Transient expression of functional serotonin 5‐HT₃ receptors by glutamatergic granule cells in the early postnatal mouse cerebellum

Abstract

Non-technical summary The serotonin 3 receptor is a ligand-gated ion channel which is activated by the neurotransmitter serotonin. This receptor is present in many parts of the brain, yet there is hardly any information on its function in the cerebellum. In this study, we use transgenic mice to show that the serotonin 3 receptor is localised in the cerebellum during the first three weeks after birth. We found that during this period, the serotonin 3 receptor regulates communication between two major types of neurons in the cerebellum, the granule cells and the Purkinje cells. In the absence of this receptor during early postnatal development, synaptic transmission between those neurons is disturbed. Taken together, these findings can help us understand the way serotonin affects the function of the cerebellum, and may provide insight into pathophysiological conditions in which the serotonergic system is compromised. AbstractThe serotonin 5-HT 3 receptor is the only ligand-gated ion channel activated by serotonin and is expressed by GABAergic interneurons in many brain regions, including the cortex, amygdala and hippocampus. Furthermore, 5-HT 3 receptors are expressed by glutamatergic Cajal-Retzius cells in the cerebral cortex. We used 5-HT 3A /enhanced green fluorescent protein (EGFP) transgenic mice to show that 5-HT 3 receptors are also ubiquitously expressed by glutamatergic granule cells in the cerebellum during the first three postnatal weeks. Using whole-cell patch clamp recordings, we show that local application of either serotonin or the selective 5-HT 3 receptor agonist SR57227A to granule cells results in a small inward current, demonstrating a post-and/or extrasynaptic localisation of the 5-HT 3 receptors. Functional 5-HT 3 receptors were also observed presynaptically at the parallel fibre-Purkinje cell synapse. Pharmacological block using the selective 5-HT 3 receptor antagonist tropisetron induced a reduction in the frequency of miniature synaptic events recorded from Purkinje cells. Paired-pulse stimulation of parallel fibres on whole-cell voltage clamped Purkinje cells from 1-week-old mice did not yet show synaptic plasticity. In the presence of tropisetron, the parallel fibre-Purkinje cell synapse showed paired-pulse depression. Taken together, these results show that functional 5-HT 3 receptors are present during early postnatal development in the cerebellum, where they modulate synaptic plasticity. Abbreviations EGL, external granule cell layer; GFAP, glial fibrillary acidic protein; IGL, internal granule cell layer; mPSC, miniature postsynaptic current; P, postnatal day; PPR, paired-pulse ratio.

The Zona Incerta Regulates Communication between the Superior Colliculus and the Posteromedial Thalamus: Implications for Thalamic Interactions with the Dorsolateral Striatum

“…To visualize neurons in ZI that contained GABA, coronal sections were processed for glutamic acid decarboxylase (GAD) using procedures adapted from previous reports (Oostland et al, 2011;Aligny et al, 2014). The sections were rinsed in 0.1 M PBS for 20 min before being placed in a PBS-based blocking solution that contained 0.3 M glycine, 5% goat serum, 1% bovine serum albumin, and 0.1% Triton X-100, pH 7.4, at room temperature for 1 h. Sections were then incubated overnight with polyclonal rabbit anti-GAD 65/67 antibody (1:250, ab49832, Abcam) diluted in PBS at 4°C.…”

Altered cerebellar organization and function in monoamine oxidase A hypomorphic mice

“…During early development, the cerebellum exhibits a transient expression of 5-HT1 and 5-HT3 receptors, which play an important role in the formation of the cerebellar neuronal network (Miquel et al, 1994; Oostland et al, 2011). This may offer the possible mechanism behind a compromised serotonergic system during development and subsequent cerebellar abnormalities in adulthood.…”

“…For example, serotonergic fibers have a greater density in vermal lobules VII to X in rats (Bishop and Ho, 1985), while the greatest density in opossum was noted in VIII to IX and lowest in lobules II to V (Bishop et al, 1985). Even during development, the postnatal transient expression of 5-HT3 receptors is relatively high in lobules I to VI and lesser in lobules VII to X (Oostland et al, 2011). These lines of information suggest that individual cerebellar lobules may have a varying sensitivity to 5-HT homeostasis, and could be the mechanism behind the lobule-specific effects we observed in MAO-A Neo mice.…”

Maturation, Refinement, and Serotonergic Modulation of Cerebellar Cortical Circuits in Normal Development and in Murine Models of Autism

“…Studies in 5-HT 3A /EGFP transgenic mice have revealed that the expression pattern of 5-HT 3 R at P7 follows the migration pathway of the cerebellar granule cells from the external to the internal granule cell layer; then, by P14, the expression starts to decrease and becomes completely absent after P21 [138]. In contrast, no coexpression of 5-HT 3 receptors has been found with glial cells, PCs, and interneurons.…”