Tac1, or tachykinin 1, has diverse functions. In animals, it is involved in neural circuits related to various behaviors and physiological responses. In plants, it contributes to regulating lateral shoot orientation. In animals, it plays roles in pathways such as those related to itch-scratching cycles, defensive responses, sexual behavior, social interactions, anhedonia-like behavior, and avoidance responses to aversive stimuli [1,2,3,4,6,7]. In plants, it opposes the influence of LAZY1 on lateral shoot orientation [5].

In mice, the ablation or suppression of Tac1-expressing neurons in the lateral and ventrolateral periaqueductal gray decreased itch-induced scratching behavior, suggesting that these neurons promote the itch-scratching cycle [1]. In the gut-to-brain axis, manipulation of the circuit involving Tac1+ neurons in the dorsal vagal complex interfered with toxin-induced defensive responses [2]. Ablation of spinal neurons expressing gastrin-releasing peptide receptor suppressed the scratching behavior evoked by Tac1-expressing neuron activation, indicating the importance of this neural connection in the itch-scratching cycle [1].

In conclusion, Tac1 is crucial in multiple biological processes, including those related to neural-mediated behaviors in animals and shoot architecture regulation in plants. Studies using mouse models, especially those involving manipulation of Tac1-expressing neurons, have revealed its role in various physiological and behavioral responses, which may provide insights into related disease conditions and plant growth regulation.