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Several neuropeptides, including gastrin-releasing peptide (GRP), modulate the immune response, specifically lymphocyte chemotaxis. In the present work the effect of GRP on the chemotaxis of murine lymphocytes from different immune locations in both, total leukocyte populations and populations depleted of adherent cells have been studied. Specificity of the GRP effect on chemotaxis using an antagonist of the GRP receptor, as well as the implication of nitric oxide (NO), using inhibitors of NO synthase and donors of NO, were investigated. The effects of GRP stimulating the chemotaxis of lymphocytes from peritoneum, axillary nodes and spleen and decreasing the chemotaxis from thymus were receptor-specific and disappeared in lymphocytes from populations depleted of adherent cells. NO synthase inhibitors blocked the GRP effect on lymphocyte chemotaxis, and this action was reversed in the presence of l-arginine. Thus, the effect of GRP on murine lymphocyte chemotaxis appears to be mediated by NO secreted by adherent cells.

Previous immunocytochemical studies in the cerebral cortex of various species have shown that the calcium-binding protein calretinin (CR) labels specific subpopulations of nonspiny non-pyramidal cells (interneurons). The present study attempts to characterize morphologically and chemically the microcircuitry of CR-immunoreactive (CR-ir) neurons in the human temporal neocortex. Postembedding immunocytochemistry for CR and GABA and combination immunocytochemistry for OR and non-phosphorylated neurofilament protein (NPNFP) or for CR and the calcium-binding proteins parvalbumin (PV) and calbindin (CB) showed CR multiterminal endings frequently innervating the distal apical dendrite or the cell body and proximal dendrites of NPNFP-ir or CB-ir pyramidal cells, respectively. Cell bodies of interneurons immunoreactive for CB or PV were innervated only occasionally by CR multiterminal endings, whereas certain GABA neurons were surrounded by them. Furthermore, CR-ir axon terminals formed either symmetrical (the majority) or asymmetrical synapses with a variety of postsynaptic elements. These results indicate that different subpopulations of CR interneurons exist that are specialized for selective innervation of somatic or dendritic regions of certain pyramidal and nonpyramidal neurons.

Chandelier cells are cortical GABAergic interneurons with a unique synaptic specificity enabling them to exert a strong inhibitory influence on pyramidal cells. By using immunocytochemistry for the calcium-binding protein calbindin D-28k in the human temporal neocortex, we have found numerous immunoreactive processes that were identified as chandelier cell axon terminals. This was a striking find since in previous immunocytochemical studies of the primate neocortex, chandelier cell axon terminals had been shown to be immunoreactive for another calcium-binding protein, parvalbumin, and colocalization studies indicate that parvalbumin and calbindin are present in almost completely separate neuronal populations. Here, we present double-label immunofluorescence experiments showing that parvalbumin and calbindin immunoreactivities are colocalized in certain neurons that include a subpopulation of chandelier cells whose cell bodies are located mainly in layers V and VI of the human temporal neocortex. The results suggest a selective laminar distribution of neurochemical subtypes of chandelier cells which is a peculiar feature of the organization of the human neocortex.

Correlative light and electron microscopic methods were used to examine the morphology, distribution and synaptic connections of double bouquet cells immunoreactive for the calcium-binding protein calbindin D-28k in the human temporal neocortex. Double bouquet cells form symmetric synapses with small dendritic shafts and dendritic spines. The distribution and proportion of synapses found in the present work are very similar to those found in previous studies on the synaptic connectivity of double bouquet cells in the monkey cerebral cortex. Thus, double bouquet cells are probably involved in similar synaptic circuits in monkeys and humans.

Potential alterations in glutamate-utilizing excitatory circuits in resected human epileptogenic frontal and temporal neocortex were investigated by using immunocytochemical methods to visualize receptor subunits which comprise the AMPA/kainate (GluR2/3) and kainate (GluR5/6/7) receptor subtypes. Examination of the patterns of immunostaining in regions of neocortex that were identified as spiking and non-spiking based on intraoperative electrocorticography revealed dramatic, microzonal decreases in immunoreactivity for the receptor subunits examined. The patches of decreased immunostaining for GluR2/3 and for GluR5/6/7 were often coincident with respect to each other. However, such abnormal regions were not necessarily correlated with any particular electrocorticographically defined regions nor any overtly abnormal cytoarchitectural features in adjacent Nissl-stained sections. Moreover in many but not all cases, the focal regions of decreased receptor subunit immunoreactivity coincided with small patches of decreased parvalbumin immunoreactivity, a calcium-binding protein which labels a subpopulation of powerful inhibitory GABAergic interneurons. These results indicate that in the human epileptogenic neocortex there may be alterations in particular excitatory and/or inhibitory synaptic systems at small, multiple neocortical foci, and that these alterations are found mostly in the same regions. We suggest that these alterations may contribute to the initiation and/or propagation of seizure activity.

The microanatomy of the human lateral temporal cortex removed from patients with intractable temporal lobe epilepsy was studied using correlative light and electron microscopic immunocytochemical methods for the localization of the calcium-binding protein parvalbumin (PV). PV immunostaining was mainly used to label a subpopulation of powerful cortical inhibitory interneurons that have been shown to be lost at epileptic foci in certain animal models of epilepsy. In the human neocortex with normal appearance, we identified the same local neuronal circuitry as in the normal monkey cortex, but in some regions of the same cortex, a fine disorganization of neuronal circuits (loss of inhibitory neurons and presumptive thalamocortical terminals) was found. This abnormal circuitry may interfere with normal cerebral activity in epileptic patients. These results also indicate that PV immunoreactivity can be a useful tool to study normal and abnormal synaptic circuits in the human cerebral cortex.