Predicting global atmospheric ice nuclei distributions and their impacts on climate.

Knowledge of cloud and precipitation formation processes remains incomplete, yet global precipitation is predominantly produced by clouds containing the ice phase. Ice first forms in clouds warmer than -36 degrees C on particles termed ice nuclei. We combine observations from field studies over a 14-year period, from a variety of locations around the globe, to show that the concentrations of ice nuclei active in mixed-phase cloud conditions can be related to temperature and the number concentrations of particles larger than 0.5 microm in diameter. This new relationship reduces unexplained variability in ice nuclei concentrations at a given temperature from approximately 10(3) to less than a factor of 10, with the remaining variability apparently due to variations in aerosol chemical composition or other factors. When implemented in a global climate model, the new parameterization strongly alters cloud liquid and ice water distributions compared to the simple, temperature-only parameterizations currently widely used. The revised treatment indicates a global net cloud radiative forcing increase of approximately 1 W m(-2) for each order of magnitude increase in ice nuclei concentrations, demonstrating the strong sensitivity of climate simulations to assumptions regarding the initiation of cloud glaciation.

Evolutionary transitions among dioecy, androdioecy and hermaphroditism in limnadiid clam shrimp (Branchiopoda: Spinicaudata).

Examinations of breeding system transitions have primarily concentrated on the transition from hermaphroditism to dioecy, likely because of the preponderance of this transition within flowering plants. Fewer studies have considered the reverse transition: dioecy to hermaphroditism. A fruitful approach to studying this latter transition can be sought by studying clades in which transitions between dioecy and hermaphroditism have occurred multiple times. Freshwater crustaceans in the family Limnadiidae comprise dioecious, hermaphroditic and androdioecious (males + hermaphrodites) species, and thus this family represents an excellent model system for the assessment of the evolutionary transitions between these related breeding systems. Herein we report a phylogenetic assessment of breeding system transitions within the family using a total evidence comparative approach. We find that dioecy is the ancestral breeding system for the Limnadiidae and that a minimum of two independent transitions from dioecy to hermaphroditism occurred within this family, leading to (1) a Holarctic, all-hermaphrodite species, Limnadia lenticularis and (2) mixtures of hermaphrodites and males in the genus Eulimnadia. Both hermaphroditic derivatives are essentially females with only a small amount of energy allocated to male function. Within Eulimnadia, we find several all-hermaphrodite populations/species that have been independently derived at least twice from androdioecious progenitors within this genus. We discuss two adaptive (based on the notion of 'reproductive assurance') and one nonadaptive explanations for the derivation of all-hermaphroditism from androdioecy. We propose that L. lenticularis likely represents an all-hermaphrodite species that was derived from an androdioecious ancestor, much like the all-hermaphrodite populations derived from androdioecy currently observed within the Eulimnadia. Finally, we note that the proposed hypotheses for the dioecy to hermaphroditism transition are unable to explain the derivation of a fully functional, outcrossing hermaphroditic species from a dioecious progenitor.

A study of the innervation of the taenia coli.

An electrophysiological and anatomical study of the guinea pig taenia coli is reported. Changing the membrane potential of single cells cannot modulate the rate of firing action potentials but does reveal electrical coupling between the cells during propagation. The amplitude of the junction potentials which occur during transmission from inhibitory nerves is unaffected in many cells during alteration of the membrane potential, indicating electrical coupling during transmission. The taenia coli is shown to consist of smooth muscle bundles which anastomose. There are tight junctions between the cells in the bundles, and these probably provide the pathway for the electrical coupling. The smooth muscle cells towards the serosal surface of the taenia coli are shown electrophysiologically to have an extensive intramural inhibitory innervation, but a sparse sympathetic inhibitory and cholinergic excitatory innervation. These results are in accordance with the distribution of these nerves as determined histochemically. As single axons are only rarely observed in the taenia coli, it is suggested that the only muscle cells which undergo permeability changes during transmission are those adjacent to varicosities in the nerve bundles. The remaining muscle cells then undergo potential changes during transmission because of electrical coupling through the tight junctions.

To what extent have functional studies of ischaemia in animals been useful in the assessment of potential neuroprotective agents?

A general consensus is being reached on the use of a combination of mortality and functional end-points in clinical trials of neuroprotective agents. However, to date, few preclinical studies have examined the effects of putative neuroprotective agents on functional outcome after ischaemia. The data described in this review show the importance of combining both histopathological and neurobehavioural studies when evaluating the neuroprotective efficacy of anti-ischaemic agents in animal models of cerebral ischaemia. Here, Jackie Hunter, Ken Mackay and Derek Rogers argue that measures of functional improvement in models of ischaemia should be incorporated to characterize further the neuroprotection afforded by a compound that could aid the selection of doses and end-point measures in early clinical trials.

Gonadotropin release from pituitary cultures following activation of endogenous ion channels.

In primary rat pituitary cell cultures, activation of Na+ channels resulted in Na+ and Ca2+ dependent gonadotropin release. This occurred with the same efficacy and over the same time course as that stimulated by gonadotropin releasing hormone (GnRH). In contrast, GnRH required extracellular Ca2+, but not Na+ for its action. These results indicate that the gonadotrope has ion channels which resemble those found in neural tissues.

Inhibition of gonadotropin-releasing hormone-stimulated luteinizing hormone release by pimozide: evidence for a site of action after calcium mobilization.

In the present work, we show that pimozide is a noncompetitive antagonist of gonadotropin-releasing hormone (GnRH)-stimulated LH release from pituitary cell cultures. For several other neurotropic agents, the concentration needed to inhibit 50% of LH release in response to GnRH correlates well with the ability to inhibit enzyme activation by calmodulin in vitro. Pimozide does not alter the affinity or amount of releasing hormone binding by the GnRH receptor. The additional observation that pimozide inhibits Ca2+ ionophore (A23187 and ionomycin)-stimulated LH release suggests that the locus of pimozide action is after Ca2+ mobilization. Pimozide is known to bind and inactivate the Ca2+-calmodulin complex, and as Ca2+ is a second messenger for GnRH, it is possible that calmodulin is the target of pimozide in this system.

Potency enhancement of a GnRH agonist: GnRH-receptor microaggregation stimulates gonadotropin release.

Binding of gonadotropin releasing hormone (GnRH, pyro-Glu1-His2-Trp3-Ser4-Tyr5-Gly6-Leu7-Arg8-Pro9-Gly-NH210) to its plasma membrane receptor is the first step leading to pituitary luteinizing hormone (LH) release. In the present study, we have prepared the ethylene glycol bis(succinimidyl succinate) (EGS) dimer of a GnRH agonist, D-Lys6-GnRH; that is, (D-Lys6-GnRH)-EGS-(D-Lys6-GnRH). The bridge length of the EGS is about 15A. This dimer stimulates LH release from pituitary cultures with full efficacy but slightly less potency than D-Lys6-GnRH indicating that the dimerization merely restricts the action of each molecule of D-Lys6-GnRH with respect to the other. When a concentration of the dimer, which alone is too low to evoke substantial LH release, is incubated with pituitary cell cultures in the presence of antibody (AB) against D-Lys6-GnRH, considerable potency enhancement occurs. LH release in response to the AB-dimer conjugate requires extracellular Ca2+ and is blocked by Pimozide. The monovalent form (i.e. reduced pepsin fragment) of AB is ineffective in stimulating release. The addition of antibody to the dimer appears to confer the ability to cross-link receptors and indicates that receptor microaggregation as such is sufficient to activate the effector system in these cells and evoke release.

Structure-function relationship of calcium ion channel antagonists at the pituitary gonadotrope.

We have compared the potencies of chemically heterogeneous classes of Ca2+ ion channel inhibitors as antagonists of GnRH-stimulated LH release from the rat pituitary. Verapamil and its more potent derivative methoxyverapamil (D600) are effective inhibitors. The 1,4-dihydropyridines, however, had no antagonistic efficacy, and diltiazem had slight inhibitory action, but only when preincubated with cells before GnRH addition. The observation that the potency series of antagonists was identical (verapanoids greater than diltiazem greater than 1,4-dihydropyridines) whether GnRH or veratridine was used to stimulate the release mechanism is consistent with the premise that the same Ca2+ channel is regulated by the receptor and by agents that evoke gonadotropin release by cell depolarization. This potency series is virtually opposite that observed for muscle tissue. Accordingly, these data suggest that the receptor-regulated Ca2+ ion channel of the pituitary gonadotrope is distinct from that described in muscle.

Activation of luteinizing hormone release from pituitary cells by polycations.

In the present work we examined the effect of cationic polymers on the pituitary gonadotrope. Such polymers are widely used to anchor gonadotropes and other cell types to culture dishes and other substrata to which they are not normally adherent. Homopolymers of Lys (eight size classes from 4,000-700,000 daltons) stimulate Ca+2-dependent LH release from pituitary cell cultures. In contrast, release does not occur in response to the epsilon-CBZ or succinyl derivatives (which have no internal charge) or in response to polymers of L-Glu, D-Glu, or Gly. The observation that polymers of D-Lys, L-Lys, and L-Arg all stimulate LH release with similar efficacy and potency indicates that simple charge interactions, rather than interaction with specific polymer-binding sites, are the cause of LH release. Since monomeric Lys neither stimulates LH release nor competitively inhibits release in response to Lys polymers, it appears that multiple charge coordination by Lys polymers is responsible for activation of the release mechanism. Putrescine, spermine, and spermidine (which have more closely spaced charges) do not stimulate LH release, suggesting that a certain minimal distance of charge separation must occur to obtain efficacy. The reduced potency of heteropolymers of Lys (spaced with Ala or Tyr) suggests that a maximal effective distance also exists. Consecutive and concomitant incubation studies indicate that LH released in response to poly-L-Lys or GnRH comes from the same pool as that released by GnRH. The time courses of release are similar for the two compounds.

Qualitative change in gonadotropin during normal aging in the male rat.

In the present work we have compared a pituitary LH extract and circulating LH from adult male rats (5 months old) with those from rats 10, 13, or 24 months old. The pituitary and circulating forms of LH prepared from old animals had a higher apparent molecular weight, judged by gel filtration, than LH preparations from younger animals. This difference may be due to increased sialic acid content of the larger form, since simultaneous neuraminidase treatment of this gonadotropin preparation and our internal reference standard ([125I]LH prepared from a normal adult rat) abolished the apparent size difference. In addition, the larger form prepared from old rats was cleared more slowly from the circulation of immature females than the form prepared from young rats. The apparent increase in sialation during normal aging could be mimicked in young animals which were castrated. Injections of testosterone propionate reversed the effect in both castrates and old animals. The data suggest that the diminished levels of metabolically active testosterone or other steroid metabolites in old male rats may result in qualitative alterations in the stored and released forms of LH.

Endocrine status versus chronologic age as predictors of altered luteinizing hormone secretion in the "aging" rat.

LH release in response to GnRH injected at 1400 h was measured in young (3-4 months), middle-aged (10-11 months), and old (19-20 months) female rats. Data were compared when animals were grouped by chronological age or according to their vaginal smear pattern 3-4 weeks before treatment, i.e. regular 4-day cycles, constant vaginal cornification (CVC), or persistently leukocytic smears (PL). Compared to young, regularly cycling females (injected on vaginal estrus or diestrus II), the amount of LH released by all age groups with CVC or PL smears was significantly diminished. However, regardless of age, the amount of LH released by CVC females was similar for each dose of GnRH. Similarly, there was no difference in the amount of LH released by the young, middle-aged, and old PL females at each dose of GnRH. Finally, the amount of LH released by the CVC females was uniformly higher than the amount of LH released by age-matched PL females. In contrast, comparison of LH release after GnRH injection in young and middle-aged rats with regular 4-day vaginal cycles showed that the middle-aged rats released significantly less LH on proestrus. These data suggest that changes in the ability of the pituitary to release LH in the older noncycling female rat occurs as a consequence of the altered endocrine status in the animal and not as a result of the chronological age per se. Changes in the ability of the pituitary of the middle-aged, regularly cycling female rat to release LH in response to GnRH may contribute to the age-related disruption of regular ovarian cycling.

Practical and theoretical issues in gene-targeting studies and their application to behaviour.

Some of the major practical and theoretical issues that are associated with gene-targeting studies in mice are discussed. The availability of sufficient space to house the extensive breeding colonies associated with studies in gene-manipulated mice is an important logistical consideration that requires consideration at an early stage. A practical example is discussed which illustrates some of these issues. Problems associated with disease control and methods of maintaining the health status of valuable colonies are also outlined. Differences in the behavioural phenotype of inbred mouse strains pose important issues for study design and selection of host mouse lines. The results from studies exploring variations in the behavioural phenotype of six common inbred strains are briefly outlined. The impact of phenotypic variation on behavioural studies is considered and the implications for experimental design are discussed.

Newer laboratory approaches for assessing visual dysfunction.

The crucial point that will be emphasized throughout this report is the potential utility of analyzing visual cortical receptive field (RF) properties of the single-cell level as a sensitive and reliable neurotoxicity screening tool. Numerous studies employing exposure of kittens to altered visual environments during the critical period have demonstrated that particular classes of RFs can be selectively affected while sparing others. There has been a rapid proliferation of new methods used to investigate such effects. An important current trend involves the development of multidisciplinary combinations of approaches. The various maneuvers reviewed here seem adaptable to studying neurotoxic insult of the sensitive properties of cortical visual neurons, particularly in the cat or monkey. Conceivably, a general disruption of cortical RF properties might be expected following toxic exposure since individual RF properties are generally not determined by completely independent mechanisms. In fact, some toxicants might produce a general degradation of RF properties akin to the electrophysiological results reported for long-term dark rearing or binocular deprivation.

5-HT6 receptor antagonists enhance retention of a water maze task in the rat.

RATIONALE: 5-HT(6) receptors are predominantly located in the brain and may be involved in cognitive processes. The aim of this study was to assess the effects of two potent and selective 5-HT(6) receptor antagonists, SB-271046-A and SB-357134-A, on learning and memory in the rat. METHODS: Spatial learning and memory was assessed by testing the effects of SB-271046-A and SB-357134-A on acquisition and retention of a water maze task. RESULTS: In the water maze, administration of SB-271046-A or SB-357134-A (3 or 10 mg/kg) had no effect on learning per se. At 10 mg/kg, however, both compounds produced a significant improvement in retention of a previously learned platform position when tested 7 days after training. By contrast, the acetylcholinesterase inhibitor, Aricept (donepezil, 0.1, 0.3 mg/kg PO) had no effect in this task. CONCLUSIONS: This study demonstrates that systemic administration of SB-271046-A and SB-357134-A produces improvements in retention of a water maze task in the rat. These data indicate that 5-HT(6) receptor antagonism may be involved in cognitive function.

Anxiolytic profile of ropinirole in the rat, mouse and common marmoset.

RATIONALE: Some features of Parkinson's disease are exacerbated by stress and anxiety and it is important to understand the effects of dopamine receptor agonists on measures of anxiety. The aim of this study was to assess the effects of the dopamine D2/D3 receptor agonist ropinirole in models of anxiety and depression in the rat, mouse and marmoset. RESULTS: In the rat elevated plus-maze test, ropinirole (0.01-1 mg/kg, i.p.) produced an inverted-U dose-response curve in the percentage time spent in the open arms. Compared with vehicle, ropinirole (0.1 mg/kg) had a significant anxiolytic-like effect, which was similar to that observed with 1.5 mg/kg diazepam. This effect was found at doses that did not affect motor behaviour or induce stereotypy. In the mouse black and white box test of anxiety, ropinirole (0.1-10 mg/kg, i.p.) increased both the rearing time and number of line crosses in the white section. This effect reached statistical significance for both measures at a dose of 0.1 mg/kg and suggests an anxiolytic-like action of the compound. By contrast, the dopamine agonist bromocriptine (0.1-10 mg/kg, i.p.) did not produce significant changes in these behaviours. In the marmoset human threat test, ropinirole (0.01-10 microg/kg, s.c.) reduced the number of postures at all doses tested and this reached statistical significance at 10 microg/kg. Ropinirole did not compromise the effect of amitriptyline in the Porsolt test of depression and in itself produced antidepressant-like effects. CONCLUSIONS: These data demonstrate that systemic administration of ropinirole produces anxiolytic-like effects in three separate models in the mouse, rat and marmoset. This may predict an action of ropinirole in man that would provide a superior profile of action over other presently available anti-parkinsonian agents.

Factors affecting septal graft amelioration of differential reinforcement of low rates (DRL) and activity deficits after fimbria-fornix lesions.

Wound-derived trophic factors released by the injured brain are thought to reach a peak 1-2 weeks after injury. It has been proposed that such factors can promote the survival, growth and functional capacity of embryonic tissue grafts. To test the generality of this hypothesis, control rats and rats with aspirative fimbria-fornix lesions were compared with 5 groups of rats with lesions and septal grafts implanted either in the same session as the lesion or after delays from 10 days to 9 months. Animals were assessed 3 months post-transplantation on an operant differential reinforcement of low rates (DRL) task and on a test of spontaneous locomotor activity. Lesions produced impairments on all measures of DRL performance. Two graft groups showed amelioration of the DRL deficits, one graft group was unchanged, and the deficits were exacerbated in two others. There was no clear relationship between lesion-graft interval and recovery. An inverse relationship was seen, however, between recovery and the developmental age of the donor tissue. In contrast, significant recovery from lesion-induced hyperactivity was observed in the two graft groups with tissue derived from the oldest embryos. There were no clear relationships between recovery on either test, lesion-graft interval, and AChE-positive reinnervation of the host brain. The results provide further evidence that septal grafts can reverse behavioural deficits induced by fimbria-fornix lesions under some conditions, but suggest that the timing of graft surgery may not be as important a factor as donor age in this model system.

Neonatal dopamine-rich grafts and 6-OHDA lesions independently provide partial protection from the adult nigrostriatal lesion syndrome.

Previous studies have shown that neonatally dopamine-depleted rats are subsensitive to dopamine antagonists and do not respond to homeostatic imbalances as adults. This suggests that these animals maintain themselves independent of the dopamine system. If this is so, they should be insensitive to treatment with adult 6-hydroxydopamine (6-OHDA) lesions. Other experiments have shown that dopamine-rich grafts in the neonatal brain will provide some protection from the severe ingestive deficits induced by bilateral 6-OHDA lesions in adulthood. Three groups of animals received either nigra grafts into the intact neonatal brain, neonatal 6-OHDA lesions, or both neonatal 6-OHDA lesions and nigra grafts. A fourth group served as sham-operated controls. Methylamphetamine and haloperidol challenges showed that the neonatally lesioned animals regulated locomotor activity, eating and drinking independent of the dopamine system. Remarkably, however, 80% of these nevertheless showed the full syndrome of aphagia, adipsia and akinesia in response to adult lesions. The grafts into intact group showed enhanced survival in that 36% of the rats were able to maintain themselves following the adult lesion. The graft into neonatally lesioned rats restored their activational response to pharmacological challenges but did not provide any additional protection from the adult lesion. This suggests that different mechanisms underlie the protection against adult nigrostriatal lesions provided by neonatal grafts and neonatal lesions.

Photothrombotic lesions of the frontal cortex impair the performance of the delayed non-matching to position task by rats.

The effects of photochemically induced lesions of the frontal cortex on the short-term memory capacity of the rat have been investigated using the delayed non-matching to position task. Pretrained animals received lesions and were tested 4 days after surgery and twice per week for 3 weeks. The lesions produced a profound impairment of performance of this task which was still evident 3 weeks after surgery. Spontaneous locomotor activity was recorded 7 days after surgery and no difference was found between the control and lesion group. These effects indicated a generalized disruption of performance of this task in the absence of motor dysfunction. These results suggest that photothrombotic lesions of the frontal cortex can produce reliable, long-term behavioural deficits.

Use of SHIRPA and discriminant analysis to characterise marked differences in the behavioural phenotype of six inbred mouse strains.

Detailed characterisation of six inbred strains of mice commonly used in transgenic and knockout research was carried out using a battery of behavioural tests (SHIRPA) followed by discriminant analysis of the data. In the primary observation screen, DBA/2 mice were relatively irritable and vocalised during handling. C57BL/6 were hyperactive as measured by transfer arousal, arena activity and touch-escape tests. By contrast, C3H were markedly hypoactive, had significantly enhanced grip strength and were also significantly impaired on the visual placing task. In the elevated plus-maze, BALB/c mice showed the highest level of open arm entries and time spent in the open arms, indicating the lowest level of anxiety. There was a clear dissociation of strains on exploratory activity, as measured in the holeboard test and spontaneous locomotor activity (LMA). DBA/2 mice were hyperactive in LMA but demonstrated relatively low levels of holeboard exploration. None of the six strains learnt the water maze spatial learning task particularly well. C57BL/6 and 129/Sv demonstrated most ability and C3H showed no evidence of having acquired the task. The SHIRPA screening battery and discriminant analysis of the data have enabled us to determine the relevant contribution of a number of behavioural measurements to the marked differences in phenotype of mouse strains. These data confirm the importance of carrying out a comprehensive profile in order to accurately characterise the phenotype of gene-targeted and transgenic mice.

Dopamine-rich grafts ameliorate whole body motor asymmetry and sensory neglect but not independent limb use in rats with 6-hydroxydopamine lesions.

The capacity of dopamine (DA)-rich embryonic grafts to influence performance in a skilled motor task has been assessed. In two separate experiments, unilateral 6-hydroxydopamine lesions of forebrain DA systems induced a neglect of the contralateral limb and an almost total preference for use of the ipsilateral limb when reaching through the bars of a cage for food pellets. If the food paw was restrained, either by a bracelet or by injection of a local anaesthetic, the lesioned rats would continue to make many reaching attempts with the contralateral paw, but on the great majority of these attempts they were unsuccessful in grasping or retrieving food. DA-rich grafts, reinnervating the denervated caudate-putamen, provided no detectable benefit to the lesioned rats, neither in reducing the ipsilateral bias in their side preference, nor in increasing their success when constrained to reaching with the contralateral limb. This failure to benefit from the grafts is not due to the grafts themselves not being viable, since the same rats showed substantial compensation of whole body motor asymmetries in spontaneous and drug-induced rotation, and a reduction of asymmetry in a battery of neurological tests of sensorimotor function. The results are discussed in terms of the degree of anatomical integration of the grafts into the host neural circuitry, and the neural organization necessary for the performance of different classes of behavior.