Neuroanatomic relationships between the GABAergic and serotonergic systems in the developing human medulla

Role of the Dorsal Raphe Nucleus in Pain Processing

The dorsal raphe nucleus (DRN) has gained attention owing to its involvement in various physiological functions, such as sleep-awake, feeding, and emotion, with its analgesic role being particularly significant. It is described as the "pain inhibitory nucleus" in the brain. The DRN has diverse projections from hypothalamus, midbrain, and pons. In turn, the DRN is a major source of projections to diverse cortex, limbic forebrain thalamus, and the midbrain and contains highly heterogeneous neuronal subtypes. The activation of DRN neurons in mice prevents the establishment of neuropathic, chronic pain symptoms. Chemogenetic or optogenetic inhibition neurons in the DRN are sufficient to establish pain phenotypes, including long-lasting tactile allodynia, that scale with the extent of stimulation, thereby promoting nociplastic pain. Recent progress has been made in identifying the neural circuits and cellular mechanisms in the DRN that are responsible for sensory modulation. However, there is still a lack of comprehensive review addressing the specific neuron types in the DRN involved in pain modulation. This review summarizes the function of specific cell types within DRN in the pain regulation, and aims to improve understanding of the mechanisms underlying pain regulation in the DRN, ultimately offering insights for further exploration.

Peripheral Neuroplasticity of Respiratory Chemoreflexes, Induced by Prenatal Nicotinic Exposure: Implication for SIDS

Sudden Infant Death Syndrome (SIDS) occurs during sleep in seemingly healthy infants. Maternal cigarette smoking and hypoxemia during sleep are assumed to be the major causal factors. Depressed hypoxic ventilatory response (dHVR) is observed in infants with high risk of SIDS, and apneas (lethal ventilatory arrest) appear during the fatal episode of SIDS. Disturbance of the respiratory center has been proposed to be involved, but the pathogenesis of SIDS is still not fully understood. Peripherally, the carotid body is critical to generate HVR, and bronchopulmonary and superior laryngeal C-fibers (PCFs and SLCFs) are important for triggering central apneas; however, their roles in the pathogenesis of SIDS have not been explored until recently. There are three lines of recently accumulated evidence to show the disorders of peripheral sensory afferent-mediated respiratory chemoreflexes in rat pups with prenatal nicotinic exposure (a SIDS model) in which acute severe hypoxia leads to dHVR followed by lethal apneas. (1) The carotid body-mediated HVR is suppressed with a reduction of the number and sensitivity of glomus cells. (2) PCF-mediated apneic response is largely prolonged via increased PCF density, pulmonary IL-1β and serotonin (5-hydroxytryptamine, 5-HT) release, along with the enhanced expression of TRPV1, NK₁R, IL1RI and 5-HT₃R in pulmonary C-neurons to strengthen these neural responses to capsaicin, a selective stimulant to C-fibers. (3) SLCF-mediated apnea and capsaicin-induced currents in superior laryngeal C-neurons are augmented by upregulation of TRPV1 expression in these neurons. These results, along with hypoxic sensitization/stimulation of PCFs, gain insight into the mechanisms of prenatal nicotinic exposure-induced peripheral neuroplasticity responsible for dHVR and long-lasting apnea during hypoxia in rat pups. Therefore, in addition to the disturbance in the respiratory center, the disorders of peripheral sensory afferent-mediated chemoreflexes may also be involved in respiratory failure and death denoted in SIDS victims.

Cannabidiol and the corticoraphe circuit in post-traumatic stress disorder

Post-Traumatic Stress Disorder (PTSD), characterized by re-experiencing, avoidance, negative affect, and impaired memory processing, may develop after traumatic events. PTSD is complicated by impaired plasticity and medial prefrontal cortex (mPFC) activity, hyperactivity of the amygdala, and impaired fear extinction. Cannabidiol (CBD) is a promising candidate for treatment due to its multimodal action that enhances plasticity and calms hyperexcitability. CBD’s mechanism in the mPFC of PTSD patients has been explored extensively, but literature on the mechanism in the dorsal raphe nucleus (DRN) is lacking. Following the PRISMA guidelines, we examined current literature regarding CBD in PTSD and overlapping symptomologies to propose a mechanism by which CBD treats PTSD via corticoraphe circuit. Acute CBD inhibits excess 5-HT release from DRN to amygdala and releases anandamide (AEA) onto amygdala inputs. By first reducing amygdala and DRN hyperactivity, CBD begins to ameliorate activity disparity between mPFC and amygdala. Chronic CBD recruits the mPFC, creating harmonious corticoraphe signaling. DRN releases enough 5-HT to ameliorate mPFC hypoactivity, while the mPFC continuously excites DRN 5-HT neurons via glutamate. Meanwhile, AEA regulates corticoraphe activity to stabilize signaling. AEA prevents DRN GABAergic interneurons from inhibiting 5-HT release so the DRN can assist the mPFC in overcoming its hypoactivity. DRN-mediated restoration of mPFC activity underlies CBD’s mechanism on fear extinction and learning of stress coping.

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CBD reduces PTSD symptoms via the DRN and corticoraphe circuit.

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Acute effects of CBD reduce DRN-amygdala excitatory signaling to lessen the activity disparity between amygdala and mPFC.

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Chronic CBD officially resolves mPFC hypoactivity by facilitating 5-HT release from DRN to mPFC.

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CBD-facilitated endocannabinoid signaling stabilizes DRN activity and restores mPFC inhibitory control.

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Chronically administered CBD acts via the corticoraphe circuit to favor fear extinction over fear memory reconsolidation.

The Serotonin Brainstem Hypothesis for the Sudden Infant Death Syndrome

The sudden infant death syndrome (SIDS) is the leading cause of postneonatal infant mortality in the United States today, with an overall rate of 0.39/1000 live births. It is defined as the sudden and unexpected death of an infant <12 months of age that remains unexplained after a complete autopsy, death scene investigation, and review of the clinical history. The serotonin brainstem hypothesis has been a leading hypothesis for SIDS over the last 2 decades. Our laboratory has studied this hypothesis over time with a variety of tissue techniques, including tissue receptor autoradiography, high performance liquid chromatography, Western blot analysis, immunocytochemistry, and proteomics. The purpose of this article is to review the progress in our laboratory toward supporting this hypothesis. We conclude that an important subset of SIDS infants has serotonergic abnormalities resulting from a "core lesion" in the medullary reticular formation comprised of nuclei that contain serotonin neurons. This lesion could lead to a failure of protective brainstem responses to homeostatic challenges during sleep in a critical developmental period which cause sleep-related sudden death.

Prenatal intermittent hypoxia sensitizes the laryngeal chemoreflex, blocks serotoninergic shortening of the reflex, and reduces 5-HT3 receptor binding in the NTS in anesthetized rat pups

We tested the hypothesis that exposure to intermittent hypoxia (IH) during pregnancy would prolong the laryngeal chemoreflex (LCR) and diminish the capacity of serotonin (5-hydroxytryptamine; 5-HT) to terminate the LCR. Prenatal exposure to IH was associated with significant prolongation of the LCR in younger, anesthetized, postnatal day (P) rat pups age P8 to P16 compared to control, room air (RA)-exposed rat pups of the same age. Serotonin microinjected into the NTS shortened the LCR in rat pups exposed to RA during gestation, but 5-HT failed to shorten the LCR in rat pups exposed to prenatal IH. Given these observations, we tested the hypothesis that prenatal hypoxia would decrease binding to 5-HT3 receptors in the nucleus of the solitary tract (NTS) where 5-HT acts to shorten the LCR. Serotonin 3 receptor binding was reduced in younger rat pups exposed to IH compared to control, RA-exposed rat pups in the age range P8 to P12. Serotonin 3 receptor binding was similar in older animals (P18-P24) regardless of gas exposure during gestation. The failure of the 5-HT injected into the NTS to shorten the LCR was correlated with a developmental decrease in 5-HT3 receptor binding in the NTS associated with exposure to prenatal IH. In summary, prenatal IH sensitized reflex apnea and blunted processes that terminate reflex apneas in neonatal rat pups, processes that are essential to prevent death following apneas such as those seen in babies who died of SIDS.

Uncovering a critical period of synaptic imbalance during postnatal development of the rat visual cortex: role of brain-derived neurotrophic factor

KEY POINTS

With daily electrophysiological recordings and neurochemical analysis, we uncovered a transient period of synaptic imbalance between enhanced inhibition and suppressed excitation in rat visual cortical neurons from the end of the fourth toward the end of the fifth postnatal weeks. The expression of brain-derived neurotrophic factor (BDNF), which normally enhances excitation and suppresses inhibition, was down-regulated during that time, suggesting that this may contribute to the inhibition/excitation imbalance. An agonist of the BDNF receptor tropomyosin-related kinase B (TrkB) partially reversed the imbalance, whereas a TrkB antagonist accentuated the imbalance during the transient period. Monocular lid suture during the transient period is more detrimental to the function and neurochemical properties of visual cortical neurons than before or after this period. We regard the period of synaptic imbalance as the peak critical period of vulnerability, and its existence is necessary for neurons to transition from immaturity to a more mature state of functioning.

ABSTRACT

The mammalian visual cortex is immature at birth and undergoes postnatal structural and functional adjustments. The exact timing of the vulnerable period in rodents remains unclear. The critical period is characterized by inhibitory GABAergic maturation reportedly dependent on brain-derived neurotrophic factor (BDNF). However, most of the studies were performed on experimental/transgenic animals, questioning the relationship in normal animals. The present study aimed to conduct in-depth analyses of the synaptic and neurochemical development of visual cortical neurons in normal and monocularly-deprived rats and to determine specific changes, if any, during the critical period. We found that (i) against a gradual increase in excitation and inhibition with age, a transient period of synaptic and neurochemical imbalance existed with suppressed excitation and enhanced inhibition at postnatal days 28 to 33/34; (ii) during this window, the expression of BDNF and tropomyosin-related kinase B (TrkB) receptors decreased, along with glutamatergic GluN1 and GluA1 receptors and the metabolic marker cytochrome oxidase, whereas that of GABAA Rα1 receptors continued to rise; (iii) monocular deprivation reduced both excitatory and inhibitory synaptic activity and neurochemicals mainly during this period; and (iv) in vivo TrkB agonist partially reversed the synaptic imbalance in normal and monocularly-deprived neurons during this time, whereas a TrkB antagonist accentuated the imbalance. Thus, our findings highlight a transitory period of synaptic imbalance with a negative relationship between BDNF and inhibitory GABA. This brief critical period may be necessary in transitioning from an immature to a more mature state of visual cortical functioning.

Embryonic hindbrain patterning genes delineate distinct cardio-respiratory and metabolic homeostatic populations in the adult

Previous studies based on mouse genetic mutations suggest that proper partitioning of the hindbrain into transient, genetically-defined segments called rhombomeres is required for normal respiratory development and function in neonates. Less clear is what role these genes and the neurons they define play in adult respiratory circuit organization. Several Cre drivers are used to access and study developmental rhombomeric domains (Eng1^Cre, HoxA2-Cre, Egr2^Cre, HoxB1^Cre, and HoxA4-Cre) in the adult. However, these drivers show cumulative activity beyond the brainstem while being used in intersectional genetic experiments to map central respiratory circuitry. We crossed these drivers to conditional DREADD mouse lines to further characterize the functional contributions of Cre defined populations. In the adult, we show that acute DREADD inhibition of targeted populations results in a variety of not only respiratory phenotypes but also metabolic and temperature changes that likely play a significant role in the observed respiratory alterations. DREADD mediated excitation of targeted domains all resulted in death, with unique differences in the patterns of cardio-respiratory failure. These data add to a growing body of work aimed at understanding the role of early embryonic patterning genes in organizing adult respiratory homeostatic networks that may be perturbed in congenital pathophysiologies.

Morphological changes of glutamatergic synapses in animal models of Parkinson's disease

The striatum and the subthalamic nucleus (STN) are the main entry doors for extrinsic inputs to reach the basal ganglia (BG) circuitry. The cerebral cortex, thalamus and brainstem are the key sources of glutamatergic inputs to these nuclei. There is anatomical, functional and neurochemical evidence that glutamatergic neurotransmission is altered in the striatum and STN of animal models of Parkinson’s disease (PD) and that these changes may contribute to aberrant network neuronal activity in the BG-thalamocortical circuitry. Postmortem studies of animal models and PD patients have revealed significant pathology of glutamatergic synapses, dendritic spines and microcircuits in the striatum of parkinsonians. More recent findings have also demonstrated a significant breakdown of the glutamatergic corticosubthalamic system in parkinsonian monkeys. In this review, we will discuss evidence for synaptic glutamatergic dysfunction and pathology of cortical and thalamic inputs to the striatum and STN in models of PD. The potential functional implication of these alterations on synaptic integration, processing and transmission of extrinsic information through the BG circuits will be considered. Finally, the significance of these pathological changes in the pathophysiology of motor and non-motor symptoms in PD will be examined.

Developmental exposure to paracetamol causes biochemical alterations in medulla oblongata

The effect and safety of prenatal and early life administration of paracetamol - routinely used over-the-counter antipyretic and analgesic medication on monoamines content and balance of amino acids in the medulla oblongata is still unknown. In this study we have determined the level of neurotransmitters in this structure in two-month old Wistar male rats exposed to paracetamol in the dose of 5 (P5, n=10) or 15mg/kg b.w. (P15, n=10) during prenatal period, lactation and till the end of the second month of life. Control group received drinking water (Con, n=10). Monoamines, their metabolites and amino acids concentration in medulla oblongata of rats were determined using high performance liquid chromatography (HPLC) in 60 postnatal day (PND60). This experiment shows that prenatal and early life paracetamol exposure modulates neurotransmission associated with serotonergic, noradrenergic and dopaminergic system in medulla oblongata. Reduction of alanine and taurine levels has also been established.

Impaired arousal in rat pups with prenatal alcohol exposure is modulated by GABAergic mechanisms

Prenatal alcohol exposure (PAE) increases the risk for The Sudden Infant Death Syndrome (SIDS) in human infants. In rat pups, the arousal response to hypoxia is modulated by medullary raphe GABAergic mechanisms. We hypothesized that arousal to hypoxia is impaired by PAE, and is associated with an increase in medullary GABA and enhanced GABAergic activity. Pregnant dams received an ethanol liquid diet (ETOH), an iso-caloric pair fed diet (PF) or a standard chow diet (CHOW). We first measured the time to arousal (latency), during four episodes of hypoxia in P5, P15, and P21 CHOW, PF, and ETOH pups. We also measured brainstem GABA concentration in the same groups of pups. Finally, we injected artificial cerebrospinal fluid (aCSF), nipecotic acid (NIP) or gabazine into the medullary raphe of P15 and P21 pups receiving the three diets. For statistical analysis, the PF and CHOW groups were combined into a single CONTROL group. Our main finding was that compared to CONTROL, arousal latency to hypoxia is increased in ETOH pups at P15 and P21, and the concentration of brainstem GABA is elevated at P21. NIP administration in CONTROL pups led to arousal latencies similar in magnitude to those in ETOH pups after aCSF injection. NIP injected ETOH pups had no further increases in arousal latency. We conclude that PAE impairs arousal latency and this is mediated or modulated by medullary GABAergic mechanisms.

Serotonin metabolites in the cerebrospinal fluid in sudden infant death syndrome

Forensic biomarkers are needed in sudden infant death syndrome (SIDS) to help identify this group among other sudden unexpected deaths in infancy. Previously, we reported multiple serotonergic (5-HT) abnormalities in nuclei of the medulla oblongata that help mediate protective responses to homeostatic stressors. As a first step toward their assessment as forensic biomarkers of medullary pathology, here we test the hypothesis that 5-HT-related measures are abnormal in the cerebrospinal fluid (CSF) of SIDS infants compared with those of autopsy controls. Levels of CSF 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA), the degradative products of 5-HT and dopamine, respectively, were measured by high-performance liquid chromatography in 52 SIDS and 29 non-SIDS autopsy cases. Tryptophan (Trp) and tyrosine (Tyr), the substrates of 5-HT and dopamine, respectively, were also measured. There were no significant differences in 5-HIAA, Trp, HVA, or Tyr levels between the SIDS and non-SIDS groups. These data preclude the use of 5-HIAA, HVA, Trp, or Tyr measurements as CSF autopsy biomarkers of 5-HT medullary pathology in infants who have died suddenly and unexpectedly. They do, however, provide important information about monoaminergic measurements in human CSF at autopsy and their developmental profile in infancy that is applicable to multiple pediatric disorders beyond SIDS.

Activation of 5-HT2A receptors upregulates the function of the neuronal K-Cl cotransporter KCC2

In healthy adults, activation of γ-aminobutyric acid (GABA)(A) and glycine receptors inhibits neurons as a result of low intracellular chloride concentration ([Cl(-)](i)), which is maintained by the potassium-chloride cotransporter KCC2. A reduction of KCC2 expression or function is implicated in the pathogenesis of several neurological disorders, including spasticity and chronic pain following spinal cord injury (SCI). Given the critical role of KCC2 in regulating the strength and robustness of inhibition, identifying tools that may increase KCC2 function and, hence, restore endogenous inhibition in pathological conditions is of particular importance. We show that activation of 5-hydroxytryptamine (5-HT) type 2A receptors to serotonin hyperpolarizes the reversal potential of inhibitory postsynaptic potentials (IPSPs), E(IPSP), in spinal motoneurons, increases the cell membrane expression of KCC2 and both restores endogenous inhibition and reduces spasticity after SCI in rats. Up-regulation of KCC2 function by targeting 5-HT(2A) receptors, therefore, has therapeutic potential in the treatment of neurological disorders involving altered chloride homeostasis. However, these receptors have been implicated in several psychiatric disorders, and their effects on pain processing are controversial, highlighting the need to further investigate the potential systemic effects of specific 5-HT(2A)R agonists, such as (4-bromo-3,6-dimethoxybenzocyclobuten-1-yl)methylamine hydrobromide (TCB-2).

Dopaminergic neurons inhibit striatal output through non-canonical release of GABA

The substantia nigra pars compacta (SNc) and ventral tegmental area (VTA) contain the two largest populations of dopamine (DA)-releasing neurons in the mammalian brain. These neurons extend elaborate projections in striatum, a large subcortical structure implicated in motor planning and reward-based learning. Phasic activation of dopaminergic neurons in response to salient or reward-predicting stimuli is thought to modulate striatal output via the release of DA to promote and reinforce motor action^1–4. Here we show that activation of DA neurons in striatal slices rapidly inhibits action potential firing in both direct-and indirect-pathway striatal projection neurons (SPNs) through vesicular release of the inhibitory transmitter γ-aminobutyric acid (GABA). GABA is released directly from dopaminergic axons but in a manner that is independent of the vesicular GABA transporter VGAT. Instead GABA release requires activity of the vesicular monoamine transporter VMAT2, which is the vesicular transporter for DA. Furthermore, VMAT2 expression in GABAergic neurons lacking VGAT is sufficient to sustain GABA release. Thus, these findings expand the repertoire of synaptic mechanisms employed by DA neurons to influence basal ganglia circuits, reveal a novel substrate whose transport is dependent on VMAT2, and demonstrate that GABA can function as a bona fide co-transmitter in monoaminergic neurons.

Late development of the GABAergic system in the human cerebral cortex and white matter

Despite the key role of γ-aminobutyric acid (GABA) neurons in the modulation of cerebral cortical output, little is known about their development in the human cortex. We analyzed several GABAergic parameters in standardized regions of the cerebral cortex and white matter in a total of 38 human fetuses and infants from 19 gestational weeks to 2.7 postnatal years using immunocytochemistry, Western blotting, tissue autoradiography, and computer-based cellular quantitation. At least 20% of GABAergic neurons in the white matter migrated toward the cortex over late gestation. After term, migration declined and ended within 6 postnatal months. In parallel, the GABAergic neuronal density increased in the cortex over late gestation, also with a peak at term. From midgestation to infancy, the pattern of GABAA receptor binding changed from uniformly low across all cortical layers to high levels concentrated in the middle laminae; glutamic acid decarboxylase (GAD65 and GAD67) levels differentially increased. Thus, the second half of gestation is a period of rapid development of the cortical GABAergic system that continues into early infancy. This period corresponds to the peak window of vulnerability to perinatal hypoxia-ischemia in which GABAergic neurons are potentially developmentally susceptible, including in the preterm infant.

Decreased GABAA receptor binding in the medullary serotonergic system in the sudden infant death syndrome

γ-Aminobutyric acid (GABA) neurons in the medulla oblongata help regulate homeostasis, in part through interactions with the medullary serotonergic (5-HT) system. Previously, we reported abnormalities in multiple 5-HT markers in the medullary 5-HT system of infants dying from sudden infant death syndrome (SIDS), suggesting that 5-HT dysfunction is involved in its pathogenesis. Here, we tested the hypothesis that markers of GABAA receptors are decreased in the medullary 5-HT system in SIDS cases compared with controls. Using tissue receptor autoradiography with the radioligand H-GABA, we found 25% to 52% reductions in GABAA receptor binding density in 7 of 10 key nuclei sampled of the medullary 5-HT system in the SIDS cases (postconceptional age [PCA] = 51.7 ± 8.3, n = 28) versus age-adjusted controls (PCA = 55.3 ± 13.5, n = 8) (p ≤ 0.04). By Western blotting, there was 46.2% reduction in GABAAα3 subunit levels in the gigantocellularis (component of the medullary 5-HT system) of SIDS cases (PCA = 53.9 ± 8.4, n = 24) versus controls (PCA = 55.3 ± 8.3, n = 8) (56.8% standard in SIDS cases vs 99.35% in controls; p = 0.026). These data suggest that medullary GABAA receptors are abnormal in SIDS infants and that SIDS is a complex disorder of a homeostatic network in the medulla that involves deficits of the GABAergic and 5-HT systems.

Mapping of endogenous morphine-like compounds in the adult mouse brain: Evidence of their localization in astrocytes and GABAergic cells

Endogenous morphine, morphine-6-glucuronide, and codeine, which are structurally identical to vegetal alkaloids, can be synthesized by mammalian cells from dopamine. However, the role of brain endogenous morphine and its derivative compounds is a matter of debate, and knowledge about its distribution is lacking. In this study, by using a validated antibody, we describe a precise mapping of endogenous morphine-like compounds (morphine and/or its glucuronides and/or codeine) in the mouse brain. First, a mass spectrometry approach confirmed the presence of morphine and codeine in mouse brain, but also, of morphine-6-glucuronide and morphine-3-glucuronide representing two metabolites of morphine. Second, light microscopy allowed us to observe immunopositive cell somas and cytoplasmic processes throughout the mouse brain. Morphine-like immunoreactivity was present in various structures including the hippocampus, olfactory bulb, band of Broca, basal ganglia, and cerebellum. Third, by using confocal microscopy and immunofluroscence co-localization, we characterized cell types containing endogenous opiates. Interestingly, we observed that morphine-like immunoreactivity throughout the encephalon is mainly present in γ-aminobutyric acid (GABA)ergic neurons. Astrocytes were also labeled throughout the entire brain, in the cell body, in the cytoplasmic processes, and in astrocytic feet surrounding blood vessels. Finally, ultrastructural localization of morphine-like immunoreactivity was determined by electron microscopy and showed the presence of morphine-like label in presynaptic terminals in the cerebellum and postsynaptic terminals in the rest of the mouse brain. In conclusion, the presence of endogenous morphine-like compounds in brain regions not usually involved in pain modulation opens the exciting opportunity to extend the role and function of endogenous alkaloids far beyond their analgesic functions.

Brainstem deficiency of the 14-3-3 regulator of serotonin synthesis: a proteomics analysis in the sudden infant death syndrome

Impaired brainstem responses to homeostatic challenges during sleep may result in the sudden infant death syndrome (SIDS). Previously we reported a deficiency of serotonin (5-HT) and its key biosynthetic enzyme, tryptophan hydroxylase (TPH2), in SIDS infants in the medullary 5-HT system that modulates homeostatic responses during sleep. Yet, the underlying basis of the TPH2 and 5-HT deficiency is unknown. In this study, we tested the hypothesis that proteomics would uncover previously unrecognized abnormal levels of proteins related to TPH2 and 5-HT regulation in SIDS cases compared with controls, which could provide novel insight into the basis of their deficiency. We first performed a discovery proteomic analysis of the gigantocellularis of the medullary 5-HT system in the same data set with deficiencies of TPH2 and 5-HT levels. Analysis in 6 SIDS cases and 4 controls revealed a 42-75% reduction in abundance in 5 of the 6 isoforms identified of the 14-3-3 signal transduction family, which is known to influence TPH2 activity (p < 0.07). These findings were corroborated in an additional SIDS and control sample using an orthogonal MS(E)-based quantitative proteomic strategy. To confirm these proteomics results in a larger data set (38 SIDS, 11 controls), we applied Western blot analysis in the gigantocellularis and found that 4/7 14-3-3 isoforms identified were significantly reduced in SIDS cases (p ≤ 0.02), with a 43% reduction in all 14-3-3 isoforms combined (p < 0.001). Abnormalities in 5-HT and TPH2 levels and 5-HT(1A) receptor binding were associated with the 14-3-3 deficits in the same SIDS cases. These data suggest a potential molecular defect in SIDS related to TPH2 regulation, as 14-3-3 is critical in this process.

Up-expression of GAD65 in the amygdala of the rat model of chronic immobilization stress with elevated blood glucose

It is considered that hypothalamus is important in the regulation of the blood glucose, but how chronic stress leads to hyperglycemia is not known. In this experiment, we used chronic immobilization stress rat as a model, and observed that only rats with increased expression of GAD65 in the amygdala had an elevated level of blood glucose. Considering there are fiber tracks between the amygdala and hypothalamus, some of which are GABAergic, this result may indicate that the change of GAD65 expression in the amygdala may be related to changes in blood glucose levels. Therefore, the amygdala may be involved in the hyperglycemic response to stress.

The serotonergic anatomy of the developing human medulla oblongata: implications for pediatric disorders of homeostasis

The caudal serotonergic (5-HT) system is a critical component of a medullary "homeostatic network" that regulates protective responses to metabolic stressors such as hypoxia, hypercapnia, and hyperthermia. We define anatomically the caudal 5-HT system in the human medulla as 5-HT neuronal cell bodies located in the raphé (raphé obscurus, raphé magnus, and raphé pallidus), extra-raphé (gigantocellularis, paragigantocellularis lateralis, intermediate reticular zone, lateral reticular nucleus, and nucleus subtrigeminalis), and ventral surface (arcuate nucleus). These 5-HT neurons are adjacent to all of the respiratory- and autonomic-related nuclei in the medulla where they are positioned to modulate directly the responses of these effector nuclei. In the following review, we highlight the topography and development of the caudal 5-HT system in the human fetus and infant, and its inter-relationships with nicotinic, GABAergic, and cytokine receptors. We also summarize pediatric disorders in early life which we term "developmental serotonopathies" of the caudal (as well as rostral) 5-HT domain and which are associated with homeostatic imbalances. The delineation of the development and organization of the human caudal 5-HT system provides the critical foundation for the neuropathologic elucidation of its disorders directly in the human brain.