Arrangement of Supramandibular and Suprahyoid Motoneurons in the Rat: A Fluorescent Tracer Study

The arrangement of the motoneurons innervating the supramandibular and suprahyoid muscles was studied in Wistar albino rats using two fluorescent tracers: nuclear yellow and true blue. All supramandibular motoneurons were found within the trigeminal motor nucleus; they appeared to be somatotopically arranged. The suprahyoid motoneurons were located in an accessory trigeminal-facial motor complex. No overlap of the motoneuron pools of the supramandibular and suprahyoid muscle group was observed. Only motoneurons ipsilateral to the treated muscles were labeled. It was shown that a one-to-one relationship always exists between motoneuron and muscl

Distribution of Synaptic Boutons in the Mesencephalic Trigeminal Nucleus of the Rat: A Quantitative Electron-Microscopical Study

The distribution of synapses and synaptic bouton types in the mesencephalic trigeminal (Me5) nucleus was examined in a quantitative electron-microscopical study. Of 588 terminal boutons that were counted in the compact caudal part of the Me5 nucleus, less than 8% formed synapses on the somata of the predominantly unipolar Me5 neurons. About 79% formed synapses on fibres located between the Me5 somata, while about 13% of the vesicle-containing terminals had no clear synaptic specialization. All of these non-synaptic terminals were G type boutons, with pleomorphic and large characteristic dense-core vesicles. Approximately 60% of the axosomatic synapses were of the S type, containing spherical vesicles and an asymmetrical or symmetrical synaptic specialization. About 20, respectively 15% of the axosomatic synapses, were of the F, respectively P type; both are symmetrical synapse types containing either a majority of flat or pleomorphic vesicles. Less than 10% of the axosomatic synapses were of the G type. Although some proportional differences were noted, an almost similar bouton type distribution pattern was found for the axodendritic synapses suggesting that the axosomatic and axodendritic synapses in the Me5 nucleus are part of the same afferent fibre plexus covering the Me5 nucleus

Brainstem influences on biceps reflex activity and muscle tone in the anaesthetized rat

This study analyzes the effect of electrical stimulation of the locus coeruleus (LC) and adjacent brainstem structures on the tonic reflex (TVR), the tonic stretch reflex (TSR) and on muscle tone (MT) in anaesthetized rat. Increases in TVR. TSR and MT of the m. biceps were evoked from regions rostrally and ventrally of LC, the caudal pontine reticular nucleus. the cuneiform nucleus and from the ventral paris of the colliculus inferior. Stimulation of the LC did not influence biceps EMG activity. The results indicate that the observed facilitation of muscle activity is due to stimulation of parts of the mesencephalic locomotor region. It is discussed that the recorded increase in TVR. TSR and MT possibly is due to an excitatory action on alpha-motoneurones on one hand and to an enhanced fusimotor drive on the other

Locus coeruleus projections to the dorsal motor vagus nucleus in the rat

The origin of the noradrenergic innervation of the preganglionic autonomic nuclei in the medulla oblongata and spinal cord is still controversial. In this investigation descending connections of the locus coeruleus to the dorsal motor vagus nucleus in the rat are studied with Phaseolus vulgaris leucoagglutinin and horseradish peroxidase as neuroanatomical tracers. Locus coeruleus projections in the motor vagus nucleus are found in the medial part at rostral levels and in the lateral part at intermediate levels of this nucleus. The terminal labeling in the lateral intermediate part of the vagus nucleus appears in an area where possibly preganglionic parasympathetic cardiac neurons are located, suggesting that the locus coeruleus might be involved in regulation of cardiovascular functions. After small iontophoretic injections of horseradish peroxidase in the motor vagus nucleus, retrogradely labeled cells are found in the ventral part of the locus coeruleus and occasionally in the dorsal part of the nucleus. The results show that the locus coeruleus-dorsal motor vagus nucleus pathway may participate in the inhibition of the cardiac preganglionic neurons in the dorsal motor vagus nucleus by the hypothalamic paraventricular nucleus

Origin, distribution and morphology of serotonergic afferents to the mesencephalic trigeminal nucleus of the rat

We have studied the localization, the morphology and sources of serotonergic input on the primary afferent neurons in the mesencephalic trigeminal nucleus (Me5) of the rat with light and electronmicroscopy immunocytochemistry and with anterograde and retrograde neuroanatomical tract tracing methods. Me5 neurons were found to receive a serotonergic input that is part of a serotonergic fibre plexus extending over the neighbouring parabrachial nucleus and locus coeruleus. These serotonergic afferents originate predominantly from serotonergic cells in the dorsal raphe nucleus

Projections of the parvocellular reticular formation to the contralateral mesencephalic trigeminal nucleus in the rat

Projections of the parvocellular reticular nucleus (PCRt) to the contralateral mesencephalic trigeminal nucleus (Me5) were studied in the rat with neurophysiological and neuroanatomical techniques. Three types of responses (classified by latencies) were recorded extracellularly in the Me5 area after electrical stimulation of the PCRt: (1) R1 fast unitary reactions (latency 0.2-0.5 ms) found throughout the entire caudal Me5 area; (2) R2 slower unitary reactions (latency 0.7-1.2 ms) recorded ventral and lateral to the caudal Me5; and (3) R3 compound potentials (latency 1.0-2.5 ms) recorded within the ventrocaudal Me5. Relayed or synaptic fields were not observed. Intracellular recordings of identified cell bodies of periodontal afferents, muscle spindle afferents and interneurones revealed no short-term postsynaptic potentials following PCRt stimulation. In some experiments jaw muscle spindle afferent activity was increased by PCRt stimulation and jaw-opening and jaw-closing reflexes were facilitated in the contralateral musculature. Neuroanatomical experiments, using Phaseolus vulgaris leucoagglutinin as an anterograde tracer, showed direct projections with intensive collateralization of PCRt fibres into the Me5 area. Synaptic contacts of PCRt fibres with primary afferent cell bodies were observed in the ventrocaudal parts of the Me5 only. The electrophysiological results are discussed in relation to the neuroanatomical findings