PubMed Health⌕ Search

Biomedical subjects

R Navarrete

Publications and source records attributed to R Navarrete.

35 records · Page 2Linked to original sources
PubMed1990

Cloning and expression in a heterologous host of the complete set of genes for biosynthesis of the Streptomyces coelicolor antibiotic undecylprodigiosin.

A fragment of DNA carrying the hitherto unisolated members of the cluster of genes (red) for biosynthesis of the red-pigmented antibiotic undecylprodigiosin of Streptomyces coelicolor A3(2) was isolated. This was done by cloning random fragments of S. coelicolor DNA into the closely related Streptomyces lividans 66 and recovering a clone that caused overproduction of undecylprodigiosin. The effect was probably due to the presence of the cloned redD gene, which functions as a positive regulator of the expression of the red cluster, activating the normally poorly expressed red genes of S. lividans. Two fragments from either end of the red cluster were cloned adjacent to each other on a low-copy-number Streptomyces vector. Double crossing-over occurring between these plasmid-borne sequences and the chromosomal copy of the same DNA in S. coelicolor led to isolation of the entire red cluster as a single cloned fragment. Isolation of antibiotic biosynthetic genes by the effects of an activator in a self-cloning experiment, and in vivo reconstitution of a large cluster of genes by homologous recombination, may turn out to be usefully generalizable procedures.

Cloning, Molecular↗
PubMed1990

Long-lasting modification of reflexes after neonatal nerve injury in the rat.

The reflex activity of motoneurones to the extensor digitorum longus (EDL) muscle following sciatic nerve crush during the first 5 days after birth (neonatal crush) or in the adult (adult crush) was studied 3-6 months later, when the axons had reinnervated their target muscles. Electromyograms (EMG) and muscle tension were recorded from the EDL muscle (a physiological flexor) on the injured and uninjured sides. Reflex responses were evoked by stimulation of the common peroneal (CP), the tibial (T) and the sural (S) nerves, ipsilateral and contralateral to the side of injury. In animals which had sustained a neonatal crush, stimulation of branches of the injured sciatic nerve elicited ipsilateral reflex responses that were about 3 times larger than those recorded from the uninjured side or in normal animals. Stimulation of the CP nerve on the uninjured side invariably elicited a contralateral reflex response from the reinnervated muscles, while stimulation of the CP nerve on the injured side either failed to produce a response or produced a very weak reflex response from the control muscles. Reflexes recorded from the reinnervated muscles by stimulation of the tibial and sural branches of the uninjured sciatic nerve were 3-7 times greater than those recorded from the uninjured side or in normal animals. The reflex responses obtained from reinnervated muscles of animals with nerve injury in adulthood were similar to those obtained from control, unoperated adult rats. These results indicate that sciatic nerve injury during a critical development period leads to a permanent enhancement of reflex responses from reinnervated fast flexor muscles not seen after similar injury in adults.

Adaptation, Physiological↗
PubMed1990

Dopamine high-affinity transport site topography in rat brain: major differences between dorsal and ventral striatum.

Investigations were conducted to determine the topography of the high-affinity dopamine uptake process within the rat striatum. [3H]Dopamine uptake into crude synaptosomes prepared from micropunch samples was found to be two- to three-fold higher in dorsal caudate-putamen relative to nucleus accumbens septi. In contrast, the concentrations of dopamine in the two regions were equivalent. The recognition site associated with high-affinity dopamine uptake was labeled using [3H]mazindol, and the binding of this ligand was also found to be two- to three-fold higher in homogenates from dorsal caudate-putamen samples relative to nucleus accumbens septi. Regional differences in uptake of [3H]dopamine or binding of [3H]mazindol were shown to be due to variations in Vmax or Bmax, not to differences in apparent affinity. Autoradiography of [3H]mazindol binding in rat striatum revealed a decreasing density of the site along the dorsal-to-ventral axis, with the highest binding occurring in the dorsolateral caudate-putamen, lower binding in the ventral caudate-putamen, and lowest levels in the septal pole of the nucleus accumbens septi. Quantification showed that the extent of this gradient was two-fold. Further autoradiographic studies revealed less striatal heterogeneity in the pattern of binding of [3H]ketanserin, another radioligand associated with the striatal dopaminergic innervation but not linked to the dopamine uptake process of the plasma membrane. The findings suggest that the dopaminergic fibers of the ventral striatum, especially the medial nucleus accumbens septi, may be relatively lacking in their capacity for dopamine uptake following its release. This organization may result in regional differences in the time-course of of extraneuronal dopamine following transmitter release and may render the dopamine-containing terminals of the ventral striatum less susceptible to the degenerative influences of neurotoxins that are incorporated by the high-affinity dopamine uptake process.

Animals↗
PubMed1989

Decreased striatal D1 binding density following mesotelencephalic 6-hydroxydopamine injections: an autoradiographic analysis.

Autoradiographic experiments performed on rats with unilateral mesotelencephalic 6-hydroxydopamine (6-OHDA) injections revealed reduced binding of [3H]SCH23390 to D1 receptors in the striatum ipsilateral to the neurotoxin as well as increased binding of [3H]spiroperidol to D2 receptors in that hemisphere. These opposite influences of injury on the dopamine receptor subtypes occurred in rats sacrificed at 2 weeks or 11 months postoperatively, but neither change was evident at 4 days postoperatively. Equilibrium saturation analysis performed on rats sacrificed at 8 weeks postoperatively indicated that D1 and D2 receptor changes reflected altered Bmax values without KD modifications. Topographic analysis of the D1 decline by quantitative autoradiography revealed that the D1 decrease was greater in dorsal striatum than ventrally. Those striatal regions that showed greater declines in D1 density correspondingly had the greater losses of [3H]mazindol binding after the denervation, suggesting that the decline of D1 binding is a postsynaptic consequence of the reduced mesostriatal dopaminergic innervation. The findings indicate opposite influences of injury on D2 and D1 receptor levels and raise important questions concerning the mechanism by which 6-OHDA injection affects the D1 sites.

Animals↗
PubMed1985

Matching of muscle properties and motoneurone firing patterns during early stages of development.

In adults, muscle fibres match the functional requirements of the motoneurone that supplies them. During early stages of postnatal development of the rat neither muscle fibre properties, nor activity patterns of motoneurones supplying fast and slow muscles have completed their differentiation. Nevertheless, even at this early stage of development the muscles have characteristic properties that are well matched to the activity patterns of immature motoneurones. With further development differentiation of motoneurone activity and muscle fibre properties goes hand in hand. If during this period of linked differentiation, connections between the motoneurones and muscle fibres are disrupted, the development of fast muscles is permanently impaired.

Action Potentials↗
PubMed1984

Differential effect of nerve injury at birth on the activity pattern of reinnervated slow and fast muscles of the rat.

The activity patterns of the reinnervated slow soleus and fast extensor digitorum longus (e.d.l.) muscles were studied in rats during the first 6 months after sciatic nerve crush at birth, using chronic electromyography. When the nerve lesion was inflicted shortly after birth, the recovery of the muscle weight and size was always much less than if the same lesion was inflicted on adult animals. As previously demonstrated, this effect is due to motoneurone and muscle fibre loss. Following reinnervation after a neonatal crush, the soleus muscle recovered its normal tonic activity pattern during postural and spontaneous locomotor activity. By contrast, in the reinnervated e.d.l. muscle, abnormal tonic motor unit activity was recorded during locomotion, in addition to the phasic activity characteristic of the normal muscle. In response to postural reflexes elicited by tilting the animal, tonic motor unit activity was recorded from the reinnervated e.d.l. muscle, whereas the normal muscle was not activated by these stimuli. The aggregate activity recorded from the reinnervated e.d.l. during spontaneous locomotion was about 2-3 times greater than normal, whereas in the reinnervated soleus no significant change took place. In animals which had their nerves crushed as adults, the activity pattern and aggregate activity of both muscles was similar to normal. The firing pattern of individual motor units from normal and reinnervated muscles was compared. After a neonatal crush, the mean frequency of firing of e.d.l. motor units was significantly lower compared to normal or to that after an adult crush, whereas in soleus no significant change was found. These results indicate that peripheral nerve lesions during early development affect predominantly the development of motoneurones with a phasic, high-frequency discharge pattern resulting in a shift towards tonic, lower-frequency motor unit activity.

Action Potentials↗
PubMed1983

Solubilization of yeast plasma membranes and mitochondria by different types of non-denaturing detergents.

A comparative study of the solubilization of yeast plasma membranes and mitochondria by different types of non-denaturing detergents has been performed. Zwittergent-14 (3-[tetradecyldimethylammonio]-1-propanesulfonate) at low concentrations (3-4 mM) produced maximum solubilization of both membranes. However, this detergent may inactivate enzymes at high concentrations. Taurodeoxycholate (in the presence of salt) and Triton X-100 were also effective in mitochondria but not in the plasma membranes. Octylglucoside only solubilized these membranes at very high concentrations (20 mM). CHAPS (3-[cholamidopropyldimethylammonio]-1-propanesulfonate) only achieved partial solubilization even at high concentrations. Our results suggest that Zwittergent-14 at low concentrations is one of the most powerful detergents for the general solubilization of native membrane proteins.

Cell Fractionation↗
PubMedDate not supplied

Percutaneous treatment of acute soft tissue lesions with naproxen gel and ketoprofen gel.

A randomized independent-group, single-blind study was performed to compare the analgesic efficacy and the local and cosmetic tolerability of 3-5 cm of 10% naproxen gel with 10% ketoprofen gel in 30 patients complaining of moderate or severe pain due to acute soft tissue lesions. Both drugs were administered topically and were applied to the painful area at least once every 12 h as required. Naproxen gel was effective, cosmetically acceptable and safe in the treatment of acute soft tissue lesions. Efficacy and tolerability of both naproxen gel and ketoprofen gel were comparable, although naproxen gel produced a significantly greater reduction in pain on deep palpation by the third day of treatment.

Administration, Topical↗