1 Basal ganglia anatomy - Gonda Multidisciplinary Brain Research ...
1 Basal ganglia anatomy - Gonda Multidisciplinary Brain Research ...
1 Basal ganglia anatomy - Gonda Multidisciplinary Brain Research ...
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Anatomy of the basal <strong>ganglia</strong><br />
Dana Cohen<br />
<strong>Gonda</strong> <strong>Brain</strong> <strong>Research</strong> Center, room 410<br />
danacoh@gmail.com
A small number of neurons…<br />
• The basal <strong>ganglia</strong> receive projections from most cortical<br />
areas<br />
• The basal <strong>ganglia</strong> project out to cortical areas involved in<br />
the generation of behavior<br />
• Act in parallel with other output systems of the cortex<br />
and thus may not play a primary role in generating<br />
behavior<br />
• Essential for several types of learning
• Neocortex<br />
The cortico-basal <strong>ganglia</strong><br />
circuits consist of:<br />
• The striatum (caudate - putamen and the core of<br />
nucleus accumbens)<br />
• The globus pallidus (GP) (lateral and medial)<br />
• The subthalamic nucleus (STN)<br />
• Substantia nigra (SN) (pars compacta and pars<br />
reticulata) and the ventral tegmental area (VTA)
Anterior to posterior coronal view
Anterior to posterior coronal view
Anterior to posterior coronal view
Input and output of the basal <strong>ganglia</strong><br />
• Cortex to striatum: glutamate<br />
• MGP and SNr: GABA
The striatum<br />
• The major input nucleus of the BG.<br />
• Made up of the putamen, the caudate nucleus and<br />
nucleus accumbens which have similar histological and<br />
anatomical characteristics.<br />
• Receive input from most of the cortex (and the thalamus)<br />
• Complex bidirectional interaction with the substantia<br />
nigra pars compacta (SNc)<br />
• Output to both segments of the globus pallidus (GP) &<br />
the substantia nigra pars reticulata (SNr)
Striatum – Medium Spiny Neurons I<br />
• MSNs = Medium Spiny Neurons<br />
• > 90% of all cells in striatum<br />
• >10,000 cortical inputs to one MSN<br />
• GABAergic projection neurons<br />
• Dense collateral network<br />
• Two states:<br />
– ‘down’ state with low resting<br />
potential and no firing<br />
– ‘up’ state characterized by short<br />
firing episodes.
Striatum – Medium Spiny Neurons II<br />
• MSNs are typically quiet with no baseline firing.<br />
• Sensory and movement related response comprises of a<br />
short high frequency burst.<br />
• Highly specific to portion of the task and parts of the<br />
movement but can respond to several events.<br />
• Affected by sequence context or reward contingency.
The interneurons of the striatum make<br />
up about 5-10% of the neurons<br />
• TANs: large aspiny neurons – Ach (Was<br />
previously thought to be the projection neuron)
The GABAergic interneurons of the striatum<br />
• FSNs: medium aspiny neurons that contain parvalbumin<br />
• Medium aspiny neurons that contain somatostatin
The medial globus pallidus and the SNr<br />
• Primarily made up of<br />
GABAergic projection neurons.<br />
• Firing rate at rest is 60-100<br />
spikes/s and is highly irregular<br />
(The ultimate Poissonian<br />
neuron).<br />
• Sensory and motor response is<br />
broad and includes increases<br />
and decreases of firing rate.
The lateral globus pallidus (GPe)<br />
• Same morphology as the MGP<br />
• High frequency pausers (HFP) & lowfrequency<br />
bursters (LFB)<br />
• Internal to the basal <strong>ganglia</strong> with no<br />
external connections for input or output
The subthalamic nucleus<br />
• Made up mainly of projection<br />
neurons. Firing rate at rest is 20-<br />
30 spikes/s with short burst<br />
following movement.<br />
• The projection neurons are<br />
glutamatergic and send their<br />
output to the GPi & SNr.<br />
• In addition to its role in the indirect<br />
pathway, has direct cortical inputs<br />
forming the hyperdirect pathway.
Direct and indirect pathways<br />
• The direct pathway causes disinhibition<br />
• The indirect pathway is more complex but likely to<br />
counterbalance the direct pathway
Feedback pathways
Cortical input to the striatum<br />
originates from most cortical areas<br />
• Primary and higher order sensory areas, motor,<br />
premotor, and prefrontal regions, and limbic cortical<br />
areas.<br />
• The input is organized topographically<br />
– Frontal areas project to rostral striatum<br />
– Sensorimotor cortex projects to dorsolateral striatum<br />
– Parietal cortex projects to caudal striatum<br />
– Highly interconnected cortices may overlap in the striatum<br />
• Numbers:<br />
– There are 17 million cortico-striatal cells<br />
– There are almost 2.8 million striatal projection neurons<br />
– No 2 striatal neurons share their cortical input
Synaptic input to distal dendrites of<br />
the MSNs
Inputs to the proximal and distal<br />
dendrites of the MSNs
Direct and indirect striatal projection neurons<br />
selectively express the D1 and D2 receptors
Components of the indirect pathway
Synaptic inputs to the SNr<br />
• The SNc and SNr<br />
cannot be distinguished<br />
based on the<br />
morphological<br />
properties of the<br />
neurons<br />
– Dopaminergic neurons<br />
– GABAergic neurons
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