Experiment: Neuropharmacology-Effect of Nicotine and MSG on Neurons

Invertebrates

Grade 9+

Neuropharmacology: Neurotransmitters in Action

We’ve explored how neurons transmit electrical signals—spikes—but chemical signaling also plays a huge role in how neurons talk to each other. In this experiment, we’ll use crickets to see firsthand how certain chemicals (like MSG and nicotine) affect neural activity.

Background

In the late 1800s, scientists debated whether neurons were individual cells (the Neural Doctrine) or a continuous mesh (the Reticular Theory). Modern electron microscopy confirmed that neurons do not fuse together; instead, they connect at tiny gaps called synapses. These ~20 nm gaps allow chemicals—neurotransmitters—to diffuse between cells to facilitate communication.

To investigate chemical effects on neurons, we’ll record spikes from the cricket’s cercal system—two posterior “antennae” that detect wind and vibration. This system provides an excellent window into the insect’s central nervous system. We’ll see how certain substances (like MSG and nicotine) can modulate neural activity. Interestingly, what’s excitatory in humans can be inhibitory in crickets, illustrating that nature reuses neurotransmitters in unique ways!

Preparation & Setup

1. Collect or acquire a cricket. Pet stores often sell them as feeder insects.
2. Anesthetize the cricket in ice water for a few minutes.
3. Secure it (tape or pins) to a piece of cork or balsa wood, leaving the cerci exposed.
4. Attach your bioamplifier electrodes—place a ground electrode near the midline, and a recording electrode close to the cerci.
5. Gently blow on the cerci and observe the spike activity in your recording software. Save a baseline recording.

Experiment 1: MSG Injection

1. Dissolve monosodium glutamate (MSG) in water to create a saturated solution.
2. Fill a small syringe (e.g. insulin syringe) with ~0.1cc of the MSG solution.
3. Inject a tiny amount of this solution near the cricket’s cerci. Wait a few seconds and then observe any changes in baseline firing.
4. Blow again on the cerci and compare the spike activity to your baseline.

Observation: Many find that MSG actually reduces or shuts down the neural activity in the cercal system of crickets, despite glutamate being excitatory in humans. This shows how the same neurotransmitter can have opposite effects in different species.

Experiment 2: Nicotine Injection

1. Create a nicotine solution by soaking shredded tobacco leaves in water for 1–2 days. The liquid may turn yellow-brown.
2. Using a syringe, inject a few drops (e.g. ~0.1cc) near the cerci.
3. Listen closely and observe. Typically, firing rates dramatically increase. The cricket may also show twitching or other heightened activity.
4. Blow on the cerci again—note the spike response now that the system is more excitable.

Why? Nicotine binds to nicotinic acetylcholine receptors, allowing positive ions to enter cells. In humans, these receptors occur primarily at the nerve-muscle junction and produce a stimulant effect. In insects, nicotine is actually a potent insecticide/toxin—here, it overstimulates the insect’s nervous system.

Discussion & Next Steps

Observations:
• MSG often inhibits the cricket's cercal system, diminishing neural response to wind.
• Nicotine excites the insect’s neurons, increasing baseline firing and response.

Thinking Further:
• Why does glutamate excite neurons in humans but inhibit them in crickets?
• Could you replicate the nicotine experiment with commercial vape liquids, adjusting for propylene glycol content?
• What other household chemicals (e.g., caffeine solutions, antihistamines) might affect neural activity?

Application: This experiment highlights how the same molecule can produce vastly different outcomes depending on the species and the specific receptors involved. By studying insect neuroscience, we gain insight into how chemical signaling underlies behavior in all animals.

Questions or Results? Send your data or stories to hello@backyardbrains.com. Keep exploring!

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