SOME NEUROPHARMACOLOGICAL STUDIES ON THE STEM BARK OF RANDIA NILOTICA STAPF. (RUBIACEAE)
SOME NEUROPHARMACOLOGICAL STUDIES ON THE STEM BARK OF RANDIA NILOTICA STAPF. (RUBIACEAE)
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Date
2007-11
Authors
MOHAMMED, Danjuma Nuhu
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Abstract
The commonest practical use of behavioural tests is probably in the search for new drugs.
Medicinal plants have been used in the development of new drugs and continue to play an
invaluable role in the drug discovery process. These plants/herbs are relatively cheap and
available and their use depends on ancestral experience. The majority of the population in
developing countries remain dependent on them for healthcare. Randia nilotica stapf is a
lowland shrub or tree widespread in the Sudan and reported from lowland habitats in Central
and East Africa as well as Cameroon and Nigeria. In ethnomedicine, a decoction is used
orally for treatment of mental breakdown and for convulsions. It is also used against epilepsy
and madness. The main objective of this project is to establish scientific basis for the use of
Randia nilotica in traditional medicine for the treatment of neurodegenerative and
neuropsychiatric illnesses. It also seeks to determine active chemical constituents of Randia
nilotica as well as its acute toxicity profile.
The test systems employed for primary screening of Randia nilotica included Lorke method
(1983) of acute toxicity determination, diazepam induced sleep, hole board test,
pentobarbitone induced sleep, performance on treadmills (rota rod), mouse beam walk assay
and amphetamine induced stereotype behaviour test. Others were electroshock induced
convulsion test, pentylenetetrazole induced convulsion test, strychnine induced convulsion
test as well as forced swim test in rats and tail suspension test in mice. In addition, electroencephalographic
studies in rats was conducted. In these experiments, rats (180-250g), Swiss
albino mice (18 –25g) and black ranger cockerels (1 day old) were used where appropriate.
The diazepam induced sleep method was used to elucidate the more potent central nervous
system active morphological parts of Randia nilotica (leaf, stem bark, root bark) as well as its
fractions (saponins, flavonoids, aqueous butanolic residue) and sub-fractions (SF1-SF5). Data
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generated was analysed using t-test and significant difference determined using one-way
analysis of variance (ANOVA) followed by Dunnet‟s and Scheffe‟s post hoc tests. Results
were expressed as mean standard error of the mean (SEM). Values that are <0.05 were
considered significant.
Results of studies carried out revealed high potency for stem bark extract compared to leaf or
root bark extracts. This is evident in the increase in duration of sleep as observed in
diazepam sleep test which was significant (p < 0.001). It increased from 38.25.78 min.
(Normal Saline) to 165.822.9 min. (stem bark), 113.512.8min. (leaf) and 6413.0min.
(root bark). Moreover, the activity of the stem bark was observed at 20mg/kg dose compared
to 200mg/kg (10 times higher) for the leaf extract. Similarly, the saponin fraction exhibited
higher potency compared to flavonoid or aq. butanolic residue of the stem bark extract.
Sleeping time was increased significantly (p < 0.05) compared with normal saline i.e from
38.26min to 11720.8min. The flavonoid and water fractions also showed significant
increases (p < 0.005) in sleeping time to 68.611min and 77.010.0min. respectively
compared to normal saline. These increases in sleep duration were observed with the extracts
at 20mg/kg (flavonoid, water fraction) and 2mg/kg (saponin fraction). This indicated that the
saponin fraction is ten times more potent than either flavonoid or aqueous fractions. SF1
showed least decrease in onset and highest increase in sleep duration followed by SF4 and
then SF2. The LD50 values determined by intraperitoneal administration in mice for stem
bark, root bark and leaf extracts were 282.2mg/kg, 282.2mg/kg and 2154.1mg/kg
respectively. Those of the saponin, flavonoid, aqueous fraction were 11.1mg/kg, 471.2mg/kg
and 471.2mg/kg respectively.
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In the hole board experiment, the hydroalcoholic stem bark extract showed a dose dependent
decrease in number of head dips which was significant (p < 0.05) at 20mg/kg body weight
from 7.72.5 mean number of head dips (normal saline) to 1.30.8. Similarly, the saponin
fraction showed a significant (p < 0.05) dose dependent decrease in mean number of head
dips in this experiment from 7.72.5 (normal saline) to 2.00.6 (5mg/kg), 1.20.4
(1.0mg/kg), 0.30.0 (2.0mg/kg) and 2.21.7 (Diazepam, 1mg/kg).
The stem bark extract did not produce any significant observable effect on motor
coordination as determined in the rota rod test. Similarly, its saponin fraction did not produce
any observable effect on motor coordination using the rota rod test.
In the Beam walk assay, significant difference (p<0.001) was observed in mean number of
foot slips between stem bark extracts of Randia nilotica (5, 10, 20mg/kg body weight),
normal saline and Diazepam (control, 1.5mg/kg). The least number of foot slips was observed
with normal saline (0.40.2) which subsequently increased in diazepam treated mice
(10.81.9). Diazepam also showed a significant (p <0.001) increase in number of foot slips
compared to normal saline and extracts at 0.5, 1.0 and 2.0mg/kg (1.40.6, 1.80.7, 1.40.7
respectively). No difference was however observed in time to reach goal box between
controls and extracts at all doses tested.
A biphasic effect was observed with stem bark extracts of Randia nilotica (5, 10, 20mg/kg)
on amphetamine-induced stereotyped behaviour in mice. There was a significant (p<0.001)
reduction in jumping/climbing episodes produced by the extract from 937.022.3 (normal
saline) to 103.231.2 (5mg/kg), 33.011.7 (10mg/kg), 69.813.8 (20mg/kg) and 13.05.0
(Chlorpromazine, 2mg/kg). Reduction in sniffing was also observed with extract at 5mg/kg
(83.418.6), which is significant (p<0.05) compared with normal saline (1308.813.2).
Higher doses paradoxically produced increases rather than decreases in sniffing. The extract
(20mg/kg) attenuated mean count in limb licking from 201.815.5 (Normal Saline) to
55.619.5. Lower doses produced increases in limb licking.
The results of the anticunvulsant tests were also mixed. In the maximal electroshock test. The
stem bark extract of Randia nilotica protected chicks against hind limb tonic extension
(HLTE) by 90% at 20mg/kg comparable to phenobarbitone (PBT) with 90% protection as
well. Both 5mg/kg and 10mg/kg produced a 50% inhibition. The saponin fraction on the
other hand, protected mice against HLTE by 50% at 2mg/kg body weight. 0.5 and 1.0mg/kg
of the saponins showed only a 20% inhibition compared with PBT (20mg/kg) which sowed
80% protection. On the other hand, the stem bark and saponin extracts did not show any
effect on pentylenetetrazole (sc-PTZ) induced and strychnine induced seizure tests in mice.
However, the mean number of myoclonic body twitches was significantly (p<0.05) reduced
by the stem bark extract in the sc-PTZ induced seizure test. 5mg/kg produced a 161%
reduction while 10 and 20mg/kg produced 250% and 265% reduction respectively.
In the tail suspension test in mice, the HA stem bark extract of Randia nilotica showed no
effect on duration of immobility time in mice at the doses tested. But some dose dependent
decrease in immobility time was observed in the forced swim test in rats. The reduction was
however not significant when compared to control. The saponins on the other hand showed a
significant (p<0.05) decrease in immobility time at 2.5mg/kg (82.4 7.9) and 10mg/kg
(80.020.7) compared with normal saline (108.624.2).
Desynchronisation in the rat electroencephalograph (EEG) of the hyperstriatum (HS), optic
tectum (OT) and pontine reticular formation (RF) was observed with the stem bark extract at
20mg/kg and 40mg/kg. A slight increase in muscle activity was also observed. At 80mg/kg
however, there was synchronisation of HS, RF and OT while a reduction in
electromyographic (EMG) activity was observed. The saponin fraction of Randia nilotica
(2.5mg/kg) slightly synchronized EEG of the HS, OT and RF but with weak activation in
EMG of the rat. At 5mg/kg and 10mg/kg body weight, synchronization of the HS, RF and OT
was observed as well as a decrease in EMG activity throughout the period of observation.
These results suggested significant sedative effects of the stem bark extract of Randia
nilotica, its saponin fraction and subfraction (SF1). This may lend some scientific support for
the uses of the plant in traditional medicinal practice in the treatment of neuropsychiatric and
neurological diseases. It may also be suggested that the extracts are relatively safe at the dose
levels tested. It can be concluded therefore that Randia nilotica merits further attention in the
search for a new compound against neurodegenerative and neuropsychiatric disorders.
Description
A DISSERTATION SUBMITTED TO THE POSTGRADUATE SCHOOL
AHMADU BELLO UNIVERSITY IN PARTIAL FULFILLMENT OF
THE REQUIRMENTS FOR THE AWARD OF DOCTOR OF
PHILOSOPHY IN PHARMACOLOGY
DEPARTMENT OF PHARMACOLOGY AND CLINICAL PHARMACY,
FACULTY OF MEDICINE,
AHMADU BELLO UNIVERSITY,
ZARIA, NIGERIA
Keywords
NEUROPHARMACOLOGICAL STUDIES,, STEM BARK,, RANDIA NILOTICA STAPF,, (RUBIACEAE).