Colocalization of Delta Sleep Inducing Peptide and Luteinizing Hormone Releasing Hormone in Neurosecretory Vesicles in Rat Median Eminence

Abstract

The colocalization of immunoreactivities similar to delta sleep inducing peptide (DSIP) and luteinizing hormone releasing hormone (LH-RH) was investigated by light and electron microscopic immunocytochemistry in the rat median eminence. At the light microspic level, DSIP and LH-RH immunostained fibers, and varicosities exhibited a similar distribution pattern throughout the median eminence. Immunoreactive axons were mainly found in the lateral part of the external layer. Using an elution-restaining technique, the coexistence of LH-RH and DSIP immunoreactivities was observed in most labelled axons. To determine the intracellular localization of DSIP and LH-RH, we used double immunocytochemical labelling with species-specific antibodies and secondary antibodies conjugated to different sizes of gold particles. The two peptides were found colocalized in single axons. Immunoreactive terminals frequently showed direct membrane apposition with tanycyte processes but rare contacts with portal capillaries. No staining was observed in tanycytes and ependymal or glial elements. Moreover, we could demonstrate that LH-RH and DSIP (or a closely related molecular form) are contained not only in the same axons, but also in the same ∼ 100-nm dense-core vesicles, suggesting cosecretion of these peptides.

Neuropeptides as synaptic transmitters

“…Virtually all LGVs were multiple/ dually labeled in both central and peripheral projections, whereas double (multiple)-labeled LGVs were relatively rare in the cell body. Although the central and peripheral projections of individual DRG neurons could not be followed, these observations showed that: (1) a mixture of neuropeptides was packed within individual LGVs, i.e., when multiple peptides were produced by one neuron, they were not selectively packaged in different LGV subpopu- Vallet et al 1991 lations; (2) LGVs (and therefore the neuropeptides packed therein) were found at both central and peripheral projections of the DRG neurons. If these points can be generalized, there is presumably no selective transport to functionally different neuronal processes (the axons and the dendrites) and/or to different branches of the same process.…”

Hormonal and neurotransmitter regulation of GnRH gene expression and related reproductive behaviors

“…To date, three neuroactive compounds have been reported to colocalize in GnRH neurons: (1) a [3-endorphin-like endogenous opioid (Leonardelli and Tramu, 1979;Beauvillain et al, 1981), (2) galanin (Coen et al, 1990;Merchenthaler et aL, 1990), and (3), g-sleep-inducing peptide (Chamay et al, 1989;Vallet et al, 1991). Colocalized galanin exhibits a sexually dimorphic distribution, varies during the estrous cycle, and may enhance GnRH release at the ME terminals (Marks et al, 1993(Marks et al, , 1994.…”

Effects of some DSIP peptide analogs on rat sleep for intraventricular infusion

“…Intensive investigation of this substance undertaken later by different research teams revealed that DSIP or some other peptide(s) similar in structure is present, free or bound, in the peripheral organs, tissues, and fluids of the body, as well as in the pituitary, hypothalamus, and limbic system of the brain, where it is localized together with a number of peptide and nonpeptide transmitters [2,6,8,14]. There are data on the participation of this peptide in quite a number of normal and abnormal reactions (stress, immune, pain, endocrine), as well as in the regulation of the circadian rhythms, the formation of alcohol and opioid dependence, etc.…”