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Invertebrate
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Grade 9+
Neuropharmacology: Neurotransmitters in Action
We’ve explored how neurons transmit electrical spikes, but chemical signalling is just as important. In this experiment you’ll use crickets to see first-hand how compounds such as MSG and nicotine alter neural activity.
About experiment
What Will You Learn?
- How neurotransmitters can increase or decrease neural firing.
- How to record spikes from a cricket’s cercal system.
- Why the same chemical can have opposite effects in different species.
Background
In the late 1800s scientists debated whether neurons were individual cells (Neuron Doctrine) or a continuous mesh (Reticular Theory). Electron microscopy confirmed that neurons are separate, meeting at tiny gaps called synapses. Chemicals—neurotransmitters—cross these ~20 nm gaps to pass messages.
We’ll record spikes from the cricket’s cercal system, two posterior appendages that detect wind and vibration. By applying MSG or nicotine we can watch the nervous system react in real time and see how evolution re-uses the same molecules in very different ways.
Experiment
Preparation, Baseline & Chemical Tests
Preparation & Baseline
- Collect a healthy cricket (pet shops sell them as feeders).
- Anaesthetise it in ice water for a few minutes.
- Secure the cricket to cork or balsa, leaving the cerci exposed.
- Place a ground electrode near the midline and a recording electrode close to the cerci.
- Blow gently on the cerci and record the baseline spikes.
Experiment 1 – MSG Injection
- Dissolve monosodium glutamate (MSG) in water to make a saturated solution.
- Fill an insulin syringe with ~0.1 cc of solution.
- Inject a small amount near the cerci, wait a few seconds, then record.
- Blow on the cerci again and compare with the baseline. Many observers find that MSG reduces or even silences firing in crickets.
Experiment 2 – Nicotine Injection
- Steep shredded tobacco in water for 1–2 days to produce a nicotine solution.
- Inject a few drops (~0.1 cc) near the cerci.
- Observe: firing rates usually rise sharply and the cricket may twitch.
- Blow on the cerci once more and note the heightened response. Nicotine overstimulates insect neurons via nicotinic acetylcholine receptors.
Discussion & Next Steps
Observations
- MSG often inhibits the cricket’s cercal system, reducing responsiveness to wind.
- Nicotine excites the nervous system, raising baseline firing and response.
Think Further
- Why does glutamate excite human neurons but inhibit cricket neurons?
- Could commercial vape liquids replicate the nicotine effect?
- What would caffeine, antihistamines or other household chemicals do?
This experiment shows how the same molecule can produce opposite outcomes depending on receptor type and species. Share your data or questions with hello@backyardbrains.com and keep exploring!
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