Sensitization of restraint-induced corticosterone secretion after chronic restraint in rats: involvement of 5-HT₇ receptors

Serotonin (5-HT) modulates the hypothalamic-pituitary-adrenal (HPA) axis response to stress. We examined the effect of chronic restraint stress (CRS; 20 min/day) as compared to control (CTRL) conditions for 14 days, on: 1) restraint-induced ACTH and corticosterone (CORT) secretion in rats pretreated with vehicle or SB-656104 (a 5-HT₇ receptor antagonist); 2) 5-HT₇ receptor-like immunoreactivity (5-HT₇-LI) and protein in the hypothalamic paraventricular nucleus (PVN) and adrenal glands (AG); 3) baseline levels of 5-HT and 5-hydroxyindolacetic acid (5-HIAA), and 5-HIAA/5-HT ratio in PVN and AG; and 4) 5-HT-like immunoreactivity (5-HT-LI) in AG and tryptophan hydroxylase (TPH) protein in PVN and AG. On day 15, animals were subdivided into Treatment and No treatment groups. Treatment animals received an i.p. injection of vehicle or SB-656104; No Treatment animals received no injection. Sixty min later, Treatment animals were either decapitated with no further stress (0 min) or submitted to acute restraint (10, 30, 60 or 120 min); hormone serum levels were measured. No Treatment animals were employed for the rest of measurements. CRS decreased body weight gain and increased adrenal weight. In CTRL animals, acute restraint increased ACTH and CORT secretion in a time of restraint-dependent manner; both responses were inhibited by SB-656104. Exposure to CRS abolished ACTH but magnified CORT responses to restraint as compared to CTRL conditions; SB-656104 had no effect on ACTH levels but significantly inhibited sensitized CORT responses. In CTRL animals, 5-HT₇-LI was detected in magnocellular and parvocellular subdivisions of PVN and sparsely in adrenal cortex. Exposure to CRS decreased 5-HT₇-LI and protein in the PVN, but increased 5-HT₇-LI in the adrenal cortex and protein in whole AG. Higher 5-HT and 5-HIAA levels were detected in PVN and AG from CRS animals but 5-HIAA/5-HT ratio increased in AG only. Finally, whereas 5-HT-LI was sparsely observed in the adrenal cortex of CTRL animals, it strongly increased in the adrenal cortex of CRS animals. No TPH protein was detected in AG from both animal groups. Results suggest that CRS promotes endocrine disruption involving decreased ACTH and sensitized CORT responses to acute restraint. This phenomenon may be associated with increased function and expression of 5-HT₇ receptors as well as 5-HT turnover in AG.

Speciation, phenotypic variation and plasticity: what can endocrine disruptors tell us?

Phenotype variability, phenotypic plasticity, and the inheritance of phenotypic traits constitute the fundamental ground of processes such as individuation, individual and species adaptation and ultimately speciation. Even though traditional evolutionary thinking relies on genetic mutations as the main source of intra- and interspecies phenotypic variability, recent studies suggest that the epigenetic modulation of gene transcription and translation, epigenetic memory, and epigenetic inheritance are by far the most frequent reliable sources of transgenerational variability among viable individuals within and across organismal species. Therefore, individuation and speciation should be considered as nonmutational epigenetic phenomena.

The age-dependent change in olfactory periglomerular neuronal populations is not affected by interrupting subventricular neuroblast migration in adult rats

The olfactory bulb (OB) is rich in the number and variety of neurotransmitter and neuropeptide containing cells, in particular in the glomerular layer. Several reports suggest that numbers of some periglomerular phenotypes could change depending on age. However, it is unclear whether the different classes of periglomerular interneurons are modified or are maintained stable throughout life. Thus, our first objective was to obtain the absolute number of cells belonging to the different periglomerular phenotypes at adulthood. On the other hand, the olfactory bulb is continously supplied with newly generated periglomerular neurons produced by stem cells located in the subventricular zone (SVZ) and rostral migratory stream. Previously, we demonstrated that the implantation of a physical barrier completely prevents SVZ neuroblast migration towards the OB. Then, another objective of this study was to evaluate whether stopping the continuous supply of SVZ neuroblasts modified the different periglomerular populations throughout time. In summary, we estimated the total number of TH-IR, CalB-IR, CalR-IR and GAD-IR cells in the OB glomerular layer at several time points in control and barrier implanted adult rats. In addition, we estimated the volume of glomerular, granular and complete OB. Our main finding was that the number of the four main periglomerular populations is age-dependent, even after impairment of subventricular neuroblast migration. Furthermore, we established that these changes do not correlate with changes in the volume of glomerular layer.

Periodic maternal separation decreases hippocampal neurogenesis without affecting basal corticosterone during the stress hyporesponsive period, but alters HPA axis and coping behavior in adulthood

Although not directly evaluated, the early rise of glucocorticoid (GC) levels, as occur after exposure to adverse early life experience, are assumed to affect hippocampal ontogeny by altering the hippocampus negative feedback on adult HPA axis. To test whether hippocampal ontogeny is affected by early exposure to stress we estimated the survival of recently formed hippocampal granule cells in rat pups subjected to periodic maternal separation (180 min/day; MS180) from postnatal days (PND) 1 to 14. Accordingly, MS180 pups injected with bromodeoxyuridine (BrdU, 50 mg/kg, ip) at PND 5 showed decreased density of doublecortin (DCX) positive BrdU-labeled cells at PND 15. MS180 and AFR pups showed similar corticosterone (CORT) basal levels between PND 3 and 12, whereas adult MS180 rats presented with higher CORT levels than AFR adults. Nonetheless, both AFR and MS180 pups and adults showed similar transient increments of CORT levels in response to stress. In addition, MS180 had no effect on the adult anxiety-like behavior evaluated in the elevated plus maze, but evoked a passive coping strategy in the forced swimming test. The data show that the decrease in hippocampal neurogenesis is an early onset phenomenon, and suggests that adverse experiences alter hippocampal ontogeny without chronic elevation of GC levels.

EphB4 is developmentally and differentially regulated in blood vessels throughout the forebrain neurogenic niche in the mouse brain: Implications for vascular remodeling

Neurogenesis is a process influenced by environmental cues that create highly specific functional niches. Recently, the role of blood vessels in the maintenance and functioning of neurogenic niches during development and in adult life has been hallmarked. In addition to their trophic support for the highly demanding neurogenic process, blood vessels regulate neuroblast differentiation and migration and define functional domains. Since neurogenesis along the forebrain neurogenic niche (FNN) is a multistage process, in which neuroblast proliferation, differentiation and migration are spatially restricted to specific locations; we evaluated the structural features of vascular beds that support these processes during critical time points in their development. Additionally, we studied the molecular identity of the endothelial components of vascular beds using the expression of the venous marker EphB4. Our results show that blood vessels along the FNN: 1) are present very early in development; 2) define the borders of the FNN since early developmental stages; 3) experience constant remodeling until achieving their mature structure; 4) show venous features during perinatal developmental times; and 5) down-regulate their EphB4 expression as development proceeds. Collectively, our results describe the formation of the intricate vascular network that may support neurogenesis along the FNN and show that blood vessels along this neurogenic niche are dynamic entities that experience significant structural and molecular remodeling throughout development.

Valproic acid modulates brain plasticity through epigenetic chromatin remodeling in the blind rat: implications for human sight recovery

Blindness is a pervasive sensory condition that imposes diverse difficulties to carry on with activities of daily living. In blind individuals, the brain is subjected to a large scale reorganization characterized by expanded cortical territories associated with somatosensory and auditory functions and the recruitment of the former visual areas to perform bimodal somatosensory and auditory integration. This poses obstacles to efforts aimed at reassigning visual functions to the recruited visual cortex in the blind, especially after the end of the ontogentic sensitive period. Devising pharmacological measures to modulate the magnitude of brain plasticity could improve our chances of recovering visual functions in the blind. Here, by using the primary somatosensory cortex (S1) in the rat as a working model, we showed that valproic acid administered through the mother's milk prevents cortical reorganization in blinded rats by delaying neuronal histone de-acetylation. These results suggest that in the future, we might be able to devise epigenetic pharmacological measures that could improve our chances of reassigning visual functions to the once deprived former visual cortex in the blind, by modulating the magnitude of brain plasticity during critical times of development.

Arsenic species, AS3MT amount, and AS3MT gene expression in different brain regions of mouse exposed to arsenite

Human exposure to inorganic arsenic (iAs) has been associated with cancer and serious injury to various internal organs, as well as peripheral neuropathy, endocrine disruption and diverse effects in the central nervous system (CNS). Using rodent models, it is possible to demonstrate As accumulation in the brain that leads to defects in operant learning, behavioral changes, and affect pituitary gonadotrophins. iAs biomethylation in the CNS is a significant process, yielding products that are more reactive and toxic than the parent compound. Mice received 2.5, 5, and 10 mg/kg/day sodium arsenite orally for 9 days. We investigated the distribution of iAs and its metabolites as well as the mRNA and protein expression of arsenic (III) methyltransferase (AS3MT), which encodes the key enzyme in iAs metabolism, in the cerebral cortex, hippocampus, striatum, mesencephalon, thalamus, cerebellum, hypothalamus, pons, medulla oblongata, and pituitary of mouse brain. Our findings show that methylated As metabolites are present in all brain regions studied suggesting that AS3MT is ubiquitously expressed in the brain and it is not inducible by dose of arsenite. There is also a dose-related accumulation of As species in all brain regions, with the highest accumulation observed in the pituitary. The higher distribution of arsenicals in pituitary can help to explain the neuroendocrine effects associated with iAs exposure.

Remodelling sympathetic innervation in rat pancreatic islets ontogeny

Background

Pancreatic islets are not fully developed at birth and it is not clear how they are vascularised and innervated. Nerve Growth Factor (NGF) is required to guide sympathetic neurons that innervate peripheral organs and also in cardiovascular system and ovary angiogenesis. Pancreatic beta cells of a transgenic mouse that over-expressed NGF in attracts sympathetic hyper-innervation towards them. Moreover, we have previously demonstrated that adult beta cells synthesize and secrete NGF; however, we do not know how is NGF secreted during development, nor if it might be trophic for sympathetic innervation and survival in the pancreas.

We analyzed sympathetic innervation and vasculature development in rat pancreatic islets at different developmental stages; foetal (F19), early postnatal (P1), weaning period (P20) and adults. We temporarily correlated these events to NGF secretion by islet cells.

Results

Sympathetic fibres reached pancreatic islets in the early postnatal period, apparently following blood vessels. The maximal number of sympathetic fibres (TH immunopositive) in the periphery of the islets was observed at P20, and then fibres entered the islets and reached the core where beta cells are mainly located. The number of fibres decreased from that stage to adulthood. At all stages studied, islet cells secreted NGF and also expressed the high affinity receptor TrkA. Foetal and neonatal isolated islet cells secreted more NGF than adults. TrkA receptors were expressed at all stages in pancreatic sympathetic fibres and blood vessels. These last structures were NGF–immunoreactive only at early stages (foetal and P0).

Conclusion

The results suggest that NGF signalling play an important role in the guidance of blood vessels and sympathetic fibres toward the islets during foetal and neonatal stages and could also preserve innervation at later stages of life.

Melatonin attenuates the decrement of dendritic protein MAP-2 immuno-staining in the hippocampal CA1 and CA3 fields of the aging male rat

Neuronal death during brain aging results, at least in part, from the disruption of synaptic connectivity caused by oxidative stress. Synaptic elimination might be caused by increased instability of the neuronal processes. In vitro evidence shows that melatonin increases MAP-2 expression, a protein that improves the stability of the dendritic cytoskeleton, opening the possibility that melatonin could prevent synaptic elimination by increasing dendritic stability. One way to begin exploring this issue in vivo is to evaluate whether long-term melatonin treatment changes the intensity of MAP-2 immuno-staining in areas commonly afflicted by aging that are rich in dendritic processes. Accordingly, we evaluated the effects of administering melatonin for 6 or 12 months on the intensity of MAP-2 immuno-staining in the strata oriens and lucidum of the hippocampal CA1 and CA3 fields of aging male rats, through semi-quantitative densitometry. Melatonin treated rats showed a relative increment in the intensity of MAP-2 immuno-staining in both regions after 6 or 12 months of treatment, as compared with age matched control rats. Although melatonin untreated and treated rats showed a decrease of MAP-2 immuno-staining in the hippocampus with increasing age, such decrement was less pronounced following melatonin treatment. These findings were confirmed by qualitative Western blot analyses. The melatonin effect seems specific because MAP-2 staining in the primary somatosensory cortex was not affected by the treatment. Thus, chronic melatonin administration increases MAP-2 immuno-staining and attenuates its decay in the adult aging hippocampus. These results are compatible with the idea that melatonin could improve dendritic stability and thus diminish synaptic elimination in the aging brain.

Semaphorin-3A and its receptor neuropilin-1 are predominantly expressed in endothelial cells along the rostral migratory stream of young and adult mice

In the adult brain, neuroblasts originating in the subventricular zone migrate through the rostral migratory stream to the olfactory bulb. While migrating, neuroblasts undergo progressive differentiation until reaching their final locations and fates. Because molecules involved in migration may also exert differentiating effects on young neurons, the identification of factors that support migration could also shed light on the processes of adult neuroblast differentiation. This is the case for members of the family of semaphorins and of its cognate receptors, the neuropilins. Here, we have evaluated the presence of semaphorin-3A and of its receptor neuropilin-1 along the rostral migratory stream in young and adult mice by using immunocytochemical, histochemical, and in situ hybridization techniques. Our morphological studies show that semaphorin-3A and neuropilin-1 are both mainly expressed on endothelial cells along the rostral migratory stream during postnatal development. Our results suggest that endothelial cells constitute the primary source and target of semaphorin-3A along the rostral migratory stream. Moreover, the present work outlines the potential role of blood vessels on neuroblast migration in the postnatal rostral migratory stream.

Development of 5-HT(1B), SERT and thalamo-cortical afferents in early nutrionally restricted rats: an emerging explanation for delayed barrel formation

Barrel formation is delayed in nutritionally restricted rats. The underlying cause of such delay is yet unclear. Because barrels appear upon the arrival of somatosensory thalamo-cortical afferents and the reorientation of the dendritic arborizations of cortical spiny stellate neurons, it is likely that at least one of these processes is altered by nutritional restriction. Also, the serotoninergic afferent system has been implicated in regulating barrel segregation and growth during early postnatal life. We then evaluated the pattern of immunostaining of the serotonin transporter (SERT) and of the serotonin receptor 1B (5-HT(1B)), as well as the growth and arrival time of somatosensory thalamo-cortical afferents, to infer the contribution of these elements in the delayed formation of barrels observed in nutritionally restricted rats. It was found that the rates of development and the segregation of thalamo-cortical fibers were normal in nutritionally restricted rats. SERT, but not 5-HT(1B) immunoreactivity, was decreased in the primary somatosensory cortex during barrel specification. The availability of both proteins in nutritionally restricted rats was lower than that observed in their well fed counterparts at later developmental times. It is concluded that the delayed formation of barrels observed in nutritionally restricted rats is due to a retarded reorientation of dendritic arbors of cortical neurons. This might happen as a secondary effect of decreasing the availability of SERT and/or increasing the availability of 5-HT(1B) receptor early in postnatal life.

Sustained improvement of motor function in hemiparkinsonian rats chronically treated with low doses of caffeine or trihexyphenidyl

The effects of chronic oral treatment with low doses of caffeine (1-3 mg/kg) and trihexyphenidyl (0.1-0.2 mg/kg) were tested on hemiparkinsonian rats, which received the following treatments in a counterbalanced order: vehicle, caffeine, trihexyphenidyl, and caffeine plus trihexyphenidyl. Three preclinical models were used: the stepping test, the cylinder test, and the staircase test. Compared to pre-lesion values, the forepaw contralateral to the dopamine-denervated side showed impaired stepping, fewer wall contacts in the cylinder test, and fewer pellets retrieved in the staircase test. In the stepping test both doses of caffeine produced a complete recovery of motor function (100%), whereas the effect of trihexyphenidyl was less intense (77-80%). In this same test the maximal effect of drugs did not develop tolerance during 2-3 weeks, and was completely reversible after drug cessation. In the cylinder test only the wall contacts performed simultaneously with both forepaws were significantly increased by caffeine (3 mg/kg) and trihexyphenidyl (0.2 mg/kg), and this effect was also reversible. In the staircase test none of the treatments improved food pellet retrieval with the contralateral forepaw. Altogether, these results show that chronic treatment with caffeine, at doses similar to daily human consumption, produces a sustained improvement in the use of the contralateral forelimb in unilaterally 6-hydroxydopamine denervated rats, without the development of tolerance. Although the combined administration of caffeine plus trihexyphenidyl showed no synergism in these models, the results suggest that low doses of caffeine (1-3 mg/kg/day) could be of therapeutic value for the reversal of motor symptoms in parkinsonian patients.

Restructuring of pancreatic islets and insulin secretion in a postnatal critical window

Function and structure of adult pancreatic islets are determined by early postnatal development, which in rats corresponds to the first month of life. We analyzed changes in blood glucose and hormones during this stage and their association with morphological and functional changes of alpha and beta cell populations during this period. At day 20 (d20), insulin and glucose plasma levels were two- and six-fold higher, respectively, as compared to d6. Interestingly, this period is characterized by physiological hyperglycemia and hyperinsulinemia, where peripheral insulin resistance and a high plasmatic concentration of glucagon are also observed. These functional changes were paralleled by reorganization of islet structure, cell mass and aggregate size of alpha and beta cells. Cultured beta cells from d20 secreted the same amount of insulin in 15.6 mM than in 5.6 mM glucose (basal conditions), and were characterized by a high basal insulin secretion. However, beta cells from d28 were already glucose sensitive. Understanding and establishing morphophysiological relationships in the developing endocrine pancreas may explain how events in early life are important in determining adult islet physiology and metabolism.

Serotonin concentration, synthesis, cell origin, and targets in the rat caput epididymis during sexual maturation and variations associated with adult mating status: morphological and biochemical studies

The caput epididymis of some mammals contains large quantities of serotonin whose origin, targets, and physiological variations have been poorly studied. We combined morphological and biochemical techniques to begin approaching these aspects of serotonin in the rat caput epididymis. Serotonin immunostaining was detected in mast, epithelial, and neuroendocrine cells. Epithelial cells displayed immunoreactivity to 5HT(1A), 5HT(2A,) and 5HT(3) serotonin receptors. Endothelial and mast cells labeled positive for 5HT(1B) serotonin receptors and spermatozoa displayed 5HT(2A) and 5HT(3) serotonin receptor immunoreactivity. Epithelial, endothelial, and mast cells stained positive for serotonin transporters. Only epithelial cells showed tryptophan hydroxylase immunoreactivity; this enzyme catalyzes the limiting step in the serotonin synthetic pathway. In addition, Western blot analyses of caput homogenates documented the presence of 2 protein bands ( approximately 51 kd and approximately 48 kd) that were immunoreactive for tryptophan hydroxylase. Chromatographic analyses documented the presence of tryptophan hydroxylase in the caput, and showed that both its activity and serotonin availability increased with sexual maturation and decreased following p-chlorophenylalanine treatment, an inhibitor of tryptophan hydroxylase activity. Interestingly, serotonin concentration and tryptophan hydroxylase activity tended to be higher in breeding males than in those with no mating experience. We think that these results support the existence of a local serotoninergic system in the rat caput epididymis that might regulate some aspects of male reproductive function.

Cells positive for microtubule-associated protein 1B (MAP 1B) are present along rat and human efferent ductules and epididymis

Microtubule-associated protein 1B (MAP 1B) is a neuronal cytoskeleton marker with predominant expression in the developing nervous system. The present study provides evidence for the expression of this cytoskeleton protein in non-neuronal and neuronal cells along rat and human efferent ductules and epididymis (initial segment, caput, and cauda). Reverse transcription/polymerase chain reaction and Western blot analysis were used to confirm the presence of MAP 1B (mRNA and protein) in rat tissues. Immunohistochemical studies revealed MAP-1B-positive staining in columnar ciliated cells present in efferent ductules and in narrow cells located in the initial segment, in both rat and human. MAP-1B-positive basal cells, located underneath the columnar cells, were only identified in the initial segment and caput epididymidis of the rat. Qualitative analysis of tissues from 40-day-old and 120-day-old rats indicated that the number of MAP-1B-positive ciliated, narrow, and basal cells per tubule increased with sexual maturation. These immunoreactive cells did not stain for dopamine beta-hydroxylase or acetylcholinesterase, indicating that they were not adrenergic or cholinergic in nature. Immunohistochemical studies also revealed the presence of MAP-1B-positive staining in interstitial nerve fibers in caput and cauda epididymidis from both rat and human. Thus, the expression of MAP 1B is not confined to a specific cell type in rat and human efferent ductules and epididymis. The functional significance of this cytoskeleton protein in tissues from the male reproductive tract requires further investigation.

Metabolic indices shift in the hypothalamic-neurohypophysial system during lactation: implications for interpreting their relationship with neuronal activity

Metabolic indices of neuronal activity are thought to predict changes in the frequency of action potentials. There are stimuli that do not shift action potential frequency but change the temporal organization of neuronal firing following modifications of excitatory inputs by inhibitory synaptic activation. To our knowledge it is unknown whether this kind of stimulus associates with adjustments of metabolic markers of neuronal activity. Here, we used the hypothalamic-neurohypophysial system of lactating rats to address whether shifts in the temporal organization of neuronal firing relate with modifications of metabolic markers of neuronal activity. Cytochrome oxidase activity, (3)H-2-deoxyglucose uptake, and the area occupied by blood vessels increased in the paraventricular nucleus and neurohypophysis of lactating rats, as compared with their virgin counterparts. Taken together, these results suggest that metabolic demands denote shifts in the temporal organization of action potentials related with the adjustment of excitatory synaptic activation, and support that changes in metabolic markers do not necessarily reflect shifts in the frequency of action potentials.

Glutathione Reductase Inhibition and Methylated Arsenic Distribution in Cd1 Mice Brain and Liver

Inorganic arsenic exposure via drinking water has been associated with cancer and serious injury in various internal organs, as well as with peripheral neuropathy and diverse effects in the nervous system. Alterations in memory and attention processes have been reported in exposed children, whereas adults acutely exposed to high amounts of inorganic arsenic showed impairments in learning, memory, and concentration. Glutathione (GSH) is extensively involved in the metabolism of inorganic arsenic, and both arsenite and its methylated metabolites have been shown to be potent inhibitors of glutathione reductase (GR) in vitro. Brain would be more susceptible to GR inhibition because of the decreased activities of superoxide dismutase (SOD) and catalase reported in this tissue. To investigate whether GR inhibition could be documented in vivo, we determined the activity and levels of GR in brain as well as in liver, the main organ of arsenic metabolism in mice exposed to 2.5, 5, or 10 mg/kg/day of sodium arsenite over a period of 9 days. In contrast to what has been observed in vitro, significant inhibition of the expression and activity of GR was observed only at the highest concentration used (10 mg/kg/day) in both organs. Although the disposition of arsenicals was higher in liver, significant amounts of inorganic and methylated arsenic forms were determined in the brain of exposed animals. The formation of monomethylarsenic (MMA) and dimethylarsenic (DMA) metabolites in the brain was confirmed by incubating brain slices for 24, 48, and 72 h with sodium arsenite.

Similar synapse density in layer IV columns of the primary somatosensory cortex of transgenic mice with different brain size: implications for mechanisms underlying the differential allocation of cortical space

The relative dimension of the areas constituting the cerebral cortex differs greatly in the brains of different mammalian species. The mechanisms by which such an evolutionary remodeling has occurred is not well understood. To begin exploring possible mechanisms, we took advantage of a transgenic mouse model in which the area of the primary somatosensory cortex (S1) shifts, to some extent independent from the area of the cortex as a whole, as a result of differences in the availability of insulin-like growth factor I (IGF-I). Electron microscopy estimations of synapse density in D3 and C3 cortical columns of the S1 layer IV revealed that this parameter was similar among wild type and transgenic mice with higher and lower availability of IGF-I. Because D3 and C3 columns were larger and smaller than normal in mice with higher and lower IGF-I availability, the total number of synapses contained in the average area of D3 and C3 columns increased and decreased, respectively. No differences in the number and overall arrangement of S1 columns were observed among animal groups. These results suggest that: 1) synapse density is a constant factor within the S1 cortical column structure; 2) the mechanisms and factors regulating cell number and synaptogenesis are affected as columns and cortical areas modify their relative dimensions; 3) altered availability of neurotrophic factors might be associated with changes in areal dimensions; and 4) changes in cortical areal dimensions within single lineages might result from the addition of minicolumns to preexisting columns.

Neither increased nor decreased availability of cortical serotonin (5HT) disturbs barrel field formation in isocaloric undernourished rat pups

Serotonin (5HT) is expressed transiently in primary sensory areas of the rat neocortex during the establishment of the thalamo-cortical topography and somatotopy. The precise role of 5HT during the specification of neocortical areas is still uncertain. We evaluated the effects of increasing and decreasing cortical serotonin concentrations on the specification of the barrel cortex using a rat model of isocaloric undernutrition. This manipulation increases brain 5HT levels during brain development. Undernourished animals were also treated with p-clorophenylalanine; an inhibitor of 5HT synthesis. Barrels representing the head were readily seen at postnatal day 5 in control and p-clorophenylalanine treated rats. In contrast, undernourished rats treated or not with p-clorophenylalanine showed no barrels representing the head but until postnatal day 7. Chromatographic analyses demonstrated that the concentration of cortical 5HT increased by 50% in undernourished pups during barrel field formation. Control and undernourished animals treated with p-clorophenylalanine had a significant reduction (90%) of 5HT in the cortex. The overall geometry of the barrel field and of individual barrels was similar among animal groups. Our results support that 5HT plays a small role in triggering and timing barrel field somatotopy.

Insulin-like growth factor I partly prevents axon elimination in the neonate rat optic nerve

Developmental neuronal death ensues after access of innervating neurons to target-derived neurotrophic factors is restricted. Recent evidence suggests, however, that growth factors such as those of the insulin family modulate neuronal death through autocrine/paracrine mechanisms. In rats, retinal ganglion neurons (RGNs) undergo massive death during early postnatal life. During this same period, the expression of various members of the insulin-like growth factor I (IGF-I) protein family is down regulated. To evaluate whether ocular IGF-I might modulate RGN death, we administered IGF-I in the posterior chamber of the eye of newborn rats. Optic nerve fiber number was estimated in control and IGF-I treated animals at postnatal day 5 when RGN death peaks. Intraocular IGF-I treatment at birth partly prevented optic nerve fiber elimination. Because the axon number in the optic nerve correlates to some extent with the RGN number, these results suggest that IGF-I may modulate RGN death in vivo through local interactions.