Depressor Neurons Research Articles

Location of neurones with cardiovascular and respiratory function, at the ventral surface of the cat's medulla

A study has been made of the ventral surface of the medulla, to identify neurones with cardiovascular and respiratory functions. Experiments were performed on chloralose-anaesthetized. artifically ventilated cats. Ventral medullary neurones were stimulated by microinjections of excitant amino acid (which selectively activates cell bodies), and responses measured in blood pressure, heart rate. renal sympathetic and phrenic nerve activity. A small region of ventral medulla was found, corresponding to the “glycinc-sensitive area”, from which large increases in blood pressure and renal nerve activity were evoked by amino acid injections. More caudally. another cell group was localized lateral to the hypoglossal nerve roots, and these neurones depressed blood pressure and renal nerve activity. Two distinct regions were found to increase phrenic nerve activity: rostral to the pressor neurones. encroaching on the trapezoid body (roughly corresponding to area “M”). and a caudal group, close to the depressor neurones (i.e. lateral to the hypoglossal roots). No respiratory response could he evoked from medial to the hypoglossal roots (area “I.”) and stimulation of neurones in area “S” generally depressed phrenic activity. Neurones with cardiovascular and respiratory actions could the distinguished anatomically. Their locations have been mapped and compared with previous studies.

Altered methionine enkephalin immunoreactivity in cerebral nuclei of spontaneously hypertensive rats.

In young SHR, methionine enkephalin-like immunoreactivity (ME) levels were lower than WKY in the tractus spinalis n. trigemini, n. reticularis lateralis, n. arcuatus and n. corporis mamillaris lateralis, whereas higher in the n. dorsalis n. vagi, n. amygdaloideus medialis and n. striae terminalis. In adult SHR, the alteration in these nuclei disappeared. ME levels were higher than those of WKY in the n. reticularis medialis and n. accumbens septi, while lower in the area lateralis hypothalami. The alteration was not due to hypertension, since acute hypertension induced with angiotensin II produced no change in these nuclei. The decrease in ME neuronal activity in bulbar sensory and somatosensory afferents, and n. arcuatus, and ME neuronal activation in the limbic depressor neurons may be involved in the development of hypertension and hyper-reactivity in SHR.

Changes in efferent activity in the renal and splenic nerves during stimulation of bulbar reticular nuclei

Acute experiments on cats have shown that stimulation of the paramedian and ventricular reticular nuclei produces clear-cut and consistent changes in efferent activity of renal and splenic nerves. These changes are far more pronounced after ventricular nucleus stimulation. The changes in sympathetic activity and SAD after stimulation of the nuclei were inconclusive, thus indicating a diffuse distribution of pressor and depressor neurons in these nuclei. Acetylcholine microinjections into the ventricular reticular nucleus was accompanied by more marked changes in the activity of the splenic nerve, whereas stimulation of the paramedian reticular nucleus affected to a greater measure the renal nerve.

Changes in the flight motor pattern during the development of the australian plague locust,Chortoicetes terminifera

The establishment of the characteristic adult flight and its motor pattern has been followed behaviourally and electrophysiologically in locusts of exactly known ages. In the last two larval instars there is repetitive firing in the flight muscles but the alternation of antagonists typical of adult flight is not present (Pig. 3). Alternation can first be seen late in the last larval instar and the full adult pattern is recognizable in most animals by day 3 of adult life. Competent flight behaviour is established by day 4 or 5. In this period the coupling between elevator and depressor neurones improves and the pattern stabilizes (Figs. 4 and 6) but the time course of the whole process varies considerable between individuals. After this the only major change is an increase in wingbeat frequency from about 15–20 Hz at fledging to 25–35 Hz in the second or third week (Fig. 5).

Motor and sensory flight neurones in a locust demonstrated using cobalt chloride.

AbstractThe central projections of motor and sensory neurons involved in the control of the wing beat in locusts have been analysed using cobalt chloride introduced axonally. From sections fo cobalt material, components of particular neuropile regions can be identified. The cobalt method offers an important advance in the analysis of insect neuropile.The flight motor neurones in the mesothoracic ganglion are all basically similar in shape, with no clear distinction between elevator and depressor neurones. All have a highly branched dendritic tree which ramifies extensively through the dorsal neuropile. A neurone innervating a particular muscle can be recognised in different individuals by characteristic features but the pattern of dendritic branching is variable. Neurones involved in both flight and walking have some branches in a deeper layer of neuropile than those concerned only with flight, where the branches lie superficially.Sensory projections from the flight sense organs are complex but compact and their positions in the neuropile are very predictable. They have large interganglionic components. The stretch receptors and wing sense organ projections lie mainly in the dorsal neuropile, whereas the other thoracic sensory receptors project ventrally, with branches to the dorsal neuropile at a few specific points. Associations between certain branches of sensory and motor neurones are demonstrated and their implications for the organisation of the flight reflexes discussed. It is suggested that parts of the motor neurone dendritic tree may be functionally equivalent to interneurones.

The neural control of cercal grooming behaviour in the cockroach, Periplaneta americana

The pro- and mesothoracic ganglia were found to inhibit cercal grooming behaviour controlled by the metathoracic ganglion. After nerve cord transection between the meso- and metathoracic ganglia, repetitive grooming movements with the metathoracic legs spontaneously occur. In experiments where the head and thoracic ganglia were serially excised, maximum activity occurred when all ganglia anterior to the metathoracic were removed. Stimulation of cercal afferents has long been known to induce evasive behaviour involving giant interneurons, but in animals with the nerve cord sectioned between the meso- and metathoracic ganglia, cercal stimulation increased cercal grooming behaviour. With asymmetrical cercal stimulation, the homolateral metathoracic leg engages in significantly more cercal grooming activity than the heterolateral metathoracic leg, thus indicating that this spontaneous activity can be modified by sensory input. When cercal afferents are stimulated with the anterior thoracic ganglia present, the metathoracic legs are coordinated in evasive running movements. With the anterior thoracic ganglia removed, the same type of cercal stimulation induces increased grooming activity with the metathoracic legs rather than running movements. The ventral nerve cord posterior to the head ganglia is preset, therefore, for escape rather than grooming activity when the cerci are stimulated, with cercal grooming continuously inhibited by the anterior thoracic ganglia. Simultaneous electrophysiological recordings from the metathoracic nerve 5 and the abdominal nerve cord showed that the efferent motor rhythm for grooming behaviour is independent of ventilative activity, also known to originate in the metathoracic ganglion. Spike patterns during grooming movements showed that different groups of levator and depressor neurons were alternatively active. Carbon dioxide concentrations which stimulated the metathoracic ventilative output caused a breakdown of cercal grooming activity, thus indicating a basic difference in the neural mechanism producing the two rhythms.

Effect of intraventricular phentolamine on hyper- and hypotensive vasomotor reflexes

Injection of small amounts of phentolamine into the lateral ventricle of the cat abolishes the blood pressure fall, evoked by vagal stimulation, and finally converts it into a pressure rise; all other vasomotor responses tested remain unchanged. In contrast, intraventricular pentobarbitone blocks both the pressor and depressor reactions following sciatic stimulation, although the vagal hypotension is again affected first. It appears probable that the depressor neurons, reached by afferent vagus fibers, are situated at the surface of the floor of the fourth ventricle and are thus accessible to intraventricular phentolamine. These neurons are activated by a-adrenergic transmission.