Tachykinins and tachykinin-receptors in the rat pineal gland

High-pressure liquid chromatography of extracts of rat pineal glands, followed by radio immunological analysis with antibodies against tachykinins, demonstrated the presence of substance P, neurokinin A and neurokinin B in the superficial rat pineal gland. Immunohistochemistry on perfusion-fixed rat brain sections showed substance P and neurokinin A to be present in nerve fibers located both in the perivascular spaces as well as intraparenchymally between the pinealocytes. After extracting total RNA, followed by reverse transcription and polymerase chain reaction amplification with primers specific for NK1-, NK2- and NK3-receptors, agarose gel analysis of the reaction products showed the presence of mRNA encoding all three neurokinin receptors. Immunohistochemical analysis showed NK1 receptor to be located in the interstitial cells of the gland. This location was confirmed by use of in situ hybridization using radioactively labeled antisense oligonucleotide probes. Double immunohistochemical stainings showed that the NK1-immunoreactive cells were not a part of the macrophages or antigen-presenting cells of the gland. Our study suggests that tachykinins, after release from intrapineal nerve fibers, are involved in an up to now unknown function, different from that of melatonin synthesis.

Deferoxamine attenuates iron-induced oxidative stress and prevents mitochondrial aggregation and alpha-synuclein translocation in SK-N-SH cells in culture

One of the defining characteristics of neurodegenerative diseases, including Parkinson's disease, is an abnormal accumulation of iron in the affected brain areas. By using SK-N-SH, a dopaminergic cell line, we have found that iron (100-250 microM FeSO(4)) decreased cell viability, increased lipid peroxidation, and the said effects were blocked by deferoxamine (DFO: 10 microM). Furthermore, DFO, in the absence of iron, enhanced the level of adenosine triphosphate (ATP), but caused chromatin condensation and cell death. Morphological studies revealed that iron (50-100 microM) altered mitochondrial morphology, disrupted nuclear membrane, and translocated alpha-synuclein from perinuclear region into the disrupted nucleus. The results of these studies suggest that DFO is able to block and attenuate iron-mediated oxidative stress. However, in the absence of excess iron, DFO itself may have deleterious effects on the morphology and hence integrity of dopaminergic neurons.

The effects of adrenergic agonists on c-fos, jun-B and nitric oxide synthase-like immunoreactivities in cultured rat pinealocytes

Pineal melatonin synthesis is enhanced by the activation of adrenergic and opioid receptors. The precise mechanism of how signal transduction is affected by the activation of these receptors, leading to an increase in melatonin synthesis, is not clear. An attempt has been made to investigate the effects of the activation of these two types of receptors that might lead to the induction of immediate early genes (IEGs) and nitric oxide synthase (NOS) expressions. The present study shows that the stimulation of cultured pinealocytes by 1 microM epinephrine (an alpha- and beta-adrenergic agonist) for 2 h increased the number of c-fos immunoreactive (IR) cells, and that this stimulatory effect was abolished by adding 10 microM prazosin (an alpha-adrenergic antagonist) to the culture medium. No significant change of c-fos-IR cells was found when cells were treated with either 1 microM isoproterenol (a beta-adrenergic agonist) or 100 microM morphine (an opioid agonist). Neither epinephrine (1 microM), isoproterenol (1 microM) nor morphine (100 microM) altered jun-B-IR cells in the culture. With regard to NOS, the number of IR cells was slightly increased after 2 h of incubation by 10 microM isoproterenol, whereas morphine (100 microM) and epinephrine (10 microM) did not change the number of IR cells. The results of this experiment have demonstrated that c-fos expression is induced by alpha-adrenergic but not beta-adrenergic agonists, nor by opioid agonists. Neither alpha-, beta-adrenergic nor opioid agonists had any significant effect on jun-B, whereas NOS was slightly increased by isoproterenol.

Gene expressions of opioid receptors and G-proteins in pineal glands

In our previous studies, the opioid receptors located on pinealocytes have been identified and characterized, and these receptors have been found to play a stimulatory role in melatonin synthesis by activating the rate limiting enzyme, N-acetyltransferase (NAT). In the present study, by using reverse transcriptase polymerase chain reaction (RT-PCR) followed by nested-PCR, segments of delta and mu opioid receptors have been amplified from mRNA of rat pineal gland and cerebral cortex. In addition, segments of delta and mu opioid receptors have also been amplified from mRNA of human pineal gland. Furthermore, G(alphai/o)- and G(beta)-protein-coupled receptor mRNAs have been amplified and identified from rat pineal gland. The regulatory effects of morphine on G(alphai/o) and G(beta) mRNA levels have been semiquantitatively analyzed. Acute morphine administration caused significant increase in G(alphai/o), and G(beta), mRNA levels in rat pineal gland, but not in other brain regions. Further studies are needed in order to elaborate the mechanisms of these opioid receptors in regulating G-protein expression in pineal gland.

Existence and function of opioid receptors on mammalian pinealocytes

Previous studies in our laboratories have identified a single population of opioid receptors in bovine pineal gland, which we have chosen to characterize further on pinealocytes isolated from the cow and rat pineal gland. The bovine pinealocytes isolated by trypsinization or mechanical manipulation revealed receptor density (Bmax) values of 206.95 +/- 131.15 and 220.34 +/- 11.80 fmol/mg protein, respectively, and dissociation equilibrium constant (Kd) values of 1.93 +/- 0.48 and 1.96 +/- 0.21 nM, respectively. The rat pinealocytes cultured for 7 days exhibited a [3H]diprenorphine binding site of 56 fmol/10(6) cells. Morphine (100 microM) enhanced the activity of N-acetyltransferase and the level of melatonin in rat pineal gland in culture incubated for 21 hr. The results of these studies suggest that opioidergic receptors exist on pinealocytes and they are involved in stimulating the activity of N-acetyltransferase and the synthesis of melatonin, thereby regulating the physiology of mammalian pineal gland.