NMDA receptor-independent mechanisms responsible for the rate of rise of cumulative depolarization evoked by trains of dorsal root stimuli on rat spinal motoneurones

The mechanisms responsible for the rate of rise (RR) of cumulative depolarization induced by dorsal root stimulus trains were investigated with intracellular recordings from motoneurones of the rat isolated spinal cord. The NMDA receptor antagonists CPP or APV depressed the cumulative depolarization but not its RR which could still be fast enough to elicit action potential wind-up. RR size was correlated with a slow synaptic potential (detected in CPP or APV solution) with which it shared similar voltage dependence. The NK1 antagonist SR 140333 depressed cumulative depolarization, RR and slow synaptic potentials. It appears that the RR (and the ability to express wind-up) was determined by summation of slow synaptic potentials partly mediated via activation of NK1 receptors.     

20 Hz membrane potential oscillations are driven by synaptic inputs in collision-detecting neurons in the frog optic tectum

Although the firing patterns of collision-detecting neurons have been described in detail in several species, the mechanisms generating responses in these neurons to visual objects on a collision course remain largely unknown. This is partly due to the limited number of intracellular recordings from such neurons, particularly in vertebrate species. By employing patch recordings in a novel integrated frog eye-tectum preparation we tested the hypothesis that OFF retinal ganglion cells were driving the responses to visual objects on a collision course in the frog optic tectum neurons. We found that the majority (22/26) of neurons in layer 6 responding to visual stimuli fitted the definition of η class collision-detectors: they readily responded to a looming stimulus imitating collision but not a receding stimulus (spike count difference ∼10 times) and the spike firing rate peaked after the stimulus visual angle reached a threshold value of ∼20–45°. In the majority of these neurons (15/22) a slow frequency oscillation (f = ∼20 Hz) of the neuronal membrane potential could be detected in the responses to a simulated collision stimulus, as well as to turning off the lights. Since OFF retinal ganglion cells could produce such oscillations, our observations are in agreement with the hypothesis that ‘collision’ responses in the frog optic tectum neurons are driven by synaptic inputs from OFF retinal ganglion cells.     

Cellular signalling properties in microcircuits

Molecules and cells are the signalling elements in microcircuits. Recent studies have uncovered bewildering diversity in postsynaptic signalling properties in all areas of the vertebrate nervous system. Major effort is now being invested in establishing the specialized signalling properties at the cellular and molecular levels in microcircuits in specific brain regions. This review is part of the TINS Microcircuits Special Feature.     

Comparison of non-surgical methods for the treatment of deep partial thickness skin burns of the hand

This paper describes a randomized, controlled, parallel-group, single-center clinical trial designed to compare non surgical treatment methods of deep partial thickness skin burns of the hand.All patients were scanned with the Laser Doppler Imaging device to determine the depth of the burn wound. Viable keratinocytes sites were determined according to the established Perfusion Units (PU) measurement system. The trial enrolled 87 patients with hand burn wounds in the section of 260–600 PU.Hand burn patients were divided into the following four groups: treated with hydrocolloid dressings; treated with mechanical debridement of monofilament polyester fibers pad and then applying silver sulfadiazine; treated with gauze dressings containing enzymatic collagenase preparation. The fourth group of patients was treated with silver sulfadiazine and gauze dressings. This group was considered as the control group. The wound healing status was assessed after 3, 7, 14 and 21 days. Burn scars and injured extremity function were assessed after six months according to the Vancouver Scar Scale and Disabilities of the Arm, Shoulder and Hand Outcome Measure.The fastest epithelialization of hand burn wounds was observed in the patients group treated with hydrocolloid dressings (15, 7 days, p < 0,05). The patients of this group also had less scars and a better hand function.     

A simple method for efficient spike detection in multiunit recordings

A number of spike detection and sorting methods exist and the availability of powerful desktop computers may suggest that the problem of spike detection is solved. However, for portable multi-channel systems, when one takes into account the power consumption limitations, computationally simple methods can be advantageous when compared to more complex algorithms. Here we describe a simple spike detection method that reduces approximately two-fold the rate of false detections compared to the single threshold spike detection method. The proposed algorithm can be employed in an analog electronic chip thus eliminating the need for the digitization of the original signal. Consequently, only the times of spike occurrence can be transmitted for further analysis.     

An NK1 Receptor-dependent Component of the Slow Excitation Recorded Intracellularly from Rat Motoneurons Following Dorsal Root Stimulation

Intracellular recording from lumbar motoneurons of the neonatal rat spinal cord in vitro was used to study how recently developed non-peptide antagonists such as SR-140333 and SR-48698, known to block distinct subtypes of tachykinin receptors peripherally, might affect synaptic transmission elicited by electrical stimulation of dorsal root fibres. SR-140333 (1 μM) preferentially antagonized responses mediated by an exogenously applied agonist acting on the NK₁ receptor subclass, while SR-48968 (0.5 μM) preferentially reduced responses mediated by an exogenously applied agonist acting on the NK₂ receptor subclass. SR-48968 did not affect fast or slow excitatory postsynaptic potentials (EPSPs) or ‘wind-up’responses induced by repetitive, low-frequency stimulation (mimicking certain types of nociceptive input); binding studies using this radiolabelled ligand disclosed specific binding activity (21 fmol/mg protein) selectively displaced by an NK₂ receptor agonist. SR-140333 reduced the late component of fast and slow EPSPs, and of wind-up. Pharmacological block of ionotropic glutamate receptors abolished all dorsal root-evoked EPSPs. In comparison to glutamate receptor blockers, SR-140333 was a weaker antagonist of slow synaptic responses, though it displayed preferential antagonism towards some components of the wind-up phenomenon. The present results provide evidence obtained with a novel NK₁ antagonist that a neuropeptide (presumably substance P), although not directly released by primary afferents onto motoneurons, is a neurotransmitter (acting via NK₁ receptors) in the pathway mediating slow synaptic responses of motoneurons, and is presumably involved in signalling nociceptive inputs from the periphery.     

Use of medications amongst older persons in Kaunas, Lithuania

Aim

To evaluate the associations between socio-economical factors and the use of medications in the elderly.

Methods

The data was collected in a cross-sectional study in 2009. We received 624 completed questionnaires (response rate — 48.9%) from elderly people aged 60–84 years living in Kaunas (Lithuania). For an evaluation of the impact of explanatory variables on the analyzed events (binary dependent variable), an Enter model of logistic regression was used.

Results

Our findings suggest that 50.8% (n=317) of respondents used at least one drug daily. 18.3% (n=114) of respondents indicated that they use medications regularly, but not on a day-by-day basis. One quarter (25.6%; n=160) used medication only on an “at need” basis. Only 5.3% (n=33) of older persons did not use any medications at all. Logistic regression showed that being male (OR=0.67; 95%CI:0.45–0.98) was associated with using medications “regularly + daily.” For the use of “daily” medications, older age (OR=1.33; 95%CI:1.15–1.53) was associated with using medications daily. An opposite association was observed for respondents having no paid work (OR=0.48; 95%CI:0.26–0.82).

Conclusions

Our study suggests that more than half of older persons in Lithuania use medications every day. Use was associated with socioeconomic factors (gender, age, and employment status).     

The determinants of the onset dynamics of action potentials in a computational model

Action potentials (APs) in the soma of central neurons exhibit a sharp, step-like onset dynamics, which facilitates the encoding of weak but rapidly changing input signals into trains of action potentials. One possibility to explain the rapid AP onset dynamics is to assume cooperative activation of sodium channels. However, there is no direct evidence for cooperativity of voltage gated sodium channels in central mammalian neurons. The fact that APs in cortical neurons are initiated in the axon and backpropagate into the soma, prompted an alternative explanation of the sharp onset of somatic APs. In the invasion scenario, the AP onset is smooth at the initiation site in the axon initial segment, but the current invading the soma before somatic sodium channels are activated produces a sharp onset of somatic APs. Here we used multicompartment neuron models to identify ranges of active and passive cell properties that are necessary to reproduce the sharp AP onset in the invasion scenario. Results of our simulations show that AP initiation in the axon is a necessary but not a sufficient condition for the sharp onset of somatic AP: for a broad range of parameters, models could reproduce distal AP initiation and backpropagation but failed to quantitatively reproduce the onset dynamics of somatic APs observed in cortical neurons. To reproduce sharp onset of somatic APs, the invasion scenario required specific combinations of active and passive cell properties. The required properties of the axon initial segment differ significantly from the currently accepted and experimentally estimated values. We conclude that factors additional to the invasion contribute to the sharp AP onset and further experiments are needed to explain the AP onset dynamics in cortical neurons.