A rapid method combining Golgi and Nissl staining to study neuronal morphology and cytoarchitecture.

The Golgi silver impregnation technique gives detailed information on neuronal morphology of the few neurons it labels, whereas the majority remain unstained. In contrast, the Nissl staining technique allows for consistent labeling of the whole neuronal population but gives very limited information on neuronal morphology. Most studies characterizing neuronal cell types in the context of their distribution within the tissue slice tend to use the Golgi silver impregnation technique for neuronal morphology followed by deimpregnation as a prerequisite for showing that neuron's histological location by subsequent Nissl staining. Here, we describe a rapid method combining Golgi silver impregnation with cresyl violet staining that provides a useful and simple approach to combining cellular morphology with cytoarchitecture without the need for deimpregnating the tissue. Our method allowed us to identify neurons of the facial nucleus and the supratrigeminal nucleus, as well as assessing cellular distribution within layers of the dorsal cochlear nucleus. With this method, we also have been able to directly compare morphological characteristics of neuronal somata at the dorsal cochlear nucleus when labeled with cresyl violet with those obtained with the Golgi method, and we found that cresyl violet-labeled cell bodies appear smaller at high cellular densities. Our observation suggests that cresyl violet staining is inadequate to quantify differences in soma sizes.

Rostrocaudal distribution of motoneurones and variation in ventral horn area within a segment of the feline thoracic spinal cord.

Retrograde transport of horseradish peroxidase, applied to cut peripheral nerves, was used to determine the rostrocaudal distribution of motoneurones supplying different branches of the ventral ramus for a single mid- or caudal thoracic segment in the cat. The motoneurones occupied a length of spinal cord equal to the segmental length but displaced rostrally from the segment as defined by the dorsal roots, with the number of motoneurones per unit length of cord higher in the rostral part of a segment (close to the entry of the most rostral dorsal root) than in the caudal part. The cross-sectional area of the ventral horn showed a rostrocaudal variation that closely paralleled the motoneurone distribution. The ratio between the number of motoneurones per unit length in the caudal and rostral regions of a segment (0.70) was similar to the ratio previously reported for the strength of functional projections of expiratory bulbospinal neurones (0.63). This is consistent with the motoneurones being the main targets of the bulbospinal neurones.

Convergence of selected inputs from sensory afferents to trigeminal premotor neurons with possible projections to masseter motoneurons in the rabbit.

Peripheral input convergence on trigeminal premotor neurons in the vicinity of trigeminal motor nucleus has been investigated. Thirty neurons were identified by their antidromic responses to microstimulation of the masseteric subnucleus of trigeminal motor nucleus (NVmot-mass). Peripheral receptive fields were found in the buccal mucosae, periodontal ligaments, palate, tongue and vibrissae for 16 neurons located in the intertrigeminal area (NVint), supratrigeminal area (NVs), main sensory trigeminal nucleus (NVsnpr) and subnucleus gamma of the oral nucleus of the spinal trigeminal tract (NVspo-gamma). Eleven neurons in the NVint, NVs and NVspo-gamma responded to passive jaw opening: nine neurons were activated and two were inhibited. None of the neurons responded to both the orofacial mechanical stimulation and passive jaw opening. Forty-six percent of neurons (13 out of 28 tested) received inputs from the inferior alveolar nerve (IAN) and 53% of neurons (8 out of 15 tested) received inputs from the infraorbital nerve (ION). Out of 15 neurons tested for inputs from the IAN and ION, 7 neurons in the NVsnpr and NVspo-gamma received input from both. Sixteen percent of neurons (4 out of 25) received inputs from the masseteric nerve (MassN). None of the neurons with inputs from IAN and/or ION also received inputs from the MassN. We suggest that trigeminal premotor interneurons with projections to the NVmot-mass fall into two broad categories, those with inputs from the IAN and/or ION and those with inputs from the MassN, possibly muscle spindle afferents, and no neuron receiving inputs from both.