# DBT JRF 2022 — Question 66

Exam: DBT JRF 2022 · Section: B · Topic: Physiology › Neuropharmacology & Adrenoceptors · Difficulty: Medium

## Question

In a neuronal culture experiment, the effect of a chemical (under study) was prevented by pretreating the cells with prazosin, an alpha1 adrenoceptor antagonist but not by propranolol, a beta adrenoceptor antagonist. The chemical under study is likely to be:

## Options

- **A.** Acetylcholine or carbachol
- **B.** Orexin or serotonin
- **C.** GABA or glutamate
- **D.** Noradrenaline or methoxamine

## Answer

Option D

## Explanation

Prazosin and propranolol pharmacology — receptor identification: Experimental setup: A chemical causes a physiological response. Prazosin ( $\alpha_1$ -adrenoceptor blocker) prevented the effect, but propranolol ( $\beta$ -adrenoceptor blocker) did NOT prevent it. Conclusion: • Since prazosin ( $\alpha_1$ blocker) blocked the effect, the chemical acts through $\alpha_1$ adrenoceptors. • The chemical must be an $\alpha_1$ adrenoceptor AGONIST. • Noradrenaline (norepinephrine): primarily an $\alpha_1$ agonist (and some $\alpha_2/\beta_1$ activity). • Methoxamine: a selective $\alpha_1$ adrenoceptor agonist. Both Noradrenaline and Methoxamine act via $\alpha_1$ receptors, consistent with the experiment. Answer: The chemical acts via $\alpha_1$ adrenoceptors; both noradrenaline and methoxamine are $\alpha_1$ agonists.

Source: https://mypyqbuddy.com/questions/in-a-neuronal-culture-experiment-the-effect-of-6a104cd5920734408bc0c751