Biomedical subjects

T Johannisson

Publications and source records attributed to T Johannisson.

10 recordsLinked to original sources

PubMed1991

Chromosomal aberrations in the mildly mentally retarded.

Chromosome analyses were performed on 52 mildly mentally retarded adults and a control group representing the non-retarded population. Chromosomal aberrations were found in 19.2% of the mentally retarded and in 1.9% of the controls. The aberrations in the retarded group consisted of trisomy 21, fragile-X, sex-chromosome aberrations and balanced translocations. The index group included a man with a fragile site Xp22.1. The aberration in the control group consisted of a karyotype with an extra marker chromosome.

Chromosome Deletion↗

PubMed1986

The inhibitory feedback pathway from the forelimb to C3-C4 propriospinal neurones investigated with natural stimulation.

Light mechanical stimulation of the skin and passive joint movements in the forelimb gave effective activation of interneurones located medially in the C3-C4 segments. Such interneurones may be inhibitory to C3-C4 propriospinal neurones (PNs) and recording from PNs revealed that the stimuli which activated the interneurones evoked inhibition in the PNs. It is postulated that a movement commanded via the C3-C4 PNs evoke impulses in forelimb afferents which by negative feedback control transmission in the C3-C4 PNs and thus govern the execution of the movements.

Afferent Pathways↗

PubMed1986

Hypermetria in forelimb target-reaching after interruption of the inhibitory pathway from forelimb afferents to C3-C4 propriospinal neurones.

Forelimb target-reaching in cats with a transection at C5/6 of the cortico- and rubrospinal tracts is known to depend on C3-C4 propriospinal neurones (PNs). An additional lesion transecting the dorsal column (DC) in C5/6, caudal to the C3-C4 PNs, gave pronounced hypermetria in lifting and protraction during target-reaching. If the additional DC lesion instead was made in C2, rostral to the C3-C4 PNs, there was only small hypermetria in lifting and none in protraction. It is postulated that the hypermetria after the C5/6 DC lesion is due to interruption of the inhibitory pathway from the forelimb to the C3-C4 PNs. It is suggested that feedback control from the forelimb of the premotoneurones is an integral part of the control of normal target-reaching.

Afferent Pathways↗

PubMed1986

Effects of dorsal column transection in the upper cervical segments on visually guided forelimb movements.

Complete transection of the dorsal column in C2 in cat gave severe defects in forelimb target-reaching and food-taking tested with retrieval of food from a cylinder. Among the symptoms were marked dysmetria in all directions and dyscoordination of movements in different joints, with only slow recovery over weeks and months. It is postulated that normal visual guidance of forelimb movements to a stationary target depends on somatosensory information to the brain via the dorsal column.

Afferent Pathways↗

PubMed1986

Projection of Ia and Ib afferents from forelimb muscles to the C3-C4 segments of the cat spinal cord.

Group Ia muscle spindle afferents were activated separately by small stretches applied to the tendons of antibrachial muscles in the forelimb in the cat. Group Ib tendon organ afferents were stimulated electrically after a selective increase of the threshold of the Ia afferents. Recordings of focal synaptic potentials were made in the C3-C4 segments in the medial part of the base of the dorsal horn. It has been found that both Ia and Ib afferents have monosynaptic connections with neurones in this medial region. Quantitatively, these two groups of afferents produced focal synaptic potentials of approximately the same size. The connections may be to inhibitory interneurones projecting to the C3-C4 propriospinal neurones, which are known to receive disynaptic IPSPs from group I muscle afferents.

Afferent Pathways↗

PubMed1984

Forebrain function: a theory about the general organization.

It is suggested that the cerebral cortex is made up of many non-overlapping units which are regulated by the thalamus in such a way that just a few of them are "on" at a time. How these units are built up and by which neurones is discussed in some detail. Explanations are proposed for some psychiatric and neurological disorders. Furthermore, two memory mechanisms are discussed briefly.

Axons↗

PubMed1983

Shared reflex pathways of group I afferents of different cat hind-limb muscles.

The convergence of group I muscle afferents of different muscle origin onto interneurones in spinal reflex pathways has been investigated using the technique of spatial facilitation of the transmission from afferents to motoneurones. The investigated pathways are those of non-reciprocal inhibition and of oligosynaptic excitation of motoneurones. Extensive convergence has been found of group I afferents from muscles operating at the same and different joints onto the interneurones interposed in both excitatory and inhibitory, disynaptic and trisynaptic pathways to motoneurones. Convergence has been found between muscle spindle Ia and/or tendon organ Ib afferents from different muscles, thereby extending observations on convergence of these subgroups of group I afferents from the same muscles. The results show that group I afferents of different muscles influence motoneurones via shared neuronal pathways and that transmission from these afferents is influenced by afferents originating in other muscles. The afferent information forwarded to individual motoneurones is therefore the ensemble picture of the length and tension of many muscles.

Action Potentials↗

PubMed1983

Segmental actions of afferents of the interosseous nerve in the cat.

Electrical stimulation of the interosseous nerve evokes oligosynaptic inhibition of extensor motoneurones and excitation of flexor motoneurones. Lowest-threshold, shortest-latency post-synaptic potentials evoked at group I strength are attributed to the action of group Ib afferents. Post-synaptic potentials evoked at slightly higher stimulus strengths (within the higher group I and the group II range) and at longer latency are attributed to the action of afferents of Pacinian corpuscles. Facilitation of post-synaptic potentials evoked from afferents in the interosseous nerve by group I muscle afferents and by joint afferents is taken to indicate convergence of these afferents onto common interneurones in reflex pathways to motoneurones. Evidence is presented that afferents of Pacinian corpuscles project to the interneurones mediating group I (non-reciprocal) reflex actions to motoneurones. Unitary monosynaptic excitatory post-synaptic potentials (e.p.s.p.s) evoked from the interosseous nerve are taken to indicate that only a very small number of muscle spindle Ia afferents course through the interosseous nerve. Dorsal root potentials evoked by low-strength electrical stimulation of the interosseous nerve are largely attributable to the action of afferents of Pacinian corpuscles.

Action Potentials↗

PubMed1981

Common interneurones in reflex pathways from group 1a and 1b afferents of ankle extensors in the cat.

1. Input from group I afferents of ankle and toe extensors, other muscles, skin nerves and descending tracts to interneurones of Rexed's laminae V-VI in the cat spinal cord was analysed using intracellular recording from these interneurones. Adequate stimuli (muscle stretches) were used to activate selectively group Ia muscle spindle afferents of triceps surae and plantaris while other fibre systems were excited electrically. 2. Ia and Ib afferents of ankle and toe extensors were found to co-excite, co-inhibit or exert opposite synaptic actions in 41, 33, and 50% of the analysed interneurones, respectively. Taking into account both excitatory and inhibitory input from these two groups of afferents, 64% of the interneurones appeared to be used in common in reflex pathways from muscle spindles and tendon organs of ankle and toe extensors. 3. Selective input from Ib afferents of triceps surae and plantaris (excitation and/or inhibition) was found in 36% of the interneurones; there was evidence for a similarly selective input from Ia afferents. 4. A great majority (over 90%) of the interneurones excited by group I afferents were also inhibited by group I afferents, from either the same or other muscles. 5. Both monosynaptic and disynaptic e.p.s.p.s from Ia and/or Ib afferents from other muscles and from fibres in the ipsilateral funiculi were found in a great proportion of the same interneurones, together with disynaptic e.p.s.p.s from low threshold cutaneous afferents. 6. Intracellular staining with horseradish peroxidase revealed four different patterns of axonal projections of the analysed interneurones: (i) projections to motor nuclei and the intermediate region, (ii and III) projections only to the intermediate region, locally or combined with projections to different rostro-caudal levels, and (iv) projections to the opposite side of the spinal cord. 7. A large proportion of interneurones projecting to motor nuclei displayed input from both Ia and Ib afferents although such an input was a feature of interneurones with other projections as well. No systematic differences in the input from group I afferents were found for interneurones with different axonal projections. In contrast disynaptic e.p.s.p.s of cutaneous origin and monosynaptic e.p.s.p.s upon stimulation of ipsilateral spinal tracts appeared predominantly in interneurones projecting to motor nuclei.

Afferent Pathways↗

PubMed1979

Autogenetic inhibition of motoneurones by impulses in group Ia muscle spindle afferents.

1. Inhibitory post-synaptic potentials evoked by adequate stimulation of group Ia muscle spindle afferents of homonymous and synergistic muscles and by selective electrical stimulation of tendon organ afferents were analysed in motoneurones of triceps surae and plantaris. 2. Selective activation of Ia afferents was verified to occur with brief stretches of triceps surae and plantaris 35 micrometer or less in amplitude with an initial muscle tension of 5 N; stretches of 30--35 micrometer were estimated to activate 80--90% of Ia afferents in these muscles. Under the same conditions the lowest thresholds for group Ib tendon organ afferents were about 40 micrometer. 3. Stretches less than or equal to 30 micrometer evoked i.p.s.p.s in 80% of triceps surae and plantaris motoneurones; lowest thresholds for evoking i.p.s.p.s wef triceps surae and plantaris motoneurones; lowest thresholds for evoking i.p.s.p.s were 10 micrometer or less. However, such low thresholds for stretch-evoked i.p.s.p.s, lower than the thresholds for activation of Ib afferents, were found mainly in spinalized, unanaesthetized (after decerebration) or lightly anaesthetized animals. The latencies of these i.p.s.p.s indicated disynaptic and trisynaptic coupling between Ia afferents and motoneurones. The i.p.s.p.s were evoked (i) from the homonymous and synergistic muscles stretched together, (ii) from the homonymous muscles alone and (iii) from the synergistic muscles alone. 4. Control experiments showed that i.p.s.p.s could be evoked by stretches sub-threshold for discharging motoneurones, thus showing that those i.p.s.p.s were not mediated by Renshaw cells. The stretch-evoked i.p.s.p.s disappeared after sectioning the nerves from the corresponding muscles, further excluding their mediation by afferents other than group Ia afferents from thf stretched muscle. 5. In order to selectively activate tendon organ afferents, thresholds for excitation of Ia afferents by electrical stimuli were increased to a level above the threshold for Ib afferents by prolonged muscle vibration (Coppin, Jack & MacLennan, 1970). I.p.s.p.s evoked by stimuli near threshold for Ib afferents appeared with latencies indicating disynaptic coupling. Later (trisynaptic) components of Ib i.p.s.p.s required somewhat stronger stimuli. 6. Amplitudes of Ia i.p.s.p.s evoked by muscle stretches activating about 80% of muscle spindle afferents were compared with amplitudes of Ib i.p.s.p.s due to less than 50% of tendon organ afferents of the same muscles. The Ia i.p.s.p.s were much smaller (16--35%) than the Ib i.p.s.p.s. The amplitudes of such Ia and Ib i.p.s.p.s constituted about 10 and 25--66%, respectively, of the maximal i.p.s.p.s evoked by electrical stimulation of all group I afferents. 7. We conclude that inhibition of motoneurones may be evoked from Ia muscle spindle afferents from homonymous and synergistic muscles as well as from Ib tendon organ afferents...

Animals↗