Complex regional pain syndrome.

Reflex sympathetic dystrophy is a complex progressive and potentially devastating condition generally affecting the extremities. Because clinical presentation is variable, diagnosis can be difficult. Recently, the Special interest Group of Pain and the Sympathetic Nervous System of the International Association for the Study of Pain developed a new taxonomy to help acknowledge and differentiate the features of reflex sympathetic dystrophy and causalgia. These are categorized under the heading of complex regional pain syndrome. Sympathetically maintained pain is also recognized as a separate component to this group of conditions. The authors present this new taxonomy and present cases of each condition.

Picolinic acid blocks the neurotoxic but not the neuroexcitant properties of quinolinic acid in the rat brain: evidence from turning behaviour and tyrosine hydroxylase immunohistochemistry.

Previous results suggest that the tryptophan metabolite, picolinic acid may have the unusual properties of antagonizing the neurotoxic but not the neuroexcitant effects of another tryptophan metabolite, quinolinic acid in the central nervous system. The present experiments tested this possibility utilizing behavioural and tyrosine hydroxylase immunohistochemical techniques. In the first series of experiments, rats received injections of relatively high concentrations of 6-hydroxydopamine (12 micrograms in 1 or 2 microliters), quinolinic acid (120 nmol in 0.5 microliters), picolinic acid (480 nmol in 0.5 microliters) or co-treatments (0.5 microliters) with quinolinic (120 nmol) plus picolinic acid (480 nmol) into the region of the substantia nigra. Results revealed that 6-hydroxydopamine and quinolinic acid alone produced a large loss of tyrosine hydroxylase-positive cells in the pars compacta of the substantia nigra. Behavioural results for all 6-hydroxydopamine (n = 10) and for some quinolinate-treated rats (n = 5) revealed ipsi- and contraversive circling following amphetamine (1 mg/kg, i.p.) and apomorphine (0.5 mg/kg, s.c.), respectively, consistent with unilateral loss of dopamine cells in the substantia nigra. The remaining quinolinate-treated rats (n = 9) circled ipsiversively following either stimulant suggesting damage to the pars reticulata. Groups treated with picolinic acid alone (n = 6) or co-injected (n = 6) showed no loss of tyrosine hydroxylase-positive cells in the substantia nigra and no circling response to the stimulants. In the second series of experiments, low concentrations of quinolinic acid (2.5, 5.0, 7.5 nmol), picolinic acid (10, 20, 30 nmol), or the two together (7.5 plus 30 nmol, respectively) were microinjected (0.5 microliter) into the dorsal striatum and circling behaviour evaluated. These results revealed dose-dependent contralateral circling with either quinolinate or picolinate; co-injection of the two tryptophan metabolites also produced contralateral circling. It was concluded that picolinic acid blocks the neurotoxic but not the neuroexcitant effects of quinolinic acid.