Demonstration of enkephalin-, substance P- and glutamate decarboxylase-like immunoreactivity in cultured cells derived from newborn rat neostriatum

Skipping ahead: A circuit for representing the past, present, and future

Envisioning the future is intuitively linked to our ability to remember the past. Within the memory system, substantial work has demonstrated the involvement of the prefrontal cortex and the hippocampus in representing the past and present. Recent data shows that both the prefrontal cortex and the hippocampus encode future trajectories, which are segregated in time by alternating cycles of the theta rhythm. Here, we discuss how information is temporally organized by these brain regions supported by the medial septum, nucleus reuniens, and parahippocampal regions. Finally, we highlight a brain circuit that we predict is essential for the temporal segregation of future scenarios.

The expression of gamma-aminobutyric acid and Leu-enkephalin immunoreactivity in primary monolayer cultures of rat striatum

Primary monolayer cultures of rat striatum were examined for gamma-aminobutyric acid (GABA) and leucine-enkephalin (L-ENK) immunoreactivity. Cultures were established on polycation-treated glass coverslips from the striata of gestational day 17 rat embryos using a serum and insulin-supplemented medium. The proportion of GABA-immunoreactive (GABA-IR) neurons increased during the first week in vitro from approximately one third to nearly one half and remained relatively constant thereafter. On the other hand, the proportion of L-ENK-IR neurons increased gradually over the culturing period, increasing from about one-fifth of the neurons initially to one-half after 3-4 weeks in vitro. The changes in the proportions of GABA- and L-ENK-IR neurons appeared to be largely a consequence of the death of non-immunoreactive neurons, not delayed expression or induction of GABA or L-ENK traits. Light microscopic analysis of somatic-proximal neuritic morphology led to a partitioning of the neuronal population into 4 groups. GABA- and L-ENK-IR groups were heterogeneous in this regard and differed only modestly.

Differential regulation of cholinergic and peptidergic development in the rat striatum in culture

The development of substance P, somatostatin, and choline acetyltransferase activity was examined in embryonic rat striatum in vivo and in culture. The study was undertaken to help define mechanisms by which diverse neurotransmitter phenotypes may be regulated within the same structure in the brain. Choline acetyltransferase (CAT) was present in striatum before gestational Day 13.5 (E13.5), and enzyme levels increased continually between E13.5 and birth. By contrast, substance P (SP) and somatostatin (SS) did not develop in vivo until E15, and peptide levels fluctuated between E15 and birth, indicating that striatal peptidergic and cholinergic development were regulated differently. To define mechanisms mediating the differential regulation of striatal peptidergic and cholinergic neurons, neurotransmitter development was examined in embryonic striatum in vitro. Cultured striatal neurons from E13.5 embryos expressed substance P and somatostatin de novo after several days in culture, and peptide levels and CAT activity increased significantly in vitro. Each transmitter phenotype was regulated in vitro by a different constellation of environmental factors, and many factors differentially influenced SP, SS, and CAT development. For example, coculture of striatum with a target tissue, the ventral mesencephalon (substantia nigra), increased CAT activity and SP levels but had no significant effect on levels of SS. Moreover, there were widely differing effects on CAT, SP, and SS development of medium conditioned by exposure to a variety of cell types, indicating that the three transmitter systems were regulated by different soluble factors. Potassium-induced membrane depolarization also exerted different effects on the different transmitter traits, elevating CAT activity but decreasing SP and SS. Finally, insulin was required for the survival of SP-containing neurons, but not for the survival of SS- or CAT-containing neurons, indicating that the survival of different populations of striatal neurons was dependent upon different factors. Our observations suggest that different populations of neurons in the striatum are regulated by different mechanisms, so that alterations in the environment may produce strikingly diverse responses in the development of different phenotypic traits within the same structure.

Studies on neurotransmitter markers and striatal neuronal cell density in Huntington's disease and dentatorubropallidoluysian atrophy

Neurotransmitter abnormalities in the basal ganglia of individual "choreic" patients (9 cases of Huntington's disease-HD and 3 cases of dentatorubropallidoluysian atrophy-DRPLA) and 14 normal controls were investigated. Choline acetyltransferase activity in the striatum was decreased in approximately half the "choreic" patients. GABA concentration in the substantia nigra or in the globus pallidus was decreased in all "choreic" cases except one case of DRPLA. Substance P concentration was also reduced in the same nuclei as GABA except in one case of HD. These findings imply: cholinergic, GABAergic or substance P-related markers found in the basal ganglia of HD are not disease-specific but also found in the other "choreic" disorder, i.e. DRPLA; most prominent biochemical changes in HD would be a decrease of GABA in the basal ganglia. Correlation analysis of the markers in the basal ganglia and the striatal neurone densities of "choreic" patients (5 cases of HD and 3 cases of DRPLA) and 7 normal controls yielded positive correlation between GABA concentration in the substantia nigra and the globus pallidus, and the neuronal cell density in "small" cells in the striatum of normal control and HD. Positive correlation between substance P concentration and the striatal neurone density was only found in the substantia nigra. Choline acetyltransferase activity in the striatum was found to be positively correlated with the density of "large" cells in the striatum rather than that of "small" cells. In DRPLA there was no direct correlation between the values of the markers in the basal ganglia and the striatal neurone density. The decrease of transmitter markers without striatal cell loss in this particular choreic disorder could be regarded as a sequence of "biochemical degeneration" of striatal neurones. Based on these findings, the underlying mechanisms of choreic involuntary movements were briefly discussed.

Simultaneous determination of leu-enkephalin localization and [3H] gamma-aminobutyric acid uptake in rat striatal cell cultures

The purpose of this study was to investigate the coexistence of gamma-aminobutyric acid (GABA) and leu-enkephalin in single neurons from the corpus striatum. Monolayer cell cultures, started from newborn rat corpus striatum, were grown in serum-free medium and examined using GABA autoradiography and leu-enkephalin immunocytochemistry in a double-label protocol. Examples of cells were found which were positive for one or the other neurotransmitter or for neither transmitter, but not for both. Furthermore, cells which appear similar by morphological criteria alone differed in transmitter specificity. We conclude that the two transmitters tested are not localized within single cells and that morphology alone is inadequate to identify functional cell classes in this area.

Immunohistochemical demonstration of substance P in the lower respiratory tract of the rabbit and not of man

Substance P (SP)-immunoreactive nerve fibres were searched for at all levels of both fetal and adult human lower respiratory tract. Because the demonstrability of substance P immunoreactivity varies between different animal species, rabbit pulmonary tissue was also subjected to SP immunohistochemistry. Human irises and corneas served as positive human controls. The specimens were taken from 10 human lungs during pulmonary operations. Tracheal tissue was obtained from three patients during bronchoscopy. Five fetal human lungs were examined. Human specimens examined included the trachea, main bronchi, segmental bronchi, and peripheral pulmonary tissue. In addition, the tracheobronchial tissues of four rabbits were studied. SP immunoreaction was demonstrated in formaldehyde-fixed cryostat sections by either the indirect immunofluorescence technique or the peroxidase-antiperoxidase procedure. Both monoclonal and conventional antibodies to SP were tested. In the rabbit SP-immunoreactive nerves were found in both the submucosa and the smooth muscle layer of the main bronchi and trachea. Specimens from human trachea, bronchi, and bronchioli were all negative. Since the SP immunoreaction was easily demonstrated in both human cornea and human iris, it was concluded that there are no SP-immunoreactive nerves in the human pulmonary tissues or that their SP content is very low and below the sensitivity of all the techniques used.