UCLA

Among the most protuberant behaviors during early developmental stages in the zebrafish is changes in heart rate.�In particular, past studies demonstrated behavioral sensitization by producing a range of behavioral modifications and often activating the autonomic nervous system. Previous work has shown that�allyl isothiocyanate�(AITC or mustard oil, MO) most likely elicits its sensitization effects through activation of TRP channels expressed on the trigeminal and Rohon Beard sensory neurons in larval zebrafish. To determine if AITC exposure activates the sympathetic nervous system in larval zebrafish, we used heart rate as a proxy for the activation of the autonomic nervous system. To confirm that our behavioral sensitization was induced by activation of TRP channels, we used Ruthenium Red (RR), which was previously shown to antagonize these receptors in zebrafish. In the present study, we found that 10��M total bath concentration of AITC significantly increased the heart rate activity in 5-day post fertilization (dpf), agarose-restrained larval zebrafish compared to control treated animals. On the other hand, 10��M total bath concentration of RR exposure prior to 10��M AITC exposure significantly decreased the heart rate activity, whereas, the equal concentration RR exposure after the AITC exposure had no suppressive effect on AITC induced increased heart rate in 5 DPF, agarose-restrained larval zebrafish. Further, we used behavioral pharmacology to dissect the molecular underpinnings of the sensitization memory. To determine whether the different neural circuits contributing to enhanced heart rate depend upon one or many different neuromodulators and ascertain how these neuromodulators influence distinct neural circuits we have conducted various extracellular receptor blockade experiments. We used D-APV, a competitive NMDAR antagonist, MK801, a non-competitive NMDAR antagonist, Methiothepin, a selective serotonin receptor antagonist, Haloperidol, a dopamine D2 receptor antagonist, Mecamylamine, a non-competitive nicotinic acetylcholine receptor antagonist, Propranolol, a non-selective beta-adrenergic receptor blocker and Atropine, a non-selective muscarinic acetylcholinergic antagonist. We discovered that AITC induced sensitization is accompanied by increase in heart rate, which implicates serotonin, dopamine receptors as well as β-adrenergic, nicotinic and muscarinic acetylcholine receptors from cardiac autonomic nervous system, but NMDA receptors don’t seem to play any role in this short term memory. Together, these results indicate the enormous potential that zebrafish hold as an animal model for the study of learning and memory, especially non-associative memory.