Brita Robertson

Neural bases of goal-directed locomotion in vertebrates--an overview.

The different neural control systems involved in goal-directed vertebrate locomotion are reviewed. They include not only the central pattern generator networks in the spinal cord that generate the basic locomotor synergy and the brainstem command systems for locomotion but also the control systems for steering and control of body orientation (posture) and finally the neural structures responsible for determining which motor programs should be turned on in a given instant. The role of the basal ganglia is considered in this context. The review summarizes the available information from a general vertebrate perspective, but specific examples are often derived from the lamprey, which provides the most detailed information when considering cellular and network perspectives.

Transganglionic transport of horseradish peroxidase in primary sensory neurons

The cut end of the sciatic nerve of adult rats was exposed to horseradish peroxidase (HRP). The rats were allowed to survive for 12 h--5 days. 12--18 h postoperatively small dorsal root ganglion cells more heavily labeled than large ones. After 48--72 h more large cells were intensely labeled. From 18 h onwards large amounts of HRP labeling was observed ipsilaterally in the superficial laminae of the dorsal horn, from 48 h also in deeper laminae and in the gracile nucleus. The heavy labeling clearly indicates the potential of the present approach for mapping purposes. The findings also indicate that short postoperative survivals can be used for rather selective marking of small cells and fibers.

Cerebral vessel laminins and IFN-γ define Trypanosoma brucei brucei penetration of the blood-brain barrier

Subspecies of Trypanosoma brucei cause severe brain diseases after penetration of the blood-brain barrier. We investigated whether cytokines that modulate inflammatory cell infiltration into the brain also influence T. brucei neuroinvasion. Migration of a rodent pathogenic T. brucei strain from the cerebral blood vessels into the brain parenchyma was impeded in IFN-gamma(-/-), IFN-gamma receptor(-/-) (IFN-gammaR(-/-)), IL-12p40(-/-), and recombinant activating gene-1(-/-) (RAG-1(-/-)) mice as compared with their WT littermates despite higher levels of parasitemia in the mutant strains. Parasites accumulated in the perivascular compartment, confined between the endothelial and the parenchymal basement membranes, in certain areas of the brains of IFN-gamma(-/-), IFN-gammaR(-/-), and RAG-1(-/-) mice. This accumulation occurred around endothelial basement membranes containing the laminin alpha4 chain, while blood vessels showing robust laminin alpha5 chain immunostaining were not associated with parasite infiltration. The number of CD4+ and CD8+ T cells infiltrating the brain parenchyma was also reduced in the IFN-gamma(-/-) and IFN-gammaR(-/-) mice. Our findings suggest that lymphocyte-derived IFN-gamma facilitates trypanosome penetration across cerebral blood vessels and that the site of penetration is determined by the composition of the basement membranes of these vessels.

Transganglionic transport of wheat germ agglutinin-HRP and choleragenoid-HRP in rat trigeminal primary sensory neurons

Horseradish peroxidase conjugates of either the lectin wheat germ agglutinin (WGA-HRP) or choleragenoid (B-HRP) have been shown to be sensitive neuroanatomical tracers. In the present study a comparison was made between these two conjugates as transganglionic tracers in trigeminal primary sensory neurons following injection into the rat mystacial vibrissae skin. Differences between the two tracers were observed in the labeling of cell bodies in the trigeminal ganglion. Injection of WGA-HRP resulted in labeling of predominantly small cell bodies, whereas B-HRP gave rise to labeling of somewhat larger cell bodies. By increasing the concentration of the injected WGA-HRP solution the number of labeled cells increased substantially, while a corresponding increase in the concentration of B-HRP resulted in a relatively small increase in the number of labeled cells. WGA-HRP injection resulted in labeling of primary afferents mainly in the substantia gelatinosa of the trigeminal subnucleus caudalis. When the concentration of the injected WGA-HRP solution was increased, labeling was also observed in the marginal and magnocellular zones. Following B-HRP injection, labeling was only observed in the magnocellular zone and innermost part of the substantia gelatinosa. This general pattern of labeling was the same when the concentration of the B-HRP solution was increased.

Trypanosoma brucei brucei crosses the blood–brain barrier while tight junction proteins are preserved in a rat chronic disease model

African trypanosomiasis, sleeping sickness in humans, is caused by the systemic infection of the host by the extracellular parasite, the African trypanosome. The pathogenetic mechanisms of the severe symptoms of central nervous system involvement are still not well understood. The present study examined the routes of haematogenous spread of Trypanosoma brucei brucei (Tbb) to the brain, in particular on the question whether parasites can cross the blood–brain barrier, as well as their effect on tight junction proteins. Rats were infected with Tbb and at various times post‐infection, the location of the parasite in the central nervous system was examined in relation to the brain vascular endothelium, visualized with an anti‐glucose transporter‐1 antibody. The tight junction‐specific proteins occludin and zonula occludens 1, and the possible activation of the endothelial cell adhesion molecules ICAM‐1 and VCAM‐1 were also studied. At 12 and 22 days post‐infection, the large majority of parasites were confined within blood vessels. At this stage, however, some parasites were also clearly observed in the brain parenchyma. This was accompanied by an upregulation of ICAM‐1/VCAM‐1. At later stages, 42, 45 and 55 days post‐infection, parasites could still be detected within or in association with blood vessels. In addition, the parasite was now frequently found in the brain parenchyma and the extravasation of parasites was more prominent in the white matter than the cerebral cortex. A marked penetration of parasites was seen in the septal nuclei. In spite of this, occludin and zonula occludens 1 staining of the vessels was preserved. The results indicate that the Tbb parasite is able to cross the blood–brain barrier in vivo, without a generalized loss of tight junction proteins.

Evolution of the basal ganglia: Dual-output pathways conserved throughout vertebrate phylogeny

The basal ganglia, including the striatum, globus pallidus interna and externa (GPe), subthalamic nucleus (STN), and substantia nigra pars compacta, are conserved throughout vertebrate phylogeny and have been suggested to form a common vertebrate mechanism for action selection. In mammals, this circuitry is further elaborated by the presence of a dual‐output nucleus, the substantia nigra pars reticulata (SNr), and the presence of modulatory input from the cholinergic pedunculopontine nucleus (PPN). We sought to determine whether these additional components of the mammalian basal ganglia are also present in one of the phylogenetically oldest vertebrates, the lamprey. We show, by using immunohistochemistry, tract tracing, and whole‐cell recordings, that homologs of the SNr and PPN are present in the lamprey. Thus the SNr receives direct projections from inwardly rectifying γ‐aminobutyric acid (GABA)‐ergic striatal neurons expressing substance P, but it is also influenced by indirect basal ganglia projections from the STN and potentially the GPe. Moreover, GABAergic SNr projection neurons are tonically active and project to the thalamus and brainstem motor areas. The homolog of the PPN contains both cholinergic and GABAergic neurons and is connected with all the nuclei of the basal ganglia, supporting its proposed role as part of an extended basal ganglia. A separate group of cholinergic neurons dorsal to the PPN corresponds to the descending mesencephalic locomotor region. Our results suggest that dual‐output nuclei are part of the ancestral basal ganglia and that the PPN appears to have coevolved as part of a mechanism for action selection common to all vertebrates. J. Comp. Neurol. 520:2957–2973, 2012.

Interferon-γ receptors in nociceptive pathways: Role in neuropathic pain-related behaviour

INTERFERON-γ receptor (IFN-γR) immunoreactivity was observed in the superficial dorsal horn and lateral spinal nucleus in rat and mouse spinal cord. Dorsal rhizotomies did not reduce immunoreactivity in the rat. IFN-γ distribution overlapped with nitric oxide synthase-1 immunoreactivity. In wild-type mice, intrathecal injections of mouse IFN-γ evoked biting behaviour, whereas mice with disruption of the functional gene for IFN-γR did not respond. Both types of mice had similar withdrawal thresholds to mechanical stimulation and reacted similarly to foot-pad carrageenan injections. In contrast to wild-type mice, IFN-γR knock-out mice did not show autotomy after sciatic nerve section. This study demonstrates a functional IFN-γR in spinal nociceptive pathways related to neuropathic pain.

The evolutionary origin of the vertebrate basal ganglia and its role in action selection

Abstract  The group of nuclei within the basal ganglia of the forebrain is central to the control of movement. We present data showing that the structure and function of the basal ganglia have been conserved throughout vertebrate evolution over some 560 million years. The interaction between the different nuclei within the basal ganglia is conserved as well as the cellular and synaptic properties and transmitters. We consider the role of the conserved basal ganglia circuitry for basic patterns of motor behaviour controlled via brainstem circuits. The output of the basal ganglia consists of tonically active GABAergic neurones, which target brainstem motor centres responsible for different patterns of behaviour, such as eye and locomotor movements, posture, and feeding. A prerequisite for activating or releasing a motor programme is that this GABAergic inhibition is temporarily reduced. This can be achieved through activation of GABAergic projection neurons from striatum, the input level of the basal ganglia, given an appropriate synaptic drive from cortex, thalamus and the dopamine system. The tonic inhibition of the motor centres at rest most likely serves to prevent the different motor programmes from becoming active when not intended. Striatal projection neurones are subdivided into one group with dopamine 1 receptors that provides increased excitability of the direct pathway that can initiate movements, while inhibitory dopamine 2 receptors are expressed on neurones that instead inhibit movements and are part of the ‘indirect loop’ in mammals as well as lamprey. We review the evidence showing that all basic features of the basal ganglia have been conserved throughout vertebrate phylogeny, and discuss these findings in relation to the role of the basal ganglia in selection of behaviour.

Interferon-γ induces characteristics of central sensitization in spinal dorsal horn neurons in vitro

&NA; Hyperexcitability of spinal dorsal horn neurons, also known as ‘central sensitization’, is a component of pain associated with pathological conditions in the nervous system. The aim of the present study was to analyze if the pro‐inflammatory cytokine, interferon‐&ggr; (IFN‐&ggr;), which can be released for extended periods of time in the nervous system during inflammatory and infectious events, can alter synaptic activity in dorsal horn neurons and thereby contribute to such hyperexcitability. Treatment of cultured dorsal horn neurons with IFN‐&ggr; for 2 weeks resulted in a significantly reduced clustering of &agr;‐amino‐3‐hydroxy‐5‐methylisoxazole (AMPA) receptor subunit 1 (GluR1) that was dependent on nitric oxide. The neurons displayed an increased frequency and amplitude of excitatory postsynaptic currents (EPSCs) upon IFN‐&ggr; treatment. Treated dorsal horn neurons also exhibited increased responsiveness to stimulation of dorsal root ganglia (DRG) axons in a two‐compartment model. Furthermore, disinhibition by the GABAA receptor antagonist picrotoxin (PTX) significantly increased EPSC frequency and induced bursting in untreated cultures but did not significantly increase the frequency in treated neurons, which displayed bursting even without PTX. GABAA agonists reduced activity more strongly in treated cultures and immunochemical staining for GABAA receptors showed no difference from controls. Since GluR1‐containing AMPA receptors (AMPARs) occur predominantly on inhibitory neurons in the dorsal horn, we suggest that the IFN‐&ggr;‐mediated increase in spontaneous activity and responsiveness to DRG axon stimulation, decrease in sensitivity to PTX and tendency for EPSC bursting result from a reduced expression of GluR1 on these neurons and not from a reduction in active GABAA receptors in the network. IFN‐&ggr; thereby likely causes disinhibition of synaptic activity and primary afferent input in the dorsal horn, which consequently results in central sensitization.

Immunocytochemical evidence for the localization of the GM1 ganglioside in carbonic anhydrase-containing and RT 97-immunoreactive rat primary sensory neurons

SummaryLocalization of GM1 ganglioside, the receptor for cholera toxin, and choleragenoid, which is the binding subunit of cholera toxin, was studied in the rat L5 dorsal root ganglion. Sections were incubated with choleragenoid and treated immunocytochemically. Choleragenoid-like immunoreactive cells were then examined for possible co-localization with carbonic anhydrase-like, RT 97 (antibody to neurofilament proteins), substance P-like, somatostatin-like and calcitonin gene-related peptide-like immunoreactivity and fluoride-resistant acid phosphatase (FRAP) activity, using adjacent sections. A subpopulation of dorsal root ganglion neurons exhibited choleragenoid-like immunoreactivity. The majority of these were medium-sized and large neurons. The strongest immunoreactivity was found in the area of the plasma membrane, but strong reactivity was also seen in the cytoplasm. The majority of the choleragenoid-like immunoreactive cells showed carbonic anhydrase-like and RT 97 immunoreactivity. Cells showing co-localization of choleragenoid-like and neuropeptide-like immunoreactivity or activity for FRAP were rarely observed. Our results suggest that the GM1 receptor is localized primarily on carbonic anhydrase-containing and RT 97-immunoreactive primary sensory neurons.