Sexual dimorphism of glial fibrillary acidic protein (GFAP) immunoreactivity in the rat interpeduncular nucleus

The intensity of immunostaining for the glial fibrillary acidic protein (GFAP) is outstandingly high in the interpeduncular nucleus. This nucleus was compared in males and females for its GFAP immunoreaction. Immunohistochemistry was carried out on free floating vibratome slices and evaluated by surface densitometry. While in males the reactions were similar, females showed individual variations. Since the interpeduncular nucleus is a hormonally inactive brain area where gonadal hormones do not induce plastic synaptic changes, it is concluded that concerning this astroglial marker a sexual dimorphism exists also outside the "endocrine brain".     

Distribution and synaptology of vasoactive intestinal polypeptide (VIP) immunoreactive structures in the rat periaqueductal grey

Light microscopic analysis of the rat midbrain periaqueductal grey (PAG) showed vasoactive intestinal polypeptide immunoreactive (VIP-ir) neurons localized at the lateral and ventral walls of the aqueduct. Some varicose VIP-ir elements were detected closely associated with the ependyma. While several VIP-ir elements were encountered immediately under the ependyma, in a few cases, VIP-ir cell bodies were seen on the luminal surface of the ependymal cells lining the aqueduct. Electron microscopy revealed that most of these cells possessed the characteristics of a local circuit neuron. All VIP-ir cells had indented nuclei. Two types were distinguished: one with rounded cell body receiving numerous axo-somatic synapses established by VIP-negative axons. The other cell type was fusiform and its surface was almost fully isolated from axonal contacts by a glial sheath. The VIP-ir processes were interconnected with other periaqueductal cells by a variety of synaptic contacts. VIP-ir axon terminals formed asymmetric synapses with immunonegative dendritic shafts often in glomerulus-like assemblies. The postsynaptic immunonegative dendrites were of the aspinous, beaded type. We suggest that VIP-ir cells and processes in the midbrain PAG establish connections between the longitudinal functional columns of this region. On the basis of their morphology, VIP-ir cells in the PAG appear to be excitatory, terminating on inhibitory interneurons. Thus, a VIP-stimulated inhibition may be instrumental in the coordination of responses evoked by the stimulation of PAG columns.     

Wall thickness of gas- and marrow-filled avian long bones: measurements on humeri, femora and tibiotarsi in crows (Corvus corone cornix) and magpies (Pica pica)

We studied how the ratio K of the internal to external diameter of gas- and marrow-filled avian long bones follows the biomechanical optima derived for tubular bones with minimum mass designed to fulfil various mechanical requirements. We evaluated radiographs of numerous humeri, femora and tibiotarsi in Corvus corone cornix and Pica pica. The K-values of the gas-filled humerus (K=0.78+/-0.03) and the marrow-filled femur (K=0.79+/-0.02) in Corvus are practically the same, while K of the marrow-filled tibiotarsus (K=0.71+/-0.04) is significantly smaller. The same is true for the gas-filled humerus (K=0.78+/-0.02) and the marrow-filled femur (K=0.77+/-0.02) and tibiotarsus (K=0.67+/-0.05) in Pica. K in Corvus is slightly larger than K in Pica, but the differences are statistically not significant. The standard deviation DeltaK of the tibiotarsi (DeltaK=0.04-0.05) is approximately two times as large as that of the humeri (DeltaK=0.02-0.03) and femora (DeltaK=0.02) in both species. Accepting the assumption of earlier authors that the ratio Q of the marrow to bone density is 0.5, our data show that the marrow-filled tibiotarsi of Corvus and Pica are optimized for stiffness, while the marrow-filled femora are far from any optimum. The relative wall thickness W=1-K of the gas-filled avian humeri studied is much larger than the theoretical optimum W*=1-K*=0.07, and thus these bones are thicker-walled than the optimal gas-filled tubular bone with minimum mass.     

Testing the biomechanical optimality of the wall thickness of limb bones in the red fox (Vulpes vulpes)

The optimum for the ratio K of the internal to external diameter of a marrow-filled tubular bone with minimum mass designed to withstand a given type of strength (yield/fatigue, stiffness, fracture or impact) depends on Q = rhom/rhob only, where rhom and rhob are the densities of marrow and bone. With computer-assisted evaluation of radiographs of 62 femurs in the red fox (Vulpes vulpes) we measured the values of K. The mean and standard deviation of K are 0.68 and 0.036, and K changes in the rather wide range from 0.59 to 0.74. Accepting the assumption of earlier authors that Q = 0.50 or 0.44, our data would support the hypothesis that the fox femurs are optimized to withstand yield, fatigue or stiffness strengths. However, since the Q-values are unknown, the possibility cannot be excluded that any studied fox bone with an appropriately selected Q-value is optimized for any strength type. Assuming Q = 0.50 or 0.44, the relative mass increments mu of the investigated fox bones are smaller than 5% under all four mechanical conditions. The evolutionary relevance of such tiny mu-values is questionable.     

Seasonal fluctuations of glial fibrillary acidic protein (GFAP) immunoreactivity in the rat suprachiasmatic nucleus

The pacemaker of the "biological clock", the suprachiasmatic nucleus (SCN) of the hypothalamus was studied in intact male rats for glial fibrillary acidic protein (GFAP) a specific marker for astrocytes. Immunohistochemical reactions were carried out in winter (January-February) and in summer (June-July). In winter the GFAP-immunoreactivity of the SCN was found low whereas in summer it was high. Gonadectomy reduced differences. Since photic stimuli that apparently trigger the observed differences reach the SCN through identified neuronal pathways we conluded that the reaction of astrocytes is an indicator of seasonally altered neuronal function in the SCN.