Equithesin: a hibernation-inducing drug?

1. Hibernating insectivore species (hedgehogs) and non-hibernating rodents (guinea pig and rat) were anaesthetized with 'equithesin' (a mixture of chloral hydrate, magnesium sulphate, and pentobarbitone sodium). 2. The physiological responses shown by the hedgehogs were similar to those observed in hedgehogs during a natural or cold-induced hibernation. 3. These responses included a strong reduction in body temperature, heart rate, respiration and oxygen consumption, and brain activity. 4. Such responses to equithesin were not observed in the non-hibernating rodent species. 5. These results suggest that equithesin is a potential tool for hibernation research.

Auditory cortex of the long-eared hedgehog (Hemiechinus auritus): II. Tuning properties.

The forebrain of hedgehogs is considered by many investigators as one of the simplest and most primitive among extant placental mammals. In a recent study we have shown that the auditory cortex of the long-eared hedgehog (Hemiechinus auritus) comprises two distinct auditory fields, which are tonotopically organized. In this study, we describe tuning properties of single cells in these two fields. Application of the Q10dB and Square Root measures for determining sharpness of tuning revealed that, although most of the cells in the more anterior field, which is considered primary, are sharply tuned, on the average they are more broadly tuned than cells in the primary auditory cortex of other mammals. In the posterior field, the distribution of narrowly and broadly tuned cells is equal. Narrowly tuned cells in both fields are equally narrow, as are the broadly tuned cells. Latencies of single cells in both fields are frequency and intensity dependent and are somewhat longer than these found in other mammals. The distribution of BFs vs. threshold intensity matches fairly well the behavioral audiogram previously described. Our findings suggest that, in spite of the view that the isocortex of hedgehogs represents a 'primitive' condition, some basic tuning properties of their auditory cortex cells are comparable to those of other mammals.

Auditory cortex of the long-eared hedgehog (Hemiechinus auritus). I. Boundaries and frequency representation.

The boundaries of the primary auditory cortex of the long-eared hedgehog, Hemiechinus auritus, were determined by single-cell recordings, myeloarchitecture and retrograde horseradish peroxidase labeling in the medial geniculate, using anesthetized animals. The auditory cortex is located on the lateral surface of the temporal cortex, medial to the rhinal fissure. Responses to pure tones revealed an orderly representation of best frequencies in the primary auditory cortex, with low frequencies represented rostrally and high frequencies caudally. A second auditory field caudal to the primary one was indicated.

The neurotoxic complex from the venom of Pseudocerastes fieldi. Contribution of the nontoxic subunit.

The neurotoxic complex (Cb) from the venom of Pseudocerastes fieldi consists of an acidic non-toxic subunit (CbI) and a basic toxic one (CbII). The complex is only partially dissociated by salt-gradient chromatography; the two components are completely separable in the presence of urea. Chromatofocusing of CbI resulted in two protein peaks, both of which potentiated toxicity of CbII. CbI inhibits hemolysis induced by CbII, but not the phospholipase A2 activity of CbII. CbI reveals phospholipase A activity with non-micellar dithiolecithin, however, it shows no activity with micellar lecithin. The amino acid composition of CbI and its enzymatic activity, as well as the structural homology with A2 phospholipases of nontoxic subunits from other presynaptic neurotoxins may suggest that, a catalytic activity of the non-toxic subunits plays a role at the target site.

Isolation and characterization of the main toxic fraction from the venom of the false horned viper (Pseudocerastes fieldi).

The venom of Pseudocerastes fieldi was subjected to gel filtration on Sephadex G-75. Most of the protein and lethality of the venom were eluted in a major symmetrical peak (C). The lethality of this peak is confined to a basic protein fraction, Cb (pI greater than 9.5) separable by DEAE-cellulose chromatography. Two proteins with molecular sizes close to 16,000 daltons were isolated from this fraction by preparative acidic gel electrophoresis in the presence of Triton X-100. One of the proteins (CbII) is lethal to mice (LD50 = 1 mg/kg) and shows phospholipase A activity as well as direct hemolytic activity. The other protein (CbI) does not reveal any known biological activity. However, upon recombination of the two a synergistic lethal activity is evident (the LD50 of the mixture = 0.25 mg/kg). It is suggested that CbI may be a specifier which potentiates the toxicity of the phospholipase A at the target site.