Tuberoinfundibular peptide of 39 residues decreases pain-related affective behavior

Paralemniscal TIP39 is induced in rat dams and may participate in maternal functions

The paralemniscal area, situated between the pontine reticular formation and the lateral lemniscus in the pontomesencephalic tegmentum contains some tuberoinfundibular peptide of 39 residues (TIP39)-expressing neurons. In the present study, we measured a 4 times increase in the level of TIP39 mRNA in the paralemniscal area of lactating mothers as opposed to nulliparous females and mothers deprived of pups using real-time RT-PCR. In situ hybridization histochemistry and immunolabeling demonstrated that the induction of TIP39 in mothers takes place within the medial paralemniscal nucleus, a cytoarchitectonically distinct part of the paralemniscal area, and that the increase in TIP39 mRNA levels translates into elevated peptide levels in dams. The paralemniscal area has been implicated in maternal control as well as in pain perception. To establish the function of induced TIP39, we investigated the activation of TIP39 neurons in response to pup exposure as maternal, and formalin injection as noxious stimulus. Both stimuli elicited c-fos expression in the paralemniscal area. Subsequent double labeling demonstrated that 95% of neurons expressing Fos in response to pup exposure also contained TIP39 immunoreactivity and 91% of TIP39 neurons showed c-fos activation by pup exposure. In contrast, formalin-induced Fos does not co-localize with TIP39. Instead, most formalin-activated neurons are situated medial to the TIP39 cell group. Our data indicate that paralemniscal neurons may be involved in the processing of maternal and nociceptive information. However, two different groups of paralemniscal neurons participate in the two functions. In particular, TIP39 neurons may participate in the control of maternal functions.

Tuberoinfundibular peptide of 39 residues (TIP39) signaling modulates acute and tonic nociception

Tuberoinfundibular peptide of 39 residues (TIP39) synthesizing neurons at the caudal border of the thalamus and in the lateral pons project to areas rich in its receptor, the parathyroid hormone 2 receptor (PTH2R). These areas include many involved in processing nociceptive information. Here we examined the potential role of TIP39 signaling in nociception using a PTH2R antagonist (HYWH) and mice with deletion of TIP39's coding sequence or PTH2R null mutation. Intracerebroventricular (icv) infusion of HYWH significantly inhibited nociceptive responses in tail-flick and hot-plate tests and attenuated the nociceptive response to hindpaw formalin injection. TIP39-KO and PTH2R-KO had increased response latency in the 55°C hot-plate test and reduced responses in the hindpaw formalin test. The tail-flick test was not affected in either KO line. Thermal hypoalgesia in KO mice was dose-dependently reversed by systemic administration of the cannabinoid receptor 1 (CB1) antagonist rimonabant, which did not affect nociception in wild-type (WT). Systemic administration of the cannabinoid agonist CP 55,940 did not affect nociception in KO mice at a dose effective in WT. WT mice administered HYWH icv, and both KOs, had significantly increased stress-induced analgesia (SIA). Rimonabant blocked the increased SIA in TIP39-KO, PTH2R-KO or after HYWH infusion. CB1 and FAAH mRNA were decreased and increased, respectively, in the basolateral amygdala of TIP39-KO mice. These data suggest that TIP39 signaling modulates nociception, very likely by inhibiting endocannabinoid circuitry at a supraspinal level. We infer a new central mechanism for endocannabinoid regulation, via TIP39 acting on the PTH2R in discrete brain regions.

The TIP39-PTH2 receptor system: unique peptidergic cell groups in the brainstem and their interactions with central regulatory mechanisms

Tuberoinfundibular peptide of 39 residues (TIP39) is the recently purified endogenous ligand of the previously orphan G-protein coupled parathyroid hormone 2 receptor (PTH2R). The TIP39-PTH2R system is a unique neuropeptide-receptor system whose localization and functions in the central nervous system are different from any other neuropeptides. TIP39 is expressed in two brain regions, the subparafascicular area in the posterior thalamus, and the medial paralemniscal nucleus in the lateral pons. Subparafascicular TIP39 neurons seem to divide into a medial and a lateral cell population in the periventricular gray of the thalamus, and in the posterior intralaminar complex of the thalamus, respectively. Periventricular thalamic TIP39 neurons project mostly to limbic brain regions, the posterior intralaminar thalamic TIP39 neurons to neuroendocrine brain areas, and the medial paralemniscal TIP39 neurons to auditory and other brainstem regions, and the spinal cord. The widely distributed axon terminals of TIP39 neurons have a similar distribution as the PTH2R-containing neurons, and their fibers, providing the anatomical basis of a neuromodulatory action of TIP39. Initial functional studies implicated the TIP39-PTH2R system in nociceptive information processing in the spinal cord, in the regulation of different hypophysiotropic neurons in the hypothalamus, and in the modulation of affective behaviors. Recently developed novel experimental tools including mice with targeted mutations of the TIP39-PTH2R system and specific antagonists of the PTH2R will further facilitate the identification of the specific roles of TIP39 and the PTH2R.

Cognitive and affective sequelae of primary hyperparathyroidism and early response to parathyroidectomy

Cognitive and affective complaints are common in patients with primary hyperparathyroidism (PHPT), but few studies have used psychometric testing to document these symptoms and their response to parathyroidectomy. The current study sought to clarify the nature of cognitive and affective impairments in PHPT and changes postparathyroidectomy. One hundred eleven patients with PHPT underwent neuropsychological evaluation prior to parathyroidectomy with 68 returning for an early postsurgical evaluation. Changes in cognition were assessed using practice effect corrected reliable change indices. Biochemical and anesthesia variables were compared between groups who improved and declined. In a subset of patients, assessment revealed a significant pattern of cognitive slowing, reductions in psychomotor speed, memory impairment, and depression prior to parathyroidectomy. Postsurgical evaluations revealed a trend for improvements on timed tests and depression but a decline in memory. Older patients responded less well to surgical intervention, as did patients who experienced more dramatic changes in biochemical status following surgery. Cognitive changes early postparathyroidectomy are characterized by improved information processing speed and decline in verbal memory, with younger patients more likely to recover during this acute phase. The need for longer-term follow-up studies and increasing utilization of neuropsychological assessments in this population are discussed.

Chemical modification of class II G protein-coupled receptor ligands: frontiers in the development of peptide analogs as neuroendocrine pharmacological therapies

Recent research and clinical data have begun to demonstrate the huge potential therapeutic importance of ligands that modulate the activity of the secretin-like, Class II, G protein-coupled receptors (GPCRs). Ligands that can modulate the activity of these Class II GPCRs may have important clinical roles in the treatment of a wide variety of conditions such as osteoporosis, diabetes, amyotrophic lateral sclerosis and autism spectrum disorders. While these receptors present important new therapeutic targets, the large glycoprotein nature of their cognate ligands poses many problems with respect to therapeutic peptidergic drug design. These native peptides often exhibit poor bioavailability, metabolic instability, poor receptor selectivity and resultant low potencies in vivo. Recently, increased attention has been paid to the structural modification of these peptides to enhance their therapeutic efficacy. Successful modification strategies have included d-amino acid substitutions, selective truncation, and fatty acid acylation of the peptide. Through these and other processes, these novel peptide ligand analogs can demonstrate enhanced receptor subtype selectivity, directed signal transduction pathway activation, resistance to proteolytic degradation, and improved systemic bioavailability. In the future, it is likely, through additional modification strategies such as addition of circulation-stabilizing transferrin moieties, that the therapeutic pharmacopeia of drugs targeted towards Class II secretin-like receptors may rival that of the Class I rhodopsin-like receptors that currently provide the majority of clinically used GPCR-based therapeutics. Currently, Class II-based drugs include synthesized analogs of vasoactive intestinal peptide for type 2 diabetes or parathyroid hormone for osteoporosis.

Parathyroid hormone 2 receptor and its endogenous ligand tuberoinfundibular peptide of 39 residues are concentrated in endocrine, viscerosensory and auditory brain regions in macaque and human

Parathyroid hormone receptor 2 (PTH2R) and its ligand, tuberoinfundibular peptide of 39 residues (TIP39) constitute a neuromodulator system implicated in endocrine and nociceptive regulation. We now describe the presence and distribution of the PTH2R and TIP39 in the brain of primates using a range of tissues and ages from macaque and human brain. In situ hybridization histochemistry of TIP39 mRNA, studied in young macaque brain, due to its possible decline beyond late postnatal ages, was present only in the thalamic subparafascicular area and the pontine medial paralemniscal nucleus. In contrast, in situ hybridization histochemistry in macaque identified high levels of PTH2R expression in the central amygdaloid nucleus, medial preoptic area, hypothalamic paraventricular and periventricular nuclei, medial geniculate, and the pontine tegmentum. PTH2R mRNA was also detected in several human brain areas by RT-PCR. The distribution of PTH2R-immunoreactive fibers in human, determined by immunocytochemistry, was similar to that in rodents, including dense fiber networks in the medial preoptic area, hypothalamic paraventricular, periventricular and infundibular (arcuate) nuclei, lateral hypothalamic area, median eminence, thalamic paraventricular nucleus, periaqueductal gray, lateral parabrachial nucleus, nucleus of the solitary tract, sensory trigeminal nuclei, medullary dorsal reticular nucleus, and dorsal horn of the spinal cord. Co-localization suggested that PTH2R fibers are glutamatergic, and that TIP39 may directly influence hypophysiotropic somatostatin containing and indirectly influence corticotropin releasing-hormone containing neurons. The results demonstrate that TIP39 and the PTH2R are expressed in the brain of primates in locations that suggest involvement in regulation of fear, anxiety, reproductive behaviors, release of pituitary hormones, and nociception.

The medial paralemniscal nucleus and its afferent neuronal connections in rat

Previously, we described a cell group expressing tuberoinfundibular peptide of 39 residues (TIP39) in the lateral pontomesencephalic tegmentum, and referred to it as the medial paralemniscal nucleus (MPL). To identify this nucleus further in rat, we have now characterized the MPL cytoarchitectonically on coronal, sagittal, and horizontal serial sections. Neurons in the MPL have a columnar arrangement distinct from adjacent areas. The MPL is bordered by the intermediate nucleus of the lateral lemniscus nucleus laterally, the oral pontine reticular formation medially, and the rubrospinal tract ventrally, whereas the A7 noradrenergic cell group is located immediately mediocaudal to the MPL. TIP39-immunoreactive neurons are distributed throughout the cytoarchitectonically defined MPL and constitute 75% of its neurons as assessed by double labeling of TIP39 with a fluorescent Nissl dye or NeuN. Furthermore, we investigated the neuronal inputs to the MPL by using the retrograde tracer cholera toxin B subunit. The MPL has afferent neuronal connections distinct from adjacent brain regions including major inputs from the auditory cortex, medial part of the medial geniculate body, superior colliculus, external and dorsal cortices of the inferior colliculus, periolivary area, lateral preoptic area, hypothalamic ventromedial nucleus, lateral and dorsal hypothalamic areas, subparafascicular and posterior intralaminar thalamic nuclei, periaqueductal gray, and cuneiform nucleus. In addition, injection of the anterograde tracer biotinylated dextran amine into the auditory cortex and the hypothalamic ventromedial nucleus confirmed projections from these areas to the distinct MPL. The afferent neuronal connections of the MPL suggest its involvement in auditory and reproductive functions.

Tuberoinfundibular Peptide of 39 residues is required for germ cell development

Tuberoinfundibular peptide of 39 residues (TIP39) was identified as a PTH 2 receptor ligand. We report that mice with deletion of Tifp39, the gene encoding TIP39, are sterile. Testes contained Leydig and Sertoli cells and spermatogonia but no spermatids. Labeling chromosome spreads with antibodies to proteins involved in recombination showed that spermatogonia do not complete prophase of meiosis I. Chromosomes were observed at different stages of recombination in single nuclei, a defect not previously described with mutations in genes known to be specifically involved in DNA replication and recombination. TIP39 was previously shown to be expressed in neurons projecting to the hypothalamus and within the testes. LH and FSH were slightly elevated in Tifp39(-/-) mice, suggesting intact hypothalamic function. We found using in situ hybridization that the genes encoding TIP39 and the PTH 2 receptor are expressed in a stage-specific manner within seminiferous tubules. Using immunohistochemistry and quantitative RT-PCR, TIP39 expression is greatest in mature testes, and appears most abundant in postmeiotic spermatids, but TIP39 protein and mRNA can be detected before any cells have completed meiosis. We used mice that express Cre recombinase under control of a spermatid-specific promoter to express selectively a cDNA encoding TIP39 in the testes of Tifp39(-/-) mice. Spermatid production and fertility were rescued, demonstrating that the defect in Tifp39(-/-) mice was due to the loss of TIP39. These results show that TIP39 is essential for germ cell development and suggest that it may act as an autocrine or paracrine agent within the gonads.

Tuberoinfundibular peptide of 39 residues in the embryonic and early postnatal rat brain

Tuberoinfundibular peptide of 39 residues (TIP39) was identified as the endogenous ligand of parathyroid hormone 2 receptor. We have recently demonstrated that TIP39 expression in adult rat brain is confined to the subparafascicular area of the thalamus with a few cells extending laterally into the posterior intralaminar thalamic nucleus (PIL), and the medial paralemniscal nucleus (MPL) in the lateral pontomesencephalic tegmentum. During postnatal development, TIP39 expression increases until postnatal day 33 (PND-33), then decreases, and almost completely disappears by PND-125. Here, we report the expression of TIP39 during early brain development. TIP39-immunoreactive (TIP39-ir) neurons in the subparafascicular area first appeared at PND-1. In contrast, TIP39-ir neurons were detectable in the MPL at embryonic day 14.5 (ED-14.5), and the intensity of their labeling increased thereafter. We also identified TIP39-ir neurons between ED-16.5 and PND-5 in two additional brain areas, the PIL and the amygdalo-hippocampal transitional zone (AHi). We confirmed the specificity of TIP39 immunolabeling by demonstrating TIP39 mRNA using in situ hybridization histochemistry. In the PIL, TIP39 neurons are located medial to the CGRP group as demonstrated by double immunolabeling. All TIP39-ir neurons in the AHi and most TIP39-ir neurons in the PIL disappear during early postnatal development. The adult pattern of TIP39-ir fibers emerge during postnatal development. However, fibers emanating from PIL can be followed in the supraoptic decussations towards the hypothalamus at ED-18.5. These TIP39-ir fibers disappear by PND-1. The complex pattern of TIP39 expression during early brain development suggests the involvement of TIP39 in transient functions during ontogeny.

Distribution of tuberoinfundibular peptide of 39 residues and its receptor, parathyroid hormone 2 receptor, in the mouse brain

Tuberoinfundibular peptide of 39 residues (TIP39) was identified as a potent parathyroid hormone 2 receptor (PTH2R) agonist. Existing anatomical data also support the suggestion that TIP39 is the PTH2R's endogenous ligand, but a comprehensive comparison of TIP39 and PTH2R distributions has not been performed. In the present study, we compared the distributions of TIP39 and PTH2R on adjacent mouse brain sections. In addition, we determined the locations of PTH2R-expressing cell bodies by in situ hybridization histochemistry and by labeling beta-galactosidase driven by the PTH2R promoter in knockin mice. An excellent correlation was found between the distributions of TIP39-containing fibers and PTH2R-containing cell bodies and fibers throughout the brain. TIP39 and the PTH2R are abundant in medial prefrontal, insular, and ectorhinal cortices, the lateral septal nucleus, the bed nucleus of the stria terminalis, the fundus striati, the amygdala, the ventral subiculum, the hypothalamus, midline and intralaminar thalamic nuclei, the medial geniculate body, the periaqueductal gray, the ventral tegmental area, the superior and inferior colliculi, the parabrachial nuclei, the locus coeruleus, subcoeruleus and periolivary areas, and the nucleus of the solitary tract. Furthermore, even the subregional distribution of TIP39- and PTH2R-immunoreactive fibers in these regions showed remarkable similarities, providing anatomical evidence that TIP39 may act on the PTH2R. Based on these observations and on previous pharmacological data, we propose that TIP39 is an endogenous ligand of the PTH2R and that they form a neuromodulator system, which is optimally positioned to regulate limbic, endocrine, and auditory brain functions. Published 2007 Wiley-Liss, Inc.

Development of a rat parathyroid hormone 2 receptor antagonist

The parathyroid hormone 2 (PTH2) receptor is a Family B G-protein coupled receptor most highly expressed within the brain. Current evidence suggests that tuberoinfundibular peptide of 39 residues (TIP39) is the PTH2 receptor's endogenous ligand. To facilitate investigation of the physiological function of the PTH2 receptor/TIP39 system, we have developed a novel PTH2 receptor antagonist, by changing several residues within the amino terminal domain of TIP39. Histidine(4), tyrosine(5), tryptophan(6), histidine(7)-TIP39 binds the PTH2 receptor with high affinity, has over 30-fold selectivity for the rat PTH2 receptor over the rat PTH1 receptor and displays no detectable agonist activity. This ligand should be useful for in vivo investigation of PTH2 receptor function.

Postnatal development and gender-dependent expression of TIP39 in the rat brain

Tuberoinfundibular peptide of 39 residues (TIP39) is a selective agonist of the parathyroid hormone 2 (PTH2) receptor. The topographical distributions of TIP39 and the PTH2 receptor in the brain, described for young male rats, suggested that TIP39 has limbic and endocrine functions. In the present study, we investigated the expression of TIP39 and the PTH2 receptor in male and female rat brain during postnatal development by means of in situ hybridization histochemistry, quantitative RT-PCR, and immunocytochemistry. TIP39's distribution and expression levels are similar in young female and male brains. TIP39 mRNA levels peak at postnatal day 14 and subsequently decline both in the subparafascicular area and in the medial paralemniscal nucleus, the two major sites where TIP39 is synthesized. A greater developmental decrease in TIP39 expression in males leads to greater levels in older females than older males. The decrease is partially reversed by prepubertal but not postpubertal gonadectomy. TIP39 peptide levels in cell bodies change in parallel with mRNA levels, whereas TIP39 appears and disappears somewhat later in nerve fibers. In addition, TIP39 peptide levels are also sexually dimorphic in older rats. In contrast, PTH2 receptor expression in the brain does not decrease during puberty and is not sexually dimorphic even in old animals. The appearance of TIP39 during early, and decline during late, postnatal development together with the gender-dependent levels in mature animals suggests that TIP39 may play a role in sexual maturation or gender-specific functions.

Afferent connections of the subparafascicular area in rat

The subparafascicular nucleus and the subparafascicular area are the major sites of synthesis of the recently discovered neuropeptide, tuberoinfundibular peptide of 39 residues (TIP39). Better knowledge of the neuronal inputs to the subparafascicular area and nucleus will facilitate investigation of the functions of TIP39. Thus, we have injected the retrograde tracer cholera toxin B subunit into the rostral, middle, and caudal parts of the rat subparafascicular nucleus. We report that the afferent projections to the subparafascicular nucleus and area include the medial prefrontal, insular, and ectorhinal cortex, the subiculum, the lateral septum, the anterior amygdaloid area, the medial amygdaloid nucleus, the caudal paralaminar area of the thalamus, the lateral preoptic area, the anterior, ventromedial, and posterior hypothalamic nuclei, the dorsal premamillary nucleus, the zona incerta and Forel's fields, the periaqueductal gray, the deep layers of the superior colliculus, cortical layers of the inferior colliculus, the cuneiform nucleus, the medial paralemniscal nucleus, and the parabrachial nuclei. Most of these regions project to all parts of the subparafascicular nucleus. However, the magnocellular subparafascicular neurons, which occupy the middle part of the subparafascicular nucleus, may not receive projections from the medial prefrontal and insular cortex, the medial amygdaloid nucleus, the lateral preoptic area, and the parabrachial nuclei. In addition, double labeling of cholera toxin B subunit and TIP39 revealed a remarkable similarity between input regions of the subparafascicular area and the brain TIP39 system. Neurons within regions that contain TIP39 cell bodies as well as regions that contain TIP39 fibers project to the subparafascicular area. Overall, the afferent connections of the subparafascicular nucleus and area suggest its involvement in central reproductive, visceral, nociceptive, and auditory regulation.

Class II G protein-coupled receptors and their ligands in neuronal function and protection

G protein-coupled receptors (GPCRs) play pivotal roles in regulating the function and plasticity of neuronal circuits in the nervous system. Among the myriad of GPCRs expressed in neural cells, class II GPCRs which couples predominantly to the Gs-adenylate cyclase-cAMP signaling pathway, have recently received considerable attention for their involvement in regulating neuronal survival. Neuropeptides that activate class II GPCRs include secretin, glucagon-like peptides (GLP-1 and GLP-2), growth hormone-releasing hormone (GHRH), pituitary adenylate cyclase activating peptide (PACAP), corticotropin-releasing hormone (CRH), vasoactive intestinal peptide (VIP), parathyroid hormone (PTH), and calcitonin-related peptides. Studies of patients and animal and cell culture models, have revealed possible roles for class II GPCRs signaling in the pathogenesis of several prominent neurodegenerative conditions including stroke, Alzheimer's, Parkinson's, and Huntington's diseases. Many of the peptides that activate class II GPCRs promote neuron survival by increasing the resistance of the cells to oxidative, metabolic, and excitotoxic injury. A better understanding of the cellular and molecular mechanisms by which class II GPCRs signaling modulates neuronal survival and plasticity will likely lead to novel therapeutic interventions for neurodegenerative disorders.

Parathyroid hormone and parathyroid hormone-related peptide, and their receptors

Parathyroid hormone (PTH) has a central role in the regulation of serum calcium and phosphate, while parathyroid hormone-related peptide (PTHrP) has important developmental roles. Both peptides signal through the same receptor, the PTH/PTHrP receptor (a class B G-protein-coupled receptor). The different biological effects of these ligands result from their modes of regulation and secretion, endocrine vs. paracrine/autocrine. The importance of PTH and PTHrP is evident by the variety of clinical syndromes caused by deficiency or excess production of either peptide, and the demonstration that intermittent injection of PTH increases bone mass, and thus provides a means to treat osteoporosis. This, in turn, has triggered increased interest in understanding the mechanisms of PTH/PTHrP receptor action and the search for smaller peptide or non-peptide agonists that have efficacy at this receptor when administered non-parenterally.