Food deprivation and hypothalamic neuropeptide gene expression: effects of strain background and the diabetes mutation.

We have used a novel method to identify genes expressed in the hypothalamus which may be potentially involved in controlling food intake and energy metabolism. We assumed that food deprivation, a powerful stimulus of food intake, would stimulate the activity of neural pathways involved in feeding behavior which should be reflected in an increase in the synthesis of any relevant neuropeptide and its messenger RNA. A study of 5 neuropeptides in 5 strains of mice has identified neuropeptide Y (NPY) as a gene whose expression in the hypothalamus is controlled by nutritional status, suggesting that hypothalamic NPY neurons are a link in the neural network regulating feeding behavior and energy metabolism. In addition, we have studied the effect of the diabetes mutation on neuropeptide gene expression during fasting and refeeding. Our findings suggest that abnormal NPY and enkephalin gene expression in the hypothalamus may be two important determinants of the expression of the diabetes mutation.     

Calcium, network activity, and the role of NMDA channels in synaptic plasticity in vitro.

Functionally effective neuronal circuits are constructed through a competitive process that requires patterned neuronal activity elicited by structured input from the environment. To explore the mechanisms of this activity-dependent synaptic restructuring, we have developed an in vitro preparation of mouse spinal cord neurons maintained in a 3-chambered cell-culture system. Sensory afferents that received chronic electrical stimulation for 3-5 d developed stronger synaptic connections than unstimulated afferents converging onto the same postsynaptic spinal cord neuron. Exposure to 100 microM DL-2-amino-5-phosphonovaleric acid (APV), an antagonist of the NMDA channel, during the stimulation period prevented the competitive advantage associated with electric stimulation. However, when APV was applied with a higher concentration of calcium (3 mM), activity-dependent synaptic plasticity was no longer inhibited by the NMDA receptor antagonist. This reversal of APV block of the plasticity was not impaired by reducing transmitter release with 3 mM magnesium (in addition to 3 mM calcium and APV). A suppressant effect of APV on spontaneous activity was observed, which was attributed to loss of the NMDA component of the EPSP. Activity-dependent plasticity was also blocked if spontaneous activity was suppressed with dilute tetrodotoxin (TTX; 5-10 nM), a dosage that reduces excitability of neurons but is insufficient to block sodium-dependent action potentials. These experiments bring into question how NMDA channel activation is involved in the processes of synaptic remodeling during development. The data suggest that postsynaptic activity is required for synaptic remodeling, but this activity need not involve NMDA receptor activation specifically for activity-evoked synaptic plasticity. Instead, the mechanism for plasticity appears to operate through calcium-dependent processes in general.     

Formation of free choline in brain tissue during in vitro energy deprivation

Free choline and ATP contents were measured in Mongolian gerbil hippocampal slices (tissue) and incubation media (media) during exposure to 30 min of aglycemia, high potassium, anoxia, or ischemia. Changes in choline levels reflected the degree of energy reduction, lower ATP levels being associated with high choline (4-fold increase during exposure to high potassium and anoxia, and 11-fold increase during ischemia). Media (extracellular) choline was particularly affected and increased about twofold during relatively mild energy depletion (e.g., aglycemia), but tissue choline content was less sensitive to energy reduction. A plot of choline vs. ATP levels indicated a nonlinear correlation, and the sharp increase in choline occurred when ATP values fell to about 2.5 nmol/mg of protein. Inhibition of acetylcholine sterase by 10 microM physostigmine during ischemia did not prevent an increase in choline contents but rather enhanced them, indicating that acetylcholine hydrolysis was not the source of free choline. Formation of free choline was Ca2+ independent. These findings suggest the involvement of phospholipase D and phosphatidylcholine hydrolysis in free choline formation during energy stress. The extent of choline formation may be an indicator of the degree of membranal damage, which in turn reflects damage to the metabolic machinery of the cell.     

Time-dependent effects of ovarian steroids on tyrosine hydroxylase activity in the limbic forebrain of female rats

Summary In this work, we have studied the time-course of the effects of pharmacological administration of ovarian steroids on tyrosine hydroxylase (TH) activity in the limbic forebrain of ovariectomized rats. Administration of estradiol produced a late decrease in TH activity. This effect was found 24 hours after the last steroid injection, disappearing at 32 hours. It was antagonized by progesterone, since a single injection of this steroid to estradiol-pretreated rats reversed to control values the estradiol-induced decrease. Nevertheless, the administration of progesterone after estradiol treatment caused a short-time decrease in the limbic activity of TH, which was observed 4 hours after the last steroid injection, disappearing subsequently. On the other hand, the administration of progesterone alone produced a biphasic effect, with a reduction at 24 hours, followed by an increase at 32 hours. These effects were only observed in the animals non-treated with estradiol, disappearing with a previous treatment with estrogens. Hence, it can be concluded that both ovarian steroids may affect the limbic TH activity. Thus, estradiol produced a late inhibitory effect on the activity of this enzyme, which was antagonized by progesterone. Administration of the last one to estradiol-treated rats produced a short-time inhibitory effect, whereas its administration to non-treated rats produced a late biphasic effect (inhibition followed by stimulation), which was not observed in estradiol-treated rats.     

Characterization of a model of malaria in the pregnant host: Plasmodium berghei in the white rat

This study characterizes a Plasmodium berghei white rat model of P. falciparum malaria in the pregnant human. Seventy-day-old and 114-day-old female rats, given an infecting inoculum at time of mating, had higher parasitemias and a more severe anemia than age- and sex-matched controls. Under these experimental conditions, the parasitemia went to crisis in all animals and there were no fatal infections. In contrast, all animals died when the infection was initiated 7 days after conception, a timing that brought a coincidence of peak parasitemia and term. Pregnancy during the post-crisis subpatent period did not cause recrudescence. At the time of delivery, the parasitemia was consistently higher in the placental (crush smear) blood than in the peripheral (tail) blood. This difference was greatest in animals giving birth shortly before or 1-2 days after the parasitemic crisis. Very young, compact parasite forms predominated in the placental blood, whereas trophozoites predominated in the peripheral blood.     

Methodological Issues Associated with an Audit of Stillbirth in a Family Medicine Practice in Israel

An audit of ‘deficient outcome’ involves the step-by-stepanalysis of every event preceding the occurrence of a preventablemedical outcome in order to determine exactly what went wrong.This paper describes methodological problems and related issuesassociated with a deficient outcome audit undertaken on fivestillbirths which occurred in a rural family medical practiceIsrael between 1985 and 1987. Problems included initial officialdisinterest towards the audit, and the high levels of suspicionand antagonism which it aroused in hospital staff approachedfor information. The problematic aspect of such audits needsmore attention. The importance of this type of audit for establishing the precisereasons for perinatal deaths, and thus for maintaining antenatalcare standards is discussed. In view of the small numbers ofsuch events likely to occur within any one family practice itis not only feasible but also desirable for more family doctorsto carry out such audits routinely, despite the difficultieswhich are involved.     

Computed tomography of the brain in the Smith-Lemli-Opitz syndrome

Computed tomographic (CT) scans of the brain in a child with Smith-Lemli-Opitz syndrome revealed enlargement of the ventricular system, hypoplasia of the cerebellum, and abnormal thickening of the gray matter, consistent with pachygyria. These findings have been previously noted in autopsies performed on patients with this disorder. We conclude that CT scanning is a valuable tool in the evaluation of children suspected of having the Smith-Lemli-Opitz syndrome.