Assessment of microplastics in coastal ecosystem of Bangladesh.

Microplastics (MPs) pose one of the major environmental threats to marine organisms and ecosystems on a global scale. The present study investigated MPs in surface water, beach sediments, and fish in two coastal areas of Bangladesh namely Cox's Bazar and Kuakata. The MPs were identified and characterized using three different techniques, including the binocular microscope, the ATR-FTIR (Attenuated Total Reflectance-Fourier Transform Infrared Spectroscopy), and SEM-EDS (Scanning Electron Microscopy- Energy Dispersive Spectroscopy). The number of MPs in seawater was 10.1 ± 3.10 and 8.52 ± 3.92 items/100 L and in beach sediment, 13.2 ± 3.68 and 9.48 ± 3.63 items/100 g in Cox's Bazar and Kuakata, respectively. In fish samples, the abundance of MPs was 7.82 ± 1.28 and 6.82 ± 1.87 items/individual species of Cox's Bazar and Kuakata, respectively, where the highest quantities of MP were found in Euthynnus affinisand Sillago sihama and the lowest in Terapon jarbua and Pampus chinensisin Cox's Bazar and Kuakata, respectively. The number of MPs in GITs (Gastrointestinal tracts) was 1.63 ± 0.991 and 1.25 ± 0.546 items/g GIT and in BW (Body Weight) were 0.042 ± 0.014 and 0.037 ± 0.014 items/g BW in Cox's Bazar and Kuakata, respectively. There revealed a positive correlation between MP abundance and GIT weight and body weight in fish species. MPs were predominantly fiber-shaped, white/transparent, and small size. The most common MP polymers were polyethylene and polypropylene. SEM images of MPs demonstrate surface roughness, cracks, mechanical weathering and oxidative weathering, demonstrating their ongoing environmental exposure. The EDS spectrum unearthed that the MPs contained several elements (C, N, O, Na, Al, Fe, and Si). Findings from this study might be useful in coastal plastic particle management and to mitigate the potential risks associated with them.

Screening for antimicrobial residues in poultry eggs in Bangladesh using Charm II radio-receptor assay technique following validation.

The aim of the study was to screen for the presence of antimicrobial residues in poultry eggs from Bangladesh using the Charm II radio-receptor assay in the absence of expensive confirmatory instrumentation. This was based on cut-off values as set in the validation guidelines according to Commission Decision 2002/657/EC and Commission Implementing Regulation (EU) 2021/808. Fortified eggs spiked with fixed concentrations of doxycycline, erythromycin A, sulphamethazine, and benzylpenicillin were used to determine the cut-off values and detection capabilities (CCß). Other validation parameters included were applicability, ruggedness, and robustness. A total of 201 egg mix samples from native organic chicken, duck, and commercial farm-raised laying hens (both brown and white eggs) were tested and after analysis 13%, 10%, and 4.5% of the egg mix samples showed positive signals for sulphonamides, macrolides/lincosamides, and tetracyclines, respectively. Presence of multiple drug residues were also suspected in 11 out of 201 egg mix samples.

Macroalgae for biomonitoring of trace elements in relation to environmental parameters and seasonality in a sub-tropical mangrove estuary.

Being a resourceful ecosystem, mangrove estuaries have always been subjected to trace elements (TEs) contamination, and therefore, the biomonitoring approach holds immense potential for surveilling the aquatic environment. To investigate the potentiality of mangrove macroalgae as biomonitors, estuarine water, intertidal-sediment, and macroalgal samples were collected from the Pasur River estuary of Sundarbans mangrove ecosystem, Bangladesh, and afterward studied through Atomic Absorption Spectrometer to quantify the levels of six concerned TEs (Fe, Mn, Zn, Cu, Pb, and Cd). This study utilized the geo-environmental and ecological indices and sediment characterization approaches (sediment quality guidelines-SQGs) for assessing the contamination scenario of the adjacent environment to macroalgae whereas the performance of studied algal groups was evaluated using Bio-contamination factor, Comprehensive bio-concentration index, and Metal accumulation index. Metal occurrence scheme in the water followed the order of Fe > Zn > Mn > Pb > Cd while Fe > Mn > Zn > Cu > Pb > Cd for both sediment and macroalgae. Both Pb and Cd exceeded the guideline limit in estuarine water and the indices approach manifested low to moderate contamination with enrichment from anthropogenic origin of Mn, Zn, and Cu in sediment. Moreover, the SQGs revealed rare biological effects of Cu on an aquatic community. Within algal samples, Chlorophyta contributed the highest biomass production, followed by Phaeophyta and Rhodophyta. Statistical relationship disclosed the influence of environmental variables on TE's accumulation in Chlorophyta. By contrast, hydrochemical's association showed prevalence over the TEs accumulation process for Phaeophyta and Rhodophyta. Bioaccumulation performance analysis revealed that the ability to accumulate TEs in macroalgal groups varied with seasons. Therefore, biomonitoring with macroalgae for the region of interest might require further temporal considerations.

Dispositional mindfulness, alexithymia and sensory processing: Emerging insights from habituation of the acoustic startle reflex response.

There is growing evidence of beneficial effects of mindfulness developed through engaging in mindfulness training/practices on sensory and cognitive processing, emotion regulation and mental health. Mindfulness has also been conceptualised as a dispositional 'trait', i.e. the naturally-occurring ability of meditation-naïve individuals to display, in varying degree, a non-judgmental non-reactive present-moment awareness in everyday life. In this study we examined possible associations between dispositional mindfulness, alexithymia and sensory processing. Eye-blink startle responses to acoustic stimuli of varying intensity [90-dB or 100-dB over 70-dB (A) background] were assessed in 26 meditation-naïve adults (50 % men) using electromyographic recordings of the orbicularis muscle. All participants completed the Five Facet Mindfulness Questionnaire and the 20-item Toronto Alexithymia Scale. A negative association was found between dispositional mindfulness and alexithymia (r = -0.513). There was stronger startle habituation to 100-dB, compared to 90-dB probes. Stronger startle habituation (larger negative habitation slope values) to 100-dB probes was significantly associated with higher dispositional mindfulness (r = -0.528) and with lower alexithymia at trend level (r = 0.333). As indicated by commonality analysis, 10.6 % of explained variance in habituation (100-dB probes) was common to both alexithymia and mindfulness, 17.3 % was unique to mindfulness, but alexithymia made negligible unique contribution (0.5 %). These findings indicate similar startle habituation pattern in people with a high level of dispositional mindfulness to that reported previously by Antonova et al. (2015) in people with moderate mindfulness meditation practice intensity. Future studies should investigate the mechanisms, such as interoceptive awareness, that might underly these relationships.

Pancreatobiliary Diseases: Evaluation by Transabdominal and Endoscopic Ultrasound.

Pancreaticobiliary diseases are the important causes of morbidity and mortality worldwide. Among the imaging modalities, Transabdominal ultrasound (TUS) is cheap, available, and noninvasive but it has some limitations. Endoscopic ultrasound (EUS) is invasive but it has some diagnostic and therapeutic advantages over TUS. This study was aimed to see the diagnostic yields of EUS and TUS in the pancreatobiliary diseases. This cross sectional study was conducted in Sir Salimullah Medical College Mitford Hospital (SSMC&MH), Dhaka, Bangladesh from March 2017 to February 2019. All (n=222) patients were evaluated clinically and with relevant investigations. TUS and EUS were done in all patients. Endoscopic retrograde cholangiopancreatography (ERCP) was done in 60 patients. Among 222 patients 56.8% were males; mean age was 46±16 years; the main presenting symptoms were abdominal pain and jaundice. In diseases of biliary tree, EUS showed dilated CBD alone or in combination with stone in 50 and 67 cases and TUS showed 37, 63 patients respectively. The difference between the findings of EUS and TUS was statistically significant (p=0.00). In gall bladder, EUS found microlithiasis in 6(2.6%) and sludges in 24(10.8%) cases whereas TUS found microlithiasis in 1(0.5%) and sludges in 17(7.7%) cases respectively (p=0.00). Both EUS and TUS detected cholelithiasis in equal number of patients 46(20.3%). On pancreatic evaluation, EUS and TUS detected pancreatic parenchymal abnormalities in 24(10.8%) and 12(5.5%) patients respectively with significant p value (0.00). In cases of pancreatic and cholangiocarcinoma the difference between the findings of EUS and TUS were statistically significant (p<0.05). EUS detected 7 cases of ampullary/peri-ampullary neoplasms whereas TUS detected only 2 cases. The sensitivity of EUS for detecting CBD dilatation, CBD stones, CBD SOL and pancreatic SOL was 85%, 91%, 93%, and 92% respectively. The sensitivity of TUS for detecting CBD dilatation, CBD stones, CBD SOL and pancreatic SOL was 42%, 52%, 40%, and 37% respectively. EUS is more sensitive than TUS in diagnosing pancreaticobiliary disorders. It is of paramount importance in patients in diagnosing CBD dilatation, choledocholithiasis, biliary microlithiasis and pancreaticobiliary neoplasm. EUS has important role before proceeding to further management by more invasive techniques like ERCP or surgery.

Positive intergroup contact modulates fusiform gyrus activity to black and white faces.

In this study, we investigated the effect of intergroup contact on processing of own- and other-race faces using functional Magnetic Resonance Imaging (fMRI). Previous studies have shown a neural own-race effect with greater BOLD response to own race compared to other race faces. In our study, white participants completed a social-categorization task and an individuation task while viewing the faces of both black and white strangers after having answered questions about their previous experiences with black people. We found that positive contact modulated BOLD activity in the right fusiform gyrus (rFG) and left inferior occipital gyrus (lIOC), regions associated with face processing. Within these regions, higher positive contact was associated with higher activity when processing black, compared to white faces during the social categorisation task. We also found that in both regions a greater amount of individuating experience with black people was associated with greater activation for black vs. white faces in the individuation task. Quantity of contact, implicit racial bias and negatively valenced contact showed no effects. Our findings suggest that positive contact and individuating experience directly modulate processing of out-group faces in the visual cortex, and illustrate that contact quality rather than mere familiarity is an important factor in reducing the own race face effect.

Levocarnitine Improves AlCl3-Induced Spatial Working Memory Impairment in Swiss albino Mice.

Background: Aluminum, a neurotoxic substance, causes oxidative stress induced-neurodegenerative diseases. Several lines of evidence suggest that levocarnitine has an antioxidant effect and also plays an important role in beta-oxidation of fatty acids. However, the role of levocarnitine in aluminum-induced neurotoxicity has not been well documented. Here we aimed to investigate the effect of levocarnitine on aluminum chloride (AlCl3)-induced oxidative stress and memory dysfunction. Methods: Male Swiss albino mice (n = 30) were treated with either control (saline) or AlCl3 or AlCl3 plus levocarnitine or levocarnitine or astaxanthin plus AlCl3 or astaxanthin alone. The spatial working memory was determined by radial arm maze (RAM). In addition, we measured the lipid peroxidation (MDA), glutathione (GSH), advanced oxidation of protein products (AOPP), nitric oxide (NO) and activity of superoxide dismutase (SOD) in the various brain regions including prefrontal cortex (PFC), striatum (ST), parietal cortex (PC), hippocampus (HIP) hypothalamus (HT) and cerebellum (CB). We used astaxanthin as a standard antioxidant to compare the antioxidant activity of levocarnitine. Results: The RAM data showed that AlCl3 treatment (50 mg/kg) for 2 weeks resulted in a significant deficit in spatial learning in mice. Moreover, aluminum exposure significantly (p < 0.05) increased the level of oxidative stress markers such as MDA, GSH, AOPP and NO in the various brain regions compared to the controls. In addition, combined administration of levocarnitine and AlCl3 significantly (p < 0.05) lowered the MDA, AOPP, GSH and NO levels in mice. Conclusion: Our results demonstrate that levocarnitine could serve as a potential therapeutic agent in the treatment of oxidative stress associated diseases as well as in memory impairment.

Comparative Study of Alginate and Omeprazole in Symptomatic Treatment of Non-erosive Gastroesophageal Reflux Disease.

Gastroesophageal reflux disease is widely reported most prevalent disease of the gastrointestinal tract. The burden of gastroesophageal reflux disease (GERD) is increasing in Asia and the majority of patients have non-erosive reflux disease. This prospective, open label, non random (consecutive), experimental study was performed due to compare the therapeutic efficacy of alginate and omeprazole in relieving symptoms of non erosive reflux disease (NERD) and was carried out in the Outpatient Department of Gastroenterology, Dhaka Medical College Hospital, Dhaka, Bangladesh from December 2013 to May 2014. Sixty patients were enrolled for this study and were divided into two groups. Among them, 30 subjects were assigned to the omeprazole group (Group I) and 30 subjects to the alginate group (Group II). Omeprazole 20mg enteric coated capsule daily and alginate 10ml three times daily were administered 14 days in this study. In ITT analysis, achieving complete symptom relief (heart burn) was 56.7% in alginate group & 60% in omeprazole group. Statistically which was not significant (p=0.793). In PP analysis, this was 65.4% and 66.7% respectively. In this study, the overall satisfaction of omeprazole & alginate was more than 86% and the mean duration of heart burn free was found 5.0±4.0 days in Group I and 3.65±2.8 days in Group II. The difference was not statistically (p>0.05) significant between two groups in this study. Therapeutic efficacy and safety profiles of alginate were comparable to omeprazole after two weeks treatment in NERD subjects. So alginate may be considered as a relevant and effective alternative medication in non-erosive reflux.

Retracted Human Health Risk of Chromium Intake From Consumption of Poultry Meat and Eggs in Dhaka, Bangladesh.

BACKGROUND: Heavy metals contamination of food is a serious threat. Long term exposure may lead to human health risks. Poultry and eggs are a major source of protein, but if contaminated by heavy metals, have the potential to lead to detrimental effects on human health. OBJECTIVES: The objective of this study is to determine chromium concentrations in poultry meat (flesh and liver) and eggs collected from poultry farms in Dhaka, Bangladesh, to calculate the daily intake of chromium from the consumption of poultry meat and eggs for adults, and to evaluate their potential health risk by calculating the target hazard quotients (THQ). METHODS: All samples of poultry feed, meat (flesh and liver) and eggs were analyzed by a graphite furnace atomic absorption spectrometer (AAS) (GFA- EX- 7i Shimadju, Japan). RESULTS: Chromium concentrations were recorded in the range of not detected (ND) to 1.3926±0.0010 mg kg-1 and 0.0678±0.0001 mg kg-1 to 1.3764±0.0009 mg kg-1 in the liver of broiler and layer chickens, respectively. Chromium concentrations were determined in the range of 0.069±1.0004 mgkg-1 to 2.0746±0.0021 mg kg-1 and 0.0362±0.0002 mg kg-1 to 1.2752±0.0014 mg kg-1 in the flesh of broiler and layer chicken, respectively. The mean concentration of chromium in eggs was 0.2174-1.08 mg kg.-1 The highest concentration of chromium 2.4196±0.0019 mg kg-1 was found in egg yolk. Target hazard quotients values in all poultry flesh, liver and eggs samples were less than one, indicating no potential health risks to consumers. CONCLUSIONS: The estimated daily intake values of chromium were below the threshold limit. Thus, our results indicate that no adverse health effects are expected as a resultof ingestion of chicken fed with tannery waste. ETHICS APPROVAL: This study was approved by the Biosafety, Biosecurity & Ethical Committee of Jahangirnagar University.

Astaxanthin ameliorates aluminum chloride-induced spatial memory impairment and neuronal oxidative stress in mice.

Aluminum chloride induces neurodegenerative disease in animal model. Evidence suggests that aluminum intake results in the activation of glial cells and generation of reactive oxygen species. By contrast, astaxanthin is an antioxidant having potential neuroprotective activity. In this study, we investigate the effect of astaxanthin on aluminum chloride-exposed behavioral brain function and neuronal oxidative stress (OS). Male Swiss albino mice (4 months old) were divided into 4 groups: (i) control (distilled water), (ii) aluminum chloride, (iii) astaxanthin+aluminum chloride, and (iv) astaxanthin. Two behavioral tests; radial arm maze and open field test were conducted, and OS markers were assayed from the brain and liver tissues following 42 days of treatment. Aluminum exposed group showed a significant reduction in spatial memory performance and anxiety-like behavior. Moreover, aluminum group exhibited a marked deterioration of oxidative markers; lipid peroxidation (MDA), nitric oxide (NO), glutathione (GSH) and advanced oxidation of protein products (AOPP) in the brain. To the contrary, co-administration of astaxanthin and aluminum has shown improved spatial memory, locomotor activity, and OS. These results indicate that astaxanthin improves aluminum-induced impaired memory performances presumably by the reduction of OS in the distinct brain regions. We suggest a future study to determine the underlying mechanism of astaxanthin in improving aluminum-exposed behavioral deficits.

The antioxidant effect of astaxanthin is higher in young mice than aged: a region specific study on brain.

Astaxanthin is a potential antioxidant which shows neuroprotective property. We aimed to investigate the age-dependent and region-specific antioxidant effects of astaxanthin in mice brain. Animals were divided into 4 groups; treatment young (3 months, n = 6) (AY), treatment old (16 months, n = 6) (AO), placebo young (3 months, n = 6) (PY) and placebo old (16 months, n = 6) (PO) groups. Treatment group was given astaxanthin (2 mg/kg/day, body weight), and placebo group was given 100 µl of 0.9% normal saline orally to the healthy Swiss albino mice for 4 weeks. The level of non-enzymatic oxidative markers namely malondialdehyde (MDA); nitric oxide (NO); advanced protein oxidation product (APOP); glutathione (GSH) and the activity of enzymatic antioxidants i.e.; catalase (CAT) and superoxide dismutase (SOD) were determined from the isolated brain regions. Treatment with astaxanthin significantly (p < 0.05) reduces the level of MDA, APOP, NO in the cortex, striatum, hypothalamus, hippocampus and cerebellum in both age groups. Astaxanthin markedly (p < 0.05) enhances the activity of CAT and SOD enzymes while improves the level of GSH in the brain. Overall, improvement of oxidative markers was significantly greater in the young group than the aged animal. In conclusion, we report that the activity of astaxanthin is age-dependent, higher in young in compared to the aged brain.

Circadian regulation of olfactory receptor neurons in the cockroach antenna.

In the cockroach, olfactory sensitivity as measured by the amplitude of the electroantennogram (EAG) is regulated by the circadian system. We wished to determine how this rhythm in antennal response was reflected in the activity of individual olfactory receptor neurons. The amplitude of the EAG and the activity of olfactory receptor neurons (ORNs) in single olfactory sensilla were recorded simultaneously for 3 to 5 days in constant darkness from an antenna of the cockroach Leucophaea maderae. Both EAG amplitude and the spike frequency of the ORNs exhibited circadian rhythms with peak amplitude/activity occurring in the subjective day. The phases of the rhythms were dependent on the phase of the prior light cycle and thus were entrainable by light. Ablation of the optic lobes abolished the rhythm in EAG amplitude as has been previously reported. In contrast, the rhythm in ORN response persisted following surgery. These results indicated that a circadian clock outside the optic lobes can regulate the responses of olfactory receptor neurons and further that this modulation of the ORN response is not dependent on the circadian rhythm in EAG amplitude.

Characterization of PDF-immunoreactive neurons in the optic lobe and cerebral lobe of the cricket, Gryllus bimaculatus.

Pigment-dispersing factor (PDF) is a neuropeptide playing important roles in insect circadian systems. In this study, we morphologically and physiologically characterized PDF-immunoreactive neurons in the optic lobe and the brain of the cricket Gryllus bimaculatus. PDF-immunoreactivity was detected in cells located in the proximal medulla (PDFMe cells) and those in the dorsal and ventral regions of the outer chiasma (PDFLa cells). The PDFMe cells had varicose processes spread over the frontal surface of the medulla and the PDFLa cells had varicose mesh-like innervations in almost whole lamina, suggesting their modulatory role in the optic lobe. Some of PDFMe cells had a hairpin-shaped axonal process running toward the lamina then turning back to project into the brain where they terminated at various protocerebral areas. The PDFMe cells had a low frequency spontaneous spike activity that was higher during the night and was often slightly increased by light pulses. Six pairs of PDF-immunoreactive neurons were also found in the frontal ganglion. Competitive ELISA with anti-PDF antibodies revealed daily cycling of PDF both in the optic lobe and cerebral lobe with an increase during the night that persisted in constant darkness. The physiological role of PDF is discussed based on these results.

Phase shifts of the circadian locomotor rhythm induced by pigment-dispersing factor in the cricket Gryllus bimaculatus.

Pigment-dispersing factors (PDFs) are octadeca-peptides widely distributed in insect optic lobes and brain. In this study, we have purified PDF and determined its amino acid sequence in the cricket Gryllus bimaculatus. Its primary structure was NSEIINSLLGLPKVLNDA-NH(2), homologous to other PDH family members so far reported. When injected into the optic lobe of experimentally blinded adult male crickets, Gryllus-PDF induced phase shifts in their activity rhythms in a phase dependent and dose dependent manner. The resulted phase response curve (PRC) showed delays during the late subjective night to early subjective day and advances during the mid subjective day to mid subjective night. The PRC was different in shape from those for light, serotonin and temperature. These results suggest that PDF plays a role in phase regulation of the circadian clock through a separate pathway from those of other known phase regulating agents.

Pigment-dispersing factor sets the night state of the medulla bilateral neurons in the optic lobe of the cricket, Gryllus bimaculatus.

Pigment-dispersing factor (PDF) is an octadeca-neuropeptide widely distributed in the insect brain and suggested to be involved in the insect circadian systems. We have examined its effects on the neuronal activity of the brain efferents in the optic stalk including medulla bilateral neurons (MBNs) in the cricket, Gryllus bimaculatus. The MBNs are visually responding interneurons connecting the bilateral medulla, which show a clear day/night change in their light responsiveness that is greater during the night. Microinjection of PDF into the optic lobe induced a significant increase in the spontaneous activity of the brain efferents and the photo-responsiveness of the MBNs during the day, while little change was induced during the night. The enhancing effects began to occur about 20 min after the injection and another 10 min was necessary to reach the maximal level. The effects of PDF were dose-dependent. When 22 nl of anti-Gryllus-PDF (1:200) IgG was injected into the medulla, the photo-responsiveness of the MBNs was suppressed in both the day and the night with greater magnitude during the night. No significant suppression was induced by injection of the same amount of IgG from normal rabbit serum. These results suggest that in the cricket optic lobe, PDF is released during the night and enhances MBNs' photo-responsiveness to set their night state.

5-HT(7)-like receptors mediate serotonergic modulation of photo-responsiveness of the medulla bilateral neurons in the cricket, Gryllus bimaculatus.

Serotonin (5-HT) suppresses the photo-responsiveness of medulla bilateral neurons (MBNs) that are involved in the coupling mechanism of the bilaterally paired optic lobe circadian pacemakers in the cricket, Gryllus bimaculatus. We found that forskolin, a highly specific activator of adenylate cyclase, mimicked the effects of serotonin on the MBNs. This fact suggests the involvement of cyclic 3', 5'-adenosine monophosphate (cAMP) in mediating the action of serotonin. We therefore tested the effects of various 5-HT receptor agonists and antagonists that are coupled to adenylate cyclase to specify the receptor involved. Application of 8-OH-DPAT that has affinity for both 5-HT(1A) and 5-HT(7) receptors suppressed the photo-responsiveness, like forskolin. The inhibitory effect of 8-OH-DPAT was effectively blocked by clozapine, a high affinity 5-HT(7) receptor antagonists with a very low affinity for 5-HT(2). Ketanserin, a selective 5-HT(2) antagonist, and NAN-190, a 5-HT(1A) antagonist, did not block it. These results suggest that serotonergic suppression of the photo-responsiveness of the MBNs is mediated by 5-HT(7)-like receptor subtypes.

Serotonin sets the day state in the neurons that control coupling between the optic lobe circadian pacemakers in the cricket Gryllus bimaculatus.

The bilaterally paired optic lobe circadian pacemakers of the cricket Gryllus bimaculatus mutually exchange photic and circadian information to keep their activity synchronized. The information is mediated by a neural pathway, consisting of the so-called medulla bilateral neurons, connecting the medulla areas of the two optic lobes. We investigated the effects of serotonin on the neural activity in this coupling pathway. Spontaneous and light-induced electrical activity of the neurons in the coupling pathway showed daily variations, being more intense during the night than the day. Microinjection of serotonin or a serotonin-receptor agonist, quipazine, into the optic lobe caused a dose- and time-dependent inhibition of spontaneous and light-induced responses, mimicking the day state. The amount of suppression was greater and the recovery from the suppression occurred faster during the night. Application of metergoline, a non-selective serotonin-receptor antagonist, increased spontaneous activity and light-evoked responses during both the day and the night, with higher effect during the day. In addition, metergoline effectively attenuated the effects of serotonin. These facts suggest that in the cricket's optic lobe, serotonin is released during the daytime and sets the day state in the neurons regulating coupling between the bilaterally paired optic lobe circadian pacemakers.