Muscular rigidity and delineation of a dopamine-specific neostriatal subregion: Tonic EMG activity in rats

In order to investigate the role of neostriatal dopamine receptors in muscular rigidity we have studied catalepsy and spontaneous muscle tone in rats receiving haloperidol injections into various parts of the neostriatum. It was found that low doses of haloperidol (250-750 ng/0.5 microliter) induced a tonic activity in the EMG of the gastrocnemius-soleus muscle when injected into the most rostral part of the neostriatum (A 8620-9650). This tonic EMG activity was found to be both dose-dependent and dopamine-specific: the haloperidol effect of 500 ng could be inhibited by 500 ng apomorphine. No muscular rigidity could be observed when haloperidol (500 ng/0.5 microliter) was injected further caudally into the neostriatum or into the medial part of the nucleus accumbens. With regard to the haloperidol-induced catalepsy as measured by means of the bar test, a similar distribution of effective and ineffective injection sites was observed; however, higher doses of haloperidol (1.5-2.5 micrograms/0.5 microliter) were required. Thus catalepsy and muscular rigidity were found to be closely related phenomena within the neostriatum. Finally, it is discussed how information relevant to tonic EMG activity is transmitted from the substantia nigra pars compacta to the superior colliculus and the ventromedial thalamus via the neostriatum and the substrate nigra pars reticulata.     

Effects of aminoglycoside antibiotics on bound calcium and contraction in guinea-pig atria.

We studied the effect of three aminoglycoside antibiotics which have been shown to replace Ca from lipid monolayers on the superficially bound Ca of isolated beating left atria from guinea-pigs. The cellular Ca content was determined by means of 45Ca after having attained complete exchange. The antibiotics dibekacin, sisomicin, and gentamicin, all reduced the cellular Ca content by 10-20% in a dose-dependent manner. The loss of superficially bound Ca was accompanied by a decline of the contractile force by 40-90%. It is concluded that in isolated atrial muscle it is the amount of Ca bound to the outer surface of the cardiac plasmalemma, rather than the extracellular Ca2+ concentration, that determines contraction height.