Spinal cord delta receptors

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). 

All opioids produce their effect by activating one or more of the three types of receptors. Thus analgesia involves the activation of the mu receptors that are located mainly at supraspinal sites and kappa receptors in the spinal cord delta receptors may also be involved but their relative contribution is unclear. Nevertheless, the actions of the opioids on these receptors is complex, as there is evidence that the same substance may act as a full agonist, or as an antagonist at different sites within the brain. 

Glaum SR, Miller RJ, Hammond DL (1994) Inhibitory actions of delta 1-, delta 2-, and mu-opioid receptor agonists on excitatory transmission in lamina II neurons of adult rat spinal cord. 

The opiate receptors in the spinal cord are predominantly of the mu and delta type and are found in the C-fibre terminal zone (the substantia gelatinosa) in the superficial dorsal horn. Considerable numbers of ORL-1 receptors are also found in this area. Up to 75% of the opiate receptors are found presynaptically on the C-fibre terminals and when activated inhibit neurotransmitter release. The opening of potassium channels will reduce calcium flux in the terminal and so there will be a resultant decrease in... 

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. 

Pugh G Jr, Abood ME, Welch SP. (1995). Antisense oligodeoxynucleotides to the kappa-1 receptor block the antinociceptive effects of delta 9-THC in the spinal cord. Brain Res. 689(1) 157-58. 

Opioid receptors are found in the dorsal horn as well as in other areas throughout the spinal cord and brain. Three major classes of opioid receptors exist mu receptors (/r), kappa receptors (k) and delta... 

Glatzer NR, Smith BN (2005) Modulation of synaptic transmission in the rat nucleus of the solitary tract by endomorphin-1. J Neurophysiol 93 2530-40 Glaum SR, Miller RJ, Hammond DL (1994) Inhibitory actions of delta 1-, delta 2-, and mu-opioid receptor agonists on excitatory transmission in lamina II neurons of adult rat spinal cord. J Neurosci 14 4965-71... 

The enkephalins are found in high concentration in the spinal cord, especially in the substantia gelatinosa, a region also enriched in mu and delta opioid receptors and in NEP and APN [10,12,29-31],... 

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]. 

There is considerable evidence that delta opioid receptor agonists act in the spinal cord to produce antinociception. This evidence includes pharmacological investigations of the antinociceptive effects of ITH- administered delta opioid receptor agonists [51,52,61,62], electrophysiological characterization of the effects of these agonists on the response properties of dorsal horn neurons [63-66], and neurochemical determinations of their effects on the release of neurotransmitters from the spinal cord [67-70]. 

The high-affinity GTPase activity in the mouse spinal cord is increased in a concentration-dependent manner by [D-Ala2]deltorphin II [82]. This increase of GTPase activity induced by [D-Ala2]deltorphin II is completely blocked by coincubation with a selective delta opioid receptor antagonist NTB [82]. 

After intrathecal injection, delta opioid agonists slow transit in the small intestine [116,117] and inhibit diarrhea [114,118]. Based on these studies, it appears that delta opioid receptors in the spinal cord, unlike those in the... 

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