Molecular dynamics simulations of end-grafted centipede-like polymers with stiff charged side chains.

We use molecular dynamics simulations to investigate centipede-like polymers with stiff charged side chains, end-grafted to a planar wall. The effect of the grafting density and the Bjerrum length on the conformational behaviour of the brush is examined in detail. In addition, we make a comparison of centipede-like polyelectrolyte (CPE) brushes with neutral centipede-like polymer (NCP) and linear polyelectrolyte (LPE) brushes. At weak electrostatic interaction, the main chains of the CPE chains adopt a strongly stretched conformation, and the monomer density profiles of side chains exhibit a clear oscillatory behaviour. With increasing Bjerrum length, the CPE brush undergoes a collapse transition. Compared to the CPE brushes, the counterion condensation effect is stronger for the LPE brushes, regardless of whether the electrostatic interaction is weak or strong and of whether the grafting density is low or high. Additionally, it is shown that the architecture of the grafted chains makes a weak contribution to the counterion condensation at strong electrostatic interaction. We also find that the electrostatic repulsion between charged side chains can enhance the stiffness of the main chains and thus limit the range of movement of the free-end monomers.

Histamine excites rat cerebellar Purkinje cells via H2 receptors in vitro.

Recent neuroanatomical studies have revealed a direct hypothalamocerebellar histaminergic pathway. However, the functional significance of the histaminergic fibers in the cerebellum is not yet clear. In this study, the effects of histamine on the firing of cerebellar Purkinje cells (PCs) were investigated in vitro. Histamine predominantly produced excitatory (106/111, 95.5%) and in a few cases inhibitory (5/111, 4.5%) responses in PCs. The histamine-induced excitation was not blocked by perfusing the slice with low Ca2+ high/Mg2+ medium (n = 8), supporting a direct postsynaptic action of histamine. The histamine H2 receptor antagonist ranitidine effectively blocked the excitatory response of PCs to histamine (n = 20), but triprolidine, an H1 receptor antagonist, could not significantly block the histamine-induced excitation, or only very slightly decreased the excitatory effect of histamine on the cells (n = 13). On the other hand, the highly selective H2 receptor agonist dimaprit mimicked the excitatory effect of histamine on PCs and this dimaprit-induced excitation was also blocked by ranitidine (n = 20), but not triprolidine (n = 8). However, the H1 receptor agonists betahistine and 2-thiazolylethylamine did not show any effect on the PCs (n = 9 and 14). These results reveal that histamine excites cerebellar PCs via H2 receptors and suggest that the hypothalamocerebellar histaminergic fibers may play an important role in functional activities of the cerebellum.

Classical conditioning of the eyeblink reflex in the decerebrate-decerebellate rabbit.

The purpose of these experiments was to test the hypothesis that a conditioned nictitating membrane reflex can be acquired in decerebrate rabbits in the absence of the cerebellum. Experiments examining the effects of large cerebellar lesions on the acquisition and performance of the conditioned reflex were performed in acutely prepared decerebrate rabbits. Most lesions encompassed all of the cerebellar nuclear regions ipsilateral to the eye receiving the unconditioned stimulus. In all rabbits included in this study the continuity between the cerebellar nuclei and the brainstem was interrupted, even in those preparations in which small regions of the nuclei were present in the lateral hemisphere. The findings demonstrate that these animals could acquire the conditioned reflex independent of whether conditioning had occurred prior to the cerebellectomy. Strong associativity was found between the latency of the conditioned response and the interstimulus interval between the conditioned and unconditioned stimuli. The behavior of the conditioned reflex observed in the decerebrate-decerebellate animals differed from that reported for awake intact rabbits in two ways. Once the conditioned behavior had been acquired, the percent of trials showing conditioned responses was somewhat less in decerebrate-decerebellate rabbits and was also more variable in these animals. The data demonstrate that the nictitating membrane reflex can be classically conditioned in the absence of the cerebellum, indicating that this structure is neither necessary nor sufficient for the acquisition of this type of conditioned behavior. In addition, an hypothesis is presented which addresses the difference between the data reported here and those previously reported by other laboratories based on observations in awake intact animals.