Histamine and spermidine content in brain during development.

Histamine concentration in fetal rat brain is high at 17 days gestation but decreases sharply just before birth. Values subsequently increase to a maximum postnatal concentration 5 to 10 days after birth, and then steadily decline to low adult values by time of weaning. Spermidine follows a pattern similar to that of histamine but with a 24- to 48-hour lag. The developmental pattern for histamine in the central nervous system is different from that for other neural amines. It appears that the marked fetal and neonatal changes in brain histamine correlate best with periods of rapid cell proliferation and growth during brain maturation.

Selective depression of serum growth hormone during maternal deprivation in rat pups.

Maternal deprivation was associated with a decline in immunoreactive growth hormone in the serum of rat pups. Pups that were returned to the mother showed a rapid reversal in this deprivation-induced decrease. The change in growth hormone concentration was not accompanied by changes in the concentrations of prolactin, thyrotropin, or corticosterone in the serum, but were correlated with alteration in the activity of ornithine decarboxylase in the brain. Treatment of neonatal rat pups with cyprohepatadine, a serotonin antagonist that suppresses growth hormone secretion, resulted in a significant decline in both serum growth hormone concentration and brain ornithine decarboxylase activity. These findings suggest that maternal deprivation elicits a specific suppression of growth hormone release which mediates the decrease in ornithine decarboxylase activity. The study is consistent with clinical findings of impaired growth hormone "responsitivity" in human maternal deprivation syndrome.

Aminoacidemias: effects on maze performance and cerebral serotonin.

The feeding of high dietary supplements of L-phenylalanine (7 percent) and L-leucine (7 percent) to weanling rats is associated with poor performance in a multiple-T, water-escape maze. Supplements high in L-tryptophan (5 percent), on the other hand, result in maze performance which is superior to that of controls. Adding 5 percent tryptophan to the high-phenylalanine diet reverses the behavioral deficit. The quality of maze performance correlated with the cerebral content of serotonin.

Maternal behavior as a regulator of polyamine biosynthesis in brain and heart of the developing rat pup.

Rat pups removed from the mother and placed in a warm incubator for 1 hour or more show a 50 percent reduction in ornithine decarboxylase activity in the brain and heart. The decline is not caused by lack of nutrition. Instead, these studies suggest that active maternal behavior is necessary to maintain normal polyamine metabolism in brain and heart of the pup during development.

Plasma dopamine beta-hydroxylase: a possible aid in the study and evaluation of hypertension.

The activity of dopamine beta-hydroxylase (DBH) in plasma ranged from 2 to 100 units per liter of plasma in 82 apparently healthy subjects (ages 22 to 35 years). A nonnormal pattern of distribution was evident: 62 subjects had values below 35 units (18 +/- 1), while 13 of the remaining 20 subjects had values above 60 units (80 +/- 5). Those with low DBH activity had lower values for urinary catecholamine excretion (31 +/- 3 micrograms), with normal and stable blood pressure; those with high DBH activity had higher values for urinary catecholamine excretion (72 +/- 6 micrograms), with greater lability of arterial blood pressure. The DBH activity was significantly elevated in patients with labile (74 +/- 2 mm-Hg) or fixed (57 +/- 2 mm-Hg) essential hypertension. The results indicate that plasma DBH activity is low and that it falls within a narrow range in young adults with normal and stable blood pressure.

Methamphetamine-induced insulin release.

Administration of methamphetamine or amphetamine to rats and mice produces a rapid increase in the level of immunoassayable plasma insulin not attributable to hyperglycemia. While in the mouse this release of insulin is followed consistently by a profound hypoglycemia, in the rat this response is variable. Studies in vitro demonstrate that insulin is released by a direct effect of methamphetamine on the pancreas.

Type A behavior and elevated physiological and neuroendocrine responses to cognitive tasks.

Qualitatively distinct patterns of cardiovascular and neuroendocrine responses were observed in male college students during mental work and during sensory intake task performance. During mental work, Type A (coronary-prone) subjects showed greater muscle vasodilatation and more enhanced secretion of norepinephrine, epinephrine, and cortisol than Type B subjects. During sensory intake, Type A hyperresponsivity was found for testosterone and, among those subjects with a positive family history of hypertension, for cortisol. As a demonstration of combined cardiovascular, sympathetic nervous system, and neuroendocrine hyperresponsivity to specific cognitive tasks in Type A subjects, this study breaks ground in the search for mechanisms mediating the increased coronary disease risk among Type A persons.

Regulation of insulin and glucose plasma levels by central nervous system beta-endorphin in preweanling rats.

Recently, our laboratory has reported that central administration of beta-endorphin to rat pups decreases hepatic and renal ornithine decarboxylase activity, a sensitive biochemical index of tissue metabolic activity. Since these organs are the major sites of insulin catabolism, it seemed possible that the plasma levels of this hormone could be altered by changes in central nervous system (CNS) beta-endorphin levels. In the current study we tested this hypothesis by administering beta-endorphin to rat pups intracisternally (ic), followed by insulin sc, and then analyzing for plasma levels of insulin and glucose at various times after the second injection. We found that the apparent biological half-life of administered insulin markedly increased in 6-day-old rats pretreated with beta-endorphin ic. Similarly, this neuropeptide prolonged the half-life of endogenous insulin, as indicated by a small but significant increase in the plasma levels of this hormone in animals given only beta-endorphin. As expected, hypoglycemia in rats injected with beta-endorphin and insulin was more pronounced than in animals given insulin alone. Naloxone administered ic reversed both actions of beta-endorphin, indicating the involvement of opioid receptors in the response. beta-Endorphin also altered insulin and glucose plasma levels in 2-, 10-, and 18-day-old rats, but there were no effects in 30-day-old animals at any of the doses used in these studies. Peripheral administration of beta-endorphin had no effect, indicating that CNS beta-endorphin's influences on insulin and glucose metabolism occur through brain-based mechanisms. The results from these studies suggest that CNS beta-endorphin may be an important modulator of insulin and glucose metabolism in preweanling rats. In as much as insulin is a major regulator of somatic growth, our findings further suggest that CNS beta-endorphin may have a major role in the control of growth during early postnatal development by influencing insulin homeostasis.

Effects of propranolol on cardiovascular and neuroendocrine responses to mental arithmetic in type A men.

beta-Adrenergic hyperreactivity has been proposed as a pathogenic mechanism of increased coronary risk in Type A individuals. This study compared the effects of propranolol, diazepam, and placebo on cardiovascular and neuroendocrine responses to a stressful cognitive task in six young Type A males. Although diazepam did not differ from placebo, propranolol attenuated heart rate and norepinephrine responses and enhanced cortisol responses to the task. Findings suggest that propranolol has reciprocal effects on the norepinephrine and cortisol components of the "fight-flight" response. Possible central nervous system mechanisms are described.

Effects of central administration of beta-endorphin on brain and liver DNA synthesis in preweanling rats.

We have previously shown that central administration of beta-endorphin results in a reduction of ornithine decarboxylase activity. Ornithine decarboxylase catalyses the rate-limiting step in the biosynthesis of the polyamines putrescine, spermidine and spermine, thought to modulate nucleic acid synthesis. The present study examines the effects of intracisternal injection of beta-endorphin on brain and liver DNA synthesis in preweanling rats. In six-day-old rats, beta-endorphin (0.75 micrograms/g brain wt) produced approximately a 70% inhibition in brain and liver DNA synthesis 1 h after injection, and values were still subnormal in both tissues 10 h later. Subcutaneous administration of beta-endorphin did not alter liver DNA synthesis. Thus, it is most likely that the suppressed liver DNA synthesis observed in animals given beta-endorphin intracisternally is mediated by central mechanisms. Co-administration of naloxone plus beta-endorphin intracisternally prevented the response, indicating an opioid receptor-mediated phenomenon. Naloxone alone caused small but significant increases in brain and liver DNA synthesis, suggesting a tonic influence on tissue DNA by endogenous opioids in the CNS. Acute inhibition of ornithine decarboxylase activity by alpha-difluoromethylornithine did not alter DNA synthesis, indicating that the decreases in DNA synthesis induced by beta-endorphin are unrelated to the ornithine decarboxylase/polyamine system. The effect appears to be restricted to early development as no significant changes in DNA synthesis were obtained in 20-day-old animals. The results from these studies indicate that CNS beta-endorphin has the ability to influence DNA synthesis in central as well as in peripheral tissues.(ABSTRACT TRUNCATED AT 250 WORDS)

Tactile/kinesthetic stimulation effects on preterm neonates.

Tactile/kinesthetic stimulation was given to 20 preterm neonates (mean gestational age, 31 weeks; mean birth weight, 1,280 g; mean time in neonatal intensive care unit, 20 days) during transitional ("grower") nursery care, and their growth, sleep-wake behavior, and Brazelton scale performance was compared with a group of 20 control neonates. The tactile/kinesthetic stimulation consisted of body stroking and passive movements of the limbs for three, 15-minute periods per day for a 10 days. The stimulated neonates averaged a 47% greater weight gain per day (mean 25 g v 17 g), were more active and alert during sleep/wake behavior observations, and showed more mature habituation, orientation, motor, and range of state behavior on the Brazelton scale than control infants. Finally, their hospital stay was 6 days shorter, yielding a cost savings of approximately $3,000 per infant. These data suggest that tactile/kinesthetic stimulation may be a cost effective way of facilitating growth and behavioral organization even in very small preterm neonates.

Inhibition of GH in maternal separation may be mediated through altered serotonergic activity at 5-HT2A and 5-HT2C receptors.

The hyposecretion of growth hormone (GH) in maternal separation (MS) of rat pups is remarkably similar to the specific suppression of GH secretion to evocative tests in infants diagnosed with Reactive Attachment Disorder of Infancy (RADI). Growth hormone-releasing factor (GRF) and somatostatin (SS) provide opposing regulation of GH secretion, and both are modified by noradrenergic and serotonergic stimuli in neonatal and adult rats. In this study, GRF administration reversed MS-induced suppression of GH secretion in 10-day-old pups, but this action of GRF was prevented by pretreatment with cyproheptadine (Cypro), a serotonergic antagonist. The normalization of GH secretion after return to the dam was not altered by pretreatment with SS. Indirect 5-HT agonists, fluoxetine (FLX) and 5-HTP, both stimulated GH secretion in 10-day-old pups. All mixed serotonin- and 5-HT1A-receptor agonists suppressed GH secretion in 10-day-old pups. Antagonists Cypro and ketanserin (Ket) suppressed FLX-induced GH secretion. In contrast, only Cypro suppressed 5-HTP-induced GH secretion. Maternal separation inhibited GH secretion stimulated by 5-HTP, but not by FLX. The serotonergic pathway acting on 5-HT2A receptors may be obligatory for GRF-mediated stimulation and is sensitive to inhibition by Cypro. In addition, a Ket-sensitive serotonergic parallel pathway acting on 5-HT2C receptors may also stimulate GH secretion by acting on GRF or SS. However, only the obligate 5-HT2A pathway appears to be suppressed in MS. These data and observations by others indicate that specific suppression of GH secretion in MS may derive from a reduction in GRF release through noradrenergic neurons, possibly impinging upon serotonergic terminals in the hypothalamus. This study may also provide insight into mechanisms by which GH secretion is suppressed in humans with RADI.

Maternal separation in neonatal rats elicits activation of the hypothalamic-pituitary-adrenocortical axis: a putative role for corticotropin-releasing factor.

Stress elicits activation of the hypothalamic-pituitary-adrenocortical (HPA) axis. Hypothalamic neurohormones, including corticotropin-releasing factor (CRF), control and promote ACTH secretion and subsequent glucocorticoid synthesis and release. The neonatal rat has been shown to be relatively hyporesponsive to certain stressors, generating a blunted or unmeasurable hormonal response. In this study, the endocrine response of 10- and 18-day-old Sprague-Dawley rat pups to maternal separation, a naturalistic stressor, was examined. Ten-day pups subjected to maternal separation exhibited a significant reduction in median eminence CRF concentration at 24 h, with no change in pituitary CRF receptor number; in 18-day pups there was no significant change in median eminence CRF concentration by 24 h, but there was a decrease in CRF receptor binding. In adult rats subjected to stressors, an acute decrease in CRF concentration in the median eminence occurs, followed by CRF receptor downregulation with sustained stress. The results observed in the 18-day pups vs. the 10-day pups likely reflects a maturation of the HPA axis response to "stressors."

Effect of 5,7-dihydroxytryptamine on serotonergic control of prolactin secretion and behavior in rats.

The intracisternal administration of 5,7-dihydroxytryptamine (5,7-DHT) to rats resulted in a potentiated response to 5-hydroxytryptophan (5-HTP) when the animals were tested 30 days later. The 5-HTP-induced changes include elevation of serum prolactin, decrease in operant responding, and the magnitude of the "serotonin behavioral syndrome" observed after 5-HTP administration. The serotonin concentration in brains of 5,7-DHT-treated animals reached maximum earlier and remained elevated longer than that of controls following administration of 5-HTP. Brain norepinephrine and dopamine concentration were not affected by 5-HTP in either group of animals. The increase in serum prolactin concentration elicited by administration of the serotonergic agonists quipazine or 5-methoxy-N,N-dimethyltryptamine and by the serotonin uptake inhibitor fenfluramine also was potentiated by pretreating rats with 5,7-DHT. These data suggest that both serotonergic receptor supersensitivity and the absence of presynaptic uptake sites contribute to the enhanced responses to 5-HTP occurring in rats previously treated with 5,7-DHT. The findings further demonstrate that both behavioral and hormonal measures can be used to assess the sensitivity of serotonergic receptors and indicate that 5,7-DHT may be useful in evaluating the role of serotonergic neurons in neuroendocrine function.

Behavioral and prolactin responses to 5-hydroxytryptophan in rats treated during development with 5,7-dihydroxytryptamine.

The serotonin precursor, 5-hydroxytryptophan (5-HTP), can induce a behavioral syndrome characterized by rigidity, splayed feet, tremor, head weaving, salivation and forepaw treading. This response to 5-HTP was markedly potentiated in adult rats treated intracisternally with 5,7-dihydroxytryptamine (5,7-DHT) during development. Prevention of the 5,7-DHT-induced reduction of brain norepinephrine with pargyline or desipramine did not diminish the potentiation of 5-HTP, suggesting that noradrenergic fibers are not contributing to the altered 5-HTP response. It was also found that treatments with 5,7-DHT potentiated the release of prolactin and the disruption of responding in a fixed-ratio operant task induced by 5-HTP. Other experiments indicated that 5,7-DHT treatments potentiated 5-HTP without affecting the action of L-dihydroxyphenylalanine. In addition, administration of the decarboxylase inhibitor, R0-4-4602, at a dose that inhibits enzyme activity in brain, blocked the 5-HTP-induced behavioral syndrome in 5,7-DHT-treated rats, indicating that 5-HTP must be converted to serotonin for 5-HTP to alter behavior. Thus, the present studies indicate that destruction of serotonergic fibers during development can produce permanent changes in central serotonergic mechanisms.

Responses to maternal separation: mechanisms and mediators.

Clinical studies indicate the predominance of psychosocial factors (nurturing environment) in the genesis of the Maternal Deprivation Syndrome. Consequences of disrupting mother-infant interactions range from marked suppression of certain neuroendocrine and physiological systems after short periods of maternal deprivation to retardation of growth and behavioral development after chronic periods. We have shown that maternal separation initiates a complex adaptive biobehavioral response in preweaning rat pups that includes (1) a decrease in the synthesis of ornithine decarboxylase, an obligatory enzyme for normal cell growth and development, (2) a reduction in DNA synthesis, an index of cell multiplication, (3) abnormal patterns of neuroendocrine secretion, and (4) a suppression of cell responses to growth hormone, prolactin and insulin, three major trophic hormones. This unique pattern of adaptation to maternal separation is not related to food or temperature changes but results from a lack of a specific type of tactile stimulation of the pup by the mother. Recently, we have shown that in the absence of "nurturing touch" the brain initiates the suppression of ornithine decarboxylase gene transcription by interfering with the cell's ability to transduce the activating signal induced by the growth promoting hormones. Studies indicate that central endorphinergic pathways may mediate this action. This is accomplished by the downregulation of specific Immediate Early Genes (c-myc and max) that normally promote the synthesis of this critical growth-regulatory enzyme. These studies of short-term maternal separation not only demonstrated that maternal care is a critical regulator of pup physiology and biobehavioral development but that there are marked similarities between this animal model of maternal separation and the delay in growth and development observed in children with the deprivation syndrome or in touch-deprived premature human neonates. Our identification of a specific type of nurturing touch as a neonatal growth requirement led us to test supplemental tactile stimulation in isolated very-premature human babies. The result of our intervention with massage was dramatic. Infants not only showed marked gains in weight and behavioral development, but also a significant enhancement in sympatho-adrenal maturation. We suggest that animal models of maternal deprivation can be used to understand the integrative processing of appropriate sensory input, CNS function and end-organ physiology required to maintain normal development.

Physiological responses to catecholamine infusions in type A and type B men.

To determine whether there are basic biological differences between Type A and Type B men, we compared hemodynamic, electrophysiologic and neuroendocrine responses to equipotent doses of isoproterenol (ISO) and norepinephrine (NE) in 10 Type A and 10 Type B men ages 18 to 29. Results showed equal hemodynamic and neuroendocrine responses to graded ISO doses in Type A and Type B individuals. In contrast, Type A men showed a more prolonged decrease in electrocardiographic T-wave amplitude (TWA) than did Type B men. Post hoc analyses of the correlates of TWA recovery during high-dose ISO infusion provide preliminary evidence for a more robust parasympathetic antagonism of sympathetic nervous system effects in Type B men, especially those with low scores on the Cook-Medley Ho scale. These findings suggest that, in addition to cognitively mediated increases in sympathetic nervous system reactivity, Type As may also be placed at increased risk of developing coronary heart disease by reduced levels of parasympathetic antagonism of sympathetic effects.

Dopamine b-Hydroxylase: Determination of half-life and appearance in lymph fluid after IV injection of 125 I-DBH into rats.

A 4 day half-life of dopamine beta-hydroxylase (DBH) was determined for rats injected IV with 125I-rat DBH from the slow exponential component of radioactivity appearing in plasma, urine, feces and combined urine and feces. Half-life estimates for 125I-rat DBH injected IV into WKY and SHR animals did not differ from Sprague Dawley (Zivic Miller) rats. Radioactivity declined in parallel in plasma, urine and feces following IV 125I-rat DBH administration and each radioactivity falloff curve could be resolved into two components. The slow phase of the decline of radioactivity excreted into urine and feces from which DBH half-life was calculated occurred between 5 and 25 days after 125I-rat DBH injection. The early fast phase which is associated with distribution of the exogenous protein in body fluids and tissues continued for approximately the first 140 hr after DBH injection. The distribution characteristics of IV administered active bovine DBH and 125I-rat DBH into the lymphatic system were examined. After active bovine DBH or 125I-rat DBH was injected IV into rats, active DBH or radioactivity, respectively, appeared in lymph fluid (thoracic duct) within 20 min; reached peak concentrations within 90 min, and thereafter, declined in parallel with the plasma concentration. The concentration of radioactivity in plasma and lymph fluid were found to be unequal at 9 hr but were equivalent 68-75 hrs after IV injection of 125I-rat DBH. Based on the amount of active DBH or radioactivity which accumulates in lymph fluid it is clear that a substantial amount (greater than 50%) of the DBH in blood circulates through the lymphatic channels. Analysis of parallel experiments with labelled serum albumin indicate that use of these methods to study plasma proteins do provide sensitive measures of biological half-life and lymphatic distribution characteristics. Specifically for DBH, the results of our study suggest that DBH normally circulates in plasma and lymph fluid with a biological half-life of 4 days.

Hepatic cyclic AMP generation and ornithine decarboxylase induction by glucagon and beta adrenergic agonists.

The relationship of hepatic ornithine decarboxylase (ODC) activity to cyclic AMP levels and nutritional status was studied in the pre-weanling rat. Previous studies demonstrated that 2 hr without food causes a loss of hepatic ODC induction after glucagon or catecholamine injection. Isoproterenol or glucagon administration produced increased hepatic cyclic AMP and tyrosine aminotransferase activity which were not prevented by nutritional deprivation. Blockade of hepatic beta 2 receptors by the selective antagonist ICI 118,551 prevented increased cAMP levels and ODC activity after isoproterenol administration. Blockade of beta 1 receptors by atenolol did not prevent increased cAMP levels or ODC induction by isoproterenol although it did block activation of cardiac ODC. The phosphodiesterase inhibitor RO20-1724 increased hepatic cAMP levels as well as ODC and TAT activities, although the increase in ODC activity was attenuated by nutritional deprivation. RO20-1724 also potentiated the induction of hepatic ODC after glucagon or isoproterenol administration. Administration of 8-bromo cAMP elevated hepatic ODC activity regardless of nutritional status but also elevated serum levels of growth hormone and corticosterone. Hepatic ODC induction by glucagon or beta 2 agonists can be dissociated from changes in cAMP levels during nutritional deprivation.

Maturation of growth hormone stimulation of kidney ornithine decarboxylase in the rat.

The effect of ovine growth hormone (GH) on kidney ornithine decarboxylase (ODC) was studied in newborn, preweanling and young adult rats. Basal kidney ODC activity was very low from 4 to 22 days after birth but rose 20-fold by day 25; it remained elevated through day 45. GH failed to stimulate ODC in the first two weeks after birth. GH did however stimulate ODC markedly from 20 through 45 days. Kidney ODC was stimulated in the neonate by vasopressin and by isoproterenol, but not by angiotensin II. Liver ODC remained relatively low and stable during development, and was responsive to GH at all ages studied. We conclude that a) the pattern of development of basal kidney ODC appears to be unique to this tissue and may be related to the postnatal maturation of renal morphology and/or function, b) neonatal kidney ODC is unresponsive to certain hormones but is not completely refractory to stimulation. These findings may have implications for the role of hormones in the maturation of the kidney and in the regulation of early renal function.