Enkephalin-related Peptides Research Articles

Multiple molecular forms of enkephalins in the guinea pig hippocampus.

The combined techniques of HPLC and radioimmunoassay were used to identify and quantitate enkephalin-related peptides in the guinea pig hippocampus. Both met- and leu-enkephalin were identified, in approximately a 2:1 ratio, as well as a third enkephalin-like molecule that is neither met- nor leu-enkephalin. The third enkephalin elutes earlier than met- or leu-enkephalin from a reversed-phase column, has a molecular weight similar to the other enkephalins, and is as active as these enkephalins are in inhibiting binding of labeled opiates to rat brain membranes. All regions of the hippocampus (dentate gyrus, CA1-2, CA3-4, and subiculum) contain all three immunoreactive peptides. Immunocytochemical techniques, using antisera raised against met-enkephalin, show with one antiserum immunoreactivity in the granule cell-mossy fiber system, and with the other scattered immunoreactive cells mostly in the CA2 region. Enkephalins are not confined to the mossy fiber system, as previously suggested, but may be a component of another hippocampal innervation.

High-performance liquid chromatographic identification of enkephalin-like peptides in the cochlea.

Met-enkephalin was identified in cochleae from guinea pigs by a combined reversed-phase high-performance liquid chromatographic separation and subsequent radioimmunoassay of the chromatographic fractions. A second Met-enkephalin-immunoreactive fraction was found in the cochlea, with a retention time shorter than that of Met-enkephalin. These findings confirm and extend earlier cytochemical observations, and suggest the differential immunocytochemical staining seen under inner and outer hair cells in the cochlea may be related to different peptides in the two efferent systems innervating the cochlea. Different molecular forms of enkephalin-related peptides may serve different functional or metabolic roles in complex efferent or local regulation of peripheral sensory processing.

Enkephalin-immunoreactive neurons in the guinea-pig hypothalamus.

An ultrastructural study of enkephalin-immunoreactive perikarya forming a hypothalamic nucleus, the magnocellular dorsal nucleus (MDN), was carried out in colchicine-treated guinea pigs. These large cells usually contain a well-developed rough endoplasmic reticulum, a prominent Golgi complex and neurosecretory granules approximately 100 nm in diameter. These granules are not numerous and sometimes appear preferentially located in the periphery of the cytoplasm. Using the PAP method on ultrathin sections, the immunostaining obtained with anti-enkephalin antisera is essentially confined to the granules but also to some ribosomes linked to membranes of the rough endoplasmic reticulum. These images suggest that the cells of the MDN synthetize the enkephalin-related peptide. Around the perikarya many nerve terminals are observed and many of them make axosomatic synaptic contacts. The exact nature of these nerve endings as well as the projection of these enkephalin-containing cells remain to be established.

Enkephalin-related peptides: Direct action on the octopus heart

Immunocytochemical evidence for the occurrence of ‘vertebrate’ peptides in the neuropil of the vena cava [12, 13] and the structural similarity between enkephalin precursor peptides and the molluscan cardioexcitatory peptide [16], led us to study the action of enkephalin-related peptides on the octopus heart. Systemic hearts of Octopus vulgaris were perfused with sea wate and test substances and a crude extract of vena cava were added for 1 min; frequency and pressure were monitored continuously. The heptapeptide Leu 5-enkephalin-Arg 6-Phe 7 and the Met 5-analogue, both in the amidized form, displayed a dose-response relationship with a sensitivity of about 10 nmol. The C-terminal tetrapeptide amides, Phe-Leu/Met-Arg-Phe-NH 2, were active at the same doses. Opiate receptors do not seem to be involved in this action on the octopus heart, as naloxone treatment had no effect. Whereas the N-terminal portion of the heptapeptide is known to be crucial for activity as an opioid, the C-terminal NH 2 group is essential for cardioexcitatory activity.