M. Ramirez

Asymmetrical distribution of aminopeptidase activity in the cortex of rat brain

The levels of soluble aminopeptidase (AP) activity were measured in the right and left frontal (FC), parietotemporal (PTC) and occipital (OC) cortex of male albino rat brains. The results showed more AP activity in the left cortex than in the right. Analyzing these results further, we found that the differences are significant for frontal cortex but not for parietotemporal nor occipital cortex. However, 76% of the rats were left-predominant for AP activity in the 3 cortical areas studied.

Regional distribution of soluble and membrane-bound aminopeptidase activities in rat brain

Soluble and membrane-bound aminopeptidase activities in 11 regions of the rat brain were assayed using L-Leucine-2-naphthylamide as a substrate. In addition, two metabolic enzymatic activities were compared: lactate dehydrogenase and aspartate aminotransferase. All enzymatic activities showed significant regional differences when the data were analyzed statistically. Soluble aminopeptidase and aspartate aminotransferase activities were significantly lower in cortical than in subcortical areas. Membrane-bound aminopeptidase activity levels were higher in cortical areas. Lactate dehydrogenase activities did not differ between cortical areas and the rest of the zones studied. However, although no wide regional differences were found for the other enzymatic activities, membrane-bound aminopeptidase varied markedly across brain regions: a fivefold difference was observed between zones such as parietotemporal cortex and medulla. The differential distribution of this enzymatic activity is consistent with the hypothesis that it could be responsible for the enzymatic inactivation of some neuroactive peptides.

Aminopeptidase activity is asymmetrically distributed in selected zones of rat brain

Levels of soluble aminopeptidase (AP), measured as arylamidase activity using L-Leucine-2-Naphthylamide (Leu-2-NA) as substrate, were determined in the soluble fraction of eleven zones of rat brain. Results showed that AP activity is asymmetrically distributed in frontal cortex and hypothalamus with both left sides having significantly higher levels of AP activity, respectively, than the right sides. Simultaneously, the activities of lactate dehydrogenase (LDH) and glutamate-oxalacetate aminotransferase (GOT) were measured in the same cerebral regions; no significant difference was recorded in these activities between either side of the rat brain in any of the zones studied. Provided that aminopeptidases are involved in the degradation of some endogenously released neuropeptides, the results suggest a new mode of expression of cerebral lateralization.

Bilateral Distribution of Oxytocinase Activity in the Medial Prefrontal Cortex of Spontaneously Hypertensive Rats with Experimental Hemiparkinsonism

Oxytocin and vasopressin are important modulators of diverse social and anxiety-related behaviors (Insel, 2010). The enzyme that regulates the function of both peptides, called oxytocinase (OX) or vasopressinase, is also involved in cognitive functions (Stragier et al., 2008; Banegas et al., 2010). Normotensive male Wistar rats exhibited a marked left predominance of OX in the medial prefrontal cortex (mPFC), an area implicated in cognitive functions and reward-related mechanisms in the rat brain and characterized by its asymmetrical organization. Brain dopamine (DA) content as well as the functions in which this neurotransmitter is involved, are asymmetrically organized in physiologic conditions (reviewed by Ramirez et al., 2004). Therefore, Parkinson’s disease (PD) represents a disruption of this bilateral pattern of brain DA. Indeed, the disease normally begins unilaterally in the early stages. Animals with hemi-parkinsonism, induced by unilateral nigrostratal lesions using 6-hydroxydopamine (6-OHDA), showed several behavioral abnormalities, not only linked to a disruption of the normal bilateral distribution of brain DA, but probably also by the alteration of other factors such as the disruption of the striking basal left predominance of OX observed in both the left and right sham controls. The bilateral distribution in lesioned animals was altered differently depending on the injured hemisphere. These results may reflect changes in the levels of oxytocin and vasopressin in the mPFC and consequently in the functions in which they are involved and might account, in part, for the cognitive abnormalities observed in hemi-parkinsonism (Henderson et al., 2003). The spontaneously hypertensive rat (SHR), is a recognised model for studies of hypertension. This strain of rat also display major symptoms of the attentiondeficit/hyperactivity disorder (ADHD) such as deficits in attention, impulsivity and hyperactivity when compared to Wistar-Kyoto rats (Russell, 2007). Indeed, SHR have been shown to have also disturbances in the dopaminergic system (Russell, 2007). The aim of this