Variations in levels of substance P-encoding beta-, gamma-preprotachykinin and substance P receptor NK-1 transcripts in the rat hypothalamus throughout the estrous cycle: a correlation between amounts of beta-preprotachykinin and NK-1 mRNA

Identification of Eya3 and TAC1 as long-day signals in the sheep pituitary

Seasonally breeding mammals such as sheep use photoperiod, encoded by the nocturnal secretion of the pineal hormone melatonin, as a critical cue to drive hormone rhythms and synchronize reproduction to the most optimal time of year. Melatonin acts directly on the pars tuberalis (PT) of the pituitary, regulating expression of thyrotropin, which then relays messages back to the hypothalamus to control reproductive circuits. In addition, a second local intrapituitary circuit controls seasonal prolactin (PRL) release via one or more currently uncharacterized low-molecular-weight peptides, termed "tuberalins," of PT origin. Studies in birds have identified the transcription factor Eya3 as the first molecular response activated by long photoperiod (LP). Using arrays and in situ hybridization studies, we demonstrate here that Eya3 is the strongest LP-activated gene in sheep, revealing a common photoperiodic molecular response in birds and mammals. We also demonstrate TAC1 (encoding the tachykinins substance P and neurokinin A) to be strongly activated by LP within the sheep PT. We show that these PRL secretagogues act on primary pituitary cells and thus are candidates for the elusive PT-expressed tuberalin seasonal hormone regulator.

Decreases in neurokinin-3 tachykinin receptor-immunoreactive and -mRNA levels are associated with salt appetite in the deoxycorticosterone-treated rat

Tachykinins are a family of neuropeptides that inhibit salt appetite. Although decreased tachykinin-mRNA levels are observed in natriorexic sodium-deplete rats, no decrease is seen in natriorexic sodium-replete rats that are administered the aldosterone-mimetic deoxycorticosterone acetate (DOCA). Since reduced synthesis of tachykinins could not account for increased appetite, we hypothesized that increased salt appetite was due to a downregulation of tachykinin receptors. Thus, we injected rats with DOCA once daily for 11 days and analyzed tachykinin receptor subtype, neurokinin 3 (NK3r)-immunoreactivity by Western blot analysis since intracerebroventricular injection of senktide (NK3r agonist) attenuates salt intake in DOCA-treated animals. We examined NK3r-immunoreactivity in several brain regions thought to be associated with the control of water and electrolyte balance including the bed nucleus of the stria terminalis, central nucleus of the amygdala, diagonal band of Broca, hippocampus, nucleus tractus solitarius, parabrachial nucleus, paraventricular nucleus of the hypothalamus, and supraoptic nucleus. Consistent with our hypothesis, we found decreased NK3r-immunoreactivity in all brain regions analyzed except for increases in the amygdala and no changes in the paraventricular nucleus of the hypothalamus. To examine whether DOCA's effects on NK3r synthesis are direct, we used differentiated N1E-115 neuroblastoma cells that express NK3r and treated them with a range of concentrations of DOCA and found a dose-dependent decrease in NK3r-mRNA abundance via Northern blotting. The present results suggest that the tachykinin receptors are downregulated after subchronic DOCA treatment and this finding is consistent with the hypothesis that suppressed inhibition of salt appetite as mediated through the tachykininergic system.

Simultaneous quantitation of substance P-encoding preprotachykinin alternatively spliced mRNAs and substance P receptor NK-1 mRNA by an RNase protection assay

Tachykinins form a family of peptides with neurotransmitter/neuromodulator function. Four tachykinins, substance P, neurokinin A, neuropeptide gamma and neuropeptide K, are encoded by the same PreProTachykinin (PPT) gene. Alternatively spliced mRNAs encode different combinations of these peptides (Brown, E.R., Harlan, R.E., Krause, J.E., Gonadal steroid regulation of substance P (SP) and SP-encoding mRNA in the rat anterior pituitary and hypothalamus, Endocrinology, 126 (1990) 330-340; Krause, J.E., Chirgwin, J.M., Carter, M.S., Xu, Z.S., Hershey, A.D., Three rat preprotachykinin mRNAs encode the neuropeptides substance P and neurokinin A, Proc. Natl. Acad. Sci. USA, 84 (1987) 881-885). The proportion of PPT mRNAs varies from tissue to tissue (Carter, M.S., Krause, J.E., Structure, expression, and some regulatory mechanisms of the rat preprotachykinin gene encoding substance P, neurokinin A, neuropeptide K, and neuropeptide gamma, J. Neurosci., 10 (1990) 2203-2214), and within the rat hypothalamus according to the estrous cycle-related hormonal status (Gautreau, A., Duval, P., Kerdelhué, B., Variations in substance P-encoding preprotachykinin and substance P receptor NK-1 mRNA transcripts in the rat hypothalamus throughout the estrous cycle: a correlation between amounts of beta-preprotachykinin and NK-1 mRNA, Mol. Brain Res., (1997) in press). Tachykinin receptors as well as tachykinins are regulated at the mRNA level. A fully quantitative method is needed to deal with the complex physiological regulation of the tachykinin system. Here, we describe an RNase protection assay that allows the simultaneous quantitation of alternatively spliced PPT mRNAs, Substance P receptor NK-1 mRNA, and glyceraldehyde-3-phosphodehydrogenase (GAPDH) mRNA as an internal control, in the rat hypothalamus. The advantages of this method are its high sensitivity (0.1 pg) and a wide range of linearity (more than 3 orders of magnitude). Moreover, this protocol provides guidelines to set up a quantitative multiprobe RNase protection assay for other genes.