An accurate, reproducible method for determining the infarct volumes of gray matter structures is presented for use with presently available image analysis systems. Areas of stained sections with optical densities above that of a threshold value are automatically recognized and measured. This eliminates the potential error and bias inherent in manually delineating infarcted regions. Moreover, the volume of surviving normal gray matter is determined rather than that of the infarct. This approach minimizes the error that is introduced by edema, which distorts and enlarges the infarcted tissue and surrounding white matter.

Tetrodotoxin was infused into the suprachiasmatic nuclei of unanesthetized and unrestrained rats continuously for 14 days. The internal timekeeping mechanism of the circadian pacemaker in the nuclei continued to oscillate unaffected by this treatment, although the toxin reversibly blocked function of both the input pathway for pacemaker entrainment and an output pathway for expression of the circadian drinking rhythm. Thus, Na+-dependent action potentials appear necessary for entrainment and expression of overt circadian rhythms, but they do not seem necessary for the pacemaker to keep accurate time. The experimental approach presented in this paper is useful because it allows systematic assessment and distinction of the input, pacemaker, and output components of a mammalian circadian timekeeping system in vivo.The suprachiasmatic nuclei (SCN) in the anterior hypothalamus appear to be the site of an endogenous circadian pacemaker in mammals (1). The nuclei receive retinal inputs for entrainment to the environmental light-dark cycle and generate neural outputs for expression of overt, measurable rhythms. Two complementary measures of SCN activity have helped to establish that the nuclei contain a functioning circadian pacemaker. These two properties, in vivo glucose utilization (2, 3) and unit discharge rates (4, 5), exhibit circadian rhythmicity. SCN energy metabolism and electrical activity are both elevated during the day and depressed during the night in nocturnal and diurnal mammals (6, 7).However, the most recent investigations using these two assays have generated some unexpectedly discordant data. On one hand, the rhythm of SCN metabolic activity appears in fetal rats 72 hr before birth (8,9). Such prenatal pacemaker function antedates the postnatal maturation of input and output pathways for photic entrainment and expression of overt circadian rhythms (10). On the other hand, when SCN action potentials are recorded in hypothalamic slices obtained from 7-, 11-, 14-, and 21-day-old rat pups, a circadian rhythm is observed only in those slices from the 14-and 21-day-old animals (11). Although other interpretations are possible, it seems that the circadian rhythm of SCN unit firing rates appears weeks after the rhythm of SCN energy metabolism first begins in utero.To resolve this discrepancy, we propose that the action potentials recorded in the SCN are not a part of the internal timekeeping mechanism of the circadian pacemaker; rather, the electrical impulses function to couple the pacemaker to its input and output pathways. We have tested this idea by chronically infusing tetrodotoxin (TTX) into the SCN of unanesthetized, unrestrained rats. TTX selectively and reversibly blocks voltage-dependent Na+ channels in axons, inhibiting the generation of action potentials without affecting resting membrane potential, K+ currents, Na+ pump mechanism, or local depolarization of postsynaptic membranes (12, 13). Importantly, in vitro recordings in hypothalamic slices demonstrate that SCN action potentials are ...

The methionine analogue methionine sulfoximine was administered to 10 rats 24 hours before occlusion of the proximal left middle cerebral artery. Three days later the rats were decapitated and the brain infarct volumes were compared with those in 10 control rats that received saline before middle cerebral artery occlusion. The mean volume of the infarct in the cerebral cortex was reduced by 33% in the group treated with methionine sulfoximine (/?<0.01). This protective effect may be mediated by a presynaptic mechanism; methionine sulfoximine profoundly inhibits brain glutamine synthetase, thereby interrupting the astrocyte-neuron glutamate shuttle and impairing neuronal glutamate release. Methionine sulfoximine also increases brain glycogen stores, and this increased energy reserve may benefit penumbral tissue during the peri-infarct period. Further study of the mechanisms by which methionine sulfoximine decreases infarct volume could lead to new therapeutic approaches for stroke. (Stroke 1990;21:322-327)

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Local administration of pitrakinra to the lung is sufficient to inhibit AHR, one of the cardinal features of asthma, indicating the therapeutic potential of inhaled pitrakinra in the treatment of atopic asthma.