Dependence of solution exchange time on cell or patch linear dimensions in concentration jump experiments using patch-clamped sensory neurones

Neurophysiology of Nicotine Addiction

Tobacco use is a major health problem, and nicotine is the main addictive component. Nicotine binds to nicotinic acetylcholine receptors (nAChR) to produce its initial effects. The nAChRs subtypes are composed of five subunits that can form in numerous combinations with varied functional and pharmacological characteristics. Diverse psychopharmacological effects contribute to the overall process of nicotine addiction, but two general neural systems are emerging as critical for the initiation and maintenance of tobacco use. Mesocorticolimbic circuitry that includes the dopaminergic pathway originating in the ventral tegmental area and projecting to the nucleus accumbens is recognized as vital for reinforcing behaviors during the initiation of nicotine addiction. In this neural system β2, α4, and α6 are the most important nAChR subunits underlying the rewarding aspects of nicotine and nicotine self-administration. On the other hand, the epithalamic habenular complex and the interpeduncular nucleus, which are connected via the fasciculus retroflexus, are critical contributors regulating nicotine dosing and withdrawal symptoms. In this case, the α5 and β4 nAChR subunits have critical roles in combination with other subunits. In both of these neural systems, particular nAChR subtypes have roles that contribute to the overall nicotine addiction process.

Nanomolar ambient ATP decelerates P2X3 receptor kinetics

Homomeric P2X receptors differ in their electrophysiological and pharmacological profiles. The rapidly activating and desensitizing P2X3 receptors are known for their involvement in pain signalling pathways. Modulatory effects on P2X3 receptors have been reported for low concentrations of ATP ([ATP]). This includes both, enhancement and reduction of receptor currents. The first has been reported to be mediated by activation of ectoprotein kinases and high affinity desensitization (HAD), respectively. Both processes influence receptor current amplitudes. Here we describe a new phenomenon, the modulatory influence of ambient low [ATP] on P2X3 receptor kinetics. First, we studied in HEK cells whether persistent ATP affects current decay. To this end, P2X3 receptor mediated currents, elicited by pressure application of saturating [ATP], were analyzed after pre-application of low [ATP]. Second, UV-flash photolysis of ATP was employed to investigate whether submicromolar [ATP] affects receptor activation. Finally we confirmed the action of nanomolar [ATP] on native P2X3 receptors of neurons freshly isolated from rat dorsal root ganglia. We found that persistent low [ATP] caused pronounced deceleration of receptor current activation and decay. This priming effect indicates a mechanism different from HAD. It could be explained by a pre-opening receptor isomerization, induced by the occupation of a high affinity binding site already at the resting state. The observed modulation of the receptor kinetics could be considered as a physiological fine tuning mechanism of the nociceptive system, driven by the actual ambient agonist concentration.

A chemical waveform synthesizer

Algorithms and methods were developed to synthesize complex chemical waveforms in open volumes by using a scanning-probe microfluidic platform. Time-dependent variations and oscillations of one or several chemical species around the scanning probe, such as formation of sine waves, damped oscillations, and generation of more complex patterns, are demonstrated. Furthermore, we show that intricate bursting and chaotic calcium oscillations found in biological microdomains can be reproduced and that a biological cell can be used as a probe to study receptor functionalities as a function of exposure to time-dependent variations of receptor activators and inhibitors. Thus, the method allows for studies of biologically important oscillatory reactions. More generally, the system allows for detailed studies of complex time-varying chemical and physical phenomena in solution or at solution/surface interfaces.

Applying small quantities of multiple compounds to defined locations of in vitro brain slices

When studying in vitro brain slices, rapidly applying multiple agonists, antagonists, drugs, or modulatory compounds is a significant technical problem. There are three major ways that multiple compounds are applied to slices: by bath, via a U-tube device, or by pressure application using a "puffer" pipette. Each of these methods has advantages and disadvantages, making each more appropriate for particular purposes. Because puffer pipettes have a small, sharp tip, they are best suited to apply a small quantity of a compound to a well-defined location within the slice. When used in this way, puffer pipettes have two shortcomings. Solution leaking from the tip of the pipette can contaminate the signal, and it is difficult to apply more than one test solution to exactly the same local area of the slice. We describe methods and newly designed devices aimed at overcoming those limitations. Relatively inexpensive approaches are described to apply eight different solutions to the same exact location deep within a brain slice. The validity of the approach is verified by measuring ligand-gated channel currents activated by glutamate (Glu), acetylcholine (ACh), and gamma-amino butyric acid (GABA).

Functional high- and low affinity agonist binding sites at native dorsal horn AMPA receptors

Transmission and processing of nociceptive information in the superficial dorsal horn (DH) of the spinal cord involves activation of AMPA-type glutamate receptors (AMPARs). We have studied the properties of native AMPARs in freshly dissociated laminae I-II neurones from postnatal rats using a modified form of the concentration-clamp technique for fast agonist application. Analysis of kainic acid dose-response curves showed the existence of two types of functional agonist binding sites governing AMPAR activation. These sites differ by their affinity for the agonist. Depending on the neurotransmitter concentration reached in the synaptic cleft, the relative contribution of high affinity and low affinity sites might play an important role in the shaping of AMPAR-mediated postsynaptic currents.