Can neuroleptics influence the function of the brain hemispheres asymmetrically?

Directed drug distribution: adding controlled brain activity to a drug

Environmental factors can alter the state of an organism so as to influence the response to drugs. This fact is widely recognized even though the responsible mechanisms are difficult to understand and control. The capacity of environmental influences to alter local drug pharmacokinetics is rarely considered. Drug localization and resulting action within the brain are influenced by vascular blood flow factors, local concentration differences in competing neurohumours, and receptor density. These are all frequently asymmetrically represented in the brain and drug effects are correspondingly laterality dependent. Attention to regional brain pharmacokinetics and the influence of environment on regional blood flow, local neurohumor concentration, and receptor density represents an untapped opportunity to enhance the desired effect of a centrally active drug at its site of action without enhancing general systemic toxicity. Combined pharmacotherapy and psychotherapy may result in superior therapeutic responses. Psychotherapy is a potential tool deliberately to manipulate environmental factors that influence physiological and physical chemical parameters that determine drug disposition.

Unilateral cerebral drug administration: pharmacokinetics of haloperidol and amphetamine

Following cannulation of the right common carotid artery of female Sprague-Dawley rats, 3 microCi (10 micrograms) of either [3H]haloperidol or [3H]amphetamine were infused. At various time intervals, drug concentrations were determined in the right and left striata, anterior forebrains, posterior forebrains and cerebella. One minute following unilateral intracarotid infusion of haloperidol, approximately a 90-100-fold right/left (ipsilateral/contralateral) difference in drug concentrations was attained in the striatum and the posterior forebrain, while more than a 75-fold difference was evident in the anterior forebrain. One minute following amphetamine infusion, a difference greater than 40-fold was seen in all forebrain structures. The right-left differences steadily declined with time as a result of the declining drug concentrations of the infused hemisphere. The pharmacokinetic parameters of both the distribution and elimination phases were similar in each forebrain region for both haloperidol and amphetamine. The kinetic parameters did, however, show specific drug differences. Bilateral drug concentrations in the striatum following intraperitoneal administration of amphetamine to unilaterally cannulated rats were nearly identical. Therefore, the cannulation procedure did not significantly alter the blood supply to either hemisphere. This is the first study to quantify drug concentrations and to analyze pharmacokinetic parameters following unilateral cerebral drug administration in conscious animals. This technique should be useful in studying functional and biochemical interhemispheric relationships as well as lateralized behaviors.

The influence of testosterone on the sex-dependent structural asymmetry of the medial habenular nucleus in the chicken

The volume of the left and right medial habenular nuclei of male and female chicks was analysed for evidence of structural asymmetry. The influence of exogenous testosterone on habenular asymmetry was also examined. Male and female chickens were injected intramuscularly with either testosterone enanthate or an oil vehicle on day 2 (15 animals per group) and were perfused at days 5, 12, and 19 respectively. Paraffin sections (8 microns) containing the medial habenular nucleus were stained with cresyl violet and both left and right medial habenular nuclei were measured by planimetry. In control chicks, males had structural asymmetry at day 12, whereas females did not show any structural asymmetry. Testosterone did not appear to influence asymmetry in the male chick but induced structural asymmetry at all three ages in the female to favour the right hemisphere. This study demonstrates a role for testosterone in influencing structural asymmetry of a nucleus in the vertebrate brain.