The neurokinin (NK) system is one of the most studied peptide systems in the CNS. Three NK receptors exist, each with a preferred ligand: substance P (SP) binds with greatest affinity to NK1, neurokinin A prefers NK2, and neurokinin B

has preferential binding to NK3. The NK system has been implicated in a wide range of functions including nociception, emetic response/vomiting, inflammatory conditions, asthma, irritable bowel syndrome, migraine, anxiety, and depression. SP and the NKi receptor are broadly distributed in the amygdala, locus ceruleus, hypothalamus, substantia nigra, peduncular nuclei, caudate putamen, nucleus accumbens, raphe nuclei, and lamina I of the spinal cord. The distribution of the receptor in limbic regions (amygdala, hypothalamus) overlaps with neurotransmitter systems known to be involved in the regulation of mood (e.g., 5HT, NE). Thus, the SP-NK receptor system has been hypothesized to play an important role in affective behaviors (i.e., anxiety and depression).162

Preclinical studies showed that SP delivered to the lateral septal nucleus, the medial amygdala, or into the intracerebral ventricles increased time spent in the closed arms of the EPM, an anxiogenic response. Furthermore, noxious stimuli and acute and chronic stress produce SP release in the brain. Specifically, maternal separation in the guinea pig and immobilization stress elevate SP levels in amygdala. Given these data NK1 receptors would be anticipated to have anxiolytic activity. Thus, the NK1 receptor knockout mouse has a phenotype that resembles mice treated with anxiolytics. Compared to wild-type controls, NK1 receptor knockout mice display fewer vocalizations in the maternal separation test, spend more time in the open arms of the EPM, and show increased exploratory behavior in the open field.

A variety of NK1 receptor antagonists (Figure 13) have been developed, primarily as analgesics, and produce anxiolytic effects in a variety of animal models162: CP-96345 is effective in the mouse light-dark shuttle box; NKP-608 increases social interaction in rat and in gerbil; L-733060, L-760735, MK-869, CP-99994, and GR-205171 attenuate guinea pig vocalizations in the maternal separation test; and GR-205171 and RP-67580 block marble burying in mice. In the EPM RP-67580 increased open arm activity in mouse with FK-888 causing similar effects in rat and mice and MK-869, L-742694, L-7330360, and CP-99994 are efficacious in the gerbil. The anxiolytic actions of these compounds occur in the absence of motor impairment or sedation.

Getting to Know Anxiety

Getting to Know Anxiety

Stop Letting Anxiety Rule Your Life And Take Back The Control You Desire Right Now! You don't have to keep letting your anxiety disorder run your life. You can take back your inner power and change your life for the better starting today! In order to have control of a thing, you first must understand it. And that is what this handy little guide will help you do. Understand this illness for what it is. And, what it isn't.

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