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The piriform cortex (PC), the primary olfactory cortex, is involved in the processes of learning and stress response and possibly plays an important role in epileptogenic activity. The results of several recent studies suggest that those PC neurons that contain neuronal nitric oxide synthase (nNOS) may play a key role during spatial learning and in the modulation of initiation, propagation and generalisation of seizures in various experimental models and may influence neuronal vulnerability after epileptic insults. The aim of this study was to characterise the pattern of distribution and morphology of nNOS-immunoreactive elements in PC of the adult rabbit. The co-localisation of nNOS and calretinin (CR) was also studied. The pattern of nNOS-ir within the rabbit PC is similar to that described previously in other mammals. The morphology of nNOS-ir elements, namely varicose fibres and Cajal-Retzius cells, suggest that NO has an important influence on PC function. Surprisingly, in the rabbit PC nNOS-ir elements show a very low level of co-localisation with CR-ir.

The aim of the study was to estimate developmental changes in the rabbit basolateral complex (BLC) by stereological and histochemical methods. Material consisted of 45 brains of New Zealand rabbits (aged from 2 to 180 days, P2 to P180) of both sexes, divided into nine groups. The following parameters were estimated: volume of the cerebral hemisphere; volume of the whole BLC and of particular BLC nuclei; neuronal density and total number of neurons in these nuclei. Developmental changes in acetylcholinesterase (AChE) activity in the BLC were also examined. The volume of the cerebral hemisphere increased until P30, whereas volumes of nuclei increased for longer--until P90. The density of neurons in all nuclei studied reached the level characteristic for an adult animal at about P30. The total number of neurons in the dorsolateral division of the lateral nucleus (Ldl) stabilized the earliest--between P30 and P60, whereas in the ventromedial division of the lateral nucleus (Lvm), basomedial (BM) and basolateral (BL) nuclei the number stabilized later--between P60 and P90. AChE activity appears minimal in the BLC on P2, reaches a maximum on P30 and then decreases to the level characteristic of an adult animal on P60. AChE activity was greater in BL than in other nuclei in all age groups. Reaching adult AChE activity 1 month earlier than the total number of neurons in the BLC may indicate a role of the cholinergic system in BLC maturation.

The aim of the present paper is to describe the morphology and topography of the nuclei of the amygdaloid complex in the rabbit. In the current study we also investigated the intensity of the enzymatic reaction for acetylcholinesterase (AChE) in the amygdaloid complex and the morphology of its neurones. Material consisted of 5 brains of adult New Zealand rabbit, stained either with cresyl violet or for AChE activity. Although, as in other mammals, the rabbit amygdala consists of two main nuclear groups (corticomedial and basolateral), it reveals a peculiar morphology pattern, forming a transition structure between those observed in the cat and rat. Especially characteristic is the arrangement of the basolateral complex. Within that the ventromedial division of the lateral nucleus seems to be the largest, while its dorsolateral division--the smallest. The arrangement of the corticomedial complex in the rabbit is similar to both the cat and rat. In the rabbit the highest acetylcholinesterase activity is found in the basolateral nucleus and the nucleus of the lateral olfactory tract. The lowest AChE staining is observed in the cortical and medial nuclei, amygdalohippocampal and anterior amygdaloid areas and intercalated masses.

Unbiased stereological methods were used for estimating the numerical density and the total number of claustral neurones projecting to the cingulate cortex in rabbit and rat. In rat the numerical density of neurones projecting to the retrosplenial granular cortex (RSG) differed significantly from those projecting to the retrosplenial agranular (RSA) and cingulate (Cg) cortices while in rabbit the numerical densities of retrogradely labelled neurones in the claustrum following injections into various areas of the cerebral cortex did not differ significantly. The total number of retrogradely labelled neurones in the claustral limbic zones did not differ significantly in both species. The quantitative analysis of claustral zones projecting to a different cingulate cortex area, both in rabbit and rat, reveals that each of these zones is rather homogeneous.

The amygdaloid body is a telencephalic structure belonging to the limbic system. The amygdaloid body consists of the two main nuclear groups: corticomedial and basolateral. The former-phylogenetically older group is composed of the central, medial, and cortical nuclei, while the latter, phylogenetically younger one, of the lateral, basolateral and basomedial ones. The results presented in our paper indicate differences in the structure and topography of the specific amygdaloid nuclei. Their subdivisions in the rabbit are not as evident as in the rat. Apart from structural differences, the cellular composition of specific nuclei does not differ distinctly. It can suggest that their intrinsic and extrinsic connections might be similar and the role and function of them is maintained (with few exceptions) through the phylogeny.