Depolarisation state- and cell type-specific regulation of medium spiny neurons in tail of striatum by projections from auditory thalamus
1 DZNE
The striatum integrates inputs from nearly all cortical and thalamic regions to optimise behavioural strategies, which is particularly well studied in its rostral subdivision. Caudal striatal regions, such as tail of striatum (TS), have received less attention. TS exhibits unique cell-type distributions and input patterns, including projections from auditory cortex (AC) and auditory thalamus (medial geniculate body; MGB). This suggests a role for TS in auditory processing to support learning. While plasticity in AC-TS projections has been observed in an auditory discrimination task, the physiology of MGB-TS synapses is not well understood. The goal of this study was therefore to determine how MGB afferents modulate medium spiny neuron (MSN) activity in TS. We recorded ex vivo from Drd1a-positive and Drd1a-negative MSNs in TS while optogenetically activating MGB inputs. Each MSN was subject to two recording protocols: (1) depolarising current steps with and without light pulse and (2) a single light pulse followed by a pulse train. MGB neurons formed direct inputs onto both Drd1a-positive and Drd1a-negative MSNs. These inputs evoked a mix of excitatory and inhibitory postsynaptic potentials (PSPs), with a prevalence of mixed PSPs in Drd1a-positive MSNs. Firing rate was affected across all MSNs, with thalamostriatal activation increasing action potential frequency specifically during high depolarisation states. Finally, we found that MGB activation modulated latency to first spike and inter-spike interval depending on MSN type and depolarisation state. Together, these results suggest that thalamostriatal synapses in TS differentially transmit information depending on postsynaptic cell type and depolarisation state.