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Biomedical subjects

D C Klein

Publications and source records attributed to D C Klein.

At least 199 records · Page 11Linked to original sources
PubMed1978

A suspension culture of pinealocytes: regulation of N-acetyltransferase activity.

A method to prepare suspension cultures of highly viable pinealocytes is described. Pineal glands of neonatal or adult rats can be used; the best yield is obtained from neonatal glands. Morphological examination of the cells indicates that they have a normal, healthy appearance and retain some structures typical of neonatal pinealocytes. During the first 24 h of culture, the cells aggregate into small clusters; after several days, larger aggregates can be seen. Biochemical studies indicate that adrenergic stimulation of these cells causes a 30- to 100-fold increase in serotonin N-acetyltransferase activity, a response which is unique to the pineal gland. The relative order of potency of several adrenergic agonists is l-isoproterenol greater than l-norepinephrine greater than or equal to l-epinephrine greater than phenylephrine. Serotonin, tyramine, histamine, carbachol, gamma-aminobutyric acid, cocaine, and desmethylimipramine are inactive. Studies using adrenergic and metabolic inhibitors indicate that the regulation of N-acetyltransferase in these cells has the same characteristics of that seen in adult tissue. In addition, these cells synthesize protein and RNA from radioactive precursors, convert tryptophan to serotonin, and N-acetylate endogenous serotonin.

Acetyltransferases↗
PubMed1977

Adrenergic control of pineal N-acetyltransferase activity: developmental aspects.

The activity of pineal N-acetyltransferase in the neonatal rat does not exhibit the large daily rhythm seen in the adult and is intermediate between the low day and high night adult values. These intermediate values appear to result from adrenergic stimulation. Blockade of adrenergic receptors or of catecholamine synthesis results in a decrease in enzyme activity in vivo. In vitro studies provide additional evidence of a completely developed postsynaptic adrenergic control system for pineal N-acetyltransferase activity at birth. Our observations indicate that the appearance of a circadian rhythm in pineal N-acetyltransferase at the end of the first week of life reflects the development of presynaptic mechanisms and structures necessary for the control of catecholamine release and uptake. These events follow the developmental appearance of the postsynaptic mechanisms required to mediate the adrenergic-cycle AMP regulation of pineal N-acetyltransferase activity, which can be detected prior to birth.

Acetyltransferases↗
PubMed1977

Inhibition of the in vitro pituitary response to luteinizing hormone-releasing hormone by melatonin, serotonin, and 5-methoxytryptamine.

The effects of pineal indole compounds on the response of the neonatal rat anterior pituitary gland to LH-releasing hormone (LHRH) were studied in organ culture. After 24 h of culture under control conditions, pituitary glands from 5-day-old female rats were routinely incubated for an additional 24 h with the test compounds. Medium LH content was determined by double antibody radioimmunoassay. LHRH (10(-9) M) induced a 10-fold increase in LH levels over control values. Melatonin at a concentration of 10(-9) M significantly reduced the LHRH-stimulated release of LH; maximal suppression to 14% was attained with 10(-8) M melatonin. Similarly, 10(-8) M LHRH caused a 26-fold elevation in medium LH which was suppressed to 62, 55, and 47% by 10(-9), 10(-8), and 10(-7) M melatonin, respectively. In short-term experiments, inhibition was evident within 30 min of treatment. A developmental study of the effect of melatonin on LH release revealed significant inhibition with pituitary glands from rats 2, 5, and 10 days of age but not with glands from animals 21 and 30 days of age. Other pineal indoles were tested for their effects on the LH response to a single dose of LHRH (3 x 10(-10) M). Serotonin at a concentration of 10(-9) M significantly suppressed LH release; maximal reduction to 37-53% occurred with 10(-8) to 10(-6) M serotonin. 5-Methoxytryptamine also produced an inhibition which was significant only at 10(-6) M, the highest concentration tested. N-Acetylserotonin, 5-hydroxyindoleacetic acid, 5-methoxyindoleacetic acid, 5-hydroxytryptophol, and 5-methoxytryptophol showed no consistent inhibitory activity at doses up to 10(-7) M. These findings indicate that melatonin, serotonin, and 5-methoxytryptamine can act directly on the neonatal pituitary gland to suppress LHRH-induced release of LH.

5-Methoxytryptamine↗
PubMed1976

On GABA function and physiology in the pineal gland.

Pineal gamma-aminobutyric acid (GABA) content and glutamic acid decarboxylase (GAD) activity were found not to be influenced by environmental light, catecholamines, sympathetic innervation, or input via the pineal stalk. The observation that GAD activity did not disappear after pineal stalk section, ganglionectomy, or 48 h of organ culture leads us to suggest that GAD activity is not located in nerve processes entering the pineal gland. Treatment in organ culture with an inhibitor of protein synthesis did not greatly influence the slow rate of decrease of GAD activity. This finding is consistent with the conclusion that GAD turnover is slow. Treatment of denervated glands or glands containing functional sympathetic nerve structures with GABA, amino-oxyacetic acid (AOAA) or bicuculline in organ culture did not alter unstimulated levels, or significantly block the adrenergic stimulation of the activity of pineal serotonin N-acetyl transferase (NAT). It is clear from our studies that GABA does not influence or modulate the adrenergic regulation of.pineal NAT activity, and that GABA content and synthesis are not regulated by an adrenergic mechanism. The role of GABA in the pineal gland remains to be discovered.

Acetylcholinesterase↗
PubMed1976

Melatonin inhibition of the neonatal pituitary response to luteinizing hormone-releasing factor.

Neonatal rat anterior pituitary glands treated in organ culture with 1 nanomolar luteinzing hormone-releasing factor (LRF) showed a tenfold increase in medium luteinizing hormone (LH) concentrations over control values. Simultaneous treatment of the glands with 1 nanomolar melatonin significantly reduced the stimulatory effect of LRF on release of LH. This finding indicates that melatonin can act directly on the neonatal pituitary to inhibit the LH response to LRF.

Animals↗
PubMed1976

Learned helplessness, depression, and the attribution of failure.

Depressed and nondepressed college students received experience with solvable, unsolvable, or no discrimination problems. When later tested on a series of patterned anagrams, depressed groups performed worse than nondepressed groups, and unsolvable groups performed worse than solvable and control groups. As predicted by the learned helplessness model of depression, nondepressed subjects given unsolvable problems showed anagram deficits parallel to those found in naturally occurring depression. When depressed subjects attributed their failure to the difficulty of the problems rather than to their own incompetence, performance improved strikingly. So, failure in itself is apparently not sufficient to produce helplessness deficits in man, but failure that leads to a decreased belief in personal competence is sufficient.

Achievement↗
PubMed1976

Sympathetic nerve endings in the pineal gland protect against acute stress-induced increase in N-acetyltransferase (EC 2.3.1.5.) activity.

Injection of the antidepressant desmyethylimipramine (DMI, 10 mg/kg) into intact rats or into rats in which the superior cervical ganglia had been decentralized caused a marked enhancement of the swimming stress-induced increase in pineal gland acetyl-CoA:serotonin N-acetyltransferase (N-acetyltransferase, EC 2.3.1.5) activity. DMI is known to block uptake, the transport of catecholamines by nerve endings. It was found that DMI had no effect on enzyme activity in superior cervical ganglionectomized (SCGX) rats which were swimming stressed. The pineal glands of these animals are devoid of nerve endings. In unstressed intact or unstressed surgically altered rats, injection of DMI caused only a minor increase in N-acetyltransferase activity, which was much smaller than that seen after stress. After 5 h in organ culture sympathetic nerve endings within the pineal gland are still intact. At this time DMI treatment of pineal glands taken from intact rats shifted the dose-response curve for epinephrine (EPI) stimulation of N-acetyltransferase activity by two orders of magnitude, but caused only a slight change in the dose-response curve for isoproterenol, which is not taken up into nerve endings. In contrast, DMI treatment in organ culture had no effect on the dose-response curve for EPI in denervated pineal glands. These results support the hypothesis that the response of pineal N-acetyltransferase activity to stimulation by stress is influenced by uptake. It would appear that in addition to terminating neuronal adrenergic transmission, this transport process physiologically protects the pineal gland against nontranssynaptic adrenergic stimulation.

Acetyltransferases↗
PubMed1976

Long-term organ culture of rat anterior pituitary glands.

An organ culture system for neonatal rat anterior pituitary glands has been developed in which cellular integrity and responsiveness to LH releasing hormone (LHRH) are maintained for at least 4 days. Anterior pituitary glands from Sprague-Dawley rats were cultured individually at 37 C in an atmosphere of 95% O2-5% CO2 in BGJb culture medium, Fitton-Jackson modification. Histological examination of 5-day-old rat pituitary glands cultured for 96 h in control medium revealed no evidence of tissue necrosis. By contrast, 40-day-old-rat anterior pituitary glands were centrally necrotic after only 24 h of incubation under the same conditions. The neonatal glands were treated for 24 h with synthetic LHRH, and medium and pituitary LH FSH concentrations were determined by double antibody radioimmunoassay. On the first day of culture, LHRH caused a dose-related release of LH with the minimal effective dose between 10(-10) and 10(-9)M. Near-maximal release appeared to be attained with 10(-6)M LHRH, which induced a 12-fold elevation in medium LH over controls. Release was evident within 3 h following stimulation with 10(-9)M LHRH. Pituitary glands were responsive to this dose at 0,24 and 72 h of culture with progressively increasing ratios between LHRH-stimulated and control LH levels of 3,13, and 24, respectively. Although FSH release by LHRH was not observed on the first day of culture, on the second day LHRH caused a dose-related secretion of this hormone. Specificity of the pituitary response was demonstrated for LH and TSH release following addition of LHRH and thyrotropin releasing hormone (TRH). The simplicity, sensitivity, reproducibility, and long-term viability of this neonatal rat anterior pituitary organ culture system make it a valuable technique for the study of gonadotropin secretion.

Age Factors↗
PubMed1976

Monoamine oxidase in rat placenta, human placenta, and cultured choriocarcinoma.

The activity of monoamine oxidase (MAO), an enzyme which metabolized catecholamines and indoleamines, was determined in rat placenta at various stages of gestation, in human term placenta, and in choriocarcinoma grown in culture. From Day 15 to Day 20 of gestation the specific activity (units/mg protein) of MAO in rat placenta increased at least 3-fold; from Day 20 to the time of parturition, it decreased about 50%. The specific activity of MAO in human placenta at term was about 50%. The specific activity of MAO in human placenta at term was about 8 times higher than that of rat placenta at term. No MAO activity was found in choriocarcinoma grown in culture.

Animals↗
PubMed1975

Regulation of pineal rhythms in chickens: refractory period and nonvisual light perception.

Pineal serotonin N-acetyltransferase activity and melatonin content exhibit marked daily rhythms in chickens; peak values occur during the period of low locomotor activity which coincides with dark in a 24-h light-dark regime. We studied the regulation of these daily rhythms by measuring pineal serotonin N-acetyltransferase activity, hydroxyindole-O-methyltransferase (HIOMT) activity, and melatonin content in experiments in which birds were exposed to light-to-dark and dark-to-light transitions at atypical times. We observed that there is a refractory period for dark-initiation of the increase in pineal N-acetyltransferase activity and melatonin content. We also learned that a dark-to-light transition causes a rapid decrease in dark-elevated pineal N-acetyltransferase activity and melatonin content. The rapid decrease occurs in blinded chickens as well as sighted ones. HIOMT activity did not change consistently in any of the experimental treatments.

Acetyltransferases↗
PubMed1975

Regulation of pineal rhythms in chickens: effects of blinding, constant light, constant dark, and superior cervical ganglionectomy.

Pineal serotonin N-acetyltransferase activity and melatonin content exhibit marked daily changes in chickens; peak values occur during the period of low locomotor activity which coincides with dark in a 24-hour light-dark cycle. The photic and neural regulation of these daily changes were studied by measuring pineal serotonin N-acetyl-transferase activity, hydroxyindole-O-methyltransferase (HIOMT) activity, and melatonin content in experiments in which chickens were subjected to light-dark cycles, constant light, and constant dark and were surgically blinded or superior cervical ganglionectomized. It was found that: 1) The daily changes in N-acetyltransferase activity and melatonin content appear to persist in constant dark, and they disappear in constant light. 2) The eyes are not necessary for photic control of the daily changes, and the effect of constant light on N-acetyltransferase activity and melatonin content may be non-visual, that is, the eyes not being necessary. 3) The occurrence of the daily change in N-acetyltransferase activity and melatonin content does not require the superior cervical ganglia; the persistence of the changes in constant dark, however, may require the ganglia. 4) HIOMT activity was lower in constant light than in light-dark cycles and lower still in constant dark than in constant light. Neither the presence of the eyes nor the superior cervical ganglia affected HIOMT activity, as previously reported.

Acetylserotonin O-Methyltransferase↗