120 Section 2/ Drugs Acting on CNSPSYCHOSTIMULANTSAmphetamines (dexamphetamine, meth-
amphetamine etc.) are central sympathomi-
metics. These are drugs of abuse and re-
peated use can cause long lasting
behavioural abnormalities and can precipi-
tate psychosis. The detail is discussed in
chapter ‘Adrenergic drugs’.
Methylphenidate is chemically and
pharmacologically similar to amphetamine.
Both act by releasing norepinephrine and
dopamine in brain. Both produce increased
mental activity with little action on central
and peripheral functions. It is well absorbed
orally, metabolized and excreted in urine.
CONVULSANTSStrychnine (alkaloid obtained from the
seeds of Strychnos nux vomica) was used
earlier due to its convulsant properties. It
acts by blocking the postsynaptic inhibition
produced by inhibitory transmitter glycine.
It acts at Renshaw cell-motor neurone
junction in spinal cord through which
inhibition of antagonistic muscles is
achieved. Picrotoxin (obtained from fish
berries) is a potent convulsant. It acts by
blocking presynaptic inhibition mediated
through GABA by preventing Cl– channel
opening. It is not used now-a-days.
Bicuculline is a synthetic convulsant and
possessing picrotoxin like action.
Pentylenetetrazol is a CNS stimulant, acting
by direct depolarization of central neurons.
But none of these compounds are now
used therapeutically and used in laborato-
ries only as a research tool.
CEREBROACTIVE DRUGSIn this category, some of the compounds are
used in the treatment of dementia and other
related cerebral disorders.PYRITINOL
It enhances cholinergic transmission and
improves cerebral microcirculation in
ischemic regions. It protects the neurons
against hypoxia & disturbance of glucose
metabolism.
Adverse effects include anorexia,
epigastric distress, vomiting, fatigue,
headache, sleep disturbances, skin rash,
pruritus and increased excitement.
It is indicated in organic brain
syndrome, intellectual impairment of
senility, encephalitis, alcohol with-
drawal state and perinatal distress,
cerebrovascular accidents, and or-
ganic psychosyndrome.PIRACETAM
It improves the functioning of the brain
involved in cognitive processes e.g.
memory, thought, learning in normal and
in subnormal conditions. It is categorized as
nootropic agent (cognition enhancers).
The beneficial effects are due to im-
proved microcirculation, promotes the me-
tabolism and modulates neurotransmission.
Adverse effects include nausea,
epigastric distress and skin rash.
It is indicated in mental retardation and
learning problems in children, confusional
state in old age, cerebrovascular accidents,