Ultrastructural evidence that androgen receptors are located at extranuclear sites in the rat hippocampal formation.

Like estrogens in female rats, androgens can affect dendritic spine density in the CA1 subfield of the male rat hippocampus [J Neurosci 23:1588 (2003)]. Previous light microscopic studies have shown that androgen receptors (ARs) are present in the nuclei of CA1 pyramidal cells. However, androgens may also exert their effects through rapid non-genomic mechanisms, possibly by binding to membranes. Thus, to investigate whether ARs are at potential extranuclear sites of ARs, antibodies to ARs were localized by light and electron microscopy in the male rat hippocampal formation. By light microscopy, AR immunoreactivity (-ir) was found in CA1 pyramidal cell nuclei and in disperse, punctate processes that were most dense in the pyramidal cell layer. Additionally, diffuse AR-ir was found in the mossy fiber pathway. Ultrastructural analysis revealed AR-ir at several extranuclear sites in all hippocampal subregions. AR-ir was found in dendritic spines, many arising from pyramidal and granule cell dendrites. AR-ir was associated with clusters of small, synaptic vesicles within preterminal axons and axon terminals. Labeled preterminal axons were most prominent in stratum lucidum of the CA3 region. AR-containing terminals formed asymmetric synapses or did not form synaptic junctions in the plane of section analyzed. AR-ir also was detected in astrocytic profiles, many of which apposed terminals synapsing on unlabeled dendritic spines or formed gap junctions with other AR-labeled or unlabeled astrocytes. Collectively, these results suggest that ARs may serve as both a genomic and non-genomic transducer of androgen action in the hippocampal formation.

Temporal lobe seizures alter the amplitude and timing of rat behavioral rhythms.

Daily rhythms of spontaneous locomotor activity (SLA) in rats were studied before and after an episode of pilocarpine-induced convulsive status epilepticus (SE). A pronounced increase in activity levels during both the light and dark phases was found 1 week after SE as compared with baseline SLA and controls administered saline. Rats with bilateral lesions of the nucleus accumbens (shell) did not exhibit any significant change in SLA 1 week after SE compared with controls. We suggest that during the first week after SE the increase in SLA was induced by abnormal neuronal activity in the hippocampus driving a descending limbic-motor pathway via the nucleus accumbens. EEG recordings revealed high-amplitude interictal spikes in hippocampal CA1. During subsequent weeks, SLA rhythms of nonlesioned chronic epileptic rats remained elevated but progressively normalized over a period of 12 weeks. Although both chronic epileptic and control groups displayed near-24-hour activity patterns under light-dark conditions, significant delays (>4 hour) in acrophase were observed after spontaneous seizures had developed. The phase delay was positively correlated with seizure history and likely the result of postictal hyperactivity associated with seizures during the normal rest period. Despite these changes, cell density in the suprachiasmatic nucleus (SCN) and intergeniculate leaflet (IGL) did not differ significantly between epileptic and control groups. In the absence of damage to brain areas directly involved with the regulation of behavioral rhythms, chronic seizure activity presumably alters the timing of activity patterns through a nonphotic mechanism, perhaps involving activation of the SCN or IGL during limbic seizures.

Seizure onset times for rats receiving systemic lithium and pilocarpine: sources of variability.

Injection of 30 mg/kg of pilocarpine 24 h after systemic injection of lithium (3 mEq/kg) results in overt limbic motor seizures within about 30 min. Results of several experiments indicated that whereas food deprivation or repeated nociceptive stimulation during the previous 24 h decreased seizure onset times (SOTs) by about 11 to 12 min, food restriction, continuous lighting, or, handling during the previous 7 to 14 days increased SOTs by comparable durations. Early handling before weaning but not injections of clomimpramine also decreased SOTs. A difference of 18 min in the means of SOTs was produced by injecting either 1.0 (increased SOT) or 1.5 mg/kg (decreased SOT) of dexamethasome during the previous 24 h. A strong (multiple r=.87) association between SOTs and the amount of damage within five specific thalamic-limbic nuclei was observed. These results, in conjunction with blood corticosterone levels taken before and after induction of the seizures, suggest the neurochemical mechanisms affecting the range in SOTs could involve the adrenocorticotropic hormone (ACTH)-corticosterone system and influence the amount of post-seizure-induced damage.

Endogenous melatonin and epileptogenesis: facts and hypothesis.

In human epilepsy, diurnal variation in seizure phenomena suggests the involvement of a time-dependent biological signal. Clinical evidence indicates that in some cases, temporal clustering of epileptic seizures is in phase with the nocturnal rise in circulating melatonin. Although this hormone has been reported to stabilize the brain against seizure-producing stimuli, these pharmacological doses are not representative of physiological conditions but would nonetheless facilitate widespread inhibitory neurotransmission characteristic of traditional anticonvulsants. Instead, it is proposed that endogenous melatonin contributes to epileptiform activity through inhibitory actions on dopaminergic activity. Dopamine is considered a natural downregulator of seizure activity in a number of species, including humans, and numerous lines of evidence suggest that melatonin is capable of stimulating a decrease in dopamine output within areas of the brain thought to participate in the control of epileptic seizures. Pharmacological manipulation of the endogenous melatonin rhythm may provide a useful therapeutic strategy against the occurrence of seizures during increased hormone production.

Diurnal variation in pilocarpine-induced generalized tonic-clonic seizure activity.

The efficacy of the cholinergic agonist pilocarpine to evoke generalized seizures in rats was examined over the 24-h photocycle. Both seizure latency and severity during the 24-h period exhibited marked diurnal variation. Seizure activity generalized more rapidly throughout the dark phase and was often characterized by wild running clonus and tonic extensor convulsions. In contrast, electrographic seizures during the light phase were mainly associated with facial/forelimb clonus and rearing typical of pilocarpine-induced seizures. These data suggest that the sensitivity of the rodent brain to pilocarpine exhibits day-night variation and seizure activity induced during the dark phase may generalize via the brainstem.

Brief communication; differential effects of a physiologically patterned low-intensity agent on the formation of an olfactory memory trace.

Male rats were exposed to a low-intensity (300-500 nT) electromagnetic (EM) field designed to simulate primed burst potentiation (PB) for 30 min preceding a one-trial olfactory learning task involving two brief encounters with a juvenile rat during a baseline (reference) and an experimental (EM) trial. The amount of time spent engaged in behaviors defining social investigation (i.e., sniffing, grooming) during the second encounter of the experimental trial was significantly elevated in adult rats receiving continuous EM stimulation prior to the initial encounter. These results support the hypothesis that LTP-like stimulation disrupts the acquisition of a learning task if the stimulus is delivered before training.

Acquisition deficit and time-dependent retrograde amnesia for contextual fear conditioning in agmatine-treated rats.

Cumulative evidence indicates that the hippocampus plays a time-limited role in contextual learning paradigms. Pharmacological studies have indicated that acquisition of background contextual cues during Pavlovian fear conditioning is dependent upon hippocampal function, whereas early inactivation of the hippocampus after training produces retrograde amnesia. When administered prior to contextual fear conditioning, agmatine (5 and 10 mg/kg, i.p.), an endogenous polyamine and N-methyl-D-aspartate (NMDA) receptor ligand found at excitatory synapses in the hippocampus, impaired the acquisition of contextual fear (measured as defensive freezing 26 hours later) without a reduction in baseline motor activity during training. Furthermore, ascending doses of agmatine were found not to exert analgesic effects on response thresholds to peripheral shock. This negated the possibility that the observed learning deficit resulted from a difference in perceived shock intensity. Post-training agmatine treatment produced a time-dependent impairment of consolidation, with subjects approaching a level of fear equivalent to that of a reference group as the delay of treatment increased (up to 6 hours). Since physiologically high levels of agmatine are able to inhibit NMDA receptor activity, these results suggest that polyamine modulation of NMDA receptors, most likely within the hippocampus, is required for the acquisition and consolidation of contextual fear stimuli.

Pretraining exposure to physiologically patterned electromagnetic stimulation attenuates fear-conditioned analgesia.

The effect of weak electromagnetic stimulation on the emergence of conditioned analgesia was examined in the adult rat. Subjects were conditioned to associate a continuous 20 kHz ultrasonic tone (CS) with 0.2 mA footshock (UCS-) over five successive days. For 30 min either before or after conditioning sessions, rats were exposed to sham or pulsed (primed burst potentiation) magnetic fields (500 nT). At the end of the conditioning phase, all animals were evaluated for anticipatory analgesia following CS presentation using a hotplate analgesiometer. Data analysis suggested a statistically significant attenuation of fear-conditioned analgesia in rats exposed to electromagnetic stimulation prior to conditioning, whereas post-conditioning exposure potentiated the reduction in pain sensitivity compared to baseline measures. The present results suggest that the emergence of fear-conditioned responses is sensitive to whole body exposure to a magnetic field pattern that has been shown to induce long-term potentiation in hippocampal slices.

Pulmonary edema during pregnancy.

Physiologic changes in the pulmonary system during pregnancy place the pregnant woman at risk for having pulmonary edema. Cardiogenic and non-cardiogenic pulmonary edema have similar clinical signs and symptoms; however, treatments may differ greatly. Understanding the types of pulmonary edema enables the obstetric nurse to provide improved care for this group of patients.

Perinatal asphyxia: surveillance of the high-risk fetus.

Methods of testing to identify the fetus at risk for developing perinatal asphyxia continue to be developed and refined. The perinatal nurse needs to be knowledgeable of each test's purpose, capabilities, limitations, and clinical issues. Appropriate nursing interventions based on this knowledge facilitates the testing process and promotes the goal of improved perinatal outcome.

Combination chemo-immunotherapy: kinetics of in vivo and in vitro generation of natural killer cells and lymphokine-activated killer cells in the rat.

Rats received a single high dose of cyclophosphamide (Cy) (150 mg/kg), followed 48 h later (on day 0) by immunization with a T cell-dependent soluble antigen, ovalbumin in Freund's complete adjuvant (FCA). The effect of this treatment on lymphoid cell subpopulations in the spleen, natural killer (NK) cell and interleukin-2 (IL-2) induced lymphokine-activated killer (LAK) cell activity was examined. Cy (with and without ovalbumin) caused a large relative increase (by day 14) in splenic OX8+, OX19- cells with NK morphology. A marked relative increase in fresh NK cell activity was noted after Cy + ovalbumin, but not consistently after Cy alone. Elevated NK activity was Cy dose- and time-dependent, was evident within 7 days post Cy/ovalbumin and persisted for at least 28 days. Pooled splenic mononuclear cells (MNC), obtained 14 days after Cy/ovalbumin, lost all cytolytic activity against YAC-1 cells when cultured in the absence of human recombinant IL-2 (rIL-2). In contrast, similarly maintained cells from normal rats displayed NK activity higher than normal 'fresh' levels. Upon culture in medium containing 500 U/ml rIL-2, however, 'augmented' NK activity was equivalent, on a per-cell basis, in both normal and Cy/ovalbumin-pretreated groups. LAK activity generated in vitro (i.e. against NK-resistant target cells) was significantly lower in the latter group, and the overall yield of cells was reduced. By day 21 after Cy/ovalbumin, augmented NK activity was significantly greater than controls, on a per-cell and total culture yield basis. Moreover, LAK activity was now similar between groups. It is concluded that the chemotherapy/immunization protocol which we have used can greatly enhance NK activity in vivo and that these cells are responsive to induction of LAK activity by IL-2 in vitro.

Inhibition of hydrogen peroxide release from activated macrophages by prior ingestion of erythrocytes or haemoglobin.

Production of hydrogen peroxide by mouse peritoneal macrophages activated with Corynebacterium parvum was induced by incubating the cells with opsonised zymosan. H2O2 release was reduced by 47% when macrophages were preincubated with opsonised sheep erythrocytes. A significant decrease also occurred when the cells were preincubated with heat-denatured haemoglobin, but not when preincubated with opsonised erythrocyte ghosts, even though the latter were taken up by the macrophages. The ability of macrophages in an infected lesion to destroy microorganisms may therefore be impaired by ingestion of extravasated erythrocytes.