Ontogeny of some neuropeptides in the primate brain

Localization of truncated TrkB and co-expression with full-length TrkB in the cerebral cortex of adult mice

Brain-derived neurotrophic factor (BDNF), one of the neurotrophins, and its specific receptor TrkB, are abundantly distributed in the central nervous system (CNS) and have a variety of biological effects, such as neural survival, neurite elongation, neural differentiation, and enhancing synaptic functions. Currently, there are two TrkB subtypes: full-length TrkB (TrkB-FL), which has a tyrosine kinase in the intracellular domain, and TrkB-T1, which is a tyrosine kinase-deficient form. While TrkB-FL is a typical tyrosine kinase receptor, TrkB-T1 is a main form expressed in the CNS of adult mammals, but its function is unknown. In this study, we performed fluorescent staining of the cerebral cortex of adult mice, by using TrkB-T1 antiserum and various antibodies of marker molecules for neurons and glial cells. We found that TrkB-T1 was expressed not only in neurons but also in astrocytes. In contrast, little expression of TrkB-T1 was found in oligodendrocytes and microglia. TrkB-T1 was expressed in almost all of the cells expressing TrkB-FL, indicating the direct interaction between TrkB subtypes. These findings suggest that a part of various functions of BDNF-TrkB signaling might be due to the interaction and cellular localization of TrkB subtypes in the cerebral cortex.

A review of nonhuman primate models of early life stress and adolescent drug abuse

Adolescence represents a developmental stage in which initiation of drug use typically occurs and is marked by dynamic neurobiological changes. These changes present a sensitive window during which perturbations to normative development lead to alterations in brain circuits critical for stress and emotional regulation as well as reward processing, potentially resulting in an increased susceptibility to psychopathologies. The occurrence of early life stress (ELS) is related to a greater risk for the development of substance use disorders (SUD) during adolescence. Studies using nonhuman primates (NHP) are ideally suited to examine how ELS may alter the development of neurobiological systems modulating the reinforcing effects of drugs, given their remarkable neurobiological, behavioral, and developmental homologies to humans. This review examines NHP models of ELS that have been used to characterize its effects on sensitivity to drug reinforcement, and proposes future directions using NHP models of ELS and drug abuse in an effort to develop more targeted intervention and prevention strategies for at risk clinical populations.

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ELS has long-lasting neurobiological and behavioral consequences.

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ELS is a major risk factor for the initiation of adolescent drug use.

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Sex differences are apparent in the consequences of ELS, including drug use.

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Nonhuman primate models of ELS are critical for understanding ELS effects on neurobiology and risk for adolescent drug use.

Quantification of central substance P receptor occupancy by aprepitant using small animal positron emission tomography

BACKGROUND

Central substance P receptors, termed NK-1 receptors, have been considered as therapeutic targets in the development of drugs against diverse conditions, including emesis, overactive bladder, and depression.

METHODS

Here, we applied small animal positron emission tomography (PET) and a radioligand for NK-1 receptors ([(18)F]FE-SPA-RQ) for measuring occupancies of these receptors by a selective antagonist (aprepitant) in order to examine the validity of this in vivo imaging system for preclinical characterization of candidate agents acting on NK-1 receptors, and as a tool for predicting optimal doses in humans.

RESULTS

PET in gerbils depicted high uptake in the striatum and dose-dependent displacement with increasing doses of aprepitant. Occupancies increased as a function of aprepitant plasma concentrations according to a one-site competition model, which agrees with reported occupancy-concentration relationships in clinical studies after correction for species differences in plasma protein-unbound aprepitant fractions. These occupancy data were further supported by ex vivo autoradiography of brain samples from aprepitant-treated gerbils. In a pilot study of a marmoset, we obtained more accurate determinations of NK-1 receptor occupancy, less affected by spillover of signals from extracranial tissues than in gerbil experiments.

CONCLUSIONS

These findings support the utility of small animals and quantitative PET in the development of drugs targeting NK-1 receptors.

A new aspect of the TrkB signaling pathway in neural plasticity

In the central nervous system (CNS), the expression of molecules is strictly regulated during development. Control of the spatiotemporal expression of molecules is a mechanism not only to construct the functional neuronal network but also to adjust the network in response to new information from outside of the individual, i.e., through learning and memory. Among the functional molecules in the CNS, one of the best-studied groups is the neurotrophins, which are nerve growth factor (NGF)-related gene family molecules. Neurotrophins include NGF, brain-derived neurotrophic factor (BDNF), neurotrophin 3 (NT-3), and NT-4/5 in the mammal. Among neurotrophins and their receptors, BDNF and tropomyosin-related kinases B (TrkB) are enriched in the CNS. In the CNS, the BDNF-TrkB signaling pathway fulfills a wide variety of functions throughout life, such as cell survival, migration, outgrowth of axons and dendrites, synaptogenesis, synaptic transmission, and remodeling of synapses. Although the same ligand and receptor, BDNF and TrkB, act in these various developmental events, we do not yet understand what kind of mechanism provokes the functional multiplicity of the BDNF-TrkB signaling pathway. In this review, we discuss the mechanism that elicits the variety of functions performed by the BDNF-TrkB signaling pathway in the CNS as a tool of pharmacological therapy.

Distribution and pharmacological characterization of primate NK-1 and NK-3 tachykinin receptors in the central nervous system of the rhesus monkey

Much attention has focused on tachykinin receptors as therapeutic targets for neuropsychiatric disorders, although their expressional distributions in the primate central nervous system (CNS) remain unclear. We cloned the genes encoding the NK-1 and NK-3 tachykinin receptors (referred to as rmNK-1 and rmNK-3) from the rhesus monkey (Macaca mulatta) brain and examined their pharmacological profiles and regional distributions in the CNS. The deduced rmNK-1 amino-acid sequence differed by only two amino acids from the human NK-1 (hNK-1). The deduced rmNK-3 amino-acid sequence was two amino acids shorter than human NK-3 (hNK-3), with a seven-amino-acid difference in sequence. Ligand binding studies revealed that the affinity of rmNK-1 to substance P (SP) was comparable to that of hNK-1 in cell lines that expressed individual receptors stably. Nonpeptide antagonists had similar effects on the binding of rmNK-1 and hNK-1. Affinity of rmNK-3 for NKB was stronger than for SP and the IC50 value was comparable with that of hNK-3. Ca2+ imaging showed that activations of both rmNK-1 and rmNK-3 by specific ligands, SP and senktide, induced increased intracellular Ca2+ in cell lines that stably expressed individual primate tachykinin receptors. The amounts of rmNK-1 and rmNK-3 mRNAs were quantitatively determined in the monkey CNS. The expression of rmNK-1 was observed in all of the cortical and subcortical regions, including the hippocampus and the amygdala. The putamen contained the most NK-1 mRNA in the brain, with less rmNK-3 mRNA found in the cortex compared to rmNK-1 mRNA. In the monkey hippocampus and amygdala, rmNK-1 mRNA was present at markedly higher concentrations than rmNK-3 mRNA. The present results provide an insight into the distinct physiological nature and significance of the NK-1 and NK-3 tachykinin systems in the primate CNS. These findings are indispensable for establishing model systems in the search for a subtype-specific tachykinin receptor agonist and antagonist for the treatment of neuropsychiatric disorders.

Heterogeneity of the developmental patterns of neurotrophin protein levels among neocortical areas of macaque monkeys

Based on morphological and physiological characteristics, the mammalian neocortex is divided into various neocortical areas and its diversity is prominent in the primates including humans. These neocortical areas are constructed during development, but the details of the developmental events remain unclear, especially at the molecular level. We measured the mRNA and protein levels of neurotrophins in various neocortical areas of developing rhesus monkeys. The expression patterns of both the neurotrophin-3 (NT-3) mRNA and the protein showed area differences. In the sensory and motor areas, NT-3 mRNA and protein levels had started to decline by a week after birth. In contrast, the levels declined after the third postnatal week in the association neocortical areas. The level of brain-derived neurotrophic factor (BDNF) protein changed in an area-dependent manner during development, but that of mRNA did not. The decline of the BDNF protein level started earlier in the sensory and motor neocortical areas than in the association neocortical areas, suggesting that sensory and motor neocortical areas develop earlier than the association areas in terms of the developmental changes in neurotrophins.

Expression of BDNF and TrkB receptor subtypes in the postnatal developing Purkinje cells of monkey cerebellum

In the previous study, we have shown the complementary expression of TrkB subtypes (TK+ and T1) in the adult monkey cerebellar cortex. In this study, to clarify when that expression pattern appeared, we examined the expressions of TrkB subtypes and its ligand brain-derived neurotrophic factor (BDNF) by immunohistochemistry and Western blot analysis. At the newborn stage, both TK+ and T1 were expressed uniformly in the cerebellar cortex. At postnatal month 3.5, the uneven expression of TrkB subtypes was observed, while the BDNF immunoreactivity was strongly detected in all regions of the cerebellar cortex. The expression patterns of TrkB subtypes and BDNF at both postnatal month 6 and year 7 were the same as those at postnatal month 3.5. Western blot analysis demonstrated that TK+ and T1 were expressed at high levels in the synaptic membrane from newborn to adult stages. Furthermore, the dimerization of TrkB subtypes changed at postnatal month 3, which was similar to the adult pattern: at the newborn stage, the TK+ and TK- homodimers; after postnatal month 3.5, the TK+ and TK- homodimers, and the TK+/TK- heterodimer. These findings suggest that the localization of TrkB subtypes in each Purkinje would be changed at postnatal month 3.5, resulting in the uneven expression of TrkB subtypes and the change of TrkB dimerization.

Expression of occ1 mRNA in the visual cortex during postnatal development in macaques

We previously reported that the occ1 gene is specifically expressed in the primary visual cortex of adult monkeys in an activity-dependent manner (Tochitani et al., Eur. J. Neurosci., 3, 297-307, 2001). In this report, we compared occ1 mRNA expression in the primary visual cortex during the development of newborn, 3-month-old and adult monkeys. occ1 mRNA was already expressed preferentially in the primary visual cortex of newborn monkeys, but the laminar pattern of occ1 expression in the visual cortex changed as development proceeded. This suggests the possible importance of experience-dependent developmental regulations of occ1 in the developing primary visual cortex.

Changes in NT-3 and TrkC in the primary visual cortex of developing macaques

In the present study, we measured the levels of neurotrophin-3 (NT-3) protein and mRNA by ELISA and quantitative RT-PCR, and examined TrkC-immunoreactive structures using immunohistochemical method. In the nervous system of the adult monkey, higher levels of NT-3 were found in the hippocampus and cerebellum. During the development of the primary visual cortex, detected amounts of NT-3 protein peaked at embryonic day 140 and then gradually decreased. TrkC imunoreactivity was observed in the neurons in layer VI of the primary visual cortex of an embryonic monkey. These results support the hypothesis that NT-3 is involved in the specification of axon targeting from layer VI to layer IV during the late embryonic stages.

TrkB dimerization during development of the prefrontal cortex of the macaque

To date, two subtypes of TrkB, a BDNF receptor, have been described. One is full-length TrkB (TK+), which has a tyrosine kinase-containing intracellular domain. The other is truncated TrkB (TK-), which has a short intracellular domain lacking the tyrosine kinase. In this study, we investigated the dimerization of TrkB subtypes in the developing monkey prefrontal cortex by means of cross-linking. At embryonic day 120, the TK+/TK+ and the 100 kDa/100 kDa homodimers were observed with BDNF stimulation. At the newborn stage, the TK+/TK+ and the TK-/TK- homodimers were observed with BDNF stimulation. At the adult stage, the TK-/TK- homodimer and the TK+/TK- heterodimer were formed by BDNF stimulation. The levels of all dimers increased in proportion to the concentration of BDNF. Moreover, the dimers were clearly formed within 5 min of treatment with BDNF. BDNF and NT-4/5 induced the dimers, whereas NT-3 formed slight dimers but NGF did not. Furthermore, anti-BDNF antibody inhibited the TrkB dimerization. Moreover, the intercellular binding proteins of TrkB were not cross-linked by BS3. Therefore, these results suggest that the change in dimerization among TrkB subtypes occurs during development of the monkey prefrontal cortex.

Prenatal blockade of vasoactive intestinal peptide alters cell death and synaptic equipment in the murine neocortex

Vasoactive intestinal peptide (VIP) is a potent growth factor that stimulates murine neocortical astrocyte genesis during the period of ontogenesis corresponding to premature delivery in humans. In rodents, part of the VIP supplied to the fetal brain is maternal VIP that crosses the placenta. If these data also apply to human brain development, premature newborns may be partly VIP-deficient because of loss of the maternal supply, and this may adversely affect their brain development. The goal of the present study was to determine the effects of VIP blockade during mouse neocortical astrocyte genesis on neuritic survival and maturation. VIP blockade by a specific VIP antagonist on embryonic d 17 and 18 induced transient, postnatal depletion of astrocytes in the upper neocortical layers. Combined use of in situ DNA fragmentation analysis (terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling method, a marker of cell death); immunohistochemical detection of synaptophysin, microtubule-associated proteins, and neurofilaments; and quantification of mRNA for synaptophysin and N-methyl-D-aspartate R1 receptor subunit revealed that early VIP blockade significantly altered programmed neuritic death and impaired neuritic differentiation. VIP inhibition induced 1) exaggerated postnatal terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling of cortical neurons, 2) long-term overexpression of synaptophysin and N-methyl-D-aspartate R1 receptor subunit, and 3) long-term overexpression of microtubule-associated protein-5 and neurofilament 160 kD. Although the functional consequences of this deviant pattern of murine neocortical development remain to be determined, these data open up new avenues for investigating some of the cognitive deficits observed in human premature infants.

Change of expression of full-length and truncated TrkBs in the developing monkey central nervous system

We examined the expression of full-length TrkB (TrkBTK+) and truncated TrkB (TrkBTK-) in the central nervous system (CNS) of the macaque monkey (Macaca fascicularis) using a western blot analysis. At the adult stage, the levels of TrkBTK+ in cerebral cortices were higher than those in other structures of CNS and the expressions of TrkBTK+ in the association cortices (except area PE) were relatively lower than those in the primary cortices. In contrast, TrkBTK- in the hippocampus and the cerebellum was significantly higher than in other structures. In various developing cerebral cortices, TrkBTK+ was detected at the same levels from embryonic day 120 (E120) to the adult period. In contrast, the expression of TrkBTK- increased remarkably after the newborn stage (NB), reached the maximum level at postnatal day 60 (P60) and maintained the same level into adulthood. The peaks of TrkBTK- in the association cortices were more delayed than in the primary cortices. The expression of TrkBTK- occurred at a time that correlates with the elimination of axons and the down-regulation of neuropeptides. The present study suggests that TrkBTK- plays an important role in the axonal remodelling and that it may act as a negative effector of TrkBTK+ in the primate CNS, reducing responsiveness to BDNF and/or NT-4/5.

Development of GAP-43 mRNA in the macaque cerebral cortex

To estimate the extent of axonal growth in various areas of the cerebral cortex, we measured the amount of GAP-43 mRNA in the cerebral cortex of developing macaque monkeys. In four areas, i.e., the prefrontal area (FD delta), the temporal association area (TE), the primary somatosensory area (PC), and the primary visual area (OC), the amount of GAP-43 mRNA was measured from the intermediate fetal period [embryonic day 120 (E120)] to the adult stage. In two other areas, i.e., the parietal association area (PG) and the secondary visual area (OB), the amount of GAP-43 mRNA was measured during the postnatal period. The amount of GAP-43 mRNA was highest at E120, decreased roughly exponentially, and approached the asymptote by postnatal day 70 (P70). The amount of GAP-43 mRNA was higher in the association areas (FD delta, TE, and PG) than in the primary sensory areas (PC and OC) during development and at the adult stage. These findings suggest that axonal growth in the cerebral cortex is most exuberant before or during the intermediate fetal period and approximately ends by P70. Furthermore, axonal growth is evidently more intensive in the association areas than in the primary sensory areas during the stage following the intermediate fetal period.

Chronic exposure to either somatostatin (SS) or octreotide, a long-lasting SS analogue, affects SS expression in the postnatal visual cortex of the rat

The peptide somatostatin (SS) is widely distributed in the mammalian brain where it modulates neuronal activity through interactions with specific membrane-bound receptor subtypes (ssts). Five different ssts were characterized so far (sst1-5) and their selective agonists were developed on the basis of their binding specificity. SS and ssts are transiently expressed in the developing brain, suggesting a functional role of somatostatinergic systems in neuronal maturation. In the present study, we investigated the effects of chronic exposure to either the SS synthetic analogue, SS-14 or octreotide (a long-acting sst2-preferring analogue) on the maturation of SS-immunoreactivity (-ir) in the primary visual cortex of the rat. SS-ir maturation was investigated both by an evaluation of the number of SS-immunoreactive cells and by radioimmunoassay (RIA) to measure the levels of SS in the postnatal visual cortex. In the visual cortex of normal rats, the number of SS-positive cells markedly increased during the second postnatal week and then significantly decreased until the adult value was reached at the third week. Early and repeated intracerebroventricular (i.c.v.) injections of either SS-14 or octreotide prevented the increase in the number of SS-positive cells, with adult values reached at the end of the first postnatal week. Similarly, administration of either SS-14 or octreotide significantly decreased the SS content of the visual cortex, measured at the end of the second postnatal week. These results show that high local concentrations of either SS-14 or octreotide interfere with SS expression in developing cortical neurons in a restricted postnatal period.

Vasoactive intestinal peptide prevents excitotoxic cell death in the murine developing brain

Excitotoxic damage may be a critical factor in the formation of brain lesions associated with cerebral palsy. When injected at birth, the glutamatergic analog ibotenate induces mouse brain lesions that strikingly mimic human microgyria. When ibotenate is injected at postnatal day 5, it produces transcortical necrosis and white matter cysts that mimic human perinatal hypoxic-like lesions. Vasoactive intestinal peptide (VIP) has potent growth-related actions and neuroprotective properties that influence mitosis and neuronal survival in culture. The goal of this study was to assess the protective role of VIP against excitotoxic lesions induced by ibotenate in developing mouse brain. VIP cotreatment reduced ibotenate-induced microgyric-like cortical lesions and white matter cysts by up to 77 and 85%, respectively. VIP protective effects were reproduced by a peptide derived from activity-dependent neurotrophic factor (ADNF), a trophic factor released by VIP-stimulated astrocytes, and by stearyl norleucine VIP, a specific VIP agonist that does not activate adenylate cyclase. Neither forskolin, an adenylate cyclase activator, nor pituitary adenylate cyclase-activating peptide, provided VIP-like protection. VIP and neurotrophic analogs, acting through a cAMP-independent mechanism and inducing ADNF release, could represent new avenues in the understanding and prevention of human cerebral palsy.

Somatostatin and brain-derived neurotrophic factor mRNA expression in the primate brain: decreased levels of mRNAs during aging

The expression of the genes for somatostatin (SRIF) and brain-derived neurotrophic factor (BDNF) was investigated in the central nervous system (CNS) of the macaque monkey (Macaca fuscata fuscata). Using Northern blot analysis, one SRIF mRNA transcript, 0.65 kb, and two BDNF mRNA transcripts, 1.6 and 4.0 kb in length, were detected in the monkey brain tissues. During the aging process (2 years, 10 years, and > 30 years), the ratio of SRIF mRNA/glyceraldehyde-3 phosphate dehydrogenase (G3PDH) mRNA significantly decreased (60-70%) in the hippocampus and in several cerebral subdivisions such as frontal cortex, temporal cortex, motor cortex, somatosensory cortex and visual cortex. BDNF mRNA was expressed in the various cerebral subdivisions and in the hippocampus. During the aging process, the gene expression of BDNF declined (20-50% for the 4.0 kb transcript, and 40-70% for the 1.6 kb transcript) in the various cerebral subdivisions. In the hippocampus, the level of the 1.6 kb mRNA at > 30 years old declined to 60% of the level at 2 years old, while the 4.0 kb mRNA did not change significantly during the aging process. Recent studies have shown that BDNF enhances the expression of SRIF mRNA in the rodent cerebral cortex (Nawa, H. et al., J. Neurochem., 60 (1993) 772-775; Nawa, H. et al., J. Neurosci., 14 (1994) 3751-3765). These studies and our present results suggest that the decrease in gene expression for a neurotrophic molecule, such as BDNF, might cause the levels of SRIF mRNA to decline in the primate brain during the aging process.

Neurotrophins and the primate central nervous system: a minireview

The central nervous system (CNS) of primates is more complex than the CNS of other mammals. Details of the development and aging of the primate CNS have recently been revealed by various neurobiological techniques. It has become clear that the primate CNS has unique characteristics, for example, the capacity for the overproduction and elimination of fibers and synapses. Some differences have also been found in the distribution of and changes with development in levels of various neuroactive substances. Recent discoveries of a variety of neurotrophins in the mammalian CNS have led to research on the neurobiology of these molecules in the primate CNS. The distribution of and changes with development in levels of nerve growth factor (NGF) in the primate CNS are closely correlated with the cholinergic system of the basal forebrain. The administration of NGF into the monkey brain prevents the degeneration of the cholinergic neurons of the basal forebrain after axotomy, a result that suggests that neurotrophins might be very valuable agents for the future treatment of neurological diseases, such as Alzheimer's and Parkinson's diseases.

A novel action of angiotensin peptides in inhibiting neurite outgrowth from isolated chick sympathetic neurons in culture

There is increasing evidence that neuropeptides have trophic functions during embryogenesis. We examined the ability of angiotensin II, substance P, somatostatin-28 and luteinising hormone-releasing hormone to influence neurite outgrowth from embryonic chick sympathetic neurons in culture. Nanomolar concentrations of angiotensin II inhibited neurite outgrowth, whereas the other peptides had no effect at similar concentrations. The effect of angiotensin II on neurite outgrowth is likely to be mediated by an atypical angiotensin receptor, as it was only weakly inhibited by [sar1,ala8]angiotensin II, and was not inhibited by losartan, an inhibitor of mammalian AT1 receptors, or PD123319, an AT2 inhibitor. Neurite outgrowth was also inhibited by angiotensin III and angiotensin IV but not by angiotensinogen I1-14. The study provides further evidence that angiotensin peptides, like classical neurotransmitters, may have trophic functions during embryogenesis.

Peptidergic transmission: from morphological correlates to functional implications

Like non-peptidergic transmitters, neuropeptides and their receptors display a wide distribution in specific cell types of the nervous system. The peptides are synthesized, typically as part of a larger precursor molecule, on the rough endoplasmic reticulum in the cell body. In the trans-Golgi network, they are sorted to the regulated secretory pathway, packaged into so-called large dense-core vesicles, and concentrated. Large dense-core vesicles are preferentially located at sites distant from active zones of synapses. Exocytosis may occur not only at synaptic specializations in axonal terminals but frequently also at nonsynaptic release sites throughout the neuron. Large dense-core vesicles are distinguished from small, clear synaptic vesicles, which contain "classical' transmitters, by their morphological appearance and, partially, their biochemical composition, the mode of stimulation required for release, the type of calcium channels involved in the exocytotic process, and the time course of recovery after stimulation. The frequently observed "diffuse' release of neuropeptides and their occurrence also in areas distant to release sites is paralleled by the existence of pronounced peptide-peptide receptor mismatches found at the light microscopic and ultrastructural level. Coexistence of neuropeptides with other peptidergic and non-peptidergic substances within the same neuron or even within the same vesicle has been established for numerous neuronal systems. In addition to exerting excitatory and inhibitory transmitter-like effects and modulating the release of other neuroactive substances in the nervous system, several neuropeptides are involved in the regulation of neuronal development.

Early neuroblasts are pluripotential: colocalization of neurotransmitters and neuropeptides

This study was undertaken in order to establish the presence of pluripotential neuroblasts in the developing chick CNS. This has been suggested by our previous observations that expression of emerging neuronal phenotypes in the chick embryo CNS is affected by exposure to neurotrophic substances (i.e., GHRH, SRIF, NGF, EGF, muscle-derived factors) or neurotoxins such as ethanol. We have proposed that one mechanism whereby these substances elicit their effects is by shifting phenotypic expression in populations of pluripotential neuroblasts. In order to establish the presence of significant populations of pluripotential neuroblasts, cultures obtained from 3-day-old whole chick embryos (E3WE) were double-stained with antibodies to markers specific for four neuronal phenotypes in various permutations. Cultures at 6 DIV were tested for the presence of tyrosine hydroxylase (TH), choline acetyltransferase (ChAT), gamma-aminobutyric acid (GABA), and somatostatin (SRIF) alone, and in various combinations. We observed a colocalization of all phenotypic markers within neuronal perikarya and processes in more than fifty percent of neuronal cells in these cultures. These data suggest that developing neuroblasts at this stage of embryogenesis possess the machinery necessary to adopt multiple neuronal phenotypes. The colocalization of neurotransmitter proteins in early neuroblasts (60 hr of embryogenesis) supports the recent concept that these substances themselves may influence phenotypic expression and also supports our idea that microenvironmental factors (i.e., ethanol, growth factors) provide signals which affect emerging phenotypes.

Lipid profiles of cerebral gray matter and livers of macaque monkeys Macaca fascicularis and Macaca fuscata fuscata: a comparative study during development

The lipid and fatty acid profiles in cerebral gray matter and livers were studied in macaque monkeys (Macaca fascicularis and M. fuscata fuscata) of different ages. In cerebral gray matter, the phosphatidylcholine/phosphatidylethanolamine (PC/PE) ratio decreased in animals more than 3 years old, while the cholesterol/lipid-phosphorus ratios and the unsaturation indices increased, as compared with those in fetuses and newborns. The level of 22:6n-3 in PE of cerebral gray matter increased up to 3 years old, mainly by replacing 20:4n-6, whereas the level in phosphatidylserine did not change significantly with age. The hepatic lipid-phosphorus levels and PC/PE ratios were lower in newborns than in animals more than 3 years old. The level of 22:6n-3 in liver phospholipid did not change, while that of 20:4n-6 was lower in animals more than 3 years old than in newborns.

Neuroactive substances in the developing dorsomedial telencephalon of the pigeon (Columba livia): differential distribution and time course of maturation

The avian hippocampal formation has previously been shown to contain many of the same neurotransmitters and related enzymes that are found in mammals. In order to determine whether the relatively delayed development of the mammalian hippocampus is typical of other vertebrates, we investigated the maturation of a variety of neuroactive substances in the hippocampal formation of the homing pigeon. The distribution of two transmitter-related enzymes, choline acetyltransferase (ChAT) and tyrosine hydroxylase (TH), the neurotransmitter GABA, and four neuropeptides (substance P, enkephalin, neuropeptide Y, and somatostatin) was studied by immunohistochemistry in the developing hippocampal complex. The pattern and/or the time course of changes in the distribution of immunoreactivity varied among the different neuroactive substances examined. Immunoreactivity to ChAT and TH was found exclusively in fibers and terminal-like processes, whereas GABA and peptide immunoreactivity was seen in cells and neuropil. Quantitative differences in the density, number, and size of stained cells were assessed by a computer-assisted image analyzer. For the majority of the substances, developmental patterns in the distribution of immunoreactivity differ between the hippocampus proper and the area parahippocampalis, the two major areas that together make up the avian hippocampal complex. The adult pattern of immunoreactivity was generally attained by 3 weeks after hatching. For many of the neuroactive substances found in cell bodies, there was a gradual decrease in the density of immunoreactive cells with a concomitant increase in the density of immunoreactive neuropil. The actual number of stained cells usually increased to a peak at 9 days posthatching and then declined until 3 weeks posthatching, when the adult value was reached. These results are discussed in relation to the advantages that the pigeon hippocampal complex may provide in the study of developmental processes. Parallels with the distribution of the same neuroactive substances in the mammalian hippocampus are used to suggest possible functional similarities between the avian and mammalian hippocampal regions.

Intracortical regionality represented by specific transcription for a novel protein, latexin

The monoclonal antibody (mAb) PC3.1 recognizes a subset of neurons distributed in the infragranular layers of the lateral neocortex of the rat. Immunoaffinity chromatography with mAb PC3.1 showed that this antibody specifically binds a peptide epitope on a 29 kDa protein named latexin. To study the molecular details of the protein, we isolated four independent cDNA clones for latexin from cDNA libraries of the rat cerebral cortex and whole brain using the amino acid sequences of latexin fragments. Analysis of these cDNA clones showed that the predicted primary structure of latexin consists of 223 amino acids, and has no strict homology to any sequences so far known. Western and Northern blots demonstrated that the latexin and its mRNA were expressed predominantly in neural tissues with some expression in non-neural tissues. The gene that encodes latexin in the rat appeared to have homologues in other mammalian species and in the chick. In situ hybridization showed that latexin mRNA is synthesized in a subset of neurons in the lateral but not the dorsal neocortex, and that the distribution profile of these neurons is quite similar to that of neurons expressing latexin. These results indicate that latexin is a novel class of neuronal protein which represents intracortical regionality, and suggest that the regional specification of the neocortex involves selective parcellation of neurons which express a particular gene.

Maturation of somatostatin immunoreactivity in the pigeon retina: morphological characterization and quantitative analysis

In addition to a modulatory function, somatostatin (SS) is likely to exert a morphogenetic and/or trophic role in the developing nervous system. In this study, a mouse monoclonal antibody directed to SS was used to investigate the posthatching development of SS-immunoreactivity (SS-ir) in the pigeon retina to provide a basis for a better understanding of the role of this peptide in retinal maturation. In the adult, SS-ir was observed in amacrine cells located in the inner nuclear layer (INL) of the entire retina. Two cell types were recognized according to their morphology. They showed a differential density distribution. Cell type indicated as "adult 1" (AD1) was characterized by pear-shaped cell bodies with single primary processes directed to the inner plexiform layer (IPL) and was mostly present in the red field. In contrast, cell type indicated as "adult 2" (AD2) was characterized by round-shaped somata with 1-3 primary processes and was highly represented in the fovea and the dorsal periphery. Posthatching maturation of the pigeon retina was characterized by drastic changes in the pattern of SS-ir. Over the first days posthatching, SS-ir was observed in sparsely distributed somata mostly located in the ganglion cell layer (GCL). This cell type indicated as "hatch" (H) was characterized by dense granular staining and became extremely rare at 7 days. Over the same period, growing SS-positive axons displaying enlarged growth cones were found in the optic tract (TrO). These observations suggest the possibility that ganglion cells transiently expressing SS are present at early stages of posthatching development. Of the two types of SS-containing cells observed in the adult, the first to be recognized morphologically was cell type AD1 which appeared at 2 days after hatching in the INL. These cells were virtually adult-like in morphology by 7 days. In contrast, cell type AD2 was not apparent until 7 days posthatching. The density (defined as number of cells/mm2 of retinal tissue) and the total number of SS-containing cells changed during posthatching maturation. In particular, the adult number of cell type AD1 was reached at about 10 days, while the number of cell type AD2 was reached at about 3 weeks posthatching. At this stage, both cell types also displayed their mature density distribution. The present findings suggest a temporal relationship between the maturation of SS-ir and developmental events which include the onset of light-driven activity and the maturation of retinal acuity.(ABSTRACT TRUNCATED AT 400 WORDS)

Postnatal development of the cholecystokinin innervation of monkey prefrontal cortex

Although the structure and function of primate prefrontal cortex undergo substantial modifications during postnatal development, relatively little is known about the maturation of neurotransmitter systems in these cortical regions. In the primate brain, cholecystokinin is present in the greatest concentrations in prefrontal regions. Thus, in this study, we used immunohistochemical techniques to investigate the postnatal development of the cholecystokinin innervation of monkey prefrontal cortex. In animals aged 4 days through adult, cholecystokinin immunoreactivity was present in nonpyramidal neurons that appeared to represent at least two distinct cell types. The most common type was a vertically oval bitufted neuron, located in layers II-superficial III, which typically had a radially descending axon that gave rise to short collaterals in layer IV. Another frequently observed cell type was a larger multipolar neuron located in the superficial half of layer III. The axon of these neurons branched locally in the vicinity of the cell body. The greatest density of cholecystokinin-containing neurons and processes was present in monkeys less than 1 month of age. The density of immunoreactive structures in every prefrontal region then progressively declined with increasing age, with the most marked changes occurring during the first postnatal year. As a result, the density of labeled neurons in adult monkeys was less than one-third of that in neonatal monkeys. However, labeled structures were significantly more dense in some ventromedial and orbital regions than in dorsal regions of the prefrontal cortex in neonatal, but not in older animals. In all animals, cholecystokinin-containing neurons were present in highest density in layers II-superficial III, and labeled terminal fields were observed in layers II, IV, and VI. In animals less than 1 month of age, fascicles of radial fibers traversed through layers III and V, whereas in animals 1 to 3 months of age, individual radial fibers rather than fiber bundles were present in layers III and V. In addition, immunoreactive pericellular arrays, which appeared to surround unlabeled nonpyramidal cells, were present in layers V and VI and the subcortical white matter in the youngest monkeys. Although many aspects of the cholecystokinin innervation of monkey prefrontal cortex remain constant during postnatal life, the distinct developmental changes in the cholecystokinin innervation of these regions suggest that it may play an important role in the maturation of the cortical circuitry that mediates the acquisition of certain cognitive abilities.

Rabbit procathepsin E and cathepsin E. Nucleotide sequence of cDNA, hydrolytic specificity for biologically active peptides and gene expression during development

The structure of rabbit procathepsin E was determined by molecular cloning of its cDNA. The proenzyme consisted of 379 amino acids and had structural features common to human and guinea-pig procathepsin E species. The highly conserved tripeptide sequence at the active site of aspartic proteinases, Asp-Thr(Ser)-Gly, is, however, replaced by Asp-Thr-Val in rabbit procathepsin E. To our knowledge, this is the first case of such a variation in aspartic proteinases. The processed form, cathepsin E, hydrolyzed various biologically active peptides maximally at around pH5. Tachykinins, such as substance P and neurokinin A, were hydrolyzed most rapidly, with specific cleavage of sequences essential for their activity. The rates of hydrolysis were several hundred-fold higher than those of cathepsin D. Furthermore, cathepsin E was able to inactivate a functional-domain peptide of fibroblast growth factor, the sequence of which resembles those of tachykinins, and it was active in the generation of functional peptides, such as endothelin and angiotensin I, from their respective precursors. Procathepsin E was detected at high levels in various fetal tissues, such as the liver, stomach and blood cells. At the adult stage, the proenzyme was detectable only in specific tissues, such as the urinary bladder, duodenum and colon. Northern-blot analysis showed similar stage-specific and tissue-specific expression of the mRNA for procathepsin E. Since tachykinins and other suited peptide substrates of cathepsin E have been shown to have mitogenic activity, (pro)cathepsin E may regulate the growth and differentiation of embryonic and fetal tissues by degrading or processing these peptides. The enzyme may also regulate the physiological activities of adult tissues which are mediated by substance P and related tachykinins.

Expression of the gene for nerve growth factor (NGF) in the monkey central nervous system

The expression of the gene for nerve growth factor (NGF) was examined in the central nervous system of adult and fetal monkeys. In adults, the highest level of NGF mRNA was found in the hippocampus and relatively high levels were observed in the cerebral cortices and thalamus. NGF mRNA was also detected in the cerebellum and the caudate nucleus. In the spinal cord, there was no evidence of the mRNA. The levels of NGF mRNA were closely correlated with those of NGF. At embryonic day 140 (E140), levels of NGF mRNA in the visual cortex and cerebellum were three times higher than those at the adult stage. Our previous study on the ontogeny of NGF (Hayashi, M. et al., Neuroscience, 36 (1990) 683-689) showed that the level of NGF in the visual cortex at E140 is the same as that at adult stage. Thus, at the fetal stage, NGF may be actively transported from the cerebral cortex to other regions of the brain, such as the basal forebrain area. By contrast, the levels of NGF and NGF mRNA in the cerebellum were almost the same at the adult and fetal stages, suggesting that NGF, which is synthesized in the cerebellum, may be taken up locally by cerebellar cells.

Endocrinology and the psychiatrist

Objective:Exegetic review of the three areas of common interest to the endocrinologist and the psychiatrist.Method:Literature review through Science Citation Index and references in BMJ, Lancet, Nature, and Science.Findings:Psychiatric symptoms, specific in each condition, may develop in the course of a classical endocrinopathy. Though introduced as a possible diagnostic aid, titration of the hypothalamico-pituitary control of the adrenal and thyroid glands has proved to be a useful research strategy and possible prognostic indicator in affective disorders. Growth in our knowledge of the behaviour effects, distribution, function and pathophysiology of neuropeptides during the last two decades opens a magic casement on their potential value in neuropsychiatric theory and therapy.Conclusion:The psychiatrist ignores endocrinology at his peril, as does the endocrinologist psychiatry, especially in regard to the emerging role of peptides in neuromodulation.

Somatostatin-like immunoreactivity in the pigeon visual system: developmental expression and effects of retina removal

The distribution of somatostatin (SS)-containing neurons was investigated by immunocytochemical methods in the central visual system of adult, developing, and retina-ablated pigeons. In normal adult brains, SS-positive cells and processes were present in the optic tectum, the nucleus of the basal optic root, the visual Wulst, and the ectostriatum. During development, progressive increase or decrease in the numerical density and the total number of SS-containing neurons occurred as determined by quantitative analysis. Changes in SS immunoreactivity also occurred as a consequence of unilateral and bilateral retina removal immediately after hatching, i.e. before retinofugal connections have been established. In spite of the segregation of visual inputs due to the almost completely crossed retinal projections, unilateral and bilateral deafferentation differentially affected SS-containing visual regions. In addition, different effects were observed on the relative packing density of labeled cells as compared to their total number. A possible role of retinal axons in regulating the distribution of SS immunoreactivity was suggested by its altered expression induced by retinal deafferentation. In addition, parallels with the distribution of SS immunoreactivity in the pigeon's visual system were used to suggest possible equivalence between cell populations in the avian and the mammalian brains.