Several identified neurons in Apiysia and Tritonia gangiia were shown to contain measurable quantities (4-6 pmol/cell body) of . A metabolic correlate for the limited distribution of 5-HT among the neurons of Trironia is provided by the finding that the enzyme, aromatic acid decarboxylase (AAD), is 500 times more active in nerve cells containing 5-HT than in neurons devoid of the amine. Although all Aplysiu neurons have some AAD activity, 5-HT cell bodies in this species are 10-fold more active than cell bodies which do not contain 5-HT. The cytoplasm of 5-HT cell bodies in Aplysia and Tritonia characteristically contains granules that have minimum diameters of approx. lo00 8, and eccentric opaque cores. This type of granule was not found in somata which did not contain measurable 5-HT. These data illustrate the metabolic and morphological specialization in 5-HT-containing neurons of molluscs. I N T R O D U C T I O NIMPLICIT within the concept of chemical transmission is the supposition that a neuron is chemically specialized to support the synthesis, storage, and metabolism of the transmitter compound liberated at its nerve terminals. In a heterogeneous nervous system where different neurons presumably utilize different transmitter substances, it should be possible to distinguish certain groups of neurons from others on the basis of unique chemical properties that may be associated with different transmitters. The nervous systems of marine gastropods are particularly well suited for obtaining answers to the question of how nerve cells are specialized for a particular transmitter compound. Physiological and pharmacological observations of molluscan ganglia, including those of Aplysiu, have revealed that a number of different transmitter subtances may be utilized within these nervous systems (reviewed by GERSCHENFELD, 1966). More recently, work by several investigators has demonstrated the feasibility of obtaining reliable chemical measurements on single nerve cells from Aplysiu ganglia (GILLER and SCHWARTZ, 1968, 1971; BERRY, 1969; MCCAMAN and DEWHURST, 1970; 197 1 ; PETERSON and KERNELL, 1970 ; SCHWARTZ, CASTELLUCCI and KANDEL, 197 1).The purpose of this investigation was to obtain direct information on the nature of neuronal specialization related to the presence of a particular transmitter substance, The results will show that only a limited number of Aplysiu and Tritoniu neurons contain measurable quantities of 5-hydroxytryptamine (serotonin, 5-HT), and that the cytoplasm of these 5-HT cell bodies contains dense-core granules frequently associated with the intracellular storage of this biogenic amine (RUDE, COGGESHALL and VAN ORDEN, 1969; COGGESHALL, 1972). With respect to the synthesis of 5-HT, we have previously reported that the enzyme which converts 5-HTP to 5-HT, aromatic acid decarboxylase (GAD), was demonstrable in all Aplysiu neurons (WEINREICH, DEW- HURST and MCCAMAN, 1972). Our present report shows that 5-HT-containing neurons 969 NEURO. 20/&D

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Several data reduction procedures have been used for converting isotope ratios, determined using gas chromatography mass spectrometry, into mole ratios for the purpose of quantitating organic compounds. In this report, these procedures are shown to be related under certain limiting approximations of original sample and internal standard isotope ratios. With the understanding that some of the procedures involve approximations, the incorporation of related systematic errors into calculated mole ratio values was investigated. The results indicate that certain data reduction procedures allow quantitation over wider mole ratio ranges and with internal standards which contain a significant quantity of unlabeled impurity.

PREVIOUS studies have indicated that levels of activities of 5-hydroxytryptophan decarboxylase (5-HTPD) and monoamine oxidase (MAO) may have a significant role in regulating tissue concentrations of 5-HT. Investigations of such enzyme activities in brain tissue have been performed on relatively gross areas (100 mg or more) which contain varying amounts of grey and white matter. For better assessment of the contribution of each of various cell types, microdissection of cortical and cerebellar areas was performed. Since the sample size of a relatively homogeneous cellular population is of the order of a few pg, new, sensitive micromethods had to be devised for the measurement of M A 0 and 5-HTPD activities. Methods currently used for the quantitative estimation of M A 0 activity by oxygen consumption, ammonia production, disappearance of amine, and fluorimetric assay of indole acetic acid formed are not sufficiently sensitive for such studies. The method frequently used for estimating the activity of the enzyme which decarboxylates 5-HTP and dihydroxyphenylalanine, is based on the fluorimetric estimation of the products 5-HT and dopamine, respectively. KUNTZMAN, SHORE, BOGDANSKI and BRODIE (1961) recently described modifications of these methods which increase their sensitivity, but, even with modifications, approximately 20-100 mg of brain tissue are required.In this paper, procedures are described for quantitative estimation of M A 0 and 5-HTPD activities in samples of nervous tissue weighing as little as 2-5 pg dry weight.

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