Hypoalgesia in mice with a targeted deletion of the tachykinin 1 gene

Abstract

The tachykinin neuropeptides, substance P and substance K, are produced in nociceptive primary sensory neurons and in many brain regions involved in pain signaling. However, the precise role and importance of these neuropeptides in pain responses has been debated. We now show that mice that cannot produce these peptides display no significant pain responses following formalin injection and have an increased pain threshold in the hotplate test. On the other hand, the mutant mice react normally in the tail f lick assay and acetic acid-induced writhing tests. These results demonstrate that substance P and͞or substance K have essential functions in specific responses to pain.The tachykinins are a family of structurally related neuropeptides. In the mouse, they are encoded by the genes Tac1 and Tac2. Tac1 produces substance P, substance P (neurokinin A), neurokinin A (3-10), neuropeptide K, and neuropeptide ␥ as a result of differential splicing and posttranslational processing (1-4). Tac2 produces the peptide neurokinin B.The undecapeptide substance P was first detected by von Euler and Gaddum (5) in 1931. Its structure was revealed by Leeman and her coworkers (6, 7) in 1971. The Tac1 cDNA was cloned in 1983 by Nakanishi and his coworkers (2,8). The Tac1 gene is expressed in many regions in the central and peripheral nervous system, as well as in nonneuronal tissues. Substance P has been implicated in a variety of physiological processes including cardiovascular, respiratory, and gastrointestinal functions; inflammatory responses; and nociception. In addition, Hunt and coworkers have suggested that substance P may be involved in axon guidance during embryonic development (9).The precise role of substance P in these processes is unclear. For example, substance P is synthesized in nociceptive primary sensory neurons, which send C-and A␦ fibers to dorsal horn projection neurons in lamina I and IV-V, and to nociceptionspecific interneurons in lamina II-III of the spinal cord. Axons of projection neurons terminate in many supraspinal nuclei that are involved in pain transmission (10, 11). Nociceptive stimulation triggers the release of substance P from C-afferent terminals in the marginal layers of the spinal cord (12), evokes slow excitatory postsynaptic potentials in second-order sensory neurons in the dorsal horn, and facilitates their activation (13). These data, together with other functional evidence (11,14), indicated an important role for substance P in the processing of nociceptive signals.We have begun to use a genetic approach to study the functions of tachykinin peptides. As a first step, we have generated mice with a targeted mutation in the Tac1 gene. These mice are viable and fertile, but exhibit striking defects in nociceptive behaviors. MATERIALS AND METHODS Generation and Breeding of Tac1؊͞؊ Mice. Tac1 mutations were established by homologous recombination in MPI2 embryonic stem (ES) cells according to standard protocols (15). One mutant ES cell line was used to derive chimeras by morula aggrega...

Contribution of Substance P and Neurokinin A to the Differential Injury-Induced Thermal and Mechanical Responsiveness of Lamina I and V Neurons

“…These data are also consistent with previous reports of behavioral deficits in animals lacking the PPT-A gene (Zimmer et al, 1998) and with our conclusion (Cao et al, 1998) that, although SP and NKA are important contributors to the behavioral response to noxious thermal stimuli, they are not required for intensity encoding. Presumably other neurotransmitters, likely glutamate and/or CGRP (calcitonin gene-related peptide), sufficiently activate dorsal horn neurons so as to maintain normal behavioral thresholds.…”

“…Furthermore, selective NK-1 receptor antagonists are antinociceptive in animals (Hill, 2000). There is, however, less agreement among studies of mice with a deletion of the PPT-A gene (Cao et al, 1998;Zimmer et al, 1998) or of the NK-1 receptor (De Felipe et al, 1998;Weng et al, 2001). Some studies reported a significant loss of injury-induced enhancement of nociceptive processing (central sensitization), but others only found deficits in acute pain processing (Cao et al, 1998;De Felipe et al, 1998;Mansikka et al, 1999;Mansikka et al, 2000;Martinez-Caro and Laird, 2000;Laird et al, 2001;Weng et al, 2001).…”

Coexpression of δ- and μ-opioid receptors in nociceptive sensory neurons

“…4 A-E), consistent with the distribution pattern of endogenous DORs. The Myc-DOR1 was further found to be localized on the cell surface but absent in CGRP-ir vesicles in small DRG neurons cultured from PPT-A gene-deleted (Tac1 −/− ) mice (37) (Fig. 4 A-D).…”

A remote and highly conserved enhancer supports amygdala specific expression of the gene encoding the anxiogenic neuropeptide substance-P

“…[89][90][91] The current study also showcases the power of applying comparative genomics, using the genomes of species as highly diverged as humans and birds, to gain insights into the regulatory mechanisms supporting the expression of genes relevant to mental health. This approach will greatly accelerate our identification and characterisation of the regulatory systems and networks required to drive the proper expression of neuronally expressed genes critical to human psychiatric health and will allow an understanding of how deficiencies within these systems might promote the initiation and progression of psychiatric disease.…”