Chloride Iontophoresis Research Articles

Mutual inhibition between Bötzinger-complex bulbospinal expiratory neurons detected with cross-correlation in the decerebrate rat

We examined the synaptic connections between pairs of Bötzinger-complex, bulbospinal expiratory neurons in decerebrate rats. All were antidromically activated from the spinal cord at the C2-C3 border. Cross-correlation histograms of 18 ipsilateral pairs showed troughs on both sides of time zero (8) and to one side of time zero (4); most (12) were accompanied by peaks at time zero. Similarly, cross-correlation histograms of the contralateral pairs (12) showed troughs on both sides of time zero (3) and to one side of time zero (3); few (2) were accompanied by peaks at time zero. We considered the troughs in these cross-correlation histograms to be evidence of inhibition between the neurons and sought confirmation of the inhibitory connection. First, using the antidromic activation stimulus, we computed post-stimulus histograms of the extracellularly recorded discharge for six neurons and found that three showed troughs. Then, we continued this approach, computing post-stimulus averages of the membrane potentials recorded intracellularly from these neurons after iontophoresis of chloride to reverse inhibitory synaptic potentials. Depolarising potentials were observed in 15 of 16 of these averages. We interpreted these as reversed inhibitory post-synaptic potentials and concluded that Bötzinger-complex, bulbospinal expiratory neurons inhibit one another in rats as they do in cats.

Synchronization of ventral-group, bulbospinal inspiratory neurons in the decerebrate rat.

We examined the synaptic connections between ventral-group, bulbospinal inspiratory neurons in 27 vagotomized, paralyzed, ventilated, and decerebrated rats using cross-correlation and spike-triggered averaging of intracellular potentials. The neurons were recorded in the medulla about the level of the obex and identified by their inspiratory firing pattern and antidromic activation from the spinal cord at C7. Whole C5 phrenic nerve recordings were made using bipolar electrodes from the central cut ends of the nerve. Most (108/137, 79%) inspiratory neurons discharged only during inspiration but some (29/137, 21%) also discharged during early expiration. Their intracellular membrane potentials displayed a pattern of depolarization during inspiration, repolarization during early expiration, and hyperpolarization during late expiration. Intracellular chloride iontophoresis changed the inspiratory membrane potential trajectories from augmenting to decrementing in 11 of 19 neurons tested (58%), and demonstrated the presence of both early-decrementing and late-augmenting waves of inhibitory postsynaptic potentials during expiration in 11 of 19 neurons tested (58%). Cross-correlation histograms were computed between pairs of extracellularly recorded neurons to detect short time scale synchronizations indicative of synaptic connections (26 ipsilateral; 23 contralateral). While none of the cross-correlation histograms for contralateral pairs showed peaks, most (23, 88%) of those for ipsilateral pairs showed peaks (mean half-amplitude width +/- SD = 1.3 +/- 0.4 ms) at time zero suggestive of common activation. Some of the latter (6, 23%) showed troughs superimposed on the central peaks (mean half-amplitude width +/- SD = 0.9 +/- 0.2 ms) at short latencies (mean latency +/- SD = 1.8 +/- 1.9 ms) suggestive of inhibition; others (8, 31%) had asymmetrical central peaks and two had bilateral peaks suggesting more complex interconnections. Averages of intracellular membrane potentials of inspiratory neurons (n = 24), triggered by action potentials of a nearby extracellularly recorded inspiratory neuron, were computed to detect synchronized postsynaptic potentials. Over half (16, 67%) showed postsynaptic potentials (mean amplitude +/- SD = 201 +/- 176 microV; mean half-amplitude width +/- SD = 2.3 +/- 0.8 ms) confirming the cross-correlation findings of common excitation. We conclude that in decerebrated rats, ventral-group inspiratory neurons projecting to the C7 spinal segment share powerful, ipsilaterally distributed excitatory inputs which enhance their synchronous activity during inspiration. They also receive inhibition during inspiration and early-decrementing and late-augmenting inhibitory inputs during expiration.

Neural organization of the ventilatory activity in the frog, Rana catesbeiana. II

The paralyzed, decerebrate frog, Rana catesbeiana, displays "fictive" oropharyngeal and pulmonary ventilations. In order to evaluate the neuronal correlates of these two centrally programmed ventilatory bursting patterns, we have performed intra- and extracellular recordings of bulbar respiratory neurons in this fictively breathing preparation. A total of 123 respiratory neurons were recorded from the caudal medulla. Of 51 antidromically activated neurons, 20 were vagal motoneurons and 31 were hypoglossal motoneurons. Respiratory neurons that depolarized during the lung (L) or non-lung (N) ventilatory phases were classified as L or N neurons, respectively. Phase spanning neurons (S) were active during both L and N phases. Some neurons showed oscillations of membrane potential synchronous with oropharyngeal ventilation. Those active during the buccal elevation phase were exclusively L neurons, whereas those having buccal depressor activity were exclusively N neurons. Synaptic drive potentials were observed in all neurons recorded intracellularly. In some neurons, hyperpolarization was caused by inhibitory postsynaptic potentials, as demonstrated by reversal of membrane potential trajectory after intracellular chloride iontophoresis. Some individual motoneurons and interneurons exhibited both pulmonary and buccal ventilatory activity, indicating that both pattern generators project to a common motor control system.

Multi-phase expiratory inhibition of phrenic motoneurons in the decerebrate cat.

We studied the membrane potential changes of 11 phrenic motoneurons (PMs), located in the C5 portion of the cervical spinal cord, in decerebrate, paralyzed and artificially ventilated cats. Intracellular chloride iontophoresis into PMs could reverse the waves of inhibitory postsynaptic potentials (IPSPs) causing membrane hyperpolarization during expiration. In all PMs, we revealed, in addition to the previously described late expiratory augmenting wave of IPSPs, an early expiratory decrementing wave of IPSPs. Moreover, in three PMs, recorded in two cats exhibiting slow respiratory rhythms, an additional wave of IPSPs was interposed between the early and late ones. The possible origins and roles of these three different waves of inhibition are discussed.

Immunocytochemical identification of proctolinlike immunoreactivity in the terminal ganglion and hindgut of the cockroach Periplaneta americana (L.).

In the American cockroach, the distribution and connections of neuronal elements of the terminal ganglion-proctodeal nerve-hindgut system were investigated by means of immunohistochemical methods and axonal CoCl2 iontophoresis. Proctolinlike immunoreactivity was localized within neurons of the terminal ganglion projecting into the proctodeal nerve on the one hand, and in nerve cells without a direct connection to this system on the other. Immunohistochemically, in whole mount preparations fibres of the proctodeal nerve and terminal structures in the hindgut musculature exhibit strong proctolinlike immunoreactivity. At the light- and electron-microscopic levels the pathways of about 30 somata of the proctodeal neural system were characterized by cobalt chloride iontophoresis. The relationships of cobalt filled and immunoreactive neuronal structures are discussed.

Identification of neuronal pathways between the stomatogastric nervous system and the retrocerebral complex of the cockroach Periplaneta americana (L.).

The neuronal pathways connecting the stomatogastric nervous system with the retrocerebral complex of the cockroach, Periplaneta americana, were investigated by means of axonal cobalt chloride iontophoresis. Somata in the hypocerebral ganglion and in the nervus recurrens sending their axons to different parts of the stomatogastric nervous system were traced. Some axons in the oesophageal nerve arise from large perikarya in the anterior part of the pars intercerebralis and pass via the NCCI to the corpora cardiaca and the oesophageal nerve. The form a profuse dendritic tree in the protocerebrum. Fibers of the NCC I and NCC II as well as the NCA I and NCA II enter the stomatogastric nervous system via the hypocerebral ganglion.

Carrier frequency-sensitive primary auditory neurons in crickets and their anatomical projection to the central nervous system

The tympanal organ of the cricket Scapsipedus marginatus contains receptor neurons that are tuned to the dominant frequency of the species-specific calling song ( F 1 units), as demonstrated by single unit recordings. F 1 units have simple threshold curves with just one characteristic frequency, and they can be characterized by their latency and adaptation rate. The pattern with which these units respond to song indicates that they are a principal source of peripheral input to the CNS for song reception. The tympanal nerve sends its sensory arborizations to the ventromedial neuropile of the prothoracic ganglion. Fibers of the tympanal nerve do not cross the midline; nor do they project to other ganglia, insofar as can be demonstrated with cobalt chloride iontophoresis.

Iontophoresis of lidocaine into frog sciatic nerve fibers

Iontophoresis applied to frog nerves with subthreshold concentration of lidocaine at the anode greatly facilitated inhibition of nerve action potential (NAP). Neither sodium chloride iontophoresis nor cathodal iontophoresis of lidocaine inhibited NAP. This experiment indicates that lidocaine entry into nerve fibers is facilitated by anodal iontophoresis.

Electron microscopic identification of postsynaptic dorsal root terminals: a possible substrate of dorsal root potentials in the frog spinal cord

Dorsal root fibers were labeled with cobaltous chloride iontophoresis for electron microscopic investigations. In the base of the dorsal horn, where most of the coarser collaterals of dorsal root fibers terminate, many dorsal root terminals were found in postsynaptic relation to synapsing profiles. According to their morphological characteristics, three kinds of presynaptic terminals could be discerned in these complex synapses: axon terminals with spheric vesicles, axon terminals with flattered vesicles and presynaptic dendrites. These latter terminals contained relatively few flattened vesicles accumulated adjacent to a short synaptic articulation surface, and they were rich in cytoplasmic organelles. The functional significance of these structural specializations in the mediation of dorsal root potentials and recurrent inhibition is discussed.

Destruction in vivo de neurones ocellaires chez la Blatte, Periplaneta americana

Cobalt chloride has on the ocellus of the cockroach Periplaneta americana, the same destroying effect as a thermocauterisation or electrocoagulation. When an iontophoretic diffusion of cobalt chloride is done without any current from the ocelli, the second-order ocellar neurons are destroyed yet no modification is observed in the vital functions of the cockroach. Cobalt chloride iontophoresis could be used to destroy ocellar neurons only if these ocellar neurons are not going to be immediately replaced. Experiments show that the ocellar neuron killed is replaced after apolysis, but if the substitute neuron is destroyed in its turn, the destruction is definitive. These results suggest two methods of destruction for second-order ocellar neurons: one for larvae and one for adult cockroaches.

Ocellus and ocellar nerves of Periplaneta americana L. (Orthoptera: Dictyoptera)

The structure of the cockroach ocellus is described following electronmicroscopical examination. A flat or slightly concave cuticular lens overlies the visual cell groups contained within the upper two-thirds of the ocellar cup. There are no pigment cells or cone cells, no orderly arrangement of visual cell groups nor layering of the latter. Each visual cell group consists of up to 5 visual cells. Visual cell axons develop from visual cells at different depths along the length of the visual cell groups and pass downwards through the reflecting tapetal layer (urate crystals). In the base of the ocellar cup, into which the visual cell axons pass in bundles, are the ocellar giant fibre branches. In this synapsing region both bar and ribbon-type synapses have been observed.The 5 large bipolar fibres in each ocellar nerve enter the brain close to the midline, pass backwards and downwards to arborise in 3 distinct regions of the ipsilateral brain neuropile. Eight cell bodies have been located associated with the 5 large neurones of the ocellar nerve plus 3 of the smaller fibres. Cobalt chloride iontophoresis has been used to visualise the pathways and cell bodies of the ocellar nerve fibres. One fibre appears to traverse the brain to the region where the nervus corporis cardiaci II has its origin. No ocellar fibres enter the ventral nerve cord directly. Some of the implications of these findings are discussed.

The treatment of deep thrombophlebitis and chronic leg ulcers with acetyl-beta-methylcholine chloride iontophoresis

Iontophoresis with acetyl-beta-methylcholine chloride was used in the treatment of nineteen patients with deep thrombophlebitis with good results in eighteen cases. The same form of therapy was employed in thirteen cases of chronic leg ulcers of various etiology; these ulcers had completely healed in twelve cases, and in the thirteenth the lesion was healing rapidly when last observed.