Endogenous pain control systems: brainstem spinal pathways and endorphin circuitry.

Prolactin is a protein hormone of the anterior pituitary gland that was originally named for its ability to promote lactation in response to the suckling stimulus of hungry young mammals. We now know that prolactin is not as simple as originally described. Indeed, chemically, prolactin appears in a multiplicity of posttranslational forms ranging from size variants to chemical modifications such as phosphorylation or glycosylation. It is not only synthesized in the pituitary gland, as originally described, but also within the central nervous system, the immune system, the uterus and its associated tissues of conception, and even the mammary gland itself. Moreover, its biological actions are not limited solely to reproduction because it has been shown to control a variety of behaviors and even play a role in homeostasis. Prolactin-releasing stimuli not only include the nursing stimulus, but light, audition, olfaction, and stress can serve a stimulatory role. Finally, although it is well known that dopamine of hypothalamic origin provides inhibitory control over the secretion of prolactin, other factors within the brain, pituitary gland, and peripheral organs have been shown to inhibit or stimulate prolactin secretion as well. It is the purpose of this review to provide a comprehensive survey of our current understanding of prolactin's function and its regulation and to expose some of the controversies still existing.

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Prolactin: Structure, Function, and Regulation of Secretion

Distribution of substance P-like immunoreactivity in the central nervous system of the rat—I. Cell bodies and nerve terminals

Experimental immunohistochemical studies on the localization and distribution of substance P in cat primary sensory neurons.

Antibodies to substance P with a high titer have been produced and used in immunohistochemical studies on the peripheral and central nervous system of the rat and the cat. Evidence was obtained for the localization of substance P in a certain population of primary sensory neurons, probably small nerve cells with unmyelinated processes. Substance P or a peptide similar to it was also observed in cell bodies in the medial habenula and in probable nerve terminals in many brain areas. The results give morphological support for a transmitter (or modulator) role of substance P in the nervous system.

http://science.sciencemag.org/content/sci/190/4217/889.full.pdf

Substance p: localization in the central nervous system and in some primary sensory neurons

Immunohistochemical evidence of substance P-like immunoreactivity in some 5-hydroxytryptamine-containing neurons in the rat central nervous system.

Immunohistochemical support for three putative transmitters in one neuron: Coexistence of 5-hydroxytryptamine, substance p- and thyrotropin releasing hormone-like immunoreactivity in medullary neurons projecting to the spinal cord

Distribution of substance P-like immuno-reactivity in the rat central nervous system as revealed by immunohistochemistry.

The indirect immunofluorescence technique of Coons and collaborators was used to study the distribution of substance P-like and luliberin (luteinizing hormone-releasing hormone)-like immunoreactivity in the eminentia mediana (eminentia medialis or infundibulum) of rats, monkeys, and human beings. In rats, abundant luliberin-positive fibers were present in the external layer (mainly lateral parts) whereas almost no substance P-immunoreactive nerves were observed in this region. In contrast, in the external layer of the primate eminentia medialis a dense plexus of substance P-positive nerve terminals was observed close to the blood vessels supplying the anterior pituitary gland. Luliberin-immunoreactive fibers were also present, but with a more even distribution all over the eminentia medialis and in lower numbers. The present findings indicate that substance P may play a role in the control of hormone secretion from the anterior pituitary, either by being released into the portal vessels, i.e., acting as a releasing or inhibitory hormone, or by an action as local regulator (modulator or transmitter) at the level of the eminentia medialis. Thus, in agreement with many earlier studies, substances other than the “classical” releasing and inhibitory hormones may be important for the regulation of the pituitary gland. Furthermore, there may exist marked species differences with regard to the type of substances involved in the central control of the pituitary.

B. Pernow

Papers

Immunohistochemical evidence of substance P-like immunoreactivity in some 5-hydroxytryptamine-containing neurons in the rat central nervous system.

Immunohistochemical support for three putative transmitters in one neuron: Coexistence of 5-hydroxytryptamine, substance p- and thyrotropin releasing hormone-like immunoreactivity in medullary neurons projecting to the spinal cord

Distribution of substance P-like immuno-reactivity in the rat central nervous system as revealed by immunohistochemistry.

Dense Plexus of Substance P Immunoreactive Nerve Terminals in Eminentia Medialis of the Primate Hypothalamus