Abstract— Total nucleic acids of rat brain have been separated by agarose gel chromatography at 2 m‐NaCl into DNA. transfer RNA plus low molecular weight RNA. and high molecular weight RNA fractions. The DNA fraction contained less than 1 per cent RNA by weight judged by either short‐term or long‐term labelling with ortho[32P]phosphate. The high molecular weight RNA fraction contained 28 s and 18 s ribosomal RNAs and a heterogeneous population of 20‐60 s RNAs, apparent after short‐term labelling and characterized by a high content of nearest‐neighbour‐labelled uridylic acid. The rapidly sedimenting (>30s) portion of these RNAs could be largely separated from ribosomal RNAs by gel filtration using 4% agarose. The ribosomal RNAs could be fully resolved into 28 s and 18 s components by agarose gel chromatography at 0.5 m‐0.6 m‐NaCl, as shown by analysis of their sedimentation and nucleotide composition.
INTRODUCHONThe effect of GABA upon the nervous system in general, and especially upon isolated structures (i.e. cell body, axon, dendrite, receptors etc.) has been intensely studied. Topical GABA application leads to an increase in the threshold of evoked potential responses of nervous cells and receptors, while it does not affect axonal conduction.' The main site of action is believed to be a t the cell body and dendrite. The C N S GABA level is determined by the balance between formation (decarboxylation of glutamic acid) and utilization (transamination). During the latter, GABA is introduced into the Krebs cycle. An increase in GABA level leads to decreased C N S excitability with an increase in the convulsion-inducing threshold. On the other hand, decreased GABA level induces convulsions due to a lowered convulsion-inducing threshold.2 The protective effect of GABA has been demonstrated in a number of experimental and clinical convulsive states.GABA effects upon processes of higher nervous activity have been studied to a lesser extent. This is probably due to the impossibility of maintaining an increased or decreased GABA level in C N S long enough without affecting other C N S functions and because of the toxicity per se of substances that affect the GABA level.The majority of researchers believes that GABA effects are a result of its generalized hyperpolarizing action and not its specific inhibitory a~t i o n .~ Iontophoretic application of GABA into the spinal and higher neural structure neurons supports this view, although a number of electrographical observations implicates marked inhibitory action.'Consideration of influence of GABA on higher nervous activities is studied in the performance of conditioned reflex behaviors in teleosts.
MATERIAL AND METHODSExperiments were carried out with 8-15 cm long teleost fish (Serranus scriba. CUV) from Kotor Bay. After being caught, fish were kept in a common fresh sea-water aquarium for 15 days prior to the experiments. The fish were fasted during the experiments. Prior to daily tests, the fish were transferred in plastic containers to a dark chamber where they received aeration through an aquarium vibrator. Experiments were carried out with relation to the observed diurnal rhythm in the active part of the day, i.e. from 5 PM to 11 P M in dark chamber. Tests were performed in a shuttle-box that was simplified and adapted according to the method applied by Bitterman in his gold fish laboratory,' and which was later modified by Agranoff.' This training box (FIGURE 1) was made of thin metal sheets painted with insulational 543
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