A comparison of three different methods of eliciting rapid activity-dependent synaptic plasticity at the Drosophila NMJ

The Drosophila NMJ is a system of choice for investigating the mechanisms underlying the structural and functional modifications evoked during activity-dependent synaptic plasticity. Because fly genetics allows considerable versatility, many strategies can be employed to elicit this activity. Here, we compare three different stimulation methods for eliciting activity-dependent changes in structure and function at the Drosophila NMJ. We find that the method using patterned stimulations driven by a K+-rich solution creates robust structural modifications but reduces muscle viability, as assessed by resting potential and membrane resistance. We argue that, using this method, electrophysiological studies that consider the frequency of events, rather than their amplitude, are the only reliable studies. We contrast these results with the expression of CsChrimson channels and red-light stimulation at the NMJ, as well as with the expression of TRPA channels and temperature stimulation. With both these methods we observed reliable modifications of synaptic structures and consistent changes in electrophysiological properties. Indeed, we observed a rapid appearance of immature boutons that lack postsynaptic differentiation, and a potentiation of spontaneous neurotransmission frequency. Surprisingly, a patterned application of temperature changes alone is sufficient to provoke both structural and functional plasticity. In this context, temperature-dependent TRPA channel activation induces additional structural plasticity but no further increase in the frequency of spontaneous neurotransmission, suggesting an uncoupling of these mechanisms.

Physiological changes throughout the ear due to age and noise - a longitudinal study

Biological and mechanical systems, whether by their overuse or their aging, will inevitably fail. Hearing provides a poignant example of this with noise-induced and age-related hearing loss. Hearing loss is not unique to humans, however, and is experienced by all animals in the face of wild and eclectic differences in ear morphology and operation. Here we exploited the high throughput and accessible tympanal ear of the desert locust, Schistocerca gregaria (mixed sex) to rigorously quantify changes in the auditory system due to noise exposure (3 kHz pure tone at 126 dB SPL) and age. We analysed tympanal dispalcements, morphology of the auditory Mullers organ and measured activity of the auditory nerve, the transduction current and electrophysiological properties of individual auditory receptors. We found that noise mildly and transiently changes tympanal displacements, decreases both the width of the auditory nerve and the transduction current recorded from individual auditory neurons. Whereas age, but not noise, decreases the number of auditory neurons and increases their resting potential. Multiple other properties of Mullers organ were unaffected by either age or noise including: the number of supporting cells in Mullers organ or the nerve, membrane resistance and capacitance of the auditory neurons. The sound-evoked activity of the auditory nerve decreased as a function of age and this decrease was exacerbated by noise, with the largest difference during the middle of their life span. This middle-aged deafness pattern of hearing loss mirrors that found for humans exposed to noise early in their life.

A dynamic clamp protocol to artificially modify cell capacitance

Dynamics of excitable cells and networks depend on the membrane time constant, set by membrane resistance and capacitance. Whereas pharmacological and genetic manipulations of ionic conductances are routine in electrophysiology, experimental control over capacitance remains a challenge. Here, we present capacitance clamp, an approach that allows to mimic a modified capacitance in biological neurons via an unconventional application of the dynamic clamp technique. We first demonstrate the feasibility to quantitatively modulate capacitance in a mathematical neuron model and then confirm the functionality of capacitance clamp in in vitro experiments in granule cells of rodent dentate gyrus with up to threefold virtual capacitance changes. Clamping of capacitance thus constitutes a novel technique to probe and decipher mechanisms of neuronal signaling in ways that were so far inaccessible to experimental electrophysiology.

Electrophysiological and Morphological Studies of SOD1 Transgenic Mice: An Animal Model of ALS

Amyotrophic lateral sclerosis (ALS) is a disease where upper and lower motor neurons die, and it is often associated with mutations of superoxide dismutase 1 (SOD1). We have used mouse models to compare physiologic and morphologic characteristics of cervical motor neurons in wild-type and mutant animals. Slices of the cervical spinal cord were prepared from old wild-type and mutant G93A and G85R mice, and intracellular recordings of membrane potential, resistance and responses to application of excitatory neurotransmitters were studied. Some motor neurons were injected with Lucifer Yellow for morphological analysis. There were no significant differences between membrane potential in the SOD1 mutants and aged wild-type mice, but membrane resistance was somewhat higher in the mutant motor neurons. Dendrites of the mutant motor neurons were not responsive to ionophoretic application of excitatory amino acids, although the cell body responded strongly. In Lucifer-filled cells, the dendrites were found to disappear. Mutant motor neurons were sometimes spontaneously active. Responses of mutant motor neurons to perfused glutamate with varying calcium concentrations in the Ringer’s solution were different from those of the wild-type cells.

Physiological and Pharmacological Studies on Cervical Motor Neurons in Slices Prepared from Neonatal and Aged Mice

The effects of age on the physiological properties of cervical motor neurons were examined in slices made from an excised spinal cord graft of ICR mice from the second day after birth to age 350 days. The membrane potential of post-natal day 2 (PD2) to PD350 was about -65 mV and did not change greatly with age, although it was slightly higher at PD2. However, there were significant changes in membrane resistance, which increased with age from about 15 to 30 MΩ. The depolarization induced by the excitatory amino acid agonists, kainic acid, NMDA and AMPA, decreased with aging in spite of the increase in membrane resistance. The motor neurons of the aged mice showed delayed recovery from excitation caused by excitatory amino acid agonists. By injecting Lucifer yellow CH into motor neurons, it was observed that the dendrite trees become thin, and some of the dendrite branches were missing in older animals.