Fig. 4

Histamine reuptake is most crucial for regulating stress-induced depression. Two states of the system have been studied A–C healthy, control condition associated with basal value of I_HA = 1250 nMs⁻¹ and B–D stressed condition associated with I_HA = 2*10⁴ nMs⁻¹. The serotonin levels are shown in blue bars and the associated histamine levels in orange bars. A, B Percentage change obtained in the system’s state under parameter variation is shown with respect to the system’s state at basal values of the respective parameters. C, D Local sensitivity analysis has been performed to identify the parameters towards which the system is most sensitive and vulnerable. Relative sensitivity signifies the vulnerability of a variable towards parameter changes, regardless of the order of the magnitude of the variable as well as the parameter. The basal values of these parameters around which this analysis is performed are τ_HA = 0.8 s⁻¹, τ_5HT = 0.8 s⁻¹, α = 69.7961 s⁻¹, β = 0.0013 s⁻¹, I_5HT = 56.3250 nMs⁻¹ and I_HA = 1250 nMs⁻¹ for the healthy condition and I_HA = 2*10⁴ nMs⁻¹ for the stressed condition