Brain histamine is implicated in learning and memory as well as wakefulness, feeding, and neuroendocrine regulation. Previously, we demonstrated histamine H₃ receptor inverse agonists upregulate histamine release in the perirhinal cortex and promote the recall of forgotten object memories. However, whether histamine H₃ receptor inverse agonists enhance other types of long-term memory and whether activation of histamine neurons is enough for the memory recovery are unclear. First, we tested whether a histamine H₃ receptor inverse agonist enhances retrieval of spatial memory on barnes maze task. Thioperamide-treated mice explored a target zone for longer time on a probe test 1 week after training than saline-treated mice. Second, we examined whether chemogenetic activation of histamine neurons in the TMN enhances retrieval of forgotten object memory. We virally targeted hM3Dq, the Gq-coupled excitatory designer receptor exclusively activated by designer drugs (DREADD), to histamine neurons in the TMN of HDC-Cre mice. The mice performed a test session 1 week after training. Pre-test activation of histamine neurons led to a significant increase in the discrimination between novel and familiar objects. These findings indicate that activation of histamine neurons enhances retrieval of forgotten long-term memories.