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Telencephalon Endbrain Telencephalon + Amygdala → limbic system Telencephalon – an extended list of components Directional terms – forebrain level dorsal superior caudal posterior rostral anterior ventral inferior Basal ganglia Telencephalon Lateral ventricle Basal ganglia nomenclature Corpus Striatum Caudate Nucleus Neostriatum Lenticular Nucleus Striatum Putamen Globus Pallidus Corpus Amygdaloideum Paleostriatum Archistriatum Pallidum Lateral surface of basal ganglia 1. Putamen 2. Tail of caudate nucleus 3. Caudatolenti cular gray bridge 4. Amygdaloid body 5. thalamus Medial surface of basal ganglia 1. head of caudate nucleus 2. body of caudate nucelus 3. caudatolenticular gray bridge 4. putamen 5. tail of caudate nucleus 6. external segment of globus pallidus 7. internal segment of globus pallidus 8. amygdaloid body 9. nucleus accumbens septi The Basal Ganglia Caudate Putamen Globus Pallidus The Basal Ganglia Basal ganglia terminology (Note: the Subthalamic Nucleus and the Substantia Nigra are functionally, but not anatomically, part of the Basal Ganglia) Caudate Putamen Glob Pall Subthal Nuc Sub Nigra Basal ganglia terminology Caudate STRIATUM Putamen Glob Pall Subthal Nuc Sub Nigra Basal ganglia terminology Caudate Putamen Glob Pall Subthal Nuc Sub Nigra LENTICULAR NUCLEUS Basal ganglia terminology Caudate Putamen Glob Pall Subthal Nuc Sub Nigra CORPUS STRIATUM Globus pallidus is divided into external (GPe; lateral) and internal (GPi; medial) segments Put GPe GPi Levels of various structures associated with movement control Lateral 3D view of basal ganglia & cortex body → parietal lobe head → frontal lobe tail → the temporal lobe body → parietal lobe anterior posterior head → frontal lobe tail → the temporal lobe Lateral 3D view of basal ganglia Lateral → medial 3D view of basal ganglia Coronal brain section at the level of basal ganglia Put GPe GPi Anterior frontal coronal section Thalamus is not present → it is more posteriorly located Head Caud Put GPe GPi Tail of caudate Position of caudate vs thalamus Origin of CNS subdivisions Basal ganglia originate from the telencephalic vesicle The basal ganglia are derived from the basal side of the telencephalic vesicle Lateral ventricle Basal ganglia The basal ganglia are derived from bulges of the telencephalic vesicle called ganglionic eminences LGE LGE MGE MGE Mouse E12.5 Medial GE → pallidum Lateral GE → striatum Human 11 wk Campbell, 2003/ Meyer, 2001 Early development Late development As the cerebral cortex grows, it also forces the underlying basal ganglia to assume a C-shape Estimated time of development of various brain regions 2 mo 6 mo Modified from Bayer SA et al. Neurotoxicology 14:83–144, 1993 Macroscropic anatomy of major basal ganglia regions Striatum (caudate and putamen) Lenticular nucleus (putamen and globus pallidus) Subthalamic nucleus Substantia Nigra Striatum = caudate + putamen Telencephalic origin Follows curvature telencephalic vesicle during development Head (Rostrum) more voluminous in the human than the body Putamen and Globus Pallidus (Lenticular Nucleus) From the junction of diencephalon and telencephalon Triangular on coronal sections Elongated on axial sections Globus Pallidus = pallidum = paleostriatum Subthalamic Nucleus Arises from the diencephalon Under the thalamus Biconvex lens shape White matter tracts in pallidum external capsule lateral medullary lamina medial medullary lamina Substantia Nigra Mesencephalic origin Pars compacta and reticulata Just beneath subthalamic nucleus Flattened ellipsoid Lies along cerebral peduncle Main loop: cortex-basal ganglia-thalamus Cortex (+) Substantia nigra (+) Thalamus (-) Basal ganglia Some basal ganglia neurons mainly receive input from cortex; others – mainly output to thalamus Basal ganglia have different input & output components Input to basal striatum ganglia Output Other basal ganglia structures Ventral (limbic) striatum nucleus accumbens septi - reward center; potential involvement in drug addiction deep portions of olfactory tubercle ventromedial portions of the caudate nucleus and putamen Nucleus Accumbens Where the anterior limb of the internal capsule does not divide the caudate and the putamen Ventral (limbic) striatum - connections Receives from limbic cortex (hippocampus, amygdala, entorhinal and perirhinal cortices (areas 28 and 35), anterior cingulate cortex (area 24), medial orbitofrontal cortex, and widespread sources within the temporal lobe) Projects to ventral pallidum Ventral pallidum The globus pallidus and the ventral pallidum are separated by the anterior commissure Striatal neurons 96% - projection neurons (medium spiny neurons) Dendrites covered with dendritic spines Input from cortex to spine heads Intrinsic basal ganglia input contacts dendritic shafts (modulates or inhibits cortical input) Axon gives rise to dense local collateral arborization with other spiny neurons GABA-ergic; also contain substance P, dynorphin, enkephalin Silent at rest, activated by cortica inputs Striatal projection neurons Total striatal neurons – 100 million 75% - medium spiny neurons Purves, et al, Neuroscience, 3rd ed. Striatal projection neurons use GABA and different neuromodulators Put GPe Put GPi GPe GPi Afferent different neurons have different patterns of termination on dendrites and soma of striatal projection neurons spine shaft spine head Other striatal neurons (4% - interneurons) Small GABA-ergic interneurons Large Cholinergic interneurons Interneurons provide local surrounding inhibition Large cholinergic interneurons are Tonically Active Neurons (TANS) function in learning and reward behavior Convergent inputs onto a medium spiny neuron from cortical neurons, dopaminergic cells of the substantia nigra, and local circuit neurons. Purves, et al, Neuroscience, 3rd ed. Striate neurons increase their rate of discharge just before an impending movement ↓ The activity of these cells may encode the decision to move toward the target Marjuana, endocannabinoids & cannabinoid receptors CB1-R Purves, et al, Neuroscience, 3rd ed. THC induces dendritic growth in basal ganglia Kolb et al., (2006) Amphetamine induces increased spine density in basal ganglia Li et al (2003) Striatum is composed of matrix & striosome compartments Striosome Matrix Acetylcholinesterase histochemistry Enkephalin immunohistochemistry All tissue outside the striosomes is the matrix compartment Striosome and Matrix compartment AchE Characteristics of striosome and matrix compartments Striosomes Matrix Acetylcholinesterase Light staining Heavy Cell development Early Late Input Medial frontal cortex, limbic cortex, substantia nigra pars compacta, ventral SNPC Sensorimotor cortex, SMA, association cortex, IL thalamic nuclei, dorsal SNPC Output Substantia nigra pars compacta Substantia nigra pars reticulata, globus pallidus Neurotransmitter GABA GABA Neuromodulators Neurotensin, dynorphin, substance Somatostatin, enkephalin, P substance P Dopamine receptor D1 D2 Pallidal neurons Receive striatal input Dendrites long, thick, smooth, sparsely branched Covered with synaptic boutons (90% striatum, 10% other eg. STN, PPN) Discoid shaped arborizations that are perpendicular to striatal axons GABA-ergic; project to & inhibit thalamus 100 times less numerous than spiny striatal neurons (convergence of input onto pallidal neurons from striatal spiny neurons) Probably help in control of fine and global movements Output of basal ganglia – GP & SNpr Purves, et al, Neuroscience, 3rd ed. Convergence of striatal neurons onto GP & SNpr neurons 75 million medium spiny striatal neurons ↓ 100/1 700 000 GP & SNpr neurons Disinhibitory circuits of basal ganglia Purves, et al, Neuroscience, 3rd ed. Nigral neurons Same dendrites as pallidal neurons No discoidal dendritic arborization SN pars compacta - dopamine SN pars reticulata - GABA Subthalamic neurons Dendritic arborizations are intermediate in number, branch points, and length between striatal and pallidal neurons Occasional spines *Use glutamate (excitatory) Dendrites can extend outside of the nucleus and get input from the zona incerta The relationships of the basal ganglia to the major components of the motor system Loop: cortex-striatum-pallidum-thalamus Cortex (+) Striatum (+) Thalamus (-) (-) Pallidum Basal ganglia - summary of connections Motor Cortex VL Thalamus Caud/Putamen direct pathway GPi/SNpr indirect pathway Subthal Nucleus GPe SNpc Basal ganglia connections Motor corte x Str Th STN Feedback circuit involving the thalamic centromedian nucleus Glutamatergic thalamostriate fibers Function - alert the individual; elicit responses that will enable it to evade painful stimuli Summary of basal ganglia outputs Somatotopic organization of the basal gangliathalamocortical motor circuit Kandel, Schwartz, Jessell; Principles of Neural Science, 4th ed. Direct vs indirect pathways Direct pathway → disinhibition of thalamic excitation Indirect pathway → modulation of direct pathway (+) (-) (-) (-) (-) (+) Fascilitates movement Inhibits movement SNpc modulates both direct and indirect pathways Substantia nigra pars compacta (SNpc) inhibits the indirect pathway Substantia nigra pars compacta (SNpc) promotes direct pathway Transmitter of SNpc is dopamine – different effects come from different dopamine receptors (D1 vs D2) SNpc → direct pathway↑ ↑ D1 D2 SNpc → indirect pathway↓ ↓ Major diseases of basal ganglia Parkinson’s Disease (parkinsonism) Huntington’s Disease (chorea, ballism) Risk factors: Parkinson Ebadi, Pfeiffer. Parkinson’s disease, 2005, 5ed. α-Synuclein & Parkinson PD pathology - Lewy body Indirect pathway in Parkinson’s disease In the indirect pathway there is a loss of excitation of the GPe by putamen resulting in a decreased inhibitory output from GPe to STN This decreased inhibitory output leads to excessive excitatory output to the GPi, increasing inhibitory output of GPi to thalamus and brainstem. Common Thread Between the Direct and Indirect Pathways in Parkinson’s Disease Both the direct and indirect pathways lead to increased inhibitory activity from GPi to the thalamus and brainstem ↑ ↓ SNpc → direct pathway ↓ ↓ Thalamocortical Circuit ↓ SNpc → indirect pathway↑ ↑ Is it Inhibition of the Thalamocortical Circuit that Causes Parkinson’s? The inhibition of thalamocortical and the midbrain projections in the motor circuit has been proposed as the primary cause for the development of parkinsonian motor signs and hypokinetic features of PD ⇐ Cardinal Features of PD Tremor (at rest) Rigidity Bradykinesia Shuffling Gait Balance Problems Basal ganglia function in PD ↑ ↑ Sites of surgical intervention in Parkinson disease Subthalamic nucleus lesion GPI lesion Kandel, Schwartz, Jessell; Principles of Neural Science, 4th ed. Transplantation of human mesencephalic tissue in human Parkinson’s disease Reason – enriched in dopaminergic neurons Source – human embryos (6-9 GW) from abortions Start – 1987; until 2005 ~350 have been transplanted Main targets Transplanted neurons survive and connect to other neurons in the brain of patients Brain integrates transplanted neurons Transplants achieve medical improvement Disadvantages Non-homogenous cellular population→ variable response Postoperative dyskinesias in 20-50% of the patients PET scan shows take-up of 18F-dopa in striatum 2 years after bilateral implantation of mesencephalic cells in caudate and putamen of a Parkinson’s disease patient. Brooks, NeuroRx, Vol. 1, 482–491, October 2004 Huntington’s DiseaseChorea/Ballism Atrophy of striatum Huntington’s disease – mostly medium spiny neurons are damaged Normal HD Large neurons are relatively spared Basal ganglia function in HD Normal HD ↑ ↑ ↓ ↓ Striatum → direct pathway ↓ ↓ Striatum → indirect pathway ↓↓ ↑ Thalamocortical Circuit HD – hyperkinetic disorder Chorea (G. choros, “dance”) consists of a sequence of rapid, jerky, somewhat agile and flowing movements involving mainly the hands and feet, the tongue, and facial muscles. Disinhibition of thalamus (=excitation) → involuntary movements Summary of PD & HD pathophysiology Parkinson Normal Normal Huntington Cortex Cortex (+) (+) (+) (+) Thalamus Thalamus SN SN (-) (-) Basal ganglia Basal ganglia Hypokinetic Hyperkinetic Blood supply of basal ganglia Striatum → penetrating branches of the anterior and middle cerebral arteries termed the lenticulostriate arteries Pallidum → anterior choroidal artery (internal carotid artery) Intracerebral hemorrhage Vv. profundae cerebri Drainage of vv. profundae cerebri Anastomoses between deep & superficial cerebral veins Basal ganglia loops – motor & non-motor functions Functions of basal ganglia loops Motor loop - automatic execution of a learned motor plan; preparation for movement Oculomotor loop - voluntary saccadiac eye movements Prefrontal loop - planning of motor activity and determining the direction of movement; cognitive function and tasks that require spatial memory Limbic loop - emotional and motivational aspects of movement, manifested as various facial expressions or other body movements Motor control integration