Serotoninergic and noradrenergic axons make contacts with neurons of the ventral spinocerebellar tract in the cat

Abstract

Contacts between monoaminergic fibers and electrophysiologically identified neurons of the ventral spinocerebellar tract were investigated in the cat. Five neurons were labeled intracellularly with rhodamine dextran, and monoaminergic fibers were revealed with antibodies against serotonin and dopamine beta-hydroxylase. The distribution of appositions between monoaminergic varicosities and the soma and the whole length of dendrites of these neurons was examined by using a three-channel confocal microscope. The analysis showed that close appositions between monoaminergic fibers and labeled processes occurred over the whole surface of the neurons. The highest percentage of such appositions was found on proximal dendrites, for both serotonin (37%) and noradrenaline (57%). The total number of serotoninergic contacts (66-134 per neuron) by far exceeded that of noradrenergic contacts (3-36 per neuron). Contacts between serotoninergic fibers and two neurons were analyzed by using electron microscopy. These neurons were labeled intracellularly with horseradish peroxidase, and serotoninergic varicosities were identified by immunocytochemistry. Six of 10 serially analyzed boutons in apposition to proximal dendrites were found to form morphologic synapses. The identification of the remaining four was inconclusive. These results indicate that many of the appositions seen in confocal microscopy may represent direct synaptic contacts. They also indicate that monoaminergic neurons may modulate activity of neurons of the ventral spinocerebellar tract by direct postsynaptic actions in addition to any effects evoked by means of volume transmission.

Nonuniform distribution of contacts from noradrenergic and serotonergic boutons on the dendrites of cat splenius motoneurons

“…1A). These results are identical to previous studies that used the same antibodies to determine the distribution of NA boutons on the dendrites of lamina VII interneurons (Maxwell et al, 2000), γ‐motoneurons (Gladden et al, 2000), ventral spinocerebellar tract neurons (Hammar and Maxwell, 2002), and commissural interneurons (Hammar et al, 2004) in the spinal cord of the cat. Together, these results show that the anti‐DβH antibodies used for this study specifically recognize a subset of axons and their collateral terminals in the cat spinal cord.…”

“…Our second goal was to compare the distribution of NA and 5‐HT boutons on the same set of motoneurons. It is known that NA neurons in the locus coeruleus and subcoeruleus project to the ventral horn and contact the dendrites of interneurons and gamma motoneurons (Westlund et al, 1983, 1984;Gladden et al, 2000;Maxwell et al, 2000;Hammer and Maxwell, 2002;Hammar et al, 2004;Noga et al, 2011), but there are no descriptions of the distribution of NA boutons on alpha motoneurons. Moreover, it is known that modulation of motoneurons by acetylcholine is exclusively mediated by C‐terminals that are restricted to the soma and proximal dendrites (Muennich and Fyffe, 2004;Wilson et al, 2004;Miles et al, 2007;Zagoraiou et al, 2009;Stepien et al, 2010).…”

Rhythmic activity of feline dorsal and ventral spinocerebellar tract neurons during fictive motor actions

“…In motoneurons, 5-HT is facilitating the persistent inward currents (Hounsgaard et al 1988;Hounsgaard and Kiehn 1989), and it is, therefore, interesting that the dorsal horn component of the DCST cells (Jankowska et al 1995), as well as Clarke's column cells (Pearson et al 2000), receive rather intense serotonergic innervations. Serotonergic innervations of VSCT cells are indeed similar to that of DSCT cells and hindlimb motoneurons (Hammar and Maxwell 2002), but there is no electrophysiological studies on how serotonin affects intrinsic properties of VSCT neurons during fictive motor activity. In addition, we would also like to bring up the possibility that VSCT and DSCT neurons may undergo a state-dependent enhancement of their excitability during fictive locomotion and scratch.…”

Quantitation of Contacts Among Sensory, Motor, and Serotonergic Neurons in the Pedal Ganglion of Aplysia

“…Recently, confocal microscopy has been used for high resolution analysis of connections between labeled neurons (Gan et al 1999;Cabirol-Pol et al 2000;Jacoby et al 2000;Hiesinger et al 2001;Hammar and Maxwell 2002;Gray and Weeks 2003). We used this technique to identify sites of proximity between sensory neurons and their followers.…”