Chemosensory integration in the spiny lobster: Ascending activity in the olfactory-globular tract

Summary In the frog,Rana esculenta, when the influence of the efferent vestibular system was eliminated, the spontaneous activity of single afferent fibres recorded from one branch of the nerve of the horizontal semicircular canal (HC) or of the nerve of the vertical anterior canal (VAC) was inhibited in 16–17% of the cases when stimulating electrically the other branch of the same ampullary nerve. Moreover, the spontaneous activity of about 200 afferent fibres was recorded from the nerves of the HC and VAC in three experimental situations. In the first one, the brain was destroyed, or the left vestibular nerve cut as it enters the brain stem, and all the branches of the left vestibular nerve were cut except for the one recorded (VAC or HC nerve); in the second one, recordings were made on the peripheral end of the ampullary nerve previously cut near the ampulla; in the third situation they were made on the ampullary nerve after having cut the vestibular nerve between the periphery and Scarpa's ganglion close to Scarpa's ganglion. Statistical comparisons of the distribution of the spontaneous frequencies and of the mean activities between the experimental situations show that the activities were greater in the second or third experimental situations than in the first one. These results could be explained by the existence of an inhibitory feedback loop outside the brain including Scarpa's ganglion and mediated by receptor-receptor fibres.Abbreviations HC horizontal semicircular canal - PE peripheral end of the ampullary nerve - VAC vertical anterior semicircular canal This research was supported by a grant from D.G.R.S.T. (Aide à la Recherche n 77.7.1127)     

Interrelations between auditory and vestibular receptors in the frog's labyrinth

Summary The influence of the efferent vestibular system being eliminated, the spontaneous activity of afferent fibres of the ampullary nerves of the horizontal and vertical anterior semicircular canals was recorded in the frog. By functionally eliminating either both papillae or all the vestibular receptors except for the papillae, and then using statistical methods, as well as by stimulating the papillae by sounds or the papillary nerve fibres by electrical stimulus, it has been shown that the auditory papillae have a facilitatory influence on the spontaneous afferent activity from the horizontal and vertical anterior canals. This influence is most likely mediated by receptor-receptor fibres arising from the auditory organs and innervating the semicircular canals.Abbreviations HC horizontal canal - VAC vertical anterior canal This research was supported by a grant from D.G.R.S.T. (Aide à la Recherche n 77.7.1127)     

Efferent activity in theOctopus statocyst nerves

Summary Single unit electrophysiological recordings were obtained from efferent fibres in the statocyst nerves ofOctopus vulgaris. A preparation comprising the CNS and a single statocyst was employed. 42% of the efferents displayed a level of resting activity; transient changes in this activity occurred at irregular intervals.The responses of the efferent units were examined during sinusoidal oscillations of the statocyst at stimulus frequencies between 0.01–1 Hz, and amplitudes up to 35°. 84% of the units showed activity synchronised with the imposed oscillations; the time taken to establish this response varied for different units (Fig. 1).The lowest stimulus frequency at which a unit could be entrained varied for different units, with those units with a resting level of activity having the lowest thresholds. The peak firing frequency of the efferents was found to increase with increasing stimulus frequency or amplitude (Fig. 3). However, the change in firing frequency was much smaller than that reported for the statocyst afferents to similar stimuli.The efferent units of the posterior crista nerve were found to respond to clockwise or anticlockwise rotations (Fig. 4), with the individual units having unipolar responses. The phase response of the units changed little with increasing stimulus amplitude but an increase in phase lag occurred with an increase in the stimulus frequency (Fig. 5). The form of this relationship (Fig. 6) was similar to that reported for the statocyst crista afferents.The principal source of the input to the efferents in these experiments was shown to be afferents from the contralateral statocyst. These results are discussed and compared with data from the vertebrate semicircular canal system.     

Response of efferent vestibular fibers to horizontal rotation in frogs (Rana esculenta L.)]

The activity of efferent vestibular fibres has been recorded on the nerve of the left vertical anterior semicircular canal detached from its ampulla during rotations in the horizontal plane. Different types of responses have been found; they are noted in table I and pictured on fig. 2.     

Relations of single semicircular canals to the pontine reticular formation.

The effects of afferent vestibular impulses on single pontine reticular formation units and on a small filament of the IIIrd cranial nerve were recorded with tungsten microelectrodes in 40 curarized guinea pigs. Single-shock and repetitive electrical stimulations were applied by means of stimulating electrodes inserted bilaterally into the perilymphatic space of single ampullae of the anterior and lateral semicircular canals. The reticular unitary response consisted mainly in excitation of the resting discharge rate: most units showed vestibular convergence being affected by separate stimulation of the single four ampullae. the reticular evoked field and unitary potentials accounted for latency values ranging from 0.3 to 2.5 msec. As for the early latencies they can be interpreted as responses mediated by direct vestibulo-reticular fibres. A delimited vestibular projection field in the parameidan pontine reticular formation was not identified.     

Action of the octavolateralis efferent system upon the lateral line of free-swimming toadfish,Opsanus tau

Summary The activation and action of the octavolateralis efferent system was studied by chronic recordings of discharge patterns from putative efferent and single primary afferent neurons in alert, free-swimming toadfish. Efferent axons isolated in the anterior lateral line nerve showed phasic discharges following touch stimuli applied to the head or trunk and demonstrated sustained discharges to visual stimuli. Resting discharge patterns of primary afferents were categorized into irregular, burster, regular, and silent classes. Afferent discharges were often modulated by low frequency (< 1 Hz) water movement around the head generated during respiratory movements. When fish with recording electrodes implanted in the lateral line nerve were visually stimulated, modulated peak discharges and average (DC) firing rates were inhibited in irregular-type units only. Inhibition of irregular-type afferent neurons also followed visual presentation of natural prey and persisted long after prey stimuli were removed from view. The inhibitory action upon lateralis afferents when activated by biologically significant visual stimuli leads to the hypothesis that the octavolateralis efferent system functions in the peripheral processing of information carried by the lateral line in natural settings.Abbreviations DC average - IO infraorbital - IPSPs inhibitory postynaptic potentials - MXC maxillary canal - OMC operculomandibular canal - SOC supraorbital canal     

Secondary hair cells and afferent neurones of the squid statocyst receive both inhibitory and excitatory efferent inputs

Summary Intracellular recordings were obtained from the hair cells and afferent neurones of the angular acceleration receptor system of the statocyst of the squid,Alloteuthis subulata. Electrical stimulation of the efferent fibres in the crista nerve (minor) evoked responses in all of the secondary hair cells recorded from (n=211). 48% of the secondary air cells responded with a small depolarization, 15% with a hyperpolarization, and 37% with a depolarization followed by a hyperpolarization. The depolarizations and hyperpolarizations had mean stimulus to response delays of 6.7 ms and 24 ms, and reversal potentials of about –1 mV and –64 mV, respectively. Both types of potential increased in amplitude, up to a point, when the stimulus shock was increased and facilitation and/or summation effects could be obtained by applying multiple shocks. These data, together with the fact that both responses could be blocked by bath application of cobalt or cadmium, indicate that the secondary hair cells receive both inhibitory and excitatory efferent inputs and that these are probably mediated via chemical synapses. No efferent responses were seen in the primary hair cells but both depolarizing and hyperpolarizing efferent responses were obtained from the afferent neurones.     

Inhibition and efferent facilitation of sensory activity in the isolated labyrinth of the frog

The functioning modalities of the efferent system were analysed in the isolated frog labyrinth. The efferent synapses of the posterior canal were activated via an axon reflex by antidromic electrical shocks (10-200 Hz) applied for increasing times (250 ms-10 s) to the anterior-horizontal nerves. Either decrease (inhibition) or increase (facilitation) in the resting discharge rate were observed in the majority of the units examined. Inhibition and facilitation, however, are peculiar to any given unit since inhibition does not reverse to facilitation or vice-versa. This fact as well as the long response latency (not less than 10 ms) and the linear dependence of both effects on the stimulation frequency suggest that inhibition and facilitation are due to the repetitive activation of two different types of efferent fibres synapsing on the hair cells. The drastic modifications in the afferent synaptic discharge produced by full activation of the efferent system indicate that the static properties (response asymmetry) as well as the dynamic properties (response adaptation) of the mechanically driven afferent response can be substantially controlled by the central nervous system at the receptor level.     

Single unit activity in the peripheral lateral line system of the cichlid fishSarotherodon niloticus L.

Summary The activities of single afferent fibers were recorded in the trunk lateral line nerve of the cichlid fishSarotherodon niloticus L. Using both electrophysiological recordings and neuroanatomical tracing techniques, the number, arrangement, and innervation of superficial (SNs) and canal (CNs) neuromasts were determined. Both, SNs and CNs, are innervated by several afferent fibers of different diameters and efferent fibers. The CNs and SNs are neuronally separated: afferent fibers which innervate both CNs and SNs were not found. Whereas the single CN is innervated by a separate set of afferent fibers, fibers innervating the SNs within rows often branched to reach all or several SNs. The SNs within a row were thus considered to form a functional unit. With the exception of SNs on the tail fin, functional units of neuromasts were in general topographically restricted to single scales.The majority of lateral line units had resting activity. On the basis of the time interval distribution of the resting activity, 4 types of units were classified: these were labelled irregular (type I), regular (type II), bimodal (type III) and silent (type IV). Type I was the most common type of resting activity (obtained in 47.8% of the recorded units). Units with this resting activity type were identified as afferents innervating either SNs or CNs. Units with resting activity of type II represented mostly afferents of CNs if their mean activity was high (around 40 imp/s). If the mean activity of this type was below 20 imp/s the units were unresponsive to local water movements and at least some were identified as efferent fibers. Resting activity of type III was found only in units originating from CNs. Only 4% of the units were silent (type IV). These units were often identified as injured neuromasts. Units originating from CNs show higher mean resting activity than those from SNs. For both SN and CN units, the mean discharge rate of the resting activity correlated with the sensitivity to stimulation for sinusoidal water movements.During stimulation of the neuromasts by sinusoidal water movements of small amplitude and different frequencies, the response characteristics of SN and CN units were determined by linear frequency analysis under steady state conditions. Most units responded linearly to small stimulus amplitudes. In this amplitude range the units' resting activity was modulated according to the stimulus frequency. Small stimulus amplitudes proportionally changed the amount of modulation but did not alter the phase of the response. CN and SN units that responded linearly produce differing frequency responses. Whereas CNs were most sensitive at frequencies of up to 200 Hz (center frequencies between 100 and 200 Hz), the center frequencies of SNs were distributed between 10 and 70 Hz with a maximum number at about 30 Hz. Bode plots for many CN and SN units indicated that the neuromasts were sensitive to the acceleration component of the water movement.The functional significance of the differences between the two types of lateral line neuromasts (SNs and CNs) were discussed.Abbreviations SN superficial neuromast - CN canal neuromast     

Morphological and electrophysiological consequences of unilateral pre- versus postganglionic vestibular lesions in the frog

The combined removal of the labyrinthine sense organs and of the ganglion of Scarpa on one side (postganglionic section) resulted in a degeneration of afferent fibres in the eighth nerve of the frog (Rana temporaria) within 2–4 days. If the eighth nerve was sectioned more peripherally (preganglionic section) and its distal part was removed together with the labyrinthine organs degeneration of afferent fibres was absent or restricted to very few fibres. Electrical stimulation of vestibular afferents in vitro evoked monosynaptic field potentials in the ipsilateral and via commissural fibres di-and polysynaptic field potentials in the contralateral vestibular nuclei. Afferent-evoked field potentials recorded on the intact side of chronic frogs ( 60 days) with a preor postganglionic lesion and afferent-evoked field potentials recorded on the operated side of chronic frogs with a preganglionic lesion had amplitudes that were very similar to those recorded in control frogs. Commissurally evoked field potentials recorded on the operated side of chronic frogs with preor postganglionic lesions were significantly increased (by about 90%) with respect to control amplitudes. In both groups the time-course of this increase was very similar, started between 15 and 30 days and saturated for survival periods longer than 60 days. Unilateral inactivation of vestibular afferents, but not degeneration, is the likely common denominator of the central process leading to the reported neural changes. A reactive supersensitivity of central vestibular neurons on the operated side for glutamate as a possible mechanism is unlikely, since converging afferent and commissural inputs are both glutamatergic and only one of them, the commissural input, was potentiated. Comparison of the time-courses of neural changes in the vestibular nuclei and postural recovery in the same individuals excludes a causal relation between both phenomena.Abbreviations HL hemilabyrinthectomy - VNC vestibular nuclear complex - HRP horseradish peroxidase - N. VIII eighth nerve - N. IX ninth nerve     

Action of vestibular receptors pn the spontaneous afferent activity of an ipsilateral semicircular canal in the frog]

In the frog, the influence of both the part of the efferent system which depends on ipsilateral vestibular inputs and the receptor-receptor fibre system on the afferent activity of semicircular canals is either null or facilitatory. The receptor-receptor fibre system being inhibitory, it seems that the part of the efferent vestibular activity which depends on ipsilateral vestibular inputs is facilitatory, which agrees with previous results.     

Vestibulo-ocular reflexes in the adult sea lamprey

Vestibulo-ocular reflexes were elicited in isolated preparations of small adult sea lampreys (Petromyzon marinus). Mechanical stimulation of the labyrinths or electrical stimulation of the vestibular nerves produced stereotyped, conjugated eye movements (Table 1) and appropriate electrical activities in individual extraocular muscles (Fig. 1). No inhibition of discharges in motor nerves was observed during stimulation of opposing reflexes. Likewise, nystagmus was never seen during continued stimulation. The primitive eye reflexes of the lamprey probably correspond to the simple excitatory pathways from single ampullae to individual eye muscles of higher vertebrates.     

Electrophysiological properties of the isolated vestibulocerebellar complex of the frog in vitro

Parameters of the electrical activity of the isolated vestibulocerebellar complex of the frog were studied under in vitro conditions. In the region of the vestibular nucleus (nc. VIII), in the presence of stimulation of the stato-acoustic nerve (n. VIII), responses from efferent vestibular neurones and from unidentified (probably vestibulospinal) neurones were recorded. The latent periods of their excitatory postsynaptic potentials (EPSPs, 1.4-2.2 ms) were indicative of mono- and disynaptic connection. Inhibitory postsynaptic potentials (IPSPs) were also observed. Stimulation of the auricular lobe of the cerebellum evoked monosynaptic IPSPs, an EPSP-IPSP complex or pure EPSPs in nc. VIII, the latter probably by way of collaterals to the cerebellum. The inhibitory character of the effect of efferents from the cerebellum to the neurones of nc. VIII was demonstrated in the focal synaptic potential and in spontaneous and evoked unit activity. If n. VIII was stimulated, both focal and unit extra- and intracellular responses characteristic of activation of the Purkinje cells by mossy (MF) or climbing (CF) afferent fibres were recorded in the cerebellar cortex. The electrophysiological picture indicates that both synaptic transmission and the functional manifestations of the individual neurones are preserved in the tested preparation.     

Comparative view of the central organization of afferent and efferent circuitry for the inner ear

In all vertebrates, eighth nerve fibres from the inner ear distribute to target nuclei situated in the dorsolateral wall of the rhombencephalon. In amniotes, primary auditory and vestibular nuclei are readily delineated in that acoustic nuclei lie dorsal and sometimes rostral to vestibular nuclei. Fishes and aquatic amphibians have, in addition to labyrinthine organs, hair cell receptors in the lateral line system. Eighth nerve and lateral line fibres from these sense organs project to the octavolateralis region of the rhombencephalon. In this region, the primary nuclei cannot be easily divided into functionally distinct units. However, modality-specific zones seem to be present for auditory as well as lateral line projections lie dorsal and sometimes rostral to those from vestibular organs. Projections from the primary auditory and vestibular nuclei to higher order centres follow pathways which are conservative in their architecture among vertebrates. Ascending auditory fibres project either directly or via relay nuclei to a large midbrain center, the torus semicircularis (inferior colliculus) and hence to the forebrain. In fishes and aquatic amphibians, the lateral line system also sends a projection to the midbrain and information from this system may be integrated with auditory input at that level. The organization of vestibulospinal and vestibulo-ocular pathways shows little variation throughout vertebrate phylogeny. The sense organs of the inner ear of all vertebrates and of the lateral line system of anamniotes receive an efferent innervation. In anamniotes and some reptiles, the efferent supply originates from a single nucleus (Octavolateralis Efferent Nucleus) while that of "higher" vertebrates arises from separate auditory and vestibular efferent nuclei. The biological significance of this innervation for all vertebrates is not yet understood. However, an important feature common to all is the association of the efferent system with the motor centres of the hindbrain.     

Vestibular efferent neurons forming projections to the saccule in the guinea pig

A comparative analysis was made of the distribution of vestibular efferent neurons projecting to the saccule and efferent cells sending out axons to the auditory nerve ("cochlear efferent neurons") in the guinea pig, using retrograde horseradish peroxidase axonal transport techniques. Saccular efferent neurons were discovered bilaterally in the subependymal granular layer at the base of the fourth cerebral ventricle and laterally to the facial nerve genu ispsilaterally in the parvocellular reticular nucleus, as well as nuclei of the superior olivary complex: the lateral olivary nucleus and lateral nucleus of the trapezoid body. Cochlear efferent neurons are located ipsilaterally in the pontine reticular caudal nucleus, in the anteroventral cochlear nucleus, and in the lateral and medial olivary nuclei. Neurons were found contralaterally in the medial nucleus of the trapezoid body. It thus emerged that location zones of vestibular saccular efferent neurons and those of cochlear efferent units partially overlapped. The possible involvement of saccular vestibular efferent neurons in the mechanisms of auditory perception is discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 22, No. 5, pp. 657–665, September–October, 1990.     

Brainstem neurons projecting to the ampullae of anterior,lateral, and posterior semicircular canals in the guinea pig

Neurons projecting to the ampullae of anterior, lateral, and posterior semicircular canals were identified in the guinea pig brainstem using horseradish peroxidase labeling techniques. Two groups of neurons forming bilateral connections were found, one located dorsally and the other ventrally to facial nerve trajectories. The dorsal group of vestibular efferent neurons projecting to all three canals was detected in the subependymal granular layer of the floor of the 4th ventricle lateral to the facial nerve genu and in the abducent nerve nucleus. Efferent neurons belonging to the ventral group were unevenly distributed through different areas of the parvocellularis nucleus and the rostral portion of the pontine caudal reticular nucleus. The morphological characteristics and distribution pattern of these cells are taken as confirmation of their heterogeneity of neuronal and functional organization in the vestibular efferent system of semicircular canal ampullae.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 20, No. 4, 1988, pp. 526–532.     

Convergence of autonomic,somatic, and vestibular afferent impulses on single units of the medullary vasomotor center of the cat

Responses of vasomotor neurons of the cat medulla to electrical stimulation of the depressor nerve and of mixed nerves of the limbs and to adequate stimulation of the vestibular apparatus were investigated. Evoked unit activity was demonstrated as groups of action potentials followed by inhibition of spontaneous activity. Three types of unit responses to stimulation of the depressor nerve and somatic afferent fibers and changes in unit activity in response to vestibular stimulation are described. The features distinguishing the convergence of afferent impulses on vasomotor neurons are discussed.Institute of Medico-Biological Problems, Ministry of Health of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 5, No. 5, pp. 460–467, September–October, 1973.     

NMDA receptors in afferent synapses of frog semicircular canals

The effects of competitive (2-amino-phosphonovaleric acid) and noncompetitive (Mg²⁺, ketamine, kynurenic acid) antagonists of N-methyl-D-aspartate (NMDA) receptors on synaptic transmission were studied in afferent synapses of the frog semicircular canals. All of these antagonists reduced the rate of background activity in the nerve of posterior semicircular canal by 30–50%, which confirms the presence of glutamate NMDA receptors in the hair cell synapses in the frog semicircular canals.Neurofiziologiya/Neurophysiology, Vol. 25, No. 3, pp. 168–169, May–June, 1993.     

Degeneration of the afferent fibers simulating the effects of motor denervation on skeletal muscle

Degeneration of afferent nerve fibres was induced in rats in order to observe its effects on the properties of the extra-junctional membrane of soleus muscle fibres. In one approach, removal of dorsal root ganglia L4 and L5 was accomplished in preparations with intact or impulse-blocked (with tetrodotoxin containing cuffs around the sciatic nerve) efferent innervation. Spike resistance to tetrodotoxin developed in the inactive deafferented preparations earlier and to a greater extent than in control, that is only impulse-blocked, preparations. In another series of experiments, efferent denervation alone proved to be less effective than the association of efferent and afferent denervation. On the other hand, section of the afferent fibres central to the dorsal root ganglia was without effect. These results are consistent with the interpretation that products of nerve degeneration contribute together with inactivity to the development of the extrajunctional membrane changes observed in skeletal muscle after denervation.     

Effect of motor stimulation and stretching on afferent activity of the neuromuscular spindle isolated from the frog]

The arrangement of muscle spindles in m. ext. long. dig. IV has been examined by microdissection. It is confirmed that spindle systems generally appear to consist of individual receptors. Stimulation effects of fast motor fibres (conduction velocities greater than 12 m/sec) on the spindles of the same muscle were studied. Receptors were isolated with their nerves and the appropriate spinal roots, the latter ones were used for stimulating efferent fibres and recording sensory discharges. Single shocks to the ventral root filaments caused afferent responses ranging from a single action potential to a train of impulses. During repetitive stimulation (train of stimuli at frequency of 10 to 150/sec) a marked increase in afferent activity was found. Afferent activity could be driven by the frequency of stimuli ("driving") and the stimulus/action potentials ratio varied from 1:1 to 1:3 or more. The rate of sensory discharge depended on the frequency of stimuli: the maximum effect, was attained at 30 to 50 stimuli/sec and, in the most responsive receptors, up to 80 stimuli/sec. Slight increases of the initial lengths of the receptors caused facilitation of sensory responses to motor stimulation. Moreover, impairing effects, which appear during sustained or high-frequency stimulation, possibly related to fatigue in intrafusal neuromuscular transmission, could be relieved by increasing the initial length. The repetitive stimulation of fast fusimotor fibres increased both dynamic and static responses and also raised the afferent activity after a period of stretching, when usually a depression occurs; these effects varied according to the preparation, its initial tension and the frequency of stimulation. The main feature of the examined motor fibres, when stimulated, is the constant excitatory action on muscle spindle static response. Results are discussed. It is suggested that the different characteristics of intrafusal muscle fibres, the receptor initial tension and the frequency of motor units discharges, may together affect muscle spindles static or dynamic performance.