingly, the increase in Fluoro-Jade labelling corresponded in time to neuron loss. The two stains therefore appear to highlight separate processes of neuronal damage. This finding indicates that distinct cellular events take place at different stages of epileptogenesis, which may differ considerably from the permanent changes observed in chronically epileptic tissue.

Substance P and enkephalin immunoreactivities in axonal boutons presynaptic to physiologically identified dorsal horn neurons. An ultrastructural multiple-labelling study in the cat.

A combination of intracellular electrophysiological recording and injection of horseradish peroxidase with ultrastructural immunocytochemistry was used to investigate the synaptic interplay between substance P- and enkephalin-immunoreactive axonal boutons and three types of functionally characterized dorsal horn neurons in the cat spinal cord. The dorsal horn neurons were classified as nociceptive specific, wide dynamic range and non-nociceptive based on their responses to innocuous and noxious stimuli. Most of the nociceptive neurons (either nociceptive specific or wide dynamic range) contained enkephalin immunoreactivity, but none of the non-nociceptive neurons were positive for enkephalin. Three types of immunoreactive boutons were found in contact with the functionally characterized dorsal horn neurons. These boutons were positive for either substance P, enkephalin, or substance P+enkephalin. Quantitative analysis revealed that the percentages of substance P-immunoreactive boutons apposed to the cell bodies, proximal dendrites and distal dendrites of nociceptive neurons were significantly higher than those of non-nociceptive neurons. Furthermore, the percentages of substance P+enkephalin-immunoreactive axonal boutons apposed to the distal dendrites of nociceptive neurons were significantly higher than those of non-nociceptive neurons and the percentages of enkephalin-immunoreactive boutons apposed to the cell bodies and proximal dendrites of nociceptive neurons were significantly higher than in non-nociceptive neurons. Finally, neither enkephalin-immunoreactive nor substance P+enkephalin-immunoreactive boutons were ever seen presynaptic to substance P-immunoreactive boutons. These results provide evidence of an anatomical substrate within the dorsal horn for the interaction of substance P-mediated with enkephalin-mediated mechanisms. The data support the idea that the modulation of nociceptive input in the dorsal horn by enkephalinergic neurons occurs mainly via a postsynaptic mechanism, and thus suggest that dorsal horn enkephalinergic neurons participate in a local inhibitory feedback loop in a distinct pathway from the previously postulated opioid-mediated depression of substance P release from primary afferent terminals.

Cholinergic nerve terminals establish classical synapses in the rat cerebral cortex: synaptic pattern and age-related atrophy.

This study addresses the issue of whether cholinergic varicosities in the cerebral cortex establish 'classical synapses' or whether they communicate with their targets non-synaptically by 'volume transmission'. Most recent studies in the neocortex have suggested that acetylcholine acts non-synaptically, however in the present study we provide ultrastructural evidence that suggests synaptic mechanisms prevail. This conclusion is based upon our ultrastructural observations that cholinergic boutons--as revealed by immunoreactivity for the specific cholinergic market, vesicular acetylcholine transporter--establish a high percentage of classical synapses in layer V of the rat parietal cortex. Furthermore, the combination of this approach with the intracellular labeling of large pyramidal neurons on slice preparations revealed significant incidences of cholinergic contacts abutting preferentially on dendritic shafts. Finally, we have gathered information suggesting that cholinergic boutons undergo atrophy with aging which could be related to the well-known cholinergic and cognitive decline. These results illustrate that the cholinergic terminations in the neocortex establish proper synaptic connections and that they experience important age-dependent atrophy.

Enkephalin-immunoreactive nociceptive neurons in the cat spinal cord.

In this combined electrophysiological-ultrastructural study in the cat spinal cord, we detected enkephalin-like immunoreactivity using internally radio-labelled monoclonal antibodies in functionally characterized neurons which had been filled intracellularly with horseradish peroxidase. Of the 4 neurons included in this study, two were positive for enkephalin immunoreactivity; one was a nociceptive specific neuron in lamina I, the other a wide dynamic range neuron in lamina V. The other two cells were devoid of immunoreactivity for enkephalin; one was a wide dynamic range neuron and the other was a non-nociceptive neuron. These results thus provide a morphological substrate within the spinal dorsal horn for the release of an endogenous opioid following administration of substance P or noxious cutaneous stimulation.

Visualization of lamina I of the dorsal horn in live adult rat spinal cord slices.

The superficial dorsal horn of the spinal cord, particularly lamina I, plays a key role in the integration and relay of pain related sensory input. To study the physiology of lamina I neurons in slices, a clear delineation of this layer can be greatly advantageous. Yet, it has remained difficult to distinguish this layer in live tissue in conventional transverse spinal slices because of its very narrow thickness at the edge of the dorsal horn. We describe here the criteria we used to delineate lamina I in live tissue using gradient contrast videomicroscopy in 400 microm-thick parasagittal spinal cord slices from adult rats (30-60-day-old). Because of the longitudinal orientation of the neurons in this layer, the resulting distinctive reticulated appearance of lamina I made it possible to readily distinguish it from lamina II. The usefulness of this distinguishing parameter is demonstrated by our ability to contrast synaptic properties of neurons in lamina I from those in lamina II. Complete morphological identification of lamina I neurons however also requires visualization of the cell in the horizontal plane. To maintain compatibility with the parasagittal slice, we used 3D reconstructions from confocal images of the recorded neurons. Rotation of the neuron in space allowed for its morphological characterization in all three planes (horizontal, parasagittal, and transverse). This approach therefore presents optimal conditions for systematic electrophysiological recording from visually identified lamina I neurons.

Bombesin, neuromedin B and neuromedin C selectively depress superficial dorsal horn neurones in the cat spinal cord.

The effects of bombesin and related peptides on functionally identified single dorsal horn neurones were studied using iontophoresis and extracellular recording in the anaesthetized and spinalized cat. Bombesin selectively depressed superficial dorsal horn neurones (in laminae I-III). The depression was of spontaneous activity as well as of synaptically elicited responses to natural stimulation of the cutaneous receptive field. Bombesin preferentially depressed neurones that responded to noxious stimulation of the cutaneous receptive field. Naloxone, bicuculline and caffeine failed to block the depression by bombesin, suggesting that the effect of the peptide may be direct and not through the indirect activation of an inhibitory system mediated by opioids, by gamma-aminobutyric acid (GABA) or by purines, respectively. Iontophoretic application of neuromedin B (n = 3) and neuromedin C (GRP-10) (n = 7) induced a similar depression to that observed with bombesin. These results provide physiological evidence that a bombesin-like peptide may play a role in the mediation or the modulation of sensory transmission in the superficial dorsal horn of the spinal cord.

Substance P released endogenously by high-intensity sensory stimulation potentiates purinergic inhibition of nociceptive dorsal horn neurons induced by peripheral vibration.

To investigate the interaction at the spinal level of endogenously released substance P with the effects of endogenously released adenosine, extracellular single-unit activity was recorded from dorsal horn neurons in the anesthetized cat. Vibration to the skin inhibited on-going activity of nociceptive neurons; 20 mg/kg caffeine reversibly blocked this inhibition, indicating mediation via adenosine receptors. In half of the cases, this inhibition was potentiated by iontophoretic application of substance P. High-intensity electrical stimulation to a sensory nerve produced excitation which was blocked by an NK-1 (substance P) receptor antagonist, implicating an endogenous neurokinin. When electrical stimulation preceded the vibrational stimulus, the inhibitory effect of vibration was potentiated. Thus, we suggest that endogenous substance P may potentiate the inhibitory response to endogenous adenosine. The results have important implications for integration of inputs from different sensory modalities, especially as they relate to nociception and pain.