tetrodotoxin and Parkinson-Disease

Topics: Abnormalities, Drug-Induced; Acetylcholine; Adrenocorticotropic Hormone; Amphetamine; Anger; Angiotensin II; Animals; Avoidance Learning; Behavior, Animal; Cats; Central Nervous System; Central Nervous System Diseases; Chick Embryo; Desipramine; Dogs; Guanethidine; Guinea Pigs; Humans; Hypnotics and Sedatives; Imipramine; Memory; Mice; Norepinephrine; Parkinson Disease; Phenacetin; Phenothiazines; Phenoxybenzamine; Rabbits; Rats; Reserpine; Serotonin; Sleep; Sleep, REM; Synapses; Synaptic Transmission; Tetrodotoxin; Theophylline

Mutations in the gene encoding leucine-rich repeat kinase 2 (LRRK2) can cause Parkinson's disease (PD), and the most common disease-associated mutation, G2019S, increases kinase activity. Because LRRK2 expression levels rise during synaptogenesis and are highest in dorsal striatal spiny projection neurons (SPNs), we tested the hypothesis that the LRRK2-G2019S mutation would alter development of excitatory synaptic networks in dorsal striatum. To circumvent experimental confounds associated with LRRK2 overexpression, we used mice expressing LRRK2-G2019S or D2017A (kinase-dead) knockin mutations. In whole-cell recordings, G2019S SPNs exhibited a fourfold increase in sEPSC frequency compared with wild-type SPNs in postnatal day 21 mice. Such heightened neural activity was increased similarly in direct- and indirect-pathway SPNs, and action potential-dependent activity was particularly elevated. Excitatory synaptic activity in D2017A SPNs was similar to wild type, indicating a selective effect of G2019S. Acute exposure to LRRK2 kinase inhibitors normalized activity, supporting that excessive neural activity in G2019S SPNs is mediated directly and is kinase dependent. Although dendritic arborization and densities of excitatory presynaptic terminals and postsynaptic dendritic spines in G2019S SPNs were similar to wild type, G2019S SPNs displayed larger spines that were matched functionally by a shift toward larger postsynaptic response amplitudes. Acutely isolating striatum from overlying neocortex normalized sEPSC frequency in G2019S mutants, supporting that abnormal corticostriatal activity is involved. These findings indicate that the G2019S mutation imparts a gain-of-abnormal function to SPN activity and morphology during a stage of development when activity can permanently modify circuit structure and function.. Mutations in the kinase domain of leucine-rich repeat kinase 2 (LRRK2) follow Parkinson's disease (PD) heritability. How such mutations affect brain function is poorly understood. LRRK2 expression levels rise after birth at a time when synapses are forming and are highest in dorsal striatum, suggesting that LRRK2 regulates development of striatal circuits. During a period of postnatal development when activity plays a large role in permanently shaping neural circuits, our data show how the most common PD-causing LRRK2 mutation dramatically alters excitatory synaptic activity and the shape of postsynaptic structures in striatum. These findings provide new insight into early functional and structural aberrations in striatal connectivity that may predispose striatal circuitry to both motor and nonmotor dysfunction later in life.

Topics: Animals; Animals, Newborn; Corpus Striatum; Dendrites; Disease Models, Animal; Excitatory Postsynaptic Potentials; Female; Gene Expression Regulation, Developmental; In Vitro Techniques; Leucine-Rich Repeat Serine-Threonine Protein Kinase-2; Male; Mice; Mice, Inbred C57BL; Mice, Transgenic; Mutation; Neurons; Parkinson Disease; Patch-Clamp Techniques; Receptors, Dopamine D1; Sodium Channel Blockers; Tetrodotoxin

Reciprocally connected GABAergic neurons of the globus pallidus (GP) and glutamatergic neurons of the subthalamic nucleus (STN) are a putative generator of pathological rhythmic burst firing in Parkinson's disease (PD). Burst firing of STN neurons may be driven by rebound depolarization after barrages of GABA(A) receptor (GABA(A)R)-mediated IPSPs arising from pallidal fibers. To determine the conditions under which pallidosubthalamic transmission activates these and other postsynaptic GABARs, a parasagittal mouse brain slice preparation was developed in which pallidosubthalamic connections were preserved. Intact connectivity was first confirmed through the injection of a neuronal tracer into the GP. Voltage-clamp and gramicidin-based perforated-patch current-clamp recordings were then used to study the relative influences of GABA(A)R- and GABA(B)R-mediated pallidosubthalamic transmission on STN neurons. Spontaneous phasic, but not tonic, activation of postsynaptic GABA(A)Rs reduced the frequency and disrupted the rhythmicity of autonomous firing in STN neurons. However, postsynaptic GABA(B)Rs were only sufficiently activated to impact STN firing when pallidosubthalamic transmission was elevated or pallidal fibers were synchronously activated by electrical stimulation. In a subset of neurons, rebound burst depolarizations followed high-frequency, synchronous stimulation of pallidosubthalamic fibers. Although GABA(B)R-mediated hyperpolarization was itself sufficient to generate rebound bursts, coincident activation of postsynaptic GABA(A)Rs produced longer and more intense burst firing. These findings elucidate a novel route through which burst activity can be generated in the STN, and suggest that GABARs on STN neurons could act in a synergistic manner to generate abnormal burst activity in PD.

Topics: 2-Amino-5-phosphonovalerate; Action Potentials; Animals; Evoked Potentials; Excitatory Amino Acid Antagonists; GABA Antagonists; gamma-Aminobutyric Acid; Globus Pallidus; Lysine; Male; Mice; Mice, Inbred C57BL; Neural Pathways; Neurons; Parkinson Disease; Patch-Clamp Techniques; Picrotoxin; Pyridazines; Quinoxalines; Receptors, GABA-A; Receptors, GABA-B; Subthalamic Nucleus; Synapses; Tetrodotoxin