Activation of 5-HT7 receptors in the mouse dentate gyrus does not affect theta-burst-induced plasticity at the perforant path synapse.

Background: The study examined the effects of 5-HT₇ receptor activation on GABAergic transmission within the dentate gyrus and plasticity at the glutamatergic perforant path input.

Methods: Immunofluorescence imaging was performed using transverse hippocampal slices from transgenic mice expressing green fluorescent protein (GFP) under the Htr7 promoter. This was followed by whole-cell patch clamp electrophysiological recordings assessing the effects of pharmacologically activating 5-HT₇ receptors on spontaneous inhibitory postsynaptic currents recorded from dentate granule cells and hilar mossy cells-two glutamatergic neuron types present in the dentate gyrus. Extracellular recordings of field excitatory postsynaptic potentials were then performed to assess whether 5-HT₇ receptor activation influenced theta-burst stimulation-evoked plasticity of the perforant path synaptic input.

Results: It was found that parvalbumin and somatostatin interneurons in the dentate gyrus expressed GFP, which suggests they express 5-HT₇ receptors. However, activation of 5-HT₇ receptors had no effect on GABAergic transmission targeting mossy cells or granule cells. There was also no effect of 5-HT₇ receptor activation on perforant path plasticity either with intact or blocked GABA_A receptor signaling.

Conclusion: The presence of 5-HT₇ receptors in a subset of parvalbumin and somatostatin interneurons in the mouse dentate gyrus could mean that they are involved in the inhibitory control of dentate gyrus activity. However, this potential effect was not evident in slice recordings of inhibitory transmission targeting principal cells and did not affect perforant path plasticity. Further experiments are needed to fully elucidate the functional role of these receptors in the dentate gyrus.