δ-opioid receptors are widely distributed throughout the CNS, most prominant expression in the forebrain regions: Caudate putamen, nucleus accumbens, amygdala, pontine nucleus, olfactory bulb, olfactory tubercle > interpeduncular nucleus, cortex (most dense in layers II-III and V-VI) > thalamus, hypothalamus, stria terminalis, hippocampus, globus pallidus, preoptic area, colliculi. Virtually no binding in the periaqueductal grey and raphe nuclei.