My main research focus is on the biophysical events underlying transmitter release and the membrane excitability of axons, using axons and synapses of the crayfish neuromuscular junction. There are three aspects to the research in my laboratory. First, we investigate the basic biophysical properties of ion channel distribution in motor axons. Second, as part of the class project for students in BI445, we use the crayfish preparation to study cellular mechanisms underlying the effects of pesticides and antiepileptic drugs (AED). Third, in collaboration with colleagues with physics and engineering expertise, we investigate the effects of ultrasound in the MHz range, and of pulsed infrared lasers, on neuronal excitability.
On the basic biophysical properties of the crayfish axon:
We take advantage of the accessibility of the crayfish axon, where simultaneous recordings from multiple locations are possible. We have demonstrated that voltage gated channels have a non-uniform density along the proximo-distal axis. Specifically, Na+ channel has a high density in the proximal, thick axonal branches and this density gradually decreases as axons branch and taper into terminal varicosities to the extent that terminals are unable to fire action potentials (Lin, 2013,16). On the other hand, there is a high density of a low threshold, fast K+ channel in the distal, thin branches and a low density in proximal axons (Lin, 2012). Why is there such non-uniformity in channel distribution? We propose that this distribution is optimized for preventing unintended “back-firing” of action potentials in distal branches.
On studies of industrial and clinical reagents:
This line of research is performed as part of my students’ class project for BI/NE445. Many pesticides and clinically used drugs have been investigated at both the molecular and animal/human level. In other words, we know how these reagents work, and we know that they are effective at a behavioral level. However, the effects of these reagents on individual cells are often not well characterized. Neurons are diverse in morphology and ion channel distribution and therefore different neurons would be expected to respond differently to these reagents. We use the crayfish neuromuscular junction to investigate this expectation. We have published a paper on deltamethrin, a commonly used house-hold and agricultural pesticide. Our novel finding was that deltamethrin could initiate action potential “backfiring” in the crayfish motor axons (Meng et al., 2016). We are currently preparing a manuscript on an AED, Levetiracetam (LEV). LEV has been used in patients who failed to respond to traditional AEDs that target ion channels. This drugs is believed to enter neurons by endocytosis during the vesicular recycling process and then modulate transmitter release, which is believed to be the mechanism underlying its antiepileptic effects. Our study, however, shows that, in addition to suppressing transmitter release during high frequency stimulation, LEV also reduces action potential amplitude. This observation significantly revises our understanding of the mechanisms underlying the antiepileptic effect of this drug.
On collaboration with colleagues with physics and engineering expertise:
The accessibility and hardy nature of the crayfish nerve-muscle preparation makes it ideal for testing the cellular mechanisms underlying neuronal modulation by physical modalities that have been made possible by newly developed technology. We are currently collaborating with Dr. Okada’s laboratory at Boston Children’s Hospital on a project, funded by the National Science Foundation, to investigate the effects of MHz ultrasound on neuronal excitation. Since ultrasound in this frequency range can penetrate the skull, improved understanding and optimization of this technology in relation to neuronal tissue could potentially help with the development of non-invasive brain stimulation in humans. We are also collaborating with Dr. Sander in the BU Electric Engineering department, to examine the effects of pulsed infrared lasers on neuronal excitability. Infrared photons with wavelength in µm range can penetrate biological tissues and are known to activate neurons. However, the mechanisms of the infrared laser action and optimal laser parameters to be used to modulate neuronal activity are not fully understood. Our efforts in this project could help advancing potential applications of infrared lasers in medicine.
In summary, my laboratory uses electrophysiological and imaging techniques to address basic neurophysiological questions related to axonal excitability. In addition, the crayfish preparation we use is proving versatile for mechanistic testing of drugs and industrial reagents at a cellular level, as well for interdisciplinary exploration of newly developed technologies on nervous system function.
- Meng L, Meyer PF, Leary ML, Mohammed YF, Ferber SD, Lin JW (2016) Effects of Deltametrhin on crayfish motor axon activity and neuromuscular transmission, Neurosci Lett. 617: 32-38.
- Lin JW (2016) Na+ current in presynaptic terminals of the crayfish opener cannot initiate action potentials. J Neurophysiol. 115: 617-621.
- Inam ZS, Nelamangala SK, Lin JW (2014) Application of a spike sorting procedure to analyze recordings in the crayfish ventral superficial flexor preparation: A high resolution approach to the study of neuromodulators on axons and synapses. The Journal of Undergraduate Neuroscience Education (JUNE) 12: 140-149.
- Lin JW (2013) Spatial gradient in the TTX sensitivity of axons at the crayfish opener neuromuscular junction. J Neurophysiol. 109: 162-170.
- Lin JW (2012) Spatial variation in membrane excitability modulated by 4-AP-sensitive K+ channels in the axons of the crayfish neuromuscular junction. J Neurophysiol 107: 2692-2702.
- Lin JW (2008) Electrophysiological events recorded at presynaptic terminals of the crayfish neuromuscular junction with a voltage indicator J Physiology 586: 4935-4950.
- Allana T, Lin JW (2008) Effects of increasing Ca2+ channel-vesicle separation on facilitation at the crayfish inhibitory neuromuscular junction. Neuroscience, 154(4): 1242-54.
- Lin JW, Fu Q, Allana T (2005) Probing the endogenous Ca2+ buffers at the presynaptic terminals of the crayfish neuromuscular junction. J Neurophysiol. 94: 377-386.
- BI 325 Principles of Neuroscience
- BI 445/645 Cellular and molecular neurophysiology