Functional MRI in conscious rats using a chronically implanted surface coil.

PURPOSE: To establish procedures for functional MRI (fMRI) in rats without the need for anesthetic agents. MATERIALS AND METHODS: Rats were trained to habituate to restraint in a harness and scanner noise. Under anesthesia, rats were then prepared with a cranial implant that permitted stabilization of the head during subsequent imaging experiments. The cranial implant included an radiofrequency (RF) coil that was used to transmit and receive radiofrequency signals during imaging. Further training was then conducted to habituate the animals to head fixation whilst in the MR scanner. RESULTS: Using this method, we were able to successfully and repeatedly record BOLD fMRI responses to hypercapnia and whisker stimulation in awake rats. Electrical stimulation of the whisker pad produced a ∼7% increase in BOLD signal in the corresponding barrel cortex as well as adjacent negative BOLD responses, whilst hypercapnia produced larger increases in BOLD signal amplitude. CONCLUSION: This methodology leaves the face and limbs free from obstruction, making possible a range of behavioral or sensory stimulation protocols. Further development of this animal model could enable traditional behavioral neuroscience techniques to be combined with modern functional neuroimaging.

Systemic inflammation alters central 5-HT function as determined by pharmacological MRI.

Considerable evidence indicates a link between systemic inflammation and central 5-HT function. This study used pharmacological magnetic resonance imaging (phMRI) to study the effects of systemic inflammatory events on central 5-HT function. Changes in blood oxygenation level dependent (BOLD) contrast were detected in selected brain regions of anaesthetised rats in response to intravenous administration of the 5-HT-releasing agent, fenfluramine (10 mg/kg). Further groups of rats were pre-treated with the bacterial lipopolysaccharide (LPS; 0.5 mg/kg), to induce systemic inflammation, or the selective 5-HT2A receptor antagonist MDL100907 prior to fenfluramine. The resultant phMRI data were investigated further through measurements of cortical 5-HT release (microdialysis), and vascular responsivity, as well as a more thorough investigation of the role of the 5-HT2A receptor in sickness behaviour. Fenfluramine evoked a positive BOLD response in the motor cortex (+15.9±2%) and a negative BOLD response in the dorsal raphe nucleus (-9.9±4.2%) and nucleus accumbens (-7.7±5.3%). In all regions, BOLD responses to fenfluramine were significantly attenuated by pre-treatment with LPS (p<0.0001), but neurovascular coupling remained intact, and fenfluramine-evoked 5-HT release was not affected. However, increased expression of the 5-HT2A receptor mRNA and decreased 5-HT2A-dependent behaviour (wet-dog shakes) was a feature of the LPS treatment and may underpin the altered phMRI signal. MDL100907 (0.5 mg/kg), 5-HT2A antagonist, significantly reduced the BOLD responses to fenfluramine in all three regions (p<0.0001) in a similar manner to LPS. Together these results suggest that systemic inflammation decreases brain 5-HT activity as assessed by phMRI. However, these effects do not appear to be mediated by changes in 5-HT release, but are associated with changes in 5-HT2A-receptor-mediated downstream signalling pathways.

A user-orientated approach to provenance capture and representation for in silico experiments, explored within the atmospheric chemistry community.

We present a novel user-orientated approach to provenance capture and representation for in silico experiments, contrasted against the more systems-orientated approaches that have been typical within the e-Science domain. In our approach, we seek to capture the scientist's reasoning in the form of annotations as an experiment evolves, while using the scientist's terminology in the representation of process provenance. Our user-orientated approach is applied in a case study within the atmospheric chemistry domain: we consider the design, development and evaluation of an electronic laboratory notebook, a provenance capture and storage tool, for iterative model development.

Semantically enhanced provenance capture for chamber model development with a master chemical mechanism.

The development and maintenance of benchmark databases within scientific communities is reliant on interactions with database users. We explore the role of semantically enhanced provenance for computational modelling processes that make use of one such database: the master chemical mechanism, a key resource within the atmospheric chemistry community.

Investigating the coupling between stimulation and neural activity: a dynamic modeling approach.

The objective of the present study was to build a dynamic model relating changes in neural responses in rat barrel cortex to an electrical whisker stimulation pulse train of varying frequencies. This work is part of a formal mathematical system currently being developed, which links stimulation to the Blood Oxygen Level Dependent (BOLD) functional Magnetic Resonance Imaging (fMRI) signal. Neural responses were measured in terms of local field potentials, which were then converted into current source density (CSD) data. Responses were found to be strongly suppressed immediately following the first stimulus pulse, before recovering to a steady state, which was maintained throughout the rest of the stimulation. The amplitude of this steady state decreases as the stimulation frequency increases. The model structure is based on the physiological pathway from the rat sensory organ to the cortex. Dynamic linear second order systems are used to model the excitatory as well as the suppressive components of the neural response. The interactions between components contain nonlinear modulations. The model was evaluated against CSD data from experiments with varying stimulation frequency (1-40 Hz), and shows a plausible fit. The model parameters obtained by optimization for different physiological conditions (anaesthetized or awake) were significantly different. Although this is a descriptive model, it may well have some physiological implications.

Feedback control in active sensing: rat exploratory whisking is modulated by environmental contact.

Rats sweep their facial whiskers back and forth to generate tactile sensory information through contact with environmental structure. The neural processes operating on the signals arising from these whisker contacts are widely studied as a model of sensing in general, even though detailed knowledge of the natural circumstances under which such signals are generated is lacking. We used digital video tracking and wireless recording of mystacial electromyogram signals to assess the effects of whisker-object contact on whisking in freely moving animals exploring simple environments. Our results show that contact leads to reduced protraction (forward whisker motion) on the side of the animal ipsilateral to an obstruction and increased protraction on the contralateral side. Reduced ipsilateral protraction occurs rapidly and in the same whisk cycle as the initial contact. We conclude that whisker movements are actively controlled so as to increase the likelihood of environmental contacts while constraining such interactions to involve a gentle touch. That whisking pattern generation is under strong feedback control has important implications for understanding the nature of the signals reaching upstream neural processes.