Human Brainstem Research Articles

Mapping the distribution of serotonin transporter in the human brainstem with high-resolution PET: Validation using postmortem autoradiography data

The human brainstem is a complex structure with several small nuclei and neural pathways of interest in the pathophysiology of central nervous system (CNS) disorders. In common with other monoaminergic systems, serotoninergic neurons originate from a group of nuclei located in the brainstem. The present study was designed to validate a user-independent approach for a detailed in vivo quantification of serotonin transporter (5-HTT) availability in the human brainstem using a template-based approach that consisted of three steps. First, 3T-MR images and parametric binding potential (BPND) [11C]MADAM images of ten healthy subjects were used to generate a PET template of 5-HTT availability. In the second step, volumes of interest (VOIs) for different brainstem nuclei were obtained using a method in which VOIs are initially delineated on MRI images using anatomical landmarks and then are finally tailored on the distribution of 5-HTT binding using a thresholding approach applied to the 5-HTT template. In the final step, the VOIs were transformed and applied individually to BPND images of 16 healthy subjects (14M/2F, 20–64years). The in vivo distribution of BPND values obtained with the template-based method were in good agreement with an individual-based approach taken as gold standard. Results were also in agreement with 5-HTT quantification using in vitro binding data obtained with autoradiography (ARG) studies using [3H]MADAM. The proposed template-based method can be applied to PET data acquired in several CNS disorders in which serotonin neurons in the brainstem might be affected.

Selective localization of oxytocin receptors and vasopressin 1a receptors in the human brainstem

ABSTRACTIntranasal oxytocin (OT) affects a suite of human social behaviors, including trust, eye contact, and emotion recognition. However, it is unclear where oxytocin receptors (OXTR) and the structurally related vasopressin 1a receptors (AVPR1a) are expressed in the human brain. We have previously described a reliable, pharmacologically informed receptor autoradiography protocol for visualizing these receptors in postmortem primate brain tissue. We used this technique in human brainstem tissue to identify the neural targets of OT and vasopressin. To determine binding selectivity of the OXTR radioligand and AVPR1a radioligand, sections were incubated in four conditions: radioligand alone, radioligand with the selective AVPR1a competitor SR49059, and radioligand with a low or high concentration of the selective OXTR competitor ALS-II-69. We found selective OXTR binding in the spinal trigeminal nucleus, a conserved region of OXTR expression in all primate species investigated to date. We found selective AVPR1a binding in the nucleus prepositus, an area implicated in eye gaze stabilization. The tissue’s postmortem interval (PMI) was not correlated with either the specific or nonspecific binding of either radioligand, indicating that it will not likely be a factor in similar postmortem studies. This study provides critical data for future studies of OXTR and AVPR1a in human brain tissue.

Loss of Ptf1a Leads to a Widespread Cell-Fate Misspecification in the Brainstem, Affecting the Development of Somatosensory and Viscerosensory Nuclei.

Cell-fate specification decisions are critical for normal CNS development. Although extensively studied in the cerebellum and spinal cord, the mechanisms mediating cell-fate decisions in the brainstem, which regulates a wide range of processes vital to the organism, remain largely unknown. Here we identified mouse Ptf1a as a novel regulator of cell-fate decisions during both early and late brainstem neurogenesis, which are critical for proper development of several major classes of brainstem cells, including neurons of the somatosensory and viscerosensory nuclei. Since loss-of-function PTF1A mutations were described in human patients, we suggest Ptf1a-dependent cell-fate misspecification as a novel mechanism of human brainstem pathology.

Proteomic MALDI-TOF/TOF-IMS examination of peptide expression in the formalin fixed brainstem and changes in sudden infant death syndrome infants

Matrix assisted laser desorption/ionisation imaging mass spectrometry (MALDI-IMS) has not previously been utilised to examine sudden infant death syndrome (SIDS). This study aimed to optimise MALDI IMS for use on archived formalin-fixed-paraffin-embedded human infant medulla tissue (n=6, controls; n=6, SIDS) to evaluate differences between multiple nuclei of the medulla by using high resolution IMS. Profiles were compared between SIDS and age/sex matched controls. LC-MALDI identified 55 proteins based on 321 peptides across all samples; 286 peaks were found using IMS, corresponding to these 55 proteins that were directly compared between controls and SIDS. Control samples were used to identify common peptides for neuronal/non-neuronal structures allowing identification of medullary regions. In SIDS, abnormal expression patterns of 41 peptides (p≤0.05) corresponding to 9 proteins were observed; these changes were confirmed with immunohistochemistry. The protein abnormalities varied amongst nuclei, with the majority of variations in the raphe nuclei, hypoglossal and pyramids. The abnormal proteins are not related to a previously identified neurological disease pathway but consist of developmental neuronal/glial/axonal growth, cell metabolism, cyto-architecture and apoptosis components. This suggests that SIDS infants have abnormal neurological development in the raphe nuclei, hypoglossal and pyramids of the brainstem, which may contribute to the pathogenesis of SIDS. Biological significanceThis study is the first to perform an imaging mass spectrometry investigation in the human brainstem and also within sudden infant death syndrome (SIDS). LC MALDI and MALDI IMS identified 55 proteins based on 285 peptides in both control and SIDS tissue; with abnormal expression patterns present for 41/285 and 9/55 proteins in SIDS using IMS. The abnormal proteins are critical for neurological development; with the impairment supporting the hypothesis that SIDS may be due to delayed neurological maturation. The brainstem regions mostly affected included the raphe nuclei, hypoglossal and pyramids. This study highlights that basic cyto-architectural proteins are affected in SIDS and that abnormal expression of these proteins in other CNS disorders should be examined. Key sentencesLC MALDI and MALDI IMS identified 55 proteins based on 285 peptides in both control and SIDS tissue.Abnormal expression patterns were present for 41/285 and 9/55 proteins in SIDS using IMS.Brainstem regions mostly affected included the raphe nuclei, hypoglossal and pyramids.

Super-Resolution Track Density Imaging: Anatomic Detail versus Quantification.

I have read with great interest the article by Hoch et al,[1][1] in this issue of the American Journal of Neuroradiology describing an MR imaging protocol to discriminate the internal anatomy of the human brain stem. Their study provides a very nice illustration of one of the key strengths of MR

Mapping the calcitonin receptor in human brain stem.

The calcitonin receptor (CTR) is relevant to three hormonal systems: amylin, calcitonin, and calcitonin gene-related peptide (CGRP). Receptors for amylin and calcitonin are targets for treating obesity, diabetes, and bone disorders. CGRP receptors represent a target for pain and migraine. Amylin receptors (AMY) are a heterodimer formed by the coexpression of CTR with receptor activity-modifying proteins (RAMPs). CTR with RAMP1 responds potently to both amylin and CGRP. The brain stem is a major site of action for circulating amylin and is a rich site of CGRP binding. This study aimed to enhance our understanding of these hormone systems by mapping CTR expression in the human brain stem, specifically the medulla oblongata. Widespread CTR-like immunoreactivity was observed throughout the medulla. Dense CTR staining was noted in several discrete nuclei, including the nucleus of the solitary tract, the hypoglossal nucleus, the cuneate nucleus, spinal trigeminal nucleus, the gracile nucleus, and the inferior olivary nucleus. CTR staining was also observed in the area postrema, the lateral reticular nucleus, and the pyramidal tract. The extensive expression of CTR in the medulla suggests that CTR may be involved in a wider range of functions than currently appreciated.

Correlation of tau pathology in eye movement related brainstem nuclei in cases of progressive supranuclear palsy (PSP) and a proposed role of perineuronal nets

Background Progressive supranuclear palsy (PSP) is characterized by hyperphosphorylated tau protein (HTP) accumulations in different brain regions. A hallmark of clinical symptoms is a vertical gaze palsy, which may be accompanied by horizontal gaze palsy, whereas the VOR is rather preserved until late in the disease. Based on monkey studies functional cell groups of the oculomotor system including transmitters have been identified in the human brainstem (Buttner-Ennever & Horn, 2010). Methods To study the spread of the disease through the oculomotor premotor network sections of 8 archival PSP cases with different eye movement deficits were immunostained for HTP. The analysis involved the glutaminergic rostral interstitial nucleus of the medial longitudinal fascicle (RIMLF) and paramedian pontine reticular formation (PPRF), the glycinergic saccadic omnipause neurons (OPN), the cholinergic oculomotor nucleus (nIII) and the vestibular nuclei (VN). Since the RIMLF and nIII contain well-developed perineuronal nets (PN) (Horn et al., 2003), we further stained sections of the PSP cases for the presence of aggrecan (ACAN) and HTP to prove a possible protective role of PNs as suggested from Alzheimer's disease cases (Morawski et al., 2010). Results All PSP-cases showed HTP-staining in neurons and glia of RIMLF, PPRF and OPNs, in late cases in motonuclei as well. Thereby a correlation between eye movement deficits and degeneration of premotor gaze centers and the complete pathways to motoneurons was found, whereas the VN are less affected. The analysis of PNs revealed that ACAN-based PNs were mainly found around HTP-negative neurons, and only few HTP-positive neurons showed weak ACAN staining. Conclusions The early and more severe degeneration of premotor centers compared to nIII support a hypothesis that in PSP the pathology progresses along neuronal chains in an anterograde fashion, and it is not confined to specific transmitters. The severe tau pathology in RIMLF and nIII in late PSP cases implies that the presence of PNs may not protect them from degeneration, but on a cellular basis the integrity of PNs is affected by tau-pathology. Support: BMBF (IFB-01EO0901, Brain-Net-01GI0505).

Visualization of human brainstem substructures using gray matter nulling 3D-MPRAGE at 7 Tesla

Background The human brainstem is one of the most complex neural entities, in both, structural and functional domains. Its plurality of small and densely packed substructures results in demanding settings for in vivo MR visualization. We addressed this issue applying ultra-high field MRI at 7 Tesla focusing on enhanced differentiation of brainstem substructures. This approach is an essential prerequisite breaking down the complex brainstem anatomy. Methods A modified 3D-MPRAGE-sequence in the sagittal and transverse plane was applied in a 7T MR-system. To compensate for B1-inhomogeneities, a highly adiabatic inversion prepulse was implemented. Five healthy volunteers were examined. The resulting images were visually correlated to histological plates and post-mortem MRI images from Duvernoy’s Atlas. Results We identified 22 structures (sagittal), clearly assignable to histology data. In the brainstem 12 substructures were manually outlined for all five subjects, also based on histology. Adopting histology nomenclature clearly identifiable structures were labeled. Conclusions Optimized 3D-MPRAGE-imaging in the gray matter nulling regime at 7 Tesla provides enhanced image contrast between substructures in the human brainstem, giving rise to better understanding anatomy and potentially related pathology.

Neural Correlates of Cognitive Modulation of Pain Perception in the Human Brainstem and Cervical Spinal Cord using Functional Magnetic Resonance Imaging: A Review.

Pain is a multifaceted and malleable sensory experience that is processed at all levels of the central nervous system (CNS). The experience of pain can vary widely across a healthy population and even within an individual and can be influenced by cognitive factors such as attention, expectation, suggestion, and attitudes. The neurophysiological role of attention in cognitive modulation of pain is the focus for the work presented in this review. Behavioral studies show that pain perception was reduced under cognitive loads that placed a continuous demand on executive functions such as working memory. Neuroimaging, pharmacological studies, and electrophysiological studies provide evidence that the underpinnings of cognitive modulation of pain involve a network of descending modulation of pain among cortical and brainstem structures. However, the role and relationship of subcortical regions in the brainstem and spinal cord during cognitive modulation of pain are not well understood. This review examines the neurophysiology of pain, processing in the CNS, and how cognitive factors such as attention can modulate nociceptive signaling and alter the perception of pain, especially at the subcortical level.

Validation of Structural Equation Modeling Methods for Functional MRI Data Acquired in the Human Brainstem and Spinal Cord.

Structural equation modeling (SEM) provides a means of investigating relationships between blood oxygenation level-dependent (BOLD) signal changes in functional MRI data across neuroanatomical regions. The objectives of this study were to demonstrate adapted SEM methods for the brainstem and spinal cord, validate statistical methods and appropriate statistical thresholds, and test the methods with existing data. SEM methods were applied using an anatomical model of regions of the thalamus, brainstem, and spinal cord that are involved with pain processing. Statistical distributions (Z-scores), significance thresholds, and corrections for multiple comparisons were determined from repeated simulations using "null" data sets. SEM analyses were then applied to data from prior studies involving noxious stimulation in healthy participants. Z-score distributions were observed to vary with the number of source regions modeled, the number of time points (volumes) included in the analysis, and the time span (epoch) used for dynamic analyses. Appropriate choices of statistical thresholds and corrections for multiple comparisons were demonstrated. The results reveal consistent network features across/within studies, as well as dependences on study conditions. They show the effectiveness of a SEM method for functional MRI data from the brainstem and spinal cord.

Interactions between musicality and native language for enhanced sound feature processing

Interactions between musicality and native language for enhanced sound feature processing

ENHANCED BRAINSTEM AND CORTICAL ENCODING OF SOUND DURING SYNCHRONIZED MOVEMENT

Event Abstract Back to Event ENHANCED BRAINSTEM AND CORTICAL ENCODING OF SOUND DURING SYNCHRONIZED MOVEMENT Sylvie Nozaradan1, 2, 3*, Marc Schönwiesner3, Laura Caron-Desrochers3 and Alexandre Lehmann3 1 MARCS Institute for Brain, Behavior and Development, Western Sydney University, Australia 2 Institute of Neuroscience, UCL, Belgium 3 International Laboratory for Brain, Music and Sound Research (BRAMS), Canada Aim. Movement to a steady beat has been widely studied as a model of alignment of motor outputs on sensory inputs. However, how the encoding of sensory inputs is shaped during synchronized movements along the sensory pathway remains unknown. Methods. To investigate this, we simultaneously recorded brainstem and cortical electro-encephalographic activity while participants listened to periodic amplitude-modulated tones. Participants listened either without moving or while tapping in sync on every second beat. Cortical responses were identified at the envelope modulation rate (beat frequency), whereas brainstem responses were identified at the partials frequencies of the chord and at their modulation by the beat frequency (sidebands). Results. During sensorimotor synchronization, cortical responses at beat frequency were larger than during passive listening. Importantly, brainstem responses were also enhanced, with a selective amplification of the sidebands, in particular at the lower-pitched tone of the chord, and no significant correlation with electromyographic measures at tapping frequency. Conclusions. These findings provide first evidence for an online gain in the cortical and subcortical encoding of sounds during synchronized movement, selective to behavior-relevant sound features. Moreover, the frequency-tagging method to isolate concurrent brainstem and cortical activities even during actual movements appears promising to reveal coordinated processes along the human auditory pathway. Acknowledgements S.N. is supported by the Australian Research Council (DE160101064). This work was also supported by a German Science Foundation Grant to S.A.K (DFG KO2268/6-1). Keywords: EEG, neural entrainment, sensorimotor synchronization, steady-state evoked potentials, human auditory brainstem, frequency-tagging Conference: ASP2016 - The 26th Annual Meeting of the Australasian Society for Psychophysiology, Adelaide Australia, Adelaide,SA, Australia, 12 Dec - 14 Dec, 2016. Presentation Type: Oral Presentation Topic: Abstract (general) Citation: Nozaradan S, Schönwiesner M, Caron-Desrochers L and Lehmann A (2016). ENHANCED BRAINSTEM AND CORTICAL ENCODING OF SOUND DURING SYNCHRONIZED MOVEMENT. Conference Abstract: ASP2016 - The 26th Annual Meeting of the Australasian Society for Psychophysiology, Adelaide Australia. doi: 10.3389/conf.fnhum.2016.221.00031 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: 24 Aug 2016; Published Online: 05 Dec 2016. * Correspondence: MD, PhD. Sylvie Nozaradan, MARCS Institute for Brain, Behavior and Development, Western Sydney University, Sydney, Australia, sylvie.nozaradan@uclouvain.be 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 Sylvie Nozaradan Marc Schönwiesner Laura Caron-Desrochers Alexandre Lehmann Google Sylvie Nozaradan Marc Schönwiesner Laura Caron-Desrochers Alexandre Lehmann Google Scholar Sylvie Nozaradan Marc Schönwiesner Laura Caron-Desrochers Alexandre Lehmann PubMed Sylvie Nozaradan Marc Schönwiesner Laura Caron-Desrochers Alexandre Lehmann 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.

Functional Magnetic Resonance Imaging of the Human Brainstem and Cervical Spinal Cord during Cognitive Modulation of Pain.

Pain is a complex sensory experience, and cognitive factors such as attention can influence its perception. Modulation of pain involves a network of subcortical structures; however, the role and relationship of these regions in cognitive modulation of pain are not well understood. The aims of this research were to evaluate the behavioral effect of cognitive modulation of pain and investigate the neural correlates of this mechanism in the brainstem and cervical spinal cord (SC), using functional magnetic resonance imaging (fMRI) and structural equation modeling (SEM). We applied noxious thermal stimulation on the C6 dermatome to 12 healthy female participants while they performed the n-Back task. Our findings demonstrate a significant attenuation in pain perception across the group as a result of the task, along with high intersubject variability in the degree of modulation. Using fMRI, our studies characterize neural responses in subcortical regions that are involved in the modulation of pain. SEM analysis reveals connectivity between the brainstem and SC at the group and individual levels, depending on cognitive load and degree of pain modulation, respectively. All together, our research demonstrates the behavioral effect of cognitive modulation on pain and provides insight into the subcortical neural response to the process.

Calretinin as a Marker for Premotor Neurons Involved in Upgaze in Human Brainstem

Eye movements are generated by different premotor pathways. Damage to them can cause specific deficits of eye movements, such as saccades. For correlative clinico-anatomical post-mortem studies of cases with eye movement disorders it is essential to identify the functional cell groups of the oculomotor system in the human brain by marker proteins. Based on monkey studies, the premotor neurons of the saccadic system can be identified by the histochemical markers parvalbumin (PAV) and perineuronal nets in humans. These areas involve the interstitial nucleus of Cajal (INC) and the rostral interstitial nucleus of the medial longitudinal fascicle (RIMLF), which both contain premotor neurons for upgaze and downgaze. Recent monkey and human studies revealed a selective excitatory calretinin (CR)-positive input to the motoneurons mediating upgaze, but not to those for downgaze. Three premotor regions were identified as sources of CR input in monkey: y-group, INC and RIMLF. These findings suggest that the expression pattern of parvalbumin and CR may help to identify premotor neurons involved in up- or downgaze. In a post-mortem study of five human cases without neurological diseases we investigated the y-group, INC and RIMLF for the presence of parvalbumin and CR positive neurons including their co-expression. Adjacent thin paraffin sections were stained for the aggrecan (ACAN) component of perineuronal nets, parvalbumin or CR and glutamate decarboxylase. The comparative analysis of scanned thin sections of INC and RIMLF revealed medium-sized parvalbumin positive neurons with and without CR coexpression, which were intermingled. The parvalbumin/CR positive neurons in both nuclei are considered as excitatory premotor upgaze neurons. Accordingly, the parvalbumin-positive neurons lacking CR are considered as premotor downgaze neurons in RIMLF, but may in addition include inhibitory premotor upgaze neurons in the INC as indicated by co-expression of glutamate decarboxylase in a subpopulation. CR-positive neurons ensheathed by perineuronal nets in the human y-group are considered as the homolog premotor neurons described in monkey, projecting to superior rectus (SR) and inferior oblique (IO) motoneurons. In conclusion, combined immunostaining for parvalbumin, perineuronal nets and CR may well be suited for the specific identification and subsequent analysis of premotor upgaze pathways in clinical cases of isolated up- or downgaze deficits.

Robust Encoding in the Human Auditory Brainstem: Use It or Lose It?

The human auditory brainstem faithfully represents the acoustic structure of sounds (Galbraith et al., 1995). In musicians, presumably because music training and exposure places high demands on the auditory system, brainstem encoding of both speech and musical sounds is more robust than in non-musicians. It is believed that the corticofugal system, a vast network of efferent connections within the auditory neuroaxis, drives top-down plastic changes underlying the enhancements in brainstem encoding in musicians and other populations with fine-tuned auditory abilities (Wong et al., 2007). Could these same mechanisms lead to impoverished brainstem encoding in those individuals whose musical skill proficiency is below average? Two recent studies on brainstem encoding in amusia, a congenital music disorder, shed a complementary light on this issue (Lehmann et al., 2015; Liu et al., 2015). Together they suggest that a subcortical deficit in auditory processing, which varies as a function of the degree of musical (dis)ability, can emerge as a consequence of limited meaningful interactions with music. We discuss how this notion of auditory detuning fits with the emerging view on top-down induced subcortical plasticity in auditory processing and address its implications for auditory rehabilitation.

Single-subject functional parcellation of the human brainstem

Single-subject functional parcellation of the human brainstem

A New Theory to Explain the Underlying Pathogenetic Mechanism of Sudden Infant Death Syndrome.

The author, on the basis of numerous studies on the neuropathology of SIDS, performed on a very wide set of cases, first highlights the neuronal centers of the human brainstem involved in breathing control in perinatal life, with the pontine Kölliker–Fuse nucleus (KFN) as main coordinator. What emerges from this analysis is that the prenatal respiratory movements differ from those post-natally in two respects: (1) they are episodic, only aimed at the lung development and (2) they are abolished by hypoxia, not being of vital importance in utero, mainly to limit the consumption of oxygen. Then, as this fetal inhibitory reflex represents an important defense expedient, the author proposes a new original interpretation of the pathogenetic mechanism leading to SIDS. Infants, in a critical moment of the autonomic control development, in hypoxic conditions could awaken the reflex left over from fetal life and arrest breathing, as he did in similar situations in prenatal life, rather than promote the hyperventilation usually occurring to restore the normal concentration of oxygen. This behaviour obviously leads to a fatal outcome. This hypothesis is supported by immunohistochemical results showing in high percentage of SIDS victims, and not in age-matched infant controls, neurochemical alterations of the Kölliker–Fuse neurons, potentially indicative of their inactivation. The new explanation of SIDS blames a sort of auto-inhibition of the KFN functionality, wrongly arisen with the same protective purpose to preserve the life in utero, as trigger of the sudden infant death.

Neural correlates of temporal summation of second pain in the human brainstem and spinal cord.

Temporal summation of second pain (TSSP) occurs when painful stimuli are presented repetitively (≥ 0.33 Hz) and results from a C-fibre evoked enhancement (or "wind-up") of the dorsal horn neurons. Based on electrophysiological studies in intact animals, windup is considered a purely central phenomenon. With advancements in functional MRI (fMRI), we can now probe the central mechanisms of this pain response in humans. The aim of this study is to characterize the fMRI responses in the healthy human brainstem and spinal cord that correspond to TSSP. Functional MRI of healthy female adults (N = 15) was conducted while brief, repetitive heat pain stimuli were applied to the right thenar eminence (C6 dermatome), and TSSP (0.33 Hz) and control (0.17 Hz) heat pain paradigms were employed. The stimulus intensity was adjusted to each participant's heat pain sensitivity. Data were analyzed by means of a general linear model, and region-of-interest analyses. As predicted, participants demonstrated significant behavioural summation of pain in the TSSP condition. FMRI results identified enhanced activity in the spinal cord dorsal horn at C6 in response to the TSSP condition. Additionally, multiple areas of the brainstem (RVM and PAG) showed greater responses with the TSSP condition. These results suggest that, in humans, increased pain perception in the TSSP condition is reflected by greater responses in the dorsal horn and in regions known to play a role in the descending modulation of pain, which may modulate the spinal cord response.

Stathmin is enriched in the developing corticospinal tract.

Understanding the intra- and extracellular proteins involved in the development of the corticospinal tract (CST) may offer insights into how the pathway could be regenerated following traumatic spinal cord injury. Currently, however, little is known about the proteome of the developing corticospinal system. The present study, therefore, has used quantitative proteomics and bioinformatics to detail the protein profile of the rat CST during its formation in the spinal cord. This analysis identified increased expression of 65 proteins during the early ingrowth of corticospinal axons into the spinal cord, and 36 proteins at the period of heightened CST growth. A majority of these proteins were involved in cellular assembly and organization, with annotations being most highly associated with cytoskeletal organization, microtubule dynamics, neurite outgrowth, and the formation, polymerization and quantity of microtubules. In addition, 22 proteins were more highly expressed within the developing CST in comparison to other developing white matter tracts of the spinal cord of age-matched animals. Of these differentially expressed proteins, only one, stathmin 1 (a protein known to be involved in microtubule dynamics), was both highly enriched in the developing CST and relatively sparse in other developing descending and ascending spinal tracts. Immunohistochemical analyses of the developing rat spinal cord and fetal human brain stem confirmed the enriched pattern of stathmin expression along the developing CST, and in vitro growth assays of rat corticospinal neurons showed a reduced length of neurite processes in response to pharmacological perturbation of stathmin activity. Combined, these findings suggest that stathmin activity may modulate axonal growth during development of the corticospinal projection, and reinforces the notion that microtubule dynamics could play an important role in the generation and regeneration of the CST.

Pain inhibits pain; human brainstem mechanisms

Conditioned pain modulation is a powerful analgesic mechanism, occurring when a painful stimulus is inhibited by a second painful stimulus delivered at a different body location. Reduced conditioned pain modulation capacity is associated with the development of some chronic pain conditions and the effectiveness of some analgesic medications. Human lesion studies show that the circuitry responsible for conditioned pain modulation lies within the caudal brainstem, although the precise nuclei in humans remain unknown. We employed brain imaging to determine brainstem sites responsible for conditioned pain modulation in 54 healthy individuals. In all subjects, 8 noxious heat stimuli (test stimuli) were applied to the right side of the mouth and brain activity measured using functional magnetic resonance imaging. This paradigm was then repeated. However, following the fourth noxious stimulus, a separate noxious stimulus, consisting of an intramuscular injection of hypertonic saline into the leg, was delivered (conditioning stimulus). During this test and conditioning stimulus period, 23 subjects displayed conditioned pain modulation analgesia whereas 31 subjects did not. An individual's analgesic ability was not influenced by gender, pain intensity levels of the test or conditioning stimuli or by psychological variables such as pain catastrophizing or fear of pain. Brain images were processed using SPM8 and the brainstem isolated using the SUIT toolbox. Significant increases in signal intensity were determined during each test stimulus and compared between subjects that did and did not display CPM analgesia (p<0.05, small volume correction). The expression of analgesia was associated with reduction in signal intensity increases during each test stimulus in the presence of the conditioning stimulus in three brainstem regions: the caudalis subdivision of the spinal trigeminal nucleus, i.e., the primary synapse, the region of the subnucleus reticularis dorsalis and in the dorsolateral pons in the region of the parabrachial nucleus. Furthermore, the magnitudes of these signal reductions in all three brainstem regions were significantly correlated to analgesia magnitude. Defining conditioned pain modulation circuitry provides a framework for the future investigations into the neural mechanisms responsible for the maintenance of persistent pain conditions thought to involve altered analgesic circuitry.