Histamine H1 receptor knockout mice exhibit impaired spatial memory in the eight-arm radial maze

Background and purpose:

In the mammalian brain, histaminergic neurotransmission is mediated by the postsynaptic histamine H₁ and H₂ receptors and the presynaptic H₃ autoreceptor, which also acts as a heteroreceptor. The H₁ receptor has been implicated in spatial learning and memory formation. However, pharmacological and lesion studies have revealed conflicting results. To examine the involvement of histamine H₁ receptor in spatial reference and working memory formation, H₁ receptor knockout mice (KO) were tested in the eight-arm radial maze. Previously, we found that the H₁ receptor-KO mice showed reduced emotionality when confronted with spatial novelty. As it is known that emotions can have an impact on spatial learning and memory performance, we also evaluated H₁ receptor-KO mice in terms of emotional behaviour in the light–dark box.

Experimental approach:

Mice lacking the H₁ receptor and wild-type mice (WT) were tested for spatial reference and working memory in an eight-arm radial maze with three arms baited and one trial per day. Emotional behaviour was measured using the light–dark test.

Key results:

The H₁ receptor-KO mice showed impaired spatial reference and working memory in the radial maze task. No significant differences between H₁ receptor-KO and WT mice were observed in the light–dark test.

Conclusions and implications:

The spatial memory deficits of the H₁ receptor-KO mice might be due to the reported changes in cholinergic neurochemical parameters in the frontal cortex and the CA1 subregion of the hippocampus, to impaired synaptic plasticity in the hippocampus, and/or to a dysfunctional brain reward/reinforcement system.