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Papers by Julian Millar

Methods in Neurosciences, 1991

Publisher Summary This chapter describes simultaneous in vivo voltammetric and electrophysiologic... more Publisher Summary This chapter describes simultaneous in vivo voltammetric and electrophysiological recording with carbon fiber microelectrodes. In a study conducted in 1981, it was found that the carbon fiber electrodes that had been designed for single-unit recording were also usable for electrochemical—voltammetric—detection of iontophoretically ejected noradrenaline, dopamine, or serotonin. In the initial experiments in vivo of the study, the electrodes were switched manually between the two types of amplifier. Later it was found that a form of linear sweep voltammetry, usually known as cyclic voltammetry, could work out at much faster sweep rates than had previously been used without damage to either the tissue or the working electrode. Using a triphasic ramp voltage lasting 15 or 20 ms in total, iontophoretically ejected amines could be detected at submicromolar levels. This new technique was called fast cyclic voltammetry (FCV). As the discovery that FCV could be used to detect dopamine released from nerve terminals following electrical stimulation of dopaminergic axons, interest in FCV increased rapidly, and it can now be numbered as one of the major techniques in neuroelectrochemistry. The chapter presents a review of the way in which these two applications of carbon fiber electrodes—namely, unit recording and FCV, can be combined together in a single electrode.

Biosensors and Bioelectronics: X

Faseb Journal 24, Apr 1, 2010

Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1990

Journal of Neuroscience Methods, 1981

Carbon fibre microelectrodes can be used to measure the local concentration of ionophoretically e... more Carbon fibre microelectrodes can be used to measure the local concentration of ionophoretically ejected catecholamines in vitro or in vivo. The method can also be used to measure the transport number for the materials. The concentration measurement takes about 20 ms and can be repeated at up to about 10 Hz without electrode poisoning or deterioration. This paper describes in detail the methodology of the technique and the apparatus required.

Experimental physiology, 2017

What is the central question of this study? Arterial hypertension is associated with impaired neu... more What is the central question of this study? Arterial hypertension is associated with impaired neurovascular coupling in the somatosensory cortex. Abnormalities in activity-dependent oxygen consumption in brainstem regions involved in the control of cardiovascular reflexes have not been explored previously. What is the main finding and its importance? Using fast-cyclic voltammetry, we found that changes in local tissue PO2 in the nucleus tractus solitarii induced by electrical stimulation of the vagus nerve are significantly impaired in spontaneously hypertensive rats. This is consistent with previous observations showing that brainstem hypoxia plays an important role in the pathogenesis of arterial hypertension. The effects of arterial hypertension on cerebral blood flow remain poorly understood. Haemodynamic responses within the somatosensory cortex have been shown to be impaired in the spontaneously hypertensive rat (SHR) model. However, it is unknown whether arterial hypertension...

J Neurochem, 2002

Fast cyclic voltammetry was used to measure NO and dopamine (DA) simultaneously in rat caudate pu... more Fast cyclic voltammetry was used to measure NO and dopamine (DA) simultaneously in rat caudate putamen (CPu) slices. Analysis of electrochemical signals obtained from mixtures of DA and NO showed that subtraction of either the DA or the NO component revealed the contribution of the other component. Application of such data manipulation to signals obtained in CPu slices indicated that DA and NO components contributed to electrochemical signals. Following electrical stimulation (>1 s), site-dependent NO-like signals were observed. Pressure ejection of NMDA yielded a biphasic electrochemical signal. The first phase (lasting 10-20 s) had electrochemical characteristics of DA and was observed only during the first application of NMDA. The second phase developed more slowly, was of longer duration (1-3 min), and had electrochemical characteristics of a mixture of DA and NO. Generation of the NO-like signal by NMDA was antagonised by L-N-monomethylarginine. Pressure ejection of NO into CPu slices caused dose- and site-dependent DA release. More DA was released in the dorsolateral than in the dorsomedial CPu. Pressure ejection of DA did not generate NO. It is concluded that electrically stimulated DA release is not mediated by prior release of NO.

Pflugers Archiv European Journal of Physiology, Sep 30, 1991

Pain, 2003

Nitric oxide (NO) was measured using a new electrochemical method with a carbon fibre microelectr... more Nitric oxide (NO) was measured using a new electrochemical method with a carbon fibre microelectrode at depths of up to 400 microm in the lumbar dorsal horn of the anaesthetised rat. The method allowed extracellular spike recording from single units together with the electrochemical recording at the same electrode. Thirty-six cells with low threshold cutaneous (brush/touch) or wide dynamic range receptive fields (brush/touch plus pinch) were studied. Adequate stimulation of the receptive fields did not alter the extracellular NO level for any cells. Percutaneous needle electrodes inserted into the receptive fields were used to stimulate the cells electrically. Twenty-one cells were stimulated using 10 mA current with 0.05 ms duration (low intensity) pulses to stimulate predominantly A-fibre afferents. Single shock stimuli gave short latency spike responses but no change in nitric oxide level. Tetanic bursts of stimuli (400 stimuli at 50 Hz) generated a burst of spikes (spike count 5...

The Journal of Physiology, 2015

Methods in Neurosciences, 1991

Publisher Summary This chapter describes simultaneous in vivo voltammetric and electrophysiologic... more Publisher Summary This chapter describes simultaneous in vivo voltammetric and electrophysiological recording with carbon fiber microelectrodes. In a study conducted in 1981, it was found that the carbon fiber electrodes that had been designed for single-unit recording were also usable for electrochemical—voltammetric—detection of iontophoretically ejected noradrenaline, dopamine, or serotonin. In the initial experiments in vivo of the study, the electrodes were switched manually between the two types of amplifier. Later it was found that a form of linear sweep voltammetry, usually known as cyclic voltammetry, could work out at much faster sweep rates than had previously been used without damage to either the tissue or the working electrode. Using a triphasic ramp voltage lasting 15 or 20 ms in total, iontophoretically ejected amines could be detected at submicromolar levels. This new technique was called fast cyclic voltammetry (FCV). As the discovery that FCV could be used to detect dopamine released from nerve terminals following electrical stimulation of dopaminergic axons, interest in FCV increased rapidly, and it can now be numbered as one of the major techniques in neuroelectrochemistry. The chapter presents a review of the way in which these two applications of carbon fiber electrodes—namely, unit recording and FCV, can be combined together in a single electrode.

Biosensors and Bioelectronics: X

Faseb Journal 24, Apr 1, 2010

Journal of Electroanalytical Chemistry and Interfacial Electrochemistry, 1990

Journal of Neuroscience Methods, 1981

Carbon fibre microelectrodes can be used to measure the local concentration of ionophoretically e... more Carbon fibre microelectrodes can be used to measure the local concentration of ionophoretically ejected catecholamines in vitro or in vivo. The method can also be used to measure the transport number for the materials. The concentration measurement takes about 20 ms and can be repeated at up to about 10 Hz without electrode poisoning or deterioration. This paper describes in detail the methodology of the technique and the apparatus required.

Experimental physiology, 2017

What is the central question of this study? Arterial hypertension is associated with impaired neu... more What is the central question of this study? Arterial hypertension is associated with impaired neurovascular coupling in the somatosensory cortex. Abnormalities in activity-dependent oxygen consumption in brainstem regions involved in the control of cardiovascular reflexes have not been explored previously. What is the main finding and its importance? Using fast-cyclic voltammetry, we found that changes in local tissue PO2 in the nucleus tractus solitarii induced by electrical stimulation of the vagus nerve are significantly impaired in spontaneously hypertensive rats. This is consistent with previous observations showing that brainstem hypoxia plays an important role in the pathogenesis of arterial hypertension. The effects of arterial hypertension on cerebral blood flow remain poorly understood. Haemodynamic responses within the somatosensory cortex have been shown to be impaired in the spontaneously hypertensive rat (SHR) model. However, it is unknown whether arterial hypertension...

J Neurochem, 2002

Fast cyclic voltammetry was used to measure NO and dopamine (DA) simultaneously in rat caudate pu... more Fast cyclic voltammetry was used to measure NO and dopamine (DA) simultaneously in rat caudate putamen (CPu) slices. Analysis of electrochemical signals obtained from mixtures of DA and NO showed that subtraction of either the DA or the NO component revealed the contribution of the other component. Application of such data manipulation to signals obtained in CPu slices indicated that DA and NO components contributed to electrochemical signals. Following electrical stimulation (>1 s), site-dependent NO-like signals were observed. Pressure ejection of NMDA yielded a biphasic electrochemical signal. The first phase (lasting 10-20 s) had electrochemical characteristics of DA and was observed only during the first application of NMDA. The second phase developed more slowly, was of longer duration (1-3 min), and had electrochemical characteristics of a mixture of DA and NO. Generation of the NO-like signal by NMDA was antagonised by L-N-monomethylarginine. Pressure ejection of NO into CPu slices caused dose- and site-dependent DA release. More DA was released in the dorsolateral than in the dorsomedial CPu. Pressure ejection of DA did not generate NO. It is concluded that electrically stimulated DA release is not mediated by prior release of NO.

Pflugers Archiv European Journal of Physiology, Sep 30, 1991

Pain, 2003

Nitric oxide (NO) was measured using a new electrochemical method with a carbon fibre microelectr... more Nitric oxide (NO) was measured using a new electrochemical method with a carbon fibre microelectrode at depths of up to 400 microm in the lumbar dorsal horn of the anaesthetised rat. The method allowed extracellular spike recording from single units together with the electrochemical recording at the same electrode. Thirty-six cells with low threshold cutaneous (brush/touch) or wide dynamic range receptive fields (brush/touch plus pinch) were studied. Adequate stimulation of the receptive fields did not alter the extracellular NO level for any cells. Percutaneous needle electrodes inserted into the receptive fields were used to stimulate the cells electrically. Twenty-one cells were stimulated using 10 mA current with 0.05 ms duration (low intensity) pulses to stimulate predominantly A-fibre afferents. Single shock stimuli gave short latency spike responses but no change in nitric oxide level. Tetanic bursts of stimuli (400 stimuli at 50 Hz) generated a burst of spikes (spike count 5...

The Journal of Physiology, 2015

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