Isolation of free and membrane-bound polysomes and mRNA highly active in translation and reverse transcription from small discrete regions of rat brain

A procedure is described for the preparation of total polysomes, membrane-bound and free polysomes and polysomal mRNA from as little as 5 mg or less of brain tissue. These preparations were highly active when tested for translation and reverse transcription in vitro. Using this method, polysomes and mRNA from rat cerebral cortex, cerebellum, hippocampus and hypothalamus were compared. The results showed that membrane-bound polysomes were more active than free polysomes in protein synthesis. The activities of polysomes and mRNA for protein and cDNA synthesis were dependent on the specific brain structures from which they were obtained. Polysomes from cerebellum and hypothalamus incorporated amino acids more actively than those from cerebral cortex or hippocampus, when tested in a reticulocyte lysate system. Cerebellar mRNA also showed the highest activity for cDNA syntehsis as compared to mRNAs from the other three tissues.

Identified spinal motoneurons of young rats possess nicotinic acetylcholine receptors of the heteromeric family

The aim of the present study was to determine whether, in young rats, spinal motoneurons possess functional nicotinic acetylcholine receptors. Motoneurons were identified either by retrograde labelling or by choline acetyltransferase immunohistochemistry. Whole-cell recordings were performed in spinal cord slices cut at the lumbar level. In voltage clamp, acetylcholine evoked a rapidly activating inward current. In current clamp, it depolarized the motoneuron membrane and induced action potential firing. The acetylcholine-evoked current was strongly reduced by d-tubocurarine or dihydro-beta-erythroidine, broad spectrum nicotinic antagonists, but was almost insensitive to methyllycaconitine, a nicotinic antagonist selective for receptors containing the alpha7 subunit. Moreover, exo-2-(2-pyridyl)-7-azabicyclo[2.2.1]heptane, an alpha7-specific agonist, was without effect. In young animals, light-microscopic autoradiography showed that in the central grey matter all laminae were intensely and equally labelled by [3H]epibatidine. A dense [125I]-alpha-bungarotoxin binding was also found in all laminae, with slightly lower levels in the superficial layers of the dorsal horns and in the ventral part of the grey matter. In adults, the density of [3H]epibatidine binding sites was much lower in the entire grey matter, except in layer 2 of the dorsal horn, and [125I]-alpha-bungarotoxin binding sites were present only in some selected areas. Our data indicate that spinal motoneurons possess functional nicotinic receptors of the heteromeric type and suggest that nicotinic cholinergic transmission may play a significant role in the developing spinal cord.

Action of tachykinins in the rat hippocampus: modulation of inhibitory synaptic transmission

Substance P and other neuropeptides of the tachykinin family can powerfully excite CA1 hippocampal interneurons present in the CA1 region. In the present work we show that, by exciting hippocampal interneurons, tachykinins can indirectly inhibit pyramidal neurons. We found that tachykinins caused a decrease in the inhibitory synaptic current interval and an increase in the inhibitory synaptic current amplitude in almost all pyramidal neurons tested. This effect was tetrodotoxin sensitive. Tachykinins did not alter the frequency or amplitude of miniature inhibitory synaptic currents and were without effect on evoked inhibitory synaptic currents. Thus, these neuropeptides acted at the somatodendritic membrane of GABAergic interneurons, rather than at their axon terminals. The effect of substance P on spontaneous inhibitory synaptic currents could be mimicked by a selective agonist of NK1 receptors, but not by selective agonists of NK2 and NK3 receptors. It was suppressed by an NK1 receptor antagonist. In CA1 interneurons located in stratum radiatum, substance P generated a sustained tetrodotoxin-insensitive inward current or induced membrane depolarization and action potential firing. This direct excitatory action was mediated by NK1 receptors. Current-voltage relationships indicate that the net tachykinin-evoked current reversed in polarity at or near the K+ equilibrium potential, suggesting that a suppression of a resting K+ conductance was involved. By increasing the excitability of CA1 GABAergic interneurons, tachykinins can powerfully facilitate the inhibitory synaptic input to pyramidal neurons. This indirect inhibition could play a role in regulating short-term and/or long-term synaptic plasticity, promoting neuronal circuit synchronization or, in some physiopathological situations, influencing epileptogenesis.

Presence of functional vasopressin receptors in spinal ventral horn neurons of young rats: a morphological and electrophysiological study

The objective of the present work was double. (i) Light microscopic autoradiography was used to determine the distribution of vasopressin and oxytocin binding sites in the spinal cord of rats. (ii) Whole-cell recordings were performed in lumbar spinal cord slices in order to assess whether these receptors are functional, whether they are located pre- or postsynaptically and whether they are present in motoneurons. In newborns, vasopressin binding sites of the V1a type were present in all laminae of the central gray at all segmental levels, whereas oxytocin binding sites were found only in the superficial layers of the dorsal horn. In adults, binding sites for both neuropeptides were also present, but were less dense. The dissociation constants for vasopressin were similar in newborns and adults. Whole-cell recordings showed that in identified motoneurons vasopressin exerted a direct effect, by inducing a membrane depolarization or by generating a sustained inward current, and an indirect effect, by enhancing glycinergic and GABAergic inhibitory transmission. Vasopressin-induced facilitation of inhibitory transmission could also be demonstrated in unidentified ventral horn neurons. All these effects were mediated by V1a but not V1b receptors. In some neurons, glycinergic transmission was also facilitated by a selective oxytocin receptor agonist. Our data, together with data obtained previously in brainstem motor nuclei, suggest that vasopressin of hypothalamic origin could play a role in motricity. The neuropeptide could act as a neuromodulator, because it would not directly activate motoneurons, but rather render them more responsive to incoming excitatory inputs. Vasopressin may thus act as a regulator of muscular force.