Subclasses Of Neurons Research Articles

Patterning and organization of motor neuron dendrites in the Drosophila larva

Precise patterns of motor neuron connectivity depend on the proper establishment and positioning of the dendritic arbor. However, how different motor neurons orient their dendrites to selectively establish synaptic connectivity is not well understood. The Drosophila neuromuscular system provides a simple model to investigate the underlying organizational principles by which distinct subclasses of motor neurons orient their dendrites within the central neuropil. Here we used genetic mosaic techniques to characterize the diverse dendritic morphologies of individual motor neurons from five main nerve branches (ISN, ISNb, ISNd, SNa, and SNc) in the Drosophila larva. We found that motor neurons from different nerve branches project their dendrites to largely stereotyped mediolateral domains in the dorsal region of the neuropil providing full coverage of the receptive territory. Furthermore, dendrites from different motor neurons overlap extensively, regardless of subclass, suggesting that repulsive dendrite-dendrite interactions between motor neurons do not influence the mediolateral positioning of dendritic fields. The anatomical data in this study provide important information regarding how different subclasses of motor neurons organize their dendrites and establishes a foundation for the investigation of the mechanisms that control synaptic connectivity in the Drosophila motor circuit.

Intrinsic innervation of the horse ileum

This paper describes the morphology and distribution of the enteric nervous system (ENS) cells and fibres immunoreactive for choline acetyltransferase (ChAT), neuronal nitric oxide synthase (nNOS), substance P (SP), calcitonin gene-related peptide (CGRP), NF200kDa (NF200), and S100 protein. The percentages of subclasses of enteric neurons in the total neuronal population were investigated by the use of anti-PGP 9.5 or anti-NSE antibodies.ChAT-IR myenteric plexus (MP) and submucosal plexus (SMP) neurons were 66±7% and 74±15%, respectively, whereas those cells expressing nNOS-IR were 38±7% and 5±1%, respectively. MP and SMP neurons expressing both phenotypes were also present. SP-IR was expressed by 14±13% of MP and 66±8% of SMP neurons whereas CGRP-IR was observed only in the SMP (43±6%). NF200-IR was expressed by 61±15% and 91±10% of the MP and SMP neurons, respectively. The majority of the CGRP-IR SMP neurons expressed also SP-IR. Almost all SP-IR neurons in both the plexuses were cholinergic. The present study quantifies the main neuronal subpopulations of the ENS of the horse ileum; these data might be utilized to understand the neuronal modifications which occur in several gastrointestinal tract disorders.

Motor Neurons with Axial Muscle Projections Specified by Wnt4/5 Signaling

SummaryAxial muscles are innervated by motor neurons of the median motor column (MMC). In contrast to the segmentally restricted motor columns that innervate limb, body wall, and neuronal targets, MMC neurons are generated along the entire length of the spinal cord. We show that the specification of MMC fate involves a dorsoventral signaling program mediated by three Wnt proteins (Wnt4, Wnt5a, and Wnt5b) expressed in and around the floor plate. These Wnts appear to establish a ventralhigh to dorsallow signaling gradient and promote MMC identity and connectivity by maintaining expression of the LIM homeodomain proteins Lhx3/4 in spinal motor neurons. Elevation of Wnt4/5 activity generates additional MMC neurons at the expense of other motor neuron columnar subtypes, whereas depletion of Wnt4/5 activity inhibits the production of MMC neurons. Thus, two dorsoventral signaling pathways, mediated by Shh and Wnt4/5, are required to establish an early binary divergence in motor neuron columnar identity.

Low-Threshold Primary Afferent Drive onto GABAergic Interneurons in the Superficial Dorsal Horn of the Mouse

Inhibition in the spinal cord dorsal horn is crucial for maintaining separation of touch and pain modalities. Disruption of this inhibition results in allodynia, allowing low-threshold drive onto pain and temperature-sensitive projection neurons. This low-threshold (LT) excitatory pathway is normally under strong inhibition. We hypothesized that superficial dorsal horn inhibitory neurons, which would be ideally located to suppress LT drive onto projection neurons in a feedforward manner, are driven by LT input. In addition, because disinhibition-induced allodynia shares some features with the immature dorsal horn such as elevated sensitivity to LT input, we also questioned whether LT drive onto inhibitory neurons changes during postnatal maturation. To investigate these questions, slices were made at different ages from transgenic mice with enhanced green fluorescent protein expression in GABAergic neurons and whole-cell recordings were made from these fluorescent neurons. Evoked synaptic activity was measured in response to electrical stimulation of the dorsal root. We demonstrate that Abeta fibers activate a significant proportion of superficial dorsal horn GABAergic neurons. This occurs with similar excitatory synaptic drive throughout postnatal maturation, but with a greater prevalence at younger ages. These GABAergic neurons are well situated to contribute to suppressing LT activation of output projection neurons. In addition, the majority of these GABAergic neurons also had convergent input from high-threshold fibers, suggesting that this novel subclass of GABAergic neurons is important for gating innocuous as well as noxious information.

Identification of distinct telencephalic progenitor pools for neuronal diversity in the amygdala

Development of the amygdala, a central structure of the limbic system, remains poorly understood. Using mouse as a model, our studies reveal that two spatially distinct and early specified telencephalic progenitor pools marked by the homeodomain transcription factor Dbx1 are major sources of neuronal cell diversity in the mature amygdala. We find that Dbx1+ cells of the ventral pallium (VP) generate excitatory neurons of the basolateral complex and cortical amygdala nuclei. Moreover, Dbx1-derived cells comprise a novel migratory stream that emanates from the preoptic area (POA), a ventral telencephalic domain adjacent to the diencephalic border. The Dbx1+ POA-derived population migrates specifically to the amygdala, and as defined by both immunochemical and electrophysiological criteria, generates a unique subclass of inhibitory neurons in the medial amygdala nucleus. Thus, this POA-derived population represents a novel progenitor pool dedicated to the limbic system.

Imaging of experience-dependent structural changes in mouse cortical circuits

Event Abstract Back to Event Imaging of experience-dependent structural changes in mouse cortical circuits Anthony Holtmaat1* 1 University of Geneva, Department of Basic Neuroscieince, Switzerland To understand the synaptic mechanisms of circuit plasticity in relation to learning and memory, neurons need to be studied in the intact brain over extended periods of time. Using high-resolution two-photon laser scanning microscopy through a chronic cranial window, neurons can be repeatedly imaged in the mouse neocortex over months. After imaging, neurons and their synapses can be reconstructed using serial section EM. Such studies have shown that dendritic spines and axonal boutons are dynamic structures, even in the adult brain. Whereas most spines are persistent for months, a small subset of dendritic spines can appear and disappear over days. The generation and loss of persistent spines in the somatosensory barrel cortex is enhanced after trimming of every other whisker (a paradigm known to induce adaptive functional changes in barrel cortex). Most new persistent spines are added on a subclass of L5B neurons located at the barrel interfaces, where adaptive functional changes are largest. Further evidence for a correlation between functional plasticity and new persistent spine formation is provided by studies in αCaMKII-T286A autophosphorylation mutants. Whisker trimming in these mice fails to induce adaptive receptive field changes and also fails to enhance the addition of new persistent spines. Ultrastructural analysis of new pines and their associated boutons shows that new spines often lack synapses shortly after they appear, whereas spines that persist for more than a few days always have synapses. New synapses are predominantly found on large multisynpase boutons, suggesting that spine growth is followed by synapse formation, preferentially on existing boutons. Altogether these data indicate that novel sensory experience drives the stabilization of new spines and promotes the formation of new synapses on subclasses of cortical neurons. These synaptic changes could underlie experience-dependent functional remodelling of specific neocortical circuits. Conference: 41st European Brain and Behaviour Society Meeting, Rhodes Island, Greece, 13 Sep - 18 Sep, 2009. Presentation Type: Oral Presentation Topic: Symposia lectures Citation: Holtmaat A (2009). Imaging of experience-dependent structural changes in mouse cortical circuits. Conference Abstract: 41st European Brain and Behaviour Society Meeting. doi: 10.3389/conf.neuro.08.2009.09.029 Copyright: The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers. They are made available through the Frontiers publishing platform as a service to conference organizers and presenters. The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated. Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed. For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions. Received: 04 Jun 2009; Published Online: 04 Jun 2009. * Correspondence: Anthony Holtmaat, University of Geneva, Department of Basic Neuroscieince, Lausanne 1015 Vaud, Switzerland, anthony.holtmaat@unige.ch Login Required This action requires you to be registered with Frontiers and logged in. To register or login click here. Abstract Info Abstract The Authors in Frontiers Anthony Holtmaat Google Anthony Holtmaat Google Scholar Anthony Holtmaat PubMed Anthony Holtmaat Related Article in Frontiers Google Scholar PubMed Abstract Close Back to top Javascript is disabled. Please enable Javascript in your browser settings in order to see all the content on this page.

A Translational Profiling Approach for the Molecular Characterization of CNS Cell Types

The cellular heterogeneity of the brain confounds efforts to elucidate the biological properties of distinct neuronal populations. Using bacterial artificial chromosome (BAC) transgenic mice that express EGFP-tagged ribosomal protein L10a in defined cell populations, we have developed a methodology for affinity purification of polysomal mRNAs from genetically defined cell populations in the brain. The utility of this approach is illustrated by the comparative analysis of four types of neurons, revealing hundreds of genes that distinguish these four cell populations. We find that even two morphologically indistinguishable, intermixed subclasses of medium spiny neurons display vastly different translational profiles and present examples of the physiological significance of such differences. This genetically targeted translating ribosome affinity purification (TRAP) methodology is a generalizable method useful for the identification of molecular changes in any genetically defined cell type in response to genetic alterations, disease, or pharmacological perturbations.

Differential Inhibition of Ca2+ Channels by α2-Adrenoceptors in Three Functional Subclasses of Rat Sympathetic Neurons

A comparison of identified sympathetic neurons in the isolated intact superior cervical ganglion revealed that secretomotor, pilomotor, and vasoconstrictor cells differ in their action potential mechanisms and in their postsynaptic alpha(2)-adrenergic responses to 10 microM norepinephrine (NE). In normal saline, the half-width of the spike afterhyperpolarization (AHP) in secretomotor neurons (103.5 +/- 6.2 ms) was twofold that recorded in vasoconstrictor neurons (47.7 +/- 2.9 ms) and 1.5-fold that in pilomotor neurons (71.4 +/- 10.3 ms). Bath-applied NE reversibly inhibited the action potential repolarization shoulder, AHP amplitude, and AHP duration in secretomotor and pilomotor neurons to a similar extent, but had no effect on vasoconstrictor neurons. The insensitivity of vasomotor neurons to NE was not an artifact produced by microelectrode recording because all three cell groups were similar in terms of resting potential and input resistance. Moreover, NE insensitivity was not a natural consequence of briefer AHP duration in vasoconstrictor cells. Adding 10 mM TEA(+) caused marked accentuation of the shoulder and AHP duration in vasoconstrictor neurons and comparable changes in the other two cell types, but did not unmask any sign of NE sensitivity in the vasoconstrictors. However, the spike shoulder and AHP in vasoconstrictors were Cd(2+) sensitive, blocked by omega-conotoxin, an N-type calcium channel antagonist, and inhibited by oxotremorine-M, a muscarinic receptor agonist. These data show that NE can differentially modulate functional subsets of mammalian sympathetic neurons and that NE insensitivity can serve as a practical experimental criterion for identification of vasomotor neurons in the isolated ganglion.

Visualizing mechanosensory endings of TrkC‐expressing neurons in HS3ST‐2‐hPLAP mice

Somatosensory neurons are classified into three main types according to their modalities: nociceptive, thermal, and mechanosensory. Within each modality group, neurons can be further divided into morphologically and functionally distinct subclasses. Here we show that heparan sulfate D-glucosaminyl 3-O-sulfotransferase 2 (HS3ST-2) is a marker for specific subsets of TrkC-expressing cutaneous low-threshold mechanosensory and proprioceptive mechanosensory neurons. Two-color in situ analysis revealed that almost all HS3ST-2 signals colocalized with TrkC but not with TrkA or TrkB mRNA. To visualize the morphological subtypes of HS3ST-2/TrkC-expressing neurons, we generated a HS3ST-2-hPLAP knock-in mouse line, in which HS3ST-2-expressing neurons and their projections are labeled by human placental alkaline phosphatase (hPLAP). AP staining in these mice demonstrated that sensory endings of muscle spindles and Golgi tendon organs as well as the cutaneous mechanosensory Merkel and longitudinal lanceolate endings in the whiskers are strongly positive for hPLAP activity. In contrast, no nociceptive endings are labeled. In the glabrous and hairy skin, rare Merkel endings and transverse lanceolate endings are weakly stained. During development, each type of nerve endings forms at different time point. Muscle innervations differentiate first, followed by formation of cutaneous sensory endings. Our results revealed the subtype identities of TrkC-positive mechanosensory neurons and demonstrated the usefulness of HS3ST-2 as a genetic marker for these subclasses of neurons.

Entorhinal Cortex Inhibits Medial Prefrontal Cortex and Modulates the Activity States of Electrophysiologically Characterized Pyramidal Neurons In Vivo

The prefrontal cortex receives multiple inputs from the hippocampal complex, which are thought to drive memory-guided behavior. Moreover, dysfunctions of both regions have been repeatedly associated with several psychiatric disorders. Therefore, understanding the interconnections and modulatory interactions between these regions is essential in evaluating their role in behavior and pathology. The effects of entorhinal cortex (EC) stimulation on the activity of identified medial prefrontal cortex (mPFC) pyramidal neurons were examined using single-unit extracellular recordings and sharp-electrode intracellular recordings in anesthetized rats. Single-pulse electrical stimulation of EC induced a powerful inhibition in the majority of mPFC neurons examined during extracellular recording. Intracellular recording showed that EC stimulation evoked a complex synaptic response, in which the greater proportion of neurons exhibited excitatory postsynaptic events and/or a short lasting and a prolonged inhibitory postsynaptic response. Furthermore, stimulation of EC selectively produced an augmentation of the bistable up-down state only in the type 2 regular spiking neurons and in a subclass of nonintrinsic bursting neurons. Taken together, these data suggest that the potent inhibition observed following EC stimulation may mask a direct excitatory response within the mPFC which markedly potentiates the bistable states in a select subpopulation of mPFC pyramidal neurons.

Parkinson’s disease and the gut: a well known clinical association in need of an effective cure and explanation

Parkinson's disease (PD) is a neurodegenerative disorder which leads to severe movement impairment; however, Parkinsonian patients frequently suffer from gastrointestinal (GI) problems which at present are poorly understood, scarcely investigated, and lack an effective cure. Traditionally, PD is attributed to the loss of mesencephalic dopamine-containing neurons; nonetheless, additional nuclei, such as the dorsal motor nucleus of the vagus nerve and specific central noradrenergic nuclei, are now identified as targets of PD. While the effects of PD on the somatic motor systems are well characterized, the influence on the digestive system still needs to be clarified. Recent findings demonstrate the occurrence of pathological alterations within peripheral neuronal networks in the GI tract of Parkinsonian patients. However, it remains unclear whether a real cell loss occurs, and whether this happens specifically for a subclass of autonomic neurons or if it reflects the sole loss of autonomic nerves. This review summarizes the neurochemical and morphological changes which might be responsible for impaired GI motility. Moreover, we focus on the experimental models to reproduce the altered digestive system of Parkinsonian patients since an experimental model able to mimic such features of PD is required. In the last part of the manuscript, we suggest potential therapeutic targets.

The neural adhesion molecule TAG-1 modulates responses of sensory axons to diffusible guidance signals

When the axons of primary sensory neurons project into the embryonic mammalian spinal cord, they bifurcate and extend rostrocaudally before sending collaterals to specific laminae according to neuronal subclass. The specificity of this innervation has been suggested to be the result both of differential sensitivity to chemorepellants expressed in the ventral spinal cord and of the function of Ig-like neural cell adhesion molecules in the dorsal horn. The relationship between these mechanisms has not been addressed. Focussing on the pathfinding of TrkA+ NGF-dependent axons, we demonstrate for the first time that their axons project prematurely into the dorsal horn of both L1 and TAG-1 knockout mice. We show that axons lacking TAG-1, similar to those lacking L1, are insensitive to wild-type ventral spinal cord (VSC)-derived chemorepellants, indicating that adhesion molecule function is required in the axons, and that this loss of response is explained in part by loss of response to Sema3A. We present evidence that TAG-1 affects sensitivity to Sema3A by binding to L1 and modulating the endocytosis of the L1/neuropilin 1 Sema3A receptor complex. However, TAG-1 appears to affect sensitivity to other VSC-derived chemorepellants via an L1-independent mechanism. We suggest that this dependence of chemorepellant sensitivity on the functions of combinations of adhesion molecules is important to ensure that axons project via specific pathways before extending to their final targets.

Cholinesterases in development and disease

Cholinesterases (ChEs) including acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) are abundant in the nervous system and other tissues. Here we describe two different aspects of ChEs and the cholinergic system. The first aspect concerns the role of cholinergic transmission in central pattern generation in the neonatal rat spinal cord and the second one describes the involvement of ChEs in the pathologies of dystrophin-deficient mutant ( mdx) mice, the animal model of Duchenne muscular dystrophy. Thus, this study is divided into two distinct parts. In the first part we show that AChE is abundant in ventral horn neurons, central canal-adjacent and partition neurons in all the observed segments (L2, L5, S1, and S2). AChE was also found in the intermediolateral and sacral parasympathetic nuclei of L2 and S1, respectively. Blocking the AChE by edrophonium produced non-stationary bursting in spinal cord preparations of developing rats. Cross-wavelet/coherence analyses of the data revealed epochs of locomotor-like activity (left–right and flexor–extensor alternation) followed by other rhythmic or non-rhythmic bursting patterns. Addition of exogenous ACh stabilized the rhythm and increased the incidence of locomotor-like pattern in the preparations. Thus, the cholinergic system in the spinal cord is capable of producing and modulating functional rhythmic bursts. Moreover, bath-applied edrophonium and exogenous ACh were found as potent means of modulation of the locomotor rhythm produced by stimulation of sacrocaudal afferents (SCAs). We show that a subclass of sacral neurons with contralateral funicular projections to the thoracolumbar cord is associated with the cholinergic system. This group of neurons may play a major role in the observed enhancement of the SCA-induced motor rhythm. In the second part we show that adult mdx-muscles are malformed with distorted neuromuscular junctions (nmjs) and impaired regulation of acetylcholine receptors. Examination of circulating ChE levels revealed that in mdx-sera, while AChE activity was elevated, BuChE activity was markedly lower than in wild-type ( wt) sera. Thus, BuChE to AChE ratio in mouse sera decreased from 6:1 in wt control to 3:1 in mdx. Because serum ChE levels may be modulated by gonadal steroids, it is possible that lack of dystrophin in mdx-mice may affect this regulation. Further studies are in progress to determine the potential endocrine regulation of ChEs in circulation and at the nmjs of mdx- and wt-mice. These studies will help clarify whether the hormonal regulation is impaired in the mdx mutant, and whether changes in circulating ChE reflect or influence the functional deficits observed in excitable tissues of diseased states.

Spatial Regulation of nanos Is Required for Its Function in Dendrite Morphogenesis

Spatial control of mRNA translation can generate cellular asymmetries and functional specialization of polarized cells like neurons. A requirement for the translational repressor Nanos (Nos) in the Drosophila larval peripheral nervous system (PNS) implicates translational control in dendrite morphogenesis [1]. Nos was first identified by its requirement in the posterior of the early embryo for abdomen formation [2]. Nos synthesis is targeted to the posterior pole of the oocyte and early embryo through translational repression of unlocalized nos mRNA coupled with translational activation of nos mRNA localized at the posterior pole [3, 4]. Abolishment of nos localization prevents abdominal development, whereas translational derepression of unlocalized nos mRNA suppresses head/thorax development, emphasizing the importance of spatial regulation of nos mRNA [3, 5]. Loss and overexpression of Nos affect dendrite branching complexity in class IV dendritic arborization (da) neurons, suggesting that nos also might be regulated in these larval sensory neurons [1]. Here, we show that localization and translational control of nos mRNA are essential for da neuron morphogenesis. RNA-protein interactions that regulate nos translation in the oocyte and early embryo also regulate nos in the PNS. Live imaging of nos mRNA shows that the cis-acting signal responsible for posterior localization in the oocyte/embryo mediates localization to the processes of class IV da neurons but suggests a different transport mechanism. Targeting of nos mRNA to the processes of da neurons may reflect a local requirement for Nos protein in dendritic translational control.

Imaging of experience-dependent structural plasticity in the mouse neocortex in vivo

The functionality of adult neocortical circuits can be altered by novel experiences or learning. This functional plasticity appears to rely on changes in the strength of neuronal connections that were established during development. Here we will describe some of our studies in which we have addressed whether structural changes, including the remodeling of axons and dendrites with synapse formation and elimination, could underlie experience-dependent plasticity in the adult neocortex. Using 2-photon laser-scanning microscopes and transgenic mice expressing GFP in a subset of pyramidal cells, we have observed that a small subset of dendritic spines continuously appear and disappear on a daily basis, whereas the majority of spines persists for months. Axonal boutons from different neuronal classes displayed similar behavior, although the extent of remodeling varied. Under baseline conditions, new spines in the barrel cortex were mostly transient and rarely survived for more than a week. However, when every other whisker was trimmed, the generation and loss of persistent spines was enhanced. Ultrastructural reconstruction of previously imaged spines and boutons showed that new spines slowly form synapses. New spines persisting for a few days always had synapses, whereas very young spines often lacked synapses. New synapses were predominantly found on large, multi-synapse boutons, suggesting that spine growth is followed by synapse formation, preferentially on existing boutons. Altogether our data indicate that novel sensory experience drives the stabilization of new spines on subclasses of cortical neurons and promotes the formation of new synapses. These synaptic changes likely underlie experience-dependent functional remodeling of specific neocortical circuits.

Satb2 Is a Postmitotic Determinant for Upper-Layer Neuron Specification in the Neocortex

Pyramidal neurons of the neocortex can be subdivided into two major groups: deep- (DL) and upper-layer (UL) neurons. Here we report that the expression of the AT-rich DNA-binding protein Satb2 defines two subclasses of UL neurons: UL1 (Satb2 positive) and UL2 (Satb2 negative). In the absence of Satb2, UL1 neurons lose their identity and activate DL- and UL2-specific genetic programs. UL1 neurons in Satb2 mutants fail to migrate to superficial layers and do not contribute to the corpus callosum but to the corticospinal tract, which is normally populated by DL axons. Ctip2, a gene required for the formation of the corticospinal tract, is ectopically expressed in all UL1 neurons in the absence of Satb2. Satb2 protein interacts with the Ctip2 genomic region and controls chromatin remodeling at this locus. Satb2 therefore is required for the initiation of the UL1-specific genetic program and for the inactivation of DL- and UL2-specific genes.

More to pheromones than meets the nose

Mice use pheromones to regulate social behavior. New work in mice now identifies the protein in urine that is essential for aggressive behavior, along with the specific subclass of neurons involved in its processing.

A subpopulation of capsaicin-sensitive porcine dorsal root ganglion neurons is lacking hyperpolarization-activated cyclic nucleotide-gated channels

Hyperpolarization-activated cyclic nucleotide-gated (HCN) channels contribute to stabilizing resting membrane potential, thus controlling neuron excitability. Subclasses of nociceptive neurons differ in their excitability, therefore, these channels could be a distinguishing marker. We investigated isolated dorsal root ganglion neurons from a non-rodent species, the pig, Sus scrofa domesticus. Single labeling revealed capsaicin-induced cobalt-uptake in 54.3% and transient receptor potential V1 (TRPV1) immunoreactivity in 55.1% of all neurons. Ruthenium red and capsazepine suppressed capsaicin-induced cobalt-uptake. HCN-1 and HCN-2 channel isoform immunoreactivity was detected in 82.6% and 88.3%, respectively, and binding of IB4 in 29.4% of all neurons. Double labeling revealed that out of the capsaicin-positive neurons, 42.3% were IB4-positive, 80.0% immunoreactive for the HCN-1, and 77.3% for the HCN-2 channel isoform, respectively. Neurons lacking HCN-1 or HCN-2 channel isoforms were mostly capsaicin-positive and IB4-negative. The soma size of neurons lacking HCN-1 and/or HCN-2 channels was small to medium. Western blot analysis showed protein products of sizes similar to those of HCN-1 and HCN-2 channel isoforms. Functionally, in patch-clamp experiments, some neurons were unresponsive to membrane hyperpolarization, thus, probably lacking HCN channels. In conclusion, in porcine dorsal root ganglion neurons there is a subset of capsaicin-positive, IB4-negative neurons lacking HCN-1 and/or HCN-2 channel isoforms.

Cre fate mapping reveals lineage specific defects in neuronal migration with loss of Pitx2 function in the developing mouse hypothalamus and subthalamic nucleus

Establishment of neuronal diversity is a central topic in developmental neurobiology. Prior studies implicated Pitx2, a paired-like homeodomain transcription factor, in mouse subthalamic nucleus neuronal development, but precise stages of neuronal differentiation affected (migration, axon outgrowth, fate specification) and underlying mechanisms were unknown. Here we report lineage tracing experiments using Pitx2 cre/+ , Pitx2 cre/null , and conditional nuclear lacZ reporter mice to track embryonic Pitx2 expressing neurons. Migration of subthalamic nucleus and hypothalamic neurons was severely arrested in Pitx2 cre/null embryos, and subclasses of subthalamic nucleus neurons identified by Lmx1b, Foxp1, and Foxp2-gene expression revealed differing sensitivities to Pitx2 dosage. Interestingly, embryonic subthalamic nucleus development was unaffected in Lmx1b null mice, suggesting that Pitx2 and Lmx1b act via independent genetic pathways. These data provide the first direct evidence for Pitx2-dependent neuronal migration in the developing hypothalamus, and demonstrate that complex transcriptional networks regulate regional specialization of distinct hypothalamic and subthalamic nucleus neurons.

Lighting a Backfire to Quench the Blaze: A Combined Drug Approach Targeting the Vanilloid Receptor TRPV1

Drug interactions and drug specificity are core themes for the pharmacologist. The paper discussed in this Viewpoint exploits the former to attain the latter. How can one improve local anesthetics so that they block pain but permit normal sensation? QX-314 is a charged derivative of lidocaine without anesthetic activity because it cannot diffuse across the cell membrane to access the neuronal voltage-dependent sodium channel. Capsaicin is a selective activator of the TRPV1 channel, the localization of which is restricted to sensory C-fiber neurons involved in nociception. Because the large pore size of the activated TRPV1 allows passage of large cations such as QX-314, combined treatment with capsaicin and QX-314 puts QX-314 uniquely into that subclass of neurons mediating pain, thereby achieving sensational specificity.