The aim of the present study is to provide a complete description of the distribution of choline acetyltransferase (ChAT) immunoreactivity (i) in the brain of the lizard Gallotia galloti, on the basis of two different primary antisera: rat anti-ChAT and rabbit anti-chicken ChAT. Considering that the brain is a segmented structure, we have analysed our data with respect to transverse segmental domains (or neuromeres), which have been previously described by several authors in the brain of vertebrates. In the telencephalon, ChATi neurons are seen in the cortex, anterior dorsal ventricular ridge, basal ganglia, diagonal band, and bed nucleus of the stria terminalis. Further caudally, ChATi cell bodies are located in the preoptic area, hypothalamus, habenula, isthmus, and all motor efferent centers of the brainstem and spinal cord. Plexuses of ChATi fibers are observed in the areas containing cholinergic cell bodies. In addition, distinct plexuses are found in the cortex, the posterior dorsal ventricular ridge, the neuropiles of all primary visual centers of the diencephalon and mesencephalon, and several non-visual nuclei of the brainstem. The distribution of ChAT immunoreactivity in the brain of G. galloti resembles in many respects that of other vertebrates, and differences are mainly observed in the pretectum and midbrain tectum. Transverse segmental domains were identified in the brainstem and forebrain of Gallotia when the cranial nerve roots and fiber tracts were used as a reference, and most cranial motor nuclei were found to occupy the same segmental positions as have been reported in the chick.

Hyposmia is one of the most prevalent symptoms of Parkinson's disease. It may occur even before the motor symptoms start. To determine whether the olfactory dysfunctions, like the motor symptoms, are associated with a loss of dopamine, the number of dopaminergic cells in the olfactory bulb of Parkinson's disease patients was studied using tyrosine hydroxylase immunohistochemistry. The quantitative analysis reveals that the total number of tyrosine hydroxylase-immunoreactive neurons in the olfactory bulb is twice as high in Parkinson patients compared to age and gender-matched controls. Because dopamine is known to inhibit olfactory transmission in the olfactory glomeruli, we suggest that the increase of dopaminergic neurons in the olfactory bulb is responsible for the hyposmia in Parkinson patients. The increase of dopamine in the olfactory bulb explains why olfaction does not improve with levodopa therapy.

In order to elucidate the geometric organization of projections from the barrel cortex to the thalamus, iontophoretic injections of the anterograde tracer Phaseolus vulgaris-leucoagglutinin were made. The injections were confined to one barrel column (i.e. barrel in layer IV + cortical tissue above and below it). Axonal terminations could be demonstrated in three thalamic nuclei: reticularis (RT), ventrobasalis (VB) and posterior (PO). Anterograde terminal labelling was obtained in RT + VB; in PO only; or in RT + VB + PO. The terminals labelled in PO were much larger than those in RT and VB. The termination areas in RT, VB and PO were shaped like rods which have a rostro-caudal orientation. These cortico-thalamic projections are discretely and topographically organized. The clearest such arrangement was found in VB. Here, projections from the A row of barrels in BF terminate dorsally, whereas those from the C row end ventrally. Barrel A1 projects to the lateral part of VB, whereas A4, to more medial parts; other rows are arranged similarly. These results were compared with the distribution of thalamo-cortical projection neurons that were labelled after iontophoretic HRP injections in individual barrels. We concluded that the corticothalamic projections originating from one barrel column contact an are of barreloids in VB.

In order to analyze the organization of the efferent projections of single barrel columns (BC, i.e. a barrel in layer IV of parietal cortex plus the cortical tissue above and below it), we made small iontophoretic injections of the anterograde tracer Phaseolus vulgaris leucoagglutinin in the barrel cortex of 20 adult mice. On the basis of reconstructions of the sites of terminal labelling, the brain regions receiving projections from the barrel cortex could be identified and classified in five groups. Each group is characterized by the topography of the distribution of efferents arising from a single BC. The projections to the trigeminal sensory complex are point to point: i.e. one BC projects only to the site of termination of the primary sensory neurons innervating the corresponding whisker follicle. In the ventrobasal thalamic nucleus BC projections are not restricted to the corresponding barreloid; instead they contract parts of barreloids belonging to one arc. In the reticular and posterior thalamic nuclei the projections from a row of BC's converge to a collective termination site, whereas in the superior colliculus the projections from an arc of BC's converge to a common termination site. There is a complete overlap of BC projections in restricted zones within SII, motor cortex, perirhinal cortex, contralateral barrelfield, caudoputamen and pons. The organization of the efferents from the barrel cortex demonstrates a contrast between feedback and feedforward projections from this important area of neocortex.