Delta receptors distribution

The plant alkaloids mimic the endogenous peptides enkephalins and endorphins (Chapter 12), which meditate nociception and sleep. There are three types of widely distributed opiate receptors. Mu receptors are concentrated in neocortex, striatum, thalamus, hippocampus, amygdala and spinal cord, delta receptors in neocortex and amydala, and kappa receptors in striatum, amygdala and hypothalamus (Mansour et al., 1988). 

Mansour A, Thompson RC, Akil H, Watson SJ (1993) Delta opioid receptor mRNA distribution in the brain comparison to delta receptor binding and proenkephalin mRNA. J Chem Neuroanat 6 351-362. 

Different peptides from the same gene product (met and leu enkephalin, substance P and neurokinin A). The former two act on the same receptor, the delta opioid receptor, whereas the latter act on different receptors, the neurokinin 1 and 2 receptors. Despite this, the receptors for the neurokinins produce the same direction of effect, a slow depolarisation, even though their distribution differs. 

If opiates are such addictive and potentially lethal compounds, why does the body respond to them As with the cannabinoids (Chapter 7), it has been discovered that the body and brain possess numerous opiate-specific receptor sites. As many as nine receptor subtypes have been identified, with three of them being the most important p (mu), k (kappa) and 8 (delta). The finding that the distribution of opiate receptors did not parallel the distribution of any known neurotransmitter prompted the search for and identification of a number of endogenous compounds specific to these receptors. These enkephalins and endorphins are manufactured within the brain and other body systems (especially the gut and intestines) and form the body s natural response to pain. They appear to be produced in bulk chains of amino acids called polypeptides , with each active neurotransmitter being composed of around five amino acid molecules. These active neurotransmitters are subsequently cleaved from the larger polypeptides at times of demand for example, it has been demonstrated that the plasma levels of these active compounds rise during childbirth, traumatic incidents and vigorous physical exercise. 

Arvidsson U, Dado R, Riedl M. Lee J, Law P, Loh HH, Elde R, Wessendorf W. Delta-opioid receptor immunoreactiv-ity distribution in brainstem and spinal cord, and relationship to biogenic amines and enkephalin. J Neurosci 1995 15 1215-1235. 

Della Bella D, Carenzi A, Frigeni V, Reggiani A, Zambon A. (1985). Involvement of monoaminergic and peptidergic components in cathinone-induced analgesia. EurJ Pharmacol. 114(2) 231-34. Desjardins GC, Brawer JR, Beaudet A. (1990). Distribution of mu, delta, and kappa opioid receptors in the hypothalamus of the rat. Brain Res. 536(1-2) 114-23. 

In the superficial layers of the rat spinal cord, the delta opioid receptor is present principally within axon terminals in laminae I and II [23]. Within laminae I and II, enkephalin-like immunoreactivity is intensely localized to axonal varicosities presynaptic to dendrites or cell bodies [24]. The cells expressing the delta opioid receptor mRNA are distributed in the laminae of the dorsal and ventral horns. The delta opioid receptor mRNA is expressed in laminae IV, V, and VII-X, with a few cells in lamina III of the thoracic cord [22]. The expression of delta opioid receptor mRNA is noted in motor neurons of the ventral horn in the spinal cord [22]. In dorsal root ganglia (DRG), delta opioid receptor mRNA is expressed with comparatively fewer levels [22]. The cells expressing delta opioid receptor mRNA in DRG are predominantly large-diameter neurons [22]. 

Subsequent to the molecular cloning and cDNA sequence analysis of the delta opioid receptor, antireceptor antibodies were raised against synthetic peptides based on the deduced amino acid sequence of this receptor. To date, there have been a limited number of studies using antibodies directed toward the amino terminus of the cloned murine receptor to assess the distribution of delta opioid receptorlike immunoreactivity in the gastrointestinal tract, and these have been confined so far to the porcine small intestine. They have shown the presence of delta opioid receptor-immuno-reactive neurons and fibers in both the myenteric and submucosal plexuses and as well as in myenteric neurons maintained in primary culture [22, 23]. Receptor-like immunoreactivity in neuronal cell bodies appears to be localized in the cytoplasm and is likely to be trafficked to nerve terminals. These neurons are coimmunoreactive for the acetylcholine-synthesizing... 

Quantitative receptor autoradiography is one technique that has been used in assessing the distribution and pharmacological characteristics of delta opioid... 

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