Neurons containing tuberoinfundibular peptide of 39 residues project to limbic, endocrine, auditory and spinal areas in rat

The nuclei of the lateral lemniscus: unexpected players in the descending auditory pathway

Introduction

In the mammalian auditory pathway, the nuclei of the lateral lemniscus (NLL) are thought to be exclusively involved in the bottom-up transmission of auditory information. However, our repeated observation of numerous NLL neurons labeled after injection of retrograde tracers into the superior olivary complex (SOC) led us to systematically investigate with retrograde tracers the descending projections from the NLL to the SOC of the rat.

Methods

We performed large injections of FluoroGold into the SOC to determine NLL contributions to descending projections, and focal injections of biotinylated dextran amine (BDA) to pinpoint the specific nuclei of the SOC innervated by each NLL.

Results

The SOC is innervated by thousands of neurons distributed across four nuclei or regions associated with the lateral lemniscus: the ipsilateral ventral and intermediate nuclei of the lateral lemniscus (VNLL and INLL); the medial paralemniscal region (PL) of both sides; and the ipsilateral semilunar nucleus (SLN), a previously unrecognized nucleus that wraps around the INLL dorsally, medially, and caudally and consists of small, flat neurons. In some experiments, at least 30% of neurons in the VNLL and INLL were retrogradely labeled. All nuclei of the SOC, except the medial and lateral superior olives, are innervated by abundant lemniscal neurons, and each SOC nucleus receives a unique combination of lemniscal inputs. The primary target of the projections from the VNLL is the ventral nucleus of the trapezoid body (VNTB), followed by the superior paraolivary nucleus (SPON), and the medial nucleus of the trapezoid body (MNTB). The INLL selectively innervates the VNTB. The PL innervates dorsal periolivary regions bilaterally. The SLN preferentially innervates the MNTB and may provide the first identified non-calyceal excitatory input to MNTB neurons.

Discussion

Our novel findings have strong implications for understanding acoustic information processing in the initial stages of the auditory pathway. Based on the proportion of lemniscal neurons involved in all the projections described, the NLL should be considered major players in the descending auditory pathway.

Synaptoporin and parathyroid hormone 2 as markers of multimodal inputs to the auditory brainstem

The distribution of the synaptic vesicle protein synaptoporin was investigated by immunofluorescence in the central auditory system of the mouse brainstem. Synaptoporin immunostaining displayed region-specific differences. High and moderate accumulations of were seen in the superficial layer of the dorsal cochlear nucleus, dorsal and external regions of the inferior colliculus, the medial and dorsal divisions of the medial geniculate body and in periolivary regions of the superior olivary complex (SOC). Low or absent labeling was observed in the more central parts of these structures such as the principal nuclei of the SOC. It was conspicuous that dense synaptoporin immunoreactivity was detected predominantly in areas, which are known to be synaptic fields of multimodal, extra-auditory inputs. Target neurons of synaptoporin-positive synapses in the SOC were then identified by double-labelling immunofluorescence microscopy. We thereby detected synaptoporin puncta perisomatically at nitrergic, glutamatergic and serotonergic neurons but none next to neurons immunoreactive for choline-acetyltransferase and calcitonin-gene related peptide. These results leave open whether functionally distinct neuronal groups are accessed in the SOC by synaptoporin-containing neurons. The last part of our study sought to find out whether synaptoporin-positive neurons originate in the medial paralemniscal nucleus (MPL), which is characterized by expression of the peptide parathyroid hormone 2 (PTH2). Anterograde neuronal tracing upon injection into the MPL in combination with synaptoporin- and PTH2-immunodetection showed that (1) the MPL projects to the periolivary SOC using PTH2 as transmitter, (2) synaptoporin-positive neurons do not originate in the MPL, and (3) the close juxtaposition of synaptoporin-staining with either the anterograde tracer or PTH2 reflect concerted action of the different inputs to the SOC.

A thalamo-preoptic pathway promotes social grooming in rodents

Social touch is an essential component of communication. Little is known about the underlying pathways and mechanisms. Here, we discovered a novel neuronal pathway from the posterior intralaminar thalamic nucleus (PIL) to the medial preoptic area (MPOA) involved in the control of social grooming. We found that the neurons in the PIL and MPOA were naturally activated by physical contact between female rats and also by the chemogenetic stimulation of PIL neurons. The activity-dependent tagging of PIL neurons was performed in rats experiencing physical social contact. The chemogenetic activation of these neurons increased social grooming between familiar rats, as did the selective activation of the PIL-MPOA pathway. Neurons projecting from the PIL to the MPOA express the neuropeptide parathyroid hormone 2 (PTH2), and the central infusion of its receptor antagonist diminished social grooming. Finally, we showed a similarity in the anatomical organization of the PIL and the distribution of the PTH2 receptor in the MPOA between the rat and human brain. We propose that the discovered neuronal pathway facilitates physical contact with conspecifics.

Current Treatments of Post-traumatic Stress Disorder and Amygdala Ablation as a Potential Cutting-Edge Therapy in Its Refractory Cases

Post-traumatic stress disorder (PTSD)is a very common psychiatric disorder occurring in an individual of any age, gender, or race who underwent trauma, with women being twice more at risk than men. It is generally seen more in American Indians, United States Latinos, and African American ethnic groups. A patient is diagnosed with PTSD if the symptoms of intrusion, avoidance, changes in cognition and emotions, arousal, and mood reactivity changes persist for more than a month and cause the individual severe difficulty in their everyday cognitive and psychological functioning. The psychological treatment includes numerous therapies including trauma-focused therapies such as cognitive behavioral therapy, cognitive processing therapy, prolonged exposure therapy, eye movement desensitization and reprocessing, and non-trauma-focused therapies such as relaxation techniques, interpersonal therapy, and mindfulness. Various pharmacological measures have also been tried with mixed results such as selective serotonin reuptake inhibitors, benzodiazepines, adrenergic drugs, atypical antipsychotics, and mood stabilizers like lithium and valproate. As numerous studies have proven, PTSD is linked with right-side stimulation of the amygdala. The purpose of this article is to highlight the use of extremely selective laser ablation of the amygdala-hippocampal unit as a successful surgical intervention for medically unresponsive PTSD and as a revolutionary solution and prospective cutting-edge therapy in the near future.

Behavioural actions of tuberoinfundibular peptide 39 (parathyroid hormone 2)

Tuberoinfundibular peptide of 39 residues (TIP39) acts via its endogenous class B G-protein coupled receptorthe parathyroid hormone 2 receptor (PTH2R). Hence, it is also known as parathyroid hormone 2. The peptide is expressed in the brain by a small number of neurons with a highly restricted distribution, which in turn project to a large number of brain regions that contain PTH2R. This peptide neuromodulator system has been extensively investigated over the past 20 years including its behavioural actions, such as its role in the control of nociception, fear and fear incubation, anxiety and depression-like behaviours, and maternal and social behaviours. It also influences thermoregulation and potentially auditory responses. TIP39 probably exerts direct effect on the neuronal networks controlling these behaviours based on the localization of PTH2R and local TIP39 actions. In addition, TIP39 also affects the secretion of several hypothalamic hormones providing the basis for indirect behavioural actions. Recently developed experimental tools have stimulated further behavioural investigations, and novel results obtained are discussed in this review.

Secretion and Function of Pituitary Prolactin in Evolutionary Perspective

The hypothalamo-pituitary system developed in early vertebrates. Prolactin is an ancient vertebrate hormone released from the pituitary that exerts particularly diverse functions. The purpose of the review is to take a comparative approach in the description of prolactin, its secretion from pituitary lactotrophs, and hormonal functions. Since the reproductive and osmoregulatory roles of prolactin are best established in a variety of species, these functions are the primary subjects of discussion. Different types of prolactin and prolactin receptors developed during vertebrate evolution, which will be described in this review. The signal transduction of prolactin receptors is well conserved among vertebrates enabling us to describe the whole subphylum. Then, the review focuses on the regulation of prolactin release in mammals as we have the most knowledge on this class of vertebrates. Prolactin secretion in response to different reproductive stimuli, such as estrogen-induced release, mating, pregnancy and suckling is detailed. Reproduction in birds is different from that in mammals in several aspects. Prolactin is released during incubation in avian species whose regulation and functional significance are discussed. Little information is available on prolactin in reptiles and amphibians; therefore, they are mentioned only in specific cases to explain certain evolutionary aspects. In turn, the osmoregulatory function of prolactin is well established in fish. The different types of pituitary prolactin in fish play particularly important roles in the adaptation of eutherian species to fresh water environments. To achieve this function, prolactin is released from lactotrophs in hyposmolarity, as they are directly osmosensitive in fish. In turn, the released prolactin acts on branchial epithelia, especially ionocytes of the gill to retain salt and excrete water. This review will highlight the points where comparative data give new ideas or suggest new approaches for investigation in other taxa.

Amylin and Leptin interaction: Role During Pregnancy, Lactation and Neonatal Development

Amylin is co-secreted with insulin by pancreatic β-cells in response to a meal and produced by neurons in discrete hypothalamic brain areas. Leptin is proportionally secreted by the adipose tissue. Both hormones control food intake and energy homeostasis post-weaning in rodents. While amylin's main site of action is located in the area postrema (AP) and leptin's is located in the mediobasal hypothalamus, both hormones can also influence the other's signaling pathway; amylin has been shown enhance hypothalamic leptin signaling, and amylin signaling in the AP may rely on functional leptin receptors to modulate its effects. These two hormones also play major roles during other life periods. During pregnancy, leptin levels rise as a result of an increase in fat depot resulting in gestational leptin-resistance to prepare the maternal body for the metabolic needs during fetal development. The role of amylin is far less studied during pregnancy and lactation, though amylin levels seem to be elevated during pregnancy relative to insulin. Whether amylin and leptin interact during pregnancy and lactation remains to be assessed. Lastly, during brain development, amylin and leptin are major regulators of cell birth during embryogenesis and act as neurotrophic factors in the neonatal period. This review will highlight the role of amylin and leptin, and their possible interaction, during these dynamic time periods of pregnancy, lactation, and early development.

Thalamic integration of social stimuli regulating parental behavior and the oxytocin system

Critically important components of the maternal neural circuit in the preoptic area robustly activated by suckling were recently identified. In turn, suckling also contributes to hormonal adaptations to motherhood, which includes oxytocin release and consequent milk ejection. Other reproductive or social stimuli can also trigger the release of oxytocin centrally, influencing parental or social behaviors. However, the neuronal pathways that transfer suckling and other somatosensory stimuli to the preoptic area and oxytocin neurons have been poorly characterized. Recently, a relay center of suckling was determined and characterized in the posterior intralaminar complex of the thalamus (PIL). Its neurons containing tuberoinfundibular peptide 39 project to both the preoptic area and oxytocin neurons in the hypothalamus. The present review argues that the PIL is a major relay nucleus conveying somatosensory information supporting maternal behavior and oxytocin release in mothers, and may be involved more generally in social cue evoked oxytocin release, too.

A Thalamo-Hypothalamic Pathway That Activates Oxytocin Neurons in Social Contexts in Female Rats

Oxytocin is released from neurons in the paraventricular hypothalamic nucleus (PVN) in mothers upon suckling and during adult social interactions. However, neuronal pathways that activate oxytocin neurons in social contexts are not yet established. Neurons in the posterior intralaminar complex of the thalamus (PIL), which contain tuberoinfundibular peptide 39 (TIP39) and are activated by pup exposure in lactating mothers, provide a candidate projection. Innervation of oxytocin neurons by TIP39 neurons was examined by double labeling in combination with electron microscopy and retrograde tract-tracing. Potential classic neurotransmitters in TIP39 neurons were investigated by in situ hybridization histochemistry. Neurons activated after encounter with a familiar conspecific female in a familiar environment were mapped with the c-Fos technique. PVN and the supraoptic nucleus oxytocin neurons were closely apposed by an average of 2.0 and 0.4 TIP39 terminals, respectively. Asymmetric (presumed excitatory) synapses were found between TIP39 terminals and cell bodies of oxytocin neurons. In lactating rats, PIL TIP39 neurons were retrogradely labeled from the PVN. TIP39 neurons expressed vesicular glutamate transporter 2 but not glutamic acid decarboxylase 67. PIL contained a markedly increased number of c-Fos-positive neurons in response to social encounter with a familiar conspecific female. Furthermore, the PIL received ascending input from the spinal cord and the inferior colliculus. Thus, TIP39 neurons in the PIL may receive sensory input in response to social interactions and project to the PVN to innervate and excite oxytocin neurons, suggesting that the PIL-PVN projection contributes to the activation of oxytocin neurons in social contexts.

All the way from the cortex: a review of auditory corticosubcollicular pathways

Enrico Mugnaini has devoted part of his long and fruitful neuroscientific career to investigating the structural similarities between the cerebellar cortex and one of the first relay stations of the mammalian auditory pathway: the dorsal cochlear nucleus. The hypothesis of the cerebellar-like nature of the superficial layers of the dorsal cochlear nucleus received definitive support with the discovery and extensive characterization in his laboratory of unipolar brush cells, a neuron type unique to certain regions of the cerebellar cortex and to the granule cell domains of the cochlear nuclei. Paradoxically, a different line of research carried out in his laboratory revealed that, unlike the mammalian cerebellar cortex, the dorsal cochlear nucleus receives direct projections from the cerebral cortex, a fact that constitutes one of the main differences between the cerebellum and the dorsal cochlear nucleus. In an article published in 1995, Mugnaini's group described in detail the novel direct projections from the rat auditory neocortex to various subcollicular auditory centers, including the nucleus sagulum, the paralemniscal regions, the superior olivary complex, and the cochlear nuclei (Feliciano et al., Auditory Neuroscience 1995; 1:287-308). This review gives Enrico Mugnaini credit for his seminal contribution to the knowledge of auditory corticosubcollicular projections and summarizes how this growing field has evolved in the last 20 years.

Incubation of Fear Is Regulated by TIP39 Peptide Signaling in the Medial Nucleus of the Amygdala

Fear-related psychopathologies such as post-traumatic stress disorder are characterized by impaired extinction of fearful memories. Recent behavioral evidence suggests that the neuropeptide tuberoinfundibular peptide of 39 residues (TIP39), via its receptor, the parathyroid hormone 2 receptor (PTH2R), modulates fear memory. Here we examined the anatomical and cellular localization of TIP39 signaling that contributes to the increase in fear memory over time following a traumatic event, called fear memory incubation. Contextual freezing, a behavioral sign of fear memory, was significantly greater in PTH2R knock-out than wild-type male mice 2 and 4 weeks after a 2 s 1.5 mA footshock. PTH2R knock-out mice had significantly reduced c-Fos activation in the medial amygdala (MeA) following both footshock and fear recall, but had normal activation in the hypothalamic paraventricular nucleus and the amygdalar central nucleus compared with wild-type. We therefore investigated the contribution of MeA TIP39 signaling to fear incubation. Similar to the effect of global TIP39 signaling loss, blockade of TIP39 signaling in the MeA by lentivirus-mediated expression of a secreted PTH2R antagonist augmented fear incubation. Ablation of MeA PTH2R-expressing neurons also strengthened the fear incubation effect. Using the designer receptor exclusively activated by designer drug pharmacogenetic approach, transient inhibition of MeA PTH2R-expressing neurons before or immediately after the footshock, but not at the time of fear recall, enhanced fear incubation. Collectively, the findings demonstrate that TIP39 signaling within the MeA at the time of an aversive event regulates the increase over time in fear associated with the event context.

SIGNIFICANCE STATEMENT

Fear-related psychopathologies such as post-traumatic stress disorder (PTSD) are characterized by excessive responses to trauma-associated cues. Fear responses can increase over time without additional cue exposure or stress. This work shows that modulatory processes within the medial nucleus of the amygdala near the time of a traumatic event influence the strength of fear responses that occur much later. The modulatory processes include signaling by the neuropeptide TIP39 and neurons that express its receptor. These findings will help in the understanding of why traumatic events sometimes have severe psychological consequences. One implication is that targeting neuromodulation in the medial amygdala could potentially help prevent development of PTSD.

Subcollicular projections to the auditory thalamus and collateral projections to the inferior colliculus

Experiments in several species have identified direct projections to the medial geniculate nucleus (MG) from cells in subcollicular auditory nuclei. Moreover, many cochlear nucleus cells that project to the MG send collateral projections to the inferior colliculus (IC) (Schofield et al., 2014). We conducted three experiments to characterize projections to the MG from the superior olivary and the lateral lemniscal regions in guinea pigs. For experiment 1, we made large injections of retrograde tracer into the MG. Labeled cells were most numerous in the superior paraolivary nucleus, ventral nucleus of the trapezoid body, lateral superior olivary nucleus, ventral nucleus of the lateral lemniscus, ventrolateral tegmental nucleus, paralemniscal region and sagulum. Additional sources include other periolivary nuclei and the medial superior olivary nucleus. The projections are bilateral with an ipsilateral dominance (66%). For experiment 2, we injected tracer into individual MG subdivisions. The results show that the subcollicular projections terminate primarily in the medial MG, with the dorsal MG a secondary target. The variety of projecting nuclei suggest a range of functions, including monaural and binaural aspects of hearing. These direct projections could provide the thalamus with some of the earliest (i.e., fastest) information regarding acoustic stimuli. For experiment 3, we made large injections of different retrograde tracers into one MG and the homolateral IC to identify cells that project to both targets. Such cells were numerous and distributed across many of the nuclei listed above, mostly ipsilateral to the injections. The prominence of the collateral projections suggests that the same information is delivered to both the IC and the MG, or perhaps that a common signal is being delivered as a preparatory indicator or temporal reference point. The results are discussed from functional and evolutionary perspectives.

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.

Regulation of hypothalamic signaling by tuberoinfundibular peptide of 39 residues is critical for the response to cold: a novel peptidergic mechanism of thermoregulation

Euthermia is critical for mammalian homeostasis. Circuits within the preoptic hypothalamus regulate temperature, with fine control exerted via descending GABAergic inhibition of presympathetic motor neurons that control brown adipose tissue (BAT) thermogenesis and cutaneous vascular tone. The thermoregulatory role of hypothalamic excitatory neurons is less clear. Here we report peptidergic regulation of preoptic glutamatergic neurons that contributes to temperature regulation. Tuberoinfundibular peptide of 39 residues (TIP39) is a ligand for the parathyroid hormone 2 receptor (PTH2R). Both peptide and receptor are abundant in the preoptic hypothalamus. Based on PTH2R and vesicular glutamate transporter 2 (VGlut2) immunolabeling in animals with retrograde tracer injection, PTH2R-containing glutamatergic fibers are presynaptic to neurons projecting from the median preoptic nucleus (MnPO) to the dorsomedial hypothalamus. Transneuronal retrograde pathway tracing with pseudorabies virus revealed connectivity between MnPO VGlut2 and PTH2R neurons and BAT. MnPO injection of TIP39 increased body temperature by 2°C for several hours. Mice lacking TIP39 signaling, either because of PTH2R-null mutation or brain delivery of a PTH2R antagonist had impaired heat production upon cold exposure, but no change in basal temperature and no impairment in response to a hot environment. Thus, TIP39 appears to act on PTH2Rs present on MnPO glutamatergic terminals to regulate their activation of projection neurons and subsequent sympathetic BAT activation. This excitatory mechanism of heat production appears to be activated on demand, during cold exposure, and parallels the tonic inhibitory GABAergic control of body temperature.

The neuroendocrine functions of the parathyroid hormone 2 receptor

The G-protein coupled parathyroid hormone 2 receptor (PTH2R) is concentrated in endocrine and limbic regions in the forebrain. Its endogenous ligand, tuberoinfundibular peptide of 39 residues (TIP39), is synthesized in only two brain regions, within the posterior thalamus and the lateral pons. TIP39-expressing neurons have a widespread projection pattern, which matches the PTH2R distribution in the brain. Neuroendocrine centers including the preoptic area, the periventricular, paraventricular, and arcuate nuclei contain the highest density of PTH2R-positive networks. The administration of TIP39 and an antagonist of the PTH2R as well as the investigation of mice that lack functional TIP39 and PTH2R revealed the involvement of the PTH2R in a variety of neural and neuroendocrine functions. TIP39 acting via the PTH2R modulates several aspects of the stress response. It evokes corticosterone release by activating corticotropin-releasing hormone-containing neurons in the hypothalamic paraventricular nucleus. Block of TIP39 signaling elevates the anxiety state of animals and their fear response, and increases stress-induced analgesia. TIP39 has also been suggested to affect the release of additional pituitary hormones including arginine-vasopressin and growth hormone. A role of the TIP39-PTH2R system in thermoregulation was also identified. TIP39 may play a role in maintaining body temperature in a cold environment via descending excitatory pathways from the preoptic area. Anatomical and functional studies also implicated the TIP39-PTH2R system in nociceptive information processing. Finally, TIP39 induced in postpartum dams may play a role in the release of prolactin during lactation. Potential mechanisms leading to the activation of TIP39 neurons and how they influence the neuroendocrine system are also described. The unique TIP39-PTH2R neuromodulator system provides the possibility for developing drugs with a novel mechanism of action to control neuroendocrine disorders.

Evolution of the vertebrate pth2 (tip39) gene family and the regulation of PTH type 2 receptor (pth2r) and its endogenous ligand pth2 by hedgehog signaling in zebrafish development

In mammals, parathyroid hormone (PTH), secreted by parathyroid glands, increases calcium levels in the blood from reservoirs in bone. While mammals have two PTH receptor genes, PTH1R and PTH2R, zebrafish has three receptors, pth1r, pth2r, and pth3r. PTH can activate all three zebrafish Pthrs while PTH2 (alias tuberoinfundibular peptide 39, TIP39) preferentially activates zebrafish and mammalian PTH2Rs. We know little about the roles of the PTH2/PTH2R system in the development of any animal. To determine the roles of PTH2 and PTH2R during vertebrate development, we evaluated their expression patterns in developing zebrafish, observed their phylogenetic and conserved synteny relationships with humans, and described the genomic organization of pth2, pth2r, and pth2r splice variants. Expression studies showed that pth2 is expressed in cells adjacent to the ventral part of the posterior tuberculum in the diencephalon, whereas pth2r is robustly expressed throughout the central nervous system. Otic vesicles express both pth2 and pth2r, but heart expresses only pth2. Analysis of mutants showed that hedgehog (Hh) signaling regulates the expression of pth2 transcripts more than that of nearby gnrh2-expressing cells. Genomic analysis showed that a lizard, chicken, and zebra finch lack a PTH2 gene, which is associated with an inversion breakpoint. Likewise, chickens lack PTH2R, while humans lack PTH3R, a case of reciprocally missing ohnologs (paralogs derived from a genome duplication). The considerable evolutionary conservation in genomic structure, synteny relationships, and expression of zebrafish pth2 and pth2r provides a foundation for exploring the endocrine roles of this system in developing vertebrate embryos.

Novel potential regulators of maternal adaptations during lactation: tuberoinfundibular peptide 39 and amylin

Maternal adaptations during lactation include milk synthesis and ejection, the appearance of maternal behaviours, reduced stress response, suppression of the ovarian cycle, and increased food and fluid intake. Several recently identified neuropeptides may participate in these adaptations, and we focus on two of them in the present study: tuberoinfundibular peptide of 39 residues (TIP39) and amylin. TIP39 is the ligand of the parathyroid hormone 2 receptor (PTH2 receptor) is induced in the posterior intralaminar complex of the thalamus (PIL) during lactation. TIP39 neurones in the PIL are activated in mother rats in response to pup exposure and project to preoptic, periventricular, paraventricular, arcuate and dorsomedial regions of the hypothalamus. Furthermore, an antagonist of the PTH2 receptor reduced suckling induced prolactin release. On the basis of their projections, TIP39 neurones might interact with additional neurones involved in maternal adaptations, including kisspeptin neurones participating in the control of gonadotrophin-releasing hormone function. TIP39 fibres might also interact with amylin, a peptide that we recently identified to appear in the preoptic area of rat dams. On the basis of its distribution, preoptic amylin could play a role in the control of maternal behaviours. We hypothesise that TIP39 neurones mediate the effects of suckling on different hypothalamic systems to affect maternal adaptations.

Maternal absence of the parathyroid hormone 2 receptor affects postnatal pup development

During the lactation period, mothers have a variety of adaptive changes in brain physiology and behaviour that allow them to properly raise their pups. The exact circuitries and mechanisms responsible for these changes are not fully understood. Recent evidence suggests that the neuropeptide tuberoinfundibular peptide of 39 residues (TIP39) and its receptor, the parathyroid hormone 2 receptor (PTH2-R), contribute to these mechanisms. To further investigate this idea, we evaluated the growth rate of pups from dams with a genetically inactivated PTH2-R (PTH2-R-KO), as well as maternal behavioural and neuroendocrine parameters. We observed that PTH2-R-KO-reared pups had a slowed growth rate. This was associated with a reduced volume of milk yielded by PTH2-R-KO dams after 30-min suckling compared to wild-type (WT) dams when pups were returned after 5 h of separation. Our data suggest a reduced sensitivity of PTH2-R-KO dams to pup stimulation. We also observed a significant reduction in suckling-induced c-Fos expression in the paraventricular hypothalamic nucleus and signs of lower prolactin levels in the PTH2-R-KO dams. Our data suggest that the reduced growth rate of PTH2-R-KO-reared pups was likely the result of alterations in the milk-production pathway rather than modifications in behaviour. Although PTH2-R-KO dams showed increased anxiety in the elevated zero-maze test, no differences from WT dams in maternal behaviour were observed. Taken together, our findings suggest the involvement of the TIP39/PTH2-R system in the pathways involved in the successful development of the pups.

Enhanced long-term fear memory and increased anxiety and depression-like behavior after exposure to an aversive event in mice lacking TIP39 signaling

Exaggerated recall for fear-provoking events leads to abnormal behaviors. We hypothesized that tuberoinfundibular-peptide-of-39-residues (TIP39) modulates fear memory by limiting long-term consequences of aversive experiences. We now show that mice lacking TIP39 signaling display enhanced fear-recall, anxiety and depression-like behavior 2 weeks after a traumatic event. We suggest that TIP39 modulates long-term fear recall and that mice lacking TIP39 or its receptor are tools for investigating fear-related psychopathologies.

Tuberoinfundibular peptide of 39 residues is activated during lactation and participates in the suckling-induced prolactin release in rat

Tuberoinfundibular peptide of 39 residues (TIP39) and the PTH-2 receptor (PTH2R) constitute a peptide-receptor neuromodulator system. Based on the abundance of TIP39 fibers and axonal terminals as well as PTH2R-containing neurons and their processes in the hypothalamic para- and periventricular and arcuate nuclei TIP39 has been suggested to play a role in neuroendocrine regulation. We showed previously that TIP39 expression decreased dramatically by adulthood. In the present study, using in situ hybridization histochemistry, real-time RT-PCR, and immunohistochemistry, we found that TIP39 mRNA and peptide expression levels are markedly elevated in the posterior intralaminar complex of the thalamus (PIL) of lactating dams, one of the three locations of TIP39-containing cell bodies in the brain. In addition, in mother rats, these TIP39 neurons showed Fos expression in response to pup exposure. Transection of TIP39 fibers originating in the PIL resulted in an ipsilateral disappearance of TIP39 immunoreactivity throughout the mediobasal hypothalamus of mother rats, suggesting that TIP39 fibers there arise from the PIL. To elucidate the function of TIP39 activation in dams, mothers separated from their pups for 4 h on postpartum d 9 received injection of a PTH2R antagonist into the lateral ventricle 5 min before returning the pups. Blood samples were taken seven times during the experimental period through jugular cannulae. The PTH2R antagonist administered in two different concentrations markedly inhibited suckling-induced elevation of plasma prolactin levels in a dose-dependent manner. These results suggest that TIP39 neurons in the PIL may regulate suckling-induced prolactin release in rat dams.

Tuberoinfundibular peptide of 39 residues modulates the mouse hypothalamic-pituitary-adrenal axis via paraventricular glutamatergic neurons

Neurons in the subparafascicular area at the caudal border of the thalamus that contain the neuropeptide tuberoinfundibular peptide of 39 residues (TIP39) densely innervate several hypothalamic areas, including the paraventricular nucleus (PVN). These areas contain a matching distribution of TIP39's receptor, the parathyroid hormone receptor 2 (PTH2R). Frequent PTH2R coexpression with a vesicular glutamate transporter (VGlut2) suggests that TIP39 could presynaptically regulate glutamate release. By using immunohistochemistry we found CRH-ir neurons surrounded by PTH2R-ir fibers and TIP39-ir axonal projections in the PVN area of the mouse brain. Labeling hypothalamic neuroendocrine neurons by peripheral injection of fluorogold in PTH2R-lacZ knock-in mice showed that most PTH2Rs are on PVN and peri-PVN interneurons and not on neuroendocrine cells. Double fluorescent in situ hybridization revealed a high level of coexpression between PTH2R and VGlut2 mRNA by cells located in the PVN and nearby brain areas. Local TIP39 infusion (100 pmol) robustly increased pCREB-ir in the PVN and adjacent perinuclear zone. It also increased plasma corticosterone and decreased plasma prolactin. These effects of TIP39 on pCREB-ir, corticosterone, and prolactin were abolished by coinfusion of the ionotropic glutamate receptor antagonists 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) and DL-2-amino-5-phosphonopentanoic acid (AP-5; 30 pmol each) and were absent in PTH2R knockout mice. Basal plasma corticosterone was slightly decreased in TIP39 knockout mice just before onset of their active phase. The present data indicate that the TIP39 ligand/PTH2 receptor system provides facilitatory regulation of the hypothalamic-pituitary-adrenal axis via hypothalamic glutamatergic neurons and that it may regulate other neuroendocrine systems by a similar mechanism.

Tuberoinfundibular peptide of 39 residues- immunoreactive fibers in the zona incerta and the supraoptic decussations terminate in the neuroendocrine hypothalamus

Tuberoinfundibular peptide of 39 residues (TIP39) is expressed by neurons in the subparafascicular area, the posterior intralaminar complex of the thalamus and the pontine medial paralemniscal nucleus. TIP39-positive fibers from these areas do not form individual bundles or fascicles, they join other pathways to reach their innervated brain areas. Fibers arise from TIP39 perikarya located in the subparafascicular area and the posterior intralaminar complex of the thalamus could be followed to the hypothalamus. After uni- and bilateral posterolateral surgical deafferentations of the hypothalamus, accumulation of TIP39 immunoreactivity was observed in the fibers caudal to the knife cut, while it disappeared completely rostral to the transection. In serial sections of the forebrain, we could follow TIP39-ir fibers coursing within the zona incerta and the supraoptic decussations. TIP39-positive fibers that join the incerto-hypothalamic pathway reach the medio-dorsal part of the hypothalamus and form moderate to high density networks in the dorsomedial and paraventricular nuclei. The other set of TIP39-positive axons from the subthalamic area join the fibers of the supraoptic decussations and run in an antero-medial direction through the most ventral portion of the hypothalamus up to the retrochiasmatic area, where they crossover. A certain portion of these TIP39-positive fibers terminates in the territories of the arcuate and the medial preoptic nuclei, as well as in the retrochiasmatic area.

TIP39 modulates effects of novelty-induced arousal on memory

Tuberoinfundibular peptide of 39 residues (TIP39) is a neuropeptide localized to neural circuits subserving emotional processing. Recent work showed that mice with null mutation for the gene coding TIP39 (TIP39-KO mice) display increased susceptibility to environmental provocation. Based on this stressor-dependent phenotype, the neuroanatomical distribution of TIP39, and knowledge that novelty-induced arousal modulates memory functions via noradrenergic activation, we hypothesized that exposure to a novel environment differently affects memory performance of mice with or without TIP39 signaling, potentially by differences in sensitivity of the noradrenergic system. We tested TIP39-KO mice and mice with null mutation of its receptor, the parathyroid hormone 2 receptor (PTH2-R), in tasks of short-term declarative and social memory (object recognition and social recognition tests, respectively), and of working memory (Y-maze test) under conditions of novelty-induced arousal or acclimation to the test conditions. Mice lacking TIP39 signaling showed memory impairment selectively under conditions of novelty-induced arousal. Acute administration of a PTH2-R antagonist in wild-type mice had a similar effect. The restoration of memory functions in TIP39-KO mice after injection of a β-adrenoreceptor-blocker, propranolol, suggested involvement of the noradrenergic system. Collectively, these results suggest that the TIP39/PTH2-R system modulates the effects of novelty exposure on memory performance, potentially by acting on noradrenergic signaling.

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.

Acoustic stress activates tuberoinfundibular peptide of 39 residues neurons in the rat brain

Strong acoustic stimulation (105 dB SPL white noise) elicited c-fos expression in neurons in several acoustic system nuclei and in stress-sensitive hypothalamic nuclei and limbic areas in rats. In the present study, using this type of loud noise for 30 min, Fos-like immunoreactivity (Fos-ir) was investigated in neurons that synthesize tuberoinfundibular peptide of 39 residues (TIP39) in the rat brain: in the subparafascicular area of the thalamus, the posterior intralaminar complex of the thalamus and the medial paralemniscal nucleus in the lateral part of the pons. By double labeling, Fos-ir was shown in nearly 80% of TIP39-positive cells in the medial paralemniscal nucleus, 43% in the posterior intralaminar complex and 18.5% in the subparafascicular area 30 min after the end of a 30-min loud noise period. In control rats, only few neurons, including 0-4% of TIP39-positive neurons showed Fos-ir. While the majority of the Fos-ir neurons were TIP39-positive in the subparafascicular area and medial paralemniscal nucleus, a fairly high number of TIP39-immunonegative, chemically uncharacterized neurons expressed c-fos in the subparafascicular area and the posterior intralaminar complex of the thalamus. These observations clearly show that some TIP39 neurons in the so-called "acoustic thalamus" and the majority of TIP39 neurons in the medial paralemniscal nucleus are sensitive to loud noise and they may participate in the central organization of responses to acoustic stress. Furthermore, the present data suggest that non-TIP39-expressing neurons may play a prevalent role in the activity of the "acoustic thalamus".

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.

Increased fear- and stress-related anxiety-like behavior in mice lacking tuberoinfundibular peptide of 39 residues

Tuberoinfundibular peptide of 39 residues (TIP39) is synthesized by two groups of neurons, one in the subparafascicular area at the caudal end of the thalamus and the other in the medial paralemniscal nucleus within the lateral brainstem. The subparafascicular TIP39 neurons project to a number of brain regions involved in emotional responses, and these regions contain a matching distribution of a receptor for TIP39, the parathyroid hormone 2 receptor (PTH2-R). We have now evaluated the involvement of TIP39 in anxiety-related behaviors using mice with targeted null mutation of the TIP39 gene (Tifp39). Tifp39(-/-) mice (TIP39-KO) did not significantly differ from wild-type (WT) littermates in the open field, light/dark exploration and elevated plus-maze assays under standard test conditions. However, the TIP39-KO engaged in more active defensive burying in the shock-probe test. In addition, when tested under high illumination or after restraint, TIP39-KO displayed significantly greater anxiety-like behavior in the elevated plus-maze than WT. In a Pavlovian fear-conditioning paradigm, TIP39-KO froze more than WT during training and during tone and context recall but showed normal fear extinction. Disruption of TIP39 projections to the medial prefrontal cortex, lateral septum, bed nucleus of the stria terminalis, hypothalamus and amygdala likely account for the fear- and anxiety-related phenotype of TIP39-KO. Current data support the hypothesis that TIP39 modulates anxiety-related behaviors following environmental provocation.

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.

Neurons containing tuberoinfundibular peptide of 39 residues are activated following male sexual behavior

Tuberoinfundibular peptide of 39 residues (TIP39)-immunoreactive (IR) neurons are present in the medial subdivision of the parvocellular subparafascicular thalamic nucleus (mSPFp) where ejaculation-specific Fos expression is localized. The mSPFp is reciprocally connected to the medial preoptic area (MPOA), bed nucleus of the stria terminalis (BNST) and the medial nucleus of the amygdala (Me), all of which are critical for the regulation of male sexual behavior. The mSPFp also receives galanin and enkephalin containing projections from a region in the lumbar spinal cord, thought to be a central ejaculation center. Therefore, we hypothesized that TIP39 neurons in the mSPFp may be part of the neuronal circuitry activated by male sexual behavior. To test this hypothesis, we examined induction of Fos in TIP39 containing neurons in the mSPFp following male sexual behavior. Mating-induced Fos expression was evaluated in sexually experienced male rats under four experimental conditions: animals that (1) remained in their home cage without any interaction with females, (2) interacted with stimulus females and displayed intromission without ejaculation, (3) displayed one ejaculation, or (4) displayed 2 ejaculations. We found that Fos was induced in TIP39-IR neurons in the mSPFp in male rats following ejaculation but much less so following intromission without ejaculation. This suggests that TIP39-IR neurons in the mSPFp are part of the afferent circuits that process genital-somatosensory information related to ejaculation, and which contribute to mating and mating-induced changes in reproductive behavior.

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.

The distribution and neurochemistry of the parathyroid hormone 2 receptor in the rat hypothalamus

This study reports the distribution of parathyroid hormone 2 receptor (PTH2R)-immunoreactive fibers in the hypothalamus using fluorescent amplification immunocytochemistry. The pattern of immunolabeling is strikingly similar to that of tuberoinfundibular peptide of 39 residues (TIP39), a peptide recently purified from bovine hypothalamus and proposed to be a ligand of the PTH2R based on pharmacological data. To investigate the anatomical basis of suggestions that TIP39 affects the secretion of several hypophysiotropic hormones we performed double-labeling studies and found that only somatostatin fibers contain PTH2R in the median eminence, which suggests that somatostatin release could be directly regulated via the PTH2R. However, several hypothalamic nuclei projecting to the median eminence contain a high density of both TIP39 and PTH2R fibers and terminals. We report here, that the PTH2R terminals also contain vesicular glutamate transporter-2, and suggest that TIP39 terminals are ideally positioned to modulate glutamatergic influences on hypophysiotropic neurons.

Forebrain projections of tuberoinfundibular peptide of 39 residues (TIP39)-containing subparafascicular neurons

Neurons containing tuberoinfundibular peptide of 39 residues (TIP39) constitute a rostro-caudally elongated group of cells in the posterior thalamus. These neurons are located in the rostral part of the subparafascicular nucleus and in the subparafascicular area, caudally. Projections of the caudally located TIP39 neurons have been previously identified by their disappearance following lesions. We have now mapped the projections of the rat rostral subparafascicular neurons using injections of the anterograde tracer biotinylated dextran amine and the retrograde tracer cholera toxin B subunit, and confirmed the projections from more caudal areas previously inferred from lesion studies. Neurons from both the rostral subparafascicular nucleus and the subparafascicular area project to the medial prefrontal, insular, ecto- and perirhinal cortex, nucleus of the diagonal band, septum, central and basomedial amygdaloid nuclei, fundus striati, basal forebrain, midline and intralaminar thalamic nuclei, hypothalamus, subthalamus and the periaqueductal gray. The subparafascicular area projects more densely to the amygdala and the hypothalamus. In contrast, only the rostral part of the subparafascicular nucleus projects significantly to the superficial layers of prefrontal, insular, ectorhinal and somatosensory cortical areas. Double labeling showed that anterogradely labeled fibers from the rostral part of the subparafascicular nucleus contain TIP39 in many forebrain areas, but do not in hypothalamic areas. Injections of the retrograde tracer cholera toxin B subunit into the lateral septum and the fundus striati confirmed that they were indeed target regions of both the rostral subparafascicular nucleus and the subparafascicular area. In contrast, TIP39 neurons did not project to the anterior hypothalamic nucleus. Our data provide an anatomical basis for the potential involvement of rostral subparafascicular neurons in limbic and autonomic regulation, with TIP39 cells being major subparafascicular output neurons projecting to forebrain regions.

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.

Calcitonin gene-related peptide-containing pathways in the rat forebrain

The present study focuses on the topographical distribution of calcitonin gene-related peptide (CGRP)-containing cell bodies and fibers and their connections and pathways in the rat forebrain. We confirm previously reported CGRP projections from the perifornical area of the hypothalamus to the lateral septum, from the posterior thalamus to the caudate putamen and cerebral cortex, and from the parabrachial nuclei to the central extended amygdala, lateral hypothalamus, and ventromedial thalamus. Despite previous descriptions of CGRP in the central nervous system, important neuroanatomical aspects of the forebrain CGRP system remained obscure, which we addressed by using brain lesion techniques combined with modern immunohistology. We first report CGRP terminal fields in the olfactory-anterior septal region and also CGRP projections from the parabrachial nuclei to the olfactory-anterior septal region, the medial prefrontal cortex, the interstitial nucleus of the anterior commissure, the nucleus of the lateral olfactory tract, the anterior amygdaloid area, the posterolateral cortical amygdaloid nucleus, and the dorsolateral part of the lateral amygdaloid nucleus. In addition, we identified a CGRP cell group in the premamillary nuclei and showed that it projects to the medial CGRP layer of the lateral septum. CGRP fibers usually join other pathways rather than forming bundles. They run along the fornix from the hypothalamus, along the supraoptic decussations or the inferior thalamic peduncle-stria terminalis pathway from the posterior thalamus, and along the superior cerebellar peduncle, thalamic fasciculus, and ansa peduncularis from the parabrachial nuclei. This description of the forebrain CGRP system will facilitate investigation of its role in higher brain functions.

Identification and characterization of the zebrafish and fugu genes encoding tuberoinfundibular peptide 39

Although the PTH type 2 receptor (PTH2R) has been isolated from mammals and zebrafish, only its mammalian agonist, tuberoinfundibular peptide 39 (TIP39), has been characterized thus far. To determine whether zebrafish TIP39 (zTIP39) functions similarly with the zebrafish PTHR (zPTH2R) and human PTH2Rs and to determine its tissue-specific expression, fugu (Takifugu rubripes) and zebrafish (Danio rerio) genomic databases were screened with human TIP39 (hTIP39) sequences. A single TIP39 gene was identified for each fish species, which showed significant homology to mammalian TIP39. Using standard molecular techniques, we isolated cDNA sequences encoding zTIP39. The fugu TIP39 precursor was encoded by a gene comprising at least three exons. It contained a hydrophobic signal sequence and a predicted prosequence with a dibasic cleavage site, similar to that found in mammalian TIP39 ligands. Phylogenetic analyses suggested that TIP39 forms the basal group from which PTH and PTHrP have been derived. Functionally, subtle differences in potency could be discerned between hTIP39 and zTIP39. The human PTH2R and zPTH2R were stimulated slightly better by both hTIP39 and zTIP39, whereas zTIP39 had a higher potency at a previously isolated zPTH2R splice variant. Whole-mount in situ hybridization of zebrafish revealed strong zTIP39 expression in the region of the hypothalamus and in the heart of 24- and 48-h-old embryos. Similarly, zPTH2R expression was highly expressed throughout the brain of 48- and 72-h-old embryos. Because the mammalian PTH2R was also most abundantly expressed in these tissues, the TIP39-PTH2R system may serve conserved physiological roles in mammals and fishes.

Tuberoinfundibular peptide of 39 residues decreases pain-related affective behavior

Tuberoinfundibular peptide of 39 residues (TIP39) is a recently identified parathyroid hormone 2 receptor ligand. Their CNS distributions suggest potential involvement in neuroendocrine, limbic and sensory processing functions. Herein we investigate the analgesic and antinociceptive actions of brain delivery of TIP39 in adult male rats. Intracerebroventricular (i.c.v.) TIP39 did not change hot-plate paw withdrawal latency or formalin test behavioral responses. TIP39 partially reversed tactile withdrawal hypersensitivity following carageenan administration. In the place/escape avoidance paradigm (PEAP), which evaluates affective components of responses to noxious stimuli by presenting a choice between a naturally preferred environment paired with stimulation of a carrageenan sensitized paw and a less preferred environment paired with stimulation of a less sensitive paw, TIP39 decreased the apparent aversiveness of sensitive paw stimulation. Because acute sensory thresholds were unaffected by TIP39, and the effects of i.c.v. TIP39 were opposite in direction from previously described effects of intrathecal TIP39, this suggests that TIP39 may modulate an affective component of nociception within the brain.

Localization and chemical characterization of the audiogenic stress pathway

Neuronal pathways involved in stress responses to extreme somatosensory stimuli were investigated by immunostaining, viral tract tracing, and experimental brain surgery in rats. Acute audiogenic stress, which elicits an immediate marked elevation in plasma ACTH and corticosterone concentrations, was used as a model. Loud noise (105 dB, 30 min) elicited c-fos activation within neurons in all of the components of the auditory system and stress-sensitive brain nuclei, including corticotropin-releasing hormone-synthesizing parvicellular neurons in the hypothalamic paraventricular nucleus (PVN). c-Fos activation was also seen in the medial paralemniscal nucleus in the pons (MPL) and in the subparafascicular nucleus (SPF) in the midbrain. After injection of neurotropic virus (pseudorabies, Bartha strain) into the PVN, neurons in the MPL and the parvicellular portion of the SPF were retrogradely infected. It has been shown by immunostaining that MPL and SPF neurons express a newly discovered neuropeptide, tuberoinfundibular peptide of 39 residues (TIP39). TIP39 is present in a fine neuronal network in the PVN. Audiogenic stress-elicited c-fos activation in TIP39-containing neurons of the MPL and SPF. TIP39 immunoreactivity disappeared from the PVN after transection of MPL and SPF projections to the nucleus. These observations suggest that TIP39-containing MPL and SPF neurons may participate in mediating audiogenic stress responses.