Effects Of (+)-Borneol On Fear Recall And Anxiety

Fear,panic and trauma related diseases are type of overreactions stimulated bycertain external events,circumstances and potential or real danger,which is a kind of adaptive defensive reaction faced with dangerous environments.Pathological panic and anxiety are characterized by various psychological diseases like social anxiety disorder,agoraphobia or specific phobia,panic disorder,obsessive-compulsive disorder,generalized anxiety disorder and post-traumatic stress disorder.These disorders comprise the most common mental disorders and are estimated to have a life-time prevalence of up to 28%among western populations.The prevalence of patients with PTSD has reached 4^th in psychological diseases.According to the epidemic statistics,more than 90%common people suffer from at least one serious traumatic event,which would induce the occurrence of PTSD.In addition to the personal suffering of patients,the economic burden caused by anxiety disorders is heavy.Therefore,there's urgent need for the development of the new psychological drugs.Various studies have showed that the psychological process involved in anxiety-related diseases have something to do with the GABAergic system.Research has revealed that the overexcited fear and anxiety-related neural system can be inhibited by the excitation of?-aminobutyric acid?GABA?receptors.As studied by pharmacological studies and experiments involving gene-targeted mouse models,GABA_A receptors have significant functions.For instance,drugs like benzodiazepines which facilitated these receptors alleviate symptoms of anxiety in people by systematic administration,and in animals the infusion into the amygdale reduced learned fear responses.?+?-Borneol is a bicyclic monoterpene found in several species of Artemisia andDipterocarpaceae and is widely applied in food and traditional Chinese medicine,used for anxiety,pain and anesthesia.Recently,?+?-Borneol has been reported to show various pharmacological effects,like the neuroprotective,analgesic,antidepressant-like,anti-inflammatory and anticonvulsant effects.Additionally,it was reported to have a positive modulation of the activation of GABA_A receptors expressed in Xenopus laevis oocytes,implicating?+?-Borneol in GABAergic transmission.Moreover,its anticonvulsant effect can be reversed by flumazeni and its analgesic effect was disrupted by bicuculline,both further suggesting pharmacological effect of?+?-Borneol on the GABAergic neurotransmitter system.Here we investigated effects of systemic and intra-hippocampal?+?-Borneol on fear recall.The hippocampus is a vital structure in regulating learning and memory as well as emotion,and it is divided into dorsal and ventral part.As is known to all,the dorsal hippocampus is related with spacial learning while the ventral part corresponds to emotion,therefore we studied the effect of?+?-Borneol on dorsal and ventral hippocampus on fear recall and anxiety,respectively.We suggest that the effect of?+?-Borneol may be different by dorsal or ventralhippocampal infusion,thereby we designed three parts in our experiment:1.Investigate the effect of?+?-Borneol on contextual and cued fear recall by dorsal or ventral hippocampal infusion;2.Investigate the effect of?+?-Borneol on anxiety by dorsal or ventral hippocampal infusion;3.Explore the potential pharmacological and neural mechanism of?+?-Borneol in fear recall and anxiety.Part 1.To investigate the role of?+?-Borneol in fear recall,both contextual and cued fear conditioning tests were conducted.In contextual fear conditioning,mice were injected with?+?-Borneol 30 minutes before fear recall test 24h or 7d after fear conditioning.Results showed that systemic manipulation attenuated the fear expression both 24h and 7d after fear conditioning.To further study the probable brain substrates,we infused?+?-Borneol into both dorsal and ventral hippocampus.Results showed that only dorsal infusion reduced contextual fear expression,indicating the effect of drug relied on dorsal but not ventral hippocampus in our experimental mode.In cued fear recall,mice were conditioned on first day,24h or 7d after fear conditioning,drug was administrated systemically 30 minutes before fear recall.Results showed that only 24h fear expression was reduced while the 7d cued fear retention was intact.In hippocampal administration,24h fear retention was impaired by ventral infusion but not the dorsal manipulation.Part 2.To study the effect of?+?-Borneol on anxiety,we assessed anxiety-like behavior by open-field test,the dark/light box test and the elevated-plus maze test.Results showed that mice increased the traveling distance and entries into the central part without affecting the total traveling distance by?+?-Borneol infused into dorsal hippocampus,implying the anxiolytic effect.In light/dark box test,mice spent more time exploring the light box by?+?-Borneol's dorsal hippocampal infusion.In the elevated-plus maze test,mice in the?+?-Borneol group spent more time in open arms and the entries into the open arms,indicating the anxiolytic effect of the drug by dorsal hippocampal infusion.However,there's no anxiolytic effect of?+?-Borneol by ventral hippocampal infusion in all the three tests.Part 3.To explore the proper pharmacological or neural mechanism of?+?-B orneol in fear recall and anxiety,we conducted the behavioral,electrophysiological and biochemical research.In contextual fear recall test,we treated mice with the GABA receptor inhibitor Bicuculline 30 minutes before drug infusion and results showed that the effect of?+?-Borneol was reversed.In electrophysiological experiment,the induced GABA current was facilitated by?+?-Borneol,thereby we confirmed that the effect of?+?-Borneol in fear recall and anxiety may depend on its regulation in GABAergic transmission.Due to the result that the drug only showed anxiolytic effect by dorsal but not ventral administration,and the effect of?+?-B orneol relied on the GABAergic modulation,we suggested that the different effect was attributed to the distinct GABA receptor subunit distribution.Our immunohistochemistry and western blot results revealed that the total GABA_A receptors,as well as the?1 subunit,in dorsal hippocampus were more than that in ventral part.However,there's no difference of?2 or?5 subunits between dorsal and ventral hippocampal distribution.As the?2 and?1 subunits are significantly involved in fast post-synaptic inhibition,therefore the behavioral effects of?+?-Borneol could be explained.In summary,?+?-Borneol's dorsal hippocampal infusion reduced contextual fear recall while its ventral hippocampal manipulation suppressed cued fear recall,and it only showed anxiolytic effects by dorsal hippocampal administration.The difference of the drug efficacy depended on its modulation in GABAergic transmission and the distinct GABA_A receptor subunits distribution in dorsal and ventral hippocampus.