Alison J. Cooper

Presynaptic mu and delta opioid receptor modulation of GABAA IPSCs in the rat globus pallidus in vitro.

The role of enkephalin and the opioid receptors in modulating GABA release within the rat globus pallidus (GP) was investigated using whole-cell patch recordings made from visually identified neurons. Two major GP neuronal subtypes were classified on the basis of intrinsic membrane properties, action potential characteristics, the presence of the anomalous inward rectifier (Ih), and anode break depolarizations. The μ opioid receptor agonist [d-Ala2-N-Me-Phe4-Glycol5]-enkephalin (DAMGO) (1 μm) reduced GABAAreceptor-mediated IPSCs evoked by stimulation within the striatum. DAMGO also increased paired-pulse facilitation, indicative of presynaptic μ opioid receptor modulation of striatopallidal input. In contrast, the δ opioid agonistd-Pen-[d-Pen2,5]-enkephalin (DPDPE) (1 μm) was without effect. IPSCs evoked by stimulation within the GP were depressed by application of [methionine 5′]-enkephalin (met-enkephalin) (30 μm). Met-enkephalin also reduced the frequency, but not the amplitude, of miniature IPSCs (mIPSCs) and increased paired-pulse facilitation of evoked IPSCs, indicative of a presynaptic action. Both DAMGO and DPDPE reduced evoked IPSCs and the frequency, but not amplitude, of mIPSCs. However, spontaneous action potential-driven IPSCs were reduced in frequency by met-enkephalin and DAMGO, whereas DPDPE was without effect. Overall, these results indicate that presynaptic μ opioid receptors are located on striatopallidal terminals and pallidopallidal terminals of spontaneously firing GP neurons, whereas presynaptic δ opioid receptors are preferentially located on terminals of quiescent GP cells. Enkephalin, acting at both of these receptor subtypes, serves to reduce GABA release in the GP and may therefore act as an adaptive mechanism, maintaining the inhibitory function of the GP in basal ganglia circuitry.

A subset of striatopallidal neurons are Fos-immunopositive following acute monoamine depletion in the rat☆

Experiments were conducted to characterise the Fos-immunopositive neurons that are observed in the dorsal rim of the striatum following monoamine depletion by the systemic administration of reserpine. Using a retrograde tract-tracer, some of these neurons could be shown to project to the globus pallidus but none were seen to project to the entopeduncular nucleus. In addition, these neurons were located in a region of both poor calbindin immunoreactivity and cholinesterase activity. It can be concluded that Fos levels are increased only in a subset of striatopallidal neurons following monoamine depletion. This subset of neurons is located in the dorsal region of the striatum where it has previously been shown that neurons can preferentially be induced to undergo apoptosis upon monoamine depletion.

Moving Through MOOCS: Pedagogy, Learning Design and Patterns of Engagement

Massive open online courses (MOOCs) are part of the lifelong learning experience of people worldwide. Many of these learners participate fully. However, the high levels of dropout on most of these courses are a cause for concern. Previous studies have suggested that there are patterns of engagement within MOOCs that vary according to the pedagogy employed. The current paper builds on this work and examines MOOCs from different providers that have been offered on the FutureLearn platform. A cluster analysis of these MOOCs shows that engagement patterns are related to pedagogy and course duration. Learners did not work through a three-week MOOC in the same ways that learners work through the first three weeks of an eight-week MOOC.

Fos immuno-positive neurons in the subthalamic nucleus following reversal of parkinsonian symptoms by antagonism of excitatory amino acid transmission in the entopeduncular nucleus of the monoamine depleted rat

Drug-induced dyskinesias are a major drawback of the dopaminergic therapies currently employed to treat Parkinsons disease. It is commonly speculated that these dyskinesias may be mediated by functional changes within the striatum. Recent research has, therefore, focused on finding new modes of therapy which will alleviate parkinsonian symptoms without directly altering neurotransmission in the striatum. It has recently been demonstrated that the behavioural symptoms observed in dopamine-depleted rodents can be alleviated by blockade of excitatory neurotransmission in the entopeduncular nucleus. A series of experiments was conducted in order to determine whether this manipulation affected the pattern of Fos immunoreactivity in the basal ganglia elicited by dopamine depletion. The results demonstrated that the most striking change in Fos levels was found in the subthalamic nucleus, indicating that reversal of parkinsonian symptoms in this manner cannot be considered as a simple redress in the balance of activity in the output structures of the basal ganglia.

Glutamate Antagonists for Parkinson’s Disease

Parkinson’s disease results from degeneration of dopaminergic neurons within the substantia nigra. The treatment of the disease was revolutionised by the introduction of dopamine replacement therapy. However, it has become increasingly clear that prolonged administration of dopamine agonists results in the onset of a spectrum of serious adverse effects, including dyskinesias. Accordingly, there is great interest in alternative strategies for the treatment of this condition. It is now realised that the loss of nigral dopamine cells and subsequent lowering of striatal dopamine levels causes a chain of pathophysiological events within the basal ganglia. One of the most prominent of these events is an elevation in the level of glutamate-mediated transmission within the striatum and the output structures of the basal ganglia.A range of glutamate antagonists has been shown to alleviate symptoms in animal models of Parkinson’s disease. Antagonists of both the N-methyl-D-aspartate (NMDA) and α-amino-3-hydroxy-5-methyl-4-isoxazole propionic acid (AMPA) subtypes of the glutamate receptor result in an improvement in motor behaviour in experimental animal models. However, systemic administration of NMDA antagonists is also associated with several adverse effects, the most common being ataxia, sedation and cognitive impairments. These problems can potentially be overcome by the use of antagonists that are selective for the subtypes of NMDA receptors which are preferentially expressed in the critical parts of the pathophysiological circuitry.Glutamate antagonists are also known to have strong neuroprotective effects. Consequently, administration of glutamate antagonists may slow the rate of loss of nigral dopaminergic neurons and thus slow the progression of Parkinson’s disease.

Apoptosis of neurons in the vestibular nuclei of adult mice results from prolonged change in the external environment

Pharmacological manipulations which result in abnormal levels of excitatory amino acid (EAA) mediated neurotransmission can result in neuronal apoptosis. We accordingly hypothesised that manipulations of the external environment which induce prolonged EAA-mediated transmission in sensory neurons may also induce apoptosis. This hypothesis was tested by placing groups of adult mice, housed in their home cage, on a turntable which slowly rotated (0.8 rev./min). This non-invasive manipulation will have resulted in abnormal discharge patterns in the vestibular nuclei. Significantly greater levels of neuronal apoptosis were seen in the vestibular complex after rotation for 48 h compared with non-rotated controls. This finding was also predicted independently from a computational approach.

Novel mechanism of modulation at a ligand‐gated ion channel; action of 5‐Cl‐indole at the 5‐HT3A receptor

The 5‐HT3 receptor is a prototypical member of the Cys‐loop ligand‐gated ion channel (LGIC) superfamily and an established therapeutic target. In addition to activation via the orthosteric site, receptor function can be modulated by allosteric ligands. We have investigated the pharmacological action of Cl‐indole upon the 5‐HT3A receptor and identified that this positive allosteric modulator possesses a novel mechanism of action for LGICs.

N‐glycosylation and expression in human tissues of the orphan GPR61 receptor

A number of members of the G protein‐coupled receptor class of cell surface receptors are ‘orphans’ with no known endogenous ligand. One of these orphan receptors is GPR61; there are little data about its expression in human cells and tissues. In this study, we investigated the post‐translational modification of GPR61 by N‐glycosylation at an identified consensus N‐glycosylation site (N12) and the impact of this modification upon the subcellular expression of the protein. The N‐glycosylation inhibitor tunicamycin reduced the apparent molecular weight of immunoreactivity associated with myc‐tagged GPR61 by 1–2 kDa, which was comparable to the evident molecular weight of the myc‐tagged N12S GPR61 mutant with disrupted consensus N‐glycosylation site. Analysis of GPR61 expression demonstrated that tunicamycin treatment reduced considerably heterologous expression of GPR61 in the cell membrane despite the N12S GPR61 mutant being readily expressed at the cell surface. These results demonstrate that GPR61 is subject to N‐glycosylation but suggest this is not a prerequisite for cell surface expression, although N‐glycosylation of other proteins may be important for cell membrane expression of GPR61. Expression of GPR61 protein was demonstrated at the cellular level in human hippocampus and human peripheral blood mononuclear cells. In the latter, there was a significantly higher expression of GPR61 in the Th17 cell subset in comparison with resting CD4+ cells, which may point toward a potential role for the GPR61 receptor in autoimmune diseases. This is the first report that GPR61 protein is subject to post‐translational modification and is expressed in immune cell subsets and the hippocampus. These findings will help guide studies to investigate the function of GPR61.