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J Lipski

Publications and source records attributed to J Lipski.

At least 109 records · Page 6Linked to original sources
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Split medulla preparation in the cat: arterial chemoreceptor reflex and respiratory modulation of the renal sympathetic nerve activity.

The study was undertaken in order to assess the changes in sympathetic output in a split medulla preparation of the cat which, as shown earlier, has impaired respiratory rhythm generation. The effects of medullary midsagittal sections on renal sympathetic nerve firing were investigated in chloralose anesthetized, paralyzed and artificially ventilated cats. Recordings of phrenic and recurrent laryngeal nerve activity served as indices of central respiratory rhythm generation. Sections, 5 mm deep from the dorsal medullary surface and extending 6 mm rostrally and 3 mm caudally to the obex, did not produce any significant changes in heart rate, blood pressure or tonic renal sympathetic nerve firing levels. They decreased or abolished, however, the respiratory rhythmicity in renal sympathetic nerve which paralleled the reduction of inspiratory discharges in phrenic and recurrent laryngeal nerves, and abolished the carotid body chemoreceptor-sympathetic reflex. The inspiratory activity remaining after the sections could still be enhanced by chemoreceptor stimulation. The inhibitory baroreceptor and pulmonary stretch receptor sympathetic reflexes, and the central excitatory effect of CO2 on renal sympathetic nerve firing were not altered. The effects of electrical stimulation within the midsagittal plane of the medulla have shown that descending pathways from the medullary inspiratory neurons (or their medullary collaterals) do not participate in the facilitation of spinal preganglionic neurons during inspiration and in relaying the pulmonary stretch receptor inhibitory sympathetic reflex. A region located close to the obex was identified from which excitatory responses in renal sympathetic nerves, compatible with the response obtained by carotid sinus nerve stimulation, could be evoked. It is concluded that a lesion in the midline of the lower medulla at the level of the obex selectively destroys cells or pathways which relay the carotid body chemoreceptor-sympathetic reflex.

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Detection of weakly expressed genes in the rostral ventrolateral medulla of the rat using micropunch and reverse transcription-polymerase chain reaction techniques.

1. The present study describes the use of reverse transcription-polymerase chain reaction (RT-PCR) to detect weakly expressed neurotransmitter receptor mRNA in tissue micropunched from the rostral ventrolateral medulla (RVLM) and other discrete areas of the medulla oblongata of the rat. 2. Micropunches were made from 240 microns transverse medullary sections. Punched regions included the RVLM, hypoglossal nucleus (XIIn), ventrolateral subnucleus of the nucleus tractus solitarius (NTS) and spinal trigeminal nucleus (STN). RNA was extracted and reverse transcribed into cDNA, which was probed for the presence of seven genes: glyceraldehyde phosphate dehydrogenase (GAPDH), neuron-specific enolase (NSE), tyrosine hydroxylase (TH), phenylethanolamine N-methyltransferase (PNMT), glucocorticoid receptor (GCR), mineralocorticoid receptor (MCR) and the adenosine 5'-triphosphate (ATP) receptor subunit P2X2-1. Each transcript was detected using a semi-nested PCR protocol, which used three primers. 3. Tyrosine hydroxylase was detected in the RVLM and NTS and PNMT was also detected in the RVLM, which agrees with the distribution of catecholamine neurons in the medulla. Expression of GCR mRNA was detected in the RVLM and the XIIn but not in the NTS (it was not probed for in the STN punches). The P2X2-1 receptor message was detected in all areas. Expression of MCR mRNA was detected in the RVLM only. 4. This method offers a simple way to detect the presence of low-abundance receptor mRNA in discrete brain regions.

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Criteria for intracellular identification of pre-sympathetic neurons in the rostral ventrolateral medulla in the rat.

Previous studies revealed that a relatively small group of reticulospinal neurons located in the rostral ventrolateral medulla (RVLM) plays a key role in the generation of resting vasomotor tone and in reflex control of arterial blood pressure. These medullary pre-sympathetic neurons have been extensively studied with extracellular microelectrodes, but so far few attempts have been made to examine their intracellular properties in vivo. This report, based on intracellular recordings from 8 RVLM pre-sympathetic neurons in anaesthetised rats, sets out criteria for intracellular identification of such neurons. We propose that two features are sufficient to classify RVLM neurons as pre-sympathetic during intracellular recording: inhibitory response to stimulation of the aortic depressor nerve with short bursts of pulses applied at low frequency; and antidromic stimulation from the upper thoracic segments. Cardiac oscillations in the membrane potential or responses during large changes in blood pressure can be due to movement artefact, and are therefore not reliable as a means of demonstrating baroreceptor input. Further intracellular studies of these neurons will undoubtedly result in further progress in understanding their function.

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Properties of reversible graded inhibition of phrenic nerve activity by pulmonary afferents.

Reversible graded inhibition of phrenic nerve activity (PNA) was observed during short, low volume lung inflations in chloralose anaesthetized, paralyzed cats. The strength of the inhibitory effect rose with the volume of inflation in a manner suggesting non-linearity. The volume threshold for the first detectable inhibition decreased with increasing delay between onest of inspiration and lung inflation. The differences between the threshold curve for different air flows were not significant. The recovery of PNA from transient inhibition was not immediate and this shows that lung inflations might activate a central inhibitory mechanism, the action of which could outlast the activation period of lung receptors. It is suggested that pulmonary stretch receptors (PSR) are responsible for the observed reactions. The present results indicate that the theory of "all or none" action of PSR on inspiratory activity is not valid for all experimental conditions, and that PSR are capable of continuous control of PNA pattern.

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