Stereotyped behavior induced by apomorphine is thought to be “autistic”, that is, impervious to environmental influence. This assumption is tested by analyzing the patterning of pecks at two differently colored stimuli in three-day old chicks treated with either 0.3 mg-kg−1 or 0.4 mg-kg−1 apomorphine. While normal chicks strongly prefer one stimulus over the other, apomorphine appears to render the choice behavior of chicks insensitive to differences between the stimuli. This result might suggest that apomorphine-treated chicks no longer perceive differences between the stimuli, but an analysis of the timing of pecks reveals that differences are still perceived since the two stimuli elicit different rates of pecking.

Apomorphine: Effects on the timing and sequencing of pecking behavior in chicks

The stereotyped behaviour was analysed in Mastomys natalensis, a species of desert rat recently introduced in laboratory practice. The components of stereotyped behaviour were similar to rat characterised by repetitive sniffing, rearing, licking, head movements and biting. Apomorphine (0.5–2.0 mg/kg), amphetamine (2.5–10 mg/kg), methylphenidate (10 – 30 mg/kg) and adamantanamine (10 – 50 mg/kg) administered intraperitoneally, induced stereotyped behaviour in dose-dependent manner. Positive response was also obtained by other drugs acting on dopamine receptors like 1-dopa, GBR 12909, piribedil, tyramine, BS 9648, BS 9641 and BS 8824. Yohimbine (2 mg/kg) failed to produce any response. Apomorphine (2 mg/kg), amphetamine (10 mg/kg), methylphenidate (30 mg/kg) and piribedil (12 mg/kg) induced stereotypy which could be blocked by dopamine receptor blockers haloperidol (1 mg/kg) or pimozide (1 mg/kg) but yohimbine (2 mg/kg) an alpha adrenoceptor blocker was ineffective. Adamantanamine, piribedil and GBR 12909 enhanced the stereotypy induced by low doses of apomorphine, amphetamine and methylphenidate. The data shows that the stereotyped behaviour in Mastomys natalensis is mediated through dopaminergic mechanisms. It appears that both excitatory and inhibitory types of dopamine receptors are involved.

An analysis of stereotyped behaviour in Mastomys natalensis

Apomorphine-induced pecking in pigeons was first reported by Amsler (1923), who also reported that removal of corpora striata could prevent it. Detailed observations on apomorphine-induced pecking were published independently and simultaneously by Burkmann (1960) and Dhawan and Saxena (1960).

G. K. Patnaik

Papers

Evidence for non-dopaminergic nature of apomorphine-induced pecking in pigeons