Content uploaded by Neveen A. Noor
Author content
All content in this area was uploaded by Neveen A. Noor on Jun 23, 2016
Content may be subject to copyright.
African Journal of Pharmacy and Pharmacology Vol. 4(11), pp. 823-828, November 2010
Available online http://www.academicjournals.org/ajpp
ISSN 1996-0816 ©2010 Academic Journals
Full Length Research Paper
Anxiolytic action and safety of Kava: Effect on rat brain
acetylcholinesterase activity and some serum
biochemical parameters
Neveen A. Noor
Department of Zoology, Faculty of Science, Cairo University, Egypt. E-mail: Neveen.nour5@gmail.com.
Accepted 18 November 2010
Kava is a herbal anxiolytic drug. The present study investigates the response of central cholinergic
neurotransmission to kava treatment by measuring acetylcholinesterase (AChE) activity in cortex,
hippocampus and striatum of adult male rats. The present study demonstrates also the effect of chronic
use of kava on some liver and kidney function parameters in the sera of rats. Kava administration (75
mg/kg) induced an increase in AChE activity in the striatum after 1 week. However, significant
decreases in the enzyme activity were obtained after 4 weeks of treatment in the three brain areas
examined. No significant changes were observed in the enzyme activity on stopping kava
administration. Kava administration for 4 weeks resulted in significant decreases in serum aspartate
transaminase (AST) and alanine transaminase (ALT) activities and creatinine level, while alkaline
phosphatase activity and albumin level did not show any significant changes. However, total protein
and urea levels were increased significantly. In conclusion, the cholinergic system in the cortex,
hippocampus and striatum may play a vital role in the anxiolytic action of kava. The present study
showed no adverse effects of kava on liver and kidney function parameters.
Key words: Kava, acetylcholinesterase, cortex, hippocampus, striatum.
INTRODUCTION
Generalized anxiety disorder (GAD) is a prevalent and
impairing disorder, associated with extensive psychiatric
and medical comorbidity (Hidalgo et al., 2007). The use
of alternative therapies has increased substantially over
the last decade, particularly for more chronic conditions
such as anxiety (Conner et al., 2001). Kava is a herbal
anxiolytic drug (Garrett et al., 2003; Pittler and Ernst,
2003; Shinomiya et al., 2005). It is an intoxicating
beverage used by South Pacific Islanders and is
traditionally prepared as an aqueous extract of the root of
the kava plant (Piper methysticum). It has been used in
Europe and North America as a mild anxiolytic (Mathews
et al., 2005). It has been reported that the anxiolytic
effects of kava seem to be as powerful as those of
conventional anxiolytics (Lindenberg and Pitule-Schödel,
1990; Woelk et al., 1993; Boerner et al., 2003). Other
randomized controlled trials suggest that kava reduces
anxiety in perimenopausal women (Cagnacci et al.,
2003), facilitates cognitive function and increase positive
affectivity (Thompson et al., 2004), and improves sleep
quality (Emser and Bartylla, 1991). The physiological
activity of kava resides in pyrone- or hydropyrone-
containing components called kavalactones (Mathews et
al., 2005).
Acetylcholine (ACh) is a fundamental neurotransmitter
in the central nervous system (CNS), where it is critically
involved in functions related to cognition and behavior, in
some cases by modulating release of other neuro-
transmitters, including glutamate, GABA, norepinephrine
and dopamine (Kellar, 2006). There is evidence that
hippocampal cholinergic systems may be particularly
involved in the modulation of anxiety (File et al., 1998;
Smythe et al., 1998). It has been found that kava affects
the GABAergic (Jussofie et al., 1994), glutamatergic
(Gleitz et al., 1996), and dopaminergic (Baum et al.,
1998), transmission. However, to date, no studies have
examined the effect of kava on the cholinergic
transmission. In 2002, the German health authorities
banned kava extract containing products based on the
suspicion of a potential liver toxicity, as derived from
824 Afr. J. Pharm. Pharmacol.
adverse effect reports (Schmidt et al., 2002). These
reports of hepatotoxicity after centuries of apparently safe
use in the South Pacific may be attributed to differences
in the manner in which the commercial extract is
prepared (Witton et al., 2003; Mathews et al., 2005).
However, two drug monitoring studies had not found a
single case of kava induced hepatotoxicity (Teschke et
al., 2003). Other data suggest that kava does lead to an
increase in liver enzymes (Clough et al., 2003a, b).
Recently, a study of Sorrentino et al. (2006) does not
back the suspicion of potential liver toxicity.
To date, no studies have examined the relation
between kava anxiolytic effect and cholinergic system. In
addition, studies that carried out to investigate the effect
of kava, in treating anxiety, on liver functions have not
produced univocal results. Therefore, the main objective
of the present study was to investigate the response of
central cholinergic neurotransmission to kava treatment
as well as kava withdrawal by measuring
acetylcholinesterase (AChE) activity in the rat cortex,
hippocampus and striatum as a neurochemical marker for
cholinergic transmission. Another aspect of the present
study is to demonstrate the effect of chronic use of kava
on some liver and kidney function parameters in the sera
of adult male rats.
MATERIALS AND METHODS
Animals
The experimental animal used in this study was the adult male
albino rat (Rattus norvegicus). Animals used for determination of
AChE activity weighing 100-160 g and those used for determination
of biochemical parameters weighing 180-240 g. The animals were
obtained from a fixed local supplier. They were maintained on stock
diet and kept under fixed appropriate conditions of housing and
handling. All experiments were carried out in accordance with
research protocols established by the animal care committee of the
National Research Center, Egypt.
Drug
Highly purified Kava (Piper methysticum) extract was purchased
from October Pharma Co., Egypt. It was dissolved in saline solution
to make a suspension and administered to the animals orally by
using a gastric tube. The whole extract was used to resemble
extract administered by human traditionally or medically.
Experimental design
The animals were divided into 2 main groups. The 1st main group
of animals was served for determination of AChE activity. Animals
of this group were subdivided into 3 subgroups. Rats of the 1st
subgroup were administered a daily oral dose of kava extract (75
mg / kg body weight, (Sorrentino et al., 2006) for 1, 2 and 4 weeks.
The rats of the 2nd subgroup were served to study the withdrawal
effect of kava. The animals of this subgroup were administered
kava extract for 4 weeks then the drug administration was stopped
for 1 week. The animals of the 3rd subgroup were administered
saline solution at each of the tested time intervals which were
served as controls.
The 2nd group of animals was used for determination of the
biochemical parameters. Rats of this group were subdivided into 2
subgroups. Animals of the 1st subgroup were administered daily
dose of kava extract (75 mg / kg) for 4 weeks and animals of the
2nd subgroup were administered saline solution for 4 weeks and
were served as controls.
Handling of tissue samples
The animals used for the determination of AChE activity were killed
by sudden decapitation after being fasted overnight. The brain of
each animal was quickly removed and rapidly transferred to an ice-
cold Petri dish and dissected to obtain the cortex, hippocampus and
striatum (Zeman and Innes, 1963; Glowinski and Iversen, 1966).
Each brain area was weighed and frozen until analyzed. AChE
activity was measured, (Simpson et al., 1964) using acetylcholine
bromide as the enzyme substrate. AChBr and hydroxylamine were
from Sigma Co., and all other chemicals were of high quality and
purchased from commercial suppliers. Each brain area was
homogenized in 1 ml of 0.1 M phosphate buffer (pH 7.00) by using
a small chilled glass Teflon tissue grinder. Homogenates were
centrifuged at 10000 r.p.m. for 15 min. at 5ºC in a refrigerated
centrifuge (GS-6r, Beckman, USA). The deposits were discarded
and the supernatant used for enzyme activity determination which
carried out in 3-4 replicates, and the optical densities were
measured against blank at 540 nm, using a spectrophotometer
(Spectronic 1201, Milton Roy Co., USA).
The results were calculated by constructing a standard curve and
the enzyme activity was expressed as µmoles AChBr
hydrolyzed/min./gm tissue. Animals served for biochemical analysis
were euthanized and blood samples were collected in tubes and
centrifuged at 3000 r.p.m. for 10 min. to obtain clear sera.
Aminotransferase enzyme, AST and ALT activities; (Breuer, 1996)
alkaline phosphatase, ALP activity; (Moss, 1982) total protein;
(Young, 1995) albumin; (Doumas et al., 1971) urea; (Tabacco et al.,
1979) and creatinine (Glick et al., 1986) were determined by using
reagent kits.
Statistical analysis
Comparison between control and treated animals and the levels of
significance were determined by using Student's t-test. Percentage
difference representing the percent of variation in concentration
with respect to the control was calculated.
% difference = (treated mean – control mean/control mean) x 100.
RESULTS
The effect of daily oral administration of kava extract on
AChE activity in the cortex, hippocampus and striatum of
adult male rats are demonstrated in Table 1. In the
cortex, kava administration induced significant decreases
(P<0.05) in AChE activity after 2 and 4 weeks of treat-
ment. However, hippocampal AChE activity showed a
significant increase after 2 weeks followed by signi-ficant
decrease after 4 weeks of kava administration. In the
striatum, AChE activity showed early significant increase
after 1 week and delayed significant decrease after 4
weeks of treatment. However, no significant changes
were observed in the enzyme activity on stopping kava
Noor 825
Table 1. Effect of oral administration of kava extract (75 mg/kg) on AChE activity-AChBr hydrolyzed/min/gm tissue in the cortex,
hippocampus and striatum of adult male albino rats.
Brain area Time of treatment Saline control Treated P-value % difference
1 week 1.42±0.03(6) n.s. -1.39
2 weeks 1.35±0.02(6) * -6.25
4 weeks 1.34±0.02(6) * -6.94
Cortex
During withdrawal period
1.44±0.03 (10)
1.54±0.04(6) n.s. 6.94
1 week 1.38±0.08(7) n.s. -6.76
2 weeks 1.79±0.13(6) * 20.95
4 weeks 1.36±0.01(6) * -8.11
Hippocampus
During withdrawal period
1.48±0.05 (6)
1.44±0.07(6) n.s. -2.70
1 week 3.32±0.24(5) * 23.42
2 weeks 2.51±0.15(6) n.s. -6.69
4 weeks 2.35±0.11(6) * -12.64
Striatum
During withdrawal period
2.69±0.11(8)
2.89±0.08(6) n.s. 7.34
Values represent mean ± S.E.M with the number of animals between parentheses. n.s.: P>0.05 nonsignificant. *:P<0.05
significant versus saline control values. % difference represents a comparison between saline control and treated values.
Table 2. Effect of oral administration of kava extract (75 mg/kg) for 4 weeks on some serum biochemical parameters
of adult male albino rats.
Blood parameters Saline control Treated P-value % difference
AST (u/L) 179.67±7.65 (6) 156.00±3.17 (6) * -13.17
ALT (u/L) 45.83±1.33 (6) 35.00±0.76 (7) ** -23.63
ALP (u/L) 107.00±2.89 (6) 113.80±3.07 (6) n.s. 6.36
Total protein (g/dL) 6.45±0.08 (8) 6.79±0.09 (8) * 5.27
Albumin (g/dL) 3.15±0.07 (8) 3.08±0.06 (8) n.s. -2.22
Urea (mg/dL) 26.86±0.67 (7) 31.40±1.69 (6) * 16.90
Creatinine (mg/dL) 0.93±0.04 (9) 0.78±0.02 (9) ** -16.13
Values represent mean ± S.E.M with the number of animals between parentheses. n.s.: P>0.05 nonsignificant. *: P<0.05
significant versus saline control values. **: P<0.01 highly significant versus saline control values. % difference represents a
comparison between saline control and treated values.
administration.
Data concerning the effect of daily kava administration
for 4 weeks on some serum biochemical parameters of
adult male albino rats are shown in Table 2. Serum AST
and ALT activities showed significant and highly
significant (P<0.01) decreases after 4 weeks of daily
administration of kava extract, being -13.17 and -23.63%
below the control level, respectively. However, serum
ALP activity showed no significant change due to kava
administration. Serum total protein and urea levels
increased significantly after 4 weeks of drug treatment,
whereas, serum creatinine showed highly significant
decrease. Serum albumin level showed a nearly control-
like value.
DISCUSSION
ACh is known to be rapidly hydrolyzed by AChE. The
duration of action of Ach at the synaptic clefts is critically
dependent on AChE activity (Cooper et al., 2003). There
is evidence that hippocampal cholinergic systems may be
particularly involved in the modulation of anxiety.
Intrahippocampal infusions of cholinergic antagonists
increase anxiety (File et al., 1998; Smythe et al., 1998).
In addition, cholinergic agonists such as nicotine induced
anxiolytic effects under certain test conditions (Ouagazzal
et al., 1999) and reduced stress-induced anxiety in
humans (Pomerleau et al., 1984; Jarvik et al., 1989).
Furthermore, Degroot et al. (2001) found that infusions of
826 Afr. J. Pharm. Pharmacol.
physostigmine in the dorsal hippocampus decreased
anxiety as measured in plus-maze and shock-probe
tests. From the present data and the above mentioned
studies, it may be suggested that the observed decrease
in AChE activity after 4 weeks may mediate the anxiolytic
effect of kava extract through increasing the cholinergic
transmission in the brain areas under investigation.
Benzodiazepines are established anxiolytic drugs (for
example: midazolam; diazepam; triazolam). Olkkola and
Ahonen (2008) reported that the actions of
benzodiazepines are due to the potentiation of the neural
inhibition that is mediated by GABA. It is thought to act
mainly via the post synaptic GABAA receptor to
potentiate the action of GABA (Yamamoto et al., 2007).
Nicotinic ACh receptors (nACh Rs) exist on GABAergic
interneurons within the neocortex (Xiang et al., 1998;
Alkondon et al., 2000). Results of Yamamoto et al. (2007)
provided evidence that the nACh Rs on GABAergic
synaptic boutons within the neocortex do indeed interact
with midazolam, allowing the endogenous ACh to
increase the release of GABA. On the other hand,
Schetinger et al. (2000) showed that diazepam presented
an inhibitory effect on AChE activity in the cerebral cortex
of the adult rat. In light of the present data, the
potentiating effect of kava extract to GABAergic
transmission may be originally mediated by inhibition of
AChE activity, leading to increase of cholinergic
transmission that can affect nACh R on GABAergic
neurons to increase the release of GABA.
The present data also showed that the decrease in
AChE activity was delayed till after 4 weeks of kava
administration in the hippocampus and striatum,
whereas, the inhibitory effect of kava extract on AChE
activity in the cortex was observed after 2 weeks of kava
administration. Therefore, it could be suggested that the
cortex may be, more likely, the target area for early
anxiolytic effect of kava mediated mediated by cholinergic
transmission. As can be noticed from the present data,
stopping kava administration for 1 week after 4 weeks of
treatment revealed non-significant changes in the
enzyme activity in the three brain areas studied. In
clinical settings, kava has been associated with better
tolerability and lack of physiological dependence and
withdrawal (Connor et al., 2001; Geier and
Konstantinowicz, 2004). In addition, Bilia et al. (2002)
found that kava was well tolerated and non-addictive at
therapeutic dosage. Therefore, the present nonsignificant
change in AChE activity after stopping kava treatment for
one week may provide an additional evidence for the
reported safety of kava.
Although, kava extract shows a similar activity profile
as the benzodiazepines (Baum et al., 1998), and without
the side effects commonly seen with those drugs (Woelk
et al., 1993; Volz and Kieser, 1997), the sales of kava
extracts were either severely restricted or prohibited in
Europe due to reports of hepatotoxicity attributed to kava
consumption (Schmidt et al., 2002). Liver biopsy showed
hepatocellular necrosis consistent with chemical hepatitis
in a case with liver failure with a history of taking kava-
containing product for 4 months (Humberston et al.,
2003). More recently, the in vitro study of Lüde et al.
(2008) indicated that the kava extracts are toxic to liver
mitochondria leading to apoptosis of exposed cells. In
contrast, Connor et al. (2001) assessed safety para-
meters for kava. The data support the safety of kava in
treating anxiety at 280 mg kava lactones/day for 4 weeks.
In addition, in vivo study of Singh and Devkota (2003),
demonstrated that the aqueous kava extracts
administrated to rats at a daily dose of 200 or 500 mg
kavalactones/kg for 2 or 4 weeks did not affect AST, ALT,
alkaline phosphatase and lactate dehydrogenase in the
sera nor malondialdehyde in the liver homogenate and in
some cases they were significantly reduced. The authors
suggesting not only a lack of toxicity but potentially a
hepatoprotective effect of kava. Furthermore, in a study
sample comprising data from three controlled trials of
kava in generalized anxiety disorder, no changes in liver
function were found (Connor et al., 2006). As can be
noticed from the present study, daily kava administration
for 4 weeks resulted in significant decreases in serum
AST and ALT activities and creatinine level, while ALP
activity and albumin level did not show any significant
changes. However, total protein and urea levels were
increased significantly.
The present results support the previous findings
indicating the safety of kava to the liver (Sorrentino et al.,
2006; Lim et al., 2007). The increase in serum urea level,
in the present results, was expected due to the increase
in total protein level. Creatinine is a chemical waste
molecule that is generated from muscle metabolism. It is
transported through the blood stream to the kidneys,
where they filter most of the Creatinine and dispose it in
the urine. As the kidneys become impaired, the
Creatinine level in the blood will rise. Thus the mea-
surement of serum Creatinine level has been found to be
a fairly reliable indicator of kidney function. Therefore, the
concomitant highly significant decrease in Creatinine
level, in the present data, suggests that there may be no
adverse effect on kidney function.
In conclusion, the cholinergic system in the cortex,
hippocampus and striatum may play a vital role in the
anxiolytic action of kava which started after 2 weeks in
the cortex and delayed in the hippocampus and striatum
till 4 weeks of treatment. The present study showed no
adverse effects of kava on liver and kidney function
parameters. Hence, the use of kava in treating anxiety
may be preferred to the use of conventional anxiolytics
due to the lack of withdrawal and addictive properties.
Nevertheless, it is recommended to follow up the liver
and kidney functions in case of long term use of kava.
ACKNOWLEDGMENT
The author wish to express his gratitude and sincere
appreciation to Dr. Heba Salah El Din Aboul Ezz,
Associate Professor of Neurophysiology, Zoology
Department, Faculty of Science, Cairo University, for
revising the manuscript and her valuable advices.
REFERENCES
Alkondon M, Pereira EFR, Eisenberg HM, Albuquerque EX (2000).
Nicotinic receptor activation in human cerebral cortical interneurons:a
mechanism for inhibition and disinhibition of neuronal networks. J.
Neurosci., 20: 66-75.
Baum SS, Hill R, Rommelspacher H (1998). Effect of kava extract and
individual kavapyrones on neurotransmitter levels in the nucleus
accumbens of rats. Prog Neuropsychopharmacol. Biol. Psychiatr., 22:
1105-1120.
Bilia AR, Gallori S, Vincieri FF (2002). Kava-kava and anxiety: Growing
knowledge about the efficacy and safety. Life Sci. 70: 2581-2597.
Boerner RJ, Sommer H, Berger W, Kuhn U, Schmidt U, Mannel M
(2003). Kava-kava extract LI 150 is as effective as opipramol and
buspirone in generalized anxiety disorder - an 8-week randomized,
double-blind, multi-centre clinical trial in 129 out-patients.
Phytomedicine, 10: 38-49.
Breuer J (1996). Report on the symposium “drug effects in clinical
chemistry methods”. Eur. J. Clin. Chem. Clin. Biochem., 34: 385-386.
Cagnacci A, Arangino S, Renzi A, Zanni AL, Malmusi S, Volpe A
(2003). Kava-Kava administration reduces anxiety in perimenopausal
women. Maturitas, 44: 103-109.
Clough AR, Jacups SP, Wang Z (2003b). Health effects of kava use in
an eastern Arnhem Land community. Inter. Med. J., 33: 336-340.
Clough AR, Baillie RS, Currie B (2003a). Liver function test
abnormalities in users of aqueous kava extracts. J. Toxicol. Clin.
Toxicol., 41: 821-829.
Connor KM, Davidson JR, Churchill LE (2001). Adverse-effect profile of
kava. CNS Spectr., 848: 850-853.
Connor KM, Payne V, Davidson JRT (2006). Kava in generalized
anxiety disorder: three placebo-controlled trials.
Psychopharmacology, 21: 249-253.
Cooper JR, Bloom FE, Roth, RH (2003). “Acetylcholine, The
Biochemical Basis of Neuropharmacology”. Oxford University Press,
New York, pp. 151-170.
Degroot A, Kashluba S, Treit D (2001). Septal GABAergic and
hippocampal cholinergic systems modulate anxiety in the plus-maze
and shock-probe tests. Pharmacol. Biochem. Behav., 69: 391-399.
Doumas BT, Watson WA, Biggs HG (1971). Albumin standard and the
measurement of serum albumin with bromocresol green. Clinica
Chemica Acta, 31: 87-96.
Emser W, Bartylla K (1991). Verbesserung der schlafqualität. Zur
wirkung von kava-extract WS 1490 auf das schlafmuster bei
gesunden. TW Neurol. Psychiatr., 5: 636-642.
File SE, Gonzales LE, Andrews N (1998). Endogenous acetylcholine in
the dorsal hippocampus reduces anxiety through actions on nicotinic
and muscarinic receptors. Behav. Neurosci., 112: 352-359.
Garrett KM, Basmadjian G, Khan IA, Schaneberg BT, Seale TW (2003).
Extracts of kava (Piper methysticum) induce acute anxiolytic-like
behavioral changes in mice. Psychopharmacology (Berl). 170: 33-41.
Geier FP, Konstantinowicz T (2004). Kava treatment in patients with
anxiety. Phytother. Res., 18: 297-300.
Gleitz J, Friese J, Beile A, Ameri A, Peters T (1996). Anticonvulsive
action of (+/-)-kavain estimated from its properties on stimulated
synaptosomes and Na+ channel receptor sites. Eur. J. Pharmacol.,
315: 89-97.
Glick MR, Ryder KW, Jackson SA (1986). Graphical comparisons of
interferences in clinical chemistry instrumentation. Clin. Chem., 32:
470-474.
Glowinski J, Iversen LL (1966). Regional studies of catecholamines in
the rat brain. I. The disposition of [3H] norepinephrine, [3H] dopamine
and [3H] DOPA in various regions of the brain. J. Neurochem., 13:
655-669.
Hidalgo RB, Tupler LA, Davidson JR (2007). An effect-size analysis of
pharmacologic treatments for generalized anxiety disorder. J.
Psychopharmacol., 21: 864-872.
Noor 827
Humberston CL, Akhtar J, Krenzelok EP (2003). Acute hepatitis induced
by kava kava. J. Toxicol. Clin. Toxicol., 41: 109-113.
Jarvik ME, Caskey NH, Rose JE, Herskovic JE, Sadeghpour M (1989).
Anxiolytic effects of smoking associated with four stressors. Addict.
Behav., 14: 379-386.
Jussofie A, Schmitz A, Hiemke C (1994). Kavapyrone enriched extract
from Piper methysticum as modulator of the GABA binding site in
different regions of rat brain. Psychopharmacology (Berl), 116: 469-
474.
Kellar KJ (2006). Overcoming inhibitions. Proc. Nat. Acad. Sci., 103:
13263-13264.
Lim STS, Dragull K, Tang CS, Bittenbender HC, Efird JT, Nerurkar PV
(2007). Effects of kava alkaloid, pipermethystine, and kavalactones
on oxidative stress and cytochrome P450 in F-344 rats. Toxicol. Sci.
97: 214-221.
Lindenberg D, Pitule-Schödel H (1990). D, L-Kavain im vergleich zu
oxazepam bei angstzuständen. Fortschr Med., 108: 49-50.
Lüde S, Török M, Dieterle S, Jäggi R, Büter KB, Krähenbühl S (2008).
Hepatocellular toxicity of kava leaf and root extracts. Phytomedicine,
15: 120-131.
Mathews JM, Etheridge AS, Valentine JL, Black SR, Coleman DP, Patel
P, So J, Burka LT (2005). Pharmacokinetics and disposition of the
kavalactone kawain: interaction with kava extract and kavalactones in
vivo and in vitro. Drug Metabol. Dispos., 33: 1555-1563.
Moss DW (1982). Alkaline phosphatase isoenzymes. Clin. Chem., 28:
2007 -2016.
Olkkola KT, Ahonen J (2008). Midazolam and other benzodiazepines.
Handb. Exp. Pharmacol., 182: 335-360.
Ouagazzal AM, Kenny PJ, File SE (1999). Modulation of behavior on
trials 1 and 2 in the elevated plus-maze test of anxiety after systemic
and hippocampal administration of nicotine. Psychopharmacology,
144: 54-60.
Pittler MH, Ernst E (2003). Kava extract for treating anxiety. The
Cochrane Database of Systemic Review. Article no. CD003383.
Pomerleau OF, Turk DC, Fertig JB (1984). The effects of cigarette
smoking on pain and anxiety. Addict. Behav., 9: 265-271.
Schetinger MRC, Porto NM, Moretto MB (2000). New benzodiazepines
alter acetylcholinesterase and ATPase activities. Neurochem. Res.,
25: 949-955.
Schmidt M, Nahrstedt A, Lüpke NP (2002). Piper methysticum (Kava) in
der Diskussion: Betrachtungen zu Qualität, Wirksamkeit und
Unbedenklichkeit. Wien. Med. Wochenschr., 152: 382-388.
Shinomiya K, Inoue T, Utsu Y, Tokunaga S, Masuoka T, Ohmori A,
Kamei C (2005) The sleep- wake cycle in sleep- disturbed rats.
Psychophamacology (Berl). 180: 564-569.
Simpson DR, Bull DL, Lndquist DA (1964). Asemimicrotechnique for the
estimation of cholinesterase activity in Boll weevils. Ann. Ent. Soc.
Am., 57: 367-371.
Singh YN, Devkota AK (2003). Aqueous kava extracts do not affect liver
function tests in rats. Planta Medica, 69: 496-499.
Smythe JW, Murphy D, Bhatnagar S, Timothy C, Costall B (1998). The
effects of intrahippocampal scopolamine infusions on anxiety in rats
as measured by the black-white box test. Brain Res. Bull., 45: 89-93.
Sorrentino L, Capasso A, Schmidt M (2006). Safety of ethanolic kava
extract: Results of a study of chronic toxicity in rats. Phytomidicine.
13: 542-549.
Tabacco A, Meiattini F, Moda E, Tarli P (1979). Simplified
enzymic/colorimetric serum urea nitrogen determination. Clin. Chem.,
25: 336-337.
Teschke R, Gaus W, Loew D (2003). Kava extracts: safety and risks
including rare hepatotoxicity. Phytomedicine, 10: 440-446.
Thompson R, Ruch W, Hasenöhrl RU (2004). Enhanced cognitive
performance and cheerful mood by standardized extracts of Piper
methysticum (kava-kava). Hum. Psychopharmacol., 19: 243-250.
Volz HP, Kieser M (1997). Kava-kava extract WS 1490 versus placebo
in anxiety disorders – a randomized placebo-controlled 25-week
outpatient trial. Pharmacopsychiatry, 30: 1-5.
Witton PA, Lau A, Salisbury A, Whitehouse J, Evans CS (2003). Kava
lactones and the kava-kava controversy. Phytochemistry, 64: 673-
679.
Woelk H, Kapoula O, Lehrl S, Schröter K, Weinholz P (1993).
Treatment of patients suffering from anxiety - double-blind study:
828 Afr. J. Pharm. Pharmacol.
Kava special extract versus benzodiazepine. Z Allgemeinmed, 69: 271-
277.
Xiang Z, Huguenard JR, Prince DA (1998). Cholinergic switching within
neocortical inhibitory networks. Science, 281: 985-988.
Yamamoto S, Yamada J, Ueno S, Kubota H, Furukawa T, Yamamoto S,
Fukuda A (2007). Insertion of 7 Nicotinic receptors at neocortical
layer V GABAergic synapses is induced by a benzodiazepine,
midazolam. Cereb. Cortex, 17: 653-660.
Young DS (1995). Effects of drugs on Clinical Lab. Tests, 4th ed. AACC
Press.
Zeman W, Innes JRM (1963). Graigie’s Neuroanatomy of The Rat.,
Academic Press, New York.
