U n i v e r s i d a d d e B a r c e l o n a

Departamento de Personalidad, Evaluación y Tratamientos Psicológicos

Cursos asistidos por ordenador a través de i n t e r n e t
jgutierrez@psi.ub.es


 

Modelos animales de la esquizofrenia
Fuente: Biological Bases of Behavior (http://salmon.psy.plym.ac.uk/year1/bbb97.htm)


 

Effect of amphetamine on unconditioned behaviours

Effect of amphetamine on unconditioned behaviours An animal model of schizophrenia has been developed.
This involves injecting animals, usually rats, with amphetamine.
The drug produces an increase in locomotion and an increase in so-called stereotyped behaviour.
A behaviour is said to be stereotyped when it is is repeated in an apparently meaningless fashion.
The cardinal features of stereotypy:
  • repetition of the behaviour
  • the invariance of the repetition i.e. the behaviour is the same each time it is emitted
  • the apparent purposeless nature of the behaviour

are exemplifed by this cat !

locomotion can be repetitive


I also believe that locomotion can be repetitive,but that debate must wait until Year 2 of the course!

The next picture shows the effect of increasing doses of amphetamine on unconditioned (and conditioned) behaviours. Note how as the dose of amphetamine is increased the nature of the unconditioned behaviour changes. For example at 3mg/kg amphetamine rats engage in a lot of rearing and locomotion, whereas above 5mg/kg of the drug, gnawing, biting, sniffing, licking and rythmic head movements are the main behaviours.


effect of increasing doses of amphetamine on unconditioned (and conditioned) behaviours

Measuring amphetamine induced stereotypy

We can further illustrate the meaning of this figure by setting up an imaginary experiment in which dogs are injected with increasing doses of amphetamine (of course it would be very difficult to justify this type of experiment on dogs). We will examine three behaviours:

  • walking
  • tail-wagging and
  • ear-flapping

The results are discussed below this figure.

Dog behaviour Intensity / frequency of behaviour Equivalent
rat behaviour
Tail wagging medium fast fast slow absent Rearing
  an imaginary experiment  
Walking slow medium fast fast absent Conditioned
responding
   
Ear flapping absent absent absent slow fast Sniffing
& licking
   
Drug dose Control 1.0 mg/kg 3.0 mg/kg 5.0 mg/kg 10.0 mg/kg  

Notice that as we increase drug dose, the intensity of these behaviours change. As we increase dose the intensity / frequency of all the behaviours tends to increase. But importantly the rate of increase varies between the behaviours.

For example tail-wagging is seen at a medium rate even under saline (control) conditions, this behaviour increases after a low dose of amphetamine (1.0 mg/kg), but declines with higher doses of the drug and is totally absent under the highest dose (10.0 mg/kg). This pattern of change is similar to the changes seen in the rats' rearing behaviour under increasing doses of amphetamine.

In contrast walking is slow under control conditions, is fastest under intermediate doses of the drug ( 3-5.0 mg/kg), but slows down under the highest dose. This is similar to the effect of increasing doses of amphetamine on rats' rearing behaviour.

Finally, ear-flapping is absent under low doses of amphetamine, but is emitted at a high rate under the highest doses (5-10.0 mg/kg) of the drug. Thus ear-flapping resembles sniffing and licking behaviour in the rats.

 

Effect of pimozide on amphetamine-induced locomotion & stereotypy

The next diagram shows the effects of pimozide (a classic antipsychotic) on locomotion and stereotypy produced by increasing doses of amphetamine. Note that pimozide

  • reduces amphetamine-induced locomotion and
  • reduces amphetamine-induced stereotyped behaviours

These results are consistent with the hypothesis that reduction of amphetamine-induced behaviours is an indication of a drug's antipsychotic potential


pimozide reduces amphetamine-induced locomotion

pimozide reduces amphetamine-induced stereotyped behaviours

 

Effect of clozapine on amphetamine-induced locomotion & stereotypy

The next diagram shows the effects of clozapine ( an atypical antipsychotic) on locomotion and stereotypy produced by increasing doses of amphetamine. Note that clozapine

  • reduces amphetamine-induced locomotion but
  • enhances amphetamine-induced stereotyped behaviours

These results are NOT consistent with the hypothesis that reduction of amphetamine-induced behaviours is an indication of a drug's antipsychotic potential


clozapine reduces amphetamine-induced locomotion

 clozapine enhances amphetamine-induced stereotyped behaviours