Target organ regulation of sympathetic neuron development.

The role of target organs in the morphological and biochemical development of sympathetic neurons was examined in the neonatal rat. The superior cervical ganglion (SCG) and its end organs, the salivary glands and iris were employed as a model system. Unilateral sialectomy and iridectomy prevented the normal developmental increase in ipsilateral ganglion tyrosine hydroxylase (T-OH) activity, a marker for adrenergic maturation. Enzyme activity remained depressed by approximately 30% for at least 6 months, the longest time tested. Ganglion morphometry was performed to investigate the basis of the abnormal biochemical ontogeny. Target organ removal significantly decreased the number of adrenergic neurons in the Scg by approximately 30%. Total ganglion volume was reduced in a parallel fashion. Thus, end organ extirpation may prevent the biochemical maturation of the SCG by decreasing adrenergic neuron survival. Sialectomy without iridectomy prevented the normal postnatal increase in ganglion T-OH activity, but did not alter iris activity. These observations suggest that target removal prevents the development of only those neurons destined to innervate that organ. In addition to preventing normal adrenergic neuron ontogeny, target extirpation also prevented the normal development of presynaptic choline acetyltransferase activity. Presynaptic ganglion terminal may have failed to mature normally secondary to adrenergic destruction, or may have responded in some other manner to target organ extirpation.     

Harmonal regulation of adult sympathetic neurons: the effects of castration on tyrosine hydroxylase activity

The effects of the hormone testosterone on neurotransmitter synthesis in peripheral sympathetic ganglia were examined in adult male Sprague-Dawley rats. Tyrosine hydroxylase (T-OH), the rate limiting enzyme in catecholamine biosynthesis was examined in the hypogastric (HG), coeliac (CG), and superior cervical ganglion (SCG) subsequent to castration. Initial studies indicated that 2 weeks after surgery, HG T-OH activity fell to approximately 30% of control. In order to more clearly define the pattern of testosterone effects, HG was examined 1, 2 and 4 weeks after surgery. T-OH activity was 67%, 50% and 11% of control at these 3 respective time points, and the observed alteration in T-OH activity appeared to parallel changes in the size of pelvic target organs. Similar hormonal effects did not occur in other peripheral sympathetic ganglia; T-OH activity was unchanged in SCG and CG when examined 1 month after castration. Enzyme activity was restored following replacement therapy with testosterone, whereas the neural metabolite 17-beta estradiol was without effect. The recovery in T-OH activity was associated with partial recovery of target organ size. These studies suggest that hormonal factors regulate neurotransmitter synthesizing enzymes in adult sympathetic neurons and may do so via consequences of alterations in target organs. These observations parallel similar events in the developing nervous system.     

Neurotrophins and target interactions in the development and regulation of sympathetic neuron electrical and synaptic properties

The electrical and synaptic properties of neurons are essential for determining the function of the nervous system. Thus, understanding the mechanisms that control the appropriate developmental acquisition and maintenance of these properties is a critical problem in neuroscience. A great deal of our understanding of these developmental mechanisms comes from studies of soluble growth factor signaling between cells in the peripheral nervous system. The sympathetic nervous system has provided a model for studying the role of these factors both in early development and in the establishment of mature properties. In particular, neurotrophins produced by the targets of sympathetic innervation regulate the synaptic and electrophysiological properties of postnatal sympathetic neurons. In this review we examine the role of neurotrophin signaling in the regulation of synaptic strength, neurotransmitter phenotype, voltage-gated currents and repetitive firing properties of sympathetic neurons. Together, these properties determine the level of sympathetic drive to target organs such as the heart. Changes in this sympathetic drive, which may be linked to dysfunctions in neurotrophin signaling, are associated with devastating diseases such as high blood pressure, arrhythmias and heart attack. Neurotrophins appear to play similar roles in modulating the synaptic and electrical properties of other peripheral and central neuronal systems, suggesting that information provided from studies in the sympathetic nervous system will be widely applicable for understanding the neurotrophic regulation of neuronal function in other systems.     

Trans-synaptic regulation of the development of end organ innervation by sympathetic neurons.

To examine the regulation of development of end organ innervation the superior cervical ganglion (SCG), and two of its target organs, the iris and pineal gland, were studied using biochemical and histofluorescent approaches. During postnatal ontogeny the activity of tyrosine hydroxylase (T-OH), which is localized to adrenergic neurons, increased 50-fold in iris, and 34-fold in pineal nerve terminals of the rat. These increases paralleled the in vitro rise in iris [3H]norepinephrine ([3H]NE) uptake, a measure of the presence of functional nerve terminal membrane. These biochemical indices of end organ innervation correlated well with developmental increases in density of innervation, adrenergic ground plexus ramification and nerve fiber fluorescence intensity as determined by fluorescence microscopy. Unilateral transection of the presynaptic cholinergic nerves innervating the SCG in 2-3-day-old rats prevented the normal development of end organ innervation: T-OH activity, [3H]NE uptake, innervation density, plexus ramification and fluorescence intensity failed to develop normally in irides innervated by decentralized ganglia. It is concluded that trans-synaptic factors regulate the maturation of adrenergic nerve terminals, and the development of end organ innervation by SCG.     

Hormonal effects on the development or cerebral lateralization

The morphology of cerebral cortical laterality patterns differs between the sexes. In the male Long-Evans rat, the thickness of the cerebral cortex is, in general, greater on the right side than on the left, with many areas showing statistically significant differences. In the female Long-Evans rat, the left side is thicker more often than the right, but the differences, in general, are not statistically significant. These laterality patterns are maintained throughout the lifetime of the animal with few variations. Some of the male and female laterality patterns reverse with old age. The numbers of neurons and glial cells in the area sampled, area 39, support the direction of cortical thickness measurements in male and female rats. Removal of the testes or ovaries at birth alters the usual cortical laterality patterns, illustrating that the sex steroid hormones play some role in determining laterality. In the neonates of both sexes, estrogen receptors are found in the cerebral cortex, but the concentration is greater in the left male cortex than in the right, the opposite being true for the female. Factors other than the sex steroid hormones, such as stress, can alter cortical laterality. Many studies indicate that plasticity of laterality is a factor to be considered when dealing with cortical morphology and, in turn, behavior.     

Effects of neonatal castration or treatment with dihydrotestosterone on numbers of neurons in the rat superior cervical sympathetic ganglion

There is a normal sexual dimorphism in the number of neurons in the rat superior cervical sympathetic ganglion (SCG), with adult males having more neurons in this ganglion than females. We confirm this finding here, report that this sex difference is not present at birth and that neonatal castration of males reduces the adult sex difference. These results indicate that perinatal levels of circulating testicular hormones play a role in regulating the numbers of neurons in the SCG. Treatment of neonatal rats with testosterone propionate or estradiol significantly increases the number of neurons in the SCG. To determine whether this effect is primary androgenic or estrogenic, the effects of dihydrotestosterone, on SCG neuron number were investigated. Dihydrotestosterone, unlike testosterone, is not aromatized to estradiol intracellularly. There was no difference in the number of neurons between animals injected from birth with vehicle or dihydrotestosterone. This difference in effects between dihydrotestosterone and testosterone suggests that the actions of testosterone may be via aromatization to estradiol, rather than action at an androgen receptor.     

Effects of nerve growtfactor on sympathetic neuron development in normal and limbless chick embryos

Wing bud removal in chick embryos has been shown to affect the generation of sympathetic neurons prior to the normal period of limb innervation [Saltis and Rush (1995) J. auton. nerv. Sys., 51, 117–127.]. Pyknotic activity occurred earlier within the peripherally deprived ganglion, suggesting that a precocious cell death of dividing sympathoblasts led to the reduced neuronal population. We have now sought to test whether the effect of limb bud extirpation can be overcome by the administration of nerve growth factor (NGF). Specifically, the peripherally deprived ganglion has been examined for mitotic activity and total neuronal numbers. In brachial ganglia from the operated side, neuron numbers decreased by 67% by embryonic day (E) 13, but by only 28% when NGF was administered from E9. Ganglia on the unoperated side were unaffected by the NGF treatment. In contrast, in embryos receiving NGF from E5 to E9, neuron numbers in the ganglia increased by more than 100%, on both the intact and operated side. This increase was accompanied by a greater proportion of ³H-thymidine-labelled neurons. We therefore conclude that NGF, in addition to its previously described role of preventing naturally occurring neuron death, can also affect the generation of sympathetic neurons. This ability of NGF to affect gangliogenesis is most likely achieved by increasing the survival of dividing neuroblasts, although a direct effect on mitosis has not been excluded.     

Hormonal regulation of atypical absence seizures

A time course study that examined the effects of the female estrous cycle on the chronic slow spike-and-wave discharges (SSWDs), gamma-aminobutyric B receptor (GABA(B)R) binding, and GABA(B)R protein expression was conducted in Long Evans hooded rats treated during development with a cholesterol synthesis inhibitor AY9944 (AY). In addition, a pharmacological study using the hormones progesterone, 17 beta-estradiol, mifepristone (intracellular progesterone receptor antagonist), tamoxifen (intracellular estrogen receptor antagonist), and allopregnanolone (progesterone metabolite) was performed to determine their effects on AY-induced seizures. The data indicate that there is a significant increase in both the duration of SSWD and GABA(B)R binding in the AY model, during the proestrus stage of the estrous cycle, the stage during which the levels of progesterone are at their highest. No changes in GABA(B)R1a or R2 protein levels were observed. In addition, the administration of both progesterone and allopregnanolone exacerbated seizures in the AY model, whereas 17 beta-estradiol attenuated the SSWD duration. Neither mifepristone nor tamoxifen blocked the effects of progesterone and 17 beta-estradiol, respectively, on SSWD duration in the AY model, suggesting that these two sex hormones are working in a manner independent of their intracellular receptors. These data suggest an important role for steroid hormones in the regulation and maintenance of AY-induced atypical absence seizures.     

Hormonal control of neuron number in sexually dimorphic spinal nuclei of the rat: III. Differential effects of the androgen dihydrotestosterone

The spinal cord of the rat contains two sexually dimorphic nuclei: the spinal nucleus of the bulbocavernosus (SNB) and the dorsolateral nucleus (DLN). These nuclei and the perineal muscles they innervate are present in males but reduced or absent in females. The sex difference in motoneuron number in these nuclei is due to an androgen-regulated motoneuron death. Developing females treated with the androgen testosterone propionate (TP) have a fully masculine number of SNB and DLN motoneurons and retain the perineal muscles they would normally have lost. Paradoxically, females treated prenatally with the androgen dihydrotestosterone propionate (DHTP) also retain the perineal musculature but as adults lack the SNB motoneurons which would normally innervate them. The SNB target muscles retained by DHTP females are anomalously innervated by motoneurons in the DLN. Counts of motoneurons and degenerating cells in the developing SNB of DHTP-treated females showed that their feminine number is the result of a failure of DHTP to prevent the death of SNB motoneurons. Furthermore, the peak number of SNB motoneurons was below that of normal females, suggesting that DHTP treatment may also have inhibited motoneuronal migration. However, DHTP treatment fully masculinized both motoneuron number and degenerating cell counts in the DLN of these females, and it is this masculinized DLN that gives rise to the anomalous projection. Taken together, these results suggest that the effects of different androgens during development are specific and complex, involving the regulation of motoneuron death, migration, and specification of peripheral projections.     

γ-氨基丁酸能神经元在新生大鼠缺氧性痫性发作中的作用

目的 通过观察新生大鼠早期发育过程中及缺氧性痫性发作后海马组织病理改变以及原癌基因c-fos蛋白、谷氨酸脱羧酶(glutamate decarboxylase,GAD)的变化,探讨γ-氨基丁酸(γ-amino butylic acid,GABA)能神经元在缺氧性痫性发作中的作用及可能的影响机制.方法 采用出生后10d的SD大鼠建立改良Jensen缺氧诱导痫性发作模型,分为痫性发作后1d、3d、7d、14d 4组,并选取相应时间点正常大鼠为对照组,采用尼氏染色方法检测海马组织的组织病理变化,免疫组织化学法检测各组海马c-fos蛋白灰度值以及GAD阳性神经元数量的改变.结果 尼氏染色结果显示,各缺氧性痫性发作组海马区形态结构正常,细胞排列略稀疏,但未见明显的细胞丢失.免疫组化结果显示,与对照组比较,c-fos蛋白灰度值在痫性发作后7d,在缺氧性痫性发作组海马CA2、CA3和DG区明显地降低(P ＜0.05);GAD阳性细胞数在痫性发作后7～ 14d,缺氧性痫性发作组海马CA1、CA3和DG区明显地减少(P＜0.05).结论 缺氧性痫性发作后14d内并没有造成大鼠海马区及时或迟发性细胞丢失,但c-fos表达在大鼠海马区有迟发性增高;缺氧性痫性发作后海马GABA神经元数量的减少可能是新生大鼠缺氧诱导痫性发作后癫痫易感性升高的原因之一.     

Biochemical and morphological effects of castration on the postorganizational development of the hypogastric ganglion

The biochemical and morphological development of the sympathetic hypogastric ganglion (HG) was examined subsequent to postnatal castration at 10-11 days of age. Previous studies suggested that tyrosine hydroxylase (T-OH) activity, an index of noradrenergic maturation, and choline acetyltransferase (ChAT) activity, a marker for preganglionic terminal formation, were dependent on gonadal hormones during normal ontogeny. In the present studies, morphometric analyses of the HG revealed that the cross-sectional area of the cell soma and nucleus were significantly reduced following postnatal castration at day 10. Conversely, castration produced no change in the number of HG neurons. In addition, postnatal castration prevents the development of postsynaptic T-OH activity to a greater extent than ganglionic protein resulting in a significant loss of T-OH specific activity. In contrast, presynaptic ChAT activity was reduced in parallel with ganglionic protein, thus ChAT specific activity was unchanged. Testosterone replacement therapy, even in groups where treatment was delayed for up to 2 weeks after castration, completely reversed deficits in both T-OH and ChAT activities. These studies suggest that altered development of ganglion protein subsequent to postnatal castration is related to decreases in the size of neurons and not to the loss of neurons. The lack of cell loss also suggest that decreased levels of postsynaptic T-OH activity results from a loss of enzyme activity per cell and the decreased levels of ChAT activity probably represent fewer presynaptic terminals per neuron. In addition, delayed testosterone replacement subsequent to castration was effective in restoring enzyme activities suggesting an 'activational' not 'organizational' role for testosterone after postnatal day 10.     

Excitatory and inhibitory effects of epinephrine on neonatal rat sympathetic preganglionic neurons in vitro

Current and voltage recordings were made from antidromically identified sympathetic preganglionic neurons (SPNs) in transverse thoracolumbar spinal cord slices removed from neonatal rats. When applied by either pressure ejection or superfusion, epinephrine (Epi) caused a slow depolarization or an inward current in 62 SPNs (42%) and a slow hyperpolarization or an outward current in 21 SPNs (14%). The responses persisted in low calcium- or tetrodotoxin-containing media. The Epi-induced depolarization or inward current was associated with increased membrane resistance; it was reduced by membrane hyperpolarization and nullified at a membrane potential of about -100 mV; a clear reversal however was not observed at more negative potential levels. In a number of SPNs the Epi-induced depolarization was accompanied by small inhibitory postsynaptic potentials. The latter were eliminated by a low calcium solution and by the glycine antagonist strychnine, suggesting that they were caused by glycine or a glycine-like substance released from interneurons subsequent to activation by Epi. The Epi-induced hyperpolarization or outward current was associated with decreased membrane resistance, and nullified around -100 mV. The alpha-adrenergic antagonist, dihydroergotamine, and alpha 1-antagonist, prazosin, reversibly blocked the excitatory, whereas the alpha 2-antagonist, yohimbine, abolished the inhibitory response, respectively. It is concluded that Epi acting on alpha 1- and alpha 2-adrenergic receptors depolarizes and hyperpolarizes the rat SPNs by decreasing or increasing membrane conductances to potassium ions.     

Prenatal stress and postnatal development of neonatal rats--sex-dependent effects on emotional behavior and learning ability of neonatal rats.

Maternal sound stress (800 Hz; 77 dB, every other minute for 15 min/day, from day 10 to 18 of gestation), combined with forced swimming stress (15 min/day), was found to cause potentiation of sound-induced loss of locomotor activity, referred to as emotional behavior, of male offspring, but not that of female offspring, at 4 weeks of age. Maternal stress also caused an increase in the total number of errors by male, but not female offspring in the water-maze test at 6 weeks of age. These effects of stress on emotional behavior and learning behavior were abolished when dams were pretreated with buspirone (30 min before the stress, from day 8 to 18 of gestation). Thus, prenatal stress might have sex-dependent effects on emotional behavior and learning ability of neonatal rats.