Brain structure hippocampus

Collection of interconnected subcortical and cortical brain structures (including hypothalamus, amygdala, and hippocampus) integrating multimodal intero- and exteroceptive information to produce coherent neuroendocrine and behavioral output, and to support memory functions. 

Note The limbic system is made up of several brain structures, including the hippocampus, amygdala, and basal forebrain (Figure 1.3b). 

Temporal lobe brain structures, in particular the hippocampal formation, appear to play a pivotal yet transient role in the formation of new explicit memories. This chapter focuses on possible neurochemical mechanisms underlying the encoding of new information in the hippocampus and the modulation of memory function by different neurotransmitter systems in the brain. 

The hippocampus has innumerable afferent and efferent connections to other brain structures both within the limbic system and beyond. There are receptors for many different chemical signals ranging from the "classical neurotransmitters such as acetylcholine to steroid hormones and neurotrophic factors. Some of these receptors are located in the synapses that form the intrinsic hippocampal circuits and others are the targets of specific projection pathways from other brain areas. A comprehensive review of all neurotransmitter interactions relevant to function is not within the scope of this chapter. There are detailed reviews of modulation of neurochemical systems on place learning in the watermaze (McNamara and Skelton, 1993) or other limbic-system dependent tasks (Izquierdo and Medina, 1995) in animals. The effects of key neurochemical, other than NMDA channel-mediated, and environmental influences are discussed below. 

A variety of brain structures seem to be essential for aversive memories. In the following, I will briefly introduce the hippocampus and amygdala involvement, without disregarding the importance, for instance, of the cerebellum for eye-blink conditioning (Thompson et al. 1997, 2000 Medina et al. 2002) and the insular cortex for conditioned taste aversion (e.g. Berman and Dudai 2001). 

Striatum and lateral septum. Interestingly, in contrast to our findings in the hippocampus, CRH has biphasic effects in these brain structures. Low doses of CRH (0.1 and 0.3 pg) were found to decrease extracellular levels of 5-HT. Higher doses of CRH (1.0 and 3.0 pg) have, however, no effect or increase 5-HT levels in the striatum and lateral septum (Price et al. 1998 Price and Lucki 2001). The biphasic effects on levels of 5-HT in these brain regions may be related to the dose-dependent effects of CRH on the firing rate of DRN 5-HT neurones as described above. Interestingly, local injection of CRH in the DRN results in a decrease in extracellular 5-HT in the striatum and septum (Price and Lucki 2001). 

There are numerous GABAergic neuronal pathways in the CNS. y-Aminobutyric acid is found in high concentrations in the cerebellum, is also found in the hypothalamus, thalamus, and hippocampus, and occurs in low concentrations in practically all brain structures as well as in the spinal cord. The amounts present are relatively high—on a pmol/g order of magnitude— rather than the nanomolar quantities seen with most major neurotransmitters. y-Aminobutyric acid also occurs in glial cells, where its role is less well defined. 

Figure 9.38 Concentration profile of copper and zinc in the scanned area of interest measured by LA-ICP-MS on brain samples (hippocampus). Calibration was performed via synthetic matrix matched laboratory standards for 1, 5 and 10 fxgg-1 of analyte (see inserted figures on left). Bottom histologically processed brain tissue in which cell bodies were stained (cresyl violet staining) in order to demonstrate the layered structure of the analyzed region. (]. S. Becker, M. Zoriy, C. Pickhardt, N. Palomero-Gallagher and K. Zilles, Anal. Chem., 77, 3208 (2005). Reproduced by permission of American Chemical Society.)...

DA receptors include a Drlike family (I) and D5 receptors), and a D2-like family (D2, D3, and D4 receptors), which differ in their distributions on neurons (Missale et al., 1998) and their regional localization in the human brain (for reviews see Seeman, 1992 Joyce and Meador Woodruff, 1997). I), receptors show a widespread neocortical distribution, and are also present in high concentration in striatum. D5 receptors are mostly detected in the hippocampus and entorhinal cortex. D2 receptors are concentrated in the striatum, with low concentration in medial temporal structures (hippocampus, entorhinal cortex, amygdala) and thalamus. The concentration of D2 receptors in the PFC is extremely low. D3 receptors are present in the striatum, where their concentration is particularly high in the ventral striatum. D4 receptors are present in the PFC and hippocampus, but not detected in the striatum. 

The hippocampus, so named because its shape vaguely resanbles that of a seahorse, is a symmetrical structure located inside the medial tanporal lobe on both sides of the human brain. It is a curved sheet of cortex folded into the medial surface of the temporal lobe, hi transverse sections from rodent brain, the hippocampus has the appearance of two interlocking Cs with three distinct sub-fields, the dentate gyrus, the hippocampus proper (cornu... 

Studies employing genetically modified mice with overexpression of (a2C-Ar+/+oe) or nup or jlc a2( -AR (a2C-AR ) have yielded particularly fruitful insights into the roles that this subtype plays in discrete physiological functions (see Table 1). The strength of the data is corroborated by the observation of reciprocal changes in responses observed in these genotypically opposite mice. The o c-AR subtype is found in a number of brain structures (e.g., hippocampus,... 

Fig. 2. Sagittal section of rat brain immunolabeled (pre-embedding immunoperoxidase) for delta 1/2. CP = caudate putamen DC = dorsal cochlear n. DG = dentate gyrus (in hippocampus) FH = forelimb/hindlimb area of cortex Fr = frontal cortex Rt = reticulothalamic n. Note high levels of labeling in the dorsal cochlear nucleus and the cerebellar molecular layer (above DC), moderate labeling in the hippocampus and light to moderate labeling in various other brain structures. Modified from Mayat et al. (1995).

AD is defined by both neuropathologic and clinical criteria. Neu-ropathologically, AD destroys neurons in the cortex and limbic structures of the brain, particularly the basal forebrain, amygdala, hippocampus, and cerebral cortex. These areas are responsible for higher learning, memory, reasoning, behavior, and emotional control. Anatomically, four major alterations in brain structure are seen ... 

The results presented in different reports point to particular brain structures that have been found to be anatomically affected in autistic persons. These are the cerebellum, the amygdala and the hippocampus [43, 47, 48]. 

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