Ontogenesis of quisqualate-associated phosphoinositide metabolism in various regions of the rat nervous system

The effect of postnatal age on phosphoinositide metabolism per se and on quisqualate-stimulated phosphoinositide metabolism was characterized in synaptoneurosomes prepared from nine different regions of the rat nervous system, namely the brainstem, cerebellum, cerebral cortex, colliculi, hippocampus, hypothalamus, olfactory bulb, spinal cord and striatum. In the hippocampus, striatum, cerebellum, cerebral cortex, brainstem, colliculus and spinal cord, the basal levels of inositol phosphate (inositol-1-phosphate+inositol-4,5-bisphosphate) formation were maximal two days after birth and declined steeply to steady-state levels from the age of 10 postnatal days. Similarly, in the olfactory bulb, basal inositol phosphate synthesis did not significantly change when measured during the period from postnatal day 10 to 42. The extent of [³H]-inositol labelling of phosphoinositides as a function of age presented similar profiles when measured in hippocampal, striatal, cerebellar and cerebral cortical synaptoneurosomes, i.e. maximal at perinatal ages and minimal at adult ages. In the hypothalamus, [³H]-inositol labelling of phosphoinositides showed an increase from postnatal day 12 to higher levels from postnatal days 14 to 18 subsequently followed by a dramatic increase from postnatal day 21 to 42. A similar developmental trend was also obtained for basal inositol phosphate synthesis.On the whole, four types of developmental profiles for quisqualate-stimulated inositol phosphate formation (expressed as the percentage of the basal level and as the difference between stimulated and basal levels of radioactive inositol phosphates) were obtained depending on the nervous system region studied. In the early, prenatally developed nervous system regions, namely the brainstem and the spinal cord, no postnatal stimulation peaks of quisqualate-induced inositol phosphate formation were recorded. This was also the case for the colliculi when the stimulation of IP formation was expressed as the difference in basal and stimulated levels of inositol phosphates. Secondly, in the olfactory bulb a region known to possess a continuous capacity for developmental plasticity both structurally and functionally during the first three weeks of postnatal development, a simultaneous sustained high level of quisqualate stimulation of phosphoinositide metabolism (fluctuating around 200% of the basal level) during the early postnatal period was evident. Thirdly, in regions of the central nervous system like the cerebellum, cerebral cortex, hippocampus and the striatum known to undergo intense developmental activity during the first two postnatal weeks, peaks of quisqualate-stimulated phosphoinositide metabolism were initially detected around the first week after birth in each of these brain areas. Finally, in the hypothalamus where structurally unique postnatal developmental processes are known to take place, quisqualate-induced inositol phosphate formation progressively increases with age to reach maxima at postnatal day 18. The transient increases in quisqualate responses in the cerebellum, hippocampus and striatum are probably specific to quisqualate since carbachol-stimulated phosphoinositide metabolism yielded different age-associated response patterns. Similar increases of carbachol- and quisqualate-mediated phosphoinositide hydrolysis were on the other hand assayed in cerebral cortical and hypothalamic synaptoneurosomes. EC₅₀, values for quisqualate (the quisqualate concentration required to produce 50% of the maximal effect) at postnatal days 6 and 10 were not significantly different in each of four types of synaptoneurosomes: cerebellar, cerebral cortical, hippocampal and striatal. On the basis of these latter results, it was deduced that the peak of quisqualate-stimulated phosphoinositide metabolism does not materialize on the basis of changes in quisqualate metabotropic receptor affinity. In conclusion, the measurement of inositol phosphate formation in synaptoneurosomes prepared from different regions of the postnatally developing nervous system indicate that there is a temporal correlation between the increased activity of quisqualate-stimulated phosphoinositide metabolism mediated by specific metabotropic glutamate receptors and region-specific developmental events. This could suggest a key role for certain metabotropic glutamate receptors in the developmental plasticity of the nervous system.     

Food deprivation alters dopamine utilization in the rat prefrontal cortex and asymmetrically alters amphetamine-induced rotational behavior

The effects of 24 and 48 h of food deprivation on changes in the activity of dopaminergic (DAergic) neurons and d-amphetamine-induced rotational behavior were studied in male and female Long-Evans rats. Food deprivation selectively altered 3,4-dihydroxyphenylacetic acid (DOPAC) in the medial prefrontal cortex (PFC) but not in the nucleus accumbens or striatum: PFC DOPAC was significantly increased and decreased bilaterally after 24 and 48 h of food deprivation, respectively. Left > right hemispheric asymmetries were seen for DOPAC and DOPAC/DA in the control animals. In a separate experiment, 24 h of food deprivation enhanced right rotational behavior, while 48 h significantly increased left rotational behavior. The results are discussed in terms of food deprivation's effects on mesocortical DAergic neurons, previous work on cortical modulation of striatal function and how these effects on rotational behavior may be determined by brain asymmetry.     

Differential disinhibition of the neonatal hypothalamic- pituitary-adrenal axis in brain-specific CRH receptor 1-knockout mice

In the adult, corticotropin-releasing hormone (CRH) is the key mediator for the behavioural and neuroendocrine response to stress. It has also been hypothesized that, during postnatal development of the stress system, CRH controls the activity of the HPA axis and mediates the effects of early disturbances, e.g. 24 h of maternal deprivation. In the current study we investigated the function of specific brain corticotropin-releasing hormone receptor type 1 (CRHR1) subpopulations in the control of the HPA axis during postnatal development under basal conditions as well as after 24 h of maternal deprivation. We used two conditional CRHR1-deficient mouse lines which lack this receptor, either specifically in forebrain and limbic structures (Cam-CRHR1) or in all neurons (Nes-CRHR1). Basal circulating corticosterone was increased in Nes-CRHR1 mice compared to controls. Corticosterone response to maternal deprivation was significantly increased in both CRHR1-deficient lines. In the paraventricular nucleus, Cam-CRHR1 animals displayed enhanced CRH and decreased vasopressin expression levels. In contrast, gene expression in Nes-CRHR1 pups was strikingly similar to that in maternally deprived control pups. Furthermore, maternal deprivation resulted in an enhanced response of Cam-CRHR1 pups in the brain, while expression levels in Nes-CRHR1 mouse pups were mostly unchanged. Our results demonstrate that brainstem and/or hypothalamic CRHR1 contribute to the suppression of basal corticosterone secretion in the neonate, while limbic and/or forebrain CRHR1 dampen the activation of the neonatal HPA axis induced by maternal deprivation.     

Perinatal expression of heat-shock protein 27 in brain regions and nonneural tissues of the piglet

Important stressful events occur at birth or within the few hours that follow this event. To unravel a possible involvement of stress proteins, it is important to determine their levels of expression. Expression of HSP27 protein was determined by Western blotting in several nonneural tissues and in brain regions of the developing pig (fetal to adult). Maximum levels of expression were observed in heart, liver, and lung. In kidney, the expression was reduced during the first hours of life. Brain parts included whole brain, cerebellum, cortex, hippocampus, hypothalamus, and striatum. HSP27 immunogenicity was observed in all the brain regions studied. In whole brain, cerebellum, cortex, hippocampus, and hypothalamus extracts, the levels of HSP27 were decreased during the first hours of age (4 h to 2 d). In striatum, levels of expression were very low—if detectable—during the early postnatal days of life. Changes in environmental parameters, like temperature and/or hypoxia can be possibly related to differential expressions of HSPs, which can result in severe adverse developmental outcomes. The results are discussed in terms of using the newborn piglet as a model to study different forms of stress on the heat-shock protein postnatal expression.     

Ontogeny of the HPA axis of the CD1 mouse following 24 h maternal deprivation at pnd 3

One of the striking characteristics of the developing neuroendocrine system of rats and mice is the stress hypo-responsive period (SHRP), i.e. low basal corticosterone secretion and the inability to increase corticosterone in response to mild stressors during the first 2 weeks of life. However, immediately after 24 h of deprivation from maternal care the response of the hypothalamic–pituitary–adrenal (HPA) axis to mild stressors is enhanced. This study examines in CD1 mouse pups the recovery pattern of markers of HPA axis (re)activity from maternal deprivation (once for 24 h from postnatal days (pnds) 3 to 4). As expected, deprivation induced a profound corticosterone response to novelty immediately after deprivation. In contrast, 1 day after reunion with the mother (pnd 5), this effect was abolished, lasting for at least 3 days. Basal corticosterone remained even below control levels. Corticotropin-releasing hormone (CRH) mRNA expression in the hypothalamic paraventricular nucleus (PVN) was suppressed for 2 days, exceeded control levels at pnds 7 and 8, and subsequently followed the gradual decline observed in controls until pnd 12. Delayed and rather short-lasting changes were found for adrenocorticotropic hormone (low at pnd 5), and glucocorticoid receptor mRNA expression (decreased in the PVN at pnd 4, and in the hippocampal CA1 area at pnd 5). Hippocampal mineralocorticoid receptor mRNA expression was unaffected. From pnds 9 to 13, both deprived and control pups gradually emerged from the SHRP in a similar temporal pattern. In conclusion, maternal deprivation at pnd 3 augments hypo-responsiveness of corticosterone secretion to mild stress for several days, but does not affect the duration of the SHRP. Whether CRH and glucocorticoid receptor changes are cause or consequence remains to be established.     

Effect of acute stress on NTPDase and 5′-nucleotidase activities in brain synaptosomes in different stages of development

The aim of the present study was to examine the effect of acute restraint stress on rat brain synaptosomal plasma membrane (SPM) ecto-nucleotidase activities at specific stages of postnatal development (15-, 30-, 60- and 90-day-old rats) by measuring the rates of ATP, ADP and AMP hydrolysis 1, 24 and 72 h post-stress. At 1 h after stress NTPDase and ecto-5′-nucleotidase activities were decreased in rats aged up to 60 days old. In adult rats elevated enzyme activities were detected, which indicated the existence of different short-term stress responses during development. A similar pattern of ATP and ADP hydrolysis changes as well as the ATP/ADP ratio in all developmental stages indicated that NTPDase3 was acutely affected after stress. The long-term effect of acute stress on NTPDase activity differed during postnatal development. In juvenile animals (15 days old) NTPDase activity was not altered. However, in later developmental stages (30 and 60 days old rats) NTPDase activity decreased and persisted for 72 h post-stress. In adult rats only ATP hydrolysis was decreased after 24 h, indicating that ecto-ATPase was affected by stress. Ecto-5′-nucleotidase hydrolysing activity was decreased within 24 h in adult rats, while in 15- and 30-day old rats it decreased 72 h post-stress. At equivalent times in pubertal rats (60 days old) a slight activation of ecto-5′-nucleotidase was detected. Our results highlight the developmental-dependence of brain ecto-nucleotidase susceptibility to acute stress and the likely existence of different mechanisms involved in time-dependent ecto-nucleotidase activity modulation following stress exposure. Clearly there are differences in the response of the purinergic system to acute restraint stress between young and adult rats.     

Time course of changes in serotonin and noradrenaline in rat brain after predictable or unpredictable shock

The effects of predictable and unpredictable shock on concentrations of serotonin (5-hydroxytryptamine, 5-HT), 5-hydroxyindoleacetic acid (5-HIAA), tryptophan (TP) and noradrenaline (NA) have been studied in 7 regions of rat brain. Two separate experiments have been carried out determining these substances both at 30 min and 2 h after the stress session. Unpredictable shock depleted NA levels in all brain regions except the striatum. However, at 2 h poststress NA in these regions increased significantly in comparison with both controls and predictably shocked rats. Predictable shock also decreased NA in locus coeruleus, brainstem and hypothalamus, which was not observed 2 h later. Both predictable and unpredictable shock decreased 5-HT in brainstem and hypothalamus. At 2 h poststress, 5-HT levels in these regions were still decreased in predictably shocked rats, but had attained control values in unpredictably shocked rats. 5-HT metabolism expressed as the 5-HIAA/5-HT ratio, was significantly increased 30 min after predictable shock in all regions except the locus coeruleus and hippocampus. Unpredictable shock produced a much more marked increase in 5-HIAA/5-HT ratio. At 2 h poststress 5-HT metabolism returned to control values in most of the brain regions of predictably shocked animals, but it remained high after unpredictable shock. The activation of serotonergic metabolism following each type of shock is different according to the nucleus in which the 5-HT nerve endings originate. Only slight increases in tryptophan were observed after both types of shock. Our results suggest that unpredictable shock is perceived as a more anxiogenic situation and that under this condition both 5-HT and NA levels are more effectively normalized with time.     

Influence of sex and experimental protocol on the effect of maternal deprivation on rectal sensitivity to distension in the adult rat

Neonatal maternal separation induces visceral hyperalgesia before and after stress in male rats. This study compares the effects on sensitivity to rectal distension in adult male and female rats, using two protocols of deprivation. Between postnatal days 1 and 14, maternal deprivation was performed for 2 h per day according to a protocol of type M (removal of all pups from home cage) or type P (separation of half of littermates). Visceral sensitivity was assessed at 12 weeks of age by the number of abdominal contractions induced by rectal distension before and after restraint stress. Calcitonin gene-related peptide (CGRP) was identified in the rectal wall by immunohistochemistry. In basal conditions, both separation protocols induced hyperalgesia, that was greater after type M than type P, and in females than in males for type P separation. Acute restraint stress induced hyperalgesia in control females only, and this effect was similarly enhanced by both type P and M separation. No difference was found between controls and deprived rats in rectal CGRP immunoreactivity which was greater in females and increased after rectal distension. These results indicate that long-term visceral hyperalgesia depends upon the type of maternal deprivation and that females are more sensitive than males.     

Ontogeny of insulin binding in different regions of the rat brain

Insulin binding was measured on crude mitochondrial or plasma membranes prepared from different rat brain regions during postnatal development. In the cerebral cortex and brainstem, insulin binding decreased 60-70% between birth and the adult period. In the cerebellum, insulin binding doubled in the first 10 postnatal days and then decreased 40% in the adult, while in the olfactory bulb, insulin binding changed little during postnatal development. Postnatal reductions of insulin binding in cerebral cortex and brainstem were from a loss of binding sites and not from a change in binding affinity. Of the major postnatal developmental processes, maximal insulin binding was most closely associated with neuronogenesis, less closely with gliogenesis and not with synaptogenesis, neural process formation or myelination.     

Developmental changes in the hypothalamic mRNA expression levels of brain-derived neurotrophic factor and serum leptin levels: Their responses to fasting in male and female rats

The actions and responses of hypothalamic appetite regulatory factors change markedly during the neonatal to pre-pubertal period in order to maintain appropriate metabolic and nutritional conditions. In this study, we examined the developmental changes in the hypothalamic mRNA levels of brain-derived neurotrophic factor (BDNF), which is a potent anorectic factor and the changes in the sensitivity of the hypothalamic expression of this factor to fasting during the neonatal to pre-pubertal period. Under fed conditions, hypothalamic BDNF mRNA expression decreased during development in both male and female rats. Similarly, the serum levels of leptin, which is a positive regulator of hypothalamic BDNF expression, also tended to fall during the developmental period. The serum leptin level and the hypothalamic BDNF mRNA level were found to be positively correlated in both sexes under the fed conditions. Hypothalamic BDNF mRNA expression was decreased by 24 h fasting (separating the rats from their mothers) in the early neonatal period (postnatal day 10) in both males and females, but no such changes were seen at postnatal day 20. Twenty-four hours’ fasting (food deprivation) did not affect hypothalamic BDNF mRNA expression in the pre-pubertal period (postnatal day 30). On the other hand, the rats’ serum leptin levels were decreased by 24 h fasting (separating the rats from their mothers at postnatal day 10 and 20, and food deprivation at postnatal day 30) throughout the early neonatal to pre-pubertal period. The correlation between serum leptin and hypothalamic BDNF mRNA levels was not significant under the fasted conditions. It can be speculated that leptin partially regulates hypothalamic BDNF mRNA levels, but only in fed conditions. Such changes in hypothalamic BDNF expression might play a role in maintaining appropriate metabolic and nutritional conditions and promoting normal physical development. In addition, because maternal separation induces a negative energy balance and short- and long-term stress responses, it is also possible that reductions in hypothalamic BDNF mRNA levels in the early neonatal period (postnatal day 10) may be partially induced by stress responses of the maternal deprivation.     

Ontogeny of somatostatin mRNA-containing perikarya in the rat central nervous system.

The distribution of neuronal perikarya containing somatostatin mRNA in the developing rat brain was investigated with in situ hybridization histochemistry. This study describes the expression of somatostatin mRNA during selected perinatal stages and demonstrates regional changes in somatostatin mRNA expression at the single cell level. The mRNA expression closely parallels previously reported developmental localization of the peptide (Inagaki et al., 1982; Shiosaka et al., 1982). As early as embryonic day 13 (E13), somatostatin mRNA was observed in discrete spinal cord and brainstem regions. At birth, densely hybridized somata could be seen primarily in ventral and caudal brain areas with small scattered neurons in the hippocampus and dorsal neocortex. After birth, somatostatin mRNA increased in forebrain regions, such as the hippocampus, dorsal neocortex, and caudate. By postnatal day 14 (P14), the distribution in the telencephalic and diencephalic regions approached that of the adult brain. Several brain regions manifested large changes in the density of somatostatin mRNA hybridization during development. For example, the cerebellar vermis and brainstem contained somatostatin mRNA perikarya during early postnatal development but decreased in these regions in the adult. During perinatal development, increases in somatostatin mRNA content were the results of increases in both the number of neurons containing somatostatin mRNA as well as in the amount of this mRNA expressed in each cell. As the brain differentiates, the apparent numbers of somatostatin mRNA containing neurons in certain brain regions are reduced. These data provide evidence for transient somatostatinergic neurons during early development in discrete areas of the occipital cortex, pyriform cortex, cerebellum, and brainstem and suggest that this peptide may play a role in the development of these regions.     

Persistent cholinergic presynaptic deficits after neonatal chlorpyrifos exposure

The commonly-used organophosphate insecticide, chlorpyrifos (CPF), impairs brain cell development, axonogenesis and synaptogenesis. In the current study, we administered CPF to neonatal rats on postnatal (PN) days 1-4 (1 mg/kg) or PN11-14 (5 mg/kg), treatments that were devoid of overt toxicity. We then examined two cholinergic synaptic markers, choline acetyltransferase activity (ChAT) and [3H]hemicholinium-3 binding (HC-3) in the hippocampus, midbrain, striatum, brainstem and cerebral cortex in the juvenile (PN30) and young adult (PN60). Across all brain regions, CPF exposure evoked significant reductions in both markers, with larger effects on HC-3 binding, which is responsive to neuronal impulse activity, than on ChAT, a constitutive marker. Superimposed on the deficits, there were gender-selective effects and distinct regional disparities in the critical exposure period for vulnerability. In the hippocampus, either the early or late treatment regimen evoked decreases in ChAT but the early regimen elicited a much larger decrease in HC-3; effects persisted into adulthood. In the midbrain, CPF administration on PN1-4 elicited deficits similar to those seen in the hippocampus; however, exposure on PN11-14 elicited changes preferentially in females. Gender selectivity was also apparent in the striatum, in this case reflecting deficits in females after CPF treatment on PN1-4. In contrast, the effects of CPF on the brainstem were relatively more robust in males; effects in the cerebral cortex were less notable than in other regions. These results indicate that neonatal CPF exposure produces widespread deficiencies in cholinergic synaptic function that persist into adulthood. The effects are likely to contribute to gender-selective alterations in behavioral performance that persist or emerge long after the termination of exposure and well after the restoration of cholinesterase activity.     

Impairment of the mitochondrial electron transport chain due to sleep deprivation in mice

It has been demonstrated that sleep deprivation is associated with altered expression of genes related to metabolic processes, response to stress and inflammation, circadian sleep/wake cycles, regulation of cell proliferation and various signaling pathways. However, the molecular mechanisms underlying these changes remain poorly understood. Thus, the present study aims to characterize the function of the mitochondrial electron transport chain in the brain using an animal model of paradoxical sleep deprivation (PSD). The question of whether sleep recovery (rebound) can reverse changes found after PSD is also addressed. Adult male inbred C57BL/6 J mice were randomly distributed into three groups: home-cage control, PSD and sleep rebound groups. The PSD and rebound groups were subjected to PSD for 72 h. After this sleep deprivation period, the rebound group was returned to its home cage and allowed to sleep in an undisturbed and spontaneous fashion for 24 h. The mitochondrial complex I-III, complex II, succinate dehydrogenase and complex II-III activities were then measured by spectrophotometric methods in sub-mitochondrial particles extracted from the prefrontal cortex, hippocampus, striatum and hypothalamus. Our results showed a significant decrease in the activity of complex I-III in the PSD and rebound groups as compared to the control group. The complex II and II-III activity were particularly decreased in the hypothalamus of the sleep rebound group. These results are consistent with the involvement of sleep in energy metabolism and corroborate previous experiments demonstrating the importance of the hypothalamus in sleep regulation.     

Effect of neonatal nociceptin or nocistatin imprinting on the brain concentration of biogenic amines and their metabolites

Noradrenaline (NA), dopamine (DA), homovanillic acid (HA), serotonin (5HT) and 5-hydroxyindole acetic acid (5HIAA) content of five brain regions (hypothalamus, hippocampus, brainstem, striatum and frontal cortex) and the cerebrospinal fluid (CSF) was measured in adult (three months old) male and female rats treated neonatally with a single dose of 10 microg nociceptin (NC) or 10 microg nocistatin (NS) for hormonal imprinting. The biogenic amine and metabolite content of cerebrospinal fluid was also determined. In NC treated animals the serotonergic, dopaminergic as well as noradrenergic systems were influenced by the imprinting. The 5HT level increased in hypothalamus, the 5HIAA tissue levels were found increased in hypothalamus. Hippocampus and striatum and the HVA levels increased highly significantly in brainstem. Dopamine level decreased significantly in striatum, however in frontal cortex both noradrenalin and 5HIAA level decreased. Nevertheless, in NS-treated rats decreased NA tissue levels were found in hypothalamus, brainstem and frontal cortex. Decreased DA levels were found in the hypothalamus, brainstem and striatum. NS imprinting resulted in decreased HVA level, but increased one in the brainstem. The 5HT levels decreased in the hypothalamus, brainstem, striatum and frontal cortex, while 5HIAA content of CSF, and frontal cortex decreased, and that of hypothalamus, hippocampus and striatum increased. There was no significant difference between genders except in the 5HT tissue levels of NC treated rats. Data presented show that neonatal imprinting both by NC and NS have long-lasting and brain area specific effects. In earlier experiments endorphin imprinting also influenced the serotonergic system suggesting that during labour release of pain-related substances may durably affect the serotonergic (dopaminergic, adrenergic) system which can impress the animals' later behavior.     

Effect of paradoxical sleep deprivation on vasoactive intestinal peptide-like immunoreactivity in discrete brain areas and anterior pituitary of the rat

To determine whether vasoactive intestinal peptide (VIP) is involved in paradoxical sleep (PS) homeostasis, VIP-like immunoreactivity (VIP-LI) of discrete brain areas was determined by radioimmunoassay after 24 and 48 h of PS deprivation by the watertank technique followed or not by 5 h of sleep rebound. This study was carried out with an environmental control (placed in dry watertank: DWC) and a nonstressed control. Such PS deprivation induced a decrease of VIP content in PS-deprived rats restricted to cortex and anterior pituitary. In the cortex, the decrease in VIP-LI was of the same magnitude after 24 and 48 h of PS deprivation and VIP-LI was normal by 5 h of sleep rebound; as such a decrease was also observed after 48 h in DWC, it could be due to the stress related to the experiment rather than lack of sleep. In the anterior pituitary, the decrease was related to the duration of deprivation with a greater decrease in VIP-LI after 48 than after 24 h of PS deprivation and specifically related to PS deprivation since it was not observed in DWC rats. After 5 h of sleep rebound, recovery of VIP-LI was total in the 24-h experiment and partial in the 48-h one. In all eight other structures studied, VIP was unchanged after experimentation. These results strongly suggest that VIP is not involved in PS homeostasis but as indicated by other experiments more probably in circadian organization of sleep.     

Plasticity and ontogeny of the central 5-HT transporter: effect of neonatal 5,7-dihydroxytryptamine lesions in the rat.

5,7-Dihydroxytryptamine (5,7-DHT) is unique as a serotonin (5-HT) neurotoxin in that i.p. injection of neonatal rats increases concentrations of 5-HT in brainstem while depleting 5-HT in cortex, hippocampus and spinal cord. To study the mechanism of this effect we measured the 5-HT transporter or uptake site, a presynaptic marker, using [3H]paroxetine binding. There were significant regional differences in Bmax of vehicle-injected rats: brainstem, diencephalon > striatum, cortex, spinal cord > hippocampus, cerebellum. There were also regional differences in the ontogeny of bindings sites: at postnatal day 7, [3H]paroxetine sites were 39% of adult levels in cortex compared to 63% in brainstem. Thirty days after 100 mg/kg 5,7-DHT i.p., Bmax of [3H]paroxetine binding was significantly increased in brainstem (+67%) and diencephalon (+136%), whereas it decreased in cortex (-59%), hippocampus (-94%) and spinal cord (-99%), striatum (-41%) and cerebellum (-37%). KD remained unaltered. In dose-response studies (0-200 mg/kg), 50 mg/kg was the threshold dose for Bmax effects and 200 mg/kg was lethal. In weekly time-course studies, changes were apparent 1 week after 5,7-DHT lesions. Binding site increases in diencephalon and brainstem were not maximal until 3 weeks after injection, whereas percent decreases in cortical sites remained unchanged at each week studied. Lesion effects on the ontogeny of [3H]paroxetine binding sites were region-dependent: cortical sites continued to increase with age but spinal sites did not. There was no significant recovery in spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)     

Effect of basic fibroblast growth factor on neurons cultured from various regions of postnatal rat brain

Neurons from various brain regions of postnatal (15 days after birth) and fetal (16 days gestation) rats were cultured in the presence of basic fibroblast growth factor (bFGF). bFGF increased the survival of neurons from postnatal septum, striatum, midbrain, and hippocampus. Fetal neurons derived from cerebral cortex, septum, striatum, midbrain, thalamus, and colliculus were far more dependent on bFGF for survival in comparison with postnatal neurons. In contrast, cerebellum neurons of postnatal and fetal rat brain did not respond to bFGF. The increase of postnatal and fetal neuronal survival with bFGF treatment (0.01–10 ng/ml) was dose-dependent and reached 2–4-fold and 5–10-fold more than the control, respectively. Fetal cortical neurons showed almost complete dependence on bFGF since almost all neurons died in control cultures. Nerve growth factor was slightly effective only on postnatal septal and striatal neurons, being ineffective on the other neurons tested. These results indicate that bFGF can function as a neurotrophic factor not only on fetal but also on postnatal neurons of the central nervous system, and that bFGF has great potential for application in vivo.     

Developmental expression of mu and delta opioid receptors in the rat brainstem: evidence for a postnatal switch in mu isoform expression

Opioid receptors are expressed in the brain during fetal and postnatal development, and the expression patterns vary with developmental age. To investigate the role of opioids in brain development, immunoblotting and immunohistochemical techniques were used to determine mu (MOR) and delta (DOR) opioid receptor expression levels and regional distributions in fetal, early postnatal and adult rat brainstem. Two immunoreactive bands were seen on Western blots of brainstem lysates for both MOR (50 and 70 kDa) and DOR (30 and 60 kDa). The expression levels of the isoforms changed dramatically between 6 and 15 days after birth. Total MOR protein was expressed at low levels in fetal and early postnatal animals with the 50-kDa band predominating. MOR expression then increased in the older animals and the 70-kDa isoform became dominant. Total DOR protein showed the opposite pattern, being high in the fetal and neonatal brainstem and low in the juvenile and adult. A postnatal switch in isoform expression for DOR was not evident in our study. In general, regional brainstem distributions in developing and adult animals were comparable to those reported in the literature, and both receptors were localized in the same areas where opioid receptor expression was high. It was concluded that MOR and DOR are developmentally regulated in the brainstem of the rat, that the isoform ratio switches postnatally from a fetal-neonatal pattern to a juvenile-adult pattern and that both receptors are generally expressed in the same brainstem regions from E16 to adult.     

Effects of prenatal protein malnutrition and acute postnatal stress on granule cell genesis in the fascia dentata of neonatal and juvenile rats

Although postnatal genesis of granule cells in the hippocampal fascia dentata is known to be influenced by prenatal protein deprivation or by stress, the combined effects of prenatal protein malnutrition and stress on these cells are unknown. This study was designed to examine this combined effect. Well-nourished and prenatally malnourished pups on postnatal day 7 (P7) were stressed by maternal separation and reduction of body temperature and on postnatal day 30 (P30) by immobilization with restraint. Bromodeoxyuridine (BrDU) was injected at the time of stress, and 2 h later, the numbers of immunolabeled cells were quantified by standard stereological techniques. In comparison to controls, prenatally malnourished rats showed a significantly lower number of cells tagged in the fascia dentata on P7 (p < or =0.05), and a significantly higher number of cells (p < or =0.05) on P30. In both age groups, control rats exposed to acute stress showed a significantly decreased number of cells tagged in the fascia dentata (p < or =0.05). In contrast, neurogenesis in malnourished rats was not significantly affected by acute stress at either age. Thus, the pattern of neurogenesis in the fascia dentata and its response to stress has been fundamentally altered by prenatal protein deprivation.