Abstract
The greater part of the striatum is composed of striosomes and matrix compartments, but we recently demonstrated the presence of a region that has a distinct structural organization in the ventral half of the mouse caudal striatum (Miyamoto et al. in Brain Struct Funct 223:4275–4291, 2018). This region, termed the tri-laminar part based upon its differential immunoreactivities for substance P and enkephalin, consists of medial, intermediate, and lateral divisions. In this study, we quantitatively analyzed the distributions of both projection neurons and interneurons in each division using immunohistochemistry. Two types of projection neurons expressing either the dopamine D1 receptor (D1R) or D2 receptor (D2R) showed complementary distributions throughout the tri-laminar part, but the proportions significantly differed among the three divisions. The proportion of D1R-expressing neurons in the medial, intermediate, and lateral divisions was 88.6 ± 8.2% (651 cells from 3 mice), 14.7 ± 3.8% (1025 cells), and 49.3 ± 4.5% (873 cells), respectively. The intermediate division was further characterized by poor innervation of tyrosine hydroxylase immunoreactive axons. The numerical density of choline acetyltransferase immunoreactive neurons differed among the three divisions following the order from the medial to lateral divisions. In contrast, PV-positive somata were distributed throughout all three divisions at a constant density. Two types of GABAergic interneurons labeled for nitric oxide synthase and calretinin showed the highest cell density in the medial division. The present results characterize the three divisions of the mouse caudal striatum as distinct structures, which will facilitate studies of novel functional loops in the basal ganglia.
Highlights
The striatum is the primary input structure of the basal ganglia and is abundantly innervated by axons originating from the cerebral cortex and thalamus
The activities of the mediumsized spiny neurons (MSNs) are regulated by dopaminergic neurons residing in the substantia nigra pars compacta, and the two MSN types differ in their expression pattern of dopamine receptors; type 1 dopamine receptors (D1Rs) are predominant in dMSNs, and type 2 dopamine receptors (D2Rs) are predominant in iMSNs (Gerfen and Surmeier 2011)
Serial coronal sections containing the entire tri-laminar part of the caudal striatum were processed for triple immunohistochemistry using antibodies against SP, Enk, and TH (Fig. 1)
Summary
The striatum is the primary input structure of the basal ganglia and is abundantly innervated by axons originating from the cerebral cortex and thalamus. Axons of dMSNs project to the substantia nigra and entopeduncular nucleus with their terminals containing GABA and substance P and dynorphin, whereas those of iMSNs innervate the globus pallidus with their terminals containing GABA and enkephalin (Harber and Watson 1983; Beckstead and Kersey 1985; Gerfen and Surmeier 2011). The activities of the MSNs are regulated by dopaminergic neurons residing in the substantia nigra pars compacta, and the two MSN types differ in their expression pattern of dopamine receptors; type 1 dopamine receptors (D1Rs) are predominant in dMSNs, and type 2 dopamine receptors (D2Rs) are predominant in iMSNs (Gerfen and Surmeier 2011). The distribution pattern of each neuronal type tends to be biased according to both the compartmental and dorsolateral–ventromedial organizations inside the striatum (Kubota and Kawaguchi 1993; Fukuda 2009; Miyamoto et al 2018)
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