Dynamical entropy is conserved during cocaine-induced changes in fetal rat motor patterns.
Our previous studies demonstrated that the intra-cisternal (IC) administration of cocaine to fetal rats increased motor activity and decreased responsiveness to perioral stimulation. One explanation for these observations comes from the behavioral pharmacology of stimulant drugs: increased motor activity is often associated with a decrease in its variety. Previous power spectral transformation of this data suggests an alternative explanation: cocaine-induced hyperactivity fixates a new behavioral pattern with complexity equal to that of saline controls. We explore these possibilities using statistical techniques derived from studies of nonlinear dynamical systems, examining patterns of the total motor activity of the individual fetus as counts per 5 s interval on either gestational day E20 or E21 for 20 min following IC injections of saline, 2.5 or 10 mg/kg of cocaine. The results are consistent with a state in which increased spontaneous activity is associated with the emergence of a new dynamical pattern which conserves entropy and provides experimental support for a fundamental conservation-variational relation, hT approximately equal to lambda 1 x DR, that has been proven for abstract models of chaotic dynamical systems. A multivariate analysis of variance (MANOVA) followed by appropriate analyses of variance (ANOVAs) and pairwise comparisons revealed that, whereas cocaine induced increases in the total amount of motor activity, the rate of increase in the variety of new sequences in activity counts over time did not change with treatment and age conditions. This invariant is quantified by an absence of change in topological entropy, delta hT = 0. The analyses also showed that, in order to maintain hT values, compensatory changes took place in the leading Lyapounov characteristic exponent, lambda 1 (the distance between sequential values 'stretched' along the increasing amplitudes of the variations) such that delta lambda 1 > 0, and the correlation dimension, DR (the hierarchical range of possible values, 'complicated clustering') was reduced, so that delta DR < 0. Our findings are consistent with the idea that the association between cocaine-induced increases in activity and decreases in adaptive response are not due to the dynamical entropy loss of decreased behavioral variety, but are rather the result of competitive interference by a drug-induced, equally complex, new pattern of spontaneous behavior.
Smotherman
W P
WP
Department of Psychology, Binghamton University, NY 13902-6000, USA.
Selz
K A
KA
Mandell
A J
AJ
D000818:Animals; D003042:Cocaine / Q000633:toxicity*; D004305:Dose-Response Relationship, Drug; D019277:Entropy; D005260:Female; D005324:Fetal Movement / Q000187:drug effects*; D008297:Male; D009294:Narcotics / Q000633:toxicity*; D017711:Nonlinear Dynamics; D011247:Pregnancy; D011297:Prenatal Exposure Delayed Effects; D051381:Rats; D017207:Rats, Sprague-Dawley
D009294:Narcotics; D003042:Cocaine