Compartmentalization of excitatory amino acid receptors in human striatum

Consciousness beyond the comparator

Gray's comparator model fails to provide an adequate explanation of consciousness for two reasons. First, it is based on a narrow definition of consciousness that excludes basic phenomenology and active functions of consciousness. Second, match/mismatch decisions can be made without producing an experience of consciousness. The model thus violates the sufficiency criterion.

Ultimate differences

Gray unwisely melds together two distinguishable contributions of consciousness: one to epistemology, the other to evolution. He also renders consciousness needlessly invisible behaviorally.

Human consciousness: One of a kind

To avoid teleological interpretations, it is important to make a distinction between functions and uses of consciousness, and to address questions concerning the consequences of consciousness. Assumptions about the phylogenetic distribution of consciousness are examined. It is concluded that there is some value in identifying consciousness an exclusively human attribute.

Context and consciousness

The commentary argues (1) that we cannot be sure that human consciousness has survival value and (2) that in order to understand the origins and, perhaps, the function of consciousness, we should examine the behavioural and neural precursors to consciousness in nonhumans. An example is given of research on the role of context in decisions regarding fleeing from probable predators in the Mongolian gerbil.

Selective vulnerability in Huntington's disease: preferential loss of cannabinoid receptors in lateral globus pallidus

Selective neuronal vulnerability is a key feature of the neuropathology of Huntington's disease. We used [3H]CP-55,940, a synthetic cannabinoid, to label cannabinoid receptors in tissue sections from individuals dying with Huntington's disease and from normal control subjects. The density of cannabinoid receptors in striatum and pallidum was measured using quantitative autoradiography. There was a greater loss of cannabinoid receptors on striatal nerve terminals in the lateral pallidum compared to the medial pallidum, in Huntington's disease of all neuropathological grades. The disparity in binding density between the lateral and medial pallidum increased with higher grades of disease. There was also a greater loss of receptors in the lateral pallidum than in the putamen. The disproportionate loss of receptors in the lateral pallidum compared to the putamen increased in magnitude with severity of neuropathological grade. These data support the relative preferential loss or dysfunction of striatal neurons projecting to the lateral pallidum compared to neurons projecting to the medial pallidum. Terminals in the lateral pallidum containing cannabinoid receptors may be affected earlier or more severely than terminals in the medial pallidum, and both pallidal segments may be affected before or more severely than cell bodies or dendrites in the striatum. Terminal loss of markers may represent a response to perikaryal injury or dysfunction, or less likely, may indicate the primary site of neuronal damage in Huntington's disease.

Fos immunoreactivity after stimulation or inhibition of muscarinic receptors indicates anatomical specificity for cholinergic control of striatal efferent neurons and cortical neurons in the rat

Cholinergic neurons play a major role in the control of striatal activity via muscarinic receptors. The action of acetylcholine also appears to be dependent on the striosome-matrix compartmentalization of the striatum. This study was designed to find out whether modification of acetylcholine tone activates neurons in the striatum and forebrain of the rat. We looked for the appearance of immunoreactivity to Fos, a regulatory protein that is thought to convert synaptic signals into changes in gene expression. Pharmacological manipulation of muscarinic receptors was found to induce specific patterns of Fos immunoreactivity in distinct neuronal populations of the forebrain, including the striatum. Oxotremorine, a non-selective muscarinic agonist, induced Fos immunoreactivity in the striatum with a large predominance in striosomes (mostly in enkephalinergic neurons), in layers 4 and 6 of the cortex, and also in the piriform cortex and septum. The muscarinic agonist pilocarpine had an identical effect in the cortex, but the striosomal prevalence was less clear-cut than that observed after oxotremorine. Treatment with dopamine-depleting agents (6-hydroxydopamine or reserpine) and inhibitors of glutamate and opiate receptor (MK-801 and naloxone respectively) had no effect on the action of oxotremorine. This suggests that the induction of Fos provoked by oxotremorine does not involve dopamine, glutamate or opiates. Atropine, a non-specific muscarinic antagonist, also induced Fos immunoreactivity in the striatum but with matrix predominance (mostly in substance P neurons), as well as in the cingulate cortex, and the olfactory tubercle. Scopolamine, a muscarinic antagonist, induced Fos in both striosomal and matrix compartments in the striatum.(ABSTRACT TRUNCATED AT 250 WORDS)