Axon collaterals emerging from the vasopressinergic neurons of the supraoptic (SON) and paraventricular (PVN) nuclei and recurving back towards their respective nuclei have been previously reported. Since such axon collaterals can play a role in the neuromodulation of SON and PVN these nuclei have been further investigated immunohistochemically under the light and electron microscope. The PAP technique, using a commercial antibody, was employed. Vasopressin-positive axon collaterals were seen to recurve towards their nuclei of origin. In the latter, vasopressinergic intrinsic neurons were also observed. Under the electron microscope, axon terminals containing vasopressin-immuno-reactive neurosecretory granules were noted. Such terminals presumably arise from the vasopressin-positive recurrent axon collaterals or from the intrinsic neurons for the purpose of neuromodulation within the SON and PVN.

To investigate the nature of esterase polymorphism, nonspecific esterases were investigated in a large number of organs obtained from rat. In starch gel electropherograms the capacity of ester hydrolysis was seen to decline predictably with successively longer chain carbon substrates. An increasing susceptibility to organophosphate inhibition was observed with progressive lengthening of the acyl chain in the substrate molecules. Attempts to hybridize an organophosphate-sensitive esterase with a resistant type yielded a few additional esterase species. Studies on an esterase fraction isolated by column chromatography revealed the highly relative nature of organophosphate inhibition. These suggested that nonspecific esterases all belong to one enzyme system that does not justify the present compartmentation into acetyl-, aryl- or carboxylesterases on grounds of substrate hydrolysis or organophosphate sensitivity. It is likely that esterase species are each built on a subunit structure and exhibit overlapping specificities through sharing of common subunits. The concept that a whole range of esterase subunits exist, each varying in its capacity to hydrolyze esters of up to an optimal chain length and arranged according to the dictates of specific tissue requirements, is in accord with the present findings.

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Acid phosphatase and esterase activities were studied in adrenal glands obtained from rats killed at regular intervals following surgical stress (cauda equina transection). Zymograms of acid phosphatase produced by starch gel electrophoresis revealed increased reactivity in the operated samples. With esterases, a slightly different pattern was observed in the operated group, which exhibited a few additional bands particularly in the cathode region. This was confirmed by densitometric analysis of the gel strips. Two of these additional bands were organophosphate-sensitive and the remaining few were activated by p-chloromercuribenzoate. These latter bands appeared to arise from splitting of the preexisting organophosphate-resistant bands present in control zymograms. Biochemical assay of the two hydrolytic enzymes demonstrated a remarkable similarity in their responses to operative stress—probably implying a general lysosomal activation. Both enzymes exhibited a peak activity 8 hr after operation, followed by a gradual decline. Both organophosphate-sensitive and organophosphate-resistant esterases contributed toward the rise in total esterase activity. Histochemical studies on tissue sections revealed a more reactive adrenal cortex in the operated group, but were of little help in localizing the additional esterase activity observed in gel strips.