Limiting glutamate transmission in a Vglut2 -expressing subpopulation of the subthalamic nucleus is sufficient to cause hyperlocomotion

Abstract

The subthalamic nucleus (STN) is a key area of the basal ganglia circuitry regulating movement. We identified a subpopulation of neurons within this structure that coexpresses Vglut2 and Pitx2, and by conditional targeting of this subpopulation we reduced Vglut2 expression levels in the STN by 40%, leaving Pitx2 expression intact. This reduction diminished, yet did not eliminate, glutamatergic transmission in the substantia nigra pars reticulata and entopeduncular nucleus, two major targets of the STN. The knockout mice displayed hyperlocomotion and decreased latency in the initiation of movement while preserving normal gait and balance. Spatial cognition, social function, and level of impulsive choice also remained undisturbed. Furthermore, these mice showed reduced dopamine transporter binding and slower dopamine clearance in vivo, suggesting that Vglut2-expressing cells in the STN regulate dopaminergic transmission. Our results demonstrate that altering the contribution of a limited population within the STN is sufficient to achieve results similar to STN lesions and high-frequency stimulation, but with fewer side effects.Parkinson disease | deep brain stimulation | vesicular transporter | optogenetics | striatum T he subthalamic nucleus (STN) has long been a structure of interest for researchers and clinicians alike. There is ample evidence that high-frequency stimulation of the STN improves symptoms such as tremor, rigidity, and slowness of movement, so called bradykinesia, in patients with Parkinson disease (see ref. 1 for review), but the mechanism through which this is achieved is still unknown. Some studies suggest that electrical stimulation causes a hyperexcitation of this structure (2), whereas others find evidence that the opposite is true (3-5). Other possible interpretations include the activation of the zona incerta, a neighboring white-matter structure (6) or of fibers coming from the motor cortex (7). Bilateral lesions of the STN improve locomotion (8), a result that is consistent with the inactivation hypothesis. However, previous studies have also found cognitive side effects when using high-frequency stimulation of the STN (9), findings supported by lesion studies in experimental animals, which led to abnormalities in operant tasks involving attention and impulsivity (10, 11). The projections of the STN to other regions help explain the multiple roles of this structure: It sends projections to other targets in the basal ganglia, such as the internal segment of the globus pallidus [also termed the entopeduncular nucleus (EP) in rodents] and the substantia nigra pars reticulata (SNr) (12, 13). The STN is also part of a circuit that includes the prefrontal cortex and the nucleus accumbens (14). It is currently unknown, however, whether these different roles reflect a heterogeneous population of cells, characterized by distinct gene expression. If that is the case, it would allow direct control over each cell population, facilitating the investigation of their respective roles. In rodents, the S...

Foxa1 is essential for development and functional integrity of the subthalamic nucleus

“…3I). These findings are in agreement with a recent study, where impaired neurotransmission in the STN was shown to induce locomotion in the presence of normal motor coordination and gait29. Taken together, this suggests that Foxa1 deletion from the STN is at the roots of the observed hyperlocomotion phenotype, whereas midbrain motor programs are not affected by the ablation of Foxa1, probably due to the continued presence of Foxa2.…”

Validated multi‐step approach for in vivo recording and analysis of optogenetically evoked glutamate in the mouse globus pallidus

“…; Schweizer et al . ) of both sexes. All experiments were performed in strict accordance with the Swedish regulation guidelines (Animal Welfare Act SFS 1998:56) and European Union legislation (Convention ETS123 and Directive 2010/63/EU).…”

“…The animals had ad libitum access to food (R36, Labfor; Lactamin, Vadstena, Sweden) and water. Animals used in this study were Pitx2-cre tg/wt mice (Targeted allele MGI:2445429; mice obtainable from MMRRC: RRID: MMRRC_000126-UCD) (Skidmore et al 2008;Schweizer et al 2014) of both sexes. All experiments were performed in strict accordance with the Swedish regulation guidelines (Animal Welfare Act SFS 1998:56) and European Union legislation (Convention ETS123 and Directive 2010/63/EU).…”

“…; Schweizer et al . , ). Consequently, we were able to quantify optogenetically evoked glutamate release from Pitx2‐Cre‐expressing synaptic terminals in the GP of anesthetized mice, isolate light artifacts and detect glutamate release not originating from opsin activity.…”

“…In this study, we establish a method for recording glutamate concentrations upon optogenetic stimulation using glutamate-sensitive multielectrode amperometry in the intact neurocircuitry of adult mice. We utilized the Pitx2-Cre transgenic mouse line which allows for selective expression of optogenetic viral constructs in glutamatergic neurons of the STN (Skidmore et al 2008;Schweizer et al 2014Schweizer et al , 2016. Consequently, we were able to quantify optogenetically evoked glutamate release from Pitx2-Cre-expressing synaptic terminals in the GP of anesthetized mice, isolate light artifacts and detect glutamate release not originating from opsin activity.…”