Biomedical subjects

J E Zadina

Publications and source records attributed to J E Zadina.

At least 19 recordsLinked to original sources

PubMed2001

In vitro demonstration of a saturable transport system for leptin across the blood-brain barrier.

A saturable blood-to-brain transport system for leptin across the blood-brain barrier (BBB) has been observed in vivo. Since the main component of the non-fenestrated microvessels of the BBB is the endothelial cell, we established an in vitro culture system of these cerebrovascular cells to study leptin transport and to determine whether the self-inhibition of leptin transport characteristic of a saturable system occurs at this level. The results show that 125I-leptin crossed from the luminal to abluminal side of a monolayer of cerebral microvessel cells significantly faster than the albumin and lactalbumin controls. This transport of 125I-leptin across an in vitro BBB was significantly faster than in the opposite direction and was dose-relatedly inhibited by the addition of unlabeled leptin. Thus, the results establish that the saturable transport system for leptin across the BBB occurs at the level of the endothelial cells of the BBB.

Animals↗

PubMed2000

Differential antagonism of endomorphin-1 and endomorphin-2 spinal antinociception by naloxonazine and 3-methoxynaltrexone.

To determine the role of spinal mu-opioid receptor subtypes in antinociception induced by intrathecal (i.t.) injection of endomorphin-1 and -2, we assessed the effects of beta-funaltrexamine (a selective mu-opioid receptor antagonist) naloxonazine (a selective antagonist at the mu(1)-opioid receptor) and a novel receptor antagonist (3-methoxynaltrexone) using the paw-withdrawal test. Antinociception of i.t. endomorphins and [D-Ala(2), MePhe(4), Gly(ol)(5)]enkephalin (DAMGO) was completely reversed by pretreatment with beta-funaltrexamine (40 mg/kg s.c.). Pretreatment with a variety of doses of i.t. or s.c. naloxonazine 24 h before testing antagonized the antinociception of endomorphin-1, -2 and DAMGO. Judging from the ID(50) values of naloxonazine, the antinociceptive effect of endomorphin-2 was more sensitive to naloxonazine than that of endomorphin-1 or DAMGO. The selective morphine-6beta-glucuronide antagonist, 3-methoxynaltrexone, which blocked endomorphin-2-induced antinociception at each dose (0.25 mg/kg s.c. or 2.5 ng i.t.) that was inactive against DAMGO, did not affect endomorphin-1-induced antinociception but shifted the dose-response curve of endomorphin-2 3-fold to the right. These findings may be interpreted as indicative of the existence of a novel mu-opioid receptor subtype in spinal sites, where antinociception of morphine-6beta-glucuronide and endomorphin-2 are antagonized by 3-methoxynaltrexone. The present results suggest that endomorphin-1 and endomorphin-2 may produce antinociception through different subtypes of mu-opioid receptor.

Analgesics, Opioid↗

PubMed2000

Analgesic effects of endomorphin-1 and endomorphin-2 in the formalin test in mice.

Two recently isolated peptides, endomorphin-1 (Tyr-Pro-Trp-Phe-NH2) and endomorphin-2 (Tyr-Pro-Phe-Phe-NH2), are highly selective micro-opioid receptor agonists with analgesic actions in the tail-flick test. To further assess the analgesic properties of these peptides, the effects of endomorphin-1, endomorphin-2, and morphine were examined in the formalin test. Male Swiss Webster mice were injected i.c.v. with endomorphin-1, endomorphin-2, or morphine (0, 1, 3, 10 microg) 5 min before injection of 20 microl of 5% formalin s.c. into the plantar surface of one hind-paw. The mice were observed for 60 min after formalin injection. Endomorphin-1 and endomorphin-2 produced dose-dependent analgesia that was shorter in duration than for morphine. Increased locomotion was observed after morphine, but not after endomorphin-1 or endomorphin-2. These findings extend previous results and suggest that endomorphins may have therapeutic potential for the treatment of acute pain.

Analgesics, Opioid↗

PubMed2000

Dissociation of analgesic and rewarding effects of endomorphin-1 in rats.

The mu-receptor is the primary mediator of the effects of morphine and the endogenous opiates, endomorphin-1 and endomorphin-2. Here we demonstrate a dissociation of the analgesic and rewarding effects of endomorphin-1 in rats. Tail-flick results revealed that endomorphin-1 produced significant analgesic effects within 10-min after injection. However, it failed to show reward properties in the standard 45- min conditioned place preference (CPP) paradigm or in an abbreviated 10-min pairing which paralleled the time frame of the tail-flick findings. Morphine induced both analgesia and reward. Endomorphin-1 therefore is the first mu opiate shown to produce potent analgesia in the absence of reward behavior, and thus may have significant clinical potential.

Analgesics↗

PubMed2000

Phe(13),Tyr(19)-melanin-concentration hormone and the blood-brain barrier: role of protein binding.

Melanin-concentrating hormone (MCH), found both peripherally and centrally, is involved in food ingestion. Although its expression in brain is increased by fasting, it is not known whether it crosses the blood-brain barrier (BBB). Use of the sensitive method of multiple-time regression analysis has shown that almost all of the peptides and polypeptides tested cross the BBB at a rate faster than the vascular marker albumin. With this same method, however, we found that the 19-amino acid 125I-Phe13,Tyr19-MCH did not cross faster than 99mTc-albumin. Several mechanisms were excluded as possible explanations for the slow rate of influx. These included degradation, association with capillary endothelial cells, and transport from brain to blood. When Phe13,Tyr19-MCH was perfused in blood-free buffer, however, it entered the brain significantly faster than albumin. This suggested protein binding as an explanation for the slow rate of influx when the MCH was administered in blood. Protein binding was confirmed by capillary zone electrophoresis, which showed that almost all of the Phe13,Tyr19-MCH added to blood migrated with a large-molecular-weight substance. Sodium dodecyl sulfate-capillary gel electrophoresis of Phe13,Tyr19-MCH in buffer additionally showed that the MCH aggregated as a trimer, a factor not preventing its influx by blood-free perfusion. Thus, the results show that blood-borne Phe13,Tyr19-MCH does not significantly cross the BBB, probably because of its binding to serum proteins.

Animals↗

PubMed2000

Passage of interleukin-1-beta across the blood-brain barrier is reduced in aged mice: a possible mechanism for diminished fever in aging.

OBJECTIVE: Cytokine signaling is the key to fighting infection. Fever is elicited by the production of inflammatory cytokines, particularly interleukin-1beta (IL-1beta), and the subsequent action of cytokines in the hypothalamus. In old age, the ability to produce fever in response to infection or to peripheral injections of IL-1beta is diminished. Intracerebroventricular injections of IL-1beta can still produce a normal fever response in the aged. A logical hypothesis to explain this discrepancy is that passage of IL-1beta across the blood-brain barrier (BBB) is altered. METHOD: We used a quantitative in vivo technique, which previously showed a saturable system transporting IL-1beta across the BBB, to investigate the speed at which radiolabeled IL-1beta crosses from blood to brain in mice of widely different ages. RESULTS: We found that passage of IL-1beta across the BBB was significantly decreased in old (23-month) mice as compared with young (2-month) or middle-aged (12-month) animals. Passage of IL-1beta across the blood-testis barrier was not significantly different among the groups. The passage of radiolabeled albumin across the BBB was not increased in any group, ruling out any disruption of the BBB by IL-1beta. CONCLUSION: These results provide a mechanism that could help explain why fever production is reduced in old age and suggest an important role for the BBB in regulating immune changes.

Aging↗

PubMed2000

Differential cardiorespiratory effects of endomorphin 1, endomorphin 2, DAMGO, and morphine.

The novel endogenous mu-opioid receptor (MOR) agonists endomorphin 1 (EM1) and 2 (EM2) were tested for their cardiorespiratory effects in conscious, freely behaving rats. After systemic (intravenous) administration of EM1, EM2, or the selective MOR agonist DAMGO, analgesia, minute ventilation (V E), heart rate (HR) and mean arterial blood pressure (BP) were measured. The threshold dose for analgesia was similar for all 3 peptides ( approximately 900 nmol/kg). All 3 compounds elicited biphasic V E responses, with marked, short-lived V E depressions (4-6 s) followed by more sustained V E increases (10-12 min). However, compared with responses elicited by EM2 or DAMGO, EM1 decreased V E only at higher doses, and produced greater V E stimulation. Morphine produced a V E decrease, but no subsequent V E increase. EM2 and DAMGO decreased HR and BP, while EM1 decreased HR, but did not decrease BP in conscious rats at doses up to 9,600 nmol/kg. In anesthetized rats, all 3 peptides decreased HR and BP. The decreases in V E, HR, and BP were blocked by the MOR antagonist, naloxone HCI (NIx). Only the HR and BP responses, however, were blocked by naloxone-methiodide (MeNIx), indicating central mediation of V E responses and peripheral mediation of cardiovascular responses. We conclude that MOR-selective compounds vary in their cardiorespiratory response characteristics which could be linked to differential cellular actions. The results support the concept that the analgesic, respiratory, and cardiovascular effects of MOR agonists can be dissociated and that EM1-like compounds could provide the basis for novel, safer analgesics.

Analgesics, Opioid↗

PubMed1999

Maturation of endomorphin-2 in the dorsal horn of the medulla and spinal cord of the rat.

The endomorphins are potent and selective endogenous agonists at the mu opioid receptor. We describe here the postnatal ontogeny of endomorphin-2 like immunoreactivity (EM2-LI) in the dorsal horn of the rat medulla and spinal cord. EM2-LI is dense in the superficial lamina of the dorsal horn of the adolescent and adult rat, with fibers also present in skin and dorsal root ganglia. No staining was noted at 3 days of age or younger. Faint and limited staining was noted by 7 days of age. The density and distribution of the immunoreactivity increased with age, reaching an adult-like distribution by 21 days of age. Stress-induced responses mediated by endogenous opioids occur late in development and may be related to the late appearance of endomorphin-2.

Aging↗

PubMed1999

Peptide transport system-1 (PTS-1) for Tyr-MIF-1 and Met-enkephalin differs from the receptors for either.

Tyr-MIF-1 (Tyr-Pro-Leu-Gly-NH2) and Met-enkephalin share a saturable transport system (peptide transport system-1, PTS-1) across the blood-brain barrier but do not readily bind to each other's receptors. This information allows the unique opportunity to differentiate the transport protein(s) from the receptors for either peptide in brain endothelial cells. PTS-1 was studied in vitro by allowing radiolabeled Tyr-MIF-1 (125I-Tyr-MIF-1) to bind to the solubilized proteins of isolated murine brain microvessels in the presence or absence of potential inhibitors. Sephadex chromatography separated bound from free labeled peptide. The binding was saturable as shown by inhibition with increasing concentrations of unlabeled Tyr-MIF-1. 125I-Tyr-MIF-1 binding was not inhibited by an unrelated peptide or iodo-tyrosine. D-Tyr-MIF-1 had no effect, demonstrating the stereospecificity of the system. Met-enkephalin decreased the binding of 125I-Tyr-MIF-1 to 84.4% of total, whereas Leu-enkephalin was without effect. Agonists for the mu, delta, and kappa opiate receptors did not change the binding, indicating that the proteins which bound to 125I-Tyr-MIF-1 were not endogenous opiate receptors. The results indicate that, in vitro, Tyr-MIF-1 binds to brain microvessel proteins with characteristics similar to PTS-1.

3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cycloh↗

PubMed1999

Differential involvement of mu-opioid receptor subtypes in endomorphin-1- and -2-induced antinociception.

We investigated the role of mu-opioid receptor subtypes in both endomorphin-1 and endomorphin-2 induced antinociception in mice using supraspinally mediated behavior. With tail pressure as a mechanical noxious stimulus, both intracerebroventricularly (i.c.v.) and intrathecally (i.t.) injected-endomorphins produced potent and significant antinociceptive activity. Antinociception induced by i.t. and i.c.v. injection of endomorphin-1 was not reversed by pretreatment with a selective mu1-opioid receptor antagonist, naloxonazine (35 mg/kg, s.c.). By contrast, antinociception induced by i.t. and i.c.v. endomorphin-2 was significantly decreased by mu1-opioid receptor antagonist. Antinociception of both i.t. and i.c.v. endomorphin-1 and -2 was completely reversed by pretreatment with beta-funaltrexamine (40 mg/kg, s.c.). The results indicate that endomorphins may produce antinociception through the distinct mu1 and mu2 subtypes of mu-opioid receptor.

Analgesics, Opioid↗

PubMed1999

Differential distribution of endomorphin 1- and endomorphin 2-like immunoreactivities in the CNS of the rodent.

Endomorphins are endogenous peptides that have high affinity and selectivity for the mu-opiate receptor and potent analgesic activity. The distributions of endomorphin 1 (Tyr-Pro-Trp-Phe-NH2; EM1) and endomorphin 2 (Tyr-Pro-Phe-Phe-NH2; EM2) in the rat central nervous system were determined by immunocytochemistry with two antisera, each demonstrating clear preference for the target antigen. Perikarya expressing EM2-like immunoreactivity were present in the posterior hypothalamus, whereas those expressing EM1-like immunoreactivity were present in both the posterior hypothalamus and the nucleus of the solitary tract (NTS). EM1-like immunoreactivity was more widely and densely distributed throughout the brain than was EM2-like immunoreactivity, whereas EM2-like immunoreactivity was more prevalent in the spinal cord than was EM1-like immunoreactivity. The greatest density of EM1-like-immunoreactive fibers was detected in the parabrachial nucleus and the NTS, with notable staining in the septum, diagonal band, bed nucleus of the stria terminalis, organum vasculosum, nucleus of Meynert, paraventricular thalamic nucleus, posterior hypothalamic nucleus, periaqueductal gray, locus coeruleus, nucleus accumbens, and amygdala. The greatest density of EM2-like-immunoreactive fibers was detected in the superficial laminae of the spinal cord dorsal horn and the nucleus of the spinal trigeminal tract. The overall pattern of immunoreactivities was similar in rat, mouse, and guinea pig, but some differences were observed. In many but not in all locations, immunoreactive fibers were prominently present in regions in which mu receptors are reported to be concentrated. The neuroanatomical results suggest that endomorphins participate in modulating nociceptive and autonomic nervous system processes and responsiveness to stress.

Animals↗

PubMed1999

Tyr-W-MIF-1-induced conditioned place preference.

Based on the evidence that Tyr-Pro-Trp-Gly NH2 (Tyr-W-MIF-1) produced dose-dependent, mu-opiate agonistic/antagonistic effects, we investigated whether Tyr-W-MIF- exhibited similar properties in the conditioned place preference (CPP) test. To examine the opiate agonistic effects on CPP, rats were conditioned with alternating ICV injections of saline and Tyr-W-MIF-1 (0 or 200 microg). This procedure resulted in Tyr-W-MIF-1-induced CPP. To examine the opiate antagonistic properties of low doses of Tyr-W-MIF-1, morphine-induced CPP was challenged with Tyr-W-MIF-1 (0, 25, 50, or 100 microg). Morphine-induced CPP was not affected by Tyr-W-MIF-1 at these doses. These findings show that in the CPP test Tyr-W-MIF-1 produced opiate agonistic effects at the high dose and was without opiate antagonistic properties at lower doses.

Animals↗

PubMed1999

Tolerance and morphine-induced cross-tolerance are not shown to Tyr-W-MIF-1 analgesia.

Tolerance and cross-tolerance between Tyr-W-MIF-1, a mixed micro-agonist/antagonist, and morphine were examined. Opiate dependence also was examined. Rats were pretreated with Tyr-W-MIF-1, morphine, or saline for 4 days. On day 5, the animals were tested for Tyr-W-MIF-1 analgesia, morphine analgesia, or naloxone-precipitated withdrawal. Tyr-W-MIF-1- and morphine-pretreated animals showed similar levels of dependence. Animals pretreated with Tyr-W-MIF-1 failed to express tolerance to Tyr-W-MIF-1 analgesia but did display cross-tolerance to morphine analgesia. Animals pretreated with morphine displayed tolerance to morphine analgesia but did not express cross-tolerance to Tyr-W-MIF-1 analgesia. Therefore, tolerance and morphine-induced cross-tolerance were not expressed to Tyr-W-MIF-1 analgesia.

Animals↗

PubMed1999

Effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides from 1994 through 1998.

Effects of peptides on the central nervous system are presented in two ways so as to provide a cross-listing. In the first table, the peptides are listed alphabetically. In the second table, the central nervous system effects are arranged alphabetically. No longer can there be any doubt that peptides affect the central nervous system, sometimes in several ways.

Peptides↗

PubMed1999

Endomorphins: novel endogenous mu-opiate receptor agonists in regions of high mu-opiate receptor density.

Endomorphin-1 (Tyr-Pro-Trp-Phe-NH2, EM-1) and endomorphin-2 (Tyr-Pro-Phe-Phe-NH2, EM-2) are peptides recently isolated from brain that show the highest affinity and selectivity for the mu (morphine) opiate receptor of all the known endogenous opioids. The endomorphins have potent analgesic and gastrointestinal effects. At the cellular level, they activate G-proteins (35S-GTP gamma-S binding) and inhibit calcium currents. Support for their role as endogenous ligands for the mu-opiate receptor includes their localization by radioimmunoassay and immunocytochemistry in central nervous system regions of high mu receptor density. Intense EM-2 immunoreactivity is present in the terminal regions of primary afferent neurons in the dorsal horn of the spinal cord and in the medulla near high densities of mu receptors. Chemical (capsaicin) and surgical (rhizotomy) disruption of nociceptive primary afferent neurons depletes the immunoreactivity, implicating the primary afferents as the source of EM-2. Thus, EM-2 is well-positioned to serve as an endogenous modulator of pain in its earliest stages of perception. In contrast to EM-2, which is more prevalent in the spinal cord and lower brainstem, EM-1 is more widely and densely distributed throughout the brain than EM-2. The distribution is consistent with a role for the peptides in the modulation of diverse functions, including autonomic, neuroendocrine, and reward functions as well as modulation of responses to pain and stress.

Afferent Pathways↗

PubMed1999

The ontogeny of endomorphin-1- and endomorphin-2-like immunoreactivity in rat brain and spinal cord.

Endomorphin-1 and endomorphin-2 are recently described peptides with high affinity and specificity for the mu opioid receptor. They are believed to be the endogenous ligands for that receptor. We describe the maturation of the endomorphins in brain and spinal cord using recently characterized antibodies to each. Endomorphin-1-like immunoreactivity was examined in brain, focusing on the periaqueductal gray of the midbrain and the diagonal band of Broca; endomorphin-2-like immunoreactivity is reported for the medulla and spinal cord. In these regions, and in all other regions studied but not described in this paper, the endomorphins were not seen at birth or at 3 days of age. Staining was present in 7-day-old and older animals. At these early ages, the pattern and density of staining are not fully developed, but appear complete by 21 days of age. The results suggest that both endomorphin-1 and endomorphin-2 develop relatively late compared to other opioid peptides.

Aging↗

PubMed1999

Vasodilator responses to the endomorphin peptides, but not nociceptin/OFQ, are mediated by nitric oxide release.

The endomorphin peptides, endogenous ligands for the mu-opioid receptor, and nociceptin (orphanin FQ; OFQ), an endogenous ligand for the ORL1 receptor, have substantial vasodilator activity in the rat. The roles of nitric oxide, vasodilator prostaglandins, and the opening of K+ATP channels in mediating vasodilator responses to these novel agonists were investigated in the hindquarters vascular bed of the rat. Under constant-flow conditions, injections of the mu-selective agonists, endomorphin 1 and 2, PL017 ([N-MePhe3, D-Pro4]-morphiceptin), and DAMGO, and the ORL1 receptor agonist, nociceptin/OFQ, produced dose-dependent decreases in hindquarters perfusion pressure. Vasodilator responses to endomorphin 1, PL017, and DAMGO were attenuated by the nitric oxide synthase inhibitor L-NAME at a time when vasodilator responses to nociceptin/OFQ were not altered. Responses to endomorphin 1 and 2, PL017, DAMGO, and nociceptin/OFQ were not altered by the cyclooxygenase inhibitor sodium meclofenamate or the K+ATP channel blocker U-37883A. The results of these studies indicate that responses to endomorphin 1 and 2, PL017, and DAMGO are mediated in large part by the release of nitric oxide, while responses to nociceptin/OFQ are mediated by an L-NAME-insensitive mechanism. Moreover, these results demonstrate that responses to these peptides are not mediated by the release of vasodilator prostaglandins or K+ATP channel opening in the hindquarters vascular bed.

Adamantane↗

PubMed1999

Comparison of active conformations of the insectatachykinin/tachykinin and insect kinin/Tyr-W-MIF-1 neuropeptide family pairs.

A comparison of solution conformations of active, restricted-conformation analogues of two sequence-similar insect/vertebrate neuropeptide family pairs shed light on the potential existence of molecular evolutionary relationships. Analogues of the locustatachykinins and the mammalian tachykinin substance P, containing a sterically hindered Aib-NMePhe/Tyr residue block, share similar low-energy turn conformations incorporating a cis peptide bond. Conversely, restricted conformation analogues of the insect kinins and the mammalian opiate peptide Tyr-W-MIF-1, with near identical C-terminal tetrapeptide sequences, adopt different conformations. The insect kinins adopt a cisPro 1-4 beta-turn, in which the Phe1 is critical for bioactivity. Tyr-W-MIF-1 prefers a transPro 2-5 turn, and an additional N-terminal Phe severely inhibits mu-opiate receptor binding. Comparisons of the chemical/conformational requirements for receptor interaction are consistent with a distant evolutionary relationship between the insectatachykinins and tachykinins, but not between the insect kinins and Tyr-W-MIF-1. Therefore, analogues of the insect kinins with pest control potential can be readily designed to avoid mammalian interactions.

Amino Acid Sequence↗