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The concept of comparing of the brains of various animals and of individual human brains was launched in the last half of the 17th century in England and was much influenced by the formation of the European scientific societies and their attempts to guide naturalist observations into a new systematics. An ambitious attempt to document this trend in an extensively illustrated work of encyclopedic pretensions was the singular publication of Samuel Collins (1618-1710), an energetic anatomist and president of the Royal College of Physicians. His little known tow-volume folio presentation, written in teh vernacular for broad acceptance, contains the seeds of a science of comparative neurology with the largest collection of brain illustrations (as well as of other organ systems) attempted in his era. Although lacking the conceptual insight that might derive from a true "comparative" anatomy and an understanding of the relations of different animals, the handsome engravings exemplified the new direction of the 'enlightenment' of the scientific revolution and are discussed in teh context of relevant events of this period.

Edward Tyson (1650-1708), a prominent London physician and an early fellow of the Royal Society is best known for his several anatomical contributions in the creation of primatology, including the preputial and coronal mucilaginous glands (Tyson's glands), later described by Alexis Littré. He also published the first comprehensive account of a single animal (the 'porpess') and placed it in the context of a systematic and experimental methodology. This rare monograph accounts for the contention that Tyson was the founder of comparative anatomy in England, by using this 'fish' to better understand the human condition. His description of the highly convoluted cetacean brain as well as his recognition of the many homologies with "land-quadrupeds", rather than the fishes it resembled, constitutes a major landmark contribution to the history of biology. The prevailing theological thrust of training in 'physick' ultimately led Tyson to evade the conundrum of how the human brain differs from that of animals, by attributing the intellectual uniqueness of man to endowments derived from God rather than the physical substance of the brain.

Regional distribution of gene expression of the axonal growth-associated protein, GAP-43, was studied in adult rat brains by in situ hybridization autoradiography to determine the features of mature neuronal populations that synthesize GAP-43 protein. Such synthesis appears to correlate with axonal growth during maturation and regrowth after axotomy. In most adult neurons, the sharp decline in GAP-43 gene expression implies a reduced capacity for axonal growth. Neurons capable of extending axonal knobs in the absence of injury may indicate a "plasticity" underlying dynamic processes of interaction between neurons and their synaptic targets. Antisense and sense (control) riboprobes were used on serial sections in the three principal axes, and the magnitude of hybridization signal was examined to determine regional patterns. GAP-43 mRNA levels are pronounced in diverse neuronal groups including the locus coeruleus, raphé nn., dopaminergic nigral and ventral tegmental nn., mitral cells, hippocampal CA3, inferior olivary n., vagal motor n. and other parasympathetic preganglionic neurons, select thalamic midline and intralaminar nn., several specific nn. of the hypothalamus and basal forebrain, the granular layer of cerebellar cortex, the infragranular neocortex, and the granular olfactory paleocortex; there is a substantial range in the magnitude of expression. Regions revealing minimal signal include most thalamic sensory relay nuclei, the granule neurons of the olfactory bulb and dentate gyrus, and the caudate and putamen. Possible concomitants of GAP-43 expression include regulation of ion flux and neurotransmitter release. Those neurons with long, extensively dispersed and numerous synaptic connections display the strongest signals and may possess the greatest propensity for continuous growth and turnover of their axon terminals, in contrast to short-axon and specific projection neurons exhibiting minimal levels. These data may enable inferring which populations display normal or experimentally induced axonal growth.

The distribution of the neuropeptide calcitonin gene-related peptide (CGRP) was studied in relation to the known subcortical somatosensory pathways and contiguous systems in the central nervous system (CNS) of rats by using peroxidase histochemical methods in order to relate zones of immunoreactivity (IR) to cytoarchitecture. CGRP is the most ubiquitous peptide found to date in sensory ganglion cells: principally small and medium-size neurons emitting thin axons inferred to be largely nociceptive in function on the basis of the peripheral distribution of their terminals. Its apparent absence in sympathetic axons provides an especially useful sensory marker. The distribution of CGRP-IR axons displays remarkable selectivity at each level of the CNS. The trigeminal root distributes axons primarily to the pericornual layers (laminae I and II) of spinal V nucleus caudalis and to subnucleus oralis, evading the subnucleus interpolaris and contributing only few axons to principal V. Although there are only a few CGRP-IR somata at each level, heavily labeled axon trajectories can be traced to the nuclei of the solitary tract, the parabrachial nuclei, several sectors of the caudal medial thalamus, and the central nucleus of the amygdala. A sector of labeled neuron somata lies contiguous to each of these axon terminal zones, the largest of which is a thalamic nucleus containing cells of distinctive dendritic architecture extending from the periaqueductal gray across the posterior group nuclei to the peripeduncular nucleus, forming a linear array at the mesodiencephalic junction. The relation of CGRP-IR axonal distribution to spinothalamic, visceral, and gustatory systems is discussed in the context of a specialized "chemosensory" component of the thin-fiber somatosensory system.

Results of experiments in which regional neuronal activity is revealed by a 2-[3H]deoxy-D-glucose (3H-2-DG)-paraffin section-emulsion autoradiography method are described. The trigeminal pathway of freely behaving mice was activated differentially by selective patterns of whisker removal. One hour after injection of concentrated 3H-2-DG, the animals were perfused systemically with a periodate/lysine/paraformaldehyde mixture (McLean, I. W., and P. K. Nakane (1974) J. Histochem. Cytochem. 22: 1077-1083), the brains were embedded in paraffin, and serial sections were taken and coated with emulsion for autoradiography. Diffusion of the isotope out of the tissue was assessed visually and by liquid scintillation counting. While substantial loss of 3H isotope into the embedding fluids (about 95%) was found, the scintillation counts and the autoradiograms showed good fixation of the isotope in situ, no evidence of isotope movement into the emulsion, and no gradients of diffusion in the sectioned material. Patterns of regional labeling were similar to those reported from brains prepared by conventional 2-[14C]deoxy-D-glucose (14C-2-DG) autoradiography; for instance, auditory and vestibular pathways in the brainstem were heavily and specifically labeled. Trigeminal structures associated with the intact (stimulated) whiskers were labeled relatively heavily, indicating that label uptake is specific with respect to neuronal activity. In the cortex, the patterns of label corresponded directly and precisely to those barrels known to receive inputs from the intact whiskers. Distribution of silver grains in the cortex and in the brainstem was correlated directly with neuronal profiles, including processes, some of which were identified by means of a Nissl counterstain. Clearly, this approach offers considerable technical advantages, in particular, the ease with which the histological material is prepared. The resolution of the autoradiograms and the quality of the histology are excellent.