Extracellular recordings of responses to tone-burst stimulation were used to determine the tonotopic organization of n. magnocellularis (NM) and n. laminaris (NL) in hatching chickens. NM cells show "primary-like" response patterns to ipsilateral stimulation, and are arranged in dorso-ventral isofrequency columns. Units responding to the highest frequency tones (about 4,100 Hz) are situated at the rostromedial pole of the medial division. Units with lower characteristic frequencies (CF's) are found at successively caudal and lateral sites, until extremely low CF's ( less than 500 Hz) are represented dorsoventrally in the daudolateral tail of the lateral division. No evidence was found of auditory input to the region which receives projections from the macula lagena. NL receives polarized, binaural, excitatory input. Units have similar CF's and thresholds to tones presented to either ear. The tonotopic organization in NL matches that found in NM--high CF's rostromedially and low CF's caudal and lateral. Quantitative procedures were developed for relating CF to the position of a unit within either nucleus. These analyses account for 79% and 89% of the frequency variance found within NM and NL, respectively, and predict the CF of a neuron by its position within each nucleus.

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The venom of the funnel-web spider Agelenopsis aperta contains several peptides that paralyze prey by blocking voltage-sensitive calcium channels. Two peptides, omega-Aga-IVB (IVB) and omega-Aga-IVC (IVC), have identical amino acid sequences, yet have opposite absolute configurations at serine 46. These toxins had similar selectivities for blocking voltage-sensitive calcium channel subtypes but different potencies for blocking P-type voltage-sensitive calcium channels in rat cerebellar Purkinje cells as well as calcium-45 influx into rat brain synaptosomes. An enzyme purified from venom converts IVC to IVB by isomerizing serine 46, which is present in the carboxyl-terminal tail, from the L to the D configuration. Unlike the carboxyl terminus of IVC, that of IVB was resistant to the major venom protease. These results show enzymatic activities in A. aperta venom being used in an unprecedented strategy for coproduction of necessary neurotoxins that possess enhanced stability and potency.

The auditory nerve of birds and mammals exhibits differences and similarities, but given the millions of years since the two classes diverged from a common ancestor, the similarities are much more impressive than the differences. The avian nerve is simpler than that of mammals, but share many fundamental features including principles of development, structure, and physiological properties. Moreover, the available evidence shows that the human auditory nerve follows this same general organizational plan. Equally impressive are reports that homologous genes in worms, flies, and mice exert the same heredity influences in man. The clear implication is that animal studies will produce knowledge that has a direct bearing on the human condition.

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