Showing papers on "Cuneate nucleus published in 1971"

Amino acids and presynaptic inhibition in the rat cuneate nucleus

Abstract: 1. Presynaptic inhibition was evoked in the rat cuneate nucleus by a peripheral conditioning stimulus. The dicarboxylic amino acid salts glutamate and aspartate and the neutral amino acids glycine and γ-aminobutyric acid (GABA) were topically applied to a restricted area of the cuneate nucleus and their effects on both resting primary afferent terminal excitability and the increase in excitability of afferent terminals during presynaptic inhibition determined. 2. Aspartate had no effect on either resting primary afferent terminal excitability or on the increase in excitability during presynaptic inhibition. 3. Glycine reduced both resting primary afferent terminal excitability and presynaptic inhibition. 4. Glutamate increased both resting primary afferent terminal excitability and presynaptic inhibition while GABA increased resting primary afferent terminal excitability but reduced the increase in excitability during presynaptic inhibition. 5. The convulsant alkaloids picrotoxin (given intravenously) and bicuculline (topically applied) blocked presynaptic inhibition. The blocking action of picrotoxin was overcome by topical application of GABA but not glutamate. 6. Simultaneous measurement of pre- and post-synaptic excitability in the cuneate nucleus showed that while glutamate increased excitability at both sites, GABA increased primary afferent terminal excitability but depressed post-synaptic excitability. 7. It is concluded that glycine and glutamate exert non-specific actions on primary afferent terminals similar to their effects at post-synaptic sites elsewhere in the C.N.S. while GABA depolarizes primary afferent terminals by a specific action at the same receptor site as the presynaptic inhibitory transmitter. The possibility is discussed that the presynaptic inhibitory transmitter in the cuneate nucleus is GABA or a closely related substance.

Origin and termination of cuneocerebellar tract

Abstract: 1. The origin and termination was determined for cells belonging to the cuneocerebellar tract in the cat, which consists of one proprioceptive component (P-CCT) activated by group I muscle afferents and one exteroceptive component (E-CCT) activated by cutaneous afferents. The recording sites of the cells were histologically verified and the termination of the axons assessed by antidromic activation from the cerebellar surface. 2. The P-CCT originates from cells in the external cuneate nucleus, where forelimb muscles are somatotopically represented. The observations suggest that practically all cells in this nucleus project to the cerebellum and are activated by muscle afferents. 3. The E-CCT originates from cells in the rostral part of the main cuneate nucleus, where they occur intermingled with lemniscal neurones. 4. The CCT terminates in the pars intermedia of lobule V of the anterior lobe and in the four rostral folia of the paramedian lobule. The majority of the cells send one branch to each projection area. 5. The P-CCT and E-CCT terminate in the same projection areas. 6. CCT neurones activated from distal and proximal parts of the limb terminate diffusely in the entire projection area, although there is some tendency for neurones activated from distal parts to terminate caudally and for neurones activated from proximal parts to terminate rostrally.

Organization of afferent connections to cuneocerebellar tract.

Abstract: 1. The afferent connections to 180 cuneocerebellar tract (CCT) neurones were studied in the cat. The neurones were classified into two groups, proprioceptive and exteroceptive. 2. The proprioceptive neurones (P-CCT) occurred in the external cuneate nucleus and were monosynaptically activated by group I muscle afferents. About 60% of these neurones received additional excitation from group II muscle afferents. 3. The P-CCT neurones received excitation from one nerve only. 4. The P-CCT neurones received postsynaptic inhibition from muscle nerves not supplying excitation. 5. The exteroceptive neurones (E-CCT) occurred in the main cuneate nucleus and received di- and polysynaptic excitation from cutaneous afferents. Most neurones received additional excitation from high threshold muscle afferents. The latter originated from receptors that were sometimes activated by pressure against deep structures but seldom, if ever, from slowly adapting stretch receptors in muscle. 6. The E-CCT neurones were usually activated from several skin and muscle nerves. 7. Stimulation of the sensorimotor area of the cerebral cortex evoked inhibition in some P-CCT neurones and excitation and/or inhibition in some E-CCT neurones. 8. The afferent organization of the CCT is compared with that of the dorsal spinocerebellar tract. The information carried by the two tracts is discussed.

Post-synaptic Inhibition in the Cuneate blocked by GABA Antagonist

Abstract: PICROTOXIN has been shown to antagonize specifically the inhibitory action of λ-aminobutyric acid (GABA) as opposed to glycine (Gly) on cells of the cuneate nucleus, either spontaneously active or excited by peripheral stimulation1. Bicucul-line also seems to be a specific antagonist of the depressant action of GABA in several regions of the mammalian nervous system2, although probably not in others3.

Prostaglandins and neuronal activity in spinal cord and cuneate nucleus

Abstract: During recent years there has been increasing interest in the role of prostaglandins in the central nervous system. The possibility that these compounds may be mediators of synaptic transmission was raised when it was shown that they are natural constituents of nervous tissue(Samuelsson,l964; Coceani & Wolfe,1965; Horton and Main,l967),and that they are released from brain following stimulation of afferent pathways(Ramwel1 & Shaw,l966;Ramwell et alIl966;Bradley et a1,1969). Additional support for this idea came from the demonstration of a specific prostaglandin synthetase in brain(van Dorp,1966). From this standpoint,prostaglandins seemed to comply with the classical attributes of a transmitter substance. Other evidence,however,is not consistent with this view. In a series of investigations,Horton and coworkers demonstrated that prostaglandinstwhether injected into the cerebral ventricles(HortonIl964)or into the blood stream(Duda et a1,1968),have persistent actions on central neurons which are incompatible with the rapid breakdown expected for a transmitter. Similar findings were reported by Phillis and Tebecis(l968)for toad spinal neurons. Also, work performed on peripheral synapses proved that a variety of stimuli promote the release of prostaglandins from tissuestand hence mimic the effects of activation of nerves(Ramwel1 & Shaw,1967;LaityI1969). The sum of experimental data indicates that prostaglandins are unlikely to mediate synaptic transmissionland that they conform better to the role of a modulator substance. It is not clear at present by what means prostaglandins affect neuronal activity. Evidence from studies with peripheral synapses suggests that they regulate the release of transmitters (Hedqvist,l970). Another possibility is that they act within the effector membrane to curtail or enhance the effectiveness of the transmitter(Hedgvist~l97O;Coceani et al, 1967). In this connectionlit is significant that prostaglandins have been shown to antagonize the action of noradrenaline on cerebellar Purkinje cellstpossibly through an action on the adenyl cyclase-cyclic AMP system.(Hoffer et a1,1969).

Subdivision of the trigeminal sensory root. Experimental study in the monkey.

Abstract: ✓ In 16 rhesus monkeys, rhizotomy of the whole trigeminal nerve and selective rhizotomy of each division were carried out, and neural degeneration techniques used, to determine whether a trigeminal root component exists which projects only to the main sensory or spinal nucleus of the trigeminal nerve. Such a root component was not found. Section of the rostral trigeminal fibers resulted in degeneration in both the main sensory nucleus and the spinal trigeminal nucleus. Section of the caudal fibers of the root produced degeneration similar to third division transection, indicating that the caudal fibers are from that division. The first- and third-division fibers were found to project to the ventral and dorsal portions of the main sensory nucleus and spinal nucleus. Findings showed that the most rostral portion of the root immediately adjacent to the motor root is predominately from the ophthalmic division. Some proprioception from the trigeminal area appears to be mediated through the medial cuneate nucle...

The action of carbon dioxide on synaptic transmission in the cuneate nucleus.

Abstract: 1. The excitability of synaptic structures in the cuneate nucleus was studied in eighteen decerebrate, unanaesthetized cats during acute changes in inspired P(CO2).2. Micro-electrode stimulation in the caudal half of the cuneate nucleus evoked antidromic and orthodromic responses which were recorded simultaneously from a forelimb nerve and from the medial lemniscus at the transected mid-brain surface.3. Increases in the concentration of inspired CO(2) (2-20%) progressively decreased the direct excitability of both the afferent fibre terminals (reflected in the antidromic potentials) and the cuneate relay neurones (reflected in the alpha wave of the orthodromic lemniscal response). Synaptically mediated responses, recorded as the beta component of the lemniscal potentials, were also depressed.4. The relation between input and output at the cuneate was determined by plotting antidromic against trans-synaptic (beta lemniscal) responses for different intensities of stimulation. The mean slope for logarithmic values of control potential amplitudes was 1.17 (+/- S.E. 0.13). It therefore appears that the transfer function for the cuneate is linear over a wide range.5. In the majority of experiments the input-output relation was unchanged or increased by raising P(CO2). It was concluded that the efficiency of synaptic transmission and release of transmitter appeared to be well maintained or possibly increased at individual active synapses during hypercarbia.6. The depressant action of CO(2) on afferent transmission can therefore be attributed largely to a block of impulse conduction in the primary afferent fibres.

Visual and Auditory Inputs into the Cuneate Nucleus

Abstract: Sound clicks or light flashes modify somatic sensory activity in the cuneate nucleus of the cat. The techniques of gross potential recording in the cuneate nucleus or medial lemniscal tract, of single unit recording in the cuneate nucleus, and of excitability testing of cuneate terminals demonstrate this heterosensory interactionsensory interaction.