Substance P and neurokinin A, two coexisting tachykinins stimulating the release of [3H]5-HT from rat cerebral cortical slices

Progesterone and norethisterone have different effects on tachykinin-like immunoreactivity in rat cortex and striatum

OBJECTIVE

The purpose of this study was to investigate the effects of progesterone and the most commonly prescribed synthetic progestogen, norethisterone, on regional immune-like reactivity of neuropeptide Y (NPY), substance P (SP), neurokinin A (NKA) and neurotensin (NT) in brains of female ovariectomized estradiol-substituted rats.

RESULTS

Norethisterone+estradiol-treated rats had 44% lower SP levels compared with estradiol-only-treated in frontal cortex and 20% lower NKA levels in comparison with progesterone+estradiol-treated in frontal cortex. Progesterone+estradiol-treated rats had 66% lower SP levels in striatum in comparison with both estradiol-only-treated and norethisterone+estradiol-treated. No significant results were found for NPY and NT.

CONCLUSION

Progesterone and the synthetic progestogen, norethisterone, have different effects on SP- and NKA-like immunoreactivity in rat cortex and striatum. The effects of NET on SP- and NKA-like immunoreactivity in frontal cortex may contribute to the mood effects ascribed to this progestogen in clinical usage.

Effects of serotonin and substance P on bulbar respiratory neurons in vivo

We studied the effects of separate or co-applications by microiontophoresis of serotonin (5-HT) and substance P(4-11) onto brainstem respiratory neurons in anesthetized or decerebrate cats. 5-HT either produced an excitation (36%, n = 10) or an inhibition (43%, n = 12) or had no effect (21%, n = 6). SP(4-11) had predominantly an excitatory effect (84%, n = 26) or no effect. Fifteen respiratory neurons responded to both 5-HT and SP(4-11). Test applications of 5-HT were made during a long application of SP(4-11). We obtained 'additive effects' when the inhibitory effect of 5-HT was superimposed to the excitation of SP(4-11) with slight modification (n = 1) or without any modification (n = 2). In other cases, called 'non-additive effects', we observed a great modification of the responsiveness of the neuron to the inhibitory effect of 5-HT (n = 2) or a complete blockade of the excitatory effect of 5-HT (n = 2) during co-application. The remaining results presented a potentiation of 5-HT effect by SP(4-11) or a biphasic response to 5-HT during SP(4-11) application. The results indicate that both 5-HT and SP receptors coexist on the membrane of the same respiratory-related neurons in the brainstem of cat and suggest an interaction between both substances in vivo in the central respiratory system.

Regional distribution of serotonin and substance P co-existing in nerve fibers and terminals in the brainstem of the rat

Two-color fluorescence immunohistochemistry was used to identify and map the distribution of nerve processes immunoreactive for both serotonin and substance P in the rat brainstem. Doubly labeled fibers were observed throughout the brainstem, but tended to be densest in cranial nerve motor nuclei and in reticular regions of the ventral medulla. In the trigeminal motor nucleus, the facial nucleus and the spinal accessory nucleus, the majority of serotonergic varicosities also appeared to contain substance P; in the occulomotor nucleus and the hypoglossal nucleus the numbers of double-labeled and single-labeled serotonergic varicosities were roughly equal. Thus, co-existence of substance P with serotonin was common in many cell groups innervating skeletal muscle. The proportion of double-labeled varicosities was significantly lower in the nucleus of the solitary tract, wherein single-labeled varicosities were much more common. Double-labeled fibers and varicosities were also significantly less common in the spinal trigeminal nucleus. In addition, double-labeling appeared to be uncommon in regions involved in the processing of special sensory information (e.g. auditory, vestibular and visual pathways). These results demonstrate a subpopulation of serotonergic fibers immunoreactive for substance P in the brainstem of the rat. The consistently high density of double-labeled processes in cranial nerve motor nuclei suggests that, as may be the case in the spinal cord, neurons containing serotonin and substance P regulate the activity of motoneurons that innervate skeletal muscle. In addition, they may be involved in other aspects of the function of the brainstem.

Substance P and neuropsychiatric disorders: an overview

Substance P (SP) is a naturally-occurring tachykinin peptide isolated from brain tissues and gastrointestinal tract. In the brain, substantia nigra and basal ganglia contain relatively high amounts of substance P. There is evidence suggesting that substance P functions as a neurotransmitter. It has been implicated in the pathophysiology of several neuropsychiatric disorders. Substance P may also serve as a useful tool in studying the effects of antidepressant drugs and electroconvulsive therapy. However, the contribution of substance P to the understanding of neuropsychiatric disorders is far from clear. Future studies should focus on the interactions and coexistence of substance P with other neurotransmitters and neuropeptides.

Evidence of NK1 and NK2 tachykinin receptors and their involvement in histamine release in a murine mast cell line

Binding of [3H]substance P (SP) and histamine release were examined using a cloned mouse mast cell line. SP binding was saturable and specific. In the presence of 30 mM Na2SO4/50 mM Tris buffer, SP interacted with two types of binding sites with Kd values of 0.3 and 40 nM. High-affinity SP binding was blocked by the inclusion of 0.5 uM of the NK1 receptor selective ligand septide in the binding mixture. Neurokinin A (NKA) evoked concentration-dependent histamine release. At concentrations in the nanomolar range, the NK1 preferring agonists SP, SP methylester and physalaemin evoked less than or equal to 5% net release of histamine, which was substantially less than the maximum effect of NKA (+37%) in the micromolar range. Pretreatment of the cells with the NK2 antagonist peptide A reduced NKA-induced histamine release. [D-Arg1,D-Phe5,D-Trp7,9,Leu11]-substance P, a putative SP antagonist, also elicited histamine release in the micromolar range, apparently acting as an agonist at the NK2 site. Compound 48/80, N-terminal SP fragments, neurokinin B and the two selective NK2 receptor antagonists cyclo(Gln-Trp-Phe-(R)-[ANC-2]Leu-Met) (peptide A) and cyclo(Gln-Trp-Phe-Gly-Leu-Met) (peptide B) were ineffective. Although the results suggest the coexistence of functional NK1 and NK2 receptors, it appears that in this mast cell line neurokinin-induced histamine release is primarily mediated by the NK2 receptor, characterized biochemically as a low affinity binding site with a Kd value of 40 nM for SP.