The effects of capsaicin, the major pungent component of hot peppers, were assessed on neuropeptide levels and on sensory function in neonatal and adult rats and in adult guinea pigs. Systemic doses of capsaicin in rats treated while neonates or while adults produced marked depletion of substance P (SP) in dorsal roots plus ganglia (DRG) and in dorsal spinal cord without altering tail-flick latencies in the treated animals. Guinea pigs had several-fold higher levels of SP than did rats in DRG and dorsal cord. In adult guinea pigs, systemic doses of capsaicin as low as 2.5 mg/kg depleted SP in DRG while a 10 mg/kg dose depleted the peptide maximally in DRG (85% decrease) and in the dorsal cord (35% decrease). High doses of capsaicin in guinea pigs had no consistent effects on levels of radioimmunoassayable cholecystokinin (CCK), vasoactive intestinal polypeptide, or somatostatin although a transient decrease in CCK levels was observed four days after dosing in DRG and in ventral cord. A single 5 mg/kg dose of capsaicin rendered animals completely insensitive to chemical irritation of the cornea without affecting sensitivity to noxious heat. Higher doses of capsaicin produced a marked insensitivity to nociceptive and non-nociceptive heat as well as to chemical irritation without affecting other sensory modalities. The SP depletion and sensory deficits produced by a single 50 mg/kg dose of capsaicin were still evident ten weeks later. The pattern of selectivity of the sensory deficits produced by capsaicin differed from that produced by morphine which was active against all forms of nociceptive stimuli. High doses of capsaicin also induced skin lesions and corneal opacities in guinea pigs. The syndrome of sensory effects produced by capsaicin in guinea pigs closely resembles the pattern of sensory deficits in familial dysautonomia, an autosomal recessive disorder in which there is a disappearance of SP from the substantia gelatinosa of the spinal cord. The results indicate that in the guinea pig capsaicin is potent at producing a unique, long-lasting syndrome of peripheral sensory deficits that may result from an action of the compound on SP-containing primary afferent neurons. Capsaicin is a valuable pharmacological tool for investigation of the neurochemistry and neurophysiology of primary afferent neurons and animals treated with the agent may be useful laboratory models of some forms of peripheral neuropathy.

No description available.

No description available.

Dorsal root ganglion (DRG) neurons are responsive to altered neuromuscular activity and play a role in diabetic peripheral neuropathy (DPN). We present evidence that small and large DRG neurons are differentially affected by exercise and diabetes. We examined gene expression in samples of small and large neurons of rat L4/L5 DRG, and the specific responses after exercise and diabetes, to identify potential molecular processes involved in activity-dependent changes. Small and large DRG neurons were collected using laser capture microdissection. Relative mRNA levels were determined using real-time polymerase chain reaction experiments. In study 1, healthy adult rats received treadmill exercise for 1 or 17 weeks, or voluntary wheel exercise for 16 weeks. In study 2, STZ-induced diabetic rats received 15 weeks of sedentary treatment or voluntary wheel exercise. Behavioural testing of thermal latency response was performed on all animals in study 2. In study 1, there were no significant changes in small or large DRG neuron gene expression after acute treadmill exercise. After chronic treadmill exercise, mRNA levels changed relative to healthy sedentary rats in small (↑ 5HT1D; ↓5HT1F) and large (↓ 5HT1A, TrkC, SYN1) DRG neurons. After chronic voluntary wheel exercise, mRNA levels changed relative to healthy sedentary rats in small (↓ 5HT1D, OPRD1, TrkA; ↑ GAP43) and large (↓ 5HT1D, Nav1.6, OPRD1, TrkA, TrkC, SYN1; ↑ 5HT3A, GAP43) DRG neurons. In study 2, there were no significant changes in large DRG neuron gene expression. In small DRG neurons, mRNA levels were changed in the diabetic sedentary group (↓TrkB; ↑5HT1F) as well as the diabetic wheel group (↓ CGRP) relative to healthy sedentary rats. 5HT1A receptor mRNA levels were higher in diabetic sedentary rats relative to diabetic wheel rats. Our results demonstrate that small and large DRG neurons respond, but in different ways, to the duration and intensity of exercise. DRG neurons show a greater response to voluntary compared to forced exercise, and chronic compared to acute exercise. The genetic changes in small DRG neurons of rats with DPN that exercise may be correlated with the positive change in progression of thermal hypoalgesia associated with exercise. / May 2016

Iron is the most abundant trace metal in the brain and is essential for many biological processes, such as neurotransmitter synthesis and myelin formation. This thesis investigates small, multifocal hypointensities that are apparent on T2*- weighted (T2*w) MRI in the basal ganglia, where presumably most iron enters the brain via the blood-brain-barrier along the penetrating arteries. These basal ganglia T2*w hypointensities are believed to arise from iron-rich microvascular mineral deposits, which are frequently found in community-dwelling elderly subjects and are associated with age-related cognitive decline. This thesis documents the characteristic spatial distribution and morphology of basal ganglia T2*w hypointensities of 98 community-dwelling, elderly subjects in their seventies, as well as their imaging signatures on T1-weighted (T1w) and T2- weighted (T2w) MRI. A fully automated, novel method is introduced for the segmentation of basal ganglia T2*w hypointensities, which was developed to reduce the high intra- and inter-rater variability associated with current semi-automated segmentation methods and to facilitate the segmentation of these features in other single- and multi-centre studies. This thesis also presents a multi parametric quantitative MRI relaxometry methodology for conventional clinical MRI scanners that was developed and validated to improve the characterisation of brain iron. Lastly, this thesis describes the application of the developed methods in the segmentation of basal ganglia T2*w hypointensities of 243 community-dwelling participants of the Austrian Stroke Prevention Study Family (ASPS-Fam) and their analysis on R2* (=1/T2*) relaxation rate and Larmor frequency shift maps. This work confirms that basal ganglia T2*w hypointensities, especially in the globus pallidus, are potentially MRI markers of microvascular mineralization. Furthermore, the ASPS-Fam results show that basal ganglia mineral deposits mainly consist of paramagnetic particles, which presumably arise from an imbalance in the brain iron homeostasis. Hence, basal ganglia T2*w hypointensities are possibly an indicator of age-related microvascular dysfunction with iron accumulation, which might help to explain the variability of cognitive decline in normal ageing.

Rowlands Dewi Kenneth. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2000. / Includes bibliographical references (leaves 113-121). / Abstract --- p.i / Acknowledgements --- p.iii / Publications --- p.iv / Abbreviations --- p.v / Contents --- p.vii / Chapter Chapter 1 --- Prostaglandins --- p.1 / Chapter 1.1 --- Introduction --- p.1 / Chapter 1.2 --- Prostanoid biosynthesis and metabolism --- p.1 / Chapter 1.3 --- Prostaglandin receptors --- p.3 / Chapter 1.3.1 --- DP-receptors --- p.3 / Chapter 1.3.2 --- EP1-receptors --- p.4 / Chapter 1.3.3 --- EP2-receptors --- p.4 / Chapter 1.3.4 --- EP3-receptors --- p.5 / Chapter 1.3.5 --- EP4-receptors --- p.6 / Chapter 1.3.6 --- FP-receptors --- p.7 / Chapter 1.3.7 --- IP-receptors --- p.8 / Chapter 1.3.8 --- TP-receptors --- p.11 / Chapter 1.4 --- Agonists and antagonists --- p.11 / Chapter Chapter 2 --- Role of prostacyclin in pain modulation --- p.14 / Chapter 2.1 --- Pain --- p.14 / Chapter 2.2 --- Prostaglandins and pain --- p.15 / Chapter 2.3 --- Prostacyclin and pain --- p.16 / Chapter 2.3.1 --- [3H]-Iloprost binding sites --- p.16 / Chapter 2.3.2 --- IP-receptor mRNA --- p.17 / Chapter 2.3.3 --- IP-receptor knockout mice --- p.17 / Chapter 2.3.4 --- Direct nociceptive action of prostacyclin --- p.18 / Chapter 2.4 --- Treatment of prostanoid-induced pain --- p.19 / Chapter Chapter 3 --- Dorsal root ganglion cells --- p.21 / Chapter 3.1 --- In vitro model of pain --- p.21 / Chapter 3.2 --- Characteristics of cultured DRG cells --- p.22 / Chapter 3.2.1 --- Size and distribution --- p.22 / Chapter 3.2.2 --- Biochemical and physiological characteristics --- p.22 / Chapter 3.2.2.1 --- Gapsaicin-sensitive neurones --- p.23 / Chapter 3.2.2.2 --- Neuropeptide content --- p.23 / Chapter 3.2.2.3 --- Elevation of [Ca2+］i --- p.24 / Chapter 3.3 --- Effect of nerve growth factor --- p.24 / Chapter Chapter 4 --- Materials and solutions --- p.26 / Chapter 4.1 --- Materials --- p.26 / Chapter 4.2 --- Solutions --- p.30 / Chapter 4.2.1 --- Culture medium --- p.30 / Chapter 4.2.2 --- Buffers --- p.31 / Chapter 4.2.3 --- Solutions --- p.32 / Chapter Chapter 5 --- Development of dorsal root ganglion cell preparation --- p.33 / Chapter 5.1 --- Introduction --- p.33 / Chapter 5.2 --- Methods --- p.34 / Chapter 5.2.1 --- Dissection of dorsal root ganglia --- p.34 / Chapter 5.2.2 --- Preparation of a single-cell suspension --- p.34 / Chapter 5.2.2.1 --- Effect of trimming dorsal root ganglia --- p.34 / Chapter 5.2.2.2 --- Enzymatic dissociation --- p.35 / Chapter 5.2.2.3 --- Mechanical dissociation --- p.36 / Chapter 5.2.3 --- Neuronal cell enrichment --- p.36 / Chapter 5.2.3.1 --- Differential adhesion --- p.36 / Chapter 5.2.3.2 --- BSA gradient --- p.37 / Chapter 5.2.3.3 --- Combination of BSA gradient and differential adhesion --- p.37 / Chapter 5.2.4 --- Cell counting --- p.37 / Chapter 5.2.5 --- Culture conditions --- p.38 / Chapter 5.2.6 --- Size distribution of DRG cells --- p.39 / Chapter 5.2.7 --- Immunocytochemistry --- p.39 / Chapter 5.3 --- Results and discussion --- p.40 / Chapter 5.3.1 --- Preparation of single-cell suspension --- p.40 / Chapter 5.3.2 --- Neuronal cell enrichment --- p.42 / Chapter 5.3.3 --- Size distribution of DRG cells --- p.32 / Chapter 5.3.4 --- Effects of mitotic inhibitors and NGF --- p.45 / Chapter 5.3.5 --- Immunocytochemistry --- p.48 / Chapter 5.4 --- Conclusions --- p.48 / Chapter Chapter 6 --- Methods --- p.53 / Chapter 6.1 --- Dorsal root ganglion cell preparation --- p.53 / Chapter 6.1.1 --- Preparation of tissue culture plates and coverslips --- p.54 / Chapter 6.1.2 --- Preparation of Pasteur pipettes --- p.54 / Chapter 6.2 --- Measurement of adenylate cyclase activity --- p.55 / Chapter 6.2.1 --- Introduction --- p.55 / Chapter 6.2.2 --- Preparation of columns --- p.55 / Chapter 6.2.3 --- Measurement of [3H]-cyclic AMP production --- p.56 / Chapter 6.2.4 --- Data analysis --- p.57 / Chapter 6.3 --- Measurement of phospholipase C activity --- p.58 / Chapter 6.3.1 --- Introduction --- p.58 / Chapter 6.3.2 --- Preparation of columns --- p.58 / Chapter 6.3.3 --- Measurement of [3H]-inositol phosphate production --- p.59 / Chapter 6.3.4 --- Data analysis --- p.60 / Chapter 6.4 --- Measurement of [Ca2+]i --- p.60 / Chapter 6.4.1 --- Introduction --- p.60 / Chapter 6.4.2 --- Preparations of cells --- p.61 / Chapter 6.4.3 --- Measurement of Fura-2 fluorescence --- p.62 / Chapter 6.5 --- Measurement of neuropeptides --- p.62 / Chapter 6.5.1 --- Introduction --- p.62 / Chapter 6.5.2 --- Preparation of cells --- p.63 / Chapter 6.5.3 --- CGRP assay --- p.64 / Chapter 6.5.4 --- Substance P assay --- p.64 / Chapter 6.5.5 --- Purification of samples using Sep-Pak cartridges --- p.65 / Chapter Chapter 7 --- Characterisation of prostacyclin receptors on adult rat dorsal root ganglion cells --- p.66 / Chapter 7.1 --- Stimulation of adenylate cyclase --- p.66 / Chapter 7.1.1 --- Introduction --- p.66 / Chapter 7.1.2 --- Agonist concentration-response curves --- p.67 / Chapter 7.1.3 --- Cross-desensitisation experiments --- p.72 / Chapter 7.1.4 --- Evidence for EP3-receptors --- p.77 / Chapter 7.1.5 --- G-protein coupling of the IP-receptor --- p.77 / Chapter 7.1.6 --- Discussion --- p.78 / Chapter 7.1.7 --- Conclusions --- p.82 / Chapter 7.2 --- Stimulation of phospholipase C --- p.82 / Chapter 7.2.1 --- Introduction --- p.82 / Chapter 7.2.2 --- Agonist concentration-response curves --- p.83 / Chapter 7.2.3 --- G-protein coupling --- p.83 / Chapter 7.2.4 --- Discussion and Conclusions --- p.84 / Chapter 7.3 --- Stimulation of changes in [Ca2+]i --- p.87 / Chapter 7.3.1 --- Introduction --- p.87 / Chapter 7.3.2 --- Preliminary results --- p.87 / Chapter 7.3.3 --- Discussion and conclusions --- p.89 / Chapter Chapter 8 --- Neuropeptide release by adult rat dorsal root ganglion cells --- p.90 / Chapter 8.1 --- Introduction --- p.90 / Chapter 8.2 --- Methods and Results --- p.91 / Chapter 8.3 --- Discussion --- p.91 / Chapter 8.4 --- Conclusions --- p.92 / Chapter Chapter 9 --- Regulation of prostacyclin receptors on adult rat DRG cells --- p.93 / Chapter 9.1 --- Introduction --- p.93 / Chapter 9.2 --- Contribution of non-neuronal cells --- p.93 / Chapter 9.3 --- Effect of DRG cell density --- p.94 / Chapter 9.4 --- Effect of indomethacin --- p.99 / Chapter 9.5 --- Contribution of endogenously-produced non-prostanoid ligands --- p.100 / Chapter 9.6 --- Effect of PKC activation --- p.102 / Chapter 9.7 --- Discussion --- p.104 / Chapter 9.8 --- Conclusions --- p.106 / Chapter Chapter 10 --- General Discussion and Conclusions --- p.107 / Chapter 10.1 --- Development of DRG cell preparation --- p.107 / Chapter 10.2 --- Effect of prostanoid mimetics on intracellular messengers --- p.108 / Chapter 10.3 --- Regulation of prostacyclin receptors --- p.109 / Chapter 10.4 --- Role of prostacyclin in pain modulation --- p.111 / References --- p.113

No description available.

The difficulty with movement initiation, or akinesia, is a cardinal symptom of Parkinson�s disease (PD) and the loss of dopaminergic cells, affecting the function of the basal ganglia, the thalamus and the motor cortex, has long been documented. From a broader perspective, it has been proposed that akinesia is caused by impaired function in different brain areas, inside and outside the basal ganglia, operating as a �behavioural arrest control system� (Klemm, 2001). Several neurotransmitters seem to modulate the activity of this system and, contrasting the well-known effects of dopamine, the involvement of adenosine has only recently emerged, particularly via A2A receptors. Adenosine plays an opposite role to dopamine in the brain: adenosine stimulation at A2A receptors inhibits movement (Ferre et al., 1991a; Hauber and Munkle, 1995; Rimondini et al., 1997), whereas A2A antagonists seem to promote movement (Kanda et al., 2000; Bara-Jimenez et al., 2003; Pinna et al., 2005). Although specific adenosine A2A and dopamine D2 receptors are known to antagonistically interact (Ferre et al., 1997; Fuxe et al., 1998; Ferre et al., 2001), little is known of the involvement of A2A receptors in regulating neural activity in the basal ganglia, a crucial point for the future use of A2A antagonists as adjuvant therapy in Parkinson�s disease. In fact, although it is generally accepted that akinesia results from altered function in the cortico-basal ganglia-cortical loop, as confirmed in several studies reporting changes in basal ganglia activity following dopamine depletion (Blandini et al., 2000; Bevan et al., 2002; Boraud et al., 2002), no study to date has systematically investigated electrophysiological changes in the basal ganglia during akinesia induced by adenosine receptor stimulation. Starting from a common behavioural effect, this study tries to bridge this gap by investigating and comparing, in two basal ganglia structures, the neural substrate of akinesia after acute dopamine D2 receptor blockade and adenosine A2A receptor stimulation. The external segment of the globus pallidus (GP, or simply globus pallidus in the rat) and the substantia nigra pars reticulata (SNr) were chosen as the recording sites because both nuclei are included into the �behavioural arrest control system� and seem to express somewhat complementary functions, as a respective key integrative station and main output of the basal ganglia. Dopamine function was manipulated by acute decrease in availability of dopamine binding sites in the brain, through specific dopamine D2 receptor blockade with systemic injections (1.0 and 1.5 mg/kg) of raclopride(3,5-dichloro-N-[(1-ethylpyrrolidin-2-y)methyl]-2-hydroxy-6-methoxy-benzamide), resulting in akinesia. Conversely, movement was inhibited by specific adenosine A2A receptor stimulation with systemic injections (2.5 and 5.0 mg/kg) of the drug CGS21680 (sodium-2-p-carboxyethylphenylamino-5-N-carboxamidoadenosine). In both situations, behaviour was assessed through specific akinesia tests. Single neuron activity before injection and changes in the firing frequency and firing pattern occurring after injection have been analysed and compared for each cell recorded from GP and SNr, during periods of behavioural rest. Synchronised firing between cell pairs has also been assessed. However, the small number of cell pairs showing correlated firing in each structure after systemic injection of drugs was not statistically relevant for further analysis and interpretation of synchronised firing during drug induced akinesia. In our experiments, both drugs inhibited movement, albeit somewhat differently, with lack of rigidity and �flat� body position after adenosine stimulation. Dopamine blockade decreased mean firing rate and dramatically altered the firing pattern in both investigated structures, generally increasing burst activity (increased percentage of spikes in bursts, mean number of bursts, mean number of spikes per burst, mean intra-burst firing frequency) and decreasing regularity of firing (increased coefficient of variation of the inter-spike intervals). Increased burst activity in the rat basal ganglia in an acute model of parkinsonian akinesia, following systemic raclopride injections, confirmed the importance of changes in the firing pattern in PD. The only electrophysiological effect of systemic A2A stimulation was decreased mean firing rate in the GP, a weak effect that could not propagate towards output stations of the basal ganglia. The lack of changes in the firing pattern, at both input and output levels of the basal ganglia, suggests a correlation with the lack of rigidity in adenosine-stimulation-induced akinesia.

Schizophrenia is among the most debilitating mental disorders, yet the pathophysiology remains unclear. The basal ganglia, a region of the brain involved in motor, cognitive, and sensory processes, may be involved in the pathophysiology of schizophrenia. Some, but not all, neuroimaging studies suggest abnormalities of the basal ganglia in schizophrenia. However, previous studies have examined whole basal ganglia nuclei as opposed to using a unified basal ganglia complex that incorporates anterior-posterior divisions, dorsal-ventral divisions, and gray-white matter segmentation. The hypothesis for the present study was that basal ganglia sub-regions forming functionally relevant subdivisions might be different in schizophrenia. Magnetic resonance imaging scans were acquired from 25 first-episode schizophrenia subjects and 24 healthy subjects. Using manual and automated neuroimaging techniques, total and segmented (gray-white matter) volumes were obtained for the caudate, putamen, and globus pallidus. For the striatum (caudate and putamen), total and segmented volumes were obtained for their respective sub-regions. These sub-regions were restructured into associative, limbic, and sensorimotor subdivisions. Schizophrenia subjects had 6% smaller gray matter volumes for the caudate and 8% smaller gray matter volumes for the associative striatum relative to healthy subjects. Basal ganglia function was studied by examining performance on a neuropsychological test that assesses frontostriatal functioning. For male subjects there was a significant negative correlation between volume of the associative striatum and performance on the neuropsychological test (r=-0.57, p=0.03). Smaller volumes of the associative striatum were associated with more errors on the neuropsychological test. This test was specific to the associative striatum, as another neuropsychological test did not reveal any correlation. In schizophrenia subjects, the relationship between basal ganglia volumes and motor symptoms severity was examined. For antipsychotic-naive subjects there was a significant negative correlation between volume of the motor striatum and severity of Parkinsonism (r=-0.65, p=0.03). The present study suggests that total basal ganglia nuclei volumes are not different in schizophrenia, but gray matter volumes of total basal ganglia nuclei and subdivisions forming functional units may be different in schizophrenia. Structural abnormalities involving the basal ganglia may lead to disrupted functional circuits in schizophrenia.

The basal ganglia are a group of subcortical nuclei that contain about 100 million neurons in humans. Different modes of basal ganglia dysfunction lead to Parkinson's disease and Huntington's disease, which have debilitating motor and cognitive symptoms. However, despite intensive study, both the internal computational mechanisms of the basal ganglia, and their contribution to normal brain function, have been elusive. The goal of this thesis is to identify basic principles that underlie basal ganglia function, with a focus on signal representation, computation, dynamics, and plasticity. This process begins with a review of two current hypotheses of normal basal ganglia function, one being that they automatically select actions on the basis of past reinforcement, and the other that they compress cortical signals that tend to occur in conjunction with reinforcement. It is argued that a wide range of experimental data are consistent with these mechanisms operating in series, and that in this configuration, compression makes selection practical in natural environments. Although experimental work is outside the present scope, an experimental means of testing this proposal in the future is suggested. The remainder of the thesis builds on Eliasmith & Anderson's Neural Engineering Framework (NEF), which provides an integrated theoretical account of computation, representation, and dynamics in large neural circuits. The NEF provides considerable insight into basal ganglia function, but its explanatory power is potentially limited by two assumptions that the basal ganglia violate. First, like most large-network models, the NEF assumes that neurons integrate multiple synaptic inputs in a linear manner. However, synaptic integration in the basal ganglia is nonlinear in several respects. Three modes of nonlinearity are examined, including nonlinear interactions between dendritic branches, nonlinear integration within terminal branches, and nonlinear conductance-current relationships. The first mode is shown to affect neuron tuning. The other two modes are shown to enable alternative computational mechanisms that facilitate learning, and make computation more flexible, respectively. Secondly, while the NEF assumes that the feedforward dynamics of individual neurons are dominated by the dynamics of post-synaptic current, many basal ganglia neurons also exhibit prominent spike-generation dynamics, including adaptation, bursting, and hysterses. Of these, it is shown that the NEF theory of network dynamics applies fairly directly to certain cases of firing-rate adaptation. However, more complex dynamics, including nonlinear dynamics that are diverse across a population, can be described using the NEF equations for representation. In particular, a neuron's response can be characterized in terms of a more complex function that extends over both present and past inputs. It is therefore straightforward to apply NEF methods to interpret the effects of complex cell dynamics at the network level. The role of spike timing in basal ganglia function is also examined. Although the basal ganglia have been interpreted in the past to perform computations on the basis of mean firing rates (over windows of tens or hundreds of milliseconds) it has recently become clear that patterns of spikes on finer timescales are also functionally relevant. Past work has shown that precise spike times in sensory systems contain stimulus-related information, but there has been little study of how post-synaptic neurons might use this information. It is shown that essentially any neuron can use this information to perform flexible computations, and that these computations do not require spike timing that is very precise. As a consequence, irregular and highly-variable firing patterns can drive behaviour with which they have no detectable correlation. Most of the projection neurons in the basal ganglia are inhibitory, and the effect of one nucleus on another is classically interpreted as subtractive or divisive. Theoretically, very flexible computations can be performed within a projection if each presynaptic neuron can both excite and inhibit its targets, but this is hardly ever the case physiologically. However, it is shown here that equivalent computational flexibility is supported by inhibitory projections in the basal ganglia, as a simple consequence of inhibitory collaterals in the target nuclei. Finally, the relationship between population coding and synaptic plasticity is discussed. It is shown that Hebbian plasticity, in conjunction with lateral connections, determines both the dimension of the population code and the tuning of neuron responses within the coded space. These results permit a straightforward interpretation of the effects of synaptic plasticity on information processing at the network level. Together with the NEF, these new results provide a rich set of theoretical principles through which the dominant physiological factors that affect basal ganglia function can be more clearly understood.