Neurogenesis in subnuclei of the rat interpeduncular nucleus and medial habenula

Biological Significance of Kisspeptin-Kiss 1 Receptor Signaling in the Habenula of Teleost Species

Kisspeptin is a neuropeptide, encoded by kisspeptin 1 (KISS1)/Kiss1 gene, which primarily acts as the regulator of reproductive functions via its receptor, kisspeptin receptor (KissR) in vertebrates. In the brain, Kiss1 gene is mainly expressed in the hypothalamic region, but KissR gene is widely distributed throughout the brain, suggesting that kisspeptin-KissR system may be involved in not only reproductive, but also non-reproductive functions. In non-mammalian vertebrates, there are two or more kisspeptin and KissR types. The zebrafish (Danio rerio) possess two kisspeptin (Kiss1 and Kiss2) and their respective receptors [Kiss1 receptor (KissR1) and KissR2]. In the brain of zebrafish, while Kiss2 is expressed in the preoptic-hypothalamic area, Kiss1 is predominantly expressed in the habenula, an evolutionarily conserved epithalamic structure. Similarly, KissR1 is expressed only in the habenula, while KissR2 is widely distributed in the brain, suggesting that the two kisspeptin systems play specific roles in the brain. The habenular Kiss1 is involved in the modulation of the raphe nuclei and serotonin-related behaviors such as fear response in the zebrafish. This review summarizes the roles of multiple kisspeptin-KissR systems in reproductive and non-reproductive functions and neuronal mechanism, and debates the biological and evolutional significance of habenular kisspeptin-KissR systems in teleost species.

Multiple origins, migratory paths and molecular profiles of cells populating the avian interpeduncular nucleus

The interpeduncular nucleus (IP) is a key limbic structure, highly conserved evolutionarily among vertebrates. The IP receives indirect input from limbic areas of the telencephalon, relayed by the habenula via the fasciculus retroflexus. The function of the habenulo-IP complex is poorly understood, although there is evidence that in rodents it modulates behaviors such as learning and memory, avoidance, reward and affective states. The IP has been an important subject of interest for neuroscientists, and there are multiple studies about the adult structure, chemoarchitecture and its connectivity, with complex results, due to the presence of multiple cell types across a variety of subnuclei. However, the ontogenetic origins of these populations have not been examined, and there is some controversy about its location in the midbrain-anterior hindbrain area. To address these issues, we first investigated the anteroposterior (AP) origin of the IP complex by fate-mapping its neuromeric origin in the chick, discovering that the IP develops strictly within isthmus and rhombomere 1. Next, we studied the dorsoventral (DV) positional identity of subpopulations of the IP complex. Our results indicate that there are at least four IP progenitor domains along the DV axis. These specific domains give rise to distinct subtypes of cell populations that target the IP with variable subnuclear specificity. Interestingly, these populations can be characterized by differential expression of the transcription factors Pax7, Nkx6.1, Otp, and Otx2. Each of these subpopulations follows a specific route of migration from its source, and all reach the IP roughly at the same stage. Remarkably, IP progenitor domains were found both in the alar and basal plates. Some IP populations showed rostrocaudal restriction in their origins (isthmus versus anterior or posterior r1 regions). A tentative developmental model of the structure of the avian IP is proposed. The IP emerges as a plurisegmental and developmentally heterogeneous formation that forms ventromedially within the isthmus and r1. These findings are relevant since they help to understand the highly complex chemoarchitecture, hodology and functions of this important brainstem structure.

Estrogen regulates GFAP-expression in specific subnuclei of the female rat interpeduncular nucleus: a potential role for estrogen receptor beta

We previously demonstrated that in rat, astrocytic glial fibrillary acidic protein- (GFAP) expression in the interpeduncular nucleus (IPN) was responsive to testosterone and in females the intensity of GFAP-immunoreactivity (IR) followed the periodic hormonal changes of the estrous cycle. The aim of this study was to test whether 17beta-estradiol (E(2)), in the absence of other ovarian hormones, can influence GFAP-expression within individual subnuclei of the IPN and to determine the cellular distribution of estrogen receptor beta (ERbeta) in the IPN. Quantitative surface-density analysis was used to compare the intensity of GFAP-IR at different anterio-posterior (AP) levels of the IPN in ovariectomized female rats 24 h after treatment with E(2) or vehicle. Estrogen-treatment resulted in a significant increase in GFAP-IR in the rostrolateral subnucleus of the IPN at AP: -5.60, in the lateral-, dorsolateral-, dorsomedial- and central subnuclei at -6.04 and in the lateral subnucleus at -6.72. No significant differences were observed at -5.80 and -6.30. These results indicate that E(2), in the absence of other ovarian hormones, modulates GFAP-expression within select IPN subnuclei and that these affects are dependent on position along the AP axis. To determine whether ERbeta was a possible mediator of the observed estrogenic effects, adjacent section pairs of the IPN were immunostained for ERbeta or GFAP. Using the 'mirror' method, ERbeta-IR was detected in the cytoplasm of GFAP-immunopositive astroglia and in the nuclei of GFAP-immunonegative neurons. These findings suggest that in the IPN, E(2) may directly modulate GFAP-expression through ERbeta-mediated mechanisms.

Developmental changes in heterogeneous patterns of neurotransmitter receptor binding in the human interpeduncular nucleus

The interpeduncular nucleus (IPN) exhibits many complex features, including multiple subnuclei, widespread projections with the forebrain and brainstem, and neurotransmitter heterogeneity. Despite the putative importance of this nucleus, very little is known about its neurochemical development in the human. The human IPN is cytoarchitectonically simple, unlike the rat IPN, which displays considerable heterogeneity. In the following study, we hypothesized that the developing human IPN is neurochemically heterogeneous despite its cytological simplicity. The chemoarchitecture in this study was defined by neurotransmitter receptor binding patterns by using quantitative tissue autoradiography for the muscarinic, nicotinic, serotoninergic, opioid, and kainate receptors. We examined neurotransmitter receptor binding in the developing human IPN in a total of 15 cases. The midbrains of five midgestational fetuses (19-26 gestational weeks) and six infants (38-74 postconceptional weeks) were examined. The midbrain of one child (4 years) and three adults (20-68 years) were analyzed as indices of maturity. At all ages examined, high muscarinic binding was localized to the lateral subdivision of the IPN, high serotoninergic binding was localized to the dorsal IPN, and high opioid receptor binding was localized to the medial IPN. The developmental profile was unique for each radioligand. We report a heterogenous distribution of neurotransmitter receptor binding in the developing human IPN, which supports a complex role for it in human brain function.

Depletion of cholinergic habenulo-interpeduncular neurons by selectively timed methylazoxymethanol acetate (MAM) treatment during pregnancy

Methylazoxymethanol acetate (MAM) was injected to female rats at the beginning of the 17th day of gestation. Resulting offspring showed a remarkable decrease in the size of the medial habenula while the interpeduncular nucleus, whose neurons are generated before the time of MAM treatment, appeared anatomically unaffected. Choline acetyltransferase was significantly reduced in the habenulae and in the interpeduncular nucleus suggesting that MAM treatment had depleted a portion of the cholinergic neurons of the medial habenula which project to the interpeduncular nucleus. Aromatic amino acid decarboxylase significantly increased in the interpeduncular nucleus, a likely effect of monoaminergic hyperinnervation in response to partial cholinergic deprivation. MAM strategy can be usefully adopted for the study of general aspects of brain development when connected nuclei showing no overlapping in neuronal generation times are involved.

Prenatal and postnatal development of substance P immunocytochemistry within subnuclei of the rat interpeduncular nucleus

In the present study, the temporal appearance and distribution of substance P within individual subnuclei has been examined during the development of the rat interpeduncular nucleus (IPN). The prenatal organization as well as migration pattern of individual IPN subnuclei are also described. The IPN was distinguishable on embryonic day (E) 19, near the ventral mesencephalon. At this age, the IPN was organized into individual subnuclei like the adult, except for a bilateral distribution of presumptive rostral neurons. Rostral neurons were merged into a single, midline subnucleus by the day of birth, thereby completing an adult pattern of subnuclear organization. SP immunoreactivity, restricted to the lateral subnuclei, was first detected at E20. The intensity of SP-positive fibers in the lateral subnucleus increased with age, and appeared to become selectively distributed along both the medial and lateral borders of this subnucleus. Additional SP-positive fibers became evident postnatally in a thin band overlying both central and intermediate subnuclei, and within the dorsal medial, central and apical subnuclei. SP-positive cell bodies were present in the rostral subnucleus on postnatal day 28, thereby completing the development of an adult pattern of SP immunoreactivity within the IPN.

Normal development and effects of early deafferentation on choline acetyltransferase, substance P and serotonin-like immunoreactivity in the interpeduncular nucleus

The normal postnatal development and response to neonatal fasciculus retroflexus (FR) lesions of serotonin, substance P (SP), and choline acetyltransferase (ChAT) distribution are described for the rat interpeduncular nucleus (IPN). Serotonin-, SP- and ChAT-containing axons differed in development, distribution, and response to deafferentation. Serotonergic axons and cell bodies were present at birth. SP was present in the FR and in the lateral subnuclei by 3 days of age but did not appear in the rostral or dorsal subnuclei until 7-14 days. Intrinsic SP perikarya were not seen until 17 days of age. The development of ChAT was late, appearing only during the second week of life and not reaching adult patterns and density until after 21 days of age. The pattern of development of cytochrome oxidase and Bodian silver staining are also described. Both cytochrome oxidase and Bodian staining paralleled the patterns of localization and development of ChAT staining. Bilateral neonatal FR lesions resulted in a permanent loss of ChAT and cytochrome oxidase staining throughout the IPN and of SP in the lateral and rostral subnuclei. No changes were seen in the serotonergic system. Following unilateral lesions, the pattern of SP loss and replacement paralleled that seen after adult lesions. The pattern of replacement of ChAT differed from that after adult lesions in that there was partial replacement in the ipsilateral intermediate subnucleus following neonatal lesions. This result suggests that late developing cholinergic axons can innervate the contralateral intermediate nucleus to a much greater extent following infant lesions than following adult lesions.