Role of the 5-HT1A receptor in development of the neonatal rat brain: preliminary behavioral studies

Astrocytic 5-HT1A receptor mediates age-dependent hippocampal LTD and fear memory extinction in male mice

NMDA receptor-dependent long-term depression (LTD) in the hippocampus is a well-known form of synaptic plasticity that has been linked to different cognitive functions. Although the underlying mechanisms remain unclear, this form of LTD cannot be induced by low-frequency stimulation (LFS) in adult mice. In this study, we found that LFS-induced LTD was not easily induced in adult animals and was age dependent. Interestingly, the level of the 5-HT1A receptor was correspondingly increased and exhibited an inverse correlation with the magnitude of LFS-LTD during development. Knockout or pharmacological inhibition of the 5-HT1A receptor reversed impaired LFS-LTD in adult mice (P60), while activation or inhibition of this receptor disturbed or enhanced LFS-LTD in adolescent mice (P21), respectively. Furthermore, the astrocytic 5-HT1A receptor in the hippocampus predominantly mediated age-dependent LFS-LTD through enhancing GABAergic neurotransmission. Finally, fear memory extinction differed among the above conditions. These observations enrich our knowledge of LTD at the cellular level and suggest a therapeutic approach for LTD-related psychiatric disorders.

The effects of a maternal advanced glycation end product-rich diet on somatic features, reflex ontogeny and metabolic parameters of offspring mice

Maternal exposure to a Western type diet during pregnancy might predispose the offspring to manifestation of metabolic and behavioral disturbances in later life. The Western type diet contains large amounts of advanced glycation end products (AGEs). In humans and experimental rodents, the intake of an AGE-rich diet (AGE-RD) negatively affected glucose homeostasis, and initiated the production of reactive oxygen species. Rats consuming the AGE-RD presented changes in behavior. It remains unclear whether maternal intake of the AGE-RD might affect developmental plasticity in offspring. We examined early somatic (weight, incisor eruption, ear unfolding, and eye opening) and neuromotor development, oxidative status, insulin sensitivity (HOMA index) and locomotor activity assessed in PhenoTyper cages in the offspring of mice fed during pregnancy with either the AGE-RD (25% bread crusts/75% control chow) or control chow. Until weaning, the somatic development of offspring did not differ between the two dietary groups. The AGE-RD offspring manifested physiological reflexes (auditory startle, eye lid, ear twitch and righting reflexes) earlier. As young adults, the male offspring of the AGE-RD dams were heavier and less insulin sensitive compared with their control counterparts. The AGE-RD offspring showed higher locomotor activity during the active phase. Our data indicate that the maternal AGE-RD during pregnancy might accelerate the maturation of reflexes in offspring, predispose the male progeny to weight gain and affect their glucose homeostasis. These effects manifest without the direct consumption of the AGE-RD by offspring. Further work is needed to determine the mechanisms by which the maternal AGE-RD affects neurobehavioral pathways in offspring, as well as sex differences in adverse metabolic responses.

Third Trimester Equivalent Alcohol Exposure Reduces Modulation of Glutamatergic Synaptic Transmission by 5-HT1A Receptors in the Rat Hippocampal CA3 Region

Fetal alcohol exposure has been associated with many neuropsychiatric disorders that have been linked to altered serotonin (5-hydroxytryptamine; 5-HT) signaling, including depression and anxiety. During the first 2 weeks of postnatal life in rodents (equivalent to the third trimester of human pregnancy) 5-HT neurons undergo significant functional maturation and their axons reach target regions in the forebrain (e.g., cortex and hippocampus). The objective of this study was to identify the effects of third trimester ethanol (EtOH) exposure on hippocampal 5-HT signaling. Using EtOH vapor inhalation chambers, we exposed rat pups to EtOH for 4 h/day from postnatal day (P) 2 to P12. The average serum EtOH concentration in the pups was 0.13 ± 0.04 g/dl (legal intoxication limit in humans = 0.08 g/dl). We used brain slices to assess the modulatory actions of 5-HT on field excitatory postsynaptic potentials in the hippocampal CA3 region at P13-P15. Application of the GABA_A/glycine receptor antagonist, picrotoxin, caused broadening of field excitatory postsynaptic potentials (fEPSPs), an effect that was reversed by application of 5-HT in slices from air exposed rats. However, this effect of 5-HT was absent in EtOH exposed animals. In slices from naïve animals, application of a 5-HT_1A receptor antagonist blocked the effect of 5-HT on the fEPSPs recorded in presence of picrotoxin, suggesting that third trimester ethanol exposure acts by inhibiting the function of these receptors. Studies indicate that 5-HT_1A receptors play a critical role in the development of hippocampal circuits. Therefore, inhibition of these receptors by third trimester ethanol exposure could contribute to the pathophysiology of fetal alcohol spectrum disorders.

The serotonin 5-HT3 receptor: a novel neurodevelopmental target

Serotonin (5-hydroxytryptamine, 5-HT), next to being an important neurotransmitter, recently gained attention as a key-regulator of pre- and postnatal development in the mammalian central nervous system (CNS). Several receptors for 5-HT are expressed in the developing brain including a ligand-gated ion channel, the 5-HT3 receptor. Over the past years, evidence has been accumulating that 5-HT3 receptors are involved in the regulation of neurodevelopment by serotonin. Here, we review the spatial and temporal expression patterns of 5-HT3 receptors in the pre- and early postnatal rodent brain and its functional implications. First, 5-HT3 receptors are expressed on GABAergic interneurons in neocortex and limbic structures derived from the caudal ganglionic eminence. Mature inhibitory GABAergic interneurons fine-tune neuronal excitability and thus are crucial for the physiological function of the brain. Second, 5-HT3 receptors are expressed on specific glutamatergic neurons, Cajal-Retzius cells in the cortex and granule cells in the cerebellum, where they regulate morphology, positioning, and connectivity of the local microcircuitry. Taken together, the 5-HT3 receptor emerges as a potential key-regulator of network formation and function in the CNS, which could have a major impact on our understanding of neurodevelopmental disorders in which 5-HT plays a role.

Dietary supplementation of female rats with elk velvet antler improves physical and neurological development of offspring

Elk velvet antler (EVA) has a traditional use for promotion of general health. However, evidence of EVA effects at different lifestages is generally lacking. This paper investigated the effects of long-term maternal dietary EVA supplementation on physical, reflexological and neurological development of rat offspring. Female Wistar rats were fed standard chow or chow containing 10% EVA for 90 days prior to mating and throughout pregnancy and lactation. In each dietary group, 56 male and 56 female pups were assessed for physical, neuromotor, and reflexologic development postnatally. Among the examined physical developmental parameters, incisor eruption occurred one day earlier in pups nursing dams receiving EVA. Among neuromotor developmental parameters, duration of supported and unsupported standing was longer for pups nursing EVA supplemented dams. Acquisition of neurological reflex parameters (righting reflex, negative geotaxis, cliff avoidance acoustic startle) occurred earlier in pups nursing dams receiving EVA. Longterm maternal EVA supplementation prior to and during pregnancy and lactation accelerated certain physical, reflexologic, and neuromotor developmental milestones and caused no discernible adverse effects on developing offspring. The potential benefits of maternal EVA supplementation on postnatal development warrants further investigation to determine whether EVA can be endorsed for the promotion of maternal and child health.

Anxiety-like behavior and cognitive flexibility in adult rats perinatally exposed to increased serotonin concentrations

Serotonin (5-hydroxytryptamine, 5HT) is a biologically active amine that regulates the development of 5HT neurons and target tissues during neurogenesis, while later it assumes the function of a neurotransmitter. Serotonin mediates many essential behaviors common to all mammals, and is held responsible for anxiety-like behavior and cognitive rigidity. Proper serotonin levels, controlled through 5HT synthesis and metabolism, are crucial for normal brain development. In this study we investigated anxiety-like behavior and cognitive flexibility in adult animals after exposing their developing brains to increased 5HT concentrations. Wistar rats were treated subcutaneously from gestational day 12 to post-natal day 21 with the immediate 5HT precursor 5-hydroxytryptophan (5HTP, 25mg/kg), a non-selective MAO inhibitor tranylcypromine (TCP, 2mg/kg), or saline. After reaching adulthood, animals were tested for anxiety-like behavior (exploratory behavior, thigmotactic behavior, social contact, and reaction to stressful stimulus) and cognitive flexibility (ability for reversal learning). Results of the behavioral studies corresponded with our previous neurochemical findings. Treatment with 5HTP, which has induced mild reduction in cortical 5HT concentrations, caused reduction in only one aspect of anxiety-like behavior (increased exploratory activity). Treatment with TCP, which lead to drastic reduction in 5HT concentration/function, resulted in a highly anxiolytic phenotype (reduced thigmotaxis, reaction to stress, and social anxiety) with improved cognitive flexibility. Although further neurochemical, anatomical and gene-expression studies are needed to elucidate the mechanisms underlying the observed behavior, we hope that our results will contribute to the understanding of the role of serotonin in anxiety-like behavior and cognitive rigidity.

Early-life blockade of 5-HT(1A) receptors alters adult anxiety behavior and benzodiazepine sensitivity

BACKGROUND

Early-life stress may affect 5-HT(1A) receptor circuitry, which could result in increased anxiety in later life. An increased anxiety phenotype in 5-HT(1A) receptor KO mice (1AKO) mice has been ascribed to 5-HT(1A) receptor absence during the early postnatal period. Thus, subtle and transient serotonergic changes during the early postnatal period may lead to an increased risk for developing stress-related disorders during adulthood.

METHODS

Wildtype and 1AKO mice on a Swiss-Webster (SW) background were treated during the early postnatal period with vehicle or the 5-HT(1A) receptor antagonist WAY-100,635.

RESULTS

Pharmacologic 5-HT(1A) receptor blockade during the early postnatal period induced long-lasting effects on anxiety and benzodiazepine sensitivity in adolescent and adult mice on a Swiss-Webster background and resembles the SW 1AKO phenotype. Furthermore, WAY-100,635-treated mice had increased cortical gamma-aminobutyric acid-A receptor (GABA(A)R) alpha(1) and alpha(3) subunit levels and increased hippocampal GABA(A)R alpha(2) subunit levels.

CONCLUSIONS

Absence of 5-HT(1A)R signaling during early stages of brain maturation predisposes an organism to affective dysfunction later in life. Because early-life treatment with WAY-100,635 in Swiss-Webster mice reduced diazepam sensitivity and increased GABA(A)R alpha subunit levels in the prefrontal cortex and hippocampus, our data suggest a putative link between early-life disruption of the serotonergic system and the emergence of increased anxiety and decreased benzodiazepine responsivity at adult age. Moreover, early-life 5-HT(1A) receptor functionality appears to be essential for the development of normal GABA(A)R functionality. This study may have clinical implications for psychoactive drug use during pregnancy and for the pharmacogenetic background of benzodiazepine sensitivity.

Effects of perinatal asphyxia on the neurobehavioral and retinal development of newborn rats

Perinatal asphyxia during delivery produces long-term deficits and represents a major problem in both neonatal and pediatric care. Several morphological, biochemical and behavioral changes have been described in rats exposed to perinatal asphyxia. The aim of the present study was to evaluate how perinatal asphyxia affects the complex early neurobehavioral development and retinal structure of newborn rats. Asphyxia was induced in ready-to-deliver mothers by removing the pups by cesarian section after 15 min of asphyxia. Somatic and neurobehavioral development was tested daily during the first 3 weeks, and motor coordination tests were performed on postnatal weeks 3-5. After completion of the testing procedure, retinas were removed for histological analysis. We found that in spite of the fast catch-up-growth of asphyctic pups, nearly all examined reflexes were delayed by 1-4 days: negative geotaxis, sensory reflexes, righting reflexes, development of fore- and hindlimb grasp and placing, gait and auditory startle reflexes. Time to perform negative geotaxis, surface righting and gait reflexes was significantly longer during the first few weeks in asphyctic pups. Among the motor coordination tests, a markedly weaker performance was observed in the grid walking and footfault test and in the walk initiation test. Retinal structure showed severe degeneration in the layer of the photoreceptor and bipolar cell bodies. In summary, our present study provided a detailed description of reflex and motor development following perinatal asphyxia, showing that asphyxia led to a marked delay in neurobehavioral development and a severe retinal degeneration.

Genetic analyses of roundabout (ROBO) axon guidance receptors in autism

Autism is a pervasive developmental disorder diagnosed in early childhood. Abnormalities of serotonergic neurotransmission have been reported in autism. Serotonin transporter (SERT) modulates serotonin levels, and is a major therapeutic target in autism. Factors that regulate SERT expression might be implicated in the pathophysiology of autism. One candidate SERT regulatory protein is the roundabout axon guidance molecule, ROBO. SerT expression in Drosophila is regulated by robo; it plays a vital role in mammalian neurodevelopment also. Here, we examined the associations of ROBO3 and ROBO4 with autism, in a trio association study using DNA from 252 families recruited to AGRE. Four SNPs of ROBO3 (rs3923890, P = 0.023; rs7925879, P = 0.017; rs4606490, P = 0.033; and rs3802905, P = 0.049) and a single SNP of ROBO4 (rs6590109, P = 0.009) showed associations with autism; the A/A genotype of rs3923890 showed lower ADI-R_A scores, which reflect social interaction. Significant haplotype associations were also observed for ROBO3 and ROBO4. We further compared the mRNA expressions of ROBO1, ROBO2, ROBO3, and ROBO4 in the lymphocytes of 19 drug-naïve autistic patients and 20 age- and sex-matched controls. Expressions of ROBO1 (P = 0.018) and ROBO2 (P = 0.023) were significantly reduced in the autistic group; the possibility of using the altered expressions of ROBO as peripheral markers for autism, may be explored. In conclusion, we suggest a possible role of ROBO in the pathogenesis of autism. Abnormalities of ROBO may lead to autism either by interfering with serotonergic system, or by disrupting neurodevelopment. To the best of our knowledge, this is the first report relating ROBO with autism.

Embryonic and postnatal development of the serotonergic raphe system and its target regions in 5-HT1A receptor deletion or overexpressing mouse mutants

The neurotransmitter 5-HT regulates early developmental processes in the CNS. In the present study we followed the embryonic and postnatal development of serotonergic raphe neurons and catecholaminergic target systems in the brain of 5-HT1A receptor knockout (KO) and overexpressing (OE) in comparison with wild-type (WT) mice from embryonic day (E) 12.5 to postnatal day (P) 15.5. Up to P15.5 no differences were apparent in the differentiation and distribution of serotonergic neurons in the raphe area as revealed by the equal number of serotonergic neurons in the dorsal raphe in all three genotypes. However, the establishment of serotonergic projections to the mesencephalic tegmentum and hypothalamus was delayed at E12.5 in KO and OE animals and projections to the cerebral cortex between E16.5 and E18.5 were delayed in OE mice. This delay was only transient and did not occur in other brain areas including septum, hippocampus and striatum. Moreover, OE mice caught up with WT and KO animals postnatally such that at P1.5 serotonergic innervation of the cortex was more extensive in the OE than in KO and WT mice. Tissue levels of 5-HT and of its main metabolite 5-hydroxyindoleacetic acid as well as 5-HT turnover were considerably higher in brains of OE mice and slightly elevated in KO mice in comparison with the WT, starting at E16.5 through P15.5. The initial differentiation of dopaminergic neurons and fibers in the substantia nigra at E12.5 was transiently delayed in KO and OE mice as compared with WT mice, but no abnormalities in noradrenergic development were apparent in later stages. The present data indicate that 5-HT1A receptor deficiency or overexpression is associated with increased 5-HT synthesis and turnover in the early postnatal period. However, they also show that effects of 5-HT1A KO or OE on the structural development of the serotonergic system are at best subtle and transient. They may nonetheless contribute to the establishment of increased or reduced anxiety-like behavior, respectively, in adult mice.

Behavioral evaluation of male and female mice pups exposed to fluoxetine during pregnancy and lactation

BACKGROUND/AIMS

Fluoxetine (FLX) has been widely prescribed for depression during pregnancy and/or lactation. Since serotonin is a neurotrophic factor, the use of FLX by mothers could disrupt brain development resulting in behavioral alterations in their progeny. This study evaluated the effects of developmental FLX exposure on anxiety, depression, aggressivity and pain sensitivity of male and female mice pups.

METHODS

Swiss dams were treated daily, by gavage, with 7.5 mg/kg of FLX during pregnancy and lactation. Pups were submitted to open-field, forced swimming, elevated plus-maze, intruder-resident and hot plate tests at adolescence and adulthood.

RESULTS AND CONCLUSION

In male pups, exposure to FLX decreased ambulation at postnatal day (PND) 40 and tended (p=0.07) to increase the latency to the first attack in the intruder-resident test at PND 70, suggesting decreased impulsivity. In female pups, FLX exposure increased immobility time in the forced swimming test at both PND 30 and 70, which is interpreted as depressive-like behavior. In conclusion, our results suggest that maternal exposure to FLX during pregnancy and lactation results in enduring behavioral alterations in male and female pups throughout life.

Pharmacotherapy of child and adolescent depression

Pediatric depression is a prevalent and recurrent condition that persists into adulthood and carries significant impairment, morbidity, and risk of mortality. Although there has been a surge of pediatric antidepressant studies in recent years, depression remains largely understudied, unrecognized, and untreated in children and adolescents. Few antidepressant trials have yielded positive results in pediatric depression. Regulatory agencies recently issued warnings against the use of selective serotonin reuptake inhibitors and newer antidepressants in depressed children and adolescents because of a possible link between their use and the appearance or worsening of suicidal ideation or attempts. The authors review data on efficacy and safety of antidepressants for the treatment of pediatric depression to provide treating clinicians with a basis on which to guide their treatment recommendations.

Early neonatal and postweaning social emotional deprivation interferes with the maturation of serotonergic and tyrosine hydroxylase-immunoreactive afferent fiber systems in the rodent nucleus accumbens, hippocampus and amygdala

The impact of early emotional experience on the development of serotonergic and dopaminergic fiber innervation of the nucleus accumbens, hippocampal formation and the amygdala was quantitatively investigated in the precocious rodent Octodon degus. Two animal groups were compared: 1) degus which were repeatedly separated from their parents during the first three postnatal weeks, after weaning they were individually reared in chronic social isolation and 2) controls which were reared undisturbed with their families. In the deprived animals 5-hydroxytryptamine-immunoreactive fiber densities were increased in the core region of the nucleus accumbens (up to 126%), in the central nucleus of the amygdala (up to 112%) and in the outer subregion of the dentate gyrus stratum moleculare (up to 149%), whereas decreased fiber densities were detected in the dentate subgranular layer (down to 86%) and in the stratum lacunosum of the hippocampal cornu ammonis region 1 (down to 86%). Tyrosine hydroxylase-immunoreactive fiber densities were increased in the core (up to 115%) and shell region (up to 113%) of the nucleus accumbens of deprived animals, whereas decreased fiber densities (down to 84%) were observed in the hilus of the dentate gyrus. In the stratum granulosum and subgranular layer the fiber densities increased up to 168% and 127% respectively. In summary, these results indicate that the postnatal establishment of the monoaminergic innervation of limbic areas is modulated in response to early emotional experience, and that this environmental morphological adaptation is highly region specific.

Development of neurological reflexes and motor coordination in rats neonatally treated with monosodium glutamate

Monosodium glutamate (MSG) treatment of neonatal rats causes neuronal degeneration in various brain areas and leads to several neurochemical, endocrinological and behavioral alterations. However, relatively little is known about the development of neurological reflexes and motor coordination of these animals. Therefore, the aim of the present study was to examine the neurobehavioral development of newborn rats treated with MSG. Rats received MSG at postnatal days 1, 3, 5, 7, and 9. Appearance of neural reflexes and reflex performance as well as motor coordination were examined for 5 weeks after birth. The efficacy of MSG treatment was confirmed by histological examination of the arcuate nucleus. We found that MSG treatment delayed the appearance of forelimb placing, forelimb grasp and righting reflexes, besides the retarded somatic development. The treated pups performed surface righting in significantly longer times. Also, worse performance was observed in the foot-fault and rota-rod tests. However, MSG-treated rats reached control levels by the end of the fifth postnatal week. These results show that MSG treatment does not cause permanent alterations in the neurobehavioral development, only delays the appearance of some reflexes and leads to temporary changes in reflex performance and motor coordination signs.

The hypotensive effect of BMY 7378 involves central 5-HT1A receptor stimulation in the adult but not in the young rat

BACKGROUND

Stimulation of central 5-hydroxytryptamine-1A (5-HT(1A)) receptors produces hypotension and bradycardia. We describe BMY 7378 (8-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-8-azaspiro[4.5]decane-7,9 dione) effects in cardiovascular function and [(3)H] 8-OH-DPAT (8-hydroxy-2-(di-n-propyl-amino) tetralin) binding sites in rat brain of different ages.

METHODS

BMY 7378 was administered to anesthetized male Wistar rats (1, 3 and 6 months old) and blood pressure and heart rate were continuously recorded. Saturation of [(3)H] 8-OH-DPAT binding to 5-HT(1A) sites in brain membranes was determined.

RESULTS

Basal diastolic blood pressure increased with age, 85 +/- 2, 106 +/- 3, and 113 +/- 2 mmHg for 1-, 3- and 6-month-old rats, respectively (p <0.05 among groups). BMY 7378 induced significant dose- and age-dependent hypotension. The selective 5-HT(1A) receptor antagonist, WAY 100635 (N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]N-(2-pyridinyl) cyclohexanecarboxamide), antagonized BMY 7378 effects in 6 month-old but not in younger rats. [(3)H] 8-OH-DPAT binding sites decreased in hippocampi and brainstem with maturation.

CONCLUSIONS

Data suggest that BMY 7378 is a hypotensive agent in the rat, but that its actions are mediated, in part, by central 5-HT(1A) receptor stimulation in the adult and by a nonserotonergic mechanism in the young rat.

Gender-specific 5-HT1A receptor changes in BrdU nuclear labeling patterns in neonatal dentate gyrus

The actions of 5-HT1A receptors on cell proliferation in the rat neonatal dentate gyrus are unknown. We injected a 5-HT1A receptor agonist (ipsapirone) or antagonist (Way 100635) 1 h before injections of BrdU in neonates of both genders between days 2-4, a peak time of dentate gyrus granule cell proliferation. The BrdU immunoreactive (IR) nuclei in the granule cell layer and subgranular zone were examined after 2 weeks. The BrdU-IR nuclear staining patterns were classified as being either diffuse (homogenous dark BrdU-staining throughout the nucleus) or punctate (multiple distinct small stained spots within the nucleus). Most BrdU-labeled nuclei with a diffuse pattern were seen in the subgranular zone while the punctate pattern nuclei were seen within the granular cell layer of the dentate gyrus. 5-HT1A antagonist showed no overall change in absolute number or pattern of labeled nuclei compared to control animals. After a 5-HT1A agonist, there was also no differences in the total number of BrdU-IR nuclei (punctate and diffuse pattern). However, in both genders, the proportion of the BrdU-labeled nuclei showing a punctate compared to diffuse pattern increased: 33% in females and 18% in males. In females, the 5-HT1A receptor agonist increased the number of nuclei showing a punctate pattern by 41%, while in males the 5-HT1A receptor agonist decreased the number of nuclei showing a diffuse pattern by 29%. These results indicate gender-specific 5-HT1A receptor action on the state of nuclear DNA in the cells of the dentate gyrus, without increasing the total number of BrdU-labeled nuclei.

Ontogeny of 5-HT1A receptor expression in the developing hippocampus

Serotonin (5-HT) has long been implicated in a number of neurodevelopmental processes including neuronal cell division, migration, neurite outgrowth, and synapse formation. However, relatively little is known about how these effects are mediated during normal brain development in vivo and the identity of the receptor subtypes involved in mediating these effects. In recent years, a number of pharmacological studies have suggested a role for the serotonin 1A (5HT1A) receptor subtype in mediating the developmental effects of 5-HT in the hippocampus. These studies, however, have been difficult to interpret due to lack of information regarding the expression and distribution of 5HT1A in the developing brain and hippocampus in particular. In the current study, specific anti-5-HT1A antibodies, developed in our laboratory [F.C. Zhou, T.D. Patel, D. Swartz, Y. Xu, M.R. Kelley, Production and characterization of an anti-serotonin 1A receptor antibody which detects functional 5-HT1A binding sites, Brain Res Mol Brain Res, 69 (1999) 186-201], were utilized to map the ontogeny and distribution of the 5HT1A receptor protein in the developing rat hippocampus through embryonic and early postnatal life. This is the first such study of 5-HT1A expression in the developing rat brain. Our findings revealed that expression of the 5HT1A receptor emerges during the initial stages of embryonic hippocampal development. Remarkably, most if not all hippocampal neurons begin to express 5HT1A shortly upon completion of their terminal mitosis. We found that 5HT1A is initially concentrated around the cell bodies and later becomes more sparsely distributed along the dendrites after the neurons have matured. In addition to postmitotic neurons, we have observed that S100 and GFAP positive glia transiently express 5HT1A during early postnatal development of the hippocampus. These findings demonstrate that the 5-HT1A receptor is positioned to mediate developmental effects of serotonin in the hippocampus. Furthermore, the temporal patterns of expression suggest a role for 5-HT1A in postmitotic events such as neuronal migration, neurite outgrowth, and phenotypic differentiation.

Variability in the benzodiazepine response of serotonin 5-HT1A receptor null mice displaying anxiety-like phenotype: evidence for genetic modifiers in the 5-HT-mediated regulation of GABA(A) receptors

Benzodiazepines (BZs) acting as modulators of GABA(A) receptors (GABA(A)Rs) are an important group of drugs for the treatment of anxiety disorders. However, a large inter-individual variation in BZ sensitivity occurs in the human population with some anxiety disorder patients exhibiting diminished sensitivity to BZ and reduced density of GABA(A)Rs. The mechanism underlying BZ treatment resistance is not known, and it is not possible to predict whether an anxiety patient will respond to BZ. 5-hydroxytryptamine1A receptor (5-HT1AR) null mice (R-/-) on the Swiss-Webster (SW) background reproduce several features of BZ-resistant anxiety; they exhibit anxiety-related behaviors, do not respond to BZ, have reduced BZ binding, and have decreased expression of the major GABA(A)R subunits alpha1 and alpha2. Here, we show that R-/- mice on the C57Bl6 (B6) background also have anxiety phenotype, but they respond to BZ and have normal GABA(A)R subunit expression. This indicates that the 5-HT1AR-mediated regulation of GABA(A)R alpha subunit expression is subject to genetic modification. Hybrid SW/B6-R-/- mice also exhibit BZ-resistant anxiety, suggesting that SW mice carry a genetic modifier, which mediates the effect of the 5-HT1AR on the expression of GABA(A)Ralpha subunits. In addition, we show that this genetic interaction in SW mice operates early in postnatal life to influence the expression of GABA(A)R alpha subunits at the transcriptional level. These data indicate that BZ-resistant anxiety results from a developmental arrest of GABA(A)R expression in SW-R-/- mice, and a similar mechanism may be responsible for the BZ insensitivity of some anxiety patients.

Separation-induced receptor changes in the hippocampus and amygdala of Octodon degus: influence of maternal vocalizations

Relatively little is known about the basic mechanisms that play a role in the vulnerability of the developing brain toward adverse environmental influences. Our study in the South American rodent Octodon degus revealed that repeated brief separation from the parents and exposure to an unfamiliar environment induces in the hippocampal formation of male and female pups an upregulation of D1 and 5-HT1A receptor density in the stratum radiatum and stratum lacunosum moleculare of the CA1 region. In the CA3 region, only the 5-HT1A receptors were upregulated; no changes were observed for D1 receptors in this region. GABA(A) receptor density in the hippocampus and amygdala was downregulated (nonsignificant trend) after parental separation. The acoustic presence of the mother during parental separation suppressed the D1 and 5-HT1A receptor upregulation in some regions of the hippocampus; no such suppressing influence was observed for the GABA(A) receptors. In the basomedial amygdala, the maternal calls enhanced the separation-induced 5-HT1A receptor upregulation in the male pups, whereas in the female pups the separation-induced receptor densities were not only suppressed by the maternal call but further downregulated, compared with the control group. These results demonstrate that early adverse emotional experience alters aminergic function within the hippocampus and amygdala and that the mother's voice, a powerful emotional signal, can modulate these effects in the developing limbic system.

Neonatal perturbation of neurotrophic signaling results in abnormal sensorimotor gating and social interaction in adults: implication for epidermal growth factor in cognitive development

Epidermal growth factor (EGF) and its structurally related proteins are implicated in the developmental regulation of various brain neurons, including midbrain dopaminergic neurons. There are EGF and EGF receptor abnormalities in both brain tissues and blood from schizophrenic patients. We administered EGF to neonatal rats to transiently perturb endogenous EGF receptor signaling and evaluated the neurobehavioral consequences. EGF-treatment-induced transient impairment in tyrosine hydroxylase expression. The animals grew normally, exhibited normal weight increase, glial growth, and gross brain structures, and later lost the tyrosine hydroxylase abnormality. During and after development, however, the rats began to display various behavioral abnormalities. Abnormal sensorimotor gating was apparent, as measured by deficits in prepulse inhibition of acoustic startle. Motor activity and social interaction scores of the EGF-treated animals were also impaired in adult rats, though not in earlier developmental stages. In parallel, there was a significant abnormality in dopamine metabolism in the brain stem of the adult animals. Gross learning ability appeared to be normal as measured by active avoidance. These behavioral alterations, which are often present in schizophrenic models, were ameliorated by subchronic treatment with clozapine. Although the molecular and/or physiologic background(s) of these behavioral abnormalities await further investigation, the results of the present experiment indicate that abnormal EGF receptor stimulation given during limited neonatal stages can result in severe and persistent cognitive/behavioral dysfunctions, which appear only in adulthood.

Role of syntaxin 1A on serotonin transporter expression in developing thalamocortical neurons

Neurotransmitter transporters are regulated through a variety of signal transduction mechanisms which may operate in order to maintain appropriate levels of transmitter in the synaptic cleft. GABA and glycine transporters both interact with components of the neurotransmitter release, such as the SNARE protein syntaxin 1A, suggesting that protein-protein interactions are a common method for regulating members of the neurotransmitter transporter family, and thus, linking the release of transmitter to its subsequent re-uptake. In the present report, the interaction of syntaxin 1A with endogenous serotonin transporters (SERT) expressed in developing thalamocortical neurons is examined. Incubation of thalamocortical cultures with botulinum toxin C1, which specifically cleaves syntaxin 1A, decreased SERT function. Serotonin (5HT) saturation analysis showed that the effect of the toxin was to decrease maximum transport capacity with little change to the affinity of the transporter for 5HT. The 5HT uptake data were consistent with biotinylation experiments showing a decrease in the surface expression of SERT following toxin treatment. In addition, co-immunoprecipitation experiments showed that SERT and syntaxin 1A form a protein complex in these neurons. These data show that components of the transmitter release machinery interact with endogenously expressed amine transporters, and suggest a mechanism for the control of transmitter levels in disorders related to aminergic signaling.

Prolonged prenatal psychotropic medication exposure alters neonatal acute pain response

Selective serotonin reuptake inhibitors (SSRIs) and benzodiazepines are frequently used to treat maternal depression during pregnancy, however the effect of increased serotonin (5HT) and gamma-amino-butyric acid (GABA) agonists in the fetal human brain remains unknown. 5HT and GABA are active during fetal neurologic growth and play early roles in pain modulation, therefore, if prolonged prenatal exposure alters neurodevelopment this may become evident in altered neonatal pain responses. To examine biologic and behavioral effects of prenatal exposure, neonatal responses to acute pain (phenylketonuria heel lance) in infants with prolonged prenatal exposure were examined. Facial action (Neonatal Facial Coding System) and cardiac autonomic reactivity derived from the relationship between respiratory activity and short term variations of heart rate (HRV) were compared between 22 infants with SSRI exposure (SE) [fluoxetine (n = 7), paroxetine (n = 11), sertraline (n = 4)]; 16 infants exposed to SSRIs and clonazepam (SE+) [paroxetine (n = 14), fluoxetine (n = 2)]; and 23 nonexposed infants during baseline, lance, and recovery periods of a heel lance. Length of maternal SSRI use did not vary significantly between exposure groups-[mean (range)] SE:SE+ 183 (31-281):141 (54-282) d (p > 0.05). Infants exposed to SE and SE+ displayed significantly less facial activity to heel lance than control infants. Mean HR increased with lance, but was significantly lower in SE infants during recovery. Using measures of HRV and the transfer relationship between heart rate and respiration, SSRI infants had a greater return of parasympathetic cardiac modulation in the recovery period, whereas a sustained sympathetic response continued in the control group. Prolonged prenatal SSRI exposure appears to be associated with reduced behavioral pain responses and increased parasympathetic cardiac modulation in recovery following an acute neonatal noxious event. Possible 5HT-mediated pain inhibition, pharmacologic factors and the developmental course remain to be studied.

Isolation-rearing of rats produces deficits as adults in the serotonergic innervation of hippocampus

Isolation-rearing of rats causes a variety of behavioral changes, including anxiety, learning deficits and sensory changes related to schizophrenia. Similar changes are seen following loss of serotonin during development. Thus, the effects of isolation-rearing on behavior may be due to changes in serotonin. Sprague-Dawley rats were raised in groups of four (social animals) or in isolation, from postnatal day 22 until postnatal day 64. The hippocampi were examined immunochemically for changes in serotonin. Our findings show that serotonin terminals are lost throughout the CA regions of hippocampus, where there is also an associated loss of dendrites, but not in the molecular layer of the dentate gyrus. Thus, some of the brain and behavioral changes seen in isolation-reared animals could be due to loss of serotonin.

Postnatal development of 5-HT(1A) receptor expression in rat somatic motoneurons

Prior work has established that hypoglossal motoneurons (HMs) change postnatally in their response to serotonin (5-HT), in part as a result of a decline in expression of 5-HT(1A) receptors. In the current study, two issues were addressed. First, using in situ hybridization we found that transient expression of 5-HT(1A) receptors occurs in other populations of brainstem (facial and trigeminal) and spinal (cervical and lumbar) motoneurons. Second, the participation of motoneuronal afferent (serotonergic) and efferent (neuromuscular) innervation in inducing and maintaining this decline in expression was investigated. Serotonergic innervation of the hypoglossal nucleus (nXII) was disrupted in neonatal rats by intra-cisternal injection of the serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT), and 5-HT(1A) receptor mRNA levels in nXII from these rats were assayed at postnatal day 21. In spite of an almost complete loss of serotonergic fibers in the region, the postnatal decrease in 5-HT(1A) receptor expression by HMs still occurred. To test for potential regulation by target-derived factors or by nerve injury, receptor mRNA levels were assayed after unilateral transection of the hypoglossal nerve in adult rats. Though this treatment resulted in re-induction of developmentally transient expression of the p75 neurotrophin receptor, 5-HT(1A) receptor expression remained low. Thus, neonatal expression of 5-HT(1A) receptors appears to be common to somatic motoneurons, but we found no evidence for changes in serotonergic innervation in influencing this expression, nor did we find evidence for its regulation by peripheral factors.

Production and characterization of an anti-serotonin 1A receptor antibody which detects functional 5-HT1A binding sites

We describe the production and characterization of a specific anti-5-HT1A receptor antibody made against a fusion protein consisting of glutathione-S-transferase (GST) coupled to a 75-amino acid sequence from the middle portion of the third intracellular loop (5-HT1A-m3i, serine253-arginine327) of the rat 5-HT1A receptor protein. This region was chosen to avoid putative phosphorylation and glycosylation sites and regions of known homology with other 5-HT receptors. Western blot analysis indicated that the polyclonal anti-5-HT1A-m3i antibody accurately recognized the fusion protein expressed in bacteria and labeled a prominent 67 kDa protein band in the hippocampus, cortex, brainstem, cerebellum and kidney with a density profile corresponding to the relative abundance of the 5-HT1A receptor in these tissues. No protein was detected in liver or muscle tissue preparations, and no protein bands were labeled in any of the above tissues following preabsorption of the antibody with the 5-HT1A-m3i fusion protein. Immunohistochemistry revealed prominent labeling in limbic structures including the hippocampus, amygdala, entorhinal cortex, and septum as well as in raphe nuclei. In the hippocampus, 5-HT1A-m3i labeling revealed a characteristic laminar pattern that coincided with that seen by autoradiographic binding of the 5-HT1A agonist [3H]-8-OH-DPAT in all strata of the hippocampal formation. In the dorsal and medial raphe nuclei, anti-5-HT1A-m3i antibodies labeled the somatodendritic membranes of 5-HT neurons, consistent with its role as an autoreceptor. The detailed matching of the anti-5-HT1A-m3i antibody with [3H]-8-OH-DPAT binding suggests that the antibody recognizes a functionally active form of the 5-HT1A receptor protein capable of binding 5-HT1A agonist ligands. These anti-5-HT1A antibodies may therefore be useful tools in localizing functional 5-HT1A receptors in specific regions of the brain as well as in studying the plasticity and ontogeny of the 5-HT1A receptor at the cellular and subcellular level.

Pediatric psychopharmacology and the interaction between drugs and the developing brain

With increasing frequency, psychotropic medications are being prescribed to young children, often for long periods of time. The interaction between psychotropics and the developing brain has not been systematically investigated in humans. Data collected from animals suggest that developing neurotransmitter systems can be exquisitely sensitive to early inhibition or stimulation by pharmacological agents, which can lead to permanent changes in adult life. Most of these data are collected from rodents, and their extrapolation to humans is difficult. More relevant models could be developed for instance using primates. In humans, the focus of research has traditionally been on the possible teratogenic effects of prenatal drug exposure. Recently introduced quantitative imaging techniques can offer new approaches to studying the effects of psychotropics on the developing brain. This research has clear implications for the safety and efficacy of psychopharmacologic drug in children.