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.     

Convergence of corticofugal impulses on pontine neurons

Convergence of corticofugal impulses in reticular and intrinsic pontine nuclei during stimulation of the frontobasal cortex (proreal, posterior orbital, and basal temporal regions) and also of the dorsal hippocampus was studied in acute experiments on cats anesthesized with a mixture of pentobarbital and chloralose. Three foci of convergence of corticofugal impulses were found in these structures: one in the reticular formation and two in the intrinsic nuclei—in their medial and lateral portions. Neurons with an excitatory type of response were shown to predominate in the reticular formation and neurons with an inhibitory or mixed type of response of neurons activated antidromically by stimulation of one brain region and synaptically during stimulation of another, that the pontine nuclei play an integrative role in the functional unification of structures of the frontobasal zones of the neocortex and hippocampus.M. Gor'kii Donetsk Medical Institute. Translated from Neirofiziologiya, Vol. 12, No. 5, pp. 472–480, September–October, 1980.     

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.     

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.     

Convergence and interaction of reticulofugal and peripheral afferent impulses on caudate neurons in the cat

Extracellular investigations on the activity of 269 caudate neurons during electrical stimulation of the midbrain reticular formation were carried out during chronic experiments on cats. Stimuli of different sensory modalities were used: auditory, mechanical, and visual. A response was observed to both reticular and peripheral stimulation in single neurons. The former produced an orthodromic response in 53% of caudate neurons, notable for its high probability of occurrence. A total of 23% of caudal neurons responded to this type of stimulation and application of stimuli of a single modality, while 14% responded polymodally. An excitatory response pattern prevailed during all types of stimulation. By applying twin stimuli to 100 caudate neurons, a capacity for interaction between reticular and acoustic inputs was discovered. Interaction was similarly observed in neurons which had reacted neither to separate application of both stimuli nor to either of the stimuli in isolation.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 19, No. 1, pp. 101–110, January–February, 1987.     

A simple technique for thermal stimulation of single semicircular canals.

Two simple thermodes for stimulating single semicircular canals have been designed in order to elicit eye nystagmus. The first, for warm stimulation, is based on the Joule effect: a silver needle is warmed up by means of a coiled nickrome wire. The temperature at the thermode tip is function of current intensity. The thermode for cold stimulation is a device in which a circulating freezing mixture cools a silver needle. The temperature at the thermode tip is proportional to the temperature of the freezing mixture.     

The semicircular canals of the hagfish Myxine glutinosa

The internal radius (r) and radius of curvature (R) of the single semicircular canals of Myxine glutinosa have unusual dimensions. In mammals and fish the increase in dimension of r and R with respect to body weight is small; in fish r is larger than in mammals of equivalent weight in order to increase the sensitivity of the canals to angular rotation and R increases correspondingly (Jones & Spells, 1963). In Myxine r is larger than in fish or mammals yet R is smaller. It is argued that the large internal radius is the result of the need to increase the sensitivity of a single canal which has to signal rotation in three planes while the small radius of curvature follows from the absence of a cupula. In order to verify that the cristae of the canals do respond to rotational velocity, recordings were obtained from the nerves serving the canals during rotation in the horizontal plane. The frequency response of several afferents recorded simultaneously at sinusoidal rotations between 0.25 and 2.0 Hz was in the form of a sine wave 90 in advance of head position, as would be expected of a velocity transducer. The gain of single afferents was an order of magnitude less than those reported for other vertebrates.     

Deep evolutionary diversification of semicircular canals in archosaurs

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Hypothalamic unit responses to impulses from the hippocampus and mesencephalic reticular formation

The effect of stimulation of the dorsal tegmentum mesencephali and dorsal hippocampus on spontaneous single unit activity of the retrochiasmal (RCA), lateral (LHA), medial dorsal (MHAd) and medial ventral (MHAv) hypothalamic regions was investigated in acute experiments on rabbits. During repetitive mesencephalic stimulation many more neurons were activated in all parts of the hypothalamus than during hippocampal stimulation. During mesencephalic stimulation more neurons were excited than inhibited in LHA, MHAd, and MHAv, but in RCA more were inhibited. During hippocampal stimulation spontaneous activity was inhibited in many more cells than during mesencephalic stimulation. Neurons on which convergence of impulses from the hippocampus and mesencephalon was observed numbered 25% in RCA, 39% in LHA, 46% in MHAd, and 29% in MHAv of the total number recorded. By their action (inhibitory or excitatory) on the hypothalamic neurons the mesencephalon and hippocampus were antagonistic in 60% of cases in RCA, 78% in LHA, and 61% in MHAd.I. P. Pavlov Institute of Physiology, Academy of Sciences of the USSR, Leningrad. Translated from Neirofiziologiya, Vol. 6, No. 5, pp. 489–495, September–October, 1974.     

Intrinsic organization of the paramedian pontine reticular formation of the cat.

A morphoquantitative analysis was carried out to clarify the cytoarchitectural organization of the paramedian pontine reticular formation (PPRF) which is considered to be an important site in the control of eye movements. The study was carried out on the cat, using the Golgi staining method. The topographic position and detailed structure of the neurons were demonstrated using morphoquantitative methods. On the basis of their neuronal arborization, fusiform neurons and two types of multipolar cells were identified. Fusiform neurons show dendrites which are given off from the two poles of the small- to medium-sized cell body. The arborization generally runs caudorostrally, ending inside the PPRF. These neurons are ubiquitous. Type 1 multipolar neurons, the most frequent elements of the neuronal population (60%), have a small- to large-sized cell body from which 2 or 3 primary spiny dendrites and the axon emerge. Their dendritic field is oval and generally oriented in the vertical plane. These neurons are scattered everywhere in the PPRF. Type 2 multipolar cells are large neurons endowed with numerous primary spiny dendrites constituting a wide round dendritic field and with a thick axon. They are located almost exclusively at the boundaries of the PPRF and preferentially in the caudal region. The characteristics of the neurons suggest that the fusiform cells may play an interneuronal role, while the multipolar neurons could have both a projective function and an important receptive role for the afferent fibers to the PPRF. The lack of homogeneity found among the multipolar neurons is in agreement with the variety of projective elements shown by functional investigations.(ABSTRACT TRUNCATED AT 250 WORDS)