Heterogeneous distribution of the limbic system-associated membrane protein in the caudate nucleus and substantia nigra of the cat

The limbic system-associated membrane protein is a glycoprotein selectively associated, in the adult, with dendrites and cell bodies of neurons of the limbic system and related brain regions. In the present study, the distribution of the limbic system-associated membrane protein was studied by immunohistochemistry in the caudate nucleus and substantia nigra of the cat to determine how its expression relates to the compartmentalization of these areas. In all areas of the caudate nucleus, the pattern of limbic system-associated membrane protein immunoreactivity was highly heterogeneous, labeling zones that were in register with areas expressing neurochemical markers that classically identify striosomes. The extrastriosomal matrix exhibited low levels of staining. The results show that the limbic system-associated membrane protein is expressed by neurons within the target areas (striosomes) of subsets of limbic afferents (originating mainly from the basolateral nucleus of the amygdala and the prefrontal cortex), whereas regions of the caudate nucleus (extrastriosomal matrix) receiving inputs from other subdivisions of the limbic system, such as the cingulate cortex and the ventral tegmental area, contain relatively low levels of limbic system-associated membrane protein immunoreactivity. Thus the expression of this antigen may reflect the targeting of specific groups of limbic afferents to regions that are intimately associated with distinct components of the limbic system. The presence of limbic system-associated membrane protein in neurons of the substantia nigra pars compacta does not appear to be related to the presence or absence of the protein in their striatal target areas.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunoreactive GAP-43 in the neuropil of adult rat neostriatum: localization in unmyelinated fibers, axon terminals, and dendritic spines

GAP-43 is a neuron-specific phosphoprotein that has been implicated in neuronal development, axonal regeneration, and synaptic plasticity. Although in mammals the caudate-putamen is among those brain areas that retain a high content of GAP-43 throughout life, the role of the phosphoprotein in the neostriatum is unknown. In order to understand better the possible function(s) of GAP-43 in the adult striatum, its cellular localization was examined with immunohistochemistry at the light and electron microscopic levels by using a sheep polyclonal antibody. At the light microscopic level immunoreactive GAP-43 was abundant throughout the neostriatal neuropil but was absent from neuronal somata. At the ultrastructural level, labeling was most prevalent in small unmyelinated axons (0.12-0.15 microns diameter). Reaction product was distributed along fibers in discrete patches about 1 micron apart and in preterminal sites from which vesicle-filled boutons arose. Staining was also present in small (0.35 microns) axon terminals that contained round vesicles and formed asymmetric synapses, mostly with thin spines. Following unilateral cortical lesions, some degenerating cortical axons in the neostriatum exhibited GAP-43 labeling. Unexpectedly, in normal striatum, GAP-43 was also occasionally found in the heads of dendritic protrusions and in thin spines that received asymmetric contacts. We speculate that in the adult neostriatum, the protein may be important in the remodeling of synapses onto medium spiny neurons that involve, in part, the corticostriatal pathway.

Lever pressing for food reward and changes in dopamine turnover and uric acid in rat caudate and nucleus accumbens studied chronically by in vivo voltammetry

The neurotransmitter dopamine (DA) is widely held to be involved in the maintenance of positively reinforced behaviour, on the basis of self-stimulation experiments and of the effects of drugs which alter DA transmission on self-stimulation, and on behaviours controlled by natural reinforcers. We have used the technique of linear sweep voltammetry at chronically implanted carbon paste electrodes to demonstrate that 30-min sessions of responding on a variable interval schedule for food pellet reward increases first uric acid and then homovanillic acid (HVA, the DA metabolite) in rat caudate. Ascorbic acid levels are reduced, but at later times. We have now established that very similar responses in magnitude and timing are seen in the nucleus accumbens. Furthermore, in individual animals, the response rates, the increases in dopamine turnover, and the changes in uric acid and ascorbic acid remain stable when studied periodically over a 3 month period. Our previous results are broadly consistent with those obtained by others using indirect single-point methods (ex vivo neurochemistry) or in vivo dialysis. However, our present extended observations made possible by the use of paste electrodes (rather than fibre electrodes or dialysis probes) open the possibilities of studying the evolution of neurochemical responses during learning, and the covariation of neurochemical and behavioural effects of drugs within individual animals.

Effect of lithium on dopamine uptake by brain synaptosomes

Lithium chloride exerts two opposite effects on dopamine uptake by synaptosomes isolated from rat caudate nucleus. Added in vitro, it inhibits dopamine uptake; whereas administered chronically in vivo, it enhances dopamine uptake in vitro. Thus, in vitro, 1, 2.5, 5 and 10 meqiv.l-1 of lithium chloride decrease [3H]dopamine uptake by 13, 17, 25 and 31%, respectively. Synaptosomes isolated from rats treated with lithium chloride for 20 days, show a 23% increase in [3H]dopamine uptake with respect to synaptosomes isolated from control rats. It is suggested that chronic lithium treatment stimulates a compensatory mechanism which overcomes its direct inhibitory effect on [3H]dopamine uptake.