Morphometric analysis of feedforward pathways from the primary somatosensory area (S1) of rats

We used biotinylated dextran amine (BDA) to anterogradely label individual axons projecting from primary somatosensory cortex (S1) to four different cortical areas in rats. A major goal was to determine whether axon terminals in these target areas shared morphometric similarities based on the shape of individual terminal arbors and the density of two bouton types: en passant (Bp) and terminaux (Bt). Evidence from tridimensional reconstructions of isolated axon terminal fragments (n=111) did support a degree of morphological heterogeneity establishing two broad groups of axon terminals. Morphological parameters associated with the complexity of terminal arbors and the proportion of beaded Bp vs stalked Bt were found to differ significantly in these two groups following a discriminant function statistical analysis across axon fragments. Interestingly, both groups occurred in all four target areas, possibly consistent with a commonality of presynaptic processing of tactile information. These findings lay the ground for additional work aiming to investigate synaptic function at the single bouton level and see how this might be associated with emerging properties in postsynaptic targets.

AN IMMUNOELECTRON MICROSCOPIC STUDY ON THE SYNAPTIC RELATIONSHIP BETWEEN DOPAMINERGIC AND GABAergic NEURONS IN THE BASOLATERALNUCLEUS OF THE RAT AMYGDALA / 解剖学报

Objective To explore the relationship between dopaminergic axon terminal and GABAergic neurons and explore the neuroanatomic mechanism of their effects in schizophrenia. Methods The co-location and the association of dopaminergic axon terminal and GABAergic neurons in the basolateral nucleus (BL) of rat amygdala were examined by using double labeling immunoelectron microscopic techniques. Dopaminergic axon terminal and GABAergic neurons were labeled with the antidopamine (anti-DA) and the anti-glutamic acid decarboxylase (anti-GAD) antibodies respectively. Results 43% of the DA-input synapses was observed to relate directly or indirectly to GAD-immunoreactive(IR) dendritic structures(DA/GAD), which includes single (38%), convergent (30%), serial (20%), and axoaxonic (12%) contact types.And 57% of the DA-input synapses was found to associate with unlabeled elements (DA/UE), which includes unlabeled perikarya (10%), dendrites (82%) and axons (8%). All of the synapses that show DA-IR terminals profiles were found to be symmetric (inhibitory) synapses.Conclusion These results suggest that the dopaminergic system in the BL of rat amygdala controls the mediations of the GABAergic interneurons via symmetric synapses. In addition, the dopaminergic axon terminal associates with the glutamatergic projection neurons and exerts influence on its activity.

ULTRASTRUCTURE OF THE DESCENDING RUBRAL FIBERS IN LAMINA V OF THE CAT TRIGEMINAL SUBNUCLEUS CAUDALIS——HRP LABELING AND DEGENERATION STUDY / 解剖学报

After a injection of kainic acid or WGA-HRP into the red nucleus, the degenerated or HRP labeled terminals in lamina V of the contralateral trigeminal subnucleus caudalis (Vc) were examined electron microscopically. It was found that the degenerated and HRP labeled terminals contained vesicles of spherical or mixed type, and formed symmetrical synapses with medium- or small-sized dendrites. These findings suggested that the descending rubral fibers might be inhibitory in regulating the activity of the neurons, and supposed to be sensory in nature. Thus the red nucleus might play certain role in modulation of the oro-facial somatosensory transmission (including pain) in lamina V of Vc, besides the rubrospinal influence on the involuntary motor functions of the spinal anterior horn. The technique for tracing neural connections with electron microscope was discussed as well.