Development of status epilepticus, sustained calcium elevations and neuronal injury in a rat survival model of lethal paraoxon intoxication

Paraoxon (POX) is an active metabolite of organophosphate (OP) pesticide parathion that has been weaponized and used against civilian populations. Exposure to POX produces high mortality. OP poisoning is often associated with chronic neurological disorders. In this study, we optimize a rat survival model of lethal POX exposures in order to mimic both acute and long-term effects of POX intoxication. Male Sprague-Dawley rats injected with POX (4mg/kg, ice-cold PBS, s.c.) produced a rapid cholinergic crisis that evolved into status epilepticus (SE) and death within 6-8min. The EEG profile for POX induced SE was characterized and showed clinical and electrographic seizures with 7-10Hz spike activity. Treatment of 100% lethal POX intoxication with an optimized three drug regimen (atropine, 2mg/kg, i.p., 2-PAM, 25mg/kg, i.m. and diazepam, 5mg/kg, i.p.) promptly stopped SE and reduced acute mortality to 12% and chronic mortality to 18%. This model is ideally suited to test effective countermeasures against lethal POX exposure. Animals that survived the POX SE manifested prolonged elevations in hippocampal [Ca(2+)]i (Ca(2+) plateau) and significant multifocal neuronal injury. POX SE induced Ca(2+) plateau had its origin in Ca(2+) release from intracellular Ca(2+) stores since inhibition of ryanodine/IP3 receptor lowered elevated Ca(2+) levels post SE. POX SE induced neuronal injury and alterations in Ca(2+) dynamics may underlie some of the long term morbidity associated with OP toxicity.

Characterization of spontaneous recurrent epileptiform discharges in hippocampal-entorhinal cortical slices prepared from chronic epileptic animals

Epilepsy, a common neurological disorder, is characterized by the occurrence of spontaneous recurrent epileptiform discharges (SREDs). Acquired epilepsy is associated with long-term neuronal plasticity changes in the hippocampus resulting in the expression of spontaneous recurrent seizures. The purpose of this study is to evaluate and characterize endogenous epileptiform activity in hippocampal-entorhinal cortical (HEC) slices from epileptic animals. This study employed HEC slices isolated from a large series of control and epileptic animals to evaluate and compare the presence, degree and localization of endogenous SREDs using extracellular and whole cell current clamp recordings. Animals were made epileptic using the pilocarpine model of epilepsy. Extracellular field potentials were recorded simultaneously from areas CA1, CA3, dentate gyrus, and entorhinal cortex and whole cell current clamp recordings were obtained from CA3 neurons. All regions from epileptic HEC slices (n=53) expressed SREDs, with an average frequency of 1.3Hz. In contrast, control slices (n=24) did not manifest any SREDs. Epileptic HEC slices demonstrated slow and fast firing patterns of SREDs. Whole cell current clamp recordings from epileptic HEC slices showed that CA3 neurons exhibited paroxysmal depolarizing shifts associated with these SREDs. To our knowledge this is the first significant demonstration of endogenous SREDs in a large series of HEC slices from epileptic animals in comparison to controls. Epileptiform discharges were found to propagate around hippocampal circuits. HEC slices from epileptic animals that manifest SREDs provide a novel model to study in vitro seizure activity in tissue prepared from epileptic animals.

Collinearity-preserving functions between Desarguesian planes

Using concepts from valuation theory, we obtain a characterization of all collinearity-preserving functions from one affine or projective Desarguesian plane into another. The case in which the planes are projective and the range contains a quadrangle has been treated previously in the literature. Our results permit one or both planes to be affine and include cases in which the range contains a triangle but no quadrangle. A key theorem is that, with the exception of certain embeddings defined on planes of order 2 and 3, every collinearity-preserving function from one affine Desarguesian plane into another can be extended to a collinearity-preserving function between enveloping projective planes.

Dantrolene inhibits the calcium plateau and prevents the development of spontaneous recurrent epileptiform discharges following in vitro status epilepticus

Status epilepticus is a clinical emergency that can lead to the development of acquired epilepsy following neuronal injury. Understanding the pathophysiological changes that occur between the injury itself and the expression of epilepsy is important in the development of new therapeutics to prevent epileptogenesis. Currently, no anti-epileptogenic agents exist; thus, the ability to treat an individual immediately after status epilepticus to prevent the ultimate development of epilepsy remains an important clinical challenge. In the Sprague-Dawley rat pilocarpine model of status epilepticus-induced acquired epilepsy, intracellular calcium has been shown to increase in hippocampal neurons during status epilepticus and remain elevated well past the duration of the injury in those animals that develop epilepsy. This study aimed to determine if such changes in calcium dynamics exist in the hippocampal culture model of status epilepticus-induced acquired epilepsy and, if so, to study whether manipulating the calcium plateau after status epilepticus would prevent epileptogenesis. The in vitro status epilepticus model resembled the in vivo model in terms of elevations in neuronal calcium concentrations that were maintained well past the duration of the injury. When used following in vitro status epilepticus, dantrolene, a ryanodine receptor inhibitor, but not the N-methyl-D-aspartic acid channel blocker MK-801 inhibited the elevations in intracellular calcium, decreased neuronal death and prevented the expression of spontaneous recurrent epileptiform discharges, the in vitro correlate of epilepsy. These findings offer potential for a novel treatment to prevent the development of epileptiform discharges following brain injuries.

Development of a prolonged calcium plateau in hippocampal neurons in rats surviving status epilepticus induced by the organophosphate diisopropylfluorophosphate

Organophosphate (OP) compounds are among the most lethal chemical weapons ever developed and are irreversible inhibitors of acetylcholinesterase. Exposure to majority of OP produces status epilepticus (SE) and severe cholinergic symptoms that if left untreated are fatal. Survivors of OP intoxication often suffer from irreversible brain damage and chronic neurological disorders. Although pilocarpine has been used to model SE following OP exposure, there is a need to establish a SE model that uses an OP compound in order to realistically mimic both acute and long-term effects of nerve agent intoxication. Here we describe the development of a rat model of OP-induced SE using diisopropylfluorophosphate (DFP). The mortality, behavioral manifestations, and electroencephalogram (EEG) profile for DFP-induced SE (4 mg/kg, sc) were identical to those reported for nerve agents. However, significantly higher survival rates were achieved with an improved dose regimen of DFP and treatment with pralidoxime chloride (25 mg/kg, im), atropine (2 mg/kg, ip), and diazepam (5 mg/kg, ip) making this model ideal to study chronic effects of OP exposure. Further, DFP treatment produced N-methyl-D-aspartate (NMDA) receptor-mediated significant elevation in hippocampal neuronal [Ca(2+)](i) that lasted for weeks after the initial SE. These results provided direct evidence that DFP-induced SE altered Ca(2+) dynamics that could underlie some of the long-term plasticity changes associated with OP toxicity. This model is ideally suited to test effective countermeasures for OP exposure and study molecular mechanisms underlying neurological disorders following OP intoxication.

Temporal characterization of changes in hippocampal cannabinoid CB(1) receptor expression following pilocarpine-induced status epilepticus

Several reports have focused on the involvement of the endocannabinoid system in hyperexcitability, particularly in seizure and epilepsy models. Our laboratory recently characterized a novel plasticity change of the cannabinoid type 1 (CB(1)) receptor in hippocampi of epileptic rats following pilocarpine-induced status epilepticus (SE). This long-term redistribution included selective layer-specific changes in CB(1) receptor expression within distinct hippocampal subregions. However, the temporal characteristics of this redistribution during the development of epilepsy had not been examined. Therefore, this study was initiated to evaluate the time course by which pilocarpine-induced SE produced changes in CB(1) receptor expression. Immunohistochemical analysis demonstrated that within 1 week following SE, there was a pronounced loss in CB(1) receptor expression throughout the hippocampus, while staining in many interneurons was preserved. By 1 month post-SE, pilocarpine-treated animals began to display epileptic seizures, and CB(1) receptor expression was characteristic of the redistribution observed in long-term epileptic rats, with decreases in CB(1) receptor immunoreactivity in the stratum pyramidale neuropil and dentate gyrus inner molecular layer, and increases in the strata oriens and radiatum of CA1-3. Observed changes in CB(1) receptor expression were confirmed at multiple time points by western blot analysis. The data indicate that overall decreases in expression following SE preempt a long-lasting CB(1) receptor redistribution, and that differential responses occur within the hippocampus to initial CB(1) receptor losses. This suggests a role for dysregulation of the endocannabinoid system during epileptogenesis and indicates that the CB(1) receptor redistribution temporally correlates with the emergence of epileptic seizures.

Long-term decrease in calbindin-D28K expression in the hippocampus of epileptic rats following pilocarpine-induced status epilepticus

Acquired epilepsy (AE) is characterized by spontaneous recurrent seizures and long-term changes that occur in surviving neurons following an injury such as status epilepticus (SE). Long-lasting alterations in hippocampal Ca(2+) homeostasis have been observed in both in vivo and in vitro models of AE. One major regulator of Ca(2+) homeostasis is the neuronal calcium binding protein, calbindin-D28k that serves to buffer and transport Ca(2+) ions. This study evaluated the expression of hippocampal calbindin levels in the rat pilocarpine model of AE. Calbindin protein expression was reduced over 50% in the hippocampus in epileptic animals. This decrease was observed in the pyramidal layer of CA1, stratum lucidum of CA3, hilus, and stratum granulosum and stratum moleculare of the dentate gyrus when corrected for cell loss. Furthermore, calbindin levels in individual neurons were also significantly reduced. In addition, the expression of calbindin mRNA was decreased in epileptic animals. Time course studies demonstrated that decreased calbindin expression was initially present 1 month following pilocarpine-induced SE and lasted for up to 2 years after the initial episode of SE. The results indicate that calbindin is essentially permanently decreased in the hippocampus in AE. This decrease in hippocampal calbindin may be a major contributing factor underlying some of the plasticity changes that occur in epileptogenesis and contribute to the alterations in Ca(2+) homeostasis associated with AE.

Aging is associated with elevated intracellular calcium levels and altered calcium homeostatic mechanisms in hippocampal neurons

Aging is associated with increased vulnerability to neurodegenerative conditions such as Parkinson's and Alzheimer's disease and greater neuronal deficits after stroke and epilepsy. Emerging studies have implicated increased levels of intracellular calcium ([Ca(2+)](i)) for the neuronal loss associated with aging related disorders. Recent evidence demonstrates increased expression of voltage gated Ca(2+) channel proteins and associated Ca(2+) currents with aging. However, a direct comparison of [Ca(2+)](i) levels and Ca(2+) homeostatic mechanisms in hippocampal neurons acutely isolated from young and mid-age adult animals has not been performed. In this study, Fura-2 was used to determine [Ca(2+)](i) levels in CA1 hippocampal neurons acutely isolated from young (4-5 months) and mid-age (12-16 months) Sprague-Dawley rats. Our data provide the first direct demonstration that mid-age neurons in comparison to young neurons manifest significant elevations in basal [Ca(2+)](i) levels. Upon glutamate stimulation and a subsequent [Ca(2+)](i) load, mid-age neurons took longer to remove the excess [Ca(2+)](i) in comparison to young neurons, providing direct evidence that altered Ca(2+) homeostasis may be present in animals at significantly younger ages than those that are commonly considered aged (> or =24 months). These alterations in Ca(2+) dynamics may render aging neurons more vulnerable to neuronal death following stroke, seizures or head trauma. Elucidating the functionality of Ca(2+) homeostatic mechanisms may offer an understanding of the increased neuronal loss that occurs with aging, and allow for the development of novel therapeutic agents targeted towards decreasing [Ca(2+)](i) levels thereby restoring the systems that maintain normal Ca(2+) homeostasis in aged neurons.

Cannabinoid CB1 receptor antagonists cause status epilepticus-like activity in the hippocampal neuronal culture model of acquired epilepsy

Status epilepticus (SE) is a major medical emergency associated with a significant morbidity and mortality. Little is known about the mechanisms that terminate seizure activity and prevent the development of status epilepticus. Cannabinoids possess anticonvulsant properties and the endocannabinoid system has been implicated in regulating seizure duration and frequency. Endocannabinoids regulate synaptic transmission and dampen seizure activity via activation of the presynaptic cannabinoid receptor 1 (CB1). This study was initiated to evaluate the role of CB1 receptor-dependent endocannabinoid synaptic transmission towards preventing the development of status epilepticus-like activity in the well-characterized hippocampal neuronal culture model of acquired epilepsy using patch clamp electrophysiology. Application of the CB1 receptor antagonists SR141716A (1 microM) or AM251 (1 microM) to "epileptic" neurons caused the development of continuous epileptiform activity, resembling electrographic status epilepticus. The induction of status epilepticus-like activity by CB1 receptor antagonists was reversible and could be overcome by maximal concentrations of CB1 agonists. Similar treatment of control neurons with CB1 receptor antagonists did not produce status epilepticus or hyperexcitability. These findings suggest that CB1 receptor-dependent endocannabinoid endogenous tone plays an important role in modulating seizure frequency and duration and preventing the development of status epilepticus-like activity in populations of epileptic neurons. The regulation of seizure activity and prevention of status epilepticus by the endocannabinoid system offers an important insight into understanding the basic mechanisms that control the development of continuous epileptiform discharges.

Altered calcium/calmodulin kinase II activity changes calcium homeostasis that underlies epileptiform activity in hippocampal neurons in culture

Epilepsy is characterized by the occurrence of spontaneous recurrent epileptiform discharges (SREDs) in neurons. A decrease in calcium/calmodulin-dependent protein kinase II (CaMK-II) activity has been shown to occur with the development of SREDs in a hippocampal neuronal culture model of acquired epilepsy, and altered calcium (Ca(2+)) homeostasis has been implicated in the development of SREDs. Using antisense oligonucleotides, this study was conducted to determine whether selective suppression of CaMK-II activity, with subsequent induction of SREDs, was associated with altered Ca(2+) homeostasis in hippocampal neurons in culture. Antisense knockdown resulted in the development of SREDs and a decrease in both immunocytochemical staining and enzyme activity of CaMK-II. Evaluation of [Ca(2+)](i) using Fura indicators revealed that antisense-treated neurons manifested increased basal [Ca(2+)](i), whereas missense-treated neurons showed no change in basal [Ca(2+)](i). Antisense suppression of CaMK-II was also associated with an inability of neurons to restore a Ca(2+) load. Upon removal of oligonucleotide treatment, CaMK-II suppression and Ca(2+) homeostasis recovered to control levels and SREDs were abolished. To our knowledge, the results demonstrate the first evidence that selective suppression of CaMK-II activity results in alterations in Ca(2+) homeostasis and the development of SREDs in hippocampal neurons and suggest that CaMK-II suppression may be causing epileptogenesis by altering Ca(2+) homeostatic mechanisms.

Evidence that injury-induced changes in hippocampal neuronal calcium dynamics during epileptogenesis cause acquired epilepsy

Alterations in hippocampal neuronal Ca(2+) and Ca(2+)-dependent systems have been implicated in mediating some of the long-term neuroplasticity changes associated with acquired epilepsy (AE). However, there are no studies in an animal model of AE that directly evaluate alterations in intracellular calcium concentration ([Ca(2+)](i)) and Ca(2+) homeostatic mechanisms (Ca(2+) dynamics) during the development of AE. In this study, Ca(2+) dynamics were evaluated in acutely isolated rat CA1 hippocampal, frontal, and occipital neurons in the pilocarpine model by using [Ca(2+)](i) imaging fluorescence microscopy during the injury (acute), epileptogenesis (latency), and chronic-epilepsy phases of the development of AE. Immediately after status epilepticus (SE), hippocampal neurons, but not frontal and occipital neurons, had significantly elevated [Ca(2+)](i) compared with saline-injected control animals. Hippocampal neuronal [Ca(2+)](i) remained markedly elevated during epileptogenesis and was still elevated indefinitely in the chronic-epilepsy phase but was not elevated in SE animals that did not develop AE. Inhibiting the increase in [Ca(2+)](i) during SE with the NMDA channel inhibitor MK801 was associated in all three phases of AE with inhibition of the changes in Ca(2+) dynamics and the development of AE. Ca(2+) homeostatic mechanisms in hippocampal neurons also were altered in the brain-injury, epileptogenesis, and chronic-epilepsy phases of AE. These results provide evidence that [Ca(2+)](i) and Ca(2+)-homeostatic mechanisms are significantly altered during the development of AE and suggest that altered Ca(2+) dynamics may play a role in the induction and maintenance of AE and underlie some of the neuroplasticity changes associated with the epileptic phenotype.

Comparison of gas chromatography/mass spectrometry and immunoassay techniques on concentrations of atrazine in storm runoff

Gas chromatography/mass spectrometry (GC/MS) and enzyme-linked immunosorbent assay (ELISA) techniques were used to measure concentrations of dissolved atrazine in 149 surface-water samples. Samples were collected during May 1992-September 1993 near the mouth of the White River (Indiana) and in two small tributaries of the river. GC/MS was performed on a Hewlett-Packard 5971A with electron impact ionization and selected ion monitoring of filtered water samples extracted by C-18 solid phase extraction; ELISA was performed with a magnetic-particle-based assay with photometric analysis. ELISA results compared reasonably well to GC/MS measurements at concentrations below the Maximum Contaminant Level for drinking water set by the U.S. Environmental Protection Agency (3.0 microg/L), but a systematic negative bias was observed at higher concentrations. When higher concentration samples were diluted into the linear range of calibration, the relation improved. A slight positive bias was seen in all of the ELISA data compared to the GC/MS results, and the bias could be partially explained by correcting the ELISA data for cross reactivity with other triazine herbicides. The highest concentrations of atrazine were found during the first major runoff event after the atrazine was applied. Concentrations decreased throughout the rest of the sampling period even though large runoff events occurred during this time, indicating that most atrazine loading to surface waters in the study area occurs within a few weeks after application.

Gender differentiated receptivity to sexuality education curricula by adolescents

Teenagers comprise a substantial proportion of the 'at risk' population for sexually transmissible diseases (STDs) and AIDS. They are, also, potentially amenable to the curriculum influences of the high school, suggesting that a high profile needs to be accorded to sexuality education curricula. The variable of receptivity along gender lines to sexuality education programs is explored and reported in this study. An instrument was constructed to measure key constitutive variables in the dimensions of meaning and attitude, and administered to a sample of Western Australian high school students (N = 533). Data were subjected to a two-way ANOVA with sex and school as the dependent variables. It was found that there are differences in receptivity to sexuality education curricula between male and female high school students; that receptivity, irrespective of gender, rises with increasing curriculum provision and with males showing higher gains when compared with females. The findings have implications for policy makers and administrators in providing access to extensive school-based sexuality education curricula.

Identification and determination of tert-alkylphenols in carp from the Trenton Channel of the Detroit River, Michigan, USA

Whole carp from the Detroit River were analyzed by gas chromatographic mass spectrometry. Seven tertiary alkyl phenols (tert-pentylphenols, tert-butyl-tert-pentylphenols, a di-tert-pentylphenol and a tri-tert-pentylphenol) and eight chlorinated derivatives of these compounds were identified from their mass spectra and confirmed with synthesized authentic standards. 2,4-Di-tert-pentylphenol was the most abundant of these compounds; in one fish sample, its concentration was about 140 ppm. The same alkyl phenols were also found in technical-grade 2,4-di-tert-pentylphenol, which is manufactured at a chemical plant located near the Detroit River. Comparison of the alkyl phenol levels in carp with those in nearby sediments showed that many of these compounds are taken up by carp and that carp can be used to roughly track local sediment contamination.

Antigonadal effects of timed melatonin infusion in pinealectomized male Djungarian hamsters (Phodopus sungorus sungorus): duration is the critical parameter

To determine which parameter of the day/night pattern of pineal melatonin secretion is the critical component signaling daylength information in the Djungarian hamster, we have developed a method for giving timed sc melatonin infusions in pinealectomized juvenile males. When given for 12 h daily, as little as 10 ng melatonin (14 pg/min) consistently induced testicular regression within 12 days. However, 10 ng melatonin infused for 4 or 6 h daily did not inhibit gonadal development. The effects of these infusions on the reproductive system did not depend on the time of day at which melatonin was administered. In complementary experiments, the minimal daily infusion duration and the critical daylength for induction of testicular regression were determined. The critical length of infusion (7-8 h) was in close agreement with the estimated duration of melatonin secretion during the critical scotophase. These findings support the hypothesis that melatonin mediates the pineal-antigonadal effects of short day exposure in the Djungarian hamster. Furthermore, the data strongly suggest that duration is the feature of nighttime melatonin release that is most important for photoperiodic time measurement in this species.

Progonadal role of the pineal in the Djungarian hamster (Phodopus sungorus sungorus): mediation by melatonin

A progonadal role of the pineal in both adult and juvenile male Djungarian hamsters has been demonstrated which confirms and extends previous reports. In short day-raised hamsters, stimulation of testicular development was achieved by transfer to long days. This stimulatory effect of long days was blocked by pinealectomy. Gonadal stimulation could be elicited in pinealectomized juveniles by timed daily infusions of melatonin. When given for 4 or 6 h daily at a dose rate of 0.83 or 83 ng/h, melatonin infusions stimulated testicular development and body growth. Measurement of plasma FSH and PRL indicated that this pubertal response resulted at least in part from a stimulatory effect of melatonin on the secretion of these hormones. Longer duration infusions (8 or 12 h) did not stimulate testicular development or body growth, and plasma FSH and PRL levels remained low. The efficacy of the short duration infusions did not appear to depend upon the time of day of administration. These findings are in close agreement with those of a previous study which investigated the antigonadal effect of long duration melatonin infusions. The present results demonstrate that melatonin administration can mimic the progonadal effects of the pineal in this species and add further support to the hypothesis that the pineal influences the reproductive system through changes in the duration of daily melatonin production.

Circadian organization of locomotor activity in the Turkish hamster (Mesocricetus brandti)

The circadian organization of locomotor activity was examined in Turkish hamsters while exposed to a light-dark (LD) cycle, constant illumination (LL), and following blinding and gonadectomy. Under LD 16:8 the activity rhythm of all hamsters became well entrained with activity beginning approximately 30 min after dark onset. In contrast, when activity rhythms free-ran as the result of exposure to LL or blinding, a variety of spontaneous perturbations in the period and/or phase of the activity rhythm were observed.

Pineal is required for testicular maintenance in the turkish hamster (mesocricetus brandti)

The effect of pinealectomy on reproductive function was examined in the Turkish hamster, Mesocricetus brandti. Pinealectomy resulted in testicular regression in this species. This result was unexpected since pinealectomy prevents short day-induced regression of the gonads in the closely related Syrian hamster, Mesocricetus auratus. Decentralization of the superior cervical ganglia and exposure to continuous illumination also caused testicular regression in the Turkish hamster. These manipulations are believed to block pineal melatonin synthesis. In each case (i.e. pinealectomy, decentralization of the superior cervical ganglia, exposure to continuous illumination), the testes regressed after approximately 3--9 weeks and underwent recrudescence after approximately 16--28 weeks. This cycle of testicular regression and recrudescence was similar to that observed in Turkish hamsters exposed to a short day photoperiod. In further experiments, the effects of exogenous melatonin were studied in Turkish and Syrian hamsters. The results of these studies suggest that, in Turkish hamsters, pineal melatonin may be involved in both the maintenance of testis function during exposure to a long day photoperiod and also in the suppression of reproductive function in short days. This is in contrast to the Syrian hamster, in which melatonin appears to be important only for inhibition of gonadal function in short days.

Modulation of gonadal activity by timed injections of melatonin in pinealectomized or intact ferrets kept under two photoperiods

These experiments investigated the way that the effects of melatonin on gonadal activity of ferrets depended upon either reproductive status or environmental lighting conditions. Melatonin (1 mg/day) injected once daily 8 h into the photoperiod prevented the retiming of oestrus by long photoperiods; oestrus occurred in animals treated in this way at the same time as in controls kept under short non-stimulatory photoperiods of 8 h light: 16 h darkness (8L : 16D). This suggests that the 'intrinsic' timing mechanism was not altered by melatonin. Melatonin injected daily into oestrous ferrets terminated oestrus prematurely when the injection was given either 8 or 14 h after the onset of the photoperiod in animals kept under either long (14L : 10D) or short (8L : 16D) photoperiods, though injections given 14 h after onset were more potent in long (but not short) light periods. Melatonin was equally effective in driving pinealectomized ferrets out of oestrus as it was in intact animals.

Melatonin could also induce as well as terminate oestrus in ferrets, but only if injections were discontinued. Thus, shifting the time of two daily injections from 8 and 11 h after 'lights on' to 14 and 17 h was ineffective, but withdrawal of melatonin from anoestrous ferrets (pinealectomized or intact) reliably induced oestrus 4–6 weeks later, irrespective of the lighting conditions. Withdrawal of oil injections had no effect.

These experiments suggest that melatonin acts on the neural mechanisms resetting the timing of oestrus, rather than by a direct 'anti-gonadotrophic' effect. Furthermore, the effect of changes in duration of photoperiod could not be replicated by simply changing the time of melatonin injections to correspond with the presumed night-time surge of endogenous melatonin. Some of the effects of melatonin on retiming oestrus can only be expressed in the absence of melatonin itself.

Studies of pineal and hypothalamic 5-HT in the ferret

Using a highly sensitive and specific radioenzymatic assay for serotonin (5-HT) in conjunction with a simple reliable technique for removal of small areas of hypothalamus, 5-HT levels have been determined at three time points in several areas of the anterior hypothalamus and the pineal of ovariectomized ferrets housed in long or short day photoperiod. The rhythm seen in all areas of anterior hypothalamus and the pineal was similar in both photoperiods. The data conflict with a previous report from this laboratory; possible reasons for this discrepancy are discussed. These findings do not support the hypothesis that a differential daily hypothalamic 5-HT rhythm is a key component in the neuroendocrine control of seasonal breeding in the ferret.

The moon illusion: a test of the vestibular hypothesis under monocular viewing conditions

The results of earlier monocular experiments on the moon illusion have been either negative or confounded. To test the role of vestibular function, 24 subjects made forced-choice distance comparisons between stimuli mounted in translucent tubes. The stimulus tube for standard distance could be positioned in three viewing angles (45 degrees up, horizontal, and 45 degrees down). A comparison tube adjustable for distance was mounted horizontally. There was a greater perception of depth in the downward looking condition. The relatively weak effects are discussed in terms of a two-hypothesis explanation of the real-life moon illusion and the poor cues for depth perception in monocular viewing.