Behavioral Effects of Adrenal Medullary Transplants in Non-Human Primates

Behavioral Effects of Adrenal Medullary Transplants in Non-Human Primates Mark Dubach Department of Psychiatry and Behavioral Sciences and Regional Pmate Research Center University of Washington Seattle, Washington, USA SUMMARY INTRODUCTION Small multiple "ribbon" autografts of intact adrenal medulla stereotaxically implanted at several sites throughout the striatum in longtailed macaques (Macaca fascicularis) have been shown to contain large amounts of viable glandular tissue as long as eight weeks after transplantation /15/. Variations of technique clearly influence viability/12/. All monkeys were maintained in specially adapted rotometer cages /30/ so that 24-hour measurements of activity and directional bias could be gathered. Lesions induced by intracerebral injection of 6-hydroxydopamine in the substantia nigra produced the expected chronic decrease in percentage of contralateral turning in most of the 24 subjects. Animals that received the longest viable ribbon grafts showed a reversal of this effect back toward base line, whereas monkeys whose grafts left little or no surviving tissue showed no behavioral improvement. Rats with unilateral lesions created by intranigral injections of 6-hydroxydopamine (6OHDA) have commonly been used to assess behavioral effects of dopaminergic grafts, and rotation was the first behavior tested/4, 20/. It represents a global aspect of behavior, which can be measured simply and objectively. It is well established that after a few days, rodents usually rotate away from the side with the lesion when given apomorphine (attributed to ipsilateral receptor supersensitivity) and toward the side with the lesion when given amphetamine (attributed to contralateral transmitter release by intact neurons). For rodents, the rotometry model has been central to numerous studies of the phenomenology, pharmacology, and neuroanatomy of 6-OHDA effects/27/, and, for rodents, it has a well-established sensitivity to the effects of fetal nigral and adrenal medullary grafts/16/. For monkeys, this model is therefore a good starting point for examining the potential reversal of behavioral lesion effects by transplants. For non-human primates, the literature on dopamine (DA) lesions and rotometry is much more limited. Early studies indicated that 6OHDA can produce nigral lesions with behavioral effects in marmosets and baboons/9, 36/. More recent studies have tested the potential graft-induced reversal of rotational effects of unilateral lesions induced by unilateral intracarotid KEY WORDS transplantation, adrenal medulla, monkey, parkinsonism, neostriatum, substantia nigra, CNS grafting Reprint address: Mark Dubach Regional Primate Reseach Center University of Washington SJ-50 Seattle, WA 98195, USA VOL 3, NO. 2-3,199297 98 administration of N-methylphenyltetrahydropyridine (MPTP)/2, 3, 8, 26, 37/. In human hemiparkinsonian patients, spontaneous ipsilateral rotation has been documented /6/, and spontaneous turning preference, as a naturalistic, quantitative aspect of clinical behavior, could be expected to provide a good model for animal testing. Rodent and non-human primate studies of graft effects, however, have focused on the acute response to the DA agonists apomorphine and amphetamine, rather than on spontaneous turning preference. These agonist models have been thoroughly studied in rodents, and the time course of agonist effects is well known; the models are very practical for making a few tests before and after transplants in large numbers of subjects. In monkeys, however, no models have been thoroughly studied, large samples are not an option, and various transplant methods and striatal placements are still being tested. The intensive study of a small number of monkeys is required for the development of transplant techniques, but the fewer the subjects, the less convincing and statistically efficient are a small number of drug tests in each subject at various times before and after transplantation. Repeated agonist treatments, furthermore, either require repeated, stressful transfers to and from special recording cages and equipment, or rely on visual observation. The continuous measurement of spontaneous turning behavior in the home cage, on the other hand, permits the course of development of lesion and graft effects to be monitored in detail. A daily record constitutes a times series and enables the use of time series analysis for describing and testing the significance of graft effects in a single subject. For these reasons, continuous rotometry was selected as an initial behavioral model for the evaluation of transplants. Several alternative mechanisms have been proposed to account for the effects of various types of DA implant in rodents and monkeys. Transplants have been reported to reverse the effects of lesions in rodents by local release of eatecholamines from the grafts, either synaptically from fetal nigrai graft processes reinnervating host striatal tissue/17/or non-synaptically by shortrange diffusion from adrenal grafts/19/. A recent study has shown that an artificial implant of encapsulated DA, without any processes or synaptic contacts, is also capable of reversing lesion effects in rodents in the apomorphine rotometry model /38/. In monkeys, Watts et al. /37/ indicated that intraventricular adrenal autografts substantially reduced apomorphine-induced rotation over a survival period of several months, while unoperated controls showed no change over the same interval; recovery was greatest in monkeys with the largest numbers of surviving graft cells. Bankiewicz et al. /3/ reported that both adrenal allografts and control surgeries reduced apomorphine-induced rotation, due in part to a trophic effect on surviving host DA neurons; in two of three hemiparkinsonian monkeys that received fetal nigral grafts, apomorphine-induced circling was greatly reduced, an effect attributed again to a trophic effect encouraging the sprouting of host DA fibers, rather than to the direct release of catecholamines from the grafts/26/. The present study was designed to address issues of technique, effectiveness, and mechanism for adrenal grafts in monkeys, by using: (1) a less invasive transplant method to reduce the potential trophic effects of the open surgical procedure itself; (2) a more precise rotometry method to provide a full account of effects of lesion and transplant; (3) 24-h monitoring of spontaneous turning to eliminate interpretational problems associated with apomorphine and amphetamine testing; (4) time series analysis to allow each subject to be its own control; (5) behavioral evaluation of all animals studied; (6) quantitative comparison of three different measures extracted from the rotometry data to determine which is most sensitive to lesion and transplant effects. The focus on adrenal grafts was in part due to a view toward clinical use of autologous adrenal tissue which is less controversial than that of fetal donor t (...truncated)