Immunohistochemical analysis of the early ontogeny of the neuropeptide Y system in rat brain

Intrinsic organization of the corpus callosum

The corpus callosum-the largest commissural fiber system connecting the two cerebral hemispheres-is considered essential for bilateral sensory integration and higher cognitive functions. Most studies exploring the corpus callosum have examined either the anatomical, physiological, and neurochemical organization of callosal projections or the functional and/or behavioral aspects of the callosal connections after complete/partial callosotomy or callosal lesion. There are no works that address the intrinsic organization of the corpus callosum. We review the existing information on the activities that take place in the commissure in three sections: I) the topographical and neurochemical organization of the intracallosal fibers, II) the role of glia in the corpus callosum, and III) the role of the intracallosal neurons.

Neurochemical organization of the ventral striatum's olfactory tubercle

The ventral striatum is a collection of brain structures, including the nucleus accumbens, ventral pallidum and the olfactory tubercle (OT). While much attention has been devoted to the nucleus accumbens, a comprehensive understanding of the ventral striatum and its contributions to neurological diseases requires an appreciation for the complex neurochemical makeup of the ventral striatum's other components. This review summarizes the rich neurochemical composition of the OT, including the neurotransmitters, neuromodulators and hormones present. We also address the receptors and transporters involved in each system as well as their putative functional roles. Finally, we end with briefly reviewing select literature regarding neurochemical changes in the OT in the context of neurological disorders, specifically neurodegenerative disorders. By overviewing the vast literature on the neurochemical composition of the OT, this review will serve to aid future research into the neurobiology of the ventral striatum.

Embryonic and postnatal development of mouse olfactory tubercle

The olfactory tubercle (OT) is located in the ventral-medial region of the brain where it receives primary input from olfactory bulb (OB) projection neurons and processes olfactory behaviors related to motivation, hedonics of smell and sexual encounters. The OT is part of the dopamine reward system that shares characteristics with the striatum. Together with the nucleus accumbens, the OT has been referred to as the "ventral striatum". However, despite its functional importance little is known about the embryonic development of the OT and the phenotypic properties of the OT cells. Here, using thymidine analogs, we establish that mouse OT neurogenesis occurs predominantly between E11-E15 in a lateral-to-medial gradient. Then, using a piggyBac multicolor technique we characterized the migratory route of OT neuroblasts from their embryonic point of origin. Following neurogenesis in the ventral lateral ganglionic eminence (vLGE), neuroblasts destined for the OT followed a dorsal-ventral pathway we named "ventral migratory course" (VMC). Upon reaching the nascent OT, neurons established a prototypical laminar distribution that was determined, in part, by the progenitor cell of origin. A phenotypic analysis of OT neuroblasts using a single-color piggyBac technique, showed that OT shared the molecular specification of striatal neurons. In addition to primary afferent input from the OB, the OT also receives a robust dopaminergic input from ventral tegmentum (Ikemoto, 2007). We used tyrosine hydroxylase (TH) expression as a proxy for dopaminergic innervation and showed that TH onset occurs at E13 and progressively increased until postnatal stages following an 'inside-out' pattern. Postnatally, we established the myelination in the OT occurring between P7 and P14, as shown with CNPase staining, and we characterized the cellular phenotypes populating the OT by immunohistochemistry. Collectively, this work provides the first detailed analysis of the developmental and maturation processes occurring in mouse OT, and demonstrates the striatal nature of the OT as part of the ventral striatum (vST).

Fast prenatal development of the NPY neuron system in the neocortex of the European wild boar, Sus scrofa

Knowledge on cortical development is based mainly on small rodents besides primates and carnivores, all being altricial nestlings. Ungulates are precocial and born with nearly mature sensory and motor systems. Almost no information is available on ungulate brain development. Here, we analyzed European wild boar cortex development, focusing on the neuropeptide Y immunoreactive (NPY-ir) neuron system in dorsoparietal cortex from E35 to P30. Transient NPY-ir neuron types including archaic cells of the cortical plate and axonal loop cells of the subplate which appear by E60 concurrent with the establishment of the ungulate brain basic sulcal pattern. From E70, NPY-ir axons have an axon initial segment which elongates and shifts closer towards the axon's point of origin until P30. From E85 onwards (birth at E114), NPY-ir neurons in cortical layers form basket cell-like local and Martinotti cell-like ascending axonal projections. The mature NPY-ir pattern is recognizable at E110. Together, morphologies are conserved across species, but timing is not: in pig, the adult pattern largely forms prenatally.

Substance P NK1 receptor in the rat corpus callosum during postnatal development

INTRODUCTION

The expression of substance P (SP) receptor (neurokinin 1, NK1) was studied in the rat corpus callosum (cc) from postnatal day 0 (the first 24 hr from birth, P0) to P30.

METHODS

We used immunocytochemistry to study the presence of intracallosal NK1-immunopositive neurons (NK1_IP-n) during cc development.

RESULTS

NK1_IP-n first appeared on P5. Their number increased significantly between P5 and P10, it remained almost constant between P10 and P15, then declined slightly until P30. The size of intracallosal NK1_IP-n increased constantly from P5 (102.3 μm²) to P30 (262.07 μm²). From P5 onward, their distribution pattern was adult-like, that is, they were more numerous in the lateral and intermediate parts of the cc, and declined to few or none approaching the midline. At P5, intracallosal NK1_IP-n had a predominantly round cell bodies with primary dendrites of different thickness from which originated thinner secondary branches. Between P10 and P15, dendrites were longer and more thickly branched, and displayed several varicosities as well as short, thin appendages. Between P20 and P30, NK1_IP-n were qualitatively indistinguishable from those of adult animals and could be classified as bipolar (fusiform and rectangular), round-polygonal, and pyramidal (triangular-pyriform).

CONCLUSIONS

Number of NK1_IP-n increase between P5 and P10, then declines, but unlike other intracallosal neurons, NK1_IP-n make up a significant population in the adult cc. These findings suggest that NK1_IP-n may be involved in the myelination of callosal axons, could play an important role in their pathfinding. Since they are also found in adult rat cc, it is likely that their role changes during lifetime.

The Role of Maternal Dietary Proteins in Development of Metabolic Syndrome in Offspring

The prevalence of metabolic syndrome and obesity has been increasing. Pre-natal environment has been suggested as a factor influencing the risk of metabolic syndrome in adulthood. Both observational and experimental studies showed that maternal diet is a major modifier of the development of regulatory systems in the offspring in utero and post-natally. Both protein content and source in maternal diet influence pre- and early post-natal development. High and low protein dams’ diets have detrimental effect on body weight, blood pressure191 and metabolic and intake regulatory systems in the offspring. Moreover, the role of the source of protein in a nutritionally adequate maternal diet in programming of food intake regulatory system, body weight, glucose metabolism and blood pressure in offspring is studied. However, underlying mechanisms are still elusive. The purpose of this review is to examine the current literature related to the role of proteins in maternal diets in development of characteristics of the metabolic syndrome in offspring.

Ontogenic expression of putative feeding peptides in the rat fetal brain and placenta

The well-demonstrated "fetal programming" paradigm is based on the observation that environmental changes can reset the developmental path and thus, gene expression during intrauterine development. As appetite-regulatory neural pathways develop in utero, we sought to determine the ontogenic expression of putative orexigenic and anorexigenic feeding-regulatory peptides in the fetal rat brain and placenta during the last third of gestation. Pregnant Sprague-Dawley rats (n = 12) at D14, D16 and D18 were sacrificed and fetal whole brain and placenta removed and examined for mRNA levels of orexigenic (neuropeptide Y (NPY), agouti-related peptide (AgRP)) and anorexigenic (cocaine and amphetamine regulated transcript (CART), pro-opiomelanocortin (POMC)) peptides and leptin receptor (OB-Rb) using real-time reverse transcription polymerase chain reactions (RT-PCR). For adult comparisons, the hypothalamus, cortex and cerebellum from male rats were also examined for feeding peptides. In the fetal brain and placenta, mRNA levels of AgRP decreased 10-fold from D14 to D16 and was undetectable at D18. Appetite inhibitory factors OB-Rb and CART mRNA levels increased from D14 to D18 in the brain and placenta. NPY and POMC expression remained unchanged from D14 to D18. The pattern of expression of feeding regulatory peptides in the fetal brain most closely resembled the expression profile of the adult cerebral cortex. The continued maturation of feeding regulatory mechanisms in late gestation indicates the potential for in utero programming of ingestive behavior.

Neuropeptide Y and its role in CNS disease and repair

Neuropeptide Y (NPY) is widely expressed throughout the CNS and exerts a number of important physiological functions as well as playing a role in pathological conditions such as obesity, anxiety, epilepsy, chronic pain and neurodegenerative disorders. In this review, we highlight some of the recent advances in our understanding of NPY biology and how this may help explain not only its role in health and disease, but also its possible use therapeutically.

Developmental programming of energy balance and its hypothalamic regulation

Developmental programming is an important physiological process that allows different phenotypes to originate from a single genotype. Through plasticity in early life, the developing organism can adopt a phenotype (within the limits of its genetic background) that is best suited to its expected environment. In humans, together with the relative irreversibility of the phenomenon, the low predictive value of the fetal environment for later conditions in affluent countries makes it a potential contributor to the obesity epidemic of recent decades. Here, we review the current evidence for developmental programming of energy balance. For a proper understanding of the subject, knowledge about energy balance is indispensable. Therefore, we first present an overview of the major hypothalamic routes through which energy balance is regulated and their ontogeny. With this background, we then turn to the available evidence for programming of energy balance by the early nutritional environment, in both man and rodent models. A wealth of studies suggest that energy balance can indeed be permanently affected by the early-life environment. However, the direction of the effects of programming appears to vary considerably, both between and within different animal models. Because of these inconsistencies, a comprehensive picture is still elusive. More standardization between studies seems essential to reach veritable conclusions about the role of developmental programming in adult energy balance and obesity.

Critical determinants of hypothalamic appetitive neuropeptide development and expression: species considerations

Over the last decade there has been a striking increase in the early onset of metabolic disease, including obesity and diabetes. The regulation of energy homeostasis is complex and involves the intricate integration of peripheral and central systems, including the hypothalamus. This review provides an overview of the development of brain circuitry involved in the regulation of energy homeostasis as well as recent findings related to the impact of both prenatal and postnatal maternal environment on the development of these circuits. There is surprising evidence that both overnutrition and undernutrition impact the development of these circuits in a similar manner as well as having similar consequences of increased obesity and diabetes later in life. There is also a special focus on relevant species differences in the development of hypothalamic circuits. A deeper understanding of the mechanisms involved in the development of brain circuitry is needed to fully understand how the nutritional and/or maternal environments impact the functional circuitry as well as the behavior and physiological outcomes.

Developmental switch in neuropeptide Y and melanocortin effects in the paraventricular nucleus of the hypothalamus

Homeostatic regulation of energy balance in rodents changes dramatically during the first 3 postnatal weeks. Neuropeptide Y (NPY) and melanocortin neurons in the arcuate nucleus, a primary energy homeostatic center in adults, do not fully innervate the paraventricular nucleus (PVN) until the third postnatal week. We have identified two classes of PVN neurons responsive to these neuropeptides, tonically firing neurosecretory (NS) and burst-firing preautonomic (PA) cells. In neonates, NPY could inhibit GABAergic inputs to nearly all NS and PA neurons, while melanocortin regulation was minimal. However, there was a dramatic, age-dependent decrease in NPY responses specifically in the PA neurons, and a 3-fold increase in melanocortin responses in NS cells. These age-dependent changes were accompanied by changes in spontaneous GABAergic currents onto these neurons. This primarily NPYergic regulation in the neonates likely promotes the positive energy balance necessary for growth, while the developmental switch correlates with maturation of homeostatic regulation of energy balance.

Neonatal exposure to citalopram, a serotonin selective reuptake inhibitor, programs a delay in the reflex ontogeny in rats

Serotonin influences the growth and development of the nervous system, as well as its behavioral manifestations. The possibility exists that increased brain serotonin availability in young animals modulates their neuro-behavioral responses. This study investigated the body weight gain and reflex ontogeny of neonatal rats treated during the suckling period with two doses of citalopram (5 mg, or 10 mg/kg, sc, daily). The time of the appearance of reflexes (palm grasp righting, free-fall righting, vibrissa placing, auditory startle response, negative geotaxis and cliff avoidance) as well as the body weight evolution were recorded. In general, a delay in the time of reflex development and a reduced weight gain were observed in drug-treated animals. These findings suggest that serotoninergic mechanisms play a role in modulating body weight gain and the maturation of most reflex responses during the perinatal period in rats.

The development of hippocampal interneurons in rodents

Interneurons are GABAergic neurons responsible for inhibitory activity in the adult hippocampus, thereby controlling the activity of principal excitatory cells through the activation of postsynaptic GABAA receptors. Subgroups of GABAergic neurons innervate specific parts of excitatory neurons. This specificity indicates that particular interneuron subgroups are able to recognize molecules segregated on the membrane of the pyramidal neuron. Once these specific connections are established, a quantitative regulation of their strength must be performed to achieve the proper balance of excitation and inhibition. We will review when and where interneurons are generated. We will then detail their migration toward and within the hippocampus, and the maturation of their morphological and neurochemical characteristics. We will finally review potential mechanisms underlying the development of GABAergic interneurons.

Programming of the appetite-regulating neural network: a link between maternal overnutrition and the programming of obesity?

The concept of a functional foetal "appetite regulatory neural network" is a new and potentially critical one. There is a growing body of evidence showing that the nutritional environment to which the foetus is exposed during prenatal and perinatal development has long-term consequences for the function of the appetite-regulating neural network and therefore the way in which an individual regulates energy balance throughout later life. This is of particular importance in the context of evidence obtained from a wide range of epidemiological studies, which have shown that individuals exposed to an elevated nutrient supply before birth have an increased risk of becoming obese as children and adults. This review summarises the key pieces of experimental evidence, by our group and others, that have contributed to our current understanding of the programming of appetite, and highlights the important questions that are yet to be answered. It is clear that this area of research has the potential to generate, within the next few years, interventions that could begin to alleviate the adverse long-term consequences of being exposed to an elevated nutrient supply before birth.

Spatiotemporal sequence of appearance of NPFF-immunoreactive structures in the developing central nervous system of Xenopus laevis

Neuropeptide FF-like immunoreactive (NPFFir) cells and fibers were analyzed through development of Xenopus laevis. The first NPFFir cells appeared in the embryonic hypothalamus, which projected to the intermediate lobe of the hypophysis, the brainstem and spinal cord. Slightly later, scattered NPFFir cells were present in the olfactory bulbs and ventral telencephalon. In the caudal medulla, NPFFir cells were observed in the nucleus of the solitary tract only at embryonic and early larval stages. Abundant NPFFir cells and fibers were demonstrated in the spinal cord. The sequence of appearance observed in Xenopus shares many developmental features with mammals although notable differences were observed in the telencephalon and hypothalamus. In general, NPFF immunoreactivity developed earlier in amphibians than in mammals.

Hypothalamic orexigenic peptides are overexpressed in young Long–Evans rats after early life exposure to fat-rich diets

Nutritional factors have a critical influence during prenatal life on the development and regulation of networks involved in body weight and feeding regulation. To establish the influence of the macronutrient type on feeding regulatory mechanisms and more particularly on stimulatory pathways (galanin and orexins), we fed female rats on either a high-carbohydrate (HC), a high-fat (HF), or a well-balanced control diet during gestation and lactation, and measured peptide expression in the hypothalamus and important hormones (leptin, insulin) in their pups at weaning. HF weanlings were 30% lighter than control and HC pups (P<0.001). They were characterized by reduced plasma glucose and insulin levels (P<0.01 or less). Their galanin and orexin systems were upregulated as shown by the significant augmentation of mRNA expression in the paraventricular nucleus and lateral hypothalamus, respectively. Inhibitory peptides like corticotropin-releasing hormone and neurotensin were not affected by this dietary treatment during early life. There was, therefore, a more intense drive to eat in HF pups, perhaps to compensate for the lower body weight at weaning. HF diets during early life had meanwhile some positive consequences: the lower metabolic profile might be beneficial in precluding the development of obesity and metabolic syndrome later in life. This is however valid only if the orexigenic drive is normalized after weaning.

Developmental increases in hypothalamic neuropeptide Y content with the embryonic age of meat- and layer-type chicks

We determined central neuropeptide Y (NPY) content of meat- and layer-type chicks at embryonic days 7, 14, 20, and at post-hatching day 1. The central NPY was detectable at day 7; hypothalamic NPY content developmentally increased with a similar pattern but a different level between both types of chicks. These results were discussed with respect to feeding behavior early period after hatching.

Developmental origins of the metabolic syndrome: prediction, plasticity, and programming

The "fetal" or "early" origins of adult disease hypothesis was originally put forward by David Barker and colleagues and stated that environmental factors, particularly nutrition, act in early life to program the risks for adverse health outcomes in adult life. This hypothesis has been supported by a worldwide series of epidemiological studies that have provided evidence for the association between the perturbation of the early nutritional environment and the major risk factors (hypertension, insulin resistance, and obesity) for cardiovascular disease, diabetes, and the metabolic syndrome in adult life. It is also clear from experimental studies that a range of molecular, cellular, metabolic, neuroendocrine, and physiological adaptations to changes in the early nutritional environment result in a permanent alteration of the developmental pattern of cellular proliferation and differentiation in key tissue and organ systems that result in pathological consequences in adult life. This review focuses on those experimental studies that have investigated the critical windows during which perturbations of the intrauterine environment have major effects, the nature of the epigenetic, structural, and functional adaptive responses which result in a permanent programming of cardiovascular and metabolic function, and the role of the interaction between the pre- and postnatal environment in determining final health outcomes.

Early origins of obesity: programming the appetite regulatory system

There is evidence that changes in perinatal nutrition programme the development of relative fat mass and the regulation of appetite in adult life. These studies have been primarily in the rodent utilizing maternal overnutrition or undernutrition imposed at different stages of pregnancy and beyond, mapping of neuropeptide localization and activity and appropriate null mutant models. Whilst the rodent offers significant advantages in terms of a short gestation and the availability of useful transgenic and null mutant models, there are also advantages to using an animal model more akin to the human, in which all components of the 'fat-brain axis' are present before birth, such as the sheep. This review summarizes recent work on the expression and localization of the 'appetite regulatory' peptides in the fetal rodent and sheep hypothalamus and their potential role in the early programming of postnatal appetite and obesity.

Distribution of neuropeptide Y-immunoreactive neurons in the human brainstem, cerebellum, and cortex during development

1. Neuropeptide Y is found throughout the central nervous system where it appears to play a wide range of often poorly understood functions. In this study, the distribution of neuropeptide Y immunoreactive (NPY-ir) neurons in the brainstem, cerebellum, and cerebral cortex of human fetuses ranging in age from 11 gestational weeks to term was investigated by immunohistochemistry. 2. The NPY-ir cells were detected in the dorsal and ventral rostral midbrain and the interpeduncular nucleus by 21 weeks and 32 weeks of gestation, respectively. Although no positive cells were found in the pons, the NPY-ir fibers were detected there at 32 gestational weeks. 3. The vagal, hypoglossal, and olivary nuclei of the medulla oblongata contained immunoreactive cells by week 21 and the medullary reticular formation by week 25 of gestation. In most of these locations, both the number and size of neuropeptide Y positive cells were greater at birth and reached maximal values of 100-400 cells per 1 mm2 and 2-5 microm in diameter, respectively. 4. In the cerebellum, numerous NPY-ir horizontal and granule cells, as well as the cells within the dentate nucleus were observed as early as 21 weeks of gestation. 5. The NPY-ir cells were also detected in the developing cerebral cortex, with the earliest activity observed within the temporal cortex at 14 weeks of gestation. By week 21, positive cells appeared in the visual, frontal, sensory, and motor cortices. Most of these cells were bipolar or multipolar in morphology but their numbers at birth were relatively low. 6. Our results show a wide distribution of the NPY-ir cells in the developing human brain and offer supporting evidence for the important modulatory role of NPY in both the fetus and adult.

Comparison of hypocretin/orexin and melanin-concentrating hormone neurons and axonal projections in the embryonic and postnatal rat brain

Hypocretin/orexin (H/O) and melanin-concentrating hormone (MCH) are peptide neuromodulators found in separate populations of neurons located within the lateral and perifornical hypothalamic regions. H/O has been linked to sleep-wakefulness regulation and to the sleep disorder narcolepsy, and both systems have been implicated in energy homeostasis, including the regulation of food intake. In the present study we compared the development of H/O and MCH-expressing neuronal populations with in situ hybridization and immunohistochemistry on adjacent sections in the embryonic and postnatal rat brain. We found that MCH mRNA and protein were present in developing neurons of the hypothalamus by embryonic day 16 (E16), whereas H/O mRNA and protein were not detected until E18. We also identified previously undescribed populations of MCH-immunoreactive cells in the lateral septum, paraventricular hypothalamic nucleus, lateral zona incerta, and ventral lateral geniculate nucleus that may play a specific role in the development of these regions. MCH immunoreactive axonal processes were also evident earlier than H/O stained fibers and at the time H/O immunoreactive processes were first identified in the hypothalamus at E20, extensive MCH axonal fiber systems were already present in many brain regions. Interestingly, however, the density of axonal fibers immunoreactive for H/O in the locus coeruleus reached peak levels at the same developmental age (P21) as MCH immunoreactive axons in the diagonal band of Broca (DBB). The peak of axon density coincided with the developmental stage at which adult patterns of feeding and sleep-waking activity become established. The present results demonstrate developmental differences and similarities between the MCH and H/O systems that may relate to their respective roles in feeding and sleep regulation.

Ontogeny of the hypothalamic neuropeptide Y system

Early onset obesity and type II diabetes is rapidly becoming an epidemic, especially within the United States. This dramatic increase is likely due to many factors including both prenatal and postnatal environmental cues. The purpose of this review is to highlight some of the recent advances in our knowledge of the development of the hypothalamic circuits involved in the regulation of energy balance, with a focus on the neuropeptide Y (NPY) system. Unlike the adult rat, during the postnatal period NPY is transiently expressed in several hypothalamic regions, along with the expected expression within the arcuate nucleus (ARH). These transient populations of NPY neurons during the postnatal period may provide local NPY production to sustain the necessary energy intake during this critical growth phase. This may be physiologically important since ARH-NPY projections do not fully develop until the 3rd postnatal week. The significance of this ontogeny is that many peripheral metabolic signals have little effect of feeding prior to the development of the ARH projections. The essential questions now are whether prenatal and/or postnatal exposure to high levels of insulin or leptin during development can cause permanent changes in the function of hypothalamic circuits. It is vital to understand not only the natural development of the hypothalamic circuits that regulate energy homeostasis, but also their abnormal development caused by maternal and postnatal environmental cues. This will be pivotal for designing intervention and therapeutics to treat early onset obesity/type II diabetes, which may very well need to be different from those designed to prevent/treat adult onset obesity/type II diabetes.

Postnatal development of the hypothalamic neuropeptide Y system

In the adult rat, arcuate-neuropeptide Y/agouti-related protein neurons have efferent projections throughout the hypothalamus and provide a potent orexigenic stimulus. At birth neuropeptide Y fibers are also present throughout the hypothalamus; however, the source of these fibers has been unknown. The present studies determined the postnatal ontogeny of arcuate-neuropeptide Y fibers into the paraventricular nucleus and dorsomedial hypothalamic nucleus, as well as the ontogeny of neuropeptide Y1 receptor expression within these areas. Agouti-related protein messenger RNA and protein expression was present exclusively in cell bodies in the arcuate throughout postnatal development, starting at P2, and was colocalized in the vast majority of arcuate-neuropeptide Y neurons. This exclusive colocalization of agouti-related protein with arcuate-neuropeptide Y neurons makes it an excellent marker for these neurons and their projections. Even though single-label neuropeptide Y fibers were abundant in the dorsomedial hypothalamic nucleus and paraventricular nucleus as early as P2, arcuate-neuropeptide Y/agouti-related protein fibers did not significantly innervate these areas until P5-6 and P10-11, respectively. In contrast, a portion of the neuropeptide Y fibers within the paraventricular nucleus as early as P2 originated from the brainstem, as indicated by their colocalization with dopamine beta hydroxylase. It remains to be determined if local sources of neuropeptide Y-expressing cells within the dorsomedial hypothalamic nucleus and paraventricular nucleus also contribute to the neuropeptide Y-immunoreactive fibers within these regions prior to the development of arcuate-neuropeptide Y/agouti-related protein projections. In addition to the dramatic change in arcuate-neuropeptide Y/agouti-related protein projections, there is also a striking change in Y1 protein expression in the hypothalamus during the first two postnatal weeks. Taken together these data suggest that the early postnatal period, during which there is a dynamic change in the hypothalamic neuropeptide Y system, may constitute a critical period in the development of this important feeding circuit.

Neuropeptide tyrosine-like immunoreactive system in the brain, olfactory organ and retina of the zebrafish, Danio rerio, during development

The anatomical distribution of neuropeptide tyrosine (NPY)-like immunoreactivity was investigated in the brain, olfactory organ and retina of the zebrafish, Danio rerio, during development and in juvenile specimens, by using the indirect immunofluorescence and the peroxidase-antiperoxidase methods. In 60 h post fertilization (hpf) embryos, NPY-like immunoreactive cell bodies appeared in the hypothalamus, within the posterior periventricular nucleus. Few positive nerve fibers were found in the hypothalamus and in the tegmentum of the mesencephalon. In 72 hpf embryos, a new group of NPY-like immunoreactive cells was found in the olfactory pit. At day 4 of development, NPY-like immunoreactive cell bodies were detected between the olfactory pit and the olfactory organ. In the hypothalamus the location of positive cell bodies was similar to that reported in the previous developmental stages. A few positive nerve fibers appeared in the tegmentum of the rhombencephalon. At days 7 and 15 of development, the distribution of NPY-like immunoreactivity was very similar to that reported at day 4. However, at day 15, NPY-like immunoreactivity appeared for the first time in amacrine cells of the retina and in nerve fibers of the tectum of the mesencephalon. In 1-month/3-month-old animals, additional groups of NPY-like immunoreactive cell bodies appeared in the glomerular layer of the olfactory bulbs, the terminal nerve, the lateral nucleus of the ventral telencephalic area, the entopeduncular nucleus and in the medial region of the reticular formation of the rhombencephalon. These results show that NPY-like immunoreactive structures appear early during ontogeny of zebrafish. The distribution of the immunoreactive system increases during the ontogeny, the juvenile stages, and reaches the complete development in mature animals. The location of NPY-like immunoreactivity indicates that, during development, NPY could be involved in several neuromodulatory functions, including the processing of visual and olfactory information. In 1-month/3-month-old animals, NPY-like immunoreactive nerve fibers are present in the pituitary, suggesting that, from these stages onward, NPY may influence the secretion of pituitary hormones.

The neuropeptide Y receptors, Y1 and Y2, are transiently and differentially expressed in the developing cerebellum

Neuropeptide Y (NPY), a peptide widely expressed in the brain, acts through the protein G-coupled receptors Y1, Y2 and Y5. In the adult rat, this peptide modulates many important functions such as the control of energy balance and anxiety. Its involvement in brain development has been less investigated. In the present study, we have analysed the expression of Y1 and Y2 in the developing rat cerebellum using RNase protection assay. Both receptors were detected in the embryo but at very low levels. Their expression then increased, reaching a peak at postnatal day 10. At later stages, we observed a down-regulation of both Y1 and Y2 mRNA levels. This pattern of expression was delayed in hypothyroid rats, suggesting that the regulation of NPY receptors was strictly related to cerebellar development stages. In situ hybridisation and immunohistochemistry analyses revealed specific localisations of the receptors. Y1 was exclusively expressed by Purkinje cells while Y2 was found mostly in granule cells of the internal granule cell layer. These observations argue in favour of specific roles for Y1 and Y2 in the developing cerebellum. In an initial attempt to characterise these roles, we have determined the number of apoptotic cells in the developing cerebellum of Y2(-/-) mice and analysed the effects of NPY on primary cultures of cerebellar granule neurones. Our data showed that the absence of Y2 did not increase cell death in the internal granule cell layer of the developing cerebellum, and that NPY by itself did not prevent the death of differentiated granule cells cultured in serum-free medium. However, we found that co-treatment of the cells by NPY and neuromediators such as NMDA or GABA strongly promoted the survival of granule neurones. Taken together, these observations suggest an involvement of the NPY receptors in cerebellar ontogenesis that remains to be demonstrated in vivo.

Ontogenetic changes in neuropeptide Y-immunoreactive cerebrospinal fluid-contacting neurons in the hypothalamus of the cloudy dogfish, Scyliorhinus torazame (Elasmobranchii)

Ontogenetic changes in neuropeptide Y-immunoreactive (NPY-ir) cerebrospinal fluid (CSF)-contacting neurons in the dogfish hypothalamus were studied immunohistochemically. NPY-ir CSF-contacting neurons first appeared in the median infundibular floor of the embryo at the 34 mm stage. At the 40 mm stage, similar neurons were found also in the saccus vasculosus (SV). The number of these neurons increased during the 54-80 mm stages, and the cells in the infundibular floor extended their basal processes to the neuropil of the median eminence, whereas the cells in the SV sent their axonal fibers to the tractus sacci vasculosi. After hatching, NPY immunoreactivity in the ventral hypothalamus became less dense, and the labeled CSF-contacting neurons tended to be confined to the nucleus lateralis tuberis, similarly as in the adults. The occurrence of NPY-ir CSF-contacting neurons in the SV was transient during the embryonic periods.

Relation Between Putative Transmitter Phenotypes and Connectivity of Subplate Neurons During Cerebral Cortical Development

During development, the earliest generated neurons of the mammalian telencephalon reside in a region of the white matter, the subplate, just beneath the cortical plate. Neurons in the subplate are only transiently present in the telencephalon: shortly after birth in the cat the majority have disappeared. During their brief life, however, subplate neurons mature; they extend long-distance and local projections, and express immunoreactivity for GABA and several neuropeptides. In the present study we examined the relation between possible transmitter phenotypes of subplate neurons and their connectivity. To do so, we used a double-label technique in which immunohistochemistry for neuropeptide Y (NPY), somatostatin (SRIF) or calbindin (CaBP) was combined with retrograde tracing. Experiments were performed in neonatal cats and in ferret kits at equivalent postconceptional ages, times when subplate neurons are numerous. Subplate neurons immunoreactive for neuropeptides and CaBP could be double-labelled by an injection of retrograde tracer either into the cortical plate or the white matter, indicating that this particular subset of subplate neurons can make local circuit projections. In contrast, peptide or CaBP immunoreactive subplate neurons could never be retrogradely labelled from a tracer injection into the thalamus. Taken together, these observations indicate that subplate neurons immunoreactive for NPY, SRIF and CaBP are likely to be interneurons exclusively. On the other hand, subplate neurons with long-distance projections to the thalamus or the contralateral hemisphere could be labelled by the retrograde transport of d-[3H]aspartate, suggesting that at least some projection subplate neurons might use an excitatory amino acid as a neurotransmitter. These results indicate that there is a defined relationship between the putative transmitter phenotypes of subplate neurons and their patterns of projection. Interneurons of the subplate express peptidergic properties while projection neurons to the thalamus may use an excitatory amino acid. Thus, these basic organizational features of the transient subplate are reminiscent of those found in the adult cortical layers.

Localization and characterization of NPY/PYY receptors in rat frontoparietal cortex during development

Neuropeptide Y (NPY) is present in most cerebrocortical areas during fetal and postnatal development. In the rat frontal cortex, a dense radial fiber network containing NPY immunoreactivity is observed transiently as early as embryonic day 17 (E17) and disappears at the end of the first postnatal week. We have investigated the distribution of NPY receptors in the frontoparietal cortex at 13 stages of development, from E15 fetuses to adults, by in vitro autoradiography, using (125)I-pPYY as a radioligand. Quantitative receptor density was measured through all cortical layers at each developmental stage. Pharmacological identification of (125)I-pPPY binding sites was made by competition experiments using pNPY or [Leu(31),Pro(34)]pNPY and pNPY(13-36), as selective competitors for Y1 and Y2 receptors, respectively. NPY receptors were first detected in the cerebral cortex at low densities at E19 in a thin layer of tissue corresponding to the inner half of the intermediate zone (IZ) and the upper ventricular zone (VZ). The neuroepithelium did not contain binding sites. High densities of sites were observed by E21 onward to P10 in the deep cortical layers corresponding to the IZ and layers V-VI. A decreasing gradient of receptor density was observed from layer VI to the marginal zone (layer I). The distribution of NPY receptors does not match with the perikarya of transient NPY-immunoreactive neurons located in the cortical plate but does coincide with their axonal extension. The receptor density decreased abruptly between P10 and P12 in deep layers, whereas a moderate expression of binding sites is detected from P10 to P12 in layers I-III. By P14, the binding level was the lowest observed in the postnatal period. From P21 onward, receptors were observed in superficial layers I-III, and their density rose by two- to threefold up to adulthood. Competition studies indicated that the NPY receptors located in the deep cortical layers of the E21 or P1 rat cortex exhibit Y2 receptor type characteristics. The binding sites detected in the superficial layers from P10 to P12 rats also show Y2 receptors characteristics, unlike the NPY receptors in layers II-III of the adult, which behave like Y1 receptors. These data show that different NPY receptor types are successively expressed in specific layers during late gestation and early postnatal life in the rat frontoparietal cortex.

Novel expression of neuropeptide Y (NPY) mRNA in hypothalamic regions during development: region-specific effects of maternal deprivation on NPY and Agouti-related protein mRNA

During development there is novel expression of NPY mRNA in the dorsomedial hypothalamic nucleus (DMH) and perifornical region (PFR), in addition to the arcuate nucleus (ARH). Furthermore, NPY mRNA levels peak in all regions on postnatal d 16 (P16) and decrease to adult levels by P30. The purpose of the present study was to determine whether NPY and agouti-related protein (AGRP) mRNA expression in the different hypothalamic regions on P11 and P16 are similarly affected by fasting. An examination of the full rostral to caudal extent of the hypothalamus revealed two additional regions displaying novel NPY mRNA expression, the parvocellular division of the paraventricular nucleus (PVH) and lateral hypothalamus (LH). Maternal deprivation for 36 h, used to bring about a fast, similarly increased (23-29%) NPY and AGRP mRNA expression in the ARH on P11 and P16. In contrast, NPY expression in the DMH and PFR were significantly decreased (19-30% and 48-53%, respectively), whereas NPY mRNA levels in the PVH and LH were not altered by this treatment. The increase in NPY and AGRP mRNA expression in the ARH in response to maternal deprivation suggests that these neuronal populations respond to signals of energy balance. In contrast, NPY expression in the DMH, PFR, PVH, and LH is differentially regulated by maternal deprivation or other factors associated with maternal separation.

Developmental expression of prolactin releasing peptide in the rat brain: localization of messenger ribonucleic acid and immunoreactive neurons

Prolactin releasing peptide (PrRP) was recently identified as the stimulator of prolactin release from the anterior pituitary. PrRP mRNA is expressed in the medulla oblongata and the hypothalamus in the rat brain. The fibers containing PrRP are widely distributed in the brain, therefore, it was postulated that PrRP may act as a neurotransmitter or neuromodulator as well as an endocrine substance. To clarify the developmental changes in the expression of PrRP during brain development, we examined PrRP in rat fetuses and neonates using in situ hybridization and immunohistochemistry. The PrRP mRNA was expressed in the nucleus of the solitary tract (NTS) at embryonic day 18 (E18) and in the ventral and lateral reticular nucleus (VLRN) of the caudal medulla oblongata at E20. The PrRP mRNA in the hypothalamus was first expressed at postnatal day 13 (P13). Reverse transcription-polymerase chain reaction analysis (RT-PCR) for PrRP revealed that PCR product, a 268 bp band, was detected from either E18 in the medulla or P13 in the hypothalamus. Immunodetection with monoclonal antibody against prepro-PrRP revealed intensive staining of cells in the NTS at E18, in the VLRN at E20 or in the dorsomedial hypothalamus at P13. Immunohistochemistry using monoclonal antibody against mature PrRP at P6 showed PrRP fibers to be distributed in the paraventricular hypothalamic nucleus, periventricular hypothalamic nucleus, medial preoptic area, basolateral amygdaloid nucleus, dorsomedial hypothalamus, ventromedial hypothalamus, periventricular nucleus of the thalamus and bed nucleus of the stria terminalis as previously shown in the adult rat. PrRP fibers were also found in the optic chiasm, dorsal endopiriform nucleus, cingulum, intermediate reticular nucleus, and caudal ventrolateral reticular nucleus at P6 and P9. However, PrRP fibers were never found in the above regions in the adult animal. These findings suggest that PrRP fibers originating in the medulla oblongata have been widely distributed in the rat brain during the early postnatal day and PrRP may play various roles in the brain development.

Neurobiological mechanisms of the onset of puberty in primates

An increase in pulsatile release of LHRH is essential for the onset of puberty. However, the mechanism controlling the pubertal increase in LHRH release is still unclear. In primates the LHRH neurosecretory system is already active during the neonatal period but subsequently enters a dormant state in the juvenile/prepubertal period. Neither gonadal steroid hormones nor the absence of facilitatory neuronal inputs to LHRH neurons is responsible for the low levels of LHRH release before the onset of puberty in primates. Recent studies suggest that during the prepubertal period an inhibitory neuronal system suppresses LHRH release and that during the subsequent maturation of the hypothalamus this prepubertal inhibition is removed, allowing the adult pattern of pulsatile LHRH release. In fact, y-aminobutyric acid (GABA) appears to be an inhibitory neurotransmitter responsible for restricting LHRH release before the onset of puberty in female rhesus monkeys. In addition, it appears that the reduction in tonic GABA inhibition allows an increase in the release of glutamate as well as other neurotransmitters, which contributes to the increase in pubertal LHRH release. In this review, developmental changes in several neurotransmitter systems controlling pulsatile LHRH release are extensively reviewed.

Dietary composition during fetal and neonatal life affects neuropeptide Y functioning in adult offspring

The aim of this study was to examine the impact of maternal diet during the gestation and lactation periods on the neuropeptide Y (NPY) system in adult offspring. Male Long-Evans rats were obtained from dams fed either on a well-balanced diet (C), a high carbohydrate diet (HC) or a high-fat diet (HF) and fed themselves on the well-balanced diet for their whole life. At 6 months of age, their feeding response to various doses of NPY injected in the lateral brain ventricle was measured in one group and NPY concentrations in microdissected nuclei of the hypothalamic were measured in a second group. The HF rats were lighter than the two other groups (P<0.001). The control rats showed a typical dose-dependent feeding response to NPY. The HC rats showed a continuous increase in the response, starting at the intermediate dose (1.0 microg) only while the HF rats had a maximal response at the lowest dose (0.5 microg). The HF rats ate twice as much as the HC rats at the lowest dose tested 1 h after injection (4.4+/-0.6 vs. 2.7+/-0.4 g; P<0.05), showing therefore the greatest sensitivity to NPY. This change in the sensitivity was not related to hypothalamic NPY concentration as it was not modified in the arcuate and paraventricular nuclei. The diet imposed on the mother could have long-lasting effects on body weight regulation of the offsprings and alter the NPY system likely through modifications at the receptor level.

Neuropeptide Y- and somatostatin-immunoreactive axons in the corpus callosum during postnatal development of the rat

Corpus callosum (CC) projections in adult mammals were generally thought to be excitatory and to use excitatory amino acids as their transmitters. Little information has been available about the electrical properties and neurochemical status of developing CC connections. The present study investigated the chemical status of rat CC axons during postnatal development by using antibodies to neuropeptide Y (NPY) and to somatostatin (SOM). Both NPY-immunoreactive (ir) and SOM-ir axons were found in the CC of the rat from newborn through adult; however, the number of SOM-ir CC axons is less than that of NPY-ir CC axons at corresponding ages. The density of both NPY-ir and SOM-ir CC axons initially increased, then peaked, and finally decreased to the mature level. In the adult, only a few NPY-ir and SOM-ir CC axons were found in the CC. These results indicate that many NPY-ir and SOM-ir CC axons are transitory during early postnatal development. The results also suggest that the functions of CC connections in adult mammals may be different from that of developing ones. The present results as well as the previous results demonstrate that both developing and mature CC connections are chemically heterogeneous.

Expression of neuropeptide Y in olfactory ensheathing cells during prenatal development

Neuropeptide Y (NPY) is expressed in a special type of glial cell, the olfactory ensheathing cells, that surround the axons of olfactory sensory neurons on their way from the olfactory epithelium to the glomeruli in the olfactory bulb. The expression of NPY in ensheathing cells was examined during prenatal development of the olfactory system by using immunohistochemistry and in situ hybridization. NPY expression was compared with the expression of growth associated protein-43, olfactory marker protein, the low-affinity nerve growth factor receptor (p75) and S-100, factors expressed in the olfactory system at known stages of development. NPY-like immunoreactivity (NPY-LI) and NPY mRNA expression was first detected in the olfactory nerve layer of the olfactory bulb at embryonic day 15. From embryonic day 16 and onward, a clear segregation could be observed in the intensity of both NPY-LI and NPY mRNA expression within the olfactory nerve layer. NPY expression was most intense in the inner part of the olfactory nerve layer. In the outer olfactory nerve layer, a clear decrease in NPY expression was observed. The inner olfactory nerve layer, showing high NPY expression, did not stain for S-100 or p75. However, NPY-LI was found to coexist with S-100-LI from the outer olfactory nerve layer until the olfactory epithelium and with p75-LI in cells surrounding the olfactory nerve. These results show that NPY is expressed in ensheathing cells before olfactory sensory neurons mature and the formation of the glomerular layer starts. NPY might be involved in the guidance, growth, or both, of olfactory sensory axons toward their target glomeruli in the olfactory bulb or have a function in the maturation of the olfactory sensory neurons.

Development of immunoreactivity to neuropeptide Y in the brain of brown trout (Salmo trutta fario)

The development of neuropeptide Y-immunoreactive (NPY-ir) neurons in the brain of the brown trout, Salmo trutta fario, was studied by using the streptavidin-biotin immunohistochemical method. Almost all NPY-ir neurons found in the brain of adults already appeared in embryonic stages. The earliest NPY-ir neurons were observed in the laminar nucleus, the locus coeruleus, and the vagal region of 9-mm-long embryos. In the lateral area of the ventral telencephalon, habenula, hypothalamus, optic tectum, and saccus vasculosus, NPY-ir cells appeared shortly after (embryos 12-14 mm in length). The finding of NPY-ir cells in the saccus vasculosus and the vagal region expand the NPY-ir structures known in teleosts. Among the regions of the trout brain most richly innervated by NPY-ir fibers are the hypothalamus, the isthmus, and the complex of the nucleus of the solitary tract/area postrema, suggesting a correlation of NPY with visceral functions. Two patterns of development of NPY-ir populations were observed: Some populations showed a lifetime increase in cell number, whereas, in other populations, cell number was established early in development or even diminished in adulthood. These developmental patterns were compared with those found in other studies of teleosts and with those found in other vertebrates. J. Comp. Neurol. 414:13-32, 1999.

Special relationship of gamma-aminobutyric acid to the ventromedial nucleus of the hypothalamus during embryonic development

The ventromedial nucleus of the hypothalamus (VMH) is a key nucleus for regulating homeostatic, neuroendocrine, and behavioral functions. We conducted immunocytochemical analyses by using antisera directed against gamma-aminobutyric acid (GABA), its synthetic enzyme glutamic acid decarboxylase (GAD67), GABA-A receptor subunits (alpha2, beta3, epsilon), estrogen receptor-alpha, and Neuropeptide Y (NPY) in the region of the VMH in embryonic mice to identify potential patterning elements for VMH formation. Cells and fibers containing GABA and GAD67 encircled the primordial VMH as early as embryonic day 13 (E13) when the cytoarchitecture of the VMH was not recognizable by Nissl stain. At E16-17 the cytoarchitecture of the VMH became recognizable by Nissl stain as GABAergic fibers invaded the nucleus, continued postnatally, and by adulthood the density of GABAergic fibers was greater inside than outside the VMH. GABA-A receptor subunit expression (beta3 by E13 and alpha2 by E15) within the primordial VMH suggested potential sensitivity to the surrounding GABA signal. Brain slices were used to test whether fibers from distal or proximal sites influenced VMH development. Coronal Vibratome slices were prepared and maintained in vitro for 0-3 days. Nissl stain analyses showed a uniform distribution of cells in the region of the VMH on the day of plating (E15). After 3 days in vitro, cellular aggregation suggesting VMH formation was seen. Nuclear formation in vitro suggests that key factors resided locally within the coronal plane of the slices. It is suggested that either GABA intrinsic to the region nearby the VMH directly influences the development and organization of the VMH, or along with other markers provides an early indicator of pattern determination that precedes the cellular organization of the VMH.

Complementary and overlapping expression of Y1, Y2 and Y5 receptors in the developing and adult mouse nervous system

Neuropeptide Y, a 36 amino acid peptide, mediates its biological effects by activating the Y1, Y2, Y5 and Y6 receptors, which are also receptors for the structurally related peptide YY. Different classes of receptors have been suggested to be involved in different neuropeptide Y functions. In this report, we have characterized the developmental regulation and compared the cellular localization of these receptors in the developing and in the adult central and peripheral nervous systems of the mouse. RNase protection assays revealed that Y1, Y2 and Y5 messenger RNAs were expressed very early in spinal cord, brain, cerebellum and dorsal root ganglion development and were often down-regulated at times corresponding to their acquirement of the adult function in neurotransmission. In situ hybridization of the adult brain showed that Y1 was widely expressed, Y2 displayed a more restricted pattern, Y5 was expressed at very low levels and only in a few brain nuclei and Y6 was not expressed. Virtually all areas containing neurons positive for Y5 also expressed Y1, whereas many Y1-positive cells clearly did not express Y5. In contrast, Y2 was not expressed by the neurons expressing Y1 or Y5. These findings suggest that neuropeptide Y signaling in the brain could be mediated by simultaneous Y1 and Y5 activation. Similar results were also obtained in peripheral sensory neurons. Furthermore, our results suggest that neuropeptide Y/peptide YY receptors play an important role in nervous system development and that selective receptor combinations are responsible for signaling the different effects of neuropeptide Y in the peripheral and central nervous systems.

Hypothalamic neuropeptide Y content and mRNA expression in weanling rats subjected to dietary manipulations during fetal and neonatal life

Hypothalamic neuropeptide Y (NPY) is present very early during the fetal life and is rapidly functional in the regulation of feeding behavior after birth. In the present experiment, we tried to determine the influence that the diet type ingested by dams during gestation and lactation would have on the growth and hypothalamic and pancreatic peptides of their progeny immediately after weaning. The dams were fed on either a high-carbohydrate (HC), a high-fat (HF) or a control diet ad libitum. At 3 days of age, the HC pups weighed significantly more than the two other groups (P < 0.02 vs. C and P < 0.002 vs. HF). At weaning, the HF rats were significantly lighter than the two other groups (P < 0.001). Food intake was significantly lower in the HF rats than in the two other groups 3 days (P < 0.002) and 5 days after weaning (P < 0.02). Plasma glucose of the HF rats was significantly lower than that of the control rats (P < 0.05) and of the HC rats (P < 0.01). Immunoreactive insulin in the HF rats was also significantly lower than that in the control rats (-53%; P < 0.001) and in the HC rats (-47%; P < 0.001). NPY content and mRNA expression in the arcuate nucleus were not significantly different between the three groups. NPY concentration only varied in the ventromedian nucleus. In the control rats, it was significantly lower than that of the HC rats (-35%; P < 0.01) and that of the HF rats (-32%; P < 0.002). These data demonstrated that the regulatory mechanisms of feeding behavior in offspring are completely and differentially modified by the macronutrient content of the diets ingested by their mother. Both peripheral and central mediators were strongly implicated. These modifications could have long-term repercussions on body weight and composition.

Ontogeny of neuropeptide Y expression in response to deprivation in lean Zucker rat pups

Hypothalamic neuropeptide Y (NPY) activity is believed to play an important role in the response to food deprivation in adult rats. Little is known, however, about the role of the hypothalamic NPY system in the control of food intake in the preweanling rat. To address this issue, we examined the effect of deprivation on arcuate nucleus preproNPY expression in lean Zucker rat pups, using in situ hybridization. PreproNPY expression within the arcuate nucleus was localized to cells in the medial portion. Twenty-four hours of food, water, and maternal deprivation significantly increased the relative abundance of preproNPY mRNA in pups on postnatal day (P) 2, P9, P12, and P15 by 14-31%. This response, however, was not observed on P5. The absence of an effect on P5 and the magnitude of the response at the other ages tested were not correlated with the amount of weight lost during deprivation.

Effect of uteroplacental insufficiency upon brain neuropeptide Y and corticotropin-releasing factor gene expression and concentrations

Various hypothalamic functions such as feeding behavior, energy expenditure, body weight gain, level of anxiety, and sexual maturation are mediated by a balance between the concentrations of neuropeptide Y (NPY) and corticotropin-releasing factor (CRF). To test the hypothesis that maternal uteroplacental insufficiency alters the offspring's brain NPY and/or CRF levels, we examined the effect of maternal uterine artery ligation with intrauterine growth restriction (IUGR) (p < 0.05) upon fetal (20 d) and postnatal (4, 14, and 21 d) brain NPY and CRF synthesis, concentrations, and regional distribution. An age-related increase in NPY (0.8 kb) and CRF (1.4 kb) mRNA levels with peak amounts at the 14-d postnatal age (p < 0.05) was observed. IUGR was associated with a 75% increase in fetal brain NPY mRNA levels (p < 0.05) with no change in NPY peptide, CRF mRNA and peptide amounts. Although the increase in NPY mRNA levels persisted postnatally (p < 0.05) at d 4 and 21, CRF mRNA amounts were 2.5-fold higher only in the 4-d IUGR (p < 0.05). Paralleling the mRNA changes, an age-related increase in RIA of NPY and CRF peptide concentrations was noted (p < 0.05). IUGR caused postnatal brain NPY and CRF peptide changes similar to corresponding mRNA levels (p < 0.05), despite normal postnatal circulating glucose, insulin, corticosterone, and leptin concentrations. The age-specific intergroup differences in the NPY and CRF peptide immunoreactivity appeared predominantly in the hypothalamic region. We conclude that maternal uteroplacental insufficiency causing IUGR leads to a pretranslational imbalance in the immediate (4 d) postnatal brain NPY and CRF peptide concentrations, thereby altering the developmental pattern. This alteration in NPY and CRF peptide concentrations, despite normalization of the metabolic milieu was associated with a persistent diminution in body weight. The IUGR-associated pretranslational increase in NPY and not CRF peptide levels at d 21, may herald changes in feeding behavior during the postsuckling phase.

Neuropeptide Y gene expression in immortalized rat hippocampal and pheochromocytoma-12 cell lines

Employing clonal cell lines derived from rat embryonic hippocampal cells, we detected neuropeptide Y (NPY) mRNA in three progenitor subcloned cell lines. These cell lines upon differentiation express markers indicative of commitment to either neuronal (H19-7; NF +, GFAP -), glial (H19-5; GFAP +, NF -), or bipotential (H583-5; NF +, GFAP + ) lineages. Induction of differentiation was associated with the persistence of the NPY mRNA, however, in the differentiated H19-7 cells a 20-fold increase in NPY mRNA levels was observed (P<0.05). NPY immunoreactivity was observed only in cells with a differentiated neuronal phenotype. The cellular radioimmunoassayable NPY peptide levels increased twelve-fold without a change in extracellular NPY peptide levels by multi-factorially induced neuronal or glial cell differentiation. The differentiated H19-5 cells expressed lower levels of NPY that could not be immunocytochemically detected. The peripheral sympathetic PC-12 neuronal cells examined in the undifferentiated and nerve growth factor-driven differentiated states expressed NPY only upon differentiation. We conclude that NPY is expressed by the cultured undifferentiated and differentiated rat hippocampal clonal cell lines, while the peripheral sympathetic PC-12 neuronal cell line only expresses the NPY gene upon differentiation. These immortalized embryonic neural cell line(s) will provide a hippocampal cell line(s) to conduct future in-vitro investigations targeted at determining the cellular and molecular mechanisms governing NPY gene expression.

Postnatal development of somatostatin- and neuropeptide Y-immunoreactive neurons in rat cerebral cortex: a double-labeling immunohistochemical study

The postnatal development of somatostatin (SOM)- and neuropeptide Y (NPY)-immunoreactive (ir) neurons was examined in rat cerebral cortex, while considering their coexistence in cortical neurons. Using double immunohistochemical staining for SOM and NPY with diaminobenzidine and benzidine dihydrochloride as chromogens, we subdivided immunoreactive cells into double-labeled SOM/NPY-, SOM only-, and NPY only-ir neurons. SOM/NPY- and SOM only-ir neurons were detectable even at the day of birth, in contrast on NPY only-ir cells which first appeared in most cortices from week two. The morphological features of double-labeled SOM/NPY neurons differed with those of SOM only- and NPY only-ir neurons. No apparent changes in the shape and size of single-labeled neurons occurred with age; throughout their postnatal life they were round and ovoid, had a thin rim of perinuclear cytoplasm, and short processes. However, the features of SOM/NPY-ir neurons were not consistent according to postnatal age; by day P7, these neurons showed immature features and they began to show more advanced neuronal characteristics by week P2, when they had a larger and more intensely-stain cytoplasm. In addition, their processes were longer, thicker and more complex than at earlier ages. At this age, SOM/NPY-ir somata were close to their near maximum size. From week P4, they became smaller and were lightly labeled. SOM/NPY-ir somata were larger than SOM only- and NYP only-ir somata at and after two weeks of age. The present results, showing different postnatal maturation patterns such as time of appearance and morphological features, raise the possibilities that double-labeled SOM/NPY and single-labeled immunoreactive neurons may be different populations regulated by different mechanisms in their development, and with different functional properties during development.

Effects of increasing gestation, cortisol and maternal undernutrition on hypothalamic neuropeptide Y expression in the sheep fetus

We have characterized the localization and the ontogenetic changes in Neuropeptide tyrosine (NPY) before birth and investigated the regulation of NPY expression by cortisol and undernutrition in the fetal sheep hypothalamus during late gestation. Using immunohistochemistry, we have identified NPY-containing neurons in the infundibular nucleus and the internal layer of the median eminence in fetal hypothalami collected between 110 and 147 days gestation. NPY projections were also present in the paraventricular nucleus (PVN) of fetal hypothalami at all ages between 110 days gestation and term. There was a significant increase in the amount of immunoreactive NPY/g hypothalamus between 87 and 113 days and 131-140 days gestation and a further significant increase after 141 days gestation. The total hypothalamic content of immunoreactive NPY increased significantly between 87 and 113 days and 141-145 days gestation. The levels of NPY mRNA: 18S rRNA in the mediobasal region of the fetal hypothalamus were significantly higher at 145-146 days gestation than at any earlier gestational age between 116 and 141 days gestation. Cortisol (2.5-3.0 mg/24 h) was infused intrafetally between 109 and 116 days gestation. The ratio of NPY mRNA: 18s rRNA in the mediobasal region of the fetal hypothalamus was significantly higher in the cortisol-infused group when compared with the saline-infused control group at 116 days gestation. Maternal, and hence fetal undernutrition, was induced between 110 and 146 days gestation. At 145-146 days gestation the ratio of NPY mRNA: 18S rRNA in the mediobasal region of the fetal hypothalamus was significantly higher in the undernutrition group when compared with control animals. We have therefore demonstrated that NPY is present in the hypothalamus of the sheep fetus before birth and that hypothalamic NPY content and NPY mRNA increase before delivery. We have also found that glucocorticoids and undernutrition stimulate increases in NPY mRNA levels in the hypothalamus before birth.

Preferential expression of the neuropeptide Y Y1 over the Y2 receptor subtype in cultured hippocampal neurons and cloning of the rat Y2 receptor

1 Neuropeptide Y (NPY) and NPY receptors are most abundant in the hippocampal formation where they modulate cognitive functions. Expression of NPY receptors in rat cultured primary hippocampal cells was investigated in the present study by use of combined molecular, pharmacological and immunohistochemical approaches, including the cloning of the rat Y2 receptor described here for the first time. 2 More than 70% of the hippocampal neurones were endowed with [125I]-[Leu31,Pro34]PYY Y1-like receptor silver grain accumulations and Y1 receptor immunostaining. These radio- and immuno-labelling signals were distributed over cell bodies and processes of bipolar, stellate and pyramidal-like neuronal cells, as confirmed by neurone-specific enolase and MAP-2 staining. 3 Competition binding profiles revealed that specific [125I]-[Leu31,Pro34]PYY binding was competitively displaced according to a ligand selectivity pattern prototypical of the Y1 receptor sub-type with [Leu31,Pro34]substituted NPY/PYY analogues >> C-terminal fragments = pancreatic polypeptides, with the non-peptide antagonist BIBP3226 being most potent. This profile excludes the possible labelling by [125I]-[Leu31,Pro34]PYY of the newly cloned Y4, Y5 and Y6 receptors. 4 The expression of the genuine Y1 receptor was confirmed by RT-PCR in hippocampal cultures. In contrast, negligible levels of Y2-like/[125I]-PYY3-36 binding were detected in these cultures in spite of the presence of its mRNA, as characterized by RT-PCR. The expression of both the Y1 and the Y2 receptor mRNAs was also noted in normal embryonic hippocampal tissues showing that signals expressed in cultured neurones were also present in utero. 5 Taken together, these results suggest that the Y1 receptor subtype may be of critical importance in the normal functioning of the rat hippocampus, especially during brain development and maturation.

Opposite effects of astrocyte-derived soluble factor(s) on the functional expression of fetal peptidergic neurons in aggregate cultures: enhancement of neuropeptide Y and suppression of somatostatin

Previous studies established that fetal rat and human neuropeptide Y (NPY) cortical neurons in aggregate cultures are differentially regulated. Whereas brain-derived neurotrophic factor (BDNF) or phorbol 12-myristate-13-acetate (PMA) induces NPY production in rat cultures, only PMA does so in human cultures. We addressed these questions: 1) Do soluble products of rat or human astrocytes (conditioned medium; rCM and hCM, respectively) enhance the functional expression of cultured NPY neurons and if so, do they enhance the expression of somatostatin (SRIF) neurons as well? 2) Is the NPY-enhancing activity (EA) in the CM species specific? rCM enhanced (approximately 2-fold) both basal and BDNF-stimulated production of NPY and coculture of rat aggregates and astrocytes did not prevent this NPY-EA. Likewise, the hCM enhanced (approximately 2.5-fold) basal and PMA-stimulated production of NPY by human aggregates. Moreover, the hCM enhanced NPY production by rat aggregates and rCM enhanced NPY production by human aggregates. In addition, rCM and hCM each enhanced BDNF-, forskolin-, or PMA-stimulated NPY production by rat aggregates. Under each of the above conditions, the rCM/hCM suppressed (approximately 50%) production of SRIF by rat aggregates. In summary, secretory products of rat and human astrocytes exert opposite effects on the functional expression of NPY and SRIF neurons in culture: enhancement of NPY and suppression of SRIF. By the criteria evaluated in this study, these astrocyte-derived activities do not exhibit species specificity.

Comparative developmental profile of the neuropeptide Y Y1 receptor gene and protein in the rat brain

Neuropeptide Y (NPY) is one of the most abundant peptides found in the mammalian central nervous system (CNS) and plays several important roles in regulating brain function. Physiological roles of NPY in the brain are mediated by at least six receptor subtypes (Y1 to Y6). In the present study, a rat Y1 receptor cRNA probe was used for in in situ hybridization experiments in order to determine the developmental profile of this receptor mRNA and to compare it with its translated protein using receptor autoradiography with the radiolabelled ligand [125I][Leu31,Pro34]PYY. The NPY Y1 receptor mRNA is expressed as early as by the 12th day of gestation while specific [125I][Leu31,Pro34]PYY binding is observed by day 14 of gestation. Thereafter, both signals steadily increased, with Y1 receptor mRNA increasing faster than its translated protein during fetal life. The in situ hybridization signals reached a plateau around birth and remained high during the first 2 post-natal weeks to display the adult distribution by the end of the 3rd post-natal week. Similarly, specific [125I][Leu31,Pro34]PYY binding constantly increased during brain maturation and reached a plateau by the end of the 3rd post-natal week. In some brain areas, such as the cerebral cortex, specific binding declined slightly before attaining its adulthood pattern. Throughout ontogenesis, the profile of both the Y1 receptor mRNA and protein was well-matched except in hypothalamic areas where relatively higher mRNA signals were observed. Taken together, these results along with previous reports describing NPY-like immunoreactivity in the early developmental rat brain, suggest that the NPY Y1 receptor may play an important role in early brain development and maturation on the basis of its very early pattern of embryonic expression.