Recent beak evolution in North American starlings after invasion

European starlings are one of the most abundant and problematic avian invaders in the world. From their native range across Eurasia and North Africa, they have been introduced to every continent except Antarctica. In 160 years, starlings have expanded into different environments throughout the world, making them a powerful model for understanding rapid evolutionary change and adaptive plasticity. Here, we investigate their spatiotemporal morphological variation in North America and the native range. Our dataset includes 1217 specimens; a combination of historical museum skins and modern birds. Beak length in the native range has remained unchanged during the past 206 years, but we find beak length in North American birds is now 8% longer than birds from the native range. We discuss potential drivers of this pattern including dietary adaptation or climatic pressures. Additionally, body size in North American starlings is smaller than those from the native range, which suggests a role for selection or founder effect. Taken together, our results indicate rapid recent evolutionary change in starling morphology coincident with invasion into novel environments.

Concurrent invasions of European starlings in Australia and North America reveal population-specific differentiation in shared genomic regions

A species' success during the invasion of new areas hinges on an interplay between the demographic processes common to invasions and the specific ecological context of the novel environment. Evolutionary genetic studies of invasive species can investigate how genetic bottlenecks and ecological conditions shape genetic variation in invasions, and our study pairs two invasive populations that are hypothesized to be from the same source population to compare how each population evolved during and after introduction. Invasive European starlings (Sturnus vulgaris) established populations in both Australia and North America in the 19th century. Here, we compare whole-genome sequences among native and independently introduced European starling populations to determine how demographic processes interact with rapid evolution to generate similar genetic patterns in these recent and replicated invasions. Demographic models indicate that both invasive populations experienced genetic bottlenecks as expected based on invasion history, and we find that specific genomic regions have differentiated even on this short evolutionary timescale. Despite genetic bottlenecks, we suggest that genetic drift alone cannot explain differentiation in at least two of these regions. The demographic boom intrinsic to many invasions as well as potential inversions may have led to high population-specific differentiation, although the patterns of genetic variation are also consistent with the hypothesis that this infamous and highly mobile invader adapted to novel selection (e.g., extrinsic factors). We use targeted sampling of replicated invasions to identify and evaluate support for multiple, interacting evolutionary mechanisms that lead to differentiation during the invasion process.

Transcript- and annotation-guided genome assembly of the European starling

The European starling, Sturnus vulgaris, is an ecologically significant, globally invasive avian species that is also suffering from a major decline in its native range. Here, we present the genome assembly and long-read transcriptome of an Australian-sourced European starling (S. vulgaris vAU), and a second, North American, short-read genome assembly (S. vulgaris vNA), as complementary reference genomes for population genetic and evolutionary characterization. S. vulgaris vAU combined 10× genomics linked-reads, low-coverage Nanopore sequencing, and PacBio Iso-Seq full-length transcript scaffolding to generate a 1050 Mb assembly on 6222 scaffolds (7.6 Mb scaffold N50, 94.6% busco completeness). Further scaffolding against the high-quality zebra finch (Taeniopygia guttata) genome assigned 98.6% of the assembly to 32 putative nuclear chromosome scaffolds. Species-specific transcript mapping and gene annotation revealed good gene-level assembly and high functional completeness. Using S. vulgaris vAU, we demonstrate how the multifunctional use of PacBio Iso-Seq transcript data and complementary homology-based annotation of sequential assembly steps (assessed using a new tool, saaga) can be used to assess, inform, and validate assembly workflow decisions. We also highlight some counterintuitive behaviour in traditional busco metrics, and present buscomp, a complementary tool for assembly comparison designed to be robust to differences in assembly size and base-calling quality. This work expands our knowledge of avian genomes and the available toolkit for assessing and improving genome quality. The new genomic resources presented will facilitate further global genomic and transcriptomic analysis on this ecologically important species.

Toxicity of sodium nitrite-based vertebrate pesticides for European starlings (Sturnus vulgaris)

In the 21st century, invasive animals rank second only to habitat destruction as the greatest threat to global biodiversity. Socially-acceptable and cost-effective strategies are needed to reduce the negative economic and environmental impacts of invasive animals. We investigated the potential for sodium nitrite (SN; CAS 7632-00-0) to serve as an avian toxicant for European starlings (Sturnus vulgaris L.). We also assessed the non-target hazard of an experimental formulation of SN that is being developed as a toxicant for invasive wild pigs (Sus scrofa L.). In gavage experiments with European starlings, we identified a lowest observed adverse effect level (LOAEL) for mortality of 2.40% technical SN (w/v; 120 mg SN/kg body mass) and a no observed adverse effect level (NOAEL) for mortality of 1.30% technical SN (65 mg/kg). The exposure of ten starlings to the experimental formulation of SN (10% SN pig toxicant) resulted in one starling mortality during four days of exposure to the toxic bait. Sodium nitrite toxicity presented a moderate hazard to European starlings; thus, the future development of SN as an avian toxicant is dependent upon its cost-effectiveness. We discuss the management of toxic effects and non-target hazards of SN for wild birds, including best practices for toxic baiting of vertebrate pests and management of invasive wild pigs.

Inefficiency of anthraquinone-based avian repellents when applied to sunflower: the importance of crop vegetative and floral characteristics in field applications

BACKGROUND

Blackbirds (Icteridae) cause significant damage to sunflower (Helianthus annuus L.) prompting the need for effective management tools. Anthraquinone-based repellents can reduce feeding by > 80% in laboratory settings, but require birds to learn the negative association through repellent ingestion. We evaluated an anthraquinone-based repellent applied directly to mature sunflower plants for its ability to reduce bird damage. We used captive male red-winged blackbirds (Agelaius phoeniceus) to evaluate efficacy of two anthraquinone-based formulations in varying concentrations and applied in a manner attainable by sunflower producers. We also assessed field application methods for repellent coverage and anthraquinone residues when using ground-rigs equipped with drop-nozzles situated below the crop canopy.

RESULTS

The repellents failed to reduce feeding and birds did not exhibit a preference between untreated and treated sunflowers at concentrations 2.7× the suggested application rate (i.e. 9.35 L ha^-1 of repellent). In the absence of disk flowers, which obstruct repellent from reaching the achenes, the repellents failed to reduce consumption. Anthraquinone concentrations in field applications were considerably less than those in the laboratory experiments and did not reduce bird damage.

CONCLUSION

Efficacy is difficult to achieve in the field due to application issues where growth patterns and floral components of sunflower limit residues on achenes, thus contact with foraging birds. Although field residues could be improved by increasing anthraquinone concentrations in tank mixtures and decreasing droplet size, repellents optimized for loose achenes are inefficient in reducing avian consumption of sunflower when applied to intact plants in a manner representative of commercial agriculture. © 2020 Society of Chemical Industry.

Environmental correlates of genetic variation in the invasive European starling in North America

Populations of invasive species that colonize and spread in novel environments may differentiate both through demographic processes and local selection. European starlings (Sturnus vulgaris) were introduced to New York in 1890 and subsequently spread throughout North America, becoming one of the most widespread and numerous bird species on the continent. Genome-wide comparisons across starling individuals and populations can identify demographic and/or selective factors that facilitated this rapid and successful expansion. We investigated patterns of genomic diversity and differentiation using reduced-representation genome sequencing of 17 winter-season sampling sites. Consistent with this species' high dispersal rate and rapid expansion history, we found low geographical differentiation and few F_ST outliers even at a continental scale. Despite starting from a founding population of ~180 individuals, North American starlings show only a moderate genetic bottleneck, and models suggest a dramatic increase in effective population size since introduction. In genotype-environment associations we found that ~200 single-nucleotide polymorphisms are correlated with temperature and/or precipitation against a background of negligible genome- and range-wide divergence. Given this evidence, we suggest that local adaptation in North American starlings may have evolved rapidly even in this wide-ranging and evolutionarily young system. This survey of genomic signatures of expansion in North American starlings is the most comprehensive to date and complements ongoing studies of world-wide local adaptation in these highly dispersive and invasive birds.

Multi-isotopic (δ2H, δ13C, δ15N) tracing of molt origin for European starlings associated with U.S. dairies and feedlots

Introduced bird species can become invasive in agroecosystems and their management is inhibited if their origin and movements are not well understood. Stable isotope measurements of feathers can be used to infer molt origins and interstate movements in North America. We analyzed stable-hydrogen (δ2H), carbon (δ13C) and nitrogen (δ 15N) isotope ratios in feathers to better understand the molt origin of European starlings (Sturnus vulgaris) collected at dairies and feedlots throughout the United States. Primary feathers were used from 596 adult and 90 juvenile starlings collected during winter at dairies and feedlots that experience starling damages in Arizona, California, Colorado, Idaho, Illinois, Iowa, Kansas, Minnesota, Missouri, Nebraska, Nevada, New Hampshire, New Mexico, New York, North Carolina, Oregon, Texas, Vermont, Washington and Wisconsin. The best-fit model indicated that the combination of feather δ2H, δ13C and δ15N values best predicted the state where samples were collected and thus supported use of this approach for tracing molt origins in European starlings. Interestingly, molt origins of starlings collected at dairies and feedlots generally west of -90° longitude (i.e. 11 of 15 states west of the Mississippi River, including Wisconsin) were assigned to the collection state and/or the state adjacent to the collection state. In contrast, molt origins of starlings collected generally east of -90° longitude (four of five eastern states) were not assigned to the collection state and/or the state adjacent to the collection state. Among all starlings (N = 686), 23% were assigned to the collection state and 19% were assigned to the state adjacent to the collection state. Among all males (N = 489) and all females (N = 197), 23% and 26% were assigned to the collection state and 19% and 13% were assigned to the state adjacent to the collection state, respectively. We observed a greater proportion (88%) of juvenile starlings assigned to states other than their collection state (i.e. potentially a result of natal dispersal) than that proportion (76%) in adult starlings. This study included an unprecedented sample of feather isotopes from European starlings throughout the United States. As a novel contribution to the ecology and management of invasive and migratory passerines, we demonstrate how such feather isoscapes can be used to predict molt origin and, potentially, interstate movements of European starlings for subsequent ecological and management investigations.

Nutritional depletion of total mixed rations by European starlings: Projected effects on dairy cow performance and potential intervention strategies to mitigate damage

European starlings are an invasive bird species in North America that are known to cause damage to commercial dairies through the consumption of total mixed rations (TMR) destined for dairy cows. We hypothesized that large foraging flocks of starlings alter the physical composition of TMR, and that this change may be significant enough to affect milk production. To better determine if production losses could potentially occur in commercial dairies as a consequence of feed consumption by foraging flocks of starlings, we conducted controlled feeding experiments using a TMR sourced from a commercial dairy that is chronically plagued with seasonal starling damage. European starlings selected the high-energy fraction of the TMR and reduced starch and crude fat availability. Using the dairy National Research Council production model equations, the nutritional changes measured in the controlled feeding experiments could potentially reduce the productivity of dairies. Model output suggests that for Holsteins producing 32 kg of milk/d, total required net energy intake (NE_I) was 31.5 Mcal/d. Within the reference TMR, NE_I supplied was 29.3 Mcal/d, whereas within the starling-consumed TMR NE_I supplied was 27.7 Mcal/d. Following our nutrition experiments, we assessed the efficacy of pelleted feed as a deterrent strategy for bird damage management in commercial dairies. Six different pelleted feed treatments of differing diameter were offered to starlings. All pellets of 0.95 cm diameter or larger inhibited starling consumption by ≥79%.

Multi-Isotopic (δ2H, δ13C, δ15N) Tracing of Molt Origin for Red-Winged Blackbirds Associated with Agro-Ecosystems

We analyzed stable-hydrogen (δ2H), carbon (δ13C) and nitrogen (δ 15N) isotope ratios in feathers to better understand the molt origin and food habits of Red-winged Blackbirds (Agelaius phoeniceus) near sunflower production in the Upper Midwest and rice production in the Mid-South of the United States. Outer primary feathers were used from 661 after-second-year (ASY) male blackbirds collected in Minnesota, Montana, North Dakota and South Dakota (spring collection), and Arkansas, Louisiana, Mississippi, Missouri and Texas (winter collection). The best-fit model indicated that the combination of feather δ2H, δ13C and δ15N best predicted the state of sample collections and thus supported the use of this approach for tracing molt origins in Red-winged Blackbirds. When considering only birds collected in spring, 56% of birds were classified to their collection state on the basis of δ2H and δ13C alone. We then developed feather isoscapes for δ13C based upon these data and for δ2H based upon continental patterns of δ2H in precipitation. We used 81 birds collected at the ten independent sites for model validation. The spatially-explicit assignment of these 81 birds to the δ2H isoscape resulted in relatively high rates (~77%) of accurate assignment to collection states. We also modeled the spatial extent of C3 (e.g. rice, sunflower) and C4 (corn, millet, sorghum) agricultural crops grown throughout the Upper Midwest and Mid-South United States to predict the relative use of C3- versus C4-based foodwebs among sampled blackbirds. Estimates of C3 inputs to diet ranged from 50% in Arkansas to 27% in Minnesota. As a novel contribution to blackbird conservation and management, we demonstrate how such feather isoscapes can be used to predict the molt origin and interstate movements of migratory blackbirds for subsequent investigations of breeding biology (e.g. sex-specific philopatry), agricultural depredation, feeding ecology, physiology of migration and sensitivity to environmental change.

Review of anthraquinone applications for pest management and agricultural crop protection

We have reviewed published anthraquinone applications for international pest management and agricultural crop protection from 1943 to 2016. Anthraquinone (AQ) is commonly found in dyes, pigments and many plants and organisms. Avian repellent research with AQ began in the 1940s. In the context of pest management, AQ is currently used as a chemical repellent, perch deterrent, insecticide and feeding deterrent in many wild birds, and in some mammals, insects and fishes. Criteria for evaluation of effective chemical repellents include efficacy, potential for wildlife hazards, phytotoxicity and environmental persistence. As a biopesticide, AQ often meets these criteria of efficacy for the non-lethal management of agricultural depredation caused by wildlife. We summarize published applications of AQ for the protection of newly planted and maturing crops from pest birds. Conventional applications of AQ-based repellents include preplant seed treatments [e.g. corn (Zea mays L.), rice (Oryza sativa L.), sunflower (Helianthus annuus L.), wheat (Triticum spp.), millet (Panicum spp.), sorghum (Sorghum bicolor L.), pelletized feed and forest tree species] and foliar applications for rice, sunflower, lettuce (Lactuca sativa L.), turf, sugar beets (Beta vulgaris L.), soybean (Glycine max L.), sweet corn and nursery, fruit and nut crops. In addition to agricultural repellent applications, AQ has also been used to treat toxicants for the protection of non-target birds. Few studies have demonstrated AQ repellency in mammals, including wild boar (Sus scrofa, L.), thirteen-lined ground squirrels (Ictidomys tridecemlineatus, Mitchill), black-tailed prairie dogs (Cyomys ludovicainus, Ord.), common voles (Microtus arvalis, Pallas), house mice (Mus musculus, L.), Tristram's jirds (Meriones tristrami, Thomas) and black rats (Rattus rattus L.). Natural sources of AQ and its derivatives have also been identified as insecticides and insect repellents. As a natural or synthetic biopesticide, AQ is a promising candidate for many contexts of non-lethal and insecticidal pest management. Published 2016. This article is a U.S. Government work and is in the public domain in the USA.

Functional significance of ultraviolet feeding cues in wild turkeys

Most birds are able to sense ultraviolet (UV) visual signals. Ultraviolet wavelengths are used for plumage signaling and sexual selection among birds. The aim of our study was to determine if UV cues are also used for the process of food selection in wild turkeys (Meleagris gallopavo). We used avoidance conditioning to test the hypothesis that UV feeding cues can be used functionally for foraging behavior in wild turkeys. Female turkeys exhibited no avoidance of untreated food and 75–98% avoidance of food treated with an UV-absorbent, postingestive repellent (0.5–4% anthraquinone; wt./wt.) during repellent exposure. Male turkeys exhibited 78–99% avoidance of food treated with 0.5–4% anthraquinone. Female and male turkeys that consumed more than 200 mg and 100 mg of anthraquinone, respectively, subsequently avoided food treated only with an UV-absorbent cue. In contrast, unconditioned females consumed 58% more food treated with the UV-absorbent cue than untreated food. Thus, wild turkeys do not prefer foods associated with UV wavelengths regardless of feeding experience. We also observed 1) a weak negative correlation between body condition and intestinal parasite infection and 2) moderate, positive correlations between consumption of food treated with the conditioned UV cue and intestinal parasite infection among male turkeys. The UV feeding cue was used to maintain food avoidance during the four days subsequent to postingestive conditioning. Moreover, the consequences of consuming food treated with the postingestive, UV-absorbent repellent were necessary for conditioned avoidance of the UV-absorbent cue. These findings suggest functional significance of UV feeding cues for avian foraging behavior, the implications of which will enable subsequent investigations regarding the sensory physiology and behavioral ecology of wild birds.

The role of a generalized ultraviolet cue for blackbird food selection

Birds utilize ultraviolet (UV) wavelengths for plumage signaling and sexual selection. Ultraviolet cues may also be used for the process of avian food selection. The aim of our study was to investigate whether a UV cue and a postingestive repellent can be used to condition food avoidance in red-winged blackbirds (Agelaius phoeniceus). We found that birds conditioned with an UV-absorbent, postingestive repellent subsequently avoided UV-absorbent food. Thus, the UV-absorbent cue (coupled with 0-20% of the conditioned repellent concentration) was used to maintain avoidance for up to 18 days post-conditioning. Similarly, birds conditioned with the UV-absorbent, postingestive repellent subsequently avoided UV-reflective food. Thus, conditioned avoidance of an UV-absorbent cue can be generalized to an unconditioned, UV-reflective cue for nutrient selection and toxin avoidance. These findings support the hypothesized function of UV vision for avian food selection, the implications of which remain to be explored for the sensory and behavioral ecology within agronomic and natural environments.

Dispersal of viable row-crop seeds of commercial agriculture by farmland birds: implication for genetically modified crops

To address some concerns about the expansion of genetically engineered pharmaceutical and industrial crops to outdoor plantings and potential impacts on the human food supply, we determined whether commercial agriculture seeds of maize or corn Zea mays L., barley Hordeum vulgare L., safflower Carthamus tinctorius L. and rice Oryza sativa L. are digested or pass viably through the digestive tract, or are transported externally, by captive mallard ducks Anas platyrhynchos L., ring-necked pheasants Phasianus colchicus L., red-winged blackbirds Agelaius phoeniceus (L.) and rock pigeons Columba livia Gmelin (with the exception of whole maize seeds which were too large to feed to the blackbirds). These crop seeds, whether free-fed or force-fed, did not pass through the digestive tract of these bird species. The birds nonetheless did retain viable seeds in the esophagus/crop and gizzard for several hours. For example, after foraging for 6 h, mallards had retained an average of 228 +/- 112 barley seeds and pheasants 192 +/- 78 in the esophagus/crop, and their germination rates were 93 and 50%, respectively. Birds externally transported seeds away from the feeding location, but in only four instances were seeds found attached to their muddy feet or legs and in no case to feathers. Risk of such crop seeds germinating, establishing and reproducing off site after transport by a bird (externally or internally) or movement of a carcass by a predator, will depend greatly on the crop and bird species, location, environmental conditions (including soil characteristics), timing, and seed condition.

Food color, flavor, and conditioned avoidance among red-winged blackbirds

The relationship between food flavors and postingestive feedback enables mammalian herbivores to procure nutrients and avoid toxins within ever-changing environments. We conducted four experiments with red-winged blackbirds (Agelaius phoeniceus) in captivity to determine the relative roles of color and flavor cues paired with negative postingestive feedback. We first conducted baseline tests to assess preferences for colors and flavors. All blackbirds preferred red- to blue-colored food, and they preferred umami- (l-alanine) flavored to bitter/astringent food (tannic acid). We observed no difference in consumption of salty (NaCl) vs sour (citric acid) foods during baseline tests (i.e., neutral flavors). We then conditioned experimentally naïve blackbirds with intraperitoneal injections of lithium chloride (LiCl) to avoid food treated with red and l-alanine, or red and NaCl (n=30 birds per conditioning group). Subsequent to conditioning with LiCl, three test groups were established from each conditioned group to evaluate color and flavor preferences, and preferences for novel color-flavor pairings (e.g., red/tannic acid vs blue/l-alanine). Blackbirds avoided red and salty food throughout the 4-day test. Avoidance conditioned with LiCl extinguished for preferred flavors, but not for colors, of food. Conditioning affected indifference for the otherwise preferred flavor and avoidance for the otherwise neutral flavor. Relative to the neutral-flavor conditioning group, the group conditioned with a preferred flavor exhibited stronger conditioned avoidance of colored food. Unlike conditioned flavor avoidance, birds were conditioned to avoid red food only when blue food was made familiar prior to conditioning. Collectively, these results illustrate that blackbirds used affective processes (flavor-feedback relationships) to shift preference for both novel and familiar flavors, and cognitive associations (colors) to avoid food, subsequent to toxin exposure. We discuss the opportunities afforded by affective and cognitive processing for reducing agricultural damage caused by blackbirds.

Self-organization of foraging behaviour: From simplicity to complexity without goals

A herbivore faces challenges while foraging—ongoing changes in its physiological condition along with variation in the nutrient and toxin concentrations of foods, spatially and temporally—that make selecting a nutritious diet a vital affair. Foraging behaviours arise from simple rules that operate across levels of resolution from cells and organs to individuals and their interactions with social and physical environments. At all these levels, behaviour is a function of its consequences: a behaviour operating on the environment to induce changes is itself changed by those events. Thus, behaviour emerges from its own functioning—behaviour self-organizes-not from that of its surroundings. This ostensible autonomy notwith-standing, no self-organizing system (cell, organ, or individual) is independent of its environs because existence consists of an ongoing exchange of energy and matter. According to this view, the notion of cause and effect is replaced with functional relationships between behaviours and environmental consequences. Changes in physical environments alter the distribution, abundance, nutritional, and toxicological characteristics of plants, which affect food preference. Social interactions early in life influence behaviour in various ways: animals prefer familiar foods and environments, and they prefer to be with companions. Animals in unfamiliar environments often walk farther, ingest less food, and suffer more from malnutrition and toxicity than animals in familiar environments. An individual's food preferences—and its ability to discriminate familiar from novel foods—arise from the functional integration of sensory (smell, taste, texture) and postingestive (effects of nutrients and toxins on chemo-, osmo-, and mechano-receptors) effects. The ability to discriminate among foods is critical for survival: all problems with poisonous plants are due to an inability to discriminate or a lack of alternatives. Animals eat a variety of foods as a result of nearing or exceeding tolerance limits for sensory and postingestive effects unique to each food. After eating any food too frequently or excessively, the likelihood increases that animals will eat alternative foods owing to exceeding sensory-, nutrient-, and toxin-specific tolerance limits. Cyclic patterns of intake of a variety of foods reflect seemingly chaotic interactions among flavours, nutrients, and toxins interacting along continua.

Proximal cues of pocket gopher burrow plugging behavior: influence of light, burrow openings, and temperature

Burrow plugging is readily observed among mammals adapted for digging (i.e., fossorial mammals) as they create and maintain their burrows. We investigated the influence of light, burrow openings, and thermal environment as cues of pocket gopher (Thomomys mazama, Thomomys talpoides) behavior. When given free access to light and no light during artificial-burrow preference trials, both Thomomys spp. consistently plugged (i.e., avoided) light treatments. Burrow openings did not notably affect plugging behavior of T. mazama. Gophers (T. talpoides) plugged the artificial burrows within the light and cold (7 degrees C) treatments, but not within the no-light, and 18 or 31 degrees C treatments when light and temperature were varied independently. Whereas the presence of light and low ambient temperatures induce burrow maintenance by pocket gophers, these cues help meliorate adverse conditions within subsurface environs.

Long-term effects of excitatory amino acid antagonists NBQX and MK-801 on the developing brain

Because of the critical role of excitatory amino acids (EAAs) in epileptogenesis and seizure-induced brain damage, EAA antagonists are now being considered as a possible therapy for seizures. However, during development EAAs play a pivotal role in learning, memory, and brain plasticity. To evaluate the long-term effects of a short course of EAA antagonists on the developing brain, a non-NMDA antagonist, NBQX, or a NMDA antagonist, MK-801, were administered over 7 days by osmotic pumps stereotaxically implanted into the lateral ventricles of normal 10 day old rats. Alternatively, 10 and 20 day old rats received a 7 day course of intraperitoneal (i.p.) NBQX. One month later, the NBQX-, MK-801-treated rats, and controls underwent a series of behavioral studies: handling test, open field, and Morris water maze. Flurothyl inhalation was used to test seizure susceptibility in all groups. Although all of the rats treated with NBQX via osmotic pumps has spontaneous seizure, rats surviving infusion of EAAs had no deficits in learning, memory, or behavior and did not differ from controls in seizure susceptibility with flurothyl. In the developing animal, a short-term course of EAA antagonists leads to no long-term adverse effects on behavior or seizure susceptibility.

Effect of kainic acid-induced status epilepticus on inositol-trisphosphate and seizure-induced brain damage in mature and immature animals

We investigated the role of excitatory amino acids in the activation of the phosphoinositide pathway during kainic acid-induced seizures in mature and immature animals. Kainic acid caused more severe seizures in the immature animals, but no hippocampal damage or induction of phosphoinositide hydrolysis. In mature animals, seizures were mild but severe hippocampal damage was seen and was associated with a marked and sustained release of inositol-trisphosphate, suggesting a role of this pathway and intracellular calcium stores in seizure-induced brain damage.

Long-term behavioral deficits following pilocarpine seizures in immature rats

The effect of seizures on subsequent long-term behavior was studied in immature rats. A similar severity of seizures were induced in 20-day old rats (P20) and 45-day old rats (P45) by intraperitoneal injections of pilocarpine at doses of 200 mg/kg and 380 mg/kg, respectively. Immediately after injection of pilocarpine, prolonged seizures with electroencephalographic ictal discharges were observed in both groups of rats. These seizures were followed by seemingly complete neurological recovery. In rats that received pilocarpine at P45 spontaneous recurrent seizures appeared after 4-10 days and persisted until completion of the study at P100. Behavioral tests performed when the rats were fully mature demonstrated that they were more aggressive when handled, more active in open field, and had deficits in learning platform position in the water maze as compared to controls. Furthermore, flurothyl seizure latency was significantly lower in pilocarpine-treated P45 rats than controls. Histology examination showed gross cell loss in the CA3 subfield of the hippocampus in four out of six pilocarpine-treated rats while no cell loss was found in control rats. Rats that received pilocarpine at P20, despite having more severe seizures than the P45 rats, had no histological lesions, did not develop spontaneous recurrent seizures, and had no significant difference in the flurothyl seizure latency test when compared to their controls. While there was no difference between the control and pilocarpine-treated rats in the handling and open field test, P20 rats receiving pilocarpine were slower in learning platform position in the water maze than the controls. Rats receiving pilocarpine at P45 performed significantly more poorly than rats treated at P20 in the water maze. These results suggest that prolonged seizures in immature rats can cause long-term behavioral deficits. However, the severity and nature of these deficits are highly age dependent.