BRS

Chapter 21 Neurotransmitters and Pathways

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Enkephalins

Striatum

Globus pallidus

Stria terminalis

Nucleus raphe dorsalis

Locus ceruleus

Hypothalamus

Amygdala

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 .

VII. NONOPIOID NEUROPEPTIDES

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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