When the polar bear was originally documented, two subspecies were identified: the American polar bear (Ursus maritimus maritimus) by Constantine J. Phipps in 1774, and the Siberian polar bear (Ursus maritimus marinus) by Peter Simon Pallas in 1776. This distinction has since been invalidated. One alleged fossil subspecies has been identified: Ursus maritimus tyrannus, which became extinct during the Pleistocene. U.m. tyrannus was significantly larger than the living subspecies. However, recent reanalysis of the fossil suggests that it was actually a brown bear.
Being both curious animals and scavengers, polar bears investigate and consume garbage where they come into contact with humans. Polar bears may attempt to consume almost anything they can find, including hazardous substances such as styrofoam, plastic, car batteries, ethylene glycol, hydraulic fluid, and motor oil. The dump in Churchill, Manitoba was closed in 2006 to protect bears, and waste is now recycled or transported to Thompson, Manitoba.
Polar bears have long provided important raw materials for Arctic peoples, including the Inuit, Yupik, Chukchi, Nenets, Russian Pomors and others. Hunters commonly used teams of dogs to distract the bear, allowing the hunter to spear the bear or shoot it with arrows at closer range. Almost all parts of captured animals had a use. The fur was used in particular to make trousers and, by the Nenets, to make galoshes-like outer footwear called tobok; the meat is edible, despite some risk of trichinosis; the fat was used in food and as a fuel for lighting homes, alongside seal and whale blubber; sinews were used as thread for sewing clothes; the gallbladder and sometimes heart were dried and powdered for medicinal purposes; the large canine teeth were highly valued as talismans. Only the liver was not used, as its high concentration of vitamin A is poisonous. As a carnivore, which feeds largely upon fish-eating carnivores, the polar bear ingests large amounts of vitamin A that is stored in their livers. The resulting high concentrations cause hypervitaminosis A, Hunters make sure to either toss the liver into the sea or bury it in order to spare their dogs from potential poisoning. Traditional subsistence hunting was on a small enough scale to not significantly affect polar bear populations, mostly because of the sparseness of the human population in polar bear habitat.
Agreements have been made between countries to co-manage their shared polar bear subpopulations. After several years of negotiations, Russia and the United States signed an agreement in October 2000 to jointly set quotas for indigenous subsistence hunting in Alaska and Chukotka. The treaty was ratified in October 2007. In September 2015, the polar bear range states agreed upon a "circumpolar action plan" describing their conservation strategy for polar bears.
Because of the way polar bear hunting quotas are managed in Canada, attempts to discourage sport hunting would actually increase the number of bears killed in the short term. Canada allocates a certain number of permits each year to sport and subsistence hunting, and those that are not used for sport hunting are re-allocated to indigenous subsistence hunting. Whereas northern communities kill all the polar bears they are permitted to take each year, only half of sport hunters with permits actually manage to kill a polar bear. If a sport hunter does not kill a polar bear before his or her permit expires, the permit cannot be transferred to another hunter.
The Soviet Union banned the harvest of polar bears in 1956; however, poaching continued, and is estimated to pose a serious threat to the polar bear population. In recent years, polar bears have approached coastal villages in Chukotka more frequently due to the shrinking of the sea ice, endangering humans and raising concerns that illegal hunting would become even more prevalent. In 2007, the Russian government made subsistence hunting legal for indigenous Chukotkan peoples only, a move supported by Russia's most prominent bear researchers and the World Wide Fund for Nature as a means to curb poaching.
The Marine Mammal Protection Act of 1972 afforded polar bears some protection in the United States. It banned hunting (except by indigenous subsistence hunters), banned importing of polar bear parts (except polar bear pelts taken legally in Canada), and banned the harassment of polar bears. On 15 May 2008, the United States Department of the Interior listed the polar bear as a threatened species under the Endangered Species Act, citing the melting of Arctic sea ice as the primary threat to the polar bear. It banned all importing of polar bear trophies. Importing products made from polar bears had been prohibited from 1972 to 1994 under the Marine Mammal Protection Act, and restricted between 1994 and 2008. Under those restrictions, permits from the United States Fish and Wildlife Service were required to import sport-hunted polar bear trophies taken in hunting expeditions in Canada. The permit process required that the bear be taken from an area with quotas based on sound management principles. Since 1994, hundreds of sport-hunted polar bear trophies have been imported into the U.S. In 2015, the U.S. Fish and Wildlife Service published a draft conservation management plan for polar bears to improve their status under the Endangered Species Act and the Marine Mammal Protection Act.
The International Union for Conservation of Nature, Arctic Climate Impact Assessment, United States Geological Survey and many leading polar bear biologists have expressed grave concerns about the impact of climate change, with some predicting extinction by 2100.
Due to warming air temperatures, ice-floe breakup in western Hudson Bay is currently occurring three weeks earlier than it did 30 years ago, reducing the duration of the polar bear feeding season. The body condition of polar bears has declined during this period; the average weight of lone (and likely pregnant) female polar bears was approximately 290 kg (640 lb) in 1980 and 230 kg (510 lb) in 2004. Between 1987 and 2004, the Western Hudson Bay population declined by 22%, although the population was listed as "stable" as of 2017. As the climate change melts sea ice, the U.S. Geological Survey projects that two-thirds of polar bears will disappear by 2050.
Steven Amstrup and other U.S. Geological Survey scientists have predicted two-thirds of the world's polar bears may disappear by 2050, based on moderate projections for the shrinking of summer sea ice caused by climate change, though the validity of this study has been debated. The bears could disappear from Europe, Asia, and Alaska, and be depleted from the Canadian Arctic Archipelago and areas off the northern Greenland coast. By 2080, they could disappear from Greenland entirely and from the northern Canadian coast, leaving only dwindling numbers in the interior Arctic Archipelago. However, in the short term, some polar bear populations in historically colder regions of the Arctic may temporarily benefit from a milder climate, as multiyear ice that is too thick for seals to create breathing holes is replaced by thinner annual ice.
Moya et al. (2007) compared two homologous series of substituted psychedelic phenethylamines and phenylisopropylamines for signaling at the 5-HT2A receptor through PLC and PLA2 responses. They employed Chinese hamster ovary (CHO)-FA4 cells stably expressing the human 5-HT2A receptor that had similar maximal responses for inositol phosphate (IP) accumulation and AA release in response to serotonin. Relative efficacies for AA release and IP accumulation varied within the series, and the substituted amphetamines had higher efficacy in both pathways. The amphetamines also produced a more robust in vivo rat HTR, mediated through the 5-HT2A receptor.
Cussac et al. (2008) reported differential agonist action for a series of serotonergic ligands, including LSD and DOI, and using CHO cells stably expressing the human 5-HT2A receptor. [They also used cells transfected with the human 5-HT2B and 5-HT2C (VSV isoform) receptors, obtaining generally similar results, but the discussion here will focus on their work with the 5-HT2A receptor.] They measured specific activation of Gq/11 proteins using a scintillation proximity assay and used a fluorescent imaging plate reader assay to measure intracellular Ca2+ responses. Serotonin and 5-carboxytryptamine gave a 20- to 50-fold greater potency for Ca2+ release than measured for Gq/11 activation, whereas DOI showed only a modest 2-to 3-fold preference for Ca2+ release. As anticipated, M100907 potently blocked serotonin-stimulated Gq/11 proteins. LSD showed a 20-fold higher potency to stimulate Gq/11 than to induce Ca2+ release. The most striking separation between activities was for the nonhallucinogenic 5-HT2A agonist lisuride, which was as potent as DOI in stimulating Gq/11, more than 1000-fold more potent than at Ca2+ release, and was a partial agonist for the two pathways. Interestingly, Ca2+ mobilization is classically considered to be a downstream consequence of Gq/11 activation and subsequent PLC stimulation. Yet the results presented here suggest that Gq/11 signaling may not be the only determinant of Ca2+ signaling. The main result of this study, however, was the ability of different agonists to differentially activate two signaling pathways in the same cell type.
Extending this work further, Nichols and Sanders-Bush (2004) performed a second microarray screen using a different Affymetrix gene chip version, identifying and validating three additional transcripts increased by 1.0 mg/kg LSD in the rat PFC: MAP kinase phosphatase 1 (mkp1), core/enhancer binding protein β (C/EBP-β), and the novel gene, induced by lysergic acid diethylamide 1 (ilad1; subsequently renamed arrestin domain containing 2 or arrdc2). As with the other LSD-induced differentially expressed genes, these also followed a dose- and time-dependent expression pattern. At the highest 1.0-mg/kg dose of LSD, expression of mkp1, C/EBP-β, and ilad1 was only partially blocked by MDL100907, indicating that activation of multiple receptors probably contributes to the effects of LSD on gene expression at this dose. Indeed, LSD is a relatively nonselective serotonin and dopamine receptor ligand, with high to moderate affinity for a number of receptors that may contribute to its effects (Nichols, 2004). 2b1af7f3a8