Chapter 21 Neurotransmitters and Pathways




Globus pallidus

Stria terminalis

Nucleus raphe dorsalis

Locus ceruleus



Hippocampal formation

Nucleus raphe magnus Substantia nigra

Posterior horn of spinal cord

FIGURE 21.7. Distribution of enkephalin-containing neurons and their projections. Enkephalinergic neurons are found primarily in local circuits of the limbic and striatal systems. Enkephalinergic neurons of the brainstem and spinal cord play a role in pain suppression mechanisms.

C. Dynorphins

■ derived from prodynorphin . ■ follow, in general, the distribution map for enkephalin. ■ found in high concentrations in the limbic system and hypothalamus .


A. Substance P (Figure 21.8) ■ a modulatory neurotransmitter.

■ found in spinal ganglion cells, which project to the substantia gelatinosa. ■ role in pain transmission (in A-delta and C fibers) and inflammatory processes. ■ synthesized in striatal neurons, which project to the globus pallidus and the substantia nigra. B. Somatostatin (Figure 21.9) ■ also called somatotropin release-inhibiting factor. ■ somatostatinergic neurons are found in the anterior hypothalamus and in the preoptic region, striatum, amygdala, cerebral cortex, and in spinal ganglion cells. ■ somatostatinergic neurons from the anterior hypothalamus project their axons to the median eminence. ■ involved in endocrine system regulation—somatostatin enters the hypophyseal portal system and regulates the release of growth hormone and thyroid-stimulating hormone.

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