Evaluation of pineal cysts with magnetic resonance imaging

AIM To evaluate radiological imaging findings of patients who had been found to have pineal cyst(PC) in brain magnetic resonance imaging(MRI).METHODS A total of 9546 patients who had brain MRI examination in March 2010-January 2018 period were studied.Fiftysix patients(44 female and 12 male) found to have PC were evaluated.Eighteen of the patients had had follow-up examinations of 2-94 mo(mean 30.50 ± 28.83).PC dimensions and volume,radiological imaging features(signal intensities,contours,internal septationloculation and contrast-enhancement features) and natural history in cases who had been followed-up were evaluated by two radiologists.RESULTS Of 9546 patients,5555 were female(58.2%) and 3991 male(41.8%).Age range was 1-99(mean 43.18 ± 20.94).PC frequency was calculated to be 0.58%.Forty-four of the 56 patients(78.57%) with PC were female and 12 male(21.43%),and their age range was 5-61(mean 31.26 ± 12.73).Thirty-five of the PCs were typical(62.50%) and 21(37.50%) were atypical.No significant difference was found between initial and final imaging sizes of PCs which were monitored by follow-up examinations(P > 0.05).CONCLUSION PCs are cysts which do not show clear size and natural changes and are more frequently observed in females and in adult ages.Most of them are isointense with cerebrospinal fluid on T1 and T2 A weighted images,hyperintense compared to cerebrospinal fluid on fluidattenuated inversion recovery; sequence and smoothly contoured.Their typical forms have peripheral rim and multilocular ones may have septal contrast-enhancement.

Spontaneous pineal apoplexy in a pineal parenchymal tumor of intermediate differentiation

Pineal apoplexy is a rare clinical presentation of pineal parenchymal tumors. We report the curative treatment of a case of pineal parenchymal tumor of intermediate differentiation with spontaneous apoplectic hemorrhage. This case is shown through computed tomography and magnetic resonance imaging of the brain, and is confirmed via histopathological studies. Recurrent upward gaze paresis was observed after the stereotactic biopsy. The paresis required an expeditious tumor resection. The mechanism of the pineal apoplectic hemorrhage remains unclear although it has been observed in different pineal region lesions. Clinical and radiological evidence of the cure 5 years post-surgery is available.

Oxidative stress and lipid peroxidation products:effect of pinealectomy or exogenous melatonin injections on biomarkers of tissue damage during acute pancreatitis

BACKGROUND:Melatonin (N-acetyl-5-methoxytripta-mine) is a free radical scavenger and a strong antioxidant,secreted by the pineal gland.In this study,we evaluated the effects of decreasing and increasing serum melatonin levels on malonyldialdehyde (MDA),superoxide dismutase (SOD),and reduced glutathione (GSH) levels in pancreatic tissue from rats with experimental acute pancreatitis.METHODS:Experimental acute pancreatitis was induced in three groups of Wistar albino rats (10 animals per group) by pancreatic ductal ligation.The first group had only acute pancreatitis and served as the control.Surgical pinealectomy was added to acute pancreatitis in the second group,removing the source of endogenous melatonin (low melatonin levels group).The third group was given 0.1 ml daily intraperitoneal injections of 20 mg/ml melatonin solution for one week (high melatonin levels group).The effects of melatonin levels were evaluated by comparison of the levels of MDA,SOD,and GS in pancreatic tissue.RESULT:We found that intraperitoneal melatonin injections decreased the levels of MDA and increased the levels of SOD and GSH in pancreatic tissue.CONCLUSION:Exogenous melatonin has a preventive effect on lipid peroxidation and oxidative damage in acute pancreatitis.

Monochromatic green light stimulation during incubation shortened the hatching time via pineal function in White Leghorn eggs

Background:Effect of monochromatic green light illumination on embryo development has been reported in chickens.The avian pineal gland is an important photo-endocrine organ formed by a mediodorsal protrusion during embryonic development.However,the involvement of pineal gland in the light transduction process remains to be elucidated.In the present study,we investigated the influence of monochromatic green light on hatching time and explored the possible mechanism via pineal function.Results:A total of 600 eggs of White Leghorn(Shaver strain)were incubated under photoperiods of either 12 h of light and 12 h of darkness using monochromatic green light(12L:12D group)or 24 h of darkness(0L:24D group)for 18 d.Compared to 0L:24D group,the green light stimulation shortened the hatching time without extending the hatch window or impairing hatchability.The liver of embryos incubated in the 12L:12D light condition was heavier than those of the 0L:24D group on d 21 post incubation which may be linked to the observed increase in the serum concentration of insulin-like growth factor 1(IGF-1);primary secretion of the liver.Histological structure analysis of pineal gland demonstrated that the light stimulation increased follicle area,wall thickness and lumen area on d 10 and d 12 post incubation.Rhythmic function analysis demonstrated that three clock related genes(brain and muscle ARNT-like-1,BMAL1;circadian locomotor output cycles kaput,CLOCK;and cryptochrome-1,CRY1)and a melatonin rate-limiting enzyme related gene(arylalkylamine N-acetyltransferase,AANAT)were rhythmically expressed in the pineal gland of the 12L:12D group,but not in the 0L:24D group.Simultaneously,the light stimulation also increased the concentration of melatonin(MT),which was linked to hepatocyte proliferation and IGF-1 secretion in previous studies.Conclusions:The 12L:12D monochromatic green light stimulation during incubation shortened hatching time without impairing hatching performance.Pineal gland’s early histological development and maturation of its rhythmic function were accelerated by the light stimulation.It may be the key organ in the photo-endocrine axis that regulates embryo development,and the potential mechanism could be through enhanced secretion of MT in the 12L:12D group which promotes the secretion of IGF-1.

The role of pineal microRNA-325 in regulating circadian rhythms after neonatal hypoxic-ischemic brain damage

Circadian rhythm disorder is a common,but often neglected,consequence of neonatal hypoxic-ischemic brain damage(HIBD).However,the underlying molecular mechanisms remain largely unknown.We previously showed that,in a rat model of HIBD,up-regulation of microRNA-325(miR-325)in the pineal gland is responsible for the suppression of Aanat,a key enzyme involved in melatonin synthesis and circadian rhythm regulation.To better understand the mechanism by which miR-325 affects circadian rhythms in neonates with HIBD,we compared clinical samples from neonates with HIBD and samples from healthy neonates recruited from the First Affiliated Hospital of Soochow University(Dushuhu Branch)in 2019.We found that circulating miR-325 levels correlated positively with the severity of sleep and circadian rhythm disorders in neonates with HIBD.Furthermore,a luciferase reporter gene assay revealed that LIM homeobox 3(LHX3)is a novel downstream target of miR-325.In addition,in miR-325 knock-down mice,the transcription factor LHX3 exhibited an miR-325-dependent circadian pattern of expression in the pineal gland.We established a neonatal mouse model of HIBD by performing doublelayer ligation of the left common carotid artery and exposing the pups to a low-oxygen environment for 2 hours.Lhx3 mRNA expression was significantly down-regulated in these mice and partially rescued in miR-325 knockout mice subjected to the same conditions.Finally,we showed that improvement in circadian rhythm-related behaviors in animals with HIBD was dependent on both miR-325 and LHX3.Taken together,our findings suggest that the miR-325-LHX3 axis is responsible for regulating circadian rhythms and provide novel insights into the identification of potential therapeutic targets for circadian rhythm disorders in patients with neonatal HIBD.The clinical trial was approved by Institutional Review Board of Children’s Hospital of Soochow University(approval No.2015028)on July 20,2015.Animal experiments were approved by Animal Care and Use Committee,School of Medicine,Soochow University,China(approval No.XD-2016-1)on January 15,2016.

Microstructural analysis of pineal volume using trueFISP imaging

AIM:To determine the spectrum of pineal microstructures (solid/cystic parts) in a large clinical population using a high-resolution 3D-T2-weighted sequence. METHODS:A total of 347 patients enrolled for cranial magnetic resonance imaging were randomly included in this study. Written informed consent was obtained from all patients. The exclusion criteria were artifacts or mass lesions prohibiting evaluation of the pineal gland in any of the sequences. True-FISP-3D-imaging (1.5-T, isotropic voxel 0.9 mm) was performed in 347 adults (55.4 ± 18.1 years). Pineal gland volume (PGV), cystic volume, and parenchyma volume (cysts exclud- ed) were measured manually. RESULTS:Overall, 40.3% of pineal glands were cystic. The median PGV was 54.6 mm 3 (78.33 ± 89.0 mm 3 ), the median cystic volume was 5.4 mm 3 (15.8 ± 37.2mm 3 ), and the median parenchyma volume was 53.6 mm 3 (71.9 ± 66.7 mm 3 ). In cystic glands, the standard deviation of the PGV was substantially higher than in solid glands (98% vs 58% of the mean). PGV declined with age (r = -0.130, P = 0.016). CONCLUSION:The high interindividual volume variation is mainly related to cysts. Pineal parenchyma volume decreased slightly with age, whereas genderrelated effects appear to be negligible.

Effect of the pineal gland on 5-hydroxytryptamine and γ-aminobutyric acid secretion in the hippocampus of male rats during the summer and winter

Objective:The present study aimed to investigate the effect of seasonal variation on neurotransmitter release in the hippocampus of normal rats and rats with pineal excision.Methods:Two time points,the summer and winter solstice,which are the longest and shortest days of the year,respectively,were selected.Male Spraguee Dawley rats that underwent a sham operation without pineal excision were included as a control group.The concentrations of 5-hydroxytryptamine(5-HT)andγ-aminobutyric acid(GABA)were determined by radioimmunoassays and enzyme-linked immunosorbent assays,respectively.Results:In the winter,the 5-HT and GABA levels in normal rats exhibited a significant difference compared with those in the operation group(P<.01).A difference was also noted in GABA levels between the normal group and the sham operation group(P<.05).The concentrations of 5-HT and GABA in the hippocampal tissues of the normal group exhibited a seasonal rhythm consisting of elevation during the summer and reduction during the winter(P<.01),while the GABA levels in the sham operation group exhibited a significant difference,with elevation during the summer and reduction during the winter(P<.01).In the operation group,GABA showed the same trend(P<.01).Conclusion:The seasonal rhythm of neurotransmitter secretion by the hippocampus(5-HT and GABA)consisted of elevation during the summer and reduction during the winter.During the winter,the pineal gland exhibited a reverse regulatory effect on the secretion of 5-HT and GABA in the hippocampus,and it exhibited seasonal selectivity with regard to the regulation of 5-HT.

Developmental stage-specific A-to-I editing pattern in the postnatal pineal gland of pigs(Sus scrofa)

Background: RNA editing is a widespread post-transcriptional modification mechanism in mammalian genomes.Although many editing sites have been identified in domestic pigs(Sus scrofa), little is known about the characteristics and dynamic regulation of RNA editing in the pineal gland(PG), a small neuroendocrine gland that synthesizes and secretes melatonin, which is primarily responsible to modulate sleep patterns.Results: This study analyzed the expression of adenosine-to-inosine(A-to-I) editing regulators and profiled the first dynamic A-to-I RNA editome during postnatal PG development. The results identified ADAR1 as the most abundantly expressed ADAR enzyme, which was down-regulated during postnatal PG development. Furthermore,47,284 high-confidence RNA editing sites were identified, the majority of which(93.6%) were of the canonical A-to-I editing type, followed by C-to-T editing. Analysis of its characteristics showed that the A-to-I editing sites mostly localized in SINE retrotransposons PRE-1/Pre0_SS. Moreover, a strong deficiency and preference for guanine nucleotides at positions of one base upstream or downstream were found, respectively. The overall editing level at the puberty stage was higher than at both infancy and adulthood stages. Additionally, genome-wide RNA editing was found to exhibit a dynamic stage-specific fashion(postnatally). Genes that underwent developmental changes in RNA editing were associated with catabolic processes as well as protein localization and transport functions,implying that RNA editing might be responsible for the molecular machineries of the postnatal developing PG.Remarkably, RNA editing in 3′-UTRs might regulate gene expression by influencing miRNA binding during PG development.Conclusions: This study profiles the first comprehensive developmental RNA editome in the pig PG, which contributes to the understanding of the importance of post-transcriptionally mediated regulation during mammalian postnatal PG development. Moreover, this study widely extends RNA editome resources in mammals.

Expression of Clock genes in the pineal glands of newborn rats with hypoxic-ischemic encephalopathy

Clock genes are involved in circadian rhythm regulation, and surviving newborns with hypoxic-ischemic encephalopathy may present with sleep-wake cycle reversal. This study aimed to determine the expression of the clock genes Clock and Bmall, in the pineal gland of rats with hypoxic-ischemic brain damage. Results showed that levels of Clock mRNA v^re not significantly changed within 48 hours after cerebral hypoxia and ischemia. Expression levels of CLOCK and BMAL1 protein were significantly higher after 48 hours. The levels of Bmall mRNA reached a peak at 36 hours, but were significantly reduced at 48 hours. Experimental findings indicate that Clock and Bmall genes were indeed expressed in the pineal glands of neonatal rats. At the initial stage （within 36 hours） of hypoxic-ischemic brain damage, only slight changes in the expression levels of these two genes were detected, followed by significant changes at 36-48 hours. These changes may be associated with circadian rhythm disorder induced by hypoxic-ischemic brain damage.

Molecular mechanisms of seasonal photoperiod effects of the pineal gland on the hippocampus in rats

Background:Based on the theory of“five Zang-organs corresponding to the seasons”in traditional Chinese medicine(TCM),physiological functions including emotions vary with the seasons.We aimed to investigate the seasonal photoperiod effects of melatonin(MT)released from the pineal gland on the MT receptor(MTR)-Gs/Gi-cyclic adenosine monophosphate(cAMP)-protein kinase A(PKA)-cAMP response element-binding protein(CREB)signaling pathway in the hippocampus.Methods:Rats were divided into three groups:control,operation(surgery with pineal gland removal),and pseudo-operation groups(same surgery as operation group but without removing pineal gland),and fed at specific time across the four seasons.The levels of MTR,adenylate cyclase(AC),cAMP,PKA,and CREB in the hippocampus were analyzed using ELISA.The concentrations of Gs and Gi were analyzed using Western blot.The expression of CREB mRNA was detected by PCR.Results:For intragroup comparisons,compared with spring,the levels of Gs/Gi in the control group were higher in summer,autumn,and winter(P=.009 in summer;P<.001 in autumn and winter);the levels of MTR,cAMP,PKA,and CREB in the control group were significantly higher in autumn and winter than in spring(all P<.001).The levels of MTR,cAMP,PKA,and CREB in each season were significantly lower in the operation group than in the control group(all P<.05).Significant differences were noted in Gs/Gi levels between the operation group and control group in spring,autumn,and winter(all P<.05).Conclusion:Our findings suggest that MTR-Gs/Gi-cAMP-PKA-CREB signaling pathway is involved in the seasonal photoperiod effects of the pineal gland on the hippocampus and may underpin seasonal changes in emotions.It can support the prevention and treatment of the seasonal onset of mental disorders,and enrich the theory of“five Zang-organs corresponding to the seasons”.

Aluminum and Glyphosate Can Synergistically Induce Pineal Gland Pathology: Connection to Gut Dysbiosis and Neurological Disease

Many neurological diseases, including autism, depression, dementia, anxiety disorder and Parkinson’s disease, are associated with abnormal sleep patterns, which are directly linked to pineal gland dysfunction. The pineal gland is highly susceptible to environmental toxicants. Two pervasive substances in modern industrialized nations are aluminum and glyphosate, the active ingredient in the herbicide, Roundup?. In this paper, we show how these two toxicants work synergistically to induce neurological damage. Glyphosate disrupts gut bacteria, leading to an overgrowth of Clostridium difficile. Its toxic product, p-cresol, is linked to autism in both human and mouse models. p-Cresol enhances uptake of aluminum via transferrin. Anemia, a result of both aluminum disruption of heme and impaired heme synthesis by glyphosate, leads to hypoxia, which induces increased pineal gland transferrin synthesis. Premature birth is associated with hypoxic stress and with substantial increased risk to the subsequent development of autism, linking hypoxia to autism. Glyphosate chelates aluminum, allowing ingested aluminum to bypass the gut barrier. This leads to anemia-induced hypoxia, promoting neurotoxicity and damaging the pineal gland. Both glyphosate and aluminum disrupt cytochrome P450 enzymes, which are involved in melatonin metabolism. Furthermore, melatonin is derived from tryptophan, whose synthesis in plants and microbes is blocked by glyphosate. We also demonstrate a plausible role for vitamin D3 dysbiosis in impaired gut function and impaired serotonin synthesis. This paper proposes that impaired sulfate supply to the brain mediates the damage induced by the synergistic action of aluminum and glyphosate on the pineal gland and related midbrain nuclei.

The Role of Pineal Gland in Regulating Circadian Corticosterone Rhythm and Its Mechanism

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Melatonin changes in the pineal gland of sleep-deprived rats following habenular nucleus lesion

The habenular nucleus （Hb） is an important structure that regulates the function of the pineal gland which may affect melatonin content in the pineal gland after sleep deprivation （SD）. In the present study, high performance liquid chromatography showed that the melatonin content in the pineal gland was significantly reduced, and y-aminobutyric acid content in the Hb was significantly increased after SD. Furthermore, the melatonin content in the pineal gland was markedly reduced after Hb lesion under normal sleep and SD conditions. Immunohistochemistry showed that the number of Fos-positive neurons was significantly decreased in the lateral and medial Hb after SD. The findings demonstrate that the reduction of melatonin in the pineal gland after SD is related to decreased activity of Hb neurons, and that the Hb can regulate sleep-wake rhythm by influencing melatonin secretion in the pineal gland.

Protective role of buffalo pineal proteins on arsenic-induced oxidative stress in blood and kidney of rats

Objective: Exposure to various toxic metals has become an increasingly recognized source of ill- ness in human and animals, worldwide. Arsenic (As) and its compounds cause adverse health effects in animals and humans. Recently, it has been suggested that the pineal gland may also have antioxidants role due to secretary product other than melatonin. With keeping this view, pre-sent investigation tested effect of buffalo (Bubalus bubalis) pineal proteins (PP) on arsenic-induced oxidative stress in RBCs (Red blood cells) and kidney of rats. Methods: Eighteen adult female Wistar rats were grouped into group-I (Control), group-II (Arsenic control), and group-III (Arsenic + Pineal proteins). Experimental rats were given 100 ppm arsenic (p.o.) for 4 weeks alone or along with pineal proteins at a dose of 100 μg/kg body weight (i.p.). Results: Interestingly, arsenic ex-posure led to the stimulation of kidney catalase (CAT) activity, but inhibition of RBCs CAT activ-ity and significantly (P<0.05) increased the RBCs and kidney lipid peroxidation level (LPO). How-ever, arsenic treatment caused depletion of glu- tathione (GSH), superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GR) in kidney tissues. In RBCs, only GR and CAT activity were significantly (P<0.05) declined. These changes were significantly (P<0.05) reversed by PP treatment in arsenic exposed animals. Conclusion: Therefore, present study indicated the significant protecting effect of buf-falo (Bubalus bubalis) PP against arsenic in-duced-oxidative stress through antioxidant de-fense systems in rats.

Dorsal midbrain syndrome secondary to pineal gland tumours: case series and review on manifestations, management and outcome

Dorsal midbrain syndrome or Parinaud syndrome is a supranuclear brainstem syndrome involving the vertical gaze centre.These are case series with three patients who were diagnosed with dorsal midbrain syndrome secondary to pineal gland tumours.The prognosis varied depending on tumour types,age of presentation and treatment received.All of them were presented with life-threatening obstructive hydrocephalus.Our first patient was successfully treated with emergency surgery followed by radiotherapy.He regained normal visual acuity and full recovery of his ocular movement.Second and third patients had undergone surgery for raised intracranial pressure.Both had an inoperable pineal gland tumour.As for our second patient,we detected a worsening of vertical gaze during his four years follow-up.However,his bilateral good visual acuity was preserved.The third patient passed away as a result of uncontrolled enlarging tumour.We also briefly reviewed the clinical presentation,diagnosis,and therapeutic approach of the three patients.One of the caveats is that urgent radiological study is crucial to differentiate the tumour type via the pathognomonic features and to delineate the tumour extension.The preferable treatment options vary among each tumour type.A multidisciplinary approach is crucial in early detection,in addition to treatment initiation and long term follow up to achieve a better outcome.

Seasonal photoperiodic influence of pineal melatonin on hypothalamic-pituitary-adrenal axis-hippocampal-receptor in male rats

Background: Based on the effect of seasonal changes on human visceral function, this study investigated the impact of seasonal photoperiod of the pineal body on hypothalamic-pituitary-adrenal axis-hippocampal-receptor in rats, aiming to reveal the mechanism by which pineal gland melatonin regulates the seasonal secretion of hippocampal neurotransmitters.Methods: Vernal equinox, summer solstice, autumn equinox, and winter solstice were selected as four experimental time points, and rats were randomly divided into normal control group, sham operation group, and pinealectomized group. The seasonal changes in corticotropin-releasing hormone(CRH),adrenocorticotropic hormone(ACTH), corticosterone, hypothalamic melatonin receptor(MTR), and hippocampal corticosterone receptor(CORTR) were examined by enzyme-linked immunosorbent assay.Results: Comparing the same group between different seasons, we showed that in the normal control group, CRH, ACTH, corticosterone, and MTR were higher, while CORTR was lower in autumn and winter than in spring(all P <.05). Compared with the normal control group, the pinealectomized group showed higher levels of corticosterone(P =.01), MTR(P =.01), and CORTR(P =.03) during spring;reduced levels of MTR and CORTR(both P <.001) during summer;higher levels of ACTH(P =.001) and MTR(P <.001),and lower levels of CRH(P =.001), corticosterone(P <.001), and CORTR(P =.003) during autumn;and lower levels of CRH(P <.001) and MTR(P =.004), and higher level of ACTH(P <.001) in winter.Conclusions: Seasonal photoperiod acts on the pineal gland to secrete different levels of melatonin,resulting in seasonal changes in the hypothalamic-pituitary-adrenal axis-hippocampal-receptor, which may be the pathophysiological basis for the onset of seasonal affective disorder.

Surgery of pineal region meningioma combining obstructive hydrocephelus

Objective:The aim of our study was to find out the best operative therapeutic regimen by reviewing the comprehension of operation,the improvement of operative method and the selection of operative approach concerning pineal region meningioma combining obstructive hydrocephalus.Methods:We retrospected the clinic data,comprehension of operation and prognosis of 6 cases of pineal region meningioma.Results:Six tumors were all removed,after that the back wall of the third ventricle was cut open.The 6 tumors were defined as meningioma by pathological examination.After 4-48 months follow-up,the manifestation of hydrocephalus disappeared,other symptoms were relieved more or less without any complication with one patient dismissing.The regular MRI examination indicated that the lesions had not reoccur and the cerebral ventricles had been normal.Conclusion:We identify the nourish arteries of the tumor and anatomy relationship between the tumor and its peripheral blood vessels through modern imaging devices,to select reasonable operative method are the premier therapy of pineal region meningioma.The back wall of the third ventricle becomes thin and the suprapineal recess develops shallow and wide,so the third ventricle-quadrigeminal cistern fistulation can effectively eliminate the obstructive hydrocephalus due to the long-term compression on the aqueduct after removing the tumor.

Delayed intra-tumoural haemorrhage in pineal germinoma: Case report and review

Intraparenchymal haemorrhage in a pineal germinoma is a very rare, though clinically significant event. We report the first case of a significantly delayed intraparenchymal haemorrhage in a pineal germinoma, 14 days after endoscopic third ventriculostomy (ETV), causing precipitous patient deterioration. We discuss potential contributing pathophysiological factors, and seek to illustrate that knowledge of its occurrence, and associated morbidity, is clinically significant in managing pineal germinoma patients with acute deterioration post obstructive hydrocephalus CSF diversion.

Night-time Rise in Rat Pineal N-Acetyltransferase due to Carbaryl Administration Is Reduced by Propranolol Treatment

The purpose of the present study was to examine the effects of administration of sublethal doses of carbaryl on nighttime rat pineal melatonin synthesis in the presence and absence of propranolol, a β-adrenergic receptor antagonist. Two groups of adult male albino rats were administered orally N-methyl-l-naphthylcarbamate (carbaryl) (8. 33mg/kg BW daily in corn oil) for six successive days; another two groups received corn oil only.On the last day of carbaryl treatment, half of the animals received an intraperitoneal injection of propranolol (20 mg/kg body weight, one hour before lights off). The other two groups were given a saline injection. Four hours after darkness onset, pineal N-acetyltransferase (NAT) and hydroxyindole-O-methyltransferase (HIOMT) activities as well as pineal concentrations of 5-hydroxytryptophan (5HTP), serotonin (5HT),5-hydroxyindole acetic acid (5HIAA) and pineal and serum melatonin levels were measured. Nocturnal NAT activity was increased due to carbaryl administration but the pesticide was ineffective in stimulating NAT activity in rats treated with propranolol.Pineal 5HT was decreased due to carbaryl administration but 5HTP and 5HIAA levels were unaffected. Pineal and serum melatonin levels were decreased due to propranolol treatment. The results indicate that carbaryl may influence pineal NAT activity by a mechanism that involves β-adrenergic neural transmission.