3D Printing Neuron Equivalent Circuits: An Undergraduate Laboratory Exercise.

The electrical equivalent circuit for a neuron is composed of common electrical components in a configuration that replicates the passive electrical properties and behaviors of the neural membrane. It is a powerful tool used to derive such fundamental neurophysiological equations as the Hodgkin-Huxley equations, and it is also the basis for well-known exercises that help students to model the passive (Ohmic) properties of the neuronal membrane. Unfortunately, as these exercises require basic knowledge of electronics, they are generally not physically conducted in biomedical courses, but remain merely conceptual exercises in a book or simulations on a computer.

Models for Spiking Neurons: Integrate-and-Fire Units and Relaxation Oscillators.

Relaxation oscillators are nonlinear electronic circuits that produce a repetitive non-sinusoidal waveform when sufficient voltage is applied. In this fashion, they are reminiscent of integrate-and-fire neuron models, except that they also include components with hysteresis, and thus require no threshold rule to determine when an impulse has occurred or to return the voltage to its reset value. Here, I discuss the pros and cons of teaching elementary neurophysiology using first-order linear integrate-and-fire neurons versus relaxation oscillator circuits.

Recording EMG Signals on a Computer Sound Card.

For a few dollars and in a few minutes, a simple circuit can be built to permit a cheap external sound card and a laptop computer to be used as a portable data acquisition system for recording EMG. The circuit uses a common audio amplifier integrated circuit to increase the gain of the EMG signals recorded from EMG surface electrodes and to match the impedance of the electrode-skin interface with the input impedance of the sound card. Data can be recorded using open source sound editing software and analyzed offline using simple Python code.

Breadboard Amplifier: Building and Using Simple Electrophysiology Equipment.

Electrophysiology is a valuable skill for the neuroscientist, but the learning curve for students can be steep. Here we describe a very simple electromyography (EMG) amplifier that can be built from scratch by students with no electronics experience in about 30 minutes, making it ideal for incorporating into a laboratory activity. With few parts and no adjustments except the gain, students can begin physiology experiments quickly while having the satisfaction of having built the equipment themselves.

Pencil-and-Paper Neural Networks: An Undergraduate Laboratory Exercise in Computational Neuroscience.

Although it has been more than 70 years since McCulloch and Pitts published their seminal work on artificial neural networks, such models remain primarily in the domain of computer science departments in undergraduate education. This is unfortunate, as simple network models offer undergraduate students a much-needed bridge between cellular neurobiology and processes governing thought and behavior. Here, we present a very simple laboratory exercise in which students constructed, trained and tested artificial neural networks by hand on paper.

Compensatory plasticity restores locomotion after chronic removal of descending projections.

Homeostatic plasticity is an important attribute of neurons and their networks, enabling functional recovery after perturbation. Furthermore, the directed nature of this plasticity may hold a key to the restoration of locomotion after spinal cord injury. Here we studied the recovery of crawling in the leech Hirudo verbana after descending cephalic fibers were surgically separated from crawl central pattern generators shown previously to be regulated by dopamine.

Assessing development of an interdisciplinary perspective in an undergraduate neuroscience course.

Neuroscience is an intrinsically interdisciplinary (ID) field yet little has been published regarding assessment of ID learning in undergraduate neuroscience students. This study attempted to empirically assess the development of an interdisciplinary perspective in 25 undergraduate neuroscience students in a neuroscience program core course. Data were collected using two simple assessment instruments: 1) written responses to the open-ended question "What is neuroscience?" and 2) a term-discipline relevance survey in which students indicated all disciplinary perspectives to which terms (such as electrode, taste, dx/dt) were relevant.

A structured-inquiry approach to teaching neurophysiology using computer simulation.

Computer simulation is a valuable tool for teaching the fundamentals of neurophysiology in undergraduate laboratories where time and equipment limitations restrict the amount of course content that can be delivered through hands-on interaction. However, students often find such exercises to be tedious and unstimulating. In an effort to engage students in the use of computational modeling while developing a deeper understanding of neurophysiology, an attempt was made to use an educational neurosimulation environment as the basis for a novel, inquiry-based research project.

Mechanisms contributing to the dopamine induction of crawl-like bursting in leech motoneurons.

Dopamine (DA) activates fictive crawling behavior in the medicinal leech. To identify the cellular mechanisms underlying this activation at the level of crawl-specific motoneuronal bursting, we targeted potential cAMP-dependent events that are often activated through DA(1)-like receptor signaling pathways. We found that isolated ganglia produced crawl-like motoneuron bursting after bath application of phosphodiesterase inhibitors (PDIs) that upregulated cAMP.

Nanowires precisely grown on the ends of microwire electrodes permit the recording of intracellular action potentials within deeper neural structures.

Aims: Nanoelectrodes are an emerging biomedical technology that can be used to record intracellular membrane potentials from neurons while causing minimal damage during membrane penetration. Current nanoelectrode designs, however, have low aspect ratios or large substrates and thus are not suitable for recording from neurons deep within complex natural structures, such as brain slices.

Materials & Methods: We describe a novel nanoelectrode design that uses nanowires grown on the ends of microwire recording electrodes similar to those frequently used in vivo.

Biogenic amines modulate pulse rate in the dorsal blood vessel of Lumbriculus variegatus.

The biogenic amines are widespread regulators of physiological processes, and play an important role in regulating heart rate in diverse organisms. Here, we present the first pharmacological evidence for a role of the biogenic amines in the regulation of dorsal blood vessel pulse rate in an aquatic oligochaete, Lumbriculus variegatus (Müller, 1774). Bath application of octopamine to intact worms resulted in an acceleration of pulse rate, but not when co-applied with the adenylyl cyclase inhibitor MDL-12,330a.

Multiple spike initiation zones in a neuron implicated in learning in the leech: a computational model.

Sensitization of the defensive shortening reflex in the leech has been linked to a segmentally repeated tri-synaptic positive feedback loop. Serotonin from the R-cell enhances S-cell excitability, S-cell impulses cross an electrical synapse into the C-interneuron, and the C-interneuron excites the R-cell via a glutamatergic synapse. The C-interneuron has two unusual characteristics.

Pros and cons of a group webpage design project in a freshman anatomy and physiology course.

To generate motivation and promote the development of written communication skills, students in a freshman-level anatomy and physiology course for nonmajors created group webpages describing historically important diseases. After the groups had been formed, each individual was assigned specific components of the disease (e.g.

Serotonergic modulation of afterhyperpolarization in a neuron that contributes to learning in the leech.

Modulation of afterhyperpolarization (AHP) represents an important mechanism by which excitability of a neuron can be regulated. In the leech brain, sensitization enhances excitability of the S-cell, an interneuron thought to play an important role in this form of nonassociative learning. This increase in excitability is serotonin (5-HT) dependent, but it is not known whether changes in AHP contribute to 5-HT-mediated enhancement of excitability.

Serotonin delays habituation of leech swim response to touch.

Serotonin, acting through a cAMP-signaling pathway, delayed habituation to criterion of the leech's swim response to touch. This delay was reversed by crushing the connective between serotonin-exposed and serotonin-naive ganglia, and correlated with an increase in spontaneous impulse activity in this connective. We suggest that increased activity in intersegmental interneurons may play a role in maintaining swim responsiveness when concentrations of serotonin are elevated.

Beyond the central pattern generator: amine modulation of decision-making neural pathways descending from the brain of the medicinal leech.

The biological mechanisms of behavioral selection, as it relates to locomotion, are far from understood, even in relatively simple invertebrate animals. In the medicinal leech, Hirudo medicinalis, the decision to swim is distributed across populations of swim-activating and swim-inactivating neurons descending from the subesophageal ganglion of the compound cephalic ganglion, i.e.

A 3-synapse positive feedback loop regulates the excitability of an interneuron critical for sensitization in the leech.

Sensitization of reflexive shortening in the leech has been linked to serotonin (5-HT)-induced changes in the excitability of a single interneuron, the S cell. This neuron is necessary for sensitization and complete dishabituation of reflexive shortening, during which it contributes to the sensory-motor reflex. The S cell does not contain 5-HT, which is released primarily from the Retzius (R) cells, whose firing enhances S-cell excitability.

A cephalic projection neuron involved in locomotion is dye coupled to the dopaminergic neural network in the medicinal leech.

It is widely appreciated that the selection and modulation of locomotor circuits are dependent on the actions of higher-order projection neurons. In the leech, Hirudo medicinalis, locomotion is modulated by a number of cephalic projection neurons that descend from the subesophageal ganglion in the head. Specifically, descending brain interneuron Tr2 functions as a command-like neuron that can terminate or sometimes trigger fictive swimming.

Distribution and development of dopamine- and octopamine-synthesizing neurons in the medicinal leech.

Although the medicinal leech is a well-studied system in which many neurons and circuits have been identified with precision, descriptions of the distributions of some of the major biogenic amines, such as dopamine (DA) and octopamine (OA), have yet to be completed. In the European medicinal leech Hirudo medicinalis and the American medicinal leech Macrobdella decora,we have presented the first immunohistochemical study of DA neurons in the entire central nervous system, and of OA-immunoreactive (ir) neurons in the head and tail brains. Dopaminergic neurons were identified using the glyoxylic acid method and antisera to DA and its rate-limiting synthetic enzyme tyrosine hydroxylase (TH).