Chapter 21 Neurotransmitters and Pathways




Globus pallidus


r t

c o



e o


Striatonigral tract


Sup. colliculus

Purkinje cell

Cerebellar nuclei

Hippocampal formation

Purkinje cell of flocculonodular lobe

Substantia nigra Lat. vestibular nucleus

FIGURE 21.10. Distribution of gamma-aminobutyric acid (GABA)-containing neurons and their projections. GABA-ergic neurons are the major inhibitory cells of the central nervous system. GABA local circuit neurons are found in the neocor tex, allocortex, and in the cerebellar cortex (Purkinje cells). Striatal GABA-ergic neurons project to the globus pallidus and the substantia nigra. Pallidal GABA-ergic neurons project to the thalamus and the subthalamic nucleus.

■ coexists with substance P and with enkephalin. ■ Purkinje, stellate, basket, and Golgi cells of the cerebellar cortex are GABA-ergic (see Figure 19.3). ■ GABA-ergic striatal neurons project to the globus pallidus and the substantia nigra.

■ GABA-ergic pallidal neurons project to the thalamus. ■ GABA-ergic nigral neurons project to the thalamus. 2. Glycine ■ the major inhibitory neurotransmitter of the spinal cord.

■ used by the Renshaw cells of the spinal cord. ■ its inhibitory action is blocked by strychnine.

B. Excitatory amino acid neurotransmitters 1. Glutamate (Figure 21.11)

■ major excitatory neurotransmitter of the brain; 60% of brain synapses are glutamatergic. ■ the neurotransmitter of the cerebellar granule cell. ■ used by the corticobulbar and corticospinal tracts. ■ used by spinal ganglion cells. ■ believed to be involved in long-term potentiation of hippocampal neurons via N -methyl-d-aspartate receptors. ■ role in kindling-induced seizures. ■ role in pain transmission (in A-delta and C fibers). ■ neocortical glutamatergic neurons project to the striatum, the subthalamic nucleus, and the thalamus. The subthalamic nucleus projects glutamatergic fibers to the globus pallidus. 2. Aspartate (see Figure 21.11) ■ a major excitatory neurotransmitter of the brain. ■ neurotransmitter of the climbing fibers of the cerebellum.

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